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Worldwide Asian longhorned beetle eradication: An example of biological applications of noncontact microwave and ultrasound radiation

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WORLDWIDE ASIAN LONGHORNED BEETLE ERADICATION: AN EXAMPLE
OF BIOLOGICAL APPLICATIONS OF NONCONTACT MICROWAVE AND
ULTRASOUND RADIATION
by
Mary Fleming
A dissertation submitted to the faculty of
The University o f Utah
in partial fulfillment o f the requirements for the degree of
Doctor o f Philosophy
Department o f Materials Science and Engineering
The University o f Utah
December 2003
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UMI Number: 3100854
UMI
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Copyright © Mary Fleming 2003
All Rights Reserved
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THE UNIVERSITY OF UTAH GRADUATE SCHOOL
SUPERVISORY COMMITTEE APPROVAL
o f a dissertation submitted by
Mary Fleming
This dissertation has been read by each member of the following supervisory committee and by
majority vote has been found to be satisfactory.
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Joseph D . Andrade
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K elli Hoover
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THE UNIVERSITY OF UTAH GRADUATE SCHOOL
FINAL READING APPROVAL
To the Graduate Council of the University of Utah:
I have read the dissertation o f_______ Mary Fleming_________ in its final form and
have found that (1) its format, citations, and bibliographic style are consistent and
acceptable; (2) its illustrative materials including figures, tables, and charts are in
place; and (3) the final manuscript is satisfactory to the supervisory committee and
is ready for submission to The Graduate School.
£ > /5 /°3
D ate
Chair: Supervisiry Committee
Approved for the Major Department
Anil V. Virkar
Chair
Approved for the Graduate Council
r
David S. Chapman
Dean o f The Graduate Schoo
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This work is dedicated to my parents, Howard and Elaine.
By example, they taught me how to dream and how to achieve those dreams.
Their love and support throughout my life have given me the courage
to grow and to challenge myself.
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ABSTRACT
Destructive pests such as the Asian longhomed beetle (Anoplophora glabripennis
Motsch.) (ALB) can be transported around the world via wooden packing materials used
in pallets and crates, placing urban and forest resources at grave risk. A potential
nondestructive technique to detect pest infestations in wooden packing materials is
noncontact ultrasound technology. Noncontact ultrasound (100 kHz to 500 kHz)
detection o f living larvae in wood was found to be unfeasible due to inference of
transmission by the tunnel air/wood interfaces in the wood. However, 100 kHz, 200 kHz,
and 500 kHz ultrasound transmission through 1-in. thick wood samples o f any orientation
was possible. C-scan images (200 kHz) showed the location ofholes drilled inside the
wood and movement o f a larva placed on top o f the wood.
The use o f microwave energy to treat these wooden packing materials in the
source country before transport to eradicate wood-boring pests infesting these materials
was also investigated. Destruction o f pests infesting wooden packing materials is required
by international guidelines. Eradication o f cerambycid larval infestations in laboratorysize pine and poplar lumber less than 6-in. thick (volume o f 216 in ) was shown to be
feasible using 2.45 GHz microwave energy. Five minutes o f 1100 W radiation produced
100% mortality o f cottonwood borer and ALB infestations in red pine, eastern white
pine, loblolly pine, and aspen samples with moisture contents ranging from 30% to 130%
o f dry weight. The parameters o f importance for scale up to commercial size loads
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commercial size loads include wood moisture content and energy to wood volume ratios.
Lethal doses o f 2.45 GHz microwave energy increased as wood moisture content
increased. The proposed optimal energy to volume ratio for up to 78% moisture content
wood samples is 2,812.5 J/in3. Total insect mortality occurred for all three time/power
combinations (1000 W for 3 minutes, 2000 W for 1.5 minutes, or 3000 W for 1 minute)
tested. Industry standard lumber dimensions and loads must be tested to determine if this
ratio is appropriate for commercial use. Energy cost in the United States o f 21 to 36 cents
per pallet was estimated for microwave treatment compared to 5 to 10 cents per pallet for
conventional heat treatment. Actual U.S. costs to exporters for methyl bromide
fumigated pallets ranged from $0.89 to $16 per pallet in 2003, whereas microwave
operating costs to exporters are crudely estimated to be 58 to 94 cents per pallet.
Commercial size microwave experiments must be conducted before these cost estimates
can be refined.
v
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TABLE OF CONTENTS
. ..........
ABSTRACT..................
ACKNOWLEDGMENTS
.......................
1
SUMMARY
2
GENERAL BACKGROUND.....................
2.1
2.2
2.3
2.4
2.5
........................
Wood Background.........................................................................
.........
-............................
2.1.1 Introduction
2.1.2 Physical Characteristics o f the Tree Trunk
.............
2.1.3 Physical Characteristics o f the Woody Cell.....................
2.1.4 Temperature and Heat Transfer in Wood.........................
2.1.5 Defects in Lumber. ....................
AsianLonghomed BeetleBackground
.................
2.2.1 Introduction................................
2.2.2 ALB Lifecycle and Host Preferences. ...............
2.2.3 ALB Worldwide and U.S. Infestations......................
2.2.4 ALB Worldwide Regulatory Control Efforts.................
2.2.5 Management ofU .S. ALB Infestations.............................
2.2.6 Current ALB Research....................
Ultrasound Background.............. ...... .............................................
2.3.1 Introduction
.......................
2.3.2 Wave Types
.........
2.3.3 General Wave Equation
.....................................
2.3.4 Principles o f Ultrasonic Wave Motion.
..............
2.3.5 Nondestructive Ultrasonic Evaluation o f Material
2.3.6 Ultrasound in Nature................
2.3.7 Applications o f Ultrasound in the Wood Industry.........
Microwave Background............. ............
2.4.1 Introduction
.......................
2.4.2 Electromagnetism.......................
2.4.3 Microwave Interaction with Material
................
2.4.4 Eradication o f Insects by Microwave Energy. ...............
2.4.5 Microwave Application in the Lumber Industry
U.S.-Approved Wooden Packing Material Treatments.................
2.5.1 Methyl Bromide Background.
..............
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iv
x
1
6
6
6
7
7
13
17
19
19
19
21
23
25
27
36
36
37
40
43
53
62
63
63
63
65
69
72
79
81
81
2.6
3
ULTRASOUND EXPERIMENTS
3.1
3.2
3.3
3.4
3.5
4
4.3
4.4
4.5
100
100
106
108
113
117
117
141
166
169
170
Introduction...................
Dielectric Study
.....................................................
4.2.1 Introduction.......................
4.2.2 Experimental Design..............................................................
4.2.3 Experimental Results and Discussion...............................
4.2.4 Conclusions.............
Wood Temperature Gradient Study Comparing
Microwave and Conventional Heat Treatments..............................
4.3.1 Experimental Design..............................................................
4.3.2 Experimental Results and Discussion................................
4.3.3 Conclusions...........................................................................
Microwave Experiments withLarvae-Infested Wood.................
4.4.1 Introduction...............
4.4.2 Microwave Experimental Design.........................................
4.4.3 Experimental Results and Discussion...................
4.4.4 Lethal Microwave Experiment Conclusions........................
References
.........................
170
170
170
182
184
194
Methyl Bromide Fumigation
Heat Treatment
.............
Microwave Treatment. .............
Conclusions
.............
References.................
FUTURE RESEARCH..
6.1
82
84
...........
TREATMENT OPERATING COST COMPARISONS
5.1
5.2
5.3
5.4
5.5
6
.........................................................
Introduction.......................................................................................
Experimental Design.........................................................................
3.2.1 Fixed Transducer Experimental Design. ..........................
...................... .......... .
3.2.2 C-Scan Experimental Design
Experimental Results and Discussion
.........
3.3.1 Fixed Transducer Experiments
......................
3.3.2 C-Scan Experiments......................................................... .
Ultrasound Conclusions..........................
References...............
••••........
MICROWAVE EXPERIMENTS
4.1
4.2
5
2.5.2 Conventional Heat Treatment
............................
................................. ......................... .....................
References
.......
.............................
..............
Microwave. ...........
194
194
195
200
201
201
201
218
232
234
236
236
239
240
242
244
245
245
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6.1.1
6.1.2
6.2
Alternative Microwave Techniques. ........
Commercializing Microwave Processing o f
Wooden Packing Materials ............
6.1.3 Cause o f Larval Death..................
References
...........
245
245
246
249
Appendicies
A.
B.
C.
D.
E.
F.
G.
NONCONTACT ULTRASOUND FIXED
TRANSDUCER VARIED FREQUENCY
...........
GRAPHS
250
NONCONTACT ULTRASOUND FIXED
TRANSDUCER VARIED COUPLANT
GRAPHS.......................
261
NONCONTACT ULTRASOUND C-SCANS
100 kHz BEST RANGE..........................................
272
NONCONTACT ULTRASOUND C-SCANS
..............................................................
100 kHz COMMON RANGE
284
NONCONTACT ULTRASOUND C-SCANS
200 kHz BEST AND COMMON RANGE.................................................
296
NONCONTACT ULTRASOUND C-SCANS
500 kHz BEST RANGE.....................................................
308
NONCONTACT ULTRASOUND C-SCANS
500 kHz COMMON RANGE
...............................
320
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ACKNOWLEDGMENTS
Projects o f this scope conducted on two continents are the result o f cooperation
among many professionals. I especially wish to thank the following people for their
assistance with this research: Jeffrey Shield, Kelli Hoover, Mahesh Bhardwaj, Sorah
Rhee, John Janowiak, Yi Fang, Ramesh Peelamandu, Gary Stead, Joe Kearns, Michael
Lanagan, Steve Perini, David Whitmore, JiPing Cheng, Victor Mastro, David Lance,
Rustum Roy, Dinesh Agrawal, Xin Wang, Wenmin Liu, Yuejin Wang, Xiaoxi Hang,
Liang Xu, Jeff Kintmel, Maria DiCola, Branden Kappes, Mike Grove, Leah Bauer, and
Debbie Miller.
Funding was provided by USD A, APHIS, PPQ under Cooperative Agreement No.
99-8100-0581-CA.
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1 SUMMARY
Wooden packing materials such as pallets and crates are used to transport
products around the world. Destructive pests such as the Asian longhomed beetle
(Anoplophora glabripennis Motsch.) (ALB) can be living undetected inside the wood
used to make these shipping materials. If these pests emerge from the wood as adults
after these shipments reach their destinations, they can multiply by laying eggs in host
trees, permitting them to invade a new location. Invasion by exotic wood boring insects
like ALB can result in destruction o f valuable timber resources elsewhere in the world.
Efforts to control the spread o f these exotic pests has not been completely successful. In
the case o f ALB, the United States has ordered that all infested trees be cut down and
burned. The first efforts to control infestations found in New York (1996) and Chicago
(1998) appeared to slow the geographical spread o f this pest, until a new infestation was
found in New Jersey in 2002. To ensure that additional pests do not cross national
borders, a number o f quarantine and control measures are being investigated, both by
inspectors at the borders and by treatment o f the packing material in the source country.
At the borders, national inspectors desperately need nondestructive techniques to
detect pest infestations in wooden boards. For a number o f years, ultrasound has been
used to nondestructively image defects in materials, as well as in medical applications
such as ultrasound imaging o f a fetus. The limiting factor, however, was the energy
required by the receiver in order to allow this technique to work. Air/material interfaces
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2
obstruct the transmission o f ultrasound to such a degree that transducer contact, either dry
or gel, with the object was required to increase the energy passing through the object and
reaching the receiver, so that detection could take place. With the advent of new noncontact transducers invented by Ultran Laboratories, Inc. (Boalsburg, PA), this barrier
was breached. Given the technological breakthrough, the ultrasonic detection o f pests
inside wood without transducer contact was potentially possible.
In order to combat the threat at the source, individual countries, as well as the
international governing bodies such as the United Nations and the European Union, have
begun to regulate the importation o f wooden packing materials. For example, as o f
March 2002 all wooden packing materials imported into U.N. member countries are
required to have been either heat treated or fumigated by methyl bromide in the exporting
country. However, 160 countries have signed a treaty, the Montreal Protocol, to phase
out the use of methyl bromide in developed countries by 2005 and in developing
countries by 2015 because o f its alleged contribution to the depletion o f the ozone layer.
Although methyl bromide fumigation o f wooden packing materials used in international
trade is exempt from this worldwide ban under the preshipment and quarantine exception,
the cost o f this chemical is increasing rapidly as the overall demand is decreasing.
Consequently, alternative treatments o f wooden packing materials that can be approved
by international governing bodies are being sought. Microwave processing is one such
treatment and became a focus o f the current research. Also o f particular interest was the
ability o f wood surface temperature to predict inner wood core temperatures during the
microwave process for use as an indicator o f proper treatment application.
Research on noncontact ultrasound detection o f living cerambycid larvae in wood
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found that ultrasonic transmission through 1-in. thick wood samples o f any orientation
was possible with 100 kHz, 200 kHz, and 500 kHz frequencies. Drilled holes or tunnels
in the wood were often but not always identifiable in c-scan images due to a lack o f
transmission. In addition, movement o f a larva placed on top o f the wood was
identifiable via discontinuities in the ultrasound scan. However, c-scan images were not
capable o f identifying living larvae located inside tunnels because the wood/air and
air/wood interfaces interfered with the ultrasound transmission. Therefore, noncontact
ultrasound was deemed not a feasible technique for the nondestructive detection o f living
larvae inside wooden packing materials. Noncontact ultrasound imaging might prove to
be useful for other forest product applications, such as density measurements for plywood
or grading o f lumber. Additional research in these areas is recommended.
Eradication o f cerambycid larval infestations in laboratory-size pine and poplar
lumber less than 6-in. thick (volume o f 216 in.3) was shown to be feasible using 2.45
GHz microwave energy. Five minutes o f 1100 W radiation produced 100% mortality for
cottonwood borer and Asian longhomed beetle infestations in red pine, eastern white
pine, loblolly pine, and aspen samples with moisture contents ranging from 30% to 130%
o f dry weight. The parameters o f importance for scale up to commercial size loads
include wood moisture content and energy to wood volume ratios. The higher the
moisture content in the wood, the higher the microwave energy necessary to be lethal to
cerambycid larvae. Volatiles, however, will be released if the microwave energy input is
too large for the available moisture content to absorb. For example, some aspen or red
pine samples with moisture contents less than 30% released volatiles when subject to 5
minutes of 1100 W radiation. The proposed optimal energy to volume ratio for up to 78%
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moisture content wood samples is 2,812.5 J/in3. Any o f the three time/power
combinations tested (1000 W for 5 minutes, 2000 W for 2.5 minutes, or 3000 W for 1
minute) resulted in 100% insect mortality. Industry standard lumber dimensions and
loads must be tested to determine if this ratio is appropriate for commercial use.
Rough energy and operating cost estimates were compared for conventional heat,
microwave, and methyl bromide treatments in the United States and in China. Electricity
and gas costs vary considerably depending on the local region. In China, for example,
electricity costs range from $0.20 to $0.30 U.S. per kilowatt hour, whereas in the United
States electricity costs are much lower, $0,037 and $0,063 per kilowatt hour in Oregon
and Utah, respectively. Microwave treatment o f wooden pallet material appears to be
competitive with methyl bromide fumigation in the United States. However, heat
treatment costs were lower in the United States than microwave treatment energy costs.
The energy cost o f microwave treatment was estimated at $0.21 to $ 0.36 per pallet and at
5 to 10 cents per pallet for conventional heat treatment. Actual U.S. costs to exporters for
methyl bromide fumigated pallets ranged from $0.89 to $32 per pallet in 2003, depending
on the method o f application. Operating costs to U.S. exporters for microwaves was
estimated to range from $0.64 to $0.72 per pallet. Thus, cost-benefit of microwaves for
the eradication o f wood-boring insects infesting solid wood packing material is
comparable, and in some cases superior, to methods currently used by the industry.
The findings reported herein provide the basis for future experiments required in
the process o f scaling up microwave equipment for the eventual commercialization of
this treatment method, while insuring that regulatory requirements can be met as well. A
limitation o f the work presented here is that the cause o f larval death was not
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5
investigated. Further research into cellular and/or physiological effects o f microwave
exposure on insects, internal heating o f the insect, external wood environment heating,
energy transfer models, and the biological effects o f the electric and magnetic fields on
the target organism would enhance our understanding o f how microwave irradiation
interacts with living organisms.
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2 GENERAL BACKGROUND
Lumber processed from trees and the beetles that complete a portion o f their
lifecycle within the fallen wood are the focus o f this microwave and ultrasound study.
Consequently, it is important to impart an understanding of both o f these organisms, plant
and insect, as well as an understanding o f both energy sources employed in this study.
2.1
Wood Background
2.1.1. Introduction
The concepts in this section are summarized from The Textbook o f Wood
Technology,1 except where otherwise cited. Trees, shrubs, and climbing woody vines are
all perennial woody plants. The major characteristic shared by these life forms is the
stem, which survives over the winter. Woody plants transport waste and nutrients up and
down their stem through a complex vascular system contained within the wood and the
surrounding inner bark. The stem grows thicker with each growing season. Plant height,
ability to stand alone, and number o f stems are used to classify woody plants. A tree is
usually quite tall (>20 ft.), while shrubs are not (<20 ft.).
In the United States (not including Hawaii) there are approximately 30 species o f
softwoods and 50 species o f hardwoods that are utilized commercially. Worldwide, there
are thousands o f wood species. The tree trunk (called a stele) is most often used to
produce wood products including the solid wooden packing materials such as pallets and
crates that are o f interest in this study. Consequently, this section will focus on the
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7
characteristics of the stele.
2.1.2 Physical Characteristics o f the Tree Trunk
A tree trunk can be divided into five regions from the center to the outer bark as
follows: the center o f the tree (the pith), the surrounding inner dead region o f the xylem
(the heartwood), the living region o f the xylem (the sapwood), the cambium layer, and
the phloem. Each region plays an important role in either the physical structure or
physiological functions of a tree. The heartwood is responsible for mechanical support of
the tree, while the sapwood transports (nutrients and wastes) and stores (starches and
sugars). The cambium layer is responsible for adding girth to the trunk by producing new
xylem and new phloem. The phloem is the bark on the outside o f the tree that is
specifically designed to protect the tree from moisture loss and physical damage. Besides
growing in width (secondary growth), both the trunk and its appendages (i.e., branches)
contribute to the height o f the trunk (primary growth).
2.1.3 Physical Characteristics o f the Woody Cell
A basic characteristic o f mature woody cells is their rigid cell walls. Cell walls
are made up o f a variety o f chemical components and include the following from highest
to lowest percentage o f oven-dry weight: cellulose, hemicellulose, lignin, tannins, volatile
oils, volatile resins, gums, latex alkaloids, dyes, coloring material, and inorganic
materials (ash). Cellulose is a polymeric chain made up o f anhydro D-glucose monomers
(Figure 2-1) linked together by oxygen atoms. In a typical woody cell wall, each chain is
composed o f approximately 10,000 monomers and is approximately 5 pm in length. The
chains making up the wall are arranged in a closely packed, stable, ribbon-shaped,
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8
O-C-H
I
H-C-OH
I
HO-C-H
I
H-C-O-O-f
O-C-H-OI
H-C-OH
I
HO-C-H
I
"”~/C-H
H-i
CH2OH
CH2OH
Figure 2-1: Two (3 D-glucose monomers2
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crystalline structure. The hydroxyl bonds (O-H) present in each chain easily bind to
other chains, and the carbon-to-carbon (C-C) bonds give the chain rigidity.
Like cellulose, hemicellulose is also a polysaccharide that is soluble in alkali and
hydrolyzable by acids, while cellulose is resistant to chemical attack. Cellulose is
surrounded by hemicellulose creating a long microfibril. The microfibrils are mostly
aligned parallel to each other. Lignin is an amorphous, rigid polymer with a phenol ring
consisting o f up to three subsituted methoxyl groups, depending on the species of tree.
The lignin is located in cavities between the microfibrils and serves to increase the
stiffness of the cell wall, because of its inherent resistance to absorbing moisture, and the
rigidity o f the chain itself. The continuous lignin matrix has some plasticity, and the
microfibrils have high tensile strength in the direction o f the elongated length. There are
also voids in the matrix that create pores in the cell wall. Cell wall densities, therefore,
vary locally. Moisture can also enter the cell wall through these pores.
All cells originate in the cambium layer. Some cells remain in this region and
continue to divide. Their daughter cells differentiate into both xylem and phloem cells.
If the cambium cell divides in the xylem direction, xylem cells are eventually created.
Conversely, division in the phloem direction eventually creates phloem cells. In the
dividing cell, the chromosomes in a single nucleus split and move apart. A cell plate then
develops between the two identical sets o f chromosomes separating the protoplast.
Finally, the two new cells enlarge until they become the same size as the original.
Pectin is present between nearest-neighbor cells, allowing movement via slippage
between the cells as their walls expand. The primary cell wall changes over time by the
addition of a thickening, relatively dense, mostly cellulose layer, that renders additional
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10
wall expansion impossible and is henceforth called the secondary cell wall. Specialized
modifications such as recesses (pits) or perforations that allow movement o f water up the
tree in the secondary wall take place during this time. Throughout this maturing process
the cell is still living.
If a cell is located in the sapwood bordering dead heartwood cells, the waste
products produced by the living cells cannot be transported because the heartwood region
acts as a barrier. Toxic levels will eventually be reached, killing the cell. Other factors in
this process include progressive depletion o f oxygen, starches, sugars, and nitrogenous
material the closer the cell gets to the heartwood border region. Eventually, the cell
reaches its final developmental stage—death (the cytoplasm dies). In the case o f a
sapwood cell, the former living cell becomes heartwood, resulting in outward movement
o f the boundary between heartwood and sapwood. Living cells in the phloem will also
eventually die leaving an outer layer o f dead bark around the tree that cracks and breaks
off.
Traditionally, a woody cell is characterized by its function, shape, and orientation.
The four types o f woody cells are vessel elements, tracheids, parenchyma, and fiber cells.
Tree species can be differentiated by the types o f cells that make up the organism, as well
as by cell arrangements.
Functionally, vessel elements primarily conduct water from the roots to the tree
canopy and are located in the xylem As soon as the individual vessel cell is fully
developed, it loses its protoplast. Back-to-back vessels cells are then connected when
enzymes eat holes in the walls that are touching, creating a water pathway. Although the
individual vessel cell remains the same length as was initially formed in the cambium
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(fusiform cambiai initial), it grows in diameter. Over the growing season, the diameter o f
the vessel may change depending on the tree species. For example, the vessel diameter in
oak trees is much larger early in the growing season than later, whereas poplar trees have
similar size vessel diameters throughout the growing season. Most individual cells are
orientated in the longitudinal direction. Collectively, the pathways are three dimensional,
spreading throughout the tree in all directions, not just longitudinally (Figure 2-2).
Unlike vessel cells, tracheids (Figure 2-3) are closed at their ends. They can be
longitudinal, vascular, or vasicentric. Their main function is mechanical in nature. Over
time, all tracheids elongate by various amounts from their initial cambium cell shape.
Longitudinal tracheids are long, regularly shaped cells that are arranged in a very orderly
fashion in radial rows. Some longitudinal tracheids have resin deposits contained within
them, whereas others are arranged in strands. Except for the lack o f perforations,
vascular tracheids are very similar to late growth vessels. They are arranged in
longitudinal rows. Both the length and the diameter o f the vascular tracheid increase as
the cell matures. Vascular tracheids are regular in shape. Vasicentric tracheids are
irregular in shape and not arranged in rows.
Parenchyma cells (Figure 2-4) are o f two types: (1) short, squatty cells that have
divided from the cambium initial cell or (2) fusiform parenchyma cells that are undivided
and essentially the same size as the initial cambiai cell. The two primary functions of
parenchyma cells are storage and carbohydrate conduction. This type o f cell keeps its
protoplast throughout the sapwood phase, which is much longer than tracheids, vessels,
or fibers. Parenchyma cells can be aggregated in the transverse direction (ray
parenchyma) or in the longitudinal direction (axial, strand or epithelial parenchyma).
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12
P
B
A
Figure 2-2: Vessel element: A) early-wood and B) late-wood
r - 'l
r
A
B
C
Figure 2-3: Tracheids: A) longitudinal, B) vascular, and C) vasicentric
A
V
B
Figure 2-4: Parenchyma cells: A) strand o f longitudinal parenchyma and
B) fusiform parenchyma cell
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13
Epithelial parenchyma cells form the outer walls of the resin canals and excrete resin into
the canals. These canals can be in the transverse (ray) or longitudinal directions.
Depending on the wood species, resin canals can range from 50-300 pm.
Fibers (Figure 2-5) are extremely long and narrow. As with tracheids, these cells
have closed ends. Fiber walls are fairly thick to very thick in width. Some fibers have an
inner gelatinous lining. Fiber diameter and wall thickness vary greatly both within
species and between species.
Tree species are divided into softwoods (e.g., pine and firs) and hardwoods (e.g.,
oak and poplar). Hardwoods have pores (vessels) that extend in the direction o f the
grain, whereas softwoods do not have these vessels. In addition, hardwoods contain a
larger number and variety o f cells and, thus, are more complex than softwoods. For
example, all softwoods have longitudinal tracheids (90 to 94% by volume for all species)
and ray parenchyma cells. Depending on the softwood species, other cell types could
include strand tracheids, ray tracheids, and epithelial parenchyma cells that surround
resin canals. In contrast, hardwoods may have vessel elements, vasicentric tracheids,
vascular tracheids, fiber tracheids, libriform fibers, strand parenchyma, fusiform
parenchyma, epithelial cells (both longitudinal and transverse), and ray parenchyma.
2.1.4
Temperature and Heat Transfer in Wood
Wood composition and defects are extremely important not only in determining
physical properties but also in predicting the microwave or ultrasound interactions that
will occur with the material. Within the cell walls, the water content, volume o f cell wall
substances, and proportional chemical composition are all factors that affect wood
properties. In addition, the arrangement and orientation o f wall materials, individual cells,
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14
Figure 2-5: Fibrous cell
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and their aggregate tissues may also play a role.
To compare water content to cell wall substances, the standard practice is to
measure the moisture content, which is the ratio o f the weight o f the water in wood
compared to the oven-dry weight o f the water. The wood sample with moisture is first
weighed and then dried in an oven until the weight no longer changes. The difference
between these two measurements constitutes the weight o f the water initially present in
the original sample. Error is introduced when wood volatiles such as resin or creosote
are present in the original wood sample and bum o ff during the drying process.
Water binds to the cell wall materials via hydrogen bonds, adheres to cell walls by
hydrophilic interactions, or fills any cavities that are present. Anisotropic dimensional
changes (swelling) in the wood sample will occur until the fiber saturation point is
reached because the wall volume expands with the addition o f water. Maximum moisture
content occurs when all available voids including the lumen in the wood sample are
filled. As moisture is reduced, anisotropic shrinkage may occur. As the wood swells or
shrinks from the maximum moisture content to the oven-dry conditions, the least
dimensional change normally occurs in the longitudinal direction (0.1 to 0.3%), whereas
the greatest change usually occurs in the tangential direction (4 to 6%). In the radial
direction, dimensional changes are usually from 2 to 3%. These changes cause distortion
in lumber, which is o f particular importance in the transmission o f ultrasound. The
moisture content in wood will vary until it reaches equilibrium with the moisture content
in the environment.
Temperature and relative humidity are both major factors in the drying process.
The steeper the gradient between the environment and the wood, the faster the movement
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16
o f moisture occurs. As the gradient lessens, the movement o f moisture also slows. This
is also true for movement o f water within the wood itself. Local water volume inside the
wood is an additional gradient, because water will move from wetter locations to drier.
Movement o f water (or gases when moisture is absent) in wood occurs via viscous flow
when the available openings are greater than a micrometer, but for smaller openings,
collisions between the molecules, creating a mean free path, are the controlling factors.
The rate o f flow o f these molecules is called the permeability o f wood.
The relative density o f wood is determined by the ratio of cell wall substances to
voids in a specified volume. The standard measurement (specific gravity) is the ratio o f
the oven-dry weight to the volume o f the green wood. Due to dimensional changes
discussed above, this measurement will vary with moisture content, unless the fiber
saturation point has been reached. Cell wall thickness, cell size, type o f cells, and
packing of the cells are also determining factors. Woods with specific gravities below
0.36 or above 0.50 are considered light or heavy, respectively.
Temperature of and heat transfer between local regions in a wood sample can
vary considerably. For example, conduction o f heat throughout the wood volume can
change with moisture content, direction o f heat flow, and specific gravity. For wood with
moisture contents greater than 40%, heat is conducted through the sample one-third faster
than for moisture contents less than 40%. When heat is flowing in the transverse
directions (either radially or tangentially), it is slower than in the longitudinal direction.
The larger the void space in wood (the lower the specific gravity), the slower the
conduction o f heat through the wood volume. O f course, wood can ignite if it reaches
critical temperatures (> 275 °C). Ignition is considered the point at which the wood
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17
begins to decompose with a release o f heat. Ignition can occur if a surface, a region, or
the entire volume of wood reaches this critical temperature; consequently, the rate and the
quantity o f energy supplied and geometric factors, such as the presence o f sharp
projecting edges, contribute to the critical combustion point for a specific sample.
Moisture content is another factor because water must first evaporate by heating
before combustion occurs. Once the moist wood begins to bum, the actual heat per pound
o f wood produced can be estimated by the following equation [2-1]:
100
heat (btu / lb) = H
me
-
V
[2 - 1]
1
100 + me
H = the heat o f combustion for 1 lb. o f oven-dry wood
(8500 btu for hardwoods and 9000 btu for softwoods)
me = moisture content o f the wood (%)
Short-term exposure o f wood to temperatures below 150 °C with a return to room
temperature does not affect the strength or the elastic properties o f wood, whereas
exposure to temperatures between 150 °C and 275 °C for any significant period o f time
can affect wood properties permanently.
2.1.5
Defects in Lumber
Defects in lumber include knots, grains, growth stress, cell injury, pitch, drying,
machining, and defects arising from external attack. A knot is actually the remnant o f a
branch that originated from the tree trunk or limb. The grain o f the wood is distorted to
accommodate the knot as additional growth is added to the tree. Knots exhibit different
characteristics from clear lumber such as higher densities. Shrinkage rates also vary from
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clear lumber.
The orientation o f woody fibers creates the grain in the wood. Straight grains are
considered most desirable. When the fibers are arranged in a helical pattern, however, a
spiral grain occurs. Both right-handed spirals and left-handed spirals can occur.
Strength, stiffness, twisting, and surface roughness can be affected by the presence o f
spiral grains. As the tree grows, tensile, compressive, and tangential stresses can occur.
These stresses can be the cause of crack development (either through the pith, separating
growth rings, or radiating from the pith) in the living tree. Compressive sheer failures that
result in slip planes that extend through a number o f nearest-neighbor cells can also occur
in living trees. Most o f these slip planes are not easily detectable, yet they can affect
bending and tensile strength. Once the tree is harvested for lumber, the relief o f these
residual growth stresses can cause cracking, splitting, bowing, crooking, or twisting. Both
air and oven drying can aggravate all o f these distortions. Individual cells can be injured
from frost causing distortion or outright collapse o f the cell wall. If resin canals are
present in the tree, empty or resin-filled pockets may develop, as well as resin seepage
into the cell walls. Bark can also be found in the wood on occasion when one region in
the cambium dies, but the surrounding region continues to grow and eventually covers
the existing bark. After harvest and during processing, additional defects in the lumber
such as cracks, collapse, or warping from the loss or gain o f moisture and the resulting
wood shrinkage and expansion can occur. From the machining required in the lumber
manufacturing process, surface roughness can occur due to a number o f reasons, such as
dullness o f the blade or the feeding rate. External attack from insects, fungi, bacteria, and
other organisms can also cause damage, such as holes and deterioration of the wood.
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2.2 Asian Longhomed Beetle Background
2.2.1 Introduction
The Asian longhomed beetle (Anoplophora glabripennis Motsch.) (ALB) is an
extremely dangerous pest that threatens U.S. and foreign forest resources. Forests and
street trees have been under attack in China for many years. “Members o f the Biological
Control Institute o f the Chinese Academy o f Agricultural Sciences (CAAS) consider
ALB as one of the most serious forest pests in China,” according to the USDA/APHIS
Initial Pest Risk Assessment on Solid Wood Packing Material from China.3 These pests
are beginning to establish themselves in the United States and Europe, as well as Asia.
Wooden packing material such as crates and pallets are considered the most likely
transoceanic transportation modes.
2.2.2 ALB Lifecycle and Host Preferences
ALB adults are black with white spots, 1 to 1 lA in. in length and have long
black/white antennae (Figure 2-6). ALB are known to attack poplar, willow, maple
(including sugar, silver, and Norway), sycamore, elm, horsechestnut, boxelder, and other
hardwood trees.4 ALB normally take one year to complete their life cycle (Figure 2-6 ).5
Adults may start to emerge from trees in June, but peak emergence is usually July.6
Emergence generally ceases by October,7 but warm weather may prolong emergence.
Upon emergence, females mate and begin a period o f oviposition that lasts between 10
and 70 days. Female beetles chew a small depression through the bark where they
oviposit a single egg. A female beetle can lay from 35 to 90 eggs during her lifetime,8
but recent studies in the laboratory suggest fecundity may be even higher.9 Eggs hatch in
approximately 15 days. Young larvae tunnel beneath the bark, feed on the cambium and
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20
Female lays egg under the
bark. Larva hatches and
begins to feed.
Ad5.1t Beetles
Larva
Tree dies within 2-3 years
Adult Beetle
tunnels out of
the tree leaving
these exit holes
Older larva tunnels
into the sapwood and
hardwood
Figure 2-6: Asian longhomed beetle lifecycle
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phloem tissue, and then move into the sapwood and heartwood as older larvae.10 The
larvae feed within the tree until early spring. Eight or more instars11 can be expected
before the larvae pupate, which occurs in late May and early June. The adults chew an
emergence hole ~1 cm in diameter. These exit holes are often how beetle infestations are
detected. Newly emerged adults can lay their eggs on their natal host tree or fly to
another tree and oviposit there.12 The entire lifecycle takes approximately one year to
complete.13 It is unknown how long adult beetles live in the field. The feeding activity o f
the larvae disrupts the flow of water and nutrients, weakens branches, and may eventually
kill the tree.14
2.2.3
ALB Worldwide and U.S. Infestations
Currently, ALB infestations can be found in Asia (China, Taiwan, Korea, and
possibly Japan), the United States (New York 1996, Illinois 1998, New Jersey 2002), and
Europe (Austria 2001) (Figure 2-7). In 1996, the first infestation o f ALB in the United
States was identified in Brooklyn, New York.15 Since then residential infestations in
Chicago, Illinois; Du Page, Illinois; Summit, Illinois; Brooklyn New York; Manhattan,
New York; and Amityville, New York, have been identified.16,17 In January 2002, two
infested trees were discovered within Central Park, a U. S. historical landmark.18 Later in
2002, an infestation was found in 101 trees over a 9-acre plot in Jersey City, New
Jersey.19 Identification o f ALB-infested packing material has occurred in at least 26
warehouses in 14 states. Additional U.S. introductions and infestations may have
already occurred but have not yet been discovered. A recent report predicts that if ALB
were to spread to urban areas throughout the United Stales, the maximum national urban
impact would be a loss o f 35% o f total canopy cover and a value loss o f $669 billion .21
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Figure 2-7: Worldwide distribution map o f Anoplophora glabripennis
(red dots signify infestations)
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23
This projection does not take into account that widespread ALB infestations in the United
States could also adversely impact forest products, commercial fruit, maple syrup,
nursery, and tourist industries (estimated at $41 billion in potential losses).22
2.2.4
ALB Worldwide Regulatory Control Efforts
Controlling the spread of the ALB, both in the United States and worldwide, is in
the best interest o f all nations. On December 17, 1998, U.S. regulations (CFR319,354)23
for solid wooden packing materials originating in China and Hong Kong were enacted to
reduce the risk o f new ALB introductions. Any such material must be heat treated or
fumigated before leaving China and Hong Kong to be allowed entry into the United
States. As o f2001, the following treatments24 are approved: methyl bromide fumigation,
preservatives, and kiln drying (Table 2-1). After the required treatment, the wooden
packing material can be utilized at any time, as long as it has been stored in a manner that
prevents reinfestation. Official Chinese phytosanitary documentation must accompany all
solid wooden packing material imported into the United States. If the proper
documentation is not presented, the USD A, APHIS inspector has two options. If there are
approved government facilities in the region, the inspector can allow the shipment to be
unpacked and the packing material destroyed or can refuse the shipment and have it sent
back to the country o f origin. Any costs incurred would be borne by the importer.
By 2005,25 methyl bromide can no longer be used as a fumigant in the United States due
to its toxicity and impact on the ozone layer. However, preshipment, quarantine, and
emergency uses will be exempt from this ban.
In March 2002, the United Nations introduced on a global scale new
phytosanitary guidelines26 addressing solid wood packing material for all their member
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Table 2-1: U.S.-approved solid wood packing treatments
outlined in CFR319.4027
Treatment
Type
Fumigation:
Methyl Bromide
Preservatives:
Arsenic
Copper Sulfate
Creosote
Copper-8quinolinate
Chlorpyrifos
Oxine-copper
Kiln drying
Temperature
Dosage
Rate
70 °F
or higher
21 °C
or higher
31b./
1000 ft.3
48 g/m3
40 °F - 69 °F
4.5 °C - 20.5 °C
51b./
1000 ft.3
80 g/m3
Minimum
Concentration
Readings (oz.) at:
0.5 hr
36
2.0 hr
30
4.0 hr
27
16.0 hr
25
0.5 hr
2.0 hr
4.0 hr
16.0 hr
60
51
46
42
Follow
label
Instructions
Moisture content
must be less than
20 % o f the dry
matter.
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25
countries. Approved treatments also include heat treatment (kiln-drying and chemical
pressure techniques utilizing steam, hot water, or dry heat) and methyl bromide
fumigation. The U.N. treatment schedules are delineated in Table 2-2. The U.N. kilndried requirements (56 °C at the core for 30 minutes) differ significantly from the U.S.
requirements for imports (kiln-dried to 20 % moisture content).
2.2.5
Management ofU .S. ALB Infestations
Once an infestation has been established in the United States, four management
strategies are used as follows: ( 1) cutting down and burning the infested trees, (2)
injecting imidacloprid (Imicide) into trees on the perimeters surrounding the quarantine
zones, (3) surveying the region for additional infestation sites, and (4) establishing
quarantine zones that restrict movement o f wood into and out o f the region. As o f
November 2001, 8,204 ALB infested trees have been cut down and destroyed in the
United States (New York and Chicago infestations).28 In an attempt to halt the spread of
the beetle, Imicide is currently being injected into infested trees around the outside
borders of some infested regions. In 2000 and 2001, 11,440 trees in the Chicago area and
23,740 trees in the New York area were chemically treated. This is a labor-intensive
process. Capsules o f Imicide were manually inserted into the tree trunk during a 6 - to 8week window between April and June. After 4 hours the capsules were removed. In
addition to this manual labor, the public (and the government personnel) must be
protected from the insecticide while it is being applied. Since the plan is for treatments to
provide protection for 3 years, efficacy has not yet been determined.
In addition to prophylactic treatment, yearly surveys are being conducted in
infested regions and buffer zones. For example, the number o f square miles infested in
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26
Table 2-2: U.N.-approved solid wood packing treatment schedules as
outlined in The International Standards for Phytosanitary Measures
Guidelines for Regulating Wood Packaging Material
in International Trade29
Treatment
Type
Temperature
Dosage
Rate
Fumigation:
Methyl Bromide
Heat Treatment:
Kiln-drying
Chemical pressure
impregnation
Minimum
Concentration
Readings (oz.) at:
Minimum exposure
time is 16 hours.
0.5 hr
36
2.0 hr
24
4.0 hr
17
16.0 hr
14
21 °C
or higher
48 g/m3
16 °C
or higher
56 g/m3
0.5 hr
2.0 hr
4.0 hr
16.0 hr
42
28
20
17
11 °C
or higher
64 g/m
0.5 hr
2.0 hr
4.0 hr
16.0 hr
48
32
22
19
All heat treatments
must attain a wood
core temperature of
56 °C for 30 minutes
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27
New York for the years 1997 to 2001 (Nov.) was as follows: 70,113,149,157, and 180,
respectively. Before 2001, only the core infestation regions were surveyed. In 2001, the
survey was expanded to include a 1Vi-mile buffer region. Bucket trucks that can bring
the spotters into the tree canopy are used, as well as tree climbers and spotters on the
ground using binoculars.
2.2.6 Current ALB Research
ALB research can be divided into five different areas as follows: (1) survey, (2)
regulatory and exclusion, (3) control, (4) biology and rearing, and (5) impact assessment.
The scope o f these efforts is worldwide. Those countries that already have infestations
are trying to control them, and those countries currently not affected are attempting to
continue to exclude the pest. Many U.S. research efforts are being conducted in
conjunction with Chinese collaborators due to their access to large quantities o f beetles in
their natural environment on the Chinese mainland. Much o f the prior research published
by Chinese scholars has not been translated into English, is not available in U.S. libraries,
and, therefore, may be missing from this dissertation.
2.2.6.1 Surveys
Estimating the presence, population, and scope o f an infested area is the goal o f
the surveys. A number o f tools such as trapping systems, infestation dynamics, acoustic
sensors, and visual surveys are being investigated in order to improve survey efforts.
Trapping beetles in their natural environment either for eradication or population
estimation purposes must use either a physical, chemical, or biological means. For
example, a long-range attractant to entice a beetle geographically located far away to
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move toward and into a trap would greatly improve trap effectiveness. However, to date
•
• •
only short-range attractants have been identified that have biological activity.
30
In
addition, beetles appear to use visual cues to find host trees; they are visually attracted to
large upright objects and dark shapes. Research conducted by Miller et al31 on diacetone
alcohol (a boxelder tree volatile) and ethanol for use as bait has not been successful.
However, they found that five different pipe and multiple-funnel trap designs captured
significant numbers o f ALB.
In addition to short-range attractants, a contact pheromone that may be useful as a
close-range attractant was identified, synthesized, and successfully tested by Zhang et
al.32 Adult beetles have been reported to disperse up to 2,664 m;33 however, most new
oviposition sites34 were found within one-eighth to one-quarter mile o f previously
infested trees. Williams35 utilized harmonic radar devices attached to ALB adults located
in South Korea, as well as capture/mark/recapture techniques to track dispersal patterns.
He found that the radar tags were workable for short time periods (a couple o f days) but
were often damaged over longer time frames. In Qintongxia, Ningxia, an autonomous
region in China, Junbao et al36 studied the dispersal pattern o f ALB using the
capture/mark/recapture method. They noted that the average dispersal distance for this
population was 106.3 m. Although similar to other wood borers, initial research37
showed that ALB larva produce an identifiable acoustic signature while feeding.
Recordings o f the feeding sounds were made both in the field and in the laboratory.
Currently, appropriate hardware and software are being modified in order to improve
vibration filtering, as well as to engineer an inexpensive, hand-held detection instrument.
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2.2.6.2 Regulatory and Exclusion Research
Keeping new ALB introductions from occurring and/or spreading is the goal o f
research on regulatory issues and exclusion o f ALB. Since the primary transportation
mechanism o f ALB into the United States is assumed to be infested solid wood packing
material, research has been done to estimate the risk, that a particular life stage present in
a tree at the time it was cut down poses, based on the likelihood that that life stage could
complete development into an adult. In various maple species, Keena and Lazarus38
found that completion o f larval development is more likely for more mature larvae than
for immature larvae or eggs. They also observed that the softer the wood, the more likely
an egg would be able to develop into an adult. These conclusions support the hypothesis
that solid wood packing material, as well as cut firewood, can be a transport mechanism
for ALB. Identification o f infested regions is also vital. Comparison o f visual survey
techniques39 currently in use in New York and Chicago showed that spotters in the tree or
in a bucket truck above the ground were more effective at detecting infestations than
spotters on the ground.
In order to confirm that the USDA’s solid wood packing material treatment
schedule (T404b4) is effective, lumber experiments have been conducted using both kiln
heat treatments and fumigation. Preliminary results reported by Mack et al40 showed that
heat-treating poplar boards (2.5-, 5-, 7.5-, 10-, and 20-cm thick) to 60 °C at the core for
30 minutes in a kiln is 100% effective for the control o f late instar ALB. Both methyl
bromide and sulfuryl fluoride fumigants were tested in temperature-controlled, smallchamber experiments on poplar lumber naturally infested with ALB larvae.41 At
temperatures between 4.4 and 21.1 °C, methyl bromide proved to be effective. Sulfuryl
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30
fluoride required very high concentrations to attain 100% mortality between 10 and
21.1 °C. Experiments at both colder and warmer temperatures are planned. In addition,
microwave and ultrasound techniques were investigated and the results were reported in
this dissertation. Research is also underway to quantify the risk o f ALB importation into
the United States via the solid wood packing material pathway.
42
2-2.6.3 Eradication Research
Eradication o f established infestations in a region is also an important
consideration for research. Both biological and chemical control methods, as well as tree
resistance, mating disruption, and physical means, are being investigated as potential
control tactics. Physical disruption o f the ALB lifecycle in the form o f chipping infested
logs was studied by Wang et al.43 After artificial insertion o f surrogate larvae into logs,
the logs were chipped. All larvae were killed in the process. Thus, Wang concluded that
chipping alone was sufficient to destroy beetles in infested logs without the need for
subsequent burning o f the chipped wood.
On the biological front, Endoreticulatus and Enterocytozoon spores, as well as
entomophagous nematodes,44 have been found in ALB larvae and adults. Studies on
these three potential biological control agents have begun. Softer et al45 tested four
species o f nematodes and found that S. carpocapsae and H marelatus (soil nematodes)
had the highest mortality rate. One method o f nematode application under investigation
is to place the nematodes in emergence holes and then monitor beetle emergence.
Bacillus thuringiensis toxins may also be a potential control tactic. Several toxins have
been identified and are currently being tested by D’Amico and Podgwaite.46
Entomopathogenic fungi such as Beauveria brongniartii are being investigated by Hajek
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et al.47 Hajek and Dubois48 found that woven cloth bands containing entomopathogenic
fungi are effective control agents for A. glabripennis; however, additional research on
where the bands should be placed on a host tree is currently underway. Other
microorganisms such as bacteria that can kill ALB larvae are also being investigated by
i 49
Podgwaite et al.
Parasitoids are being studied as potential biological control agents. The following
parasitoids of cerambyids have been identified: Dastarcus longulus Sharp (Coleoptera:
Colydiidae) (larval),50 Schleroderma guani Xiao et Wu (Hymenoptera:
Bethylidae)(larval),51 Bullaea spp. (Dipter: Tachinidae) (larval) ,52 Megarhyssa spp.
(Hymenopter: Ichneumonidae) (larval),53 D. longulus (pupal),54 S. guani (larval and
pupal),55 Aprostocetus sp. (Hymenoptera: Eulophidae) , 36 an ectoparasitoid E. albitarsis
(early larval) , 57 Billaea irrorata (Meigen)(Diptera, Tachinidae) (full grown larval) , 58 and
Dolichomitus populneur (Ratzeburg)(Hymenoptera, Ichneumonidae)(full grown
larval).59 According to Smith et al, 60 ALB larval mortality rates ranged between 25%
and 95% for D. longulus. Rearing technologies for the most promising parasitoids, D.
longulus and S. guani, are under development by Chinese collaborators.
Chemical insecticides are another potential means o f ALB control. Haack et al61
performed tests using imidacloprid, thiamethoxam, azadirachtin, emamectin benzoate,
and thiacloprid on various tree species including poplar, silver maple, boxelder,
American elm, other elm species, and willow. Moderately successful results were found
with imidacloprid, azadirachtin, and emamectin benzoate in field trials conducted in
China. Imidacloprid was the most effective producing 81% and 100% mortality o f large
•
f\ 0
•
•
larvae and adults still inside the tree, respectively. McLane et al also investigated the
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effectiveness o f systemic insecticides, especially imidacloprid. Their preliminary results
showed that trunk injection was a more efficacious alternative than soil injection.
However, large variations in insecticide levels within individual trees were observed,
regardless of the injection method used. In addition, the authors speculated that the
measured levels o f insecticide reaching target insects was too low to be effective against
ALB larvae, although adult beetles were killed with these treatments. Further field trials
and laboratory experiments are being conducted on these and other insecticide
alternatives.
Research to determine what tree species are resistant/preferred by ALB is also
currently underway. Testing the hardwood species that are being replanted in Chicago
and in New York after ALB infested trees have been destroyed to see if they are also
susceptible to attack by ALB is an important component to the control effort. Of the tree
63
species tested, preliminary results reported by Haack et al found that Carpinus
caroliniana and Celtis occidentalis were the least susceptible to ALB oviposition, and
Ostrya virginiana and Tilia americana were preferred hosts. Hoover et al64 are
developing a hierarchical ALB preferred tree species list from their greenhouse
experiments. Results from initial tests showed that artificially inserted ALB larvae
survived in all three o f the species tested including red oak, sugar maple, and green ash.
The survival rates, however, were markedly different; survival was 67% in oak, 50% in
maple, and 17% in ash on day 90 following insertion.
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2.2.6A Biology and Rearing
Haack et al65 are studying the distribution o f ALB within trees and have
determined that all life stages survive the winter. In ash the fewest eggs appeared to
survive to the larval stage, in silver and Norway maple survival rate was greater, and in
boxelder and horsechestnut trees survival was the highest. The researchers based this
conclusion on the assumption that each oviposition site found contained one egg.
However, observations in the laboratory (Keena 2001) and in potted trees (Morewood,
pers. comm.) show that females often chew excavation sites in which they do not
oviposit. For example, Keena66 reported that many excavations sites (270) were made by
an individual female beetle, but only approximately one-quarter o f the pits were egg
repositories. Also in the laboratory, Lazarus and McCullough67 found that egg pits were
found on sycamore and eastern cottonwood samples, but no eggs hatched. As with
Haack’s results discussed above, Lazarus and McCullough also found that some host
species had a greater egg-to-larva survival rate than others. The order from highest
survival rate to lowest for their study was as follows: sugar maple, white oak, northern
red oak, honeylocust, sycamore, and eastern cottonwood. Interestingly, Haack et al68 also
observed that in most U.S. infestations the tree canopy was attacked first by ALB,
whereas in China the beetle attacks the trunk and major branches throughout the tree.
One U.S. stand, however, was attacked in the same manner as the trees sampled in China.
Both the Chinese stand and one o f the U.S. stands contained trees with small trunk
diameters and many branches and twigs located low on the trunk and were grown in rows
(a fence in the U.S. stand and windrows in China). In contrast, the trees in the other U.S.
stands that were attacked first in the canopy were much larger in diameter and had larger
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branches. The researchers surmised that the absence o f twigs lower down on the larger
diameter tree trunks was unattractive since adult beetles feed on twigs. Instead the
beetles fed higher in the canopy. Of course, the reverse would hold true for the smaller
diameter trees seen in China and one o f the U.S. stands. The twigs were located
throughout the trunk and therefore the beetles could feed and attack anywhere on the
trunk. This conclusion assumes that the beetle will feed and then lay their eggs in the
same vicinity. This assumption is supported somewhat by observations reported by
Lazarus and McCullough.69 They filmed mating pairs of beetles in a chamber to observe
their behavior. The following sequence was noted in all cases: the female and male had
multiple matings during the observation period. After each mating, in most cases, the
females fed on twigs, then dug the egg pit and laid an egg. It would make sense, if this
sequence holds true, that the presence o f feeding twigs might be an attractive site for an
egg-laying female.
Temperature70 has a marked affect on the life span and egg-laying behavior o f the
species. The cooler the temperatures (15 to 20 °C), the longer the expected lifespan for
both sexes, whereas the warmer the temperature (25 °C), the greater the number o f eggs
laid by the female.
ALB flight propensity is a key component in the rate and distance an infestation
will spread in a region. Keena71 found that after emergence, both males and females
walk around the tree section that they emerged from. The choice to fly occurs more often
(-50%) when the tree section is dry and when there is little wind (0 to 0.5 m/s). Males
are more likely to fly than females, especially when there is plenty o f food at the
emergence site, whereas females prefer to dig egg pits instead o f flying to a new site.
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This suggests that the quality o f the environment is key for female flight. The poorer the
environment, the more likely the female is to fly. O f course, female flight patterns are
the controlling factor for the spread o f the infestation. Hu and Huang72 reported that the
male finds the female via a sex pheromone at long distances, and visual cues offered by
the female are important at short distances. However, as mentioned previously, this result
has not been reproduced despite efforts by others.
Rearing is an important component o f the research effort. In order to conduct a
large research program, a stable supply o f insects in all life stages is required.
Consequently, rearing the insects in captivity is a valuable tool. Diets to feed these
insects have been developed by Hajek et al,73 Keena,74 and Lance et al75 Hajek had a
colony o f approximately 1640 individuals as o f January 2001, and Keena had 2,500
larvae and 30 mating pairs. Keena estimates that the rearing cost per beetle is
approximately $50. All three colonies have produced healthy adults capable o f flight and
reproduction. Both Hajek and Keena have reported that a cold period (a chill) is often
necessary in order for ALB larvae to continue development. Refinement of the rearing
protocol is an ongoing process with all three colonies.
2.2.6.5 Impact Assessment
Assessing the risk and the potential impact o f widespread ALB infestations in the
United States is currently being modeled by a number o f techniques. Both urban76 and
forest77 impacts are currently being assessed, as well as development o f predictive
no
population modeling.
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36
2,3 Ultrasound Background
2.3.1 Introduction
Ultrasound is arbitrarily defined as a sound wave with a frequency (16 kHz to
>20 MHz), that cannot be heard by the human ear. Sound waves are propagated
through a medium by the motion of particles responding to the force applied from the
incident wave. Based on this particle motion, ultrasound is usually classified into
three wave types: longitudinal, shear, and surface waves, each o f which is described
in section 2.3.2.
All ultrasonic wave motion can be described by the general wave equation. A
summary of the main concepts can be found in section 2.3.3.
When an incident wave passes from a region o f one acoustic density
(impedance) to a region with a different acoustic density, it is either transmitted or
reflected across the boundary. Many principles that apply to optics, such as Snell’s law
o f refraction, Huygen’s principle, and diffraction, also apply to ultrasound and will be
discussed in detail in section 2.3.4. Also discussed is the effect o f attenuation and
absorption on ultrasonic wave propagation in a medium. The Doppler effect (the
receiving transducer measures different acoustic frequencies when the ultrasound
emitter/medium/ultrasound receiver system is stationary versus when one or more
components o f the system is moving) also can occur. However, this phenomenon is not
discussed in detail since the ultrasonic systems (including the c-scan setup) used in this
research project send and receive the signal while all components are stationary.
Ultrasonic applications can be separated into two broad categories: those where
the waves pass through a material without any effect (low power) on the material and
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those that change the material in some manner (high power). Nondestructive ultrasonic
evaluation of material is a low intensity application that is further discussed in section
2.3.5.
In nature, ultrasound plays a significant role. Certain insects such as flying
crickets, praying mantids, and tiger beetles take evasive action when ultrasonic waves hit
them. Bats, on the other hand, use ultrasound to find prey and to navigate. According to
one researcher, ice in wood emits ultrasonic waves as it melts. Additional details are
provided in section 2.3.6.
2.3.2 Wave Types
One model79 o f wave motion in solids is based on a three-dimensional lattice of
atoms with springs (interatomic electrical forces) connecting them. When pressure from
the sound wave is applied, the atoms move from their original position, disturbing their
neighboring atoms. The atom will eventually reach a critical distance and will spring
back towards its original position. O f course, the neighboring atom movement then
disturbs its neighbors as well and the wave is propagated through the material until the
initial energy is dissipated. In gases,80 a change in volume occurs first by compression
and then rarefaction as a result o f the pressure per unit area applied. Longitudinal, shear,
and surface waves are all initiated by ultrasonic pressure, but the resulting atomic motion
is different.
2.3.2.1 Longitudinal Waves
If the movement o f the atoms is in the direction o f the pressure applied, then the
resulting waves are called longitudinal or compression waves.81 The bulk velocity o f
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sound,82 Cb, for this type o f wave in a solid is equation [2 -2 ]:
2f
(l~o)
] ~2
[2-2]
f
=
v
(1
+
o)(l
2u)j
<Pj
where v is Poisson’s ratio, Y is Young’s modulus o f elasticity (dyn/cm2), and p is the
density (g/cm2) o f the material in the direction o f propagation. In other words, the
velocity o f sound through a bulk material is dependent upon the following: the ratio o f
the decrease in the thickness o f the solid to the length increase under the load applied, the
ability o f material to recover its deformation elastically after the stress is applied, and the
density o f the material. In liquids, the velocity o f sound,83 Ci, is equation [2-3]:
C, = ( p P s ) 2
[2-3]
where (3Sis the adiabatic compressibility factor and p is the density o f the liquid.
Adiabatic compressibility assumes that the volume o f the liquid is reduced without heat
or energy exchange with the system. Therefore, the temperature o f the liquid must
change. While in a gas, the velocity o f sound84 is equation [2-4]:
c =r
(
Tc2 ^ ( T '
\ +^ iL 1 6 2 Jc
T
64 p QV
I M)
1
J[ r j
[2-4]
where y is the ratio o f specific heats o f the gas at constant pressure vs. constant volume, R
is the gas constant, T is the absolute temperature, M is the molecular weight, p is the
pressure, Tc is the critical temperature o f the gas, and pc is the critical pressure o f the gas.
According to Bhardwaj,85 “The velocity o f longitudinal waves in steel is 580,000 cm/s,
for water it is 150,000 cm/s, and for air it is 33,000 cm/s.”
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23.2.2 Shear Waves
When pressure on the medium is applied in one direction and the atoms move
perpendicular to this direction, a shear wave (also called transverse) results. Propagation
o f these waves usually occurs only in solids because they are dependent on attractive
force between the atoms, which are not as strong in gases and liquids.
86
The bulk
velocity o f shear waves,87 cs, is equation [2-5]:
c. =
^ Y ^ 2 *
'
n ,- i
/
^
[2-5]
\P j
\Pj
where v is Poisson’s ratio, Tis Young’s modulus o f elasticity, p is the density o f the
material in the direction o f propagation, and p is the shear modulus.
2.3.2.3 Surface Waves
Combinations of shear and longitudinal waves may result when the ultrasonic
wave is bounded by two different mediums (i.e., a solid and gas) on the surface o f a
material, as in the case o f Rayleigh waves.88 The resulting particle motion is elliptical
with penetration approximately one longitudinal wavelength into the material and a
velocity o f equation [2 -6 ]:
c
- r C
R ~
R
I2’ 6]
s
where Cs is the bulk velocity o f the shear wave in equation [2-5] and K
r
is a constant.
Ultrasonic Raleigh waves can be used to detect surface defects in solids. Although Lamb
waves, which generate complex vibrations in relatively thin plates, are a second type o f
ultrasonic surface wave, they will not be discussed further.
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2.3.3
General Wave Equation
The following information on the general wave equation, energy density, and
intensity is summarized from the first chapter in G.L Gooderman’s book Ultrasonics. 89
In general, waves can be considered a local disturbance (perhaps due to pressure, volume,
density, or displacement) that propagates energy through the medium. Once the
disturbance has passed the medium returns to its initial state. The fundamental equation
o f wave motion in one dimension is equation [2-7]:
d 2e
d tl
■= c
2 d 29
[2-7]
d x2
where theta, 0 , represents a parameter that is a measure of the disturbance, c is the
velocity o f the wave, t is the time, and x is the position. To understand this equation, one
should assume that at a specific time one point on the wave is at position x, but at some
time later that point has moved to a different location, x = 0 = x +/- ct, where c is the
velocity and t is the time. The mathematicians (Laplace specifically) deduced from
experimental observations that taking the second derivative o f time with respect to 0 is
equal to the velocity squared times the second derivative o f position with respect to 0 .
If an experimental observation follows this relationship, wave motion is
occurring. This equation stems back to Newton first law F=ma, where the second
derivative o f 0 with respect to time is the acceleration and l/m *£F must equal the lefthand side of equation [2-7] above. If the forces in each direction (x,y,z) are not equal,
then the block o f mass m will be accelerated in a direction, say direction x. Now
assuming the disturbance is displacement, the force can be obtained in terms of stressstrain relations in a medium. When a force is applied to a solid rectangular material, the
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41
solid can be displaced by tensile strains in three different directions xx, yy, and zz and
deformed by shear strains also in three directions xz, yz, and yx. Now we chose a point
A which is at the coordinate (x,y,z) and apply a force which moves point A to point H at
coordinate (x+Ax, y + Ay, z+Az). Tensile strain is defined as the proportional change in
length in one direction (i.e., Al/lo). Assuming, the stresses are small and only those acting
in the x directions are unbalanced, the net force on a parallelpiped is equation [2 -8]:
da
<3cr
Qa
F = -——Sxdydzy— ^ S yS x d zy— ^SzSxSy
dx
dy
dz
[2-81
1 J
where <7xx is the normal force in the x direction, crxy and oxz are the shear forces, and Sx,
Sy, and 8z are the lengths o f the respective sides o f the material. The mass is density
times volume, p8x8y8z. Therefore, substituting these equations for mass and force into
Newton’s second law, the following equation [2-9] results:
dx
, dcr*y , dera ..
dy
dz
n d 20
dt2
[2-9]
Assuming the stresses experienced by the material are much less than the elastic limit,
strain on the medium is directly proportional to the stress. With this assumption, the
stress in the xx direction can be related to the strain, e, in the following manner
[2-10]:
(j
^ xx
= c^e
+ Ic^e
I xx
-hc^e
yy + ciA
14 e>-x '-fc, .1<e
5^ z.v '+c^e
^ 16 ^
1 *"12
[2-101J
L
The elastic constants o f the material are denoted by c in this equation. All o f the other
stress components (oxx, cryy, azz, ayz, ozx, axy) can be related to the resulting strain
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42
similarly. For a completely isotropic material, the elastic constants can be reduced to
two, X and p, also known as Lame’s constants. These constants can be related to Young’s
modulus (Y) [2-11], the bulk modulus (k)[2-12], the shear modulus (p) [2-13], and
Poisson’s ratio (v)[2-14] as follows:
y = /d(3A_+2/v)
X + fi
[2-11]
[2- 12]
[2-13]
P =P
[2-14]
V
2(X + ju)
In three dimensions the general wave equation takes the following form [2-15]:
8
1e -f —d1—e d20
+
8x2
dy2
dz2
1
—
d29
—- ——
c2 dt2
[2-15]
A general wave equation in the form o f equation [2-15] can be written to describe
each o f the wave types (longitudinal, surface, and shear). The respective velocity term, c,
is denoted in equations [2-2], [2-3], [2-4], [2-5], and [2-6]. Since particles oscillate when
a sound wave is present, there is kinetic energy associated with the wave. The energy
density, E (energy per unit volume), for a wave traveling only in the positive x direction
can be expressed as equation [2-16]:
f p 0U 2 \ _ P 2 _ n m p 0cs
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[2-16]
where P is the pressure amplitude, U is the velocity amplitude, c is the velocity o f sound,
p0 is the density o f the unstressed medium, © is the angular frequency, 81 is the amplitude
o f the wave traveling in the positive x direction, and A, is the wavelength. Intensity, the
amount o f energy transmitted in one second through a unit area, is equal to the energy
density times the velocity o f sound [2-17]:
[2-17]
2.3.4
Principles of Ultrasonic Wave Motion
Ultrasound can be reflected, refracted, or diffracted. Reflection occurs when the
ultrasonic wave encounters a boundary between two mediums and some or part of the
wave bounces off the boundary back into the original medium. A portion o f the incident
wave may be transmitted across the interface into the second medium. Refraction occurs
when the transmitted wave changes direction. The angle o f incidence o f the wave is quite
important. When the angle o f incidence is perpendicular to the interface, the transmitted
portion of the wave continues in the same direction and the reflected portion travels back
along the same path as the incident wave. The portions o f the wave reflected [2-18] and
transmitted [2-19] can be defined by their respective coefficients:90
r
R =
Z ,
~ Z ;
[2-18]
[2-19]
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44
where Zj and Z2 are the acoustic impedances o f the incident and the transmitted media,
respectively. Acoustic impedance (z) is a property o f the material that is dependent upon
the material density (p) and the velocity o f sound (c) in the material. Also called acoustic
density, the equation for acoustic impedance91 is as follows [2-20]
2 = pc
[2-20]
The transmission and reflection coefficients must add up to 1. In general, one can expect
that if zi is less than Z2, then the transmitted portion o f the wave will be greater than the
reflected portion. In addition, if the angle o f incidence is oblique, the reflected portion o f
the wave will change direction by an angle equal to the incident angle (Figure 2-8). The
transmitted portion o f the wave, on the other hand, will refract at the interface. This
occurs because the speed o f the wave is changed when the wave passes into a different
medium
When refraction o f a longitudinal wave occurs, the following relationship [2-21]
between the velocity in medium 1 (ci), the velocity in medium 2 (C2), the angle of
incidence (0i), and the angle o f refraction (0x) is as follows:
sm.6j '
I
ci J
^sin 0T
K C2 j
Diffraction is the constructive interference o f overlapping waves. This occurs
when two waves that are completely in phase with each other overlap and their
amplitudes add together. Waves are completely in phase when their path lengths differ
by zero wavelengths or a whole number o f wavelengths.92 Destructive interference, on
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Incident
Wave
Medium 1
Medium 2
•
6t Transmitted
Wave
Figure 2-8: Schematic o f material/wave interaction
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46
the other hand, occurs when the overlapping waves are out of phase and the scattered
rays cancel each other.93 One model o f wave interference was proposed by Huygen and is
called Huygen’s principle.94,95 He suggested that when a wave is initiated at a point, the
wave front radiates uniformly out in a sphere. Unlike plane wave fronts where the
pressure amplitude is assumed to remain constant, the spherical wave front pressure
amplitude decreases as the wave advances. In addition, acoustic impedance is
considered complex for this model. However, when r, the distance from the originating
wave, is greater than 1.1 times the wavelength, the difference between the real impedance
and the complex impedance is less than 1%. As summarized by Bhaardwaj,96
interference occurs when two or more spherical wave fronts from different point sources
overlap. The resulting wave front will no longer be spherical due to constructive and
destructive interference. Moreover, the acoustic pressure at points on this new wave
front will be a composite of maxima and minima resulting from two or more originating
wave fronts. Interpretation o f ultrasonic signals that have been reflected from a sample
must take into account these varying acoustic pressure intensities. For a circular-shaped
transducer the locations o f maxima [2-22] and minima [2-23] acoustic pressure points on
the central source transducer axis can be calculated by the following equations:
Y+ _ D 2 - A2( i m + l f
m~
4A.(2m + 1)
[2-22]
(m = 0,l,2,3...)
[2-23]
The diameter o f the transducer is D, X is the wave length,
is the distance o f the
maximum from the transducer, and Y'n is the distance o f the minimum from the
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47
transducer. Maxima and minima are located close together near the transducer. This
region is called the zone o f confusion (Figure 2-9) because the amplitudes o f these peaks
and troughs are very sensitive to slight changes in locations o f the reflectors in the
medium being examined. From personal experience, Bhardwaj suggests that the best
ultrasonic observations, i.e., those that are free from the deleterious effects o f
interference, can be made between Y^o +/- 30%. Any distance further than Y^o from the
receiving transducer is called the far field or Fraunhofer zone, whereas the distance
shorter than Y*o is called the near field or Fresnel zone.
In addition to reflection and transmission wave interference, Bhardwaj discusses
how diffraction can also result from the bending o f ultrasonic waves around a scattering
object. For example, close to a circular emitting transducer, the ultrasonic beam moves in
a quasi-collimated manner, the diameter o f which is approximately equal to that o f the
transducer. However, at the near field-far field transition, the wave bends or diverges due
to diffraction. The angle o f divergence or diffraction (angled) is given by equation
[2-24]:
angled = sin
' 1.22/0
[2-24]
D
where X is the wavelength in the medium o f ultrasound transmission and D is the
diameter o f circular transducer.
When ultrasound from a highly diffracting or from a relatively large transducer
hits the edge o f a material, it is further distorted because o f diffraction caused by the
interaction o f the wave and the edge. This is popularly known as the edge effects o f the
transducer (the boundary between air alone and ultrasonic waves). The ultrasonic waves
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48
Far Field
Near Field
Zone of Confusion
Relative
Acoustic
Pressure
First Maximum
4Jt
First Minimum
Distance o f Target from Transducer
Figure 2-9: Relative acoustic pressure along the central axis o f an ultrasonic
source (transducer) when a reflecting target is brought from infinity
toward it in a medium. [Y'„ minima, Y 1"m maxima]97
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49
bend in these zones and the beam begins to diverge at the first maximum, causing
diffraction (Figure 2-10). In some cases (usually with large diameter transducers),
bending o f the wave can also originate at the second minimum (Y"2), resulting in
additional diffraction. Diffraction effects due to bending can cause false signals. Edge
effects can be minimized by reducing the size of the interrogating ultrasonic beam, in
conjunction with dampening the transducer.
As an ultrasonic wave passes through a material, its intensity is decreased because
o f interaction with the material. For dispersive materials, this energy/intensity loss is
called attenuation; whereas for nondispersive materials, the loss is called absorption.
Attenuation is caused by a number of different factors. The three o f particular interest
are the scattering o f waves when they hit some type o f physical discontinuity (i.e., grain
boundary, defect, porosity, etc.), the spreading of the ultrasonic beam, and mode
conversion. Ensminger98 summarizes ultrasonic attenuation due to beam spreading and
scattering in the following manner. The intensity o f a wave at a specific distance, x, from
its origin can be mathematically described as [2-25]:
J
7
1 - I oe
where I0 is the initial intensity o f the wave, and a is the attenuation coefficient for the
medium in which the wave is traveling. The attenuation coefficient is proportionally
dependent on frequency. A spherical wave front originating at a point source has a
specific energy associated with it. As the wave travels unhindered through space the
spherical area gets larger, yet the total energy (if no losses due to other causes occur)
stays the same. Thus, the following relationship is true [2-26]:
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[2-25]
50
ultrasonic beam
Side Lobes
Near Field
Far Field
Main Lobe
o f Acoustic
Energy
Figure 2-10: Diffraction caused by transducer edge effects on ultrasonic waves"
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51
I t f = / 2r22
[2-26]
In other words, as r gets larger, I must get smaller (the beam attenuated) in order to
maintain the same amount o f total energy. A second mechanism o f attenuation is
scattering. When the wave front hits an obstacle it can be reflected or refracted. Single
scattering occurs when the wave is redirected out o f the main beam by the obstacle.
Multiple scattering occurs when the beam is redirected in and out o f the main beam by
more than one scattering object. In this case, some or all o f the energy associated with
the redirected wave can be lost to the main beam. In addition, phase relationships
between the main beam and the scattered waves can be affected due to path length
differences and the potential for some o f the energy to be converted into slower wave
modes. Mathematical modeling o f this complex phenomenon is quite difficult, especially
for anisotropic materials. Some simple models have been proposed such as the one by
Rayleigh to describe the scattering o f energy by a single scattering object. The ratio o f the
amplitude o f the scattered wave to the incident wave, S/I, is equal to the following
relationship [2-27]:
S
I
nV
RX
Ak
Ap
— + __cr
cos#
k
p
[2-27]
where V and R are the volume and radius o f the scatterer respectively. K is the elasticity
of the medium and Ak is the difference between the elasticity o f the medium and the
elasticity of the particle, p is the density o f the medium, and Ap is the difference between
the density o f the medium and the density o f the particle. Theta, 0, is the scattering angle.
The total attenuation o f the main beam is assumed to be a summation o f the individual
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52
scattering event effects. Models for rigid cylinder and rigid sphere scattering object
geometries have also been proposed. According to Gooberman,100 these are based on the
following three assumptions:
1. When the scattering object is much larger than the wavelength, the radiation is
reflected and not diffracted around the object so there is an acoustic shadow
behind the object.
2. If the object is much smaller than the wavelength, scattering is likely minimal
and the incident radiation will diffract around the object.
3. When the wavelength and the object are o f the same order o f magnitude, the
radiation undergoes a much more complex scattering pattern that varies with
body dimensions.
The models themselves can be found in this reference. Mode conversion of the
wave energy is the final attenuation method discussed here . Ensminger101 states that this
occurs when the acoustical energy is transferred to rotation or vibration o f atoms within a
molecule or some other energy form (e.g., heat). This mode conversion could be caused
by relaxation, which is when a time lag occurs between the applied stress (the acoustic
pressure) and the resulting strain (the physical or chemical effect) or visa versa. This
type o f energy loss in a particular medium may occur only at specific frequencies, called
the relaxation frequencies. In liquids, energy losses can also be attributed to viscosity
and thermal conductivity.102 When wave propagation is hindered by viscous drag, energy
loss can occur. In addition, the region subject to the ultrasonic wave will be at a higher
pressure (thus at a higher temperature) than the region at a lower pressure. Since the heat
will be conducted to the lower temperature regions, energy is lost in this process.
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2.3.5
Nondestructive Ultrasonic Evaluation of Material
Nondestructive ultrasonic evaluation of material can be accomplished by a
number o f methods such as pulse-echo, through-transmission, and pitch-catch
methods.103 The pulse-echo method uses the same transducer as both the emitter and the
receiver o f the ultrasound waves. The through-transmission method, on the other hand,
utilizes two transducers: the emitter on one surface o f the test material and the receiver on
the opposite surface for longitudinal wave transmission. The pitch-catch method also
utilizes two transducers, as the emitter and the receiver, except both transducers are
located on the same side o f the test material. Other techniques include the resonance
method, which has generally been replaced by pulse methods described above and the
acoustic emission technique. The acoustic emission technique104 is designed to take
advantage o f the spontaneous emission o f acoustic signals from a material that is under
external stress. The region of the material that is undergoing the stress will not be able to
carry the load indefinitely. So, at some point, the stressed region will distribute the load
over the non-stressed regions o f the material, resulting in a sudden relaxation o f stress
and an emission o f an acoustic signal. In metals, the acoustic signal can be generated by
the nucleation and propagation o f cracks, by the slip o f dislocations or grain boundaries,
or by some other relaxation activity. The frequency o f the emitted signal can range from
audible to ultrasonic. However, the sound level is usually very low. In addition, natural
ultrasonic emissions have been detected during ice formation in Eucalyptus plants.105 The
number of ultrasonic signals were counted as the stem temperature was first lowered to 8 °C, then raised to 0 °C. The experiment showed that the number o f ultrasonic signals
captured increased as stem temperature was lowered below freezing to a maximum at
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54
-8 °C. As the thawing process occurred, the number of events gradually decreased until
ceasing at above freezing temperatures.
In general, ultrasonic waves can be produced and/or detected by a number of
devices, including electromechanical, pneumatic, and mechanical.106,107 By definition,
transducers convert one form o f energy into another form. Electromechanical transducers
transform electrical energy into acoustical energy and visa versa. Piezoelectric and
magnostrictive transducers are two examples of this electromechanical class.
Piezoelectric materials are ionic in nature and lack centers o f symmetry. Unstressed, they
do not exhibit dipole moments. However, if the unit cell is physically compressed or
extended (physically deformed), an effective dipole moment will occur and a voltage
develops between the faces o f the material (Figure 2-11). When a pressure wave hits a
piezoelectric element being used as a receiver, compressive stress is applied to the
crystal. The corresponding voltage change can then be measured. Under the presence of
an alternating electric field, on the other hand, piezoelectric transducers will physically
expand and contract in conjunction with the field. If the resulting acoustic wave is o f the
right frequency, the piezoelectric element is then a generator o f ultrasonic waves.
Magnostrictive materials can be used in a similar fashion because they change
dimensions under the influence o f a magnetic field. Whistles and sirens are examples o f
pneumatic generation o f ultrasound. They use a stream o f gas as the energy source,
which is then converted into ultrasonic energy. Rotating counterweights are an example
of mechanical generation o f ultrasonic waves. Two weights, one on either side o f a
connector, are rotated in opposite directions, which causes the connector to mechanically
vibrate and emit low ultrasonic frequencies.
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+
+
a
+
+
b
+
+
+
+
e
Figure 2-11: Example o f the piezoelectric effect in the quartz unit cell:108
a) cell unstressed, b) cell in compression, and c) cell in extension
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56
The propagation characteristics that can be measured by ultrasonic testing
equipment are the velocity and the attenuation o f the wave. Historically, velocity of
ultrasound has been measured by the following basic methods:109
1. If the frequency is known, the velocity is measured by determining the
length o f a continuous wave. Frequency is the number o f cycles in a
period o f time, and length o f the continuous wave is the distance
traveled per cycle. Therefore the frequency (cycles/time) multiplied
by the length o f the wave (distance/cycle) equals the velocity
(distance/time).
2. If the distance the wave will travel is known, the velocity can be
calculated by measuring the time necessary for the wave to travel the
set distance. Distance divided by time is velocity.
3. If the velocity in one medium is known and the wave is traveling
between two mediums, the velocity can be calculated when the angle
of refraction is measured, as per equation [2-21].
As the wave passes through a material, energy is lost from scattering and
absorption This attenuation of the wave is associated with a decrease in wave amplitude.
Both attenuation and velocity are related to the amplitude o f the wave by equation
[2-28]:110
A=
cos(fcc - cot)
[2-28]
where the amplitude at position x is denoted by A, Ao is amplitude at the origin, a is the
attenuation coefficient, k is the propagation constant ( 2 ti/ 1 = co/ c ) ,
g>
is the angular
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57
frequency (2nf), c is velocity, and t is time. If the maximum amplitude resolution (Aref)
can be calibrated for a nondestructive ultrasonic evaluation system and a peak-to-peak
amplitude can be measured in volts (A;), then attenuation (a) is as follows [2 -2 9 ]11
a = 20 log ' A '
\ A e f
[2-29]
J
A number o f different systems have been designed over the years, which take
advantage o f these methods to measure velocity and to calculate attenuation.
Interferometers, resonance devices, pulse-superposition systems, and pulse-echo-overlap
devices are examples that will be summarized briefly from Ensminger’s book,
Ultrasonics.112 Interferometers have a fluid or a gas column bounded on one side with an
emitting transducer and a reflector on the other. The column is designed so that standing
waves can be sustained at a fixed frequency. The reflector is moved by a micrometer
adjustment toward the transducer. This causes the reflecting wave to go in and out of
phase with the incident wave. The amplitude o f the reflecting wave measured by the
piezoelectric transducer increases and decreases with the resulting constructive and
destructive interference. The wavelength is two times the distance that the reflector
moved from maxima to maxima. The measured velocity times the fixed frequency gives
the velocity. Attenuation can also be calculated with this setup. As the reflector is
moved away from the transducer by a distance x, the amplitude o f the wave is measured.
The decay in the maxima o f amplitude is a measure o f attenuation. The resonance
method uses either a transducer/reflector system or two transducers placed a fixed
distance away from each other. Frequency is varied by the emitting transducer until at
least two resonance frequencies are identified. Velocity, c, is related to the distance
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between the transducer and the reflector (1) and the difference between the two resonating
frequencies (Af) in the following manner [2-30]:
c = 2/A /
[2-30]
This resonance method can be used for gases, solids, and liquids. For the pulsesuperposition method, on the other hand, the transducer sends a pulse through the
material. When timed correctly, the first echo and the newly initiating pulse overlap or
superposition, which is indicated by signal amplitude changes. The distance covered by
the wave is twice the sample thickness, and the pulse repetition rate (phase shift
corrected) measures the travel time within the sample. Velocity is these two multiplied
together. The transducer in this method is coupled directly to the sample and is excellent
for monitoring velocity and velocity changes. The final method, pulse-echo-overlap, is
the same principle as the pulse-echo method except the frequency is adjusted so that the
echo o f one pulse is recorded on one sweep o f the oscillator and the next echo on the next
sweep. When they exactly overlap, the time o f travel between the signals can be
measured. Distance is again twice the sample thickness. Both pulse-echo methods are
not suitable for measuring velocity in highly attenuative material because the pulses
attenuate too rapidly.
As mentioned earlier, ultrasound travels by pushing particles ahead o f the wave in
the transmitting medium. When the particles
11"3
in the transmitting medium are loosely
bonded, have a low density, and/or have a very high mean free path such as with air,
ultrasonic energy is lost in the gap between the molecules. Ultrasound velocity is also
reduced under such conditions. Higher density mediums, such as water with better
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59
intermolecular bonds, are more effective at transferring the energy from particle to
particle; thus, attenuation is less in water than in air.
Velocity and attenuation, alone, are not the final goal in nondestructive material
testing. O f interest, though, is how velocity and attenuation can be related to defects or
discontinuities, material thickness, viscosity, moisture content, surface roughness, and
different phase concentration, as well as material properties like elastic moduli (Young’s
modulus, shear modulus, and po is son’s ratio). For example, void content in polymer
composites has been assessed with ultrasonic techniques.114 A short pulse o f ultrasonic
energy was passed through the polymer panel and the transmitted portion was measured
on the other side o f the panel. Attenuation in an area with voids was different from an
area without voids. Thus, attenuation was related to void content and
acceptable/unacceptable attenuation levels were determined. Interfaces are o f particular
importance in ultrasonic systems. Historically, the air/solid impedance mismatch (orders
of magnitude) is too great for practical ultrasonic nondestructive materials evaluation by
noncontact mode. For example, the acoustic impedance, Z, for air is 415 Rayl (IRayl = 1
kg/m2s), whereas for steel it is 51 MRayl.115 This exhorbitant mismatch results in near
total reflection o f ultrasound at the air-material interface, thus making noncontact
ultrasound impossible. Consequently, a liquid or gel coupling between the transducer
and the test material has been traditionally utilized in order to minimize the impedance
mismatch. Dry coupling with physical contact between the transducers and the test
material was developed in the early 1980s.116 However, it was not until the 1990s that
the air/solid challenge was overcome. Piezoelectric elements fronted with acoustic
impedance transitional layers that maximize transduction in air have been developed
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60
from less than 100 kHz to greater than 5MHz. In comparison with direct contact
transducers, the sensitivity o f these air-coupled transducers is approximately 30 dB
lower.117 The sensitivity o f transducers refers to the comparison o f the amplitude o f the
electric voltage generated by the transducer to the ultrasonic signal received by the
transducer.118 As an example of nondestructive testing using noncontact ultrasound
techniques, orientated strandboard (a wood composite) research will be briefly
discussed.119 Measurement o f velocity in the test material, (Vm), material thickness (dm),
and attenuation o f the wave in the material was possible with noncontact ultrasound using
a combination o f the results from pulse-echo and through-transmission methods.
Characterization o f ultrasonic propagation in the air column between the transducers
provides measurements o f the velocity o f ultrasound in air (Va) and the round trip time of
flight in the air column (ta) from transducer 1 to transducer 2 and back to transducer 1.
Once the sample has been place in the ultrasonic beam, time o f flight through the material
itself (tam) and the time o f flight between transducer 1 and transducer 2 (Tc) is recorded.
Pulse-echo, time-of-flight measurements from the first transducer to the top surface and
back (ti), as well as from the second transducer to the bottom surface and back (ta) were
necessary. Using these measurements the following equations can be solved to determine
the material thickness (dm) [2-31] and the velocity [2-32] o f the ultrasonic wave through
the material (Vm).
d m= V
r a * t*am = Va * t a -
[2-31]
[2-32]
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61
Attenuation energy in dB was also calculated by the integrated response (IR)
method. The first peak of ultrasonic energy captured by the receiving transducer
represents the transmitted ultrasonic energy (the second peak is reflected energy, etc).
Integration of the area under the first peak is the power corresponding to the transmitted
energy. Both the power corresponding to the transmitted energy in the air column alone
(IRa) and the power corresponding to the transmitted energy through the sample (IRc)
placed between the transducers must be calculated. The net power (IRm) [2-3] is as
follows:
[2-33]
IRm is thus a measure o f the energy attenuated by the material. This measurement is also
independent o f frequency and is related to the transmission coefficient, T, [2-34]:
« „ = 2 0 iog(r )
[2-34]
The transmission coefficient in this equation is assumed to be independent o f material
thickness and ultrasonic attenuation; however, this is not completely true.120 Density o f
the material is equal to the material impedance (Zm) divided by the velocity in the test
material (Vm) [1.4.7]. If Zm is related to the transmission coefficient (T) by the
relationship in equation [2-35] as suggested, material density should be able to be
determined with integrated response and velocity measurements.
Pm
171
Z,m
V,m
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[2-35]
62
tfl
r ji
(2 -T )± 2 {1 -T )i
[2-36]
Zi is the acoustic impedance in air. In the strandboard study,122 density profiles were
mapped by the Quintek Density profiler, while the modulus of elasticity and the modulus
o f rupture were measured with an Instron 4260 in a three-point bending experiment. A
high correlation between ultrasound velocity and mechanical strength, as well as between
ultrasound velocity and material thickness, was found. Attenuation-density correlations
for single layer boards were higher than for triple layer boards. However, the correlations
for noncontact ultrasound attenuation were not as good as for contact ultrasound
attenuation. Similar material-specific studies on a wide variety o f materials are
necessary to fully understand the material property/noncontact ultrasound parameter
correlations.
2.3.6
Ultrasound in Nature
Predator and prey may use ultrasonic emission and detection as part o f their
survival techniques. For example, bats use sound to navigate as they fly, as well as to
locate prey.123 Ultrasonic pulses generated by the bat are reflected o ff objects or off prey
in its path and then are detected by the bat. Porpoises also use ultrasound in a similar
way. Frequency, repetition rate, and amplitude o f ultrasonic waves are varied by both
species in a complex way while using echolocating signals. A number o f species preyed
upon by bats have been shown to detect ultrasonic waves and then to take evasive action.
Ultrasonic bombardment caused both free-flying preying mantid males124 and flying
crickets125 to take evasive action. Adult-tethered flying tiger beetles126 also displayed
behavior modifications such as head rolls, hind leg kicks, and wing beat frequency
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63
changes among others when subject to ultrasonic waves. These behaviors appear to be
evasive in nature. However, there does not appear to be any literature on the effect o f
ultrasonic bombardment on beetles in the larval stage.
2.3.7
Applications ofUltrasound in the Wood Industry
Research on the use o f ultrasound to scan wood for various conditions has been
conducted for the pulp and paper industry.
127
Currently, East Alabama Lumber
os
uses
ultrasound technology in its milling process to optimize the cutting o f cants up to 12-in.
thick. The goal is to maximize the production o f clear, defect-free lumber from Southern
yellow pine cants. Consequently, the ultrasound scanning equipment is used to detect
defects, such as knots or cracks, as well as decay or bacterial infections in the wood.
Grain distortions can also be detected. A signal processor is used to manipulate the raw
data from the scanner and assign a grade to the cant. The configuration of the 18 saws
used by the plant to produce dimension lumber, decking, or low-grade boards can then be
automatically changed to optimize the products produced from each individual cant. A
prototype ultrasound system manufactured by Perceptron was first placed on line at East
Alabama Lumber in 1999. The mill produces 85 million board ft./year with a maximum
o f 20-ft long lumber.
2.4 Microwave Background
2.4.1
Introduction
A microwave is an electromagnetic wave whose frequency ranges between 300
MHz and 300 GHz (corresponding wavelengths are between 1 mm and 1 m) (Figure 212).129 As with all other electromagnetic waves, microwaves do not require a medium to
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64
XR
UV
(not to scale)
Wave Type
Wavelength (m)
Frequency (Flz)
R (radio)
M (microwave)
IR (infrared)
V (visible)
UV (ultraviolet)
XR (x-ray)
G (gamma)
>1 x 10'1
1 x 1O'3 to 1 x 10'?
7 x 10"7 to 1 x 10'3
4 x 10'7 to 7 x 10-7
lx l O'8 to 4x 10~7
1 x 10‘n to 1 x 1(T8
<1 x l(Tn
<3 x 109
3 x 109 to 3 x 1 0 ”
3 x 1011 to 4 x 1014
4 x 1014 to 7.5 x 1014
7.5 x 1014to 3 x 1016
3 x'1016 to 3x 1019
>3 x 1019
Figure 2-12: Electromagnetic spectrum
130
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65
propagate; they can travel through empty space. Microwave energy can be used to
transmit information (e.g., radar, satellite communications), to interact with material nondestruetively for evaluation purposes, or to interact with materials physically with the
purpose o f changing the material in some way.
Microwave frequencies are regulated nationally and internationally; therefore,
there are limited frequencies available for specified applications. The applications in this
dissertation fall under the Federal Communications Commission131 category o f Industrial,
Scientific and Medical Equipment. There are 11 frequencies (6.78 MHz, 13.56 MHz,
27.12 MHz, 40.68 MHz, 915 MHz, 2450 MHz, 5800 MHz, 24125 MHz, 61.25 GHz,
122.50 GHz and 245 GHz) allocated for use by ISM equipment. The 2.45 GHz
frequency with a wavelength o f approximately 12 cm is most commonly used for
material processing, including the present work.
In order to set this dissertation into perspective, a short discussion o f the theory of
electromagnetism will be presented. Then, microwave interactions with materials will be
discussed. Finally, a short description o f microwave applications for insect control and
wood processing will be presented.
2.4.2
The theory o f electromagnetism
Electromagnetism
models the interaction between the electric and
magnetic fields and their effect on the relative motions o f bodies or charges. This theory'
includes Newton’s equations o f motion, Lorentz’s force, and Maxwell’s equations, as
well as models o f observed material properties. From Newton,133 there are three basic
laws o f motion including: (1) a body at rest will stay at rest or a body in motion in some
direction will continue on that path unless some force is applied to change that, (2) the
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66
change o f the body’s motion will be in some proportion to the force that is applied and
will occur in the same direction as the force [2-37] and, (3) for every action there is an
equal and opposite reaction. Lorentz’s force134 models the electric field and magnetic
field’s effect on a charge [2-38], This takes into account the resultant force o f the electric
field on the charge q0 (Coulomb’s force), as well as the magnetic force experienced by q0
moving with velocity v0.
F = ma
P-37]
? = q0EEG
- 5
F
+ q0v0xB.
[2-38]
where F is the force vector; m is the mass, a is acceleration vector, q0 is
the charge experiencing the force, v0 is velocity o f q0, and B is the
magnetic force vector
A combination o f these two equations can be used to describe the movement o f a particle
with charge q, mass m, and a velocity v in a specified region containing electric and
magnetic fields [2-39].
qE + qv xB - ma
[2-39]
In electromagnetic theory, Maxwell’s equations135 are used to describe how the electric
and magnetic fields in the above equations are generated. The first three equations of
Maxwell’s equations were actually developed by Gauss or Faraday, whereas Ampere and
Maxwell were responsible for the fourth equation. Maxwell unified all o f these equations
into one theory. Most of these equations revolve around the concept o f flux,136 which is
the strength o f a field (electric or magnetic fields in this case) times the area o f the plane
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67
penetrated by the field. Of importance to this theory is flux through a closed surface,
where one must pass through the surface in order to move from one region to another.
Gauss’ first law describes the net electric flux when a point charge, q, is completely
surrounded by a sphere in free space [2-40]. Unlike the electric field where the electric
field lines originate on the electric charge, the magnetic field lines are continuous loops
in free space. Thus, Gauss’ law of magnetism states that the net magnetic flux over the
closed surface will equal zero [2-41]. The third law is called Faraday’s law o f induction,
which describes how an electric field is generated by a magnetic field that is changing
over time [2-42]. In a similar manner, the fourth equation (Ampere-MaxwelT s law)
describes how a changing electric field (either a conduction current or a changing electric
flux) over time generates a magnetic field [2-43].
js» d A -
[2-41]
0
=
J
P-42]
dt
+
E=the electric field at any point on the gaussian surface
dA=a small element o f the surface area
Q=total positive charge
B=the magnetic field
ds=a small element o f displacement
1= current
t=time
<Dm=magnetic flux
d>e=electric flux
p<y=permeability o f space=47ix 10'7N/A2
Eo^permittivity ofspace=8.8542 x I O'12 C2/N-m2
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P -43]
68
Assuming that the electric and magnetic fields are perpendicular and
confined to the xy plane and that the wave travels in a specific direction (also called a
transverse wave), equation [2-42] and equation [2-43] can be related in empty space with
1=0 and Q=0. After evaluation, two electromagnetic wave equations for free space result,
equations [2-44] and [2-45].
d 2E _
d 2E
[2-44]
dx2 ~ M°£° dt2
d 2s
d2B
[2' 45]
where c= 1/(poe0)0 5=3.00x108m/s
The electric and magnetic fields will vary at a specific point from a maximum in the +y
direction through 0 to a maximum in the - y direction and back as time passes. Looking
at the same wave for one instant o f time, the field varies in the same manner (from max
+y through 0 to max -y and back) with distance in the x direction. Although the wave
may not actually be sinusoidal, it is periodic; therefore, the following mathematical
equations can be use to express the electric field [2-46] and the magnetic field [2-47] for
a plane-polarized wave:
E = Emcos(kx-ojt)
P-46]
B = Bmcos(kx-o)t)
[2-47]
where Bm= maximum value o f the electric field
Em~ maximum value o f the magnetic field
x is the position,
k = wave number = 2 n/X
t-tim e
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69
co = angular frequency=27if.
The relationship between the wavelength and the frequency is as follows [2-48]:
j =V =c
[2-48]
where c = the speed o f light= 3.0 x 10 8m/s
co=angular frequency
f ^frequency
A,=wavelength
2.4.3
Microwave Interaction with Material
Three possible interactions can occur when a microwave interacts with a material.
The wave can be transmitted, reflected, or absorbed (Figure 2-13). Frequency plays an
important role in microwave/material interaction, as does temperature for some materials.
For 2.45 GHz frequency, materials137 such as solid metals are excellent reflectors of
microwaves; therefore, microwave energy is neither transmitted nor absorbed. Some
ceramics such as silicon dioxide or glasses w ill transmit most o f the microwave power at
room temperatures, but at higher temperatures microwave absorption is more efficient.
Microwave power absorbed is directly proportional to frequency (f), dielectric
constant (s’), and loss tangent (tan 8). Microwave power absorbed (P) can be expressed
by equation [2-49].138 E is the electromagnetic field vector, whereas s0 is the dielectric
constant of free space, 8.85 x 10'12 F/m. The dielectric constant and the loss factor are
both dependent on temperature139 and on frequency.140
P = 2 rfsr (f,T)e„ tan $T,T)|E|2
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[2-49]
Incident
Microwave
Energy
Material
Transmission
Ms»t*rrisl
Incident
Microwave
Energy
Incident
Microwave
Energy
[
------------- j—» ' '
!
Material
Reflection
Figure 2-13: Interactions between microwaves and materials
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71
The complex dielectric constant, s*, consists s ’ and e” [2-50].141 The real part, s’, is
called the dielectric constant, and the imaginary part e” is called the dielectric loss factor.
s* = e'-je"
[2' 50^
The dielectric constant {er) is a material property that measures the amount o f input
microwave energy that can be stored within the material itself. The dielectric loss factor,
on the other hand, corresponds to the heat dissipation o f the input microwave energy.
The loss tangent is the ratio of the stored energy capability to the heat dissipated energy
capability [2-51].
tan<5 = 4
£
[2-51i
Heat generation with microwave heating is attributed to quite different
mechanisms than with conventional heating.142 Convection, conduction, and radiation
heat surfaces first in conventional heat chambers. Diffusion o f heat into the core o f the
material will then occur. Heat transfer is thus the mechanism. Typical temperature
gradients in this case are higher on the surface and lower in the center o f the material
until the material reaches thermal equilibrium. Microwave heating,143 on the other hand,
transfers energy by penetrating the bulk o f the material and interacting with electrons,
ions, or dipoles present in the material. The heat released from either translation (ions
and electrons) or rotation (dipoles) is throughout the material, causing volumetric
heating. Surface temperatures may be lower than interior positions due to loss o f heat to
the surrounding air.
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Penetration depth of the microwave energy into a material is also an important
factor for microwave/material interactions. Assuming a homogenous material, the depth
o f penetration is defined as that point where the microwave energy has dissipated to onehalf o f the initial [2-52].144
D
c
P
P -52]
tmS-JV
where c is the speed o f light, tan 8 is the dielectric loss,
/ i s the frequency, and s ’ is the dielectric constant.
2.4.4
Eradication o f Insects by Microwave Energy
The use o f microwave energy to eradicate insects in a variety o f hosts such as soil,
potatoes, wood, fruits, stored grain, dried herbs, cabbage, and walnuts has been studied.
2.4.4.1 Wood Hosts
Termites are a problem found in a number o f wood species. Microwave
irradiation o f kiln-dried, Douglas Fir (3.5 cm x 8 cm x 28 cm) artificially infested with
dry wood worker termites, Incisitermes minor (Hagen), was evaluated by Lewis et al.145
in the laboratory. The microwave parameters studied were 2.45 GHz frequency and
power o f 2000 W (inner chamber dimensions o f 36.8 cm x 40 cm x 22.9 cm), 1000 W
(inner chamber dimensions of 34.3 cm x 34.3 cm x 25.4 cm) or 500 W (inner chamber
dimensions o f 29.2 cm x 28.6 cm x 20.3 cm). One hundred percent termite mortality was
reached at 90 seconds o f 500 W irradiation and longer, 60 seconds o f 1000 W irradiation
and longer, and 20 seconds o f 2000 W irradiation and longer. In an earlier study, Lewis
et al146 studied microwave irradiation (700 W, 8-minute application, frequency not
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73
specified) o f termites (Incisitermes minor) infesting kiln-dried Douglas Fir (1 ft. x 4 ft. or
2 ft. x 4 ft.) boards used to construct the studs and the wall boards o f the test building.
Localized or spot microwave irradiation o f specific boards was conducted with an
unshielded device. Mean mortality o f the termites approached 90% for the artificially
infested boards (with great variability from board to board) and 98% for the naturally
infested boards. According to Lewis et al147 microwave irradiation has been available in
California since 1989 for termite control.
Beetles are other pests that infest wood. High-frequency microwave (10 GHz, 35
GHz, and 74 GHz) irradiation o f the mountain pine beetle (Dendroctonus ponderosae
Hopk.) and the darkling beetle (Tenebrio molitor L.) was conducted by Whitney and
Kharadly.148 Low-level radiation exposure (10 to 100 mW for 0.5 to 3 hours) of pupae
from both species, as well as o f larvae and eggs o f the mountain pine beetle, did not
significantly affect these insects compared to the nontreated control groups. These
results were in direct contradiction to earlier studies 149’150’151 that found that low-level
radiation exposure (similar or less than that reported above) of 10 GHz frequencies
resulted in abnormal development and reduced survival o f the darkling beetle. Whitney
and Kharadly theorized that individual beetle strains could have different propensities to
respond to microwave irradiation or any other factor that may lead to developmental
malformations or reduced survival.
In 1975, Burdette et al152 studied the effect o f 2.45 GHz microwave radiation on
powder post beetle (Anobiid) larvae infesting yellow poplar wood boards. Temperature
o f the board was measured immediately after exposure to 1500 W o f microwave energy
for 30 seconds to 5 minutes. Mortality o f 100% occurred if the board temperature
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reached 50 °C or higher. Moisture content, dielectric constant, and loss tangent affected
the rate o f heating in the lumber. However, the moisture content of the lumber used in
these experiments was not reported. Exposure times ranging from 0.165 to 1 minute
were required to attain 50 °C or higher. Thickness o f the boards was also not described in
this report.
Jiang et al153 studied the effect o f direct 2.45 GHz and 915 MHz microwave
radiation on stem borer larvae (not in wood) and on stem borer larvae inside living tree
trunks. The larvae investigated included Anoplophora glabripennis, as well as other stem
borer species. Both continuous and pulse microwave energy applications were made.
The most lethal combination o f microwave parameters for direct larval exposure to
microwave energy was 2.45 GHz frequency, 600 W o f power, and an exposure o f 3 to 10
seconds. At this treatment level, 100% o f eggs, larvae, pupae, and adults directly
irradiated were killed. The best microwave parameters for penetration into the living tree
trunk were 915 MHz frequency, 400 W o f power, and an exposure o f 6 to 8 seconds. The
microwave energy reached a depth o f 17.5 cm in the tree trunk; however, insect mortality
was not mentioned.
Andreuccetti et al154 studied lethal temperatures for woodworm (Hylotrupes
bajulus L.) larvae with conventional hot water bath and microwave heating. In a hot
water bath, 50% o f the smaller larvae (less than 0.1 g in weight) could be expected to die
at 51.9 °C. For larvae larger than this (0.1 to 0.178 g), 50% could be expected to die at
53.3 °C. The group concluded that lethal temperatures using the hot water bath technique
depended on the size o f the larvae. The group also reported that microwave heating (2.45
GHz) o f a wooden block (dimensions, power level, moisture content, and wood species
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not delineated) for 20 seconds showed that the temperature o f the woodworm larvae
reached 57 °C, while the surrounding wood reached a temperature o f 45 °C. Using these
results and additional data155 on a second woodworm species {oligomerus ptilinoides
Wollaston) studied in 1995, Bini156 developed a 2.45 GHz laboratory microwave
applicator with a maximum power output o f 250 W to treat painted wooden boards (e.g.,
artifacts and other valuable objects) artificially infested with woodworms. The painted
side of a 3-cm board was placed face down over a hole made in a wooden board.
Microwave energy was directed at the unpainted side, while temperature o f the painted
side was monitored via an infrared device. Microwave heating cycles were chosen so
that the painted side was maintained between 40 and 50 °C during the “o ff’ portion o f the
cycle. They found that eggs o f Hylotrupes bajulus, larvae o f Oligomerus ptilinoides
weighing 1 to 8 mg, and pupae o f Oligomerus ptilinoides were eradicated when subjected
to 200 W o f power for a variety o f heating cycles (e.g., 2 minutes on, 1 minute off, 2
minutes on). The prototype microwave system designed by this group for this application
appears to be an open air system. Consequently, the following safety features were
incorporated in order to minimize the release o f radiation into the environment: (1) a
circular corrugated flange built around the microwave applicator and (2) microwave
absorbers placed under the bench supporting the wood sample to dampen the radiation
that passed through the board. According to this group, the measured leakage was less
than 2 mW/cm2, which is within the acceptable industrial exposure limits o f 5 mW/cm2
described in CENELEC ENV157 and other guidelines.158
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2.4A.2 Potato and Soil Hosts
The microwave effect on potato-cyst and free-living soil nematodes were studied
in two separate research projects. Both dry and wet potato-cyst nematodes 159
(Globodera-rostochiensis Woll. Behrens and Globodera-pallida Stone Behrens) were
irradiated with microwave alone or treated with sodium hypochlorite alone. Viability o f
the cyst-nematodes with microwave irradiation (parameters not stated) was reduced for
wetted cysts but had no effect on dry cysts. De Pomerai’s group 160 focused on the effect
o f 750 MHz (0.5 Watt, -45 V/m E-field) radiation on the free-living soil nematode
Caenorhabditis elegans (exposed for 18 hours continuously). The purpose of this
research was to provide some insight into the effect o f cell phone frequencies on the
human body. Consequently, they chose the 750 MHz frequency and a very low (0.5 W)
power level. The two nematode strains used in these experiments carried stress-inducible
reporter constructs (E. coli lacZ reporter genes), which facilitate the monitoring of heatshock responses. This study reported that microwave exposed larvae grew larger in
length than unexposed larvae. In addition, heat shock responses were induced by the
process. The temperature profile of the nematode, however, was unchanged during
microwave exposure. Consequently, the researchers concluded that unidentified nonthermal mechanisms were responsible for both the growth and heat shock responses.
2.4.4.3 Fruit Hosts
The efficacy o f 915 MHz microwave irradiation for eradicating codling moth
J
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larvae (Cydiapomonella, L., 3 and 4 instar) infesting Bing and Rainier sweet cherries
(.Punus avium L.) was studied by Ikediala et al.161 Infested cherries (3.1 to 13.0 g in
weight) were exposed to 1 kW power output for a maximum o f 7 minutes. All batches
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were held at one of three target pit temperatures (45, 50, and 55 °C) for 2 minutes.
Temperature was measured with fiberoptic probes. Insect mortality o f 98% was reached
for the infested Bing cherries with a combination of microwave radiation (55 °C for 2
minutes plus ramp time) and 1-day in cold storage. A 95% mortality rate was reached
with a 2-minute hold at 50 °C and 1-day cold storage. Other treatment combinations for
Ring cherries and all combinations for Ranier cherries exhibited less than 72% insect
mortality. Fruit quality after microwave treatment was considered good. Reagan et al162
treated wool textiles with 2.45 GHz microwave radiation in order to eradicate the
webbing clothes moth, Tineola bisselliella (Humm.). Each lifestage (eggs, larvae, and
adult) o f the moth were placed in a polystyrene box lined with worsted wool gabardine
before 2.45 GHz microwave treatment. Exposure time was varied from 0.5 to 5 minutes.
Power was not specified. All eggs, larvae, and adults were deemed not viable after
exposure to 4 or more minutes of irradiation. The material properties o f the wool or the
dye were not adversely affected by these treatment schedules.
Mature larvae o f the fruit fly, Anastrepha suspensa (Loew), placed in a beaker o f
water were irradiated with 2.45 GHz microwave energy at very low power levels (11 W
to 122 W) by Sharp et al.163 Once the target water temperature of 44 to 50 °C (measured
with fiberoptic probes) was reached, the microwave power was turned off. Greater than
99% mortality occurred with 3 power/time/temperature conditions, which were 16 W for
20.5 minutes, 49 °C; 16 W for 22.7 minutes, 50 °C; and 30 W for 10.8 minutes, 50 °C.
Commodity damage resulted when fruit temperatures were greater than 50 °C.
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2.4.4.4 Stored-Grain Hosts
Grain such as wheat, barley, oats, and com, as well as rice can become infested
with insects either before or during storage. Nelson164 summarized research on the
following types o f grain insects irradiated with 2.45 GHz microwave energy: rice weevil
{Sitophilus orycae L.),165,166 the granary weevil {Sitophilus granaries L.),167 and the
confused flour beetle {Tribolium confusum).16* Greater than 99% mortality o f adult rice
weevils resulted when the host rice material reached 83 °C with exposure to 2.45 GHz
microwave energy. When wheat reached 86 °C, adult granary weevils were eradicated.
Mortality of 95% has been reported for eggs, larvae, pupae, and adult of confused flour
beetles infesting flour that reached between 57 and 66 °C with microwave radiation.
Comparing microwave with radio frequency, however, Nelson’s summary showed that
lower host-media temperatures were required in all three insect species (all life stages
reported) for 99% mortality or greater when RF (radio frequency) energy was used.
Tilton and Vardell169 looked at partial vacuum (35 Torr) and 2.45 GHz microwave energy
(0.28 power density unit) as a potential treatment combination for stored grain insects in
com, rye, and wheat. Mortality of less than 99% was found for the grain borer
Ryzopertha dominica (F.) and the Angoumois grain moth in wheat, whereas 99% or great
mortality resulted with rye and com for both o f these insects. Complete eradication of
the maize weevil is com and the rice weevil in rye was also reported under these
microwave/vacuum conditions. Microwave treatment alone was not able to control the
infestations as well as the microwave/vacuum combination. Halverson et al.170 used high
frequency microwaves (10.6 GHz, 51 J/g and 53 J/g) to irradiate maize weevil (93% or
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79
greater reported mortality) in white wheat and red flour beetles (94% mortality or greater)
in ground wheat.
2.4.4.5 Dried Herb Hosts
Insect infestations in dried plants such as herbs are uniquely suitable for
microwave eradication according to David Hall.171 He suggests that the microwave
radiation selectively heats the liquid inside the insect without harming the dry herbs.
When irradiated with 2.45 GHz microwave energy (power not noted), 100% mortality of
a small number o f dermastid beetle (Trogoderma inclusium LeConte) and drugstore
beetle (Stegobium paniceum L.) adults and larvae placed in stacks o f dried specimens was
achieved under the following conditions: 75 seconds for 2.5- to 5-cm high stacks; 95
seconds for 8- to 9-cm high stacks, and 120 seconds for 15-cm high stacks.
2.4.4.6 Other Hosts
Other insect/microwave studies include fire ant control,172 lethal effects of
microwaves on cabbage maggots,173 and insect control in confectionary walnuts.174
2.4.5
Microwave Application in the Lumber Industry
In order to give a flavor o f the applications microwave energy may have in the
lumber industry, a sampling o f current research and o f industry use is presented below.
TrusJoist,175 a Weyerhaeuser company located in Idaho, currently uses patented
microwave technology to dry and bond veneer. Veneer sheets are peeled off logs first.
Then strands are cut that are 2-ft to 8-ft long. With microwave energy, these strands are
dried to 11% moisture content. Once aligned with other strands, adhesive is applied.
With pressure and microwave heating, the veneer is then cured.
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Microwave drying o f paper is one application that has been investigated by
Kumar and Mujumdar.176 Their study utilized 2.45 GHz microwave energy with 700 W
maximum power and hand sheets made from two different kinds of pulp. Paper
properties such as density, burst index, fold, and tear strength after microwave drying
were compared to the paper properties after conventional drying. All measured properties
were equal or better for the microwave-treated papers.
Bark removal from frozen logs requires thawing the wood at least partially.
Gilbert and Turcotte177 looked at defrosting black spruce and trembling aspen (15 to 30
cm in diameter) with 2.45 GHz microwave energy. They found that the microwave
energy needed to thaw the logs was the same regardless of the power level. Microwave
heating was not uniform in these experiments. Surface temperatures were higher than
core temperatures. They also found that 140 J/ton of wood was the microwave energy
requirement for 25 cm diameter logs with 90% moisture content. The researchers
concluded that thawing logs for bark removal with microwave energy could be an
effective technique.
Wood bending178 is another manufacturing process that may benefit from
microwave heating. Both preheating the wood before bending and drying the wood after
bending can be accomplished by 2.45 GHz microwave heating o f lumber with initial
moisture content o f 25-30% and a final moisture content between 8 and 12% after drying.
•j
For birch blanks (35 x 35 mm), it was shown that 3 W/cm was optimal to ensure that
overheating did not occur. At this microwave intensity, excellent wood bending
conditions could be attained in much less time than with steam treatment (15-20 times
less). Microwave drying after bending can also be accomplished in much less time than
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convection heat treatment (200 times less).
Microwave drying lumber179 to 10% final moisture content can be accomplished
with 2.45 GHz or 0.915 GHz generators. Electricity is the most expensive operating cost.
Consequently, microwave energy consumption is extremely important. For each
kilogram of water evaporated from the lumber, energy consumption was found to be 0.85
to 1.3 kW per hour for wood with moisture contents between 70 and 100%.
2.5 U.S- Approved Wooden Packing Material Treatments
2.5.1
Methyl Bromide Background
All information introduced in this section is summarized from the United States
Environmental Protection Agency Ozone Depletion Rules and Regulations180 unless
otherwise cited. Methyl bromide (bromomethane) is used as a pesticide worldwide to
control pests in the soil, in commodities, and in structures. Pressurized, methyl bromide
can be stored as a liquid. Under ambient conditions, however, this toxic pesticide is a
gas. Methyl bromide is nonspecific; consequently nontarget species (including humans),
as well as targeted species can be affected by exposure to this pesticide. Due to its alleged
environmental effects, such as depletion o f the ozone layer, the use o f this pesticide is
being phased out in 160 countries as delineated in the Montreal Protocol. This
international treaty requires that all industrial nations reduce their use o f methyl bromide
by 70% in 2003 and by 100% in 2005, excepting critical agricultural and emergency uses
as well as permissible preshipment and quarantine uses. Developing nations are required
to reduce their consumption o f this compound by 20% in 2005 and 100% in 2015.
The U.S. government is complying with the Montreal Protocol under the auspices
o f the 1990 Clean Air Act. Preshipment and quarantine exceptions include specific
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methyl bromide fumigation requirements by a foreign government to allow the product to
be imported. For example, U.S. cherry imports to Japan must be fumigated by methyl
bromide; thus this application will be allowed. Currently, the United States has approved
methyl bromide treatments for wooden packing materials originating in China (see ALB
background section for details). In addition, most pallets and wooden packing material
exported from the United States to countries around the world must be fumigated or heat
treated. Therefore, methyl bromide fumigation of exported wooden packing materials is
permitted by the U.S. government, under the preshipment and quarantine exception.
Despite exemptions for regulatory purposes, the cost of methyl bromide in the
United States has increased substantially over the last 4 years. The cost per lb. increased
from $2.00 in 1999 to $3.20 in 2000.181 The commercial cost for methyl bromide in
2000 was $7.24/lb.182 Consequently, many o f the larger pallet manufacturers have
switched from methyl bromide to heat treatment. Hundreds of smaller manufacturers, on
the other hand, still use methyl bromide fumigation.183 In 2003, typical U.S. midwest
commercial charges to fumigate a 2700 ft3 trailer ranged from $300 to fumigate the trailer
at the company’s plant to $600 if the fumigation was performed at the customer’s site. If
the shipper chose to do his own fumigation, the start-up costs for license and detection
equipment would be at least $3,000 to $5,000. In addition, safety precautions and
personnel training must occur because o f the toxicity o f methyl bromide to human beings.
2.5.2 Conventional Heat Treatment
The use o f gas-fired kilns for drying lumber has seen widespread use across the
United States. In addition, many o f the major U.S. pallet manufacturers184 have switched
from methyl bromide fumigation to heat treatment schedules for insect control over the
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83
last few years. As o f May 1994, the USDA Forest Service185 reported that there were
more than 7000 dry kilns across the country. Most of these kilns heat with steam and are
run between 160 and 180 °F. Heating schedules are based either on time or on moisture
content. Twenty-nine billion board feet was reported dried by manufacturers in 19921993.
Heat treatment to eradicate insects such as the Asian longhomed beetle and
pinewood nematode can also be conducted in gas-fired kilns. The lumber does not
necessarily have to be dried, however. As mentioned in section 2.2, the U.N. treatment
schedules require that lumber be heated to 56 °C at the core for 30 minutes. For
pinewood nematode, the USDA Forest Service186 showed that all nematodes and adult
pine sawyers infesting green lumber (2 in. x 4 in. and 6 in. x 6 in.) were killed once the
wood temperature reached 60 °C. One hour o f heat treatment was required to reach this
temperature for the 2 in. x 4 in. x 48 in. lumber, whereas an additional 3 hours of
treatment was required for the 6 in. x 6 in. x 48 in. lumber.
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2.6 References
Ganshin AJ, de Zeeuw C. Textbook of Wood Technology Structure, Identification,
Properties, and Uses o f the Commercial Woods o f the United States and Canada. 4th ed.
New York, NY: McGraw-Hill Book Company; 1980:11-403.
2Zumdahl SS. Chemistry. Lexington, MA: D.C. Heath & Co; 1986:958
3United States Department o f Agriculture Animal, Plant Protection and Quarantine. New
Pest Advisory Group Report. Riverdale, MD: Sept. 25,1996.
4United States Forest Service Northeastern Area. Host list for asian longhomed beetle in
Chicago and New York, http://www.na.fe.fed.wu/spfo/alb/gen/hostlist.htm. 2001.
5United States Department o f Agriculture Animal, Plant Protection and Quarantine.
Asian longhomed beetle (Anoplophora glabripennis), USDA-APHIS-PPQ fact sheet.
http://www.aphis.usda.gov/oa/pubs/fsalb.pdf; 2001.
6United States Department o f Agriculture Animal, Plant Protection and Quarantine. New
Pest Advisory Group Report. Riverdale, MD: Sept. 25,1996.
7Ibid.
8United States Department o f Agriculture Animal, Plant Protection and Quarantine.
Asian longhomed beetle {Anoplophora glabripennis). USDA-APHIS-PPQ fact sheet
http://www.aphis.usda.gov/oa/pubs/fealb.pdf2001.
9Keena, M.A. Anoplophora glabripennis from egg to adult. In: Proceedings U.S.
Department o f Agriculture 11th Interagency Research Forum on Gypsy Moth and Other
Invasive Species. General Technical Report NE-273 2001; 22-23.
10Peng J, Liu Y. Iconography o f Forest Insects In Hunan China. Hunan, China: Hunan
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Beetle Research and Development Review Nov. 6-8, 2001 Annapolis, MD. USDA Forest
Service, USDA Agriculture Research Service, & USDA Animal & Plant Health
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^Agricultural Research Magazine. Asian longhomed beetles. United States Department
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13United States Department o f Agriculture Animal, Plant Protection and Quarantine.
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http://www.aphis.usda.gov/oa/pubs/fealb.html 2002.
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85
14United States Department of Agriculture Animal, Plant Protection and Quarantine.
Asian longhomed beetle: questions & answers, Sept. 1998.
www.aphis.usda.gov/oa/alb/qaalb.html 1998.
15United States Department of Agriculture Animal, Plant Protection and Quarantine. New
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China, July 14, 2000. ww.aphis.usda.gov/oa/alb/albmap.html 2000.
17United States Forest Service Northeastern Area. Asian longhomed beetle infestation
data, Illinois, http ://www.na.fs.fed.us/spfo/alb/data/ilinfest.html 2001.
18Associated Press. Beetle hits New York’s Central Park. Chicago Tribune Feb. 10, 2002
19New York Times. Tree-munching Asian longhomed beetles are discovered in Jersey
City. New York Times Saturday Oct. 11, 2002. www.newyorktimes.com 2002.
20United States Department o f Agriculture Animal, Plant Protection and Quarantine.
Introductions & warehouse detections o f longhomed beetles from cargo originating in
China, July 14, 2000. www.aphis.usda.gov/oa/alb/albmap 2000.
21Nowak DJ, Pasek JE, Sequeira RA, et al. Potential effect o f Anoplophora glabripennis
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22United States Department o f Agriculture Animal, Plant Protection and Quarantine.
Asian longhomed beetle (Anoplophora glabripennis). USDA-APHIS-PPQ fact sheet
http://www.aphis.usda.gov/oa/pubs/fsalb.pdf2001
23United States Department o f Agriculture Animal and Plant Health Inspection Service.
Solid wood packing material from China; interim rule 7CFR319-354.
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24United States Department o f Agriculture Animal and Plant Health Inspection Service.
Solid wood packing material from China: A summary ofU.S. entry requirements
according to 7CFR319.40. http://www.aphis.usda.gov/oa/alb/swpmsum.html 1998; 1-4.
25United States Environmental Protection Agency. Methyl bromide questions and
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26United Nations. Guidelines for regulating wood packaging material in international
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27United States Department o f Agriculture Animal and Plant Health Inspection Service.
Solid wood packing material from China: A summary ofU.S. entry requirements
according to 7CFR 319.40. http://www.aphis.usda.gov/oa/alb/swpmsum.html 1998; 1-4.
28Markham CK, Stefan MB. Asian longhomed beetle cooperative eradication program:
program status and research needs report. First Annual Asian Longhomed Beetle
Research and Development Review Nov. 6-8,2001 Annapolis, MD. USDA Forest
Service, USDA Agriculture Research Service, & USDA Animal & Plant Health
Inspection Service 2001; .2-9.
29United Nations. Guidelines for regulating wood packaging material in international
trade. International Standards for Phytosanitary Measures Publication No. 15 March
2002 ; 1- 12 .
30Lance DR, Wang B, Francese J, et al. Behavior o f Anoplophora glabripennis. First
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Annapolis, MD. USDA Forest Service, USDA Agriculture Research Service, & USDA
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31Miller DR, Hanula JL, Sun J, et al. Trapping systems for Asian longhomed beetle and
other cerambycidae in China and North America. First Annual Asian Longhomed Beetle
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Service, USDA Agriculture Research Service, & USDA Animal & Plant Health
Inspection Service 2001; 52.
32Zhang A, Oliver J, Aldrich J. Semiochemically mediated enhancement of native
beneficials and suppression o f key pest insects. First Annual Asian Longhomed Beetle
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33Smith MT, Bancroft JS, Gao RT, et al. Dispersal potential o f Asian longhomed beetle.
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2001 Annapolis, MD. USDA Forest Service, USDA Agriculture Research Service, &
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34Sawyer AJ. Infestation dynamics of Asian longhomed beetle in the U.S. First Annual
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36Wen J, Li Y, Xia N, et al. Study on dispersal pattern of Anoplophora glabripennis
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2001 Annapolis, MD. USDA Forest Service, USDA Agriculture Research Service, &
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38Keena M, Lazarus L. Assessment of Asian longhomed beetle development in cut wood.
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39Sawyer AJ. Infestation dynamics o f Asian longhomed beetle in the U.S. First Annual
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MD. USDA Forest Service, USDA Agriculture Research Service, & USDA Animal &
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40Mack RG, Xu Zhixin. Heating in a kiln as a regulatory treatment for Anoplophora
glabripennis in solid wood packing. First Annual Asian Longhomed Beetle Research and
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4'Barak AV, Wang Y. Fumigation as a regulatory treatment for Anoplophora
glabripennis (ALLB) and other wood boring species found in solid wood packing (SWP).
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2001 Annapolis, MD. USDA Forest Service, USDA Agriculture Research Service, &
USDA Animal & Plant Health Inspection Service 2001; 61.
42Wang B, Mastro VC, Luo Y, et al. Pathways and risk o f introducing Anoplophora and
other invasive wood-boring pests in solid wood packing materials from China. First
Annual Asian Longhomed Beetle Research and Development Review Nov. 6-8, 2001
Annapolis, MD. USDA Forest Service, USDA Agriculture Research Service, & USDA
Animal & Plant Health Inspection Service 2001; 68.
43Wang B, McLane W, Mastro V. Effects o f chipping on immature Anoplophora
glabripennis in logs. First Annual Asian Longhomed Beetle Research and Development
Review Nov. 6-8, 2001 Annapolis, MD. USDA Forest Service, USDA Agriculture
Research Service, & USDA Animal & Plant Health Inspection Service 2001; 89.
44Bauer LS, Miller D. Survey of Asian longhomed beetle entomopathogens for potential
use in biological control. First Annual Asian Longhomed Beetle Research and
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Agriculture Research Service, & USDA Animal & Plant Health Inspection Service 200;
69.
45Solter LF, Keena MA, Cate J, et al. Testing o f rhabditoid nematodes as biological
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46D ’Amico V, Podgwaite JD. Developing a Bt biopesticide against the Asian longhomed
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47Hajek AE, Bauer LS, Li L. Evaluating non-target impact o f insect pathogenic fungi
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48Hajek AE, Dubois TLM. Behavior o f Asian longhomed beetle. First Annual Asian
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49Podgwaite JD, D’Amico V. Microorganisms associated with Asian longhomed beetle.
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50Smith MT, Fuester R, Yang Z. Investigations o f natural enemies for biological control
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51Ibid.
52Ibid.
53Ibid.
54Ibid.
55Ibid.
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56lb ld .
57Herard F, Cocquempot C, Simonot O. Development ofbiological control technology
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58Ibid.
59Ibid.
60Smith MT, Fuester R, Yang Z. Investigations o f natural enemies for biological control
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62McLane W, Cowan D, Wang B, et al. Systemic insecticides for control of Anoplophora
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63Haack RA, Poland T, Petrice T, et al. Host range o f the Asian longhomed beetle. First
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71Keena M. Determine Asian longhomed beetle flight propensity in the laboratory. First
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74Keena M. Continuously propagate in quarantine Asian longhomed beetle populations
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83Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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84Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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85Bhardwaj MC. Principles and methods o f ultrasonic characterization o f materials.
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86Ibid.
87Ensminger D. Ultrasonics: Fundementals, Technology, Applications. New York, NY:
Marcel Dekker, Inc 1988; 17.
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88Bhardwaj MC. Principles and methods of ultrasonic characterization o f materials.
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90Bhardwaj MC. Principles and methods of ultrasonic characterization o f materials.
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9'ibid.
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95Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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96Bhardwaj MC. Principles and methods of ultrasonic characterization o f materials.
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97Bhardwaj MC. Principles and methods o f ultrasonic characterization o f materials.
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98Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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100Gooberman GL. Ultrasonics: Theory and Application. New York, NY: Hart Publishing
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101Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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102Gooberman GL. Ultrasonics: Theory and Application. New York, NY: Hart Publishing
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103Bhardwaj MC. Principles and methods of ultrasonic characterization of materials.
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108Gooberman GL. Ultrasonics: Theory and Application. New York, NY: Hart Publishing
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109Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
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110Ibid
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113Bhatia AB. Ultrasonic absorption: an introduction to the theory o f sound absorption &
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117Ibid.
118Ensminger D. Ultrasonics: Fundamentals, Technology, Applications. New York, NY:
Marcel Dekker, Inc 1988; 237.
119Wu Q, Vun R, Bhardwaj MC, et al. Through-thickness Ultrasonic Transmission
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Nondestructive Testing of Wood, University o f Western Hungary, Soporon, Hungary,
Sept. 13-15,2000; 77-86.
I20Bhardwaj M. Non-destructive evaluation: introduction of non-contact ultrasound In:
Schwartz M (ed.). Encyclopedia o f Smart Materials. New York, NY: John Wiley & Sons;
2002; 690-714.
121Ibid.
122Wu Q, Vun R, Bhardwaj MC, et al. Through-thickness Ultrasonic Transmission
Properties o f Oriented Strandboard. Proceedings, 12th International Symposium on
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Sept. 13-15,2000; 77-86.
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159Tumer SJ, Marks RJ, Brady RC. The effect of microwave radiation and sodium
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3 ULTRASOUND EXPERIMENTS
3.1 Introduction
Nondestructive ultrasound was proposed as a method to detect the presence of
Asian longhomed beetles (ALB) hitchhiking in wooden packing materials such as pallets
and crates. If feasible, this technology would be used by port inspectors attempting to
eliminate the unintentional importation o f exotic pests in commercial trade shipping
materials. The goals o f this study were as follows:
1. To determine if noncontact, ultrasonic energy can detect living, ALB larvae in
lumber (usually 1-in. and 4-in. thick) used to produce pallets and crates.
2. To determine the feasibility o f this approach for on-site port inspections of pallets
and crates.
In order to reach the first goal, four major conditions had to be met. The noncontact
ultrasound system must be sensitive enough to capture the energy transmitted through
wood o f various species, thickness, orientations, and moisture content conditions.
Second, there had to be a measurable difference between ultrasound transmission through
wood and through larvae. Third, there must be some ability to distinguish dead from
living larvae. Finally, the system had to be able to show that there was a living larva
inside the wood.
Since this was a new application for noncontact ultrasound, the first step was to
build a fixed transducer system that could detect ultrasonic transmission through 1-in.
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
thick wood without surface contact. The second step was to characterize this transmission
through various species o f 1-in. thick wood. In addition, comparison between
transmission of ultrasound via traditional dry-coupled transducers, gel-coupled
transducers, and the noncontact transducers in contact with the wood was made in order
to determine how many orders o f magnitude are lost when transmitting through air.
Utilizing these background results and a newly developed raster scanning (c-scan)
system, images were produced of ultrasound (100,200, and 500 kHz) transmission and in
some cases reflection through the following mediums: an air column, a 9-mm thick
polystyrene sample, a living ALB larvae lying on top of the polystyrene, a 1-in. thick
wood sample (both green and dry aspen, as well as red pine), a living ALB larva on top
of a wood sample, a 1-in. thick wood sample with an empty hole, and a 1-in. thick wood
sample with a larva placed in the hole. Additional c-scan experiments with 100 kHz,
200 kHz, and 500 kHz frequencies were conducted on cross-grain and end-grain, 1-in.
solid red pine samples that were frozen, maintained at room temperature, subjected to 10
hours o f oven drying, or subjected to 25 hours of oven drying. Drilling holes in the wood
and placing a larva inside the hole do not completely mimic what one would find in
nature because o f larval feeding habits. As the larvae feed on the wood at the head of the
tunnel, they excrete sawdust like waste called frass that fills the tunnel behind them.
Consequently, in artificially infested wood the ultrasound waves would be interacting
with a combination o f sawdust and air inside the naturally bored tunnels, instead o f the
air-filled drilled holes. This may or may not affect the success o f the project. Therefore,
one final set o f c-scan experiments was conducted on sections of logs containing larvae in
naturally bored tunnels.
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The major aims o f this study were to characterize noncontact ultrasound
transmission through wood, effects o f waves on larval motion, and detection of living
larvae. Consequently, the experimental objectives in each of these areas are as follows:
Characterization o f noncontact ultrasound transmission through wood:
1. Determine if fixed noncontact transducers are sensitive enough to capture
ultrasonic transmission that has been reduced by two air/wood interfaces as
well as the various interfaces within the 1-in. thick wood sample, taking into
account various wood species, wood orientations, and varying moisture
contents.
2. Determine if noncontact ultrasound c-scans (200 kHz and 500 kHz) can
capture transmission and reflection signals from 1-in. thick wood samples of
different species, moisture contents, and wood orientations.
3. Characterize the transmission loss due to the air/wood interfaces by
comparing the integrated response transmission signals received by drycoupled and gel-coupled contact transducers to that received by the
noncontact transducers.
Larval motion:
1. Determine if this c-scanning technique can detect larval motion by placing a
moving cottonwood borer larva on a polystyrene block (a good transmitter of
ultrasound) and capture the transmitted ultrasonic energy (200kHz) via c-scan.
2. Determine if a moving cottonwood borer larva can be detected on top o f wood
with transmitted ultrasonic energy (200 kHz).
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103
Ultrasound detection of larvae in wood:
1. Determine if a moving cottonwood borer larva placed inside a drilled hole can
be detected in a 1-in. thick piece of green or dry wood.
2. Determine if a living cottonwood borer larva could be detected in its natural
tunnel inside green wood samples.
For transmission-mode, ultrasonic evaluation of materials, the magnitude of the
wave reaching the receiver is quite important. As was mentioned in section 2.3, there are
a number of factors such as interfaces and attenuation by the material through which the
wave is passing, which can reduce the energy before it reaches the receiver. When an
ultrasound wave hits an interface from one medium to another, the transmission is
affected by the acoustic impedances o f the two materials. There are two possible cases.
The wave could travel from a lower acoustic density material to a higher acoustic density
material or visa versa. After the wave has passed through the interlace, a portion o f the
transmitted energy can then be lost in the material itself due to scatter, beam spreading, or
phase relationships between the main beam and the scattered waves. There may be a
number of interfaces and bulk materials that the wave must travel through before
reaching the receiver.
In general, when the acoustic impedance of the first medium is lower than that of
the second material that the ultrasound wave passes through, the transmitted portion of
the wave will be greater than the reflected portion o f the wave. Since the acoustic
impedance is directly proportional to the density of the material, the denser the material is
the greater the acoustic impedance. Thus, when the first medium is less dense than the
second medium, the transmitted portion o f the wave will be greater than the reflected
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portion o f the wave. When comparing two different materials as the second medium, the
more dense (the higher the Z) the material, the lesser the transmission will be when the
ultrasound wave is moving from a lower density first medium to a higher density second
medium.
However, when the acoustic impedance o f the first medium the wave travels
through is higher than that of the second material, the transmission coefficient [2-19] will
be larger than the reflection coefficient [2-18]. When comparing two different materials
as the second medium, the greater the density (the higher the Z) the greater the
transmission coefficient.
When noncontact ultrasound transducers are used, the transducer acoustic
impedance is designed to closely match the acoustic impedance o f air, thereby,
transmitting most o f the energy in air. Some of the energy is lost while the wave is
traveling through the air and before it reaches the wood sample. Experiments, which
measure the transmission through the air column alone, quantify this energy loss through
the air. The second interface is the air/wood interface. The ultrasonic energy must pass
through a less dense material, air, to a more dense material, wood. However, the density
o f the wood depends on what medium is filling the pores present in the wood. For the
wood samples tested in this dissertation, the pores could be filled or partially filled with
liquid water (the most dense,1 0.998 g/cm3 at 100 kPa and 20 °C), ice (0.919 g/cm3 at 1
atm and 0 °C2) or air (the least dense). Acoustic impedances3 o f ice (3.4 x 106 kg/m2s) is
greater than that o f water (1.48 x 106 kg/m2s) even though the density of ice is less than
that o f water. Thus, it is expected that the most transmission will be through air-filled
pores, then ice-filled pores, and finally the least transmission is expected through liquid-
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filled pores. As the ultrasound wave passes through water (either ice or liquid), it is
expected to have less attenuation than when an ultrasound wave is passing through air.
This is because water has higher density and stronger intermolecular bonds than air.
Since pressure is the means by which an ultrasound wave propagates, more energy is lost
or attenuated in the larger gaps between the air molecules than the smaller gaps between
the water molecules. Ice, however, is less dense than liquid water. The lattice structure
for ice is more rigid, however, than that o f water. In order to investigate the effect o f ice,
water, and air on noncontact, ultrasound transmission, a number o f experiments using
three different frequencies were conducted. However, other effects such as scatter can
cause additional attenuation o f the signal. O f course, scatter is also affected by local
conditions within the wood. In addition, there are many other interfaces from defects and
individual cells within the sample, which the ultrasound must pass through before the
final wood/air and air/receiver interfaces.
When contact transducers are used, on the other hand, transmission occurs from a
relatively high Z of the transducer matching layers to either higher or lower Z, depending
on the condition o f the wood. There will be less transmission when the wood has a lower
Z (air-filled pores) than when the wood has a higher Z (liquid or solid water). Within the
wood itself, the ultrasonic waves will be attenuated in a similar manner as described in
the experiment above. A higher transmission is expected with contact transducers than
with noncontact transducers as the first and last air/wood interfaces do not occur for the
signal originated and captured by contact transducers.
In addition, the attenuation coefficient, a , is frequency dependent. As frequency
is increased, the attenuation coefficient is also expected to increase. Higher frequencies
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(thus higher a) are expected to attenuate more.
3.2
Experimental Design
An NCA 1000 Noncontact Ultrasonic Analyzer sold by Second Wave Systems,
Boalsburg, Pennsylvania (Figure 3-1) was used in all experiments. The system includes
a computer processor, a sample platform (moveable or stationary), transducer stands and
cables. The integrated response for noncontact transducer experiments was calculated in
the following manner. Integration o f the area under the first peak is the power
corresponding to the transmitted energy. Both the power corresponding to the
transmitted energy in the air column alone (IRg) and the power corresponding to the
transmitted energy through the sample (IRc) placed between the transducers must be
calculated. The net power (IRm) reported is then as follows [3-1]:
IRm - I K ~ IRa
[3-1]
IRn, is thus a measure o f the energy attenuated by the material. For these wood
experiments, IRm is a negative number. Thus, the more negative IRm is the lesser the
transmission and the greater the attenuation. For contact transducer experiments (both
gel and dry), however, transmission is measured through a test material, 24.9-mm thick
polystyrene, to obtain the standard IR reading, IRst [3-2].
[3_2]
Polystyrene was chosen as the factory standard because it is the most acoustically
transparent material with an acoustic impedance o f 2.44 MRayl, which is well matched
with the transducers.
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Analyzer
Transducers
^
___
Sample
Moveable or
Stationary Platform
Figure 3-1: NCA 1000 analyzer system set-up
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108
The wood samples were harvested, processed, and stored in the same manner as
delineated in the microwave section 4.4.2.1. In order to reduce the number o f variables,
the chosen samples were fairly clear of cracks and defects, although in some cases, a
well-defined knot was present. Consequently, there is some bias associated with the
study system. Moisture content and specific gravity4 were determined according to
ASTM #D 2395-93 Method A: Volume by Measurement. The equation for moisture
content [3-3] is as follows:
mc(%) = 100 *
\I-F )
[3-3]
where I is the initial green weight, F is the final dry weight
o f the specimen, and me is the moisture content.
3.2.1
Fixed Transducer Experimental Design
The fixed transducer experiments were conducted using three different
frequencies, various materials, and various wood species, as well as live larva inside
wood samples. The experimental design for the eight trials is delineated below.
3.2.1.1. Water and Ice Experiments Varying Frequency
In order to determine the effect o f water and ice alone on transmission, three
frequencies (100 kHz, 200 kHz, and 500 kHz) were transmitted through an air-filled,
acrylic container with a flat bottom approximately 1,5-mm thick. Then, 25 mm o f
distilled water was placed in the container and transmission was measured for the same
three frequencies. The same container o f water was then frozen and the experiments
were conducted again. The resulting ice was somewhat rough, which can affect the
readings. The NCA 1000 system settings for each o f the frequencies were as follows:
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(A) 100 kHz experiments: 118 kHz frequency, 22 kHz bandwidth, 50%
amplitude, 45% chirp A, and chirp B
(B) 200 kHz experiments: 202 kHz frequency, 39 kHz bandwidth, 450 ms
chirp duration, 65% chirp A, and chirp B.
(C) 500 kHz experiments: 480 kHz frequency, 180 kHz bandwidth, 450
ms chirp duration, 65% chirp A, and chirp B.
The integrated response for each condition was calculated using equations [2-19] and [234]. Comparisons with the measured integrated response were then made.
3.2.1.2 Wood Sample Experiments Varying Frequency
The goal o f this set o f trials was to determine which frequency was most suited
for transmission through the wood samples, as well as the effects o f moisture content,
frozen/unfrozen states, and wood orientation on ultrasound transmission. Three
frequencies (100 kHz, 200 kHz, and 500 kHz) were transmitted through five positions on
the same 1-in. thick, red pine samples. Five o f the samples were orientated with the
cross-grain face perpendicular to the ultrasound wave and five o f the samples were
orientated with the end-grain face perpendicular to the ultrasound wave (Figure 3-2).
The following NCA 1000 system parameters were the same regardless o f the
frequency: amplitude 50%, Chirp step A 45%, Chirp step B 45%, image size 51 mm x 51
mm, and a 1 mm step size. The specific NCA 1000 frequency and bandwidth settings for
the 100 kHz experiments were 119 kHz and 22 kHz, respectively. For the 200 kHz trials,
a bandwidth o f 39 kHz and a frequency o f 202 kHz were used. Finally, for the 500 kHz
images, a 480 kHz frequency NCA 1000 setting and a 180 kHz bandwidth setting were
used.
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Figure 3-2: Fixed transducer, cross-grain (left) and end-grain (right) wood orientations.
The five transmission regions (1 to 5) are indicated in red
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Ill
3.2.1.3 Fixed Transducer Experiments Varying Couple Mechanism:
Drv-coupled. Gel-coupled, and Air-coupled
The goal o f these experiments was to determine the effect o f the couplant on the
magnitude of the transmitted signal received. Two separate trials were conducted using
200 kHz transducers. The first set was designed to compare dry-coupled with fixed
contact readings through 1-in. thick, cross-grain aspen, and 1-in. thick, red pine samples.
Various conditions such as moisture content and drilled holes were investigated for both
types o f wood. The second set o f trials focused on one wood type, 1-in. thick red pine,
and compared noncontact transmission with gel-coupled and dry-coupled transmission
through both cross-grain and end-grain. All transducers were connected to the NCA
1000 system. For both the dry contact and gel contact experiments, finger pressure was
used to hold the transducers to the wood sample.
For the first set, 200 kHz, unfocused, contact transducer (WD50-.25, serial
numbers: 172926 and124941, Ultran Laboratories, Inc., Boalsburg, PA) readings were
compared to 200 kHz unfocused, noncontact transducers (NCT 102, serial numbers:
250131 and 250227, Ultran Laboratories, Inc., Boalsburg, PA). The settings used with
the contact transducer experiments were 250 kHz frequency, 140 bandwidth, 50 ps
duration, 10 ps alternate duration, 75 amplitude, 45% chirp A, and 45% chirp B. The
settings for the 200 kHz noncontact transducers connected to the NCA 1000 system were
225 kHz frequency, 112 bandwidth, 650 ps duration, 10 ps alternate duration, 75
amplitude, 45% chirp A, and 45% chirp B. Once transmission through the air column
(noncontact transducers) or through the factory-supplied test sample (gel and dry contact
transducers) was taken, transmission for each set o f transducers was then measured
through 1-in. thick, green, cross-grain, red pine without holes; 1-in. thick, dry, cross­
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112
grain, red pine without holes; 1-in. thick dry, cross-grain aspen without holes and; 1-in.
thick dry, cross-grain aspen with ~V2-in. drilled hole and; 1-in. thick dry, cross-grain, red
pine with ~V2-in. drilled hole.
For the second set o f trials, 200 kHz, unfocused contact transducers (WD50-25,
serial numbers: 172926 and124941, Ultran Laboratories, Inc., Boalsburg, PA) were used
for both the dry and gel experiments on 1-in. red pine samples. For the gel experiments
the ultrasonic couplant used was Ultragel II (Echoultrasound, Box 118 Reedsville, PA
17084). Unfocused, 200 kHz, noncontact transducers (NCT-102, serial numbers: 250131
and 250227, Ultran Laboratories, Inc., Boalsburg, PA) were used for the noncontact
trials. Two different wood orientations (one to five samples each depending on the type
o f transducers used) were chosen and measurements were taken at specified points on
each sample (one to five different points depending on the type o f transducer used)
(Figure 3-2). Transmission measurements were taken for wood that had been frozen, kept
at room temperature, dried for 10 hours in a conventional 80 °C drying oven, or dried for
25 hours under the same drying conditions. The NCA1000 settings for the noncontact
experiments were 188 kHz frequency, 73 kHz bandwidth, 300 ps duration, 25 ps
alternate duration, 50 amplitude, 45% chirp A, and 45% chirp B. The NCA 1000 settings
for both the dry contact and the gel contact experiments were 265 kHz frequency, 200
kHz bandwidth, 100 ps duration, 25 ps alternate duration, 25 amplitude, 45% chirp A,
and 45% chirp B. Due to its destructive nature, the gel-coupled experiments were
conducted on only two samples. The ultrasound waves were directed through the cross­
grain face on one sample and the end-grain face on another sample (Figure 3-2). Dry-
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113
coupled and noncontact 200 kHz experiments were conducted on 10 samples (5 through
the cross-grain face and 5 through the end-grain face).
3.2.2 C-Scan Experimental Design
Both transmission and reflection experiments were conducted. The scans ranged
from red (the higher the transmitted or reflected signal received) to blue (the lower the
signal received). The range o f integrated signal response corresponding to the color
range is reported in parenthesis in the results section. Dimensions o f all scans were 50
mm x 50 mm x 0.5 mm unless otherwise stated.
3.2.2.1 Transmission Mode 100 kHz Transducers
The results o f this trial should lead to a better understanding o f how moisture
content and frozen/unfrozen states affect the 100 kHz c-scans. In addition, the 100 kHz
images generated will be compared to the 200 kHz and 500 kHz images to determine the
effect o f frequency on the c-scans. In this series o f transmission images, the c-scan NCA
1000 system settings were 119 kHz frequency, 22 bandwidth, 300 ps duration, 25 ps
alternate duration, 50 amplitude, 45% chirp A, and 45% chirp B. Transmission of 100
kHz ultrasound waves was captured through the air column alone, as well as through 1in. red pine samples o f two different orientations (cross- and end-grain faces). Each
sample was subject to four different states (frozen state, room temperature, 10-hour dried,
and 25-hour dried) during this trial. Wood was dried in a conventional drying oven at
80 °C.
3.2.2.2 Transmission Mode 200 kHz Transducers
Two 200 kHz noncontact focused transducers (NCT102-FL150 Ultran
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Laboratories, Inc., Boalsburg, PA) were set 150 mm apart and readings were taken in the
transmission mode. Three different sets o f 200 kHz experiments were conducted. The
first trial focused on images through the same material under different moisture contents.
The second trial produced images through different materials, defects, and artificially
inserted larva. The third trial tested the ability of ultrasound waves to identify larvae
residing in naturally bored tunnels in the wood samples.
3.2.2.2.1 200 kHz Transmission, 1-in. Thick Red Pine, Various
Moisture Contents
The goals o f these trials were to see how moisture content and frozen vs. unfrozen
states affected the c-scans. In addition, basic 200 kHz c-scans were to be used for
comparison with 100 kHz and 500 kHz c-scans. In this series o f transmission images, the
c-scan NCA 1000 system settings were 188 kHz frequency, 73 bandwidth, 300 [is
duration, 25 ps alternate duration, 50 amplitude, 45% chirp A, and 45% chirp B.
Transmission o f 200 kHz ultrasound waves was captured through the air column alone, as
well as through 1-in. red pine samples. Each sample was initially in the frozen state, then
at room temperature, dried for 10 hours, and then dried for 25 hours. Two different
orientations, cross-grain and end-grain faces, were investigated. Wood was dried in a
conventional drying oven at 80 °C.
3.22.2.2 200 kHz Transmission, Various Materials, Defects and
CWB Larvae
The goal o f these trials was to set up baseline c-scans through acoustically
friendly materials, such as polystyrene, as well as through wood. Then, various variables
such as artificially drilled holes in the wood, dry wood versus moist wood, and live larvae
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were introduced in order to determine if they could be detected by the ultrasound scans.
For these trials, the settings used were 225 kHz frequency, 112 bandwidth, 650 ps
duration, 10 fis alternate duration, 75 amplitude, 45% chirp A, and 45% chirp B.
Transmission o f 200 kHz ultrasound waves was captured through air alone; 9-mm thick
polystyrene; a CWB larva on 9-mm polystyrene surface; 1-in. thick green, cross-grain,
aspen (both with and without holes); 1-in. thick green, cross-grain, red pine (both with
and without holes); 1-in. thick dry, cross-grain aspen (both with and without holes); and
1-in. thick dry, cross-grain red pine (both with and without holes); a CWB larva on each
wood sample; and a CWB larva inside the drilled hole (each wood sample). The larva
used in these experiments was 1lU-m. long and weighed 1.5 g. To attain dry samples, the
red pine and the aspen samples were placed in a drying oven at 80 °C. They were taken
out when the weight did not change.
3.2.2.2.3 200 kHz Transmission o f CWB Larvae in Naturally Bored
Wood
The major goal o f this trial was to determine if larvae in their natural habitat could
be detected and deemed living or dead by ultrasound c-scans. CWB larvae were reared in
the laboratory in the same manner as described in section 4.4.2.2.2. Then, the larvae
were inserted under the bark o f freshly cut black willow logs. The logs were sealed with
Saran wrap and the larvae allowed to develop for 2 months. The logs were sectioned into
35-mm deep pieces and a transmission-mode, c-scan was made o f five samples with 200
kHz focused transducers (NCT 102-P50, 25-mm diameter, 50-mm point focus). Due to
the sectioning o f the logs, the ultrasound was passed through the cross-grain face (Figure
3-2). The scan area was 180 x 160 mm and the step index was 1 mm. The NCA1000
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116
system settings were as follows: 190 KHz frequency, 79 kHz bandwidth, 450
jjis
chirp
duration, 65% chirp A, and 65% chirp B. A photograph of each sample was taken and
visual observations were made as to the number and content o f tunnel holes. This
information was then compared to the c-scan image.
3.2.2.3 Transmission Mode 500 kHz Transducers
Two sets o f trials were also conducted with 500 kHz noncontact focused
transducers (NCT75-FL115, Ultran Laboratories, Inc., Boalburg PA). The goals o f these
trials were multifold. One purpose was to compare the effect of moisture content on the
500 kHz c-scans. Another purpose was to provide the 500 kHz base images for
frequency comparisons with the 200 kHz and the 100 kHz images. Finally, the trials
were to provide the baseline images o f two different wood species for comparison, dry
red pine and dry aspen. As with the 200 kHz trials, one set compared the 500 kHz
transmission through cross- and end-grain, 1-in. red pine samples, after frozen, room
temperature, 10-hour dry, and 25-hour dry treatments. The second trial looked at
transmission through oven dried (65 °C for 72 hours), 1-in. thick aspen.
For the first study, the c-scan NCA 1000 system settings were frequency 480 kHz,
bandwidth 180 kHz, 50% amplitude, Chirp step A 45%, and Chirp step B 54%. The
image size was 51 mm x 51 mm and the step size was 1.0 mm.
For the second trial the 500 kHz, focused transducers (NCT75-FL115 Ultran,
Boalsburg PA) were set 50 mm apart. All c-scan NCA 1000 system settings for this
series were 550 kHz frequency, 225 bandwidth, 200 ps duration, 10 ps alternate duration,
75 amplitude, 45% chirp A, and 45% chirp B. The transmission measurements were
taken through oven dried (65 °C for 72 hours), 1-in. thick aspen.
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3.2.2.4 Reflection Mode 500 kHz Transducers
This short set of experiments was designed to show the difference between
reflection and transmission images that can be generated. One 500 kHz noncontact
focused transducer (NCT75-FL115 Ultran Laboratories, Inc., Boalsburg PA) was both
the emitter and the receiver. Distance between the sample and the transducer was 110
mm. NCA 1000 system settings were 550 kHz frequency, 225 band width, 75 amplitude,
45% chirp A, and 45% chirp B. Reflection o f 500 kHz ultrasound waves was captured
off the following mediums: 9-mm thick polystyrene (+20 to +30dB), a CWB larva on 9mm polystyrene surface (+20 to +30dB), 1-in. thick green (moisture content 25.3%) and
oven dried (65 °C for 72 hours) red pine (both with and without holes), 1-in. thick dry
aspen and red pine (both with and without holes), a CWB larva on the green (me 25.3%)
wood sample, and a CWB larva inside the drilled hole (dry red pine wood sample).
3.3 Experimental Results and Discussion
3.3.1 Fixed Transducer Experiments
3.3.1.1 Fixed Noncontact Transducer Varying Frequency Results
for Ice. Water, and Air
As can be noted in Table 3-1, there is more transmittance from air-water interface
than from air-ice interface. However, there is no appreciable frequency-dependent (100
kHz to 500 kHz) attenuation, either by water or by ice.
3.3.1.2 Fixed Noncontact Transducer Varying Frequency Results
for Red Pine
The noncontact red pine transmission results for each o f the three individual
frequencies tested (100 kHz, 200 kHz, and 500 kHz) are summarized below by wood
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Table 3-1: Noncontact ultrasound transmittance measurements
through water and ice
Frequency
(kHz)
500
Acoustic
Impedance
(xlO8 kg/m2s)
3.19
25 mm
distilled
water in
container
500
25 mm ice
in
container
Acrylic
flatbottomed
container
1.5 mm
IRm
Experimental
(dB)
-63.5
IRm
Calculated
(dB)
-66
air/acrylic
interface
IRa
(dB)
+78
IRc
(dB)
+14.5
1.48
+80
+20
-60
-59
air/water
interface
500
3.4
+80
+15
-65
200
3.19
+64
+1
-63
-66
air/ice
interface
-66
air/acrylic
interface
25 mm
distilled
water in
container
200
1.48
+64
+5
-59
-59
air/water
interface
25 mm ice
in
container
Acrylic
flatbottomed
container
1.5 mm
200
3.4
+64
0
-64
100
3.19
+59
-2
-61
-66
air/ice
interface
-66
25 mm
distilled
water in
container
100
1.48
+59
+4
-55
-59
air/water
interface
25 mm ice
in
container
100
3.4
+59
-4
-63
-66
air/ice
interface
Material
Acrylic
flatbottomed
container
1.5 mm
air/acrylic
interface
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orientation (cross-grain and end-grain). Measured and observed characteristics o f the
wood after each treatment, such as moisture content and physical changes, are
summarized below in Tables 3-2 and 3-3, respectively. Comparisons between the three
frequencies were then made. Three different couplants (air, dry and gel) were also
investigated and reported. Details for each experiment are provided in Appendix A.
3.3.1.2.1 Fixed Noncontact Transducer, 100 kHz Results
All 100 kHz average IRm readings for the cross-grain-orientated experiments
were between -63 and -90 dB. The frozen and room temperature transmission readings
are approximately the same, except for RP3, position 3 (Table 3-4). Moisture content in
the frozen samples ranged from 27 to 41%; at room temperature, the moisture content
was 17 to 23%. After 10 hours at 105 °C, the samples contained 0.7 to 3.4% moisture
content. Transmission readings for these samples tended to be one-half or more orders o f
magnitude (20 dB=l order o f magnitude) less than the frozen or room temperature
readings. This trend is not as expected. Less water content should translate into less
sample density; thus transmission could be expected to increase. However, when sample
RP9 was dried even further (1% me to 0.2% me), the transmission did increase from
~ -85 dB (10-hour dry) to ~ -64 dB (25-hour dry), which was even greater than the frozen
readings. Physically, the only observed difference between the 25-hour RP9 sample and
the 10-hour RP9 sample was slight bowing. Standard deviations associated with average
IRm’s for individual positions varied from 0.07 to 1.39 dB.
Average transmission o f 100 KHz ultrasound through end-grain samples (RP14 RP24) ranged between -57 and- 97 dB (~2 order o f magnitude difference) for all four
treatments (Table 3-5). As with the cross-grain samples, the frozen and room
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Table 3-2; Summary of moisture content by treatment for wood samples
SAMPLE
Frozen
Moisture
Content (%)
28.7
30.6
31.1
28.2
27.7
27.2
27.8
30.5
28.2
41.0
RP3
RP9
RP1Q
RP12
RP13
RP14
RP16
RP19
RP21
RP24
TREATMENT
10-Hour Dry
Room Temp.
Moisture
Moisture
Content (%)
Content (%)
3.4
22.2
1.0
22.7
0.7
23.0
1.1
16.7
0.7
21.9
4.4
22.5
4.5
20.4
3.2
22.4
1.7
17.3
2.4
18.9
25-Hour Dry
Moisture
Content (%)
0.1
0.2
0.0
0.1
0
0
0
0
0
0
Table 3-3; Summary o f physical observations of samples
Expt
#
Frozen
Dimensions
Frozen
comment
RT
comments
10-hour
comments
25-hour
comments
(in.)
4x4x1
through core
4x4x1
through core
4x4x15/16
through core
4x41/32x15/16
through core
4x4x1
through core
4x41/16x15/16
against grain
No cracks
No knots
No cracks
No knots
No cracks
No knots
No cracks
No knots
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
No bowing
No cracks
Slight bow up
No cracks
No bowing
No cracks
No bowing
No cracks
No cracks
No knots
No cracks
Big knot
No bowing
No cracks
Bowed up
No cracks
Big knot
No bowing
No cracks
Bowed up
No cracks
Big knot
RP16
4x4x15/16
against grain
No cracks
big knot
RP19
4x4x15/16
against grain
No cracks
No knots
No bowing
No cracks
Big knot
Bowed up
No cracking
Bowed down
No cracks
Big knot
Bowed up
No cracking
No bowing
No cracks
Bowed up
Small crack
btwn 2 & 3
Big knot
Bowed down
No cracks
Big knot
Bow up
No cracks
RP21
315/16x4x15/16
against grain
4x4x15/16
against grain
No cracks
No knots
No bowing
No cracks
Bowed down
No cracks
Bowed down
No cracks
No cracks
No knots
Bowed up
No cracks
Bowed up
No cracks
Lots bowed
up. No cracks
RP3
RP9
RP10
RP12
RP13
RP14
RP24
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Table 3-4: Summary o f 100 kHz readings from cross-grain,
red pine samples
Expt#
RP3
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP9
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP10
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RPJ2
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP13
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg. IRm
(dB)
Room Temp.
Avg. IRm
(dB)
10-Hour Dry
Avg. IRm
(dB)
25-Hour Dry
Avg. IRm
(dB)
-74
-72
-77
-88
-73
-75 .
-71
-72
-74
-73
-87
-84
-86
-86
-86
n.a.
n.a.
n.a.
n.a.
n.a
-71
-72
-73
-75
-73
n.a.
n.a.
n.a.
n.a.
n.a
-89
-85
-83
-88
-84
-67
-63
-63
-68
-65
-69
-69
-73
-70
-71
-69
-67
-69
-71
-71
-86
-80
-84
-85
-84
n.a.
n.a.
n.a.
n.a.
n.a
-69
-70
-66
-71
-71
n.a.
-68
-69
-69
-68
n.a.
n.a.
-83
-81
-82
n.a.
n.a.
n.a.
n.a.
n.a
-73
-76
-68
-76
-72
-73
-73
-68
-76
-73
-87
-89
-89
-89
-90
n.a.
n.a.
n.a.
n.a.
n.a.
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Table 3-5: Summary o f 100 kHz readings from end-grain,
red pine samples
Expt#
RP14
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP16
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP19
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP21
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP24
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg
IRm
Room Temp.
Avg.
IRm
10-Hour Dry
Avg.
IRm
25-Hour Dry
Avg.
IRm
-76
-69
-61
-64
-66
-76
-68
-62
-62
-64
-89
-94
-64
-81
-84
n.a.
n.a.
-60
-60
-63
-73
-68
-67
-71
-72
-70
-68
-64
-65
-69
-82
-86
-95
-88
-97
n.a.
n.a.
n.a.
n.a.
n.a.
-71
-76
-74
-70
-82
-62
-68
-65
-69
-71
-77
-83
-84
-88
-91
n.a.
n.a.
n.a.
n.a.
n.a
-63
-63
-61
-63
-68
-63
-61
-60
-63
-63
-80
-79
-79
-86
-79
-61
-58
-57
-63
-59
-84
-75
-69
-75
-73
n.a.
-71
-67
-68
-76
n.a.
-93
-93
-91
-96
n.a.
n.a.
n.a.
n.a.
-68
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123
temperature transmission was approximately the same, whereas the 10-hour dry
transmission was more than lA orders o f magnitude lower in all but one case, RP14
position 3. Like the cross-grain experiments above, increased transmission occurred after
the 25-hour dry treatment (0% moisture content) as compared to the 10-hour dry
treatment (1.7 to 4.5% moisture content). Standard deviations associated with average
IRm’s for individual positions varied from 0.23 to 3.13 dB. The integrated response
values for the room temperature and the 25-hour dried wood had very small standard
deviations (<0.27 dB), while frozen sample readings were more variable (up to 3.13 dB).
As the frozen wood samples were taken out of the freezer and transmission
measurements were taken at room temperature, the frozen transmission variations in the
frozen samples could be due to local differences in melting or local scatter. Also,
physical changes occurred during the drying process. All five samples were bowed after
10 hours of drying, and two o f the five (RP14 and RP19) were bowed at room
temperature. Only one small crack developed in one sample after 25 hours o f drying.
Knots were present in two samples (RP14 and RP16).
In summary, the 100 KHz transmission readings for each treatment were within
the same range, -57 to -97 dB regardless o f the orientation. Both frozen and room
temperature readings were approximately the same regardless o f orientation. Variability
for the frozen readings (~1 order o f magnitude) was greater than for the other conditions
(~
Va to
%orders o f magnitude), which could be due to local melting at room temperature
or local scatter. An initial reduction in moisture content seemed to reduce the
transmission o f 100 KHz through the samples regardless o f orientation. As expected,
however, increased transmission occurred when the moisture content in the wood was
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124
very close to zero. Very little- to no-cracking occurred during the drying process for
either orientation, but bowing was widespread for the end-grain samples. Given the
natural complexity o f wood (e.g., local moisture content and density differences, natural
cell geometry, and defects, such as knots and cracks) and the small sample size, these
trends are not conclusive. Additional studies are needed before conclusions can be
drawn.
3.3.1.2.2 Fixed Noncontact Transducer, 200 kHz Results
All 200 KHz transmission readings for the cross-grain samples (RP3 to RP13)
were approximately in the same range for all treatments (-58 to -8 2 dB), except frozen
samples where data were not available (Table 3-6). Standard deviations associated with
average IRm’s for individual positions varied from 0.03 to 0.85 dB. Comparing each
position across the three treatments for all five samples, there were no specific trends
seen between the 10-hour dry transmission readings, the 25-hour dry readings, and the
room temperature readings. All readings for both o f these treatments were within 10 dB
(l/2orders of magnitude). Physically, there were no major changes for any o f the samples
throughout the treatments. Consequently, moisture content o f less than 23% does not
greatly affect 200 kHz transmission through the cross-grain samples.
Except for the frozen treatment, all the 200 kHz transmission readings for the endgrain samples (RP14 to RP24) were also approximately in the same range, -59 to -85 dB
(Table 3-7). The frozen transmission readings were extremely variable (4 to -79 dB).
Standard deviations associated with average IRm’s for individual positions varied from
0.03 to 1.25 dB ignoring the frozen standard deviations, which reached 34.4 dB. Potential
reasons for the wide variation in the frozen readings could be local melting or local
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Table 3-6: Summary of 200 kHz readings from cross-grain,
red pine samples
Expt #
RP3
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP9
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP10
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP12
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP13
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg. IRm
(dB)
Room Temp.
Avg. IRm
(dB)
10-Hour Dry
Avg. IRm
(dB)
25-Hour Dry
Avg. IRm
(dB)
n.a.
n.a.
n.a.
n.a.
n.a.
-78
-74
-75
-75
-74
-72
-67
-79
-70
-70
-73
-67
-80
-71
-68
n.a.
n.a.
n.a.
n.a.
n.a.
-72
-76
-75
-82
-72
-76
-66
-66
-73
-66
-76
-66
-69
-75
-69
n.a.
n.a.
n.a.
n.a.
n.a.
-67
-68
-72
-70
-70
-67
-58
-70
-65
-62
-69
-59
-69
-66
-64
n.a.
n.a.
n.a.
n.a.
n.a.
-68
-67
-73
-66
-67
-67
-58
-69
-61
-63
-58
-65
-68
-62
-63
n.a.
n.a.
n.a.
n.a.
n.a.
-73
-78
n.a.
n.a.
n.a.
-69
-72
-72
-77
-77
-67
-73
-73
-76
-76
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Table 3-7: Summary of 200 kHz readings from end-grain,
red pine samples
Expt #
RP14
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP16
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP19
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP21
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP24;
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg
IRm
Room Temp.
Avg.
IRm
10-Hour Dry
Avg.
IRm
25-Hour Dry
Avg.
IRm
4
4
4
4
n.a.
-67
-66
-63
-64
-65
-70
-72
-66
-62
-68
-72
-73
-67
-61
-68
-68
-72
4
4
4
-69
-77
-69
-78
-86
-69
-85
-71
n.a.
-80
-67
-83
-70
-67
-79
4
-47
-70
-70
-70
-69
-68
-68
-79
-79
-77
-71
-71
-78
-79
-67
-68
-70
-75
-82
-65
-73
-64
-79
-70
-69
-74
-65
-74
-73
-71
-66
-60
-73
-62
-70
-76
-59
-75
-64
-73
-74
-72
-69
-67
n.a.
-73
-61
-76
-74
n.a.
n.a.
-63
-83
-73
n.a.
n.a.
n.a.
-83
-73
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127
scatter. Disregarding these frozen readings, moisture content within the range studied (0
to 23%) does not seem to affect the 200 kHz transmission through end-grain samples.
In summary, neither orientation nor moisture content (up to 23%) affected 200
kHz transmission through 1-in. red pine samples. Frozen samples did affect
transmission, however. Disregarding the frozen readings, all average IRm values ranged
between -58 and -83 dB, a 1lA order of magnitude difference.
3.3.1.2.3 Fixed Noncontact Transducer, 500 kHz Results
Regardless o f wood treatment (frozen, room temperature, 10-hour dry, 25-hour
dry) all o f the 500 KHz cross-grain transmission readings through 1-in. red pine fell
basically within the same range (-66 to -97 dB) with standard deviations ranging from
0.02 to 6.34 dB (Table 3-8). The frozen and room temperature readings were comparable
in most cases. The 10-hour dry transmission was greater than the frozen and room
temperature transmission for every position, except positions 2 and 4 on sample RP14.
The 25-hour transmission readings were approximately the same as the 10-hour
transmission readings.
Regardless o f the treatment, all o f the 500 kHz transmission readings for endgrain samples (Figure 3-9) were in approximately the same range (-65 to -98 dB) with
standard deviations from 0.0 to 6.50 dB. The frozen and 25-hour treatments had the
highest variability, 1% orders o f magnitude. The trend was for the completely dry sample
to transmit more 500 kHz ultrasound than the room temperature, moist samples. The
frozen readings did not exhibit consistently more or less transmission than the room
temperature readings. The same could be said for the 10-hour dry and 25-hour dry
reading comparison.
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128
Table 3-8: Summary o f 500 kHz readings from cross-grain, red pine samples
Expt #
RP3
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP9
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP10
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP12
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP13
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg. IRm
(dB)
Room Temp.
Avg. IRm
(dB)
10-Hour Dry
Avg. IRm
(dB)
25-Hour Dry
Avg. IRm
(dB)
-80
-78
-96
-88
-81
-82
-79
-92
-90
-83
-77
-78
-89
-79
-79
-76
-75
-86
-82
-79
n.a.
n.a.
n.a.
n.a.
n.a.
-83
-83
-87
-95
-89
-83
-77
-86
-86
-83
-85
-77
-82
-90
-84
-72
-68
-83
-76
-72
-77
-70
-83
-77
-75
-68
-66
-81
-69
-67
-70
-65
-79
-68
-68
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
-78
-83
-78
-75
n.a.
n.a.
-75
-67
-68
n.a.
n.a.
n.a.
-70
-71
-85
-85
-89
-95
-93
-84
-84
-94
-95
-96
-78
-95
-83
-97
-95
-79
-81
-94
-88
-94
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129
Table 3-9: Summary of 500 kHz readings from end-grain, red pine samples
Expt #
RP14
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP16
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP19
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP21
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
RP24
Pos 1
Pos 2
Pos 3
Pos 4
Pos 5
Frozen
Avg
IRm
Room Temp.
Avg.
IRm
10-Hour Dry
Avg.
IRm
25-Hour Dry
Avg.
IRm
-83
-90
-67
-70
-71
-86
-87
-74
-72
-75
-77
-81
n.a.
-72
-73
-76
-79
-66
-66
-72
-89
-91
-84
-90
-87
-85
-90
-81
-90
-90
-87
-92
-99
-96
-80
-81
-89
-90
-86
-86
-92
-89
-88
-86
-94
-93
-92
n.a.
n.a.
n.a.
-82
-88
-76
-88
-80
-82
-80
-78
-88
-85
-78
-76
-73
-79
-78
-79
-78
-70
-80
-76
-74
-72
-72
-79
-73
-75
-71
-65
-75
-75
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
n.a.
-94
-84
n.a.
n.a.
-70
-98
-86
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130
In summary, 500 kHz transmission ranges were the same (-65 to —98 dB)
regardless of the orientation, frozen/nonfrozen state or moisture content (0 to 31%).
Most o f the frozen and room temperature readings were comparable, as were the 10-hour
and 25-hour transmission regardless o f orientation. The dry 25-hour transmissions were
greater than the moist, room temperature transmissions for all but 3 o f 50 positions.
3.3.1.2.4 Comparison of 100 kHz, 200 kHz and 500 kHz Noncontact
Transmission Results
As long as the 1-in. red pine sample was not frozen, the average IRm readings for
moisture contents between 0 and 23% were within the range o f -60 to -98 dB regardless
o f frequency or orientation. Most o f the frozen readings for 100 kHz and 500 kHz also fit
within this range. Only the 200 kHz end-grain frozen readings were different (4 to -79
dB). Excluding the frozen end-grain readings and across all three frequencies tested,
variability between samples ranged from %to 1Vi orders o f magnitude (Vt to 1 order for
100 kHz, %to 1lA orders for 200 kHz, and %to 1Vi orders for 500 kHz). Graphical
examples of cross- and end-grain transmission comparisons o f 100 kHz, 200 kHz, and
500 kHz are shown in Figures 3-3 and 3-4.
In Figure 3-3, there is a noticeable frequency dependence o f ultrasound
attenuation for cross-grain orientation. As expected, 500 kHz transmission readings were
less than 200 kHz transmission for all cross-grain samples (Appendix A). The 100 kHz
transmission readings were not as expected, especially the 10-hour dry samples. In almost
every case, the 100 kHz transmission dropped sharply to below both 200 and 500 kHz
readings. Except for these 10-hour dry samples, most samples transmitted equal or
greater ultrasound energy o f 100 kHz than 200 kHz, which was in turn greater
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131
A ) R P 1 0 P o s it io n 1
-30
'• .......
| •'
i
-40 - Frozen Room
T.
-50 -
B ) R P10
| ...........
10 hr
dry
Position 2
-30 -|
25 hr
dry
-40 - Frozen
§
-60
Room
-50 -
-70
•1 r 60 ■
a '—'-70 -
-80
H
10 hr
dry
T.
25 hr I
dry j
-80 -
-90
-90 -
-100
-100 -1
Wood Treatment
■100 kHz
-200 kHz
•100 kHz
-500 kHz
C) RP10 P o s i t i o n
10 hr
dry
-200 kHz
D)
3
-40
25 hr
dry
-50
-60 S
xs'
W
-70 -
j-60
-80 -
-80
-90 -
-90
•500 kHz
R P10
1. —
-30
-30 -|
-40 - Frozen Room
T.
-50 -
Wood Treatment
—
1
Frozen Room
T.
Position 4
1---------
10 hr
dry
25 hr
dry
'-70
-100
-100
Wood Treatment
Wood Treatment
•100 kHz
■100 kHz
-500 kHz
-200 kHz
-200 kHz
-500 kHz
1 ) RP10 Position 5
-30
-40
PQ
3 -50
a
©
1
1
1
H
Frozen
Room
T.
10 hr
dry
25 hr
dry
-60
-70
-80 -90 -100
100 kHz
Wood Treatment
-200 kHz
-500 kHz
Figure 3-3: Cross-grain sample (RP10) 100 kHz, 200 kHz, and 500 kHz
transmission comparison by measurement position: A) position 1,
B) position 2, C) position 3, D) position 4, and E) position 5
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132
A)
RP21 P o s i t i o n
B ) R P 2 1 P o s i t io n 2
1
-30
Frozen Room T. 10 hr dry 25 hr dry
-40
B
O
■a
-50
Frozen Room
T.
-60
-70
§s»
H
-80
-90
-100
Wood Treatment
W o o d T r e a tm e n t
■100 kHz
-200 kHz
■100 kHz
><;nn v u?
C) R P 2 1
P o s i t io n 3
-30
Frozen
-50
.2
S
Room
T.
-500 kHz
D ) R P 2 1 P o s it io n 4
-30
-40
-200 kHz
10 hr
dry
25 hr
dry
^-60
-40
s
.2
.2
Room
T.
-50
a
10hr
dry
25 hr
dry
60
-80
§ s 70
b
H -80
-90
-90
'-70
1
■
Frozen
X
------------ \ •
/I
■ /
-100
-100
Wood Treatment
Wood Treatment
■100 kHz
-200 kHz
■100 kHz
-500 kHz
-200 kHz
■500 kHz
E) RP21 Position 5
-30
-40 - Frozen Room
10 hr
25 hr
B
-50
J
T.
dry
dry
.2
-6 0
1g g- - 7 0
2
H
-8 0
-9 0
-100
Wood Treatment
■100 kHz
-200 kHz
-500 kHz
Figure 3-4: End-grain sample (RP21) 100 kHz, 200 kHz, and 500 kHz transmission
comparison by measurement position: A) position 1, B) position 2, C) position 3,
D) position 4, and E) position 5
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133
than 500 kHz.
In Figure 3-4, the frequency dependence was also noticeable in the end-grain
RP21 samples. As predicted, the 100 kHz transmission was greater than the 200 kHz
transmission, which was great than the 500 kHz transmission. The one exception was the
10-hour dry samples where the 100 kHz transmission was consistently lower than both
the 200 kHz and 500 kHz readings. The other end-grain experiments (RP14, RP16,
RP19, RP24), however, did not always show this frequency dependence (Appendix A).
Equally often, the 200 kHz transmission was greater than the 100 kHz
transmission, which was in turn greater than the 500 kHz. Also of note is the occasional
dramatic increase in 200 kHz transmission from -60 dB to +4 dB. In this small number
of experiments, the frequency - transmission trends were not consistent. One explanation
is that the bulk attenuation mechanisms must have a greater effect than originally
expected.
From these results, one can conclude that all three frequencies (100 kHz, 200
kHz, and 500 kHz) can transmit enough energy through red pine wood samples up to 1in. thick and moisture contents o f up to 23% for nondestructive testing. Transmission
through frozen wood may be more variable than nonfrozen, possibly due to local
differences in melting or local scatter. Low moisture content (0.7 to 4.5% moisture
content) seems to affect 100 kHz transmission. Given the complex nature of wood,
additional experiments are required in order to confirm these observations, as well as to
develop an understanding o f the forces at work.
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134
3.3.1.3 Fixed 200 kHz Transducer Experiments Varying Couple
Mechanism: Dry-coupled. Gel-coupled, and Air-coupled
For the first set o f experiments, the 200 kHz transmission loss due to the two
additional air/wood interfaces experienced by the noncontact transducer system ranged
from 2.1 to 2.9 orders o f magnitude as compared to the contact transducer system. The
contact transducer integrated response was approximately the same for dry aspen (no
holes) and red pine (both dry and green, no holes). With holes, however, the contact
transducer transmission drops (between 14 and 1 orders of magnitude). This is as
expected because the drilled hole is filled with air, giving two additional wood/air and
air/wood interfaces for the ultrasound to pass through. Thus, the ultrasound transmission
drops. As with the contact transducers, the noncontact ultrasound wave is attenuated by
approximately !4 order of magnitude when it passes through the hole drilled into either
dried aspen or dried red pine. The results o f the dry contact vs. noncontact transducer
experiments are summarized in Table 3-10.
The results o f the second set of experiments comparing air-, gel-, and dry-coupled
transmission through 1-in. red-pine samples are as follows for the cross-grain samples.
Room temperature transmission readings through the five, cross-grain, 1-in. red pine
samples range from -66 to -82 dB for air-coupled and from -26 to -38 dB for drycoupled transducers. Thus, a 1 to 1lA order o f magnitude reduction from contact (drycoupled) to noncontact (air-coupled) was seen with moist samples. For the 10-hour dried,
cross-grain samples, transmission values dropped 14 to 1% orders o f magnitude between
the dry-coupled and the air-coupled samples. The 25-hour dried transmission readings
had a %to 1 order o f magnitude variation, with the air-coupled samples again
transmitting less than
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135
Table 3-10: Dry- vs. air-coupled 200 kHz transmission results
Type of
Sample
Dry Contact
IRc Range
(dB)
Factory
sample or
air column
Red pine
green
1-in. thick
no hole
Red pine
dried
1-in. thick
no hole
Red pine
dried
1-in. thick
with hole
Aspen
dried
1-in. thick
no hole
Aspen
dried
1-in. thick
with hole
+41 to +43
(IRA)sample
Dry Contact
IRm
(IRc-IRst)
(dB)
Noncontact
IRc
(dB)
Noncontact
IRm
(IRc - IRst)
(dB)
Order o f
Magnitude
Difference
(20 dB=l
order)
+63
(IRa) air
+15 to +17
15-41=
-26
-22
-22-63=
-85
58 dB
loss in air
2.9 orders
+15 to +17
15-41=
-26
-9
-9-63=
-72
45 dB
loss in air
2.3 orders
+1 to +3
1-41=
-40
-20
-20-63=
-83
43 dB
loss in air
2.2 orders
+19 to +21
19-41=
-22
-12
-12-63=
-75
53 dB
loss in air
2.7 orders
-3 to -4
-3-41=
-44
-22
-22-63=
-85
41 dB
loss in air
2.1 orders
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the dry-coupled ultrasound (Appendix B). One graphical example is portrayed in
Figure 3-5.
Transmission trials through end-grain samples also showed that all air-coupled,
200 kHz readings were less than the corresponding dry-contact readings. Room
temperature readings ranged from -61 to -79 dB for air-coupled to -35 to -61 dB for
dry-coupled, a %to VA orders o f magnitude difference. The 10-hour dry samples
showed a 1 to 2 order of magnitude difference, whereas the 25-hour samples showed a
variation of lA to % orders of magnitude. As in the cross-grain section, one graphical
example o f the end-grain transmission is portrayed in Figure 3-6. The trends are nearly
the same between the air-coupled and dry-coupled transmission even though they are
some magnitude apart.
Due to the destructive nature of the gel-couplant, only one sample and one
position o f each orientation were tested for each treatment. As expected, the cross-grain
transmission was greater for gel-coupled trials than for dry-coupled trials, which were in
turn greater than air-coupled trials regardless of treatment (Figure 3-7).
Except for the 10-hour reading, the end-grain sample showed the same trend
where gel-coupled transmitted more 200 kHz ultrasound than dry-coupled, which in turn
transmitted more than the air-coupled ultrasound (Figure 3-8).
In summary, dry-coupled 200 kHz transmission was greater by lA to 2 orders of
magnitude than air-coupled transmission, regardless of orientation, moisture content or
frozen/nonfrozen state. Gel and dry transmissions were within Vi orders of magnitude of
each other. In all but one case, the gel values were greater than the dry values for both
cross-grain and end-grain cases. As expected, air-coupled transmission was always less
with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission
A ) R o o m T e m p e r a tu r e R P 1 0
-1 0 - ...—--- T..... ..... 1-;------ ----- l
1
'
2
io
e
(ft
i
2
3
4
5
-3 0 -
m - -----
~
-20
2
-3 0 -
I
-4 0 -
«
2 0 -
• * ----- -------- -----------
i
O
_L
s
B ) 1 0 -H o u r D ry R P 1 0
-10
-50 -
1
-6 0 -
£
-7 0 -
-
-50 -60 -
4 ------- ♦ --------------------------♦
-70 -
-8 0 -
-80
P o s it io n
■air-contact —
P o s itio n
dry-contact
—®— air-contact
dry-contact
C ) 2 5 -H o u r D r y R P 1 0
-10
S' '20 ~
2- -3 0 s
•I
’4 0
1
-5 0 -
| -60
"
-
H -7 0 -80
P o sitio n
- air-coupled —
dry-coupled
Figure 3-5: Cross-grain sample (RP10) graphs representing air- and dry-coupled,
200 kHz , ultrasonic transmission through A) room temperature sample,
B) 10-hour dry sample, and C) 25-hour dry sample
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138
B)
A ) F rozen R P 21
pa
3
-
S
-20 H
-40 -
M
-40 -
-20
T em perature R P 2 1
I
1
-60 -
-60
-80
-80
P o s it io n
P o s it io n
- air-coupled
-0— air-coupled
-d ry-coupled
-d iy -co u p led
C ) 1 0-H our D r y R P 2 1
D ) 2 5 -H o u r D r y R P 2 1
0
-20
-
s -20 .2
J -4 0 S
1
-80
-60
-80
P o s it io n
air-coupled —■— dry-coup led
- air-coupled
-d ry-cou p led
Figure 3-6: End-grain sample RP21 graphs representing air- and dry-coupled,
200 kHz, ultrasonic transmission through A) frozen sample, B) room
temperature sample, C) 10-hour dry sample, and
D) 25-hour dry sample
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139
A) R P 1 2 Room Temperature
B )R P 1 2 1 0 -h o u r D ry
(fi
S -20 H
3
-20
-
I0S
45 -40
S
-60 -
-60 -
-80
-80
P o sition
—®— air-coupled
—®— g e l cou p led
P o s it io n
—■— dry-coupled
—«— air-coupled
—®— gel-cou p led
—■— dry-coupled
Q R P 1 2 2 5 -h o u r D ry
-20
-
a
.2
-40 -
H
-60 -
P o s it io n
- air-coupled
- g el-co u p led
-dry -cou p led
Figure 3-7: Sample RP 12 graphs representing air-, dry-, and gel-coupled ultrasonic
transmission through cross-grain samples: A) frozen, B) room temperature,
and C) 25-hour dry
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140
A ) R P 24 F rozen
0
B)
RP24 Room Temperature
■20
S , -20 e
.2
CA
JS
■40
■60
-80
-80
P o s it io n
P o s itio n
— air-coupled
#—gel-coupled
-air-coupled
dry-coupled
■gel-coupled
D ) R P 2 4 2 5 -h o u r D ry
QRP24 10-hour Dry
-20
-dry-coupled
s
"O
'•a*'
-
-20 -
S
•1 -40 .1
S
86 -60 -
-40 -60 -
H -80 -100
P o s it io n
P o s it io n
air-coupled
-air-coupled
gel-coupled
-gel-coupled
-dry-coupled
Figure 3-8: Sample RP 24 graphs representing air-, dry-, and gel-coupled ultrasonic
transmission for end-grain samples: A) frozen, B) room temperature,
C) 10-hour dry, and D) 25-hour dry
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141
than both air- and gel-coupled transmission (% to 3 orders of magnitude).
3.3.2 C-Scan Experiments
3.3.2.1 Transmission Mode 100 kHz Transducers
Transmission scans utilizing 100 kHz ultrasound waves were only completed for
1-in. red pine samples o f the two different orientations of cross-grain (five samples, RP3
to RP13) and end-grain (five samples, RP14 to RP24). In order to better analyze the data,
two different ranges were selected for each c-scan image. The first range encompassed
the entire original IRm collection data as seen by the NCA 1000 (see Appendix C for all
o f the best-range, 100 kHz c-scans). In order to better compare the three different
frequencies, a second range, -22 dB to -1.33 dB, was chosen (see Appendix D for all of
the common-range, 100 kHz c-scans). When available the digital photo o f the sample
was also included.
Transmission through the 1-in. samples was possible regardless of orientation
(cross- or end-grain). Details showing areas of greater and lesser transmission were
distinguishable for all but the 25-hour dry images, most of which appeared jumbled. One
typical set o f best-range, c-scans for each orientation, is shown in Figures 3-9 and 3-10
below.
It is clear that the transmission patterns seen in the cross-grain images are
considerably different from the end-grain images because of the grain/ultrasound
interactions. With 100 kHz transmission, grain orientation can be discerned.
In the same way, examples o f the cross- and end-grain images with the same
range are shown in Figures 3-11 and 3-12, respectively. There was a trend among the
cross-grain and end-grain 100 kHz images scanned showing that the frozen wood and
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142
-3.72
-0.45
-2.08
2.82
-4.32
-2.35
1.19
!
I
D
3.56
1.59
Color Scale (dB)
C
Color Scale (dB)
B
1.08 1 4.43
-2.27
-0.60
2.75
Color Scale (dB)
-0.38
I
-1.041 -0.19' 0.66
-0.61
0.23
Color Scale (dB)
E
Figure 3-9: Cross-grain, red pine sample 10 best-range images at 100 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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143
18.1 1 -6.88 1 4.34
-12 5
-1 27
Color Scale (dB)
,
.-,—
10.4 1 -2.81 1 4.78
-6.61
-0.98
Color Scale (dB)
,
-14.3 1 -5.45 1 3.4
-9.87
-1.02
Color Scale (dB)
-1.12 I -0.50 I 0.12
-0.81
-0.19
Color Scale (dB)
D
Figure 3-10: End-grain, red pine sample 16 best-range images at 100 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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144
WM
-22
I -11.7
-16.8
|
-1.33
-22
-11.7
-16.8
-6.5
I -1.33
-6.5
Color Scale (dB)
Color Scale (dB)
B
■22 I -11.7
-16.8
I -6.5
Color Scale (dB)
•22
I -11.7
-16.8
-6.5
Color Scale (dB)
Figure 3-11: Cross-grain, red pine sample 10 common-range images at 100 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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145
-22
1.33
| -11.7
-16.8
-22
-16.8
-6.5
-1.33
| -11.7
-6.5
Color Scale (dB)
Color Scale (dB)
B
-22
22
| -11.7
-16.8
-6.5
Color Scale (dB)
1.33
I -11.7
-16.8
-6.5
Color Scale (dB)
D
Figure 3-12: End-grain, red pine sample 16 common-range images at 100 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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146
room temperature samples transmitted less ultrasound than the 25-hour dry. The 10-hour
transmission differences were not as consistent.
3.3.2.2 Transmission Mode 200 kHz Transducers
3.3.2.2.1 Transmission Through 1-in. Red Pine, Cross- and End-Grain
Transmission scans utilizing 200 kHz ultrasound waves were completed for 1-in.
red pine samples of two different orientations, cross-grain (five samples, RP3 to RP13)
and end-grain (five samples, RP14 to RP24). Digital photos o f the sample were also
included when available.
Transmission through the 1-in. samples was possible regardless of orientation
(cross- or end-grain). In general, however, the end-grain samples allowed more
transmission than the cross-grain samples for both the frozen and room temperature
conditions. Details showing areas o f greater and lesser transmission were distinguishable
for all images, regardless o f moisture content, frozen/nonfrozen state, or orientation. A
typical set o f c-scans for each orientation is shown in Figures 3-13 and 3-14.
3.3.2.2.2 Transmission Through Various Materials, Defects, and
Larvae
In order to provide baseline images, transmission of 200 kHz ultrasound waves
through air alone (62 dB to 72 dB), 9-mm thick polystyrene (-1 to 11 dB), and a CWB
larva on 9-mm polystyrene surface (-1 to 11 dB) was captured in the scans (see Figure 315A, B, C). A digital photo o f the sample set-up was also provided. (Figure 3-15D).
Transmission through air alone was greater than through the polystyrene sample, as
expected (note the darker red color in the air c-scan). Transmission through the CWB
larva placed on top o f the polystyrene was much less and was the smallest through the
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147
DO
■
mm
-22
-16.8
-22
-16.8
-6.5
-1.3:
-6.5
Color Scale (dB)
Color Scale (dB)
B
C
-11.7
-16.8
-11.7
33
-6.5
Color Scale (dB)
-22
| -ll'.7
-16.8
|
-1.3j
-6.5
Color Scale (dB)
D
Figure 3-13: Cross-grain, red pine sample 10 common-range images at 200 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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148
-22
| -11!7
-16.8
|
-1.33
-22 | -ll'7 | -1.34
-16.8
-6.5
-6.5
Color Scale (dB)
Color Scale (dB)
B
I
-22
-11.7
-16.8
I -1.33
-6.5
Color Scale (dB)
-22
| -11.7
-16.8
|
-1.33
-6.5
Color Scale (dB)
D
Figure 3-14: End-grain, red pine sample 14 common-range images at 200 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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149
A
B
Larval
movement
C
D
Figure 3-15: Transmission-mode 200kHz c-scan of A) air alone, B) 9-mm thick
polystyrene, C) CWB larva on polystyrene (note the misalignment
o f the larva indicating larval movement, and D) a photograph
o f the equipment set-up
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150
center o f the larva as indicated by the blue and turquoise colors. Discontinuity lines in the
c-scan captured the larval movement. Next, transmission c-scans were captured through
solid 1-in. thick, 43.7% moisture content green aspen (-6 to +9 dB) with the CWB larva
placed on top o f the aspen sample (-6 to +9 dB). Then, an empty hole o f dimensions
13/3 2
in. in diameter and 2 '4 in. deep was drilled into the sample (-6 to +9 dB), and the CWB
larva was placed in the hole (-6 to +9 dB) (Figure 3-16A, B, D, E). Digital photographs
o f the sample set-ups were also provided in Figure 3-16C and F. The lack of
homogeneity o f the wood itself is quite evident by the mottled image. The larva on top o f
the wood could be identified by the reduction in ultrasound transmission due to the
addition o f interfaces (transducer/air, air/larva, larva/air, air/wood, wood/air,
air/transducer). Movement o f the larva during the scan can also be identified by the
discontinuity o f the image. The hole is distinguishable because the transmission of the
ultrasound through the air pocket was much less than through the relatively solid wood
sample. As can be noted in Figure 3-16D, the scan does not show the hole with sharp
boundaries. Instead, the hole is shown with wavy boundaries. Upon visual inspection,
the inner surface o f the hole was ridged and had small splinters of wood sticking into the
hole. This is probably due to the drill bit; all of the samples exhibited this phenomenon.
By filling the hole with a larva, I was hoping to enhance the ultrasound transmission
However this did not occur. Most likely there was a thin air layer surrounding the larva,
creating two wood/air/larva interfaces. These interfaces presented barriers to ultrasound
transmission sufficient to prevent the transducer receiver from detecting a significant
difference between the hole alone and the larva-filled hole.
In the same manner, transmission c-scans were captured through 1-in. thick,
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151
Moving Larva
Figure 3-16: Transmission-mode 200kHz c-scan of a 1-in. thick green aspen sample with
moisture content of 43.7% under the following conditions: A) sample alone,
B) moving CWB larva on top o f the sample, C) photograph of the sample,
D) sample with an empty hole, E) sample with the CWB larva in hole,
and F) photograph o f wood sample with hole
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25.3% moisture content, red pine (Figure 3-17) under the following conditions: solid
sample alone (-4 to +16 dB), larva on top of solid sample (-4 to +16 dB), an empty hole
o f dimensions nlz2 in. in diameter and 2l/j in. deep drilled into the sample (+7 to +16
dB), and a CWB larva placed in the hole (+7 to +16 dB). There was a knot in the center
o f this wood sample which corresponds to the yellow/light blue region in Figure 3-17A.
The larva, placed on top o f this knot, was distinguishable from the surrounding wood
because it was a larger blue area (Figure 3-17B). Like the aspen experiments discussed
above, the movement of the larva’s head was also identifiable by the discontinuity in the
scan. Compared to the solid, green aspen sample, the red pine sample had higher
transmission (note the larger red area in Figure 3-17A vs. Figure 3-16A). This could be
due to lower moisture content in the red pine sample (25.3% vs. 43.7%).
The results from the experiments using oven-dried wood support this moisture
content dependence o f 200 kHz ultrasound transmission. The 1-in. thick dry aspen
sample c-scans are shown in Figure 3-18A: hole alone (-6 to 9 dB) and Figure 3-18B:
larva in hole (-6 to 9 dB). A digital photo o f the sample was also provided in Figure 318C. Compared to the green aspen, transmission through the wood increased as
evidenced by a redder scan.
Dry red pine also transmitted a higher signal than green (Figure 3-19). In the
drying
process, the red pine sample cracked as indicated on the scans. As with the green
samples, both the dry red pine and the dry green pine sample c-scans did not distinguish
between the hole alone and the larva in the hole.
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153
Larva head moving
Figure 3-17: Transmission-mode 200kHz c-scan of a 1-in. thick green red-pine sample
with moisture content of 25.3% under the following conditions: A) sample alone,
B) CWB larva (only head moving) on top of the sample, C) photograph of the
Sample, D) sample with an empty hole, E) sample with the CWB in hole,
and F) photograph o f wood sample with hole
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154
A
B
Figure 3-18: Transmission-mode 200kHz c-scan of a 1-in. thick oven-dry aspen sample
under the following conditions: A) sample with an empty hole, B) sample with
the CWB larva in hole, and C) photograph of wood sample with hole
Crack
Crack
Crack
Figure 3-19: Transmission-mode 200kHz c-scan of a 1-in. thick oven-dry red pine
sample under the following conditions: A) sample with an empty hole, B) sample with
the CWB larva in hole, and C) photograph of wood sample with hole
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155
3.3.2.2.3 Natural Tunnel CWB Larvae Experiments
(Transmission-Mode 200 kHz)
From visual examination of the log sections, it was observed that the larvae had
tunneled along the perimeter of the log. Consequently, there were no tunnels or larvae
present in the core regions o f the samples scanned (Figure 3-20). When the logs were
sectioned, the resulting tunnel went all the way through the sample (top to bottom); none
stopped part way through the sample. All o f the tunnels were filled with a frass/air
combination, air only, or a larvae/frass/air combination. The air-filled holes were easily
identified in the c-scan by their shape and by their dark red color, indicating that the
ultrasound wave passed through an air column only. Splits or cracks that went frass-/airfilled holes could usually be identified by some combination o f dark and medium blue
colorings, as well as their shapes. Occasionally, a frass-/air-filled hole was not
identifiable on the c-scan. This may be due to the volume of frass in the hole or the
packing o f the frass, allowing more ultrasound to be transmitted.
The wood itself was not homogenous; therefore, differences in density, moisture
content, voids, or other factors also show up on the c-scan in a manner that may mask the
tunnel within the noise or look like a tunnel even when it is not one. The holes packed
with larvae also showed up a combination o f dark and medium blue in color, indicating
that there was minimal transmission o f ultrasound through the hole.
The larva-filled holes could not be distinguished from the frass-filled holes. This
is probably due to an air layer surrounding the larva, which is absorbing or reflecting the
ultrasound in a manner that is similar to the air trapped between and around the frass. Of
the five sections, three o f the samples (labeled 1 to 3) did not contain any larvae in the
tunnels, and two o f the samples (labeled 4 and 5) contained live larvae in tunnels.
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156
6 Frass
filled ■"
holes,
only 5 ^
canfoe^
located
2 empty holes
6 Frass
m
Crack in
6 Frass
SL
Figure 3-20: Transmission-mode, 200 kHz ultrasound c-scans of 35 mm thick sections of
black willow logs infested with live cottonwood borer larvae and the corresponding
photograph o f the each of the five samples labeled 1 through 5
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157
2 Larva
2 Frass
filled
holes
2 Frass
2 Larva
filled
holes
2 Frass
1 larva
Figure 3-20 cont.
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Sample 1 (see Figure 3-20, sample 1) contained six frass-filled holes and two air-filled
holes. One o f the lfass-filled holes was difficult to identify on the c-scan. All of the
others could be located. Sample 2 contained six frass-filled holes and a crack in the
wood. As can be seen in Figure 3-20, sample 2, the location of all seven of these features
could be found on the c-scan image (see Figure 3-20, sample 2). Visual examination of
sample 3 also showed six frass-filled holes, all of which were located on the c-scan (see
Figure 3-20, sample 3). Sample 4 was found to have two frass-filled holes, two larvafilled holes and a crack in the wood. All sites could be located; however, the larva-filled
holes could not be distinguished from the frass filled holes (see Figure 3-20, sample 4).
With visual examination o f sample 5 two frass-filled holes were found and one larvafilled hole. All three holes were located on the image; however, the larva-filled hole
could not be distinguished from the frass-filled holes.
3.3.2.3 Transmission Mode 500 kHz Transducers
3.3.2.3.1 Transmission, 1-in. Thick Red Pine, Cross- and End-Grain
As with the 100 kHz c-scan trials reported in section 3.3.2.1 above, the ranges
selected for each 500 kHz c-scan image were the original (best-range) IRm range
(Appendix F) and the common -22 dB to -1.33 dB range (Appendix G). Examples of
each o f the two orientations are shown in Figures 3-21 and 3-22 for the best range and
Figures 3-23 and 3-24 for the common-range. Both orientations allowed for the
transmission o f 500 kHz ultrasound. However, it is difficult to determine from the
images alone which are the cross-grain and which are the end-grain samples.
As can be noted in the images shown in Figure 3-23, the 500 kHz transmission
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159
18.1
-5.06
-14.9
-9.98
-23
-0.15
| -8.24
-13.2
Color Scale (dB)
Color Scale (dB)
B
A
-28
| -18ll
-23
|
-8.24
-13.2
-11.9
T
5.28
-3.32
-7.61
0.98
Color Scale (dB)
Color Scale (dB)
D
E
Figure 3-21: Cross-grain, red pine sample 14 best-range images at 500 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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160
-29.1
3.9
I -16.5
-
22.8
-
10.2
Color Scale (dB)
12.1
-21
-25.5
-16.6
Color Scale (dB)
-22
B
I
-24.1
T
_ -14.8
-19.4
I -5.49
-10.1
Color Scale (dB)
10.6
-30.4 | -20.5
-25.5
-15.6
Color Scale (dB)
D
Figure 3-22: End-grain, red pine sample 16 best-range images at 500 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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161
■22
■22
-11.7
-16.8
-16.8
-6.5
-11.7
-16.8
-1.33
-6.5
Color Scale (dB)
-6.5
Color Scale (dB)
Color Scale (dB)
-22
-11.7
-22
| -11.7
-16.8
1.33
-6.5
Color Scale (dB)
D
Figure 3-23: Cross-grain, red pine sample 10 common-range images at 500 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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162
•22
| -11.7
-16.8
-6.5
Color Scale (dB)
-22
I -11.7
-16.8
|
!
- 1.33
-6.5
Color Scale (dB)
I
-22
11.7
-16.8
-1.33
-6.5
Color Scale (dB)
D
Figure 3-24: End-grain, red pine sample 16 common-range images at 500 kHz:
A) digital photo, B) frozen, C) room temperature,
D) 10-hour dry, and E) 25-hour dry
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163
was much more for the frozen samples than for the room temperature samples. Other
trends are difficult to discern.
3.3.2.3.2 Transmission Through 1-in. Thick, Dry Aspen
Transmission o f 500 kHz ultrasound through 1-in. thick, dry aspen samples (-30
to -4 dB) was not as good as transmission o f 200 kHz (Figure 3-25 and Figure 3-18).
When comparing the hole and the solid 500 kHz images, the hole was not even visible .
This is due to higher attenuation o f the 500 kHz signal, resulting in a poor signal.
3.3.2.4 Reflection Mode 500 kHz Transducers
Baseline reflection images o ff o f 9-mm polystyrene (+20 to +30 dB) with and
without a larva are shown in Figures 3-26A and B, respectively. The larva was hardly
moving during this trial; therefore, the captured image has only one small discontinuity
that can be observed Both images exhibit a yellow stripe down the right side that are due
to mechanical shifting during the c-scan. A digital photo o f the sample is shown in
Figure 3-26C.
Reflected signals captured from 1-in. thick green red pine (Figure 3-27A and B)
show the concentric rings in the sample. The live shape o f the larvae can be identified in
the center o f the sample (Figure 3-27B) Once the sample is dried, however, the rings are
not as distinguishable (Figure 3-28B). In addition, Figure 3-28A contains a drilled hole,
which is not visible. This is probably due to the ultrasound signal reflecting mainly off
the surface and not deeper into the wood. In addition, the CWB larva in the hole (Figure
3-28B) was not distinguishable with 500 kHz ultrasound energy. A digital photo is also
included for reference purposes (Figure 3-28C).
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164
A
B
Figure 3-25: Transmission-mode 500kHz c-scan of a 1-in. thick oven-dry aspen sample
under the following conditions: A) sample with an empty hole, B) sample with
the CWB larva in hole, C) photograph o f wood sample with hole
Figure 3-26: Reflection-mode 500kHz c-scan o f A) 9-mm thick polystyrene, B) CWB
larva on polystyrene (the larva was barely moving), C) photograph o f set-up
A
B
Figure 3-27: Reflection-mode 500kHz c-scan o f a 1-in. thick green red pine sample with
moisture content o f 25.3% under the following conditions: A) sample alone,
and B) CWB larva on top o f the sample
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Figure 3-28: Reflection-mode 500kHz c-scan o f a 1-in. thick oven-dry red pine sample
under the following conditions: A) sample with an empty hole, B) sample with
the CWB larva in hole, and C) photograph o f wood sample with hole
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166
The green aspen 500 kHz reflection series shown in Figure 3-29 did not image the
larva as clearly as occurred in the red pine experiments.
3.4
Ultrasound Conclusions
From the above ultrasound experiments, a number o f conclusions can be made.
Noncontact, air-coupled ultrasound energy of 100 kHz, 200 kHz, and 500 kHz
frequencies is capable o f transmitting a discemable signal through 1-in. thick, red pine
wood samples o f less than 23% moisture content. The range o f received signal (-60 to 98
dB) from fixed transducers was the same regardless o f changes in moisture content less
than 23% or from different orientations. As expected, gel- and dry-coupled 200 kHz
transducers transmitted from V* to 3 orders of magnitude better than air-coupled 200 kHz
transducers, regardless o f orientation, moisture content, or frozen/nonfrozen state.
Excellent c-scan images can be generated for all three frequencies through 1-in. red pine
and for 200 kHz frequencies through 1-in. thick aspen for various conditions. Only 100
kHz images o f dry wood were not well defined. Artificially drilled holes in the wood
samples could be identified in the 200 and 500 kHz c-scans. Both the larva itself and its
movement could also be recognized when the larva was placed on top o f the wood.
However, neither the larva nor its movement could be identified with noncontact
ultrasound transmission when the larva was inside either an artificially drilled tunnel or
inside a naturally bored tunnel. This is probably due to the energy loss at the wood/air
and air/larva interfaces inside the holes. Therefore, the final conclusion reached is that
noncontact ultrasonic energy is not a feasible alternative for detecting live ALB larvae in
lumber.
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Figure 3-29: Reflection-mode 500kHz c-scan o f a 1-in. thick green aspen (moisture
content 43.7%) sample under the following conditions: A) solid sample,
B) CWB larva on top o f sample, and C) photograph o f wood sample
with larva placed on top
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Given the small sample size studied in this research, characterization o f the
noncontact ultrasound-wood interactions is by necessity limited in scope. Confusing
observations in the current study cannot be explained with the data collected. Systematic
empirical studies that focus on the ffequency-dependence o f noncontact ultrasonic
attenuation by wood features such as natural cell geometry, cracks, knots, as well as
environmental effects are a necessity if this new noncontact ultrasound technology is to
find applications in the wood processing industry.
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169
3.5 References
JLide DR (ed). Handbook o f Chemistry and Physics. 75th ed. Ann Arbor, MI: CRC Press;
1994: 6-10.
2Cutnell JD, Johnson KW. Physics. 3rd ed. New York, NY: Wiley; 1995: 315.
3Bhardwaj M. Ultran Laboratories, Inc. (Boalsburg, PA) unpublished data 4/20/03.
4American Society for Testing Materials. Standard test methods for specific gravity o f
wood and wood-based materials. In: Ann. Book of ASTM Standards. West
Conshohocken, PA: ASTM Standard D2395; 1996 Vol. 4.10.
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4 MICROWAVE EXPERIMENTS
4.1 Introduction
The primary goals o f these experiments were twofold: (1) to demonstrate that at
specific levels o f microwave power the treatment was lethal to cerambycid larvae such as
ALB and (2) to determine which parameters significantly affect the treatment process to
facilitate subsequent efforts to scale-up to commercial wood dimensions. In order to
reach these goals, a set o f dielectric experiments was undertaken to provide a basic
understanding o f microwave interaction with the wood. In addition, a comparison was
made o f wood temperatures reached during microwave processing vs. conventional heat
processing. Determination o f whether surface temperature might be a potential indicator
o f wood core temperature was also a goal. If true, a temperature sensitive compound
placed on the wood surface could possible be used to visually prove that the microwave
process was completed, a useful tool for U.S. port inspectors.
4.2 Dielectric Study
4.2.1 Introduction
To characterize wood/microwave interactions, dielectric measurements were
taken for wood samples o f various thickness, moisture content and grain orientation.
Four different wood species (red pine, Eastern white pine, aspen, and loblolly pine) were
characterized. Moisture content ranged from dry (<5%) to 145% o f dry weight.
As mentioned in section 2, microwave-material interaction will result in some
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171
combination of transmission, reflection, and/or absorption (Figure 2-13). Consequently,
incident microwave energy will split into transmitted energy, absorbed energy, and
reflected energy [4-1],
Incident
= Absorbed + Transmitted + Reflected
MW Energy
Energy
Energy
Energy
(MWE)
(A)
(T)
(R)
[4-1]
Relative values [4-2] for absorption, reflection, and transmission can be calculated by
normalizing equation [4-1].
A
T
R
1 —---------1---------- 1--------MWE MWE MWE
[4-2]
To determine the relative values o f absorption, reflection, and transmission, dielectric
experiments were performed utilizing a Hewlett-Packard 8510T analyzer (Figure 4-1)
and two different measurement techniques, transmission and cavity perturbatioa The
transmission experiments were conducted at 10 GHz, and then dielectric constants were
estimated for 2.45 GHz. The cavity perturbation method was applied to calculate both
the dielectric constant and dielectric loss for 2.45 GHz.
For both methods, a microwave generator (Agilent 85IOC with capability to
measure between 45 MHz and 26 GHz) synthesized electromagnetic waves at various
frequencies (Figure 4-1). The microwaves then traveled through a 50 ohm coaxial cable
to a waveguide adapter flange before reaching the sample positioned inside a waveguide.
The reflected wave traveled back the same cable and was captured by a GPIB card in the
network analyzer at Port A. The transmitted wave passes through the sample and is
eventually captured by a GPIB card in the network analyzer at Port B. Data from Port A
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172
'i
HP8510T
Network Analyzer
Pentium II
Processor
Coaxial cable
Adaptor
Adaptor
Sample
Holder
Figure 4-1: Diagram o f the Hewlett-Packard 8510T dielectric measurement system
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173
and Port B are transmitted to a Pentium II computer where a technician does the
calculations using HP software1to obtain the scattering parameters measured at each
port, Sn (the reflection coefficient) and S21 (the transmission coefficient), respectively.
The desired dielectric properties, Sn and S21, are voltage ratios [4-3,4-4],
Si 1 ~ voltage returning to port A
Initial voltage leaving port A
[4-3]
S21 ~ voltage measured at port B
Initial voltage leaving port A
Since relative reflected power and relative transmitted power are the square o f the
respective coefficients, relative absorption can then be calculated [4-5].
Relative Absorption —1 - (Sn2+ S212)
[4-5]
Although multiple reflections at the air-wood boundary contribute to the magnitude and
phase o f Snand S2icoefficients (Figure 4-2), the majority o f the contribution to each
coefficient is the initial reflected or transmitted portion. Consequently, the multiple
reflection contributions are neglected.
'y
For the transmission technique as described by Lanagan, the dielectric constant is
calculated using equation [4-6].3 Since kc and ko are constants and Sn and S21 are
measured, e^. is the only unknown and can be calculated for each microwave frequency.
As wood is anisotropic, there are three commonly accepted directions of
measurement, which are longitudinal, radial and tangential. However, wood properties in
the radial and tangential directions are only minimally different when the electric field
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174
/
/
Sn
P
O
R
T
P
O
R
T
^---------j
S21
B
A
Wood
/
/
Figure 4-2: Multiple reflections occurring at the air-wood boundary as an incident
microwave interacts with a wood sample
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kc = cut off wave number = 6.557 GHz for WR-90
rectangular waveguide
ko = free space wave number
vector is perpendicular to the longitudinal direction;4 therefore, no distinction is made
between these two directions in this study. When a microwave is directed at the crossgrain face, it is expected to have a higher dielectric constant in dry wood than if it is
directed at the end-grain face. According to Torgovnikov,5 this is due to the cell
elongation and the microfibrils, which are both aligned parallel to the stem. The cellulose
chains that make up the wood are known to have larger dielectric constants when the
electric field is traveling along the fiber, which is in the longitudinal direction.
Consequently, one can expect that the dielectric constant measured through the cross­
grain face will be the largest.
The dielectric properties o f cellulose chains are not the determining factor when
moisture is present, however. According to Torgovnikov,6 water is often the determining
7
factor affecting the dielectric properties o f wood. Von Hippel and Rosenberg
8
measured the dielectric parameters o f water. At room temperature (20 to 25°C), the
dielectric constant for water associated with 2.45 GHz frequency was reported to be 77
whereas with 10 GHz it was 55, which is a 40% difference. Dielectric constant data at
both 10 GHz and 2.45 GHz for wood (species not specified) o f different moisture
contents and different densities, as determined experimentally by Torgovnikov,9 are
summarized in Table 4-1 below. The difference between the two frequencies was fairly
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176
Table 4-1: Dielectric constant o f room temperature wood samples o f various
densities and moisture contents10
0%
Dielectric Constant (Room Temperature Sample)
at Various Moisture Contents
60%
30%
20%
10%
1.4
1.4
1.8
1.6
2.1
1.8
2.7
2.4
4.1
3.3
7.8
6.3
0 .0
0.1
0 .2
0.1
0.2
0.2
1.6
1.5
2.0
1.8
2.5
2.1
3.2
2.9
5.3
4.3
10.2
8.3
0.1
0.1
0.2
0.1
0.2
0.2
1.7
1.7
2.3
2.0
2 .9
3.8
3.4
6.5
2.4
5.3
12.8
10.3
0 .0
0 .2
0.2
0.1
0.2
0.2
2.45 GHz
10 GHz
1.9
1.8
2.5
2.1
3.3
2.7
4.3
3.8
7.6
6.2
15.0
12.2
2 .4 5 G H z is " X ”
tim e s m o re th a n 10
GHz
0.1
0.2
0 .2
0.1
0.2
0.2
2.1
2.0
2.8
2.3
3.7
3.0
4.9
4.3
8.9
7.2
17.5
14.1
0.1
0 .2
0 .2
0.1
0.2
0 .2
2.45 GHz
10 GHz
2.2
2.2
3.0
2.5
4.0
3.2
5.4
4.8
10.1
8.2
18.0
14.5
2 .4 5 G H z is “X "
tim e s m o re th a n 1 0
GHz
0 .0
0 .2
0 .3
0.1
0.2
0.2
Wood Density/
Frequency
Moisture Content
100%
0.3 g /c m 3
2.45 GHz
10 GHz
2 .4 5 G H z is “X ”
tim e s m o r e th a n 1 0
GHz
0.4 g /c m 3
2.45 GHz
10 GHz
2 .4 5 G H z is “X ”
tim e s m o r e th a n 1 0
GHz
0.5 g /c m 3
2.45 GHz
10 GHz
2 .4 5 G H z is “X "
tim e s m o re th a n 10
GHz
0 .6 g /c m 3
0 . 7 g /c m 3
2.45 GHz
10 GHz
2 .4 5 G H z is " X ”
tim e s m o re th a n 10
GHz
0 .8 g /c m 3
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177
constant. The dielectric constant at 2.45 GHz and at 10 GHz was found to be the same or
within 10% for dry wood and between 10% and 20% for wood that contained moisture.
Two assumptions were made to estimate the 2.45 GHz dielectric constant from
the 10 GHz dielectric constant data collected using the transmission technique: the
dielectric constants for room temperature green wood samples at 2.45 GHz were
estimated as 1.2 times more than those calculated at 10 GHz, and the dielectric constant
would be the same at both 2.45 GHz and 10 GHz for the wood with no moisture content
(dry).
For cavity perturbation experiments, the experimental procedures and equipment
described in Dube et al.n were used. This technique initially introduced by Bethe and
Schwinger,12 modified by Spencer et al.13 and Waldron14 is based on the observation that
both resonance frequency and microwave cavity quality factor (Q) change when a sample
is placed inside a resonating cavity. The governing equations15’16 for these changes are
below [4-7,4-8],
j E tE 2d V
- c & = (e'-l)
fs
[4-7]
Vs
2fE ldV
X
\
J
Qs
jE ^ d V
I
Qc
=s
[4-8]
| E?dV
fc = Chamber resonating frequency
fs = Sample (in chamber) resonating frequency
Ei = Electric Field in empty chamber
E2 = Electric Field in loaded chamber
Qs = Q of the loaded cavity
e’ = real part o f the permittivity
s” = imaginary part of the
permittivity
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178
Vs = Sample volume
Vc = Chamber volume
Qc = Q o f the empty cavity
Given the following conditions, simplifications to the governing equations [4-9, 4-10]17
can be made: the sample touches the walls o f the cavity where the electric field lines end,
the sample’s surface is parallel to the electric field, and the electric field is at a maximum
where the sample is located.
e'=
fsS
£" =
frr
fc-f,
K
\
+1
[4-9]
J
N1 r n
J4
\Q s
(
>
i]
[4-10]
[Qc)
1fi
As summarized by Lanagan, in a rectangular cavity, the resonatmg frequencies, fr and
fs, are a function o f cavity dimensions. Assuming a rectangular cavity with dimensions d,
e, and g (Figure 4-3), d is in the x direction, e is in the y direction, and g is in the z
direction. In resonating cavities, the electromagnetic wave is traveling in the g direction.
When it reaches the plates covering the ends o f the cavity, it reflects and creates a
standing wave. The resonant frequency, fr, is a function o f the dimensions o f the cavity
[4-11].
f
«Jd2 + g 2
= - = C
A
2dg
c = speed o f light
A, = electromagnetic wavelength
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[4-11]
179
d
Figure 4-3: Rectangular waveguide
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180
In the center of the cavity, the electric field is maximum, and the magnetic field is zero.
At the surfaces o f the cavity, the opposite is true. The cavity will lose some portion o f
the energy stored in the electric and magnetic fields to its walls. Consequently, the
conductivity and surface area o f the cavity walls affect the amount o f energy lost. The Q
o f the cavity is used to quantify the cavity’s ability to maintain the input energy [4-12].
0 = 27i(time average stored energy at the resonant frequency)
(energy dissipated in one period)
[4-12]
Experimentally, the equipment measures the power at each frequency within a specified
range. The frequencies that resonate can be found by determining at which frequencies
the maximum power occurs (Figure 4-4). One half o f the power under the log
power/frequency curve is at 3 dB. Two different frequencies have this power level,
designated as fi and f \. The quality o f the cavity can be found by the ratio o f the
resonant frequency (fr) to the frequency difference (A f= f2 - fi) at 3 dB [4-13].
[4-13]
Power is proportionate to the square o f the voltage. Therefore, power can be obtained by
squaring the scattering parameters, S21. Thef r is determined from the maximum in S21
Moisture content (me) and density o f the wood samples were determined by ASTM
standard D2395.19 The following equations were used [4-14, 4-15]:
me =
100
I F J
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[4-14]
181
6
5
Log Power
(dB)
4
3
2
1
£2
Frequency (Hz)
Figure 4-4: Graphical representation o f data collected by the HP851OT
utilizing the cavity perturbation method
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182
(kF
density = ----Iwh
[4-15]
where I is the initial green weight o f the wood in grams. F is the final dry weight in
grams. The dimensions of the green block are length (1), width (w) and height (h) in
inches. K is 0.061 when weight is in g and volume in cubic inches
4.2.2 Experimental Design
4.2.2.1 Transmission Technique Experimental Set-Up
Experiments were conducted on green and oven-dried samples o f the following
wood species: aspen, red pine, Eastern white pine, Chinese poplar (species unknown),
and loblolly pine. Two different sample sizes were chosen as follows: 10.20 mm x
22.85 mm x 9.5 mm and 10.20 mm x 22.85 mm x 21 mm. The samples were placed in
an x-band waveguide (WR90, inside dimension o f .900 x .450 inches, frequency limits o f
8.2 to 12.4 GHz). Coaxial cable adapter flanges were then connected to either end o f the
x-band waveguide (Figure 4-1). The 10 GHz microwave signal generated by the HP
8510T was directed at the cross-grain face (electric field parallel to the grain) for all
wood types and at the end-grain face (electric field perpendicular to the grain) on four o f
the five wood types (Figure 4-5). Dielectric measurements at 10 GHz were taken for one
sample of each wood type, moisture content, thickness, and orientation combination.
From the reflection and transmission voltage data collected by the system, the dielectric
constant was calculated, as well as the percentage o f microwave power transmitted,
reflected, and absorbed by the wood sample.
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183
Transmitted
Microwave
Incident
Microwave
T l/r
•
A/
Cross-Grain
Face
•
End-Grain
Face
Figure 4-5: Cross-grain (electric field vector is parallel to the grain, dielectric
properties measured in the longitudinal direction) and end-grain faces
(microwave field is perpendicular to the grain, dielectric properties
measured in the radial or tangential directions)
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184
4.2.2.2 Cavity Perturbation Technique Experimental Set-up
A single-mode waveguide (Figure 4-6) was fabricated using a rectangular S band
wave guide (WR284) of the following dimensions: 2.824 in. x 1.335 in. x 13 in. A slit
for feeding the wood sample was machined in the center of one side o f the waveguide. In
order to create a single mode cavity, brass stock (0.003 in. thick) was placed over open
ends o f the waveguide, leaving a 1.261 in. wide aperture in the center o f the waveguide.
A coaxial waveguide adapter (Arra Inc., Bayshore, NY, Model # 284-460) was clamped
to the flanges on either end o f the waveguide. The Hewlett-Packard 8510T analyzer
system was connected to the two adapters (Figure 4-1). The cut-off frequency for this
waveguide was 2.087 GHz. The standard recommended maximum frequency is 3.95
GHz. Therefore, frequencies between 2 and 4 GHz were generated for all o f the
perturbation experiments. The resonating frequency closest to 2.45 GHz was chosen in
the empty chamber experiment.
Red pine and aspen samples (0.3 in. x 0.3 in. x 1.335
in.) were placed inside the cavity via the slit in the top. The peak power intensity,
resonating frequency and the Af 3 dB were recorded. For each wood type, measurements
on four separate samples were taken. An overview o f the samples is given in Table 4-2.
4.2.3 Experimental Results and Discussion
4.2.3.1 Transmission Technique Experimental Results and Discussion
From Table 4-3, it can be seen that dry wood transmits more microwave energy
than green wood does at 10 GHz. As the sample length is increased, the portion o f the
microwave transmitted decreases. Hence, these results show that green wood is an
excellent absorber o f microwave energy regardless o f wood type studied. Dry wood,
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185
Slit for WQod
Sample
Brass Stoi
S-Band Waveguide
Aperture
Figure 4-6: Diagram o f the single mode cavity
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186
Table 4-2: Wood volume, weight, density, and moisture content for
each sample both green and dry
Sample Type
Wood Volume
(in3)
Sample
Weight (g)
Density
(g/in3)
Moisture
Content (%)
Red pine
Red pine
Red pine
Red pine
#1
#2
#3
#4
0.09
0.10
0.09
0.09
1.0
1.0
1.0
1.0
0.63
0.63
0.63
0.68
4.17
1.01
13.64
5.26
Aspen
Aspen
Aspen
Aspen
#5
#6
#7
#8
0.10
0.10
0.17
0.09
1.5
1.5
1.5
1.5
0.71
0.75
0.44
0.76
32.74
26.05
26.05
31.58
Red pine
Red pine
Red pine
Red pine
#ldry
#2dry
#3dry
#4dry
0.09
0.09
0.08
0.08
0.96
0.96
0.96
0.96
0.63
0.63
0.63
0.68
0
0
0
0
Aspen
Aspen
Aspen
Aspen
#5dry
#6dry
#7dry
#8dry
0.09
0.09
0.09
0.09
1.13
1.19
1.19
1.14
0.71
0.75
0.44
0.76
0
0
0
0
Table 4-3. Green wood and dry wood microwave reflection, transmission, and
absorption at 10 GHz for aspen, loblolly pine, Eastern white pine,
and red pine
10 GHZ
Type of
Wood
D R Y (cross-grain/end-grain)
Size
Aspen
9.5mm
Loblolly 9.5mm
E.WtPine 9.5mm
Red Pine 9.5mm
Aspen
21mm
Loblolly 21mm
E.Wt Pine 21mm
Red Pine 21mm
Percent
Reflected
Percent
Percent
Transmitted Absorbed
GREEN(cross-grain/end-grain)
Percent
Percent
Percent
Reflected
Transmitted Absorbed
7/7
86/86
7 /8
83/ 82
85/ 86
79/ 76
7 /7
10/11
8/7
13/ 16
24/7
50/ 37
27/ 35
26/ 17
11/26
.3/.7
2/5
49/ 63
64/ 65
73/ 78
80/ 79
70/ 71
80/ 78
62/ 70
12/ 13
20/ 18
12/ 14
29/ 2 0
27/ 16
42/ 25
28/ 25
37/ 18
2/ . 9
0/0
1 / .I
0/ . 2
70/ 83
58/ 75
71 / 75
64/ 82
7/7
8/8
8/8
11/11
8/8
9/10
91.1
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187
on the other hand, is a much poorer absorber o f microwave energy.
The comparison o f end- and cross-grain measurements of each wood species at 10
GHz shows that dry transmission and absorption readings were under < 1% for all 9.5imrn samples except red pine which were within 3%. The end- and cross-grain
measurements o f the 21-mm dry sample were all within 2%, except for red pine which
were within 9%. Reflection readings were within 1% or less with varying orientations.
Orientation, therefore, may have a minimal effect on transmission and absorption o f 10
GHz microwaves through dry wood and does not appear to affect reflection.
The comparisons o f end- and cross-grain orientations for green wood within a
species resulted in higher variations. Differences in green wood transmission at 10 GHz
ranged from 0.4 to 15% for the 9.5-mm samples and 0 to 1.1% for the 21-mm samples.
However, neither orientation consistently transmitted microwaves better than the other
across wood species. Differences in green wood absorption for the 9.5-mm samples
ranged from 1 to 14% and 4 to 18% for the 21-mm samples. All cross-grain absorption
readings were lower than the end-grain readings for the green wood samples regardless o f
wood species or thickness. Reflection readings were also affected by wood orientation.
Reflection from end-grain, 9-mm samples was 8 to 17% less than cross-grain samples o f
the same thickness. The 21-mm samples o f cross-grain orientation were 3 to 17% more
reflective than end grain samples. Thus, reflection off moist samples is greater for cross
grain samples than end grain samples regardless o f wood type.
The dielectric constants for 10 GHz and estimates for 2.45 GHz are shown in
Table 4-4. The dielectric constant for a wood species was constant under dry conditions
regardless of orientation or thickness. This result was contrary to the expected outcome o f
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188
Table 4-4: Dielectric constants calculated for 10 GHz and estimated for 2.45 GHz
for aspen, loblolly pine, Eastern white pine, and red pine,
green and dry respectively
Dielectric
Constant
% Moisture
Content
2.45 GHz
10 GHz
Wood Type
Aspen
9.5 mm
21 mm
Loblolly Pine
9.5 mm
21 mm
PoplanChina
9.5 mm
21 mm
Eastern White Pine
9.5 mm
21 mm
Red Pine
9.5 mm
21 mm
Specific
Gravity
(g/in3)
144.9
0.305
124.6
0.430
74
0.4
88.8
0.350
46.4
0.374
E s tim a te d
C a lc u la te d
Dry
Green
cross-grain/end-grain
Dry
Green
cross-grain/en d-grain
1.5/1.5
1.5/1.5
2.7/3.S
3.2/4.4
1.5/1.5
1.5/1.5
3 .2 1 4 2
3 .9 /5 3
1.7/1.7
1.7/1.7
9.7/16.6
5.0/5.3
1.7/1.7
1.7/1.7
11.7/20.0
6.0/6.4
1.6/na
1.7/na
4.1/na
3.9/na
1.6/na
1.7/na
4.9/na
4.6/na
1.5/1.5
1.5/1.5
7.7/5.0
3.2/4.0
1.5/1.5
1.5/1.5
9.2/6.0
3.8/4.7
1.7/1.7
1.8/1.8
2.0/6.2
3.0/10.1
1.7/1.7
1.8/1.8
2.0/7.4
3.6/12.1
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189
a higher dielectric constant for the cross-grain face than for the end-grain face. The
dielectric constant is a material constant. By definition, its value should not change from
sample to sample or with changes in sample thickness. Previous studies, such as
Torgovnikov’s20 work mentioned in section 4.2.1, showed that increased moisture
content also corresponds to increased dielectric constants. The trials reported in
Table 4-4 show that with moisture present the dielectric constant varies considerably with
changes in orientation and in sample thickness. Torgovnikov’s work also showed that
increased density corresponded to increased dielectric constants for dry wood. In
general, the results shown in Table 4-4 agree with his conclusions. Dielectric constants
from lowest to highest density (0.305 to 0.43) were as follows: 1.5,1.5, 1.7,1.7, and 1.7.
4.2.3.2 Cavity Perturbation Technique Experimental Results and
Discussion
Eight resonant frequencies between 2 and 4 GHz were seen for the empty
waveguide (Figure 4-7). The 2.45 GHz peak was analyzed to obtain baseline data for the
empty chamber (Table 4-5).
The peak frequency, Af at 3dB, and peak intensity results
for the red pine and aspen samples (both dry and green) are also reported in Table 4-5.
Also shown are the calculated Q, dielectric constant, and dielectric loss.
The peak frequencies registered for each o f the four samples with equivalent
moisture content were almost identical (within ± 0.007). The frequency difference at
3dB, however, was more than twice as high for green than for dry samples. As expected,
peak intensity was considerably less for green than for dry samples because o f the
absorption o f microwaves by the water in the wood. The quality o f the chamber lessened
with the addition o f samples, especially those with moisture. However, regardless o f
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§,
-6 0 -
oi ^
04
oi
^
04
04
CO
CO
CO
CO
CO
CO
CO
LO
CO
Frequency (GHz)
Figure 4-7: Resonant frequencies in empty WR-284 waveguide
between 2 and 4 GHz
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191
Table 4-5: Peak frequency, Af at 3dB, peak intensity, Q, dielectric constant, and
dielectric loss data including error for the empty chamber, the green
red pine, green aspen, dry red pine, and dry aspen samples
Dielectric
Constant
s’
Dielectric
Loss
(s”/e”)
119.39
2.75
0.20
-9.1
110.92
2.79
0.22
22.86
-9.5
105.25
3.15
0.25
18.94
-7.7
127.24
2.67
0.20
0.21
0.02
Sample Type
Peak
Frequency
(GHz)
Af at
3dB
(MHz)
Peak
Intensity
(dB)
Q
Empty
Chamber
Red pine #1
green
Red pine #2
green
Red pine #3
green
Red pine #4
green
Standard
deviation for
green red pine
Aspen
#5
green
Aspen
#6
green
Aspen
#7
green
Aspen
#8
green
Standard
deviation for
green aspen
Red pine
#ldry
Red pine
#2dry
Red pine
#3 dry
Red pine
#4dry
Standard
deviation for
dry red pine
Aspen
#5 dry
Aspen
#6dry
Aspen
#7dry
Aspen
#8dry
Standard
deviation for
dry aspen
2.424
10
-1.5
242.4
2.408
20.17
-8.5
2.407
21.70
2.406
2.410
2.403
23.97
-10.1
100.25
3.19
0.23
2.400
28.10
-11.7
85.41
3.52
0.27
2.393
32.85
-13.1
72.85
2.93
0.24
2.402
25.35
-10.4
94.75
3.44
0.25
0.27
0.02
2.417
10.59
-2.5
228.23
1.83
0.02
2.417
10.64
-2.5
227.16
1.80
0.02
2.418
10.62
-2.5
227.68
1.77
0.03
2.418
10.59
-2.5
228.33
1.76
0.02
0.03
0.00
2.416
10.62
-2.6
227.50
1.90
0.02
2.416
10.59
-2.6
228.14
1.90
0.02
2.415
10.65
-2.6
226.76
2.03
0.02
2.416
10.7
-2.5
225.79
1.95
0.02
0.06
0.00
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192
wood species the quality of the chamber was approximately the same with oven-dry
samples. The average dielectric constant o f dry aspen was 1.965 ± 0.06, and that o f dry
red pine was 1.795 ± 0.03. The green samples registered higher average dielectric
constants of 2.91 ± 0.21 for green red pine and 3.23 ± 0.27 for green aspen. The
variance for the green samples was much larger than for the dry samples. The dielectric
loss was much smaller for the oven-dry samples regardless o f species (0.02 to
0.03 ± 0.00) than for the green samples (0.20-0.27 ± 0.02). Since the dielectric loss is a
measure o f energy dissipated as heat and the dielectric constant is the measure o f energy
stored by the material, these results show that dry wood has less absorption and
correspondingly less heat dissipation than green wood. This most likely signifies that the
bulk o f the microwave energy is transmitting through the wood. Since there is minimal
water to interact with, the potential heat released from the dipole rotation is minimal,
corresponding to lower dielectric loss figures. Taking this analysis further, since the
microwave power absorbed is directly proportional to frequency (f), dielectric constant
( s ’), and loss tangent (tan 5), this indicates that absorption o f 2.45GHz microwave power
is likely to be more for wood containing moisture than for dry wood.
Comparing the two techniques to obtain dielectric constants (Table 4-6), the green
samples resonance constants were in the range o f the transmission constants, whereas the
dry samples transmission constants were 5.9% to 33% lower than the resonance
constants. Torgovnikov’s22 dielectric constant data reported in Table 4-1 showed that an
increase in dielectric constant occurred with an increase in moisture content. This trend
was expected to hold true for the dielectric constant measurements regardless o f the
method used. However, the aspen sample used for the transmission method had a
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Table 4-6: Comparison o f the transmission and resonance techniques
to obtain dielectric constants
Dielectric
Constant
% M o istu r e
W ood T ype
Aspen
Red Pine
Content
Trans/Reson
Specific
Gravity
(g/in3)
144.9/29.1
0.305
46.4/6.06
0.374
Transmission
2.45 GHz Est.
Dry
Green
Resonance
2.45 GHz
Dry
Green
1.5
3.2-4.2
2.0
3.2
1.7
2.0-7.4
1.8
2.9
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194
moisture content o f 144% and a dielectric constant between 3.3 and 5.2, and the aspen
samples used for the resonance method had average moisture contents o f 29% and
dielectric constants between 2.93 and 3.52. Given these large moisture content
differences, the minimal differences between the resonance and transmission dielectric
constants were somewhat surprising. In all cases, every wet sample had higher dielectric
constants than the same samples after being dried. Since these experiments were not
conducted on intermediate moisture contents for each sample, the reasons for the
difference noted between the resonance and transmission dielectric constants cannot be
determined.
4.2.4 Conclusions
From the above experiments, I conclude that dry wood has a better transmittance
compared to wet wood for both 2.45 GHz and 10 GHz microwave energy. Neither
orientation nor thickness appeared to affect transmission in dry wood, whereas moist
wood was affected by these parameters. A consistent trend for either parameter,
however, was not observed. Both transmission and resonance techniques provided
comparable results.
4.3 Wood Temperature Gradient Study Comparing
Microwave and Conventional Heat Treatments
4.3.1
Experimental Design
The heating mechanism for conventional heat treatment is conduction, and
microwave heating is volumetric. The following study was designed to compare the
temperature gradients resulting from two different methods.
For these experiments, samples of red pine were chosen. Wood was cut in cubes
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195
o f 4 in. x 4 in. x 4 in. K-type thermocouples or fiber optic temperature probes were
placed at three different locations in order to monitor the temperature gradient in the
microwave and in the conventional heating oven. The positioning o f the measurement
units can be seen in Figure 4-8. The mid and center holes for the probes were drilled lA in. in diameter and approximately 2-in. deep in the wood.
For the conventional heat treatment experiments, a warming oven (Fisher
Isotemp™ model # 2550, 116 V, 9 A) was preheated to 105 °C. Three K-type unshielded
thermocouple wires were threaded through the door. Each thermocouple was connected
to an Omega silver-plated selector switch (model #SW142-6-B: 2 pole, V2 din). K-type
compensating leads connected the switch to the digital thermometer readout (Omega
model #2168 A). Initially at room temperature, the wood sample was placed in the center
o f the hot oven and thermocouples were put into place (Figure 4-8). Temperature
readings were recorded every minute for the first 20 minutes and then every 10 minutes
thereafter. Once the center core o f the wood reached a temperature of 60 °C, the
experiment was ended because that is above the core temperature required by the
International Phytosanitary guidelines. The 6 kW microwave system, including the fiber
optic probes described in section 4.4.2.3, was used in these experiments. The room
temperature samples were placed in the center o f the chamber. Fiber optic probes were
placed in position (Figure 4-8). The 2.45 GHz microwave generator was set to apply
1000 W of power for 3 minutes. Temperature readings were recorded every 30 seconds.
4.3.2
Experimental Results and Discussion
For conventional oven heating, the temperature gradient was exactly as predicted
for all experiments. A typical example is shown in Figure 4-9 for a 4-in. cube red pine
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196
Surface probe
Mid probe
Center probe
Figure 4-8: Fiber optic and K-type thermocouple temperature probe positions
in red pine 4 in. x 4 in. x 4 in. block
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197
120
100
8
1
a
I
H
0
20
60
40
80
T im e (m in u tes)
O ven Temp. —• — Surface
A ■B etw een ■ O - Center
Figure 4-9: Conventional heat treatment temperature gradient for
red pine sample (4 in. x 4 in. x 4 in.) o f 53% moisture content
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198
sample with 53% moisture content. Due to the open door, the preheated oven-air
temperature dropped when the sample was loaded. However, within 3 minutes the oven
air temperature reached 100 °C. As can be noted in Figure 4-9, the wood surface
te m perature
reached the oven-air temperature o f 105 °C within 30 minutes and was
maintained there. Three minutes into the experiment, inner wood temperatures had
reached only 31 °C or less. The center core o f the wood required 60 minutes under these
experimental conditions to reach 56 °C. At 73 minutes, the mid and center positions
reached essentially the same temperature o f 62 °C and 60 °C, respectively.
Three typical examples o f the 1000 W, 2.45 GHz microwave treatment o f red
pine with moisture contents between 58 and 63% are shown in Figure 4-10. The
temperature profiles o f WRP 15, WRP16, and WRP17 show that all three positions
(surface, mid, and center) started at room temperature at time 0. Surface temperatures
were higher than one or both inner wood positions for the first minute. After the first 1 to
1V2 minutes, the mid temperature reading was higher than the surface temperature. By 2
minutes, both inner positions had equal or higher temperatures than the surface in all
cases. After 3 minutes o f irradiation, two o f the samples had center temperatures
approximately equal to the off-center temperature, and the third’s center temperature
continued to lag behind. One potential reason for these temperature profiles may relate to
the moisture contents o f the wood. As noted in the microwave background section,
microwave energy interacts with water by rotating the dipoles in the water molecules,
which generates frictional heat. If the water molecules closest to the surface absorbed
most of the available microwave energy, the mid and center positions might be somewhat
shielded from microwave interactions. This could translate into higher initial
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199
A ) R ed P m e W R P 15
100
dU
S u
H P.
50
0
0 0.5
1 1.5 2 2.5 3
T im e ( m i n )
■surface
100
-m id
-center
B ) R e d P in e W R P 1 6
dC
M
«S <
w 50
h a
0
“i
r
0 0.5 1 1.5 2 2.5 3
Time (min)
■Surface —■ — M id —A —Center
C) R e d
P in e W R P 17
100
dC?
S M
a>
H
50
p.
0
0 0.5
1 1.5 2 2.5 3
T im e (m in )
■Surface —Si—Mid —A—Center
Figure 4-10: Time-temperature plot o f 4-in. cube, red pine samples subject to
3 minutes o f 1000 W, 2.45 GHz, microwave treatment
A)WRP 15, B) WRP 16, and C) WRP 17
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200
temperatures at the surface. As moisture is dissipated, more of the microwave energy
may reach the inner positions. This would account for the mid position heating up at a
faster rate than the center position. Eventually, the center position reaches the mid
position temperatures. The surface o f the wood dissipates heat into the surrounding air;
therefore, the temperatures in this region do not rise as much as the center or mid
positions and their temperatures can overtake the surface temperatures. Within 214
minutes both interior positions had reached temperatures over 56 °C.
These findings suggest that use o f potential surface temperature indicator
compounds to ensure proper microwave treatment would have to take into account a time
component since the inner temperatures were not higher than the surface temperatures
throughout the early treatment stages. In addition, in the later treatment stages, the
surface temperatures reached a plateau, while the inner temperatures continued to
increase.
4.3.3 Conclusions
Much shorter time frames are needed to reach 56 °C throughout the sample with
1000 W, 2.45 GHz microwave treatments (214 minutes) than with conventional heat
treatments at 105 °C (1 hour). Inner wood temperatures were likely affected by moisture
content when samples were subjected to microwave treatment. This may be due to the
water closest to the surface absorbing the available microwave energy and thus shielding
the water located in deeper positions from microwave interaction. Given these
observations, surface temperatures alone do not appear to be a good indicator o f inner
wood temperatures in microwave trials.
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201
4.4 Microwave Experiments with Larvae-Infested Wood
4.4.1
Introduction
Initial microwave feasibility studies were conducted in China using native poplar
and Asian longhomed beetle larvae to determine if microwave treatment o f infested
lumber can effectively kill this species. Because ALB can only be used within the
confines o f quarantine facilities in the United States, trials to confirm these findings were
conducted using wood infested with cottonwood borer larvae as a surrogate species.
Combining the experiments brought the sample size to almost 450 larvae. Various pine
and poplar wood species with varying moisture contents were included in these trials to
compare treatment efficacy in different wood densities and conditions. Once feasibility o f
this method was established, factors that might affect the commercial viability o f this
treatment method were investigated, including the potential for fire or the effect o f wood
geometry on lethal microwave parameters. During microwave treatment, measurements
were also taken to compare the temperature o f the larva to the surrounding wood
temperature.
4.4.2
Microwave Experimental Design
4.4.2.1 Experimental Wood Sample Preparations
The following four native U.S. wood species were chosen for the U.S. microwave
experiments because o f their specific gravity, moisture content, and availability: aspen
(Populus tremuloides), Eastern white pine (Pinus strobus), red pine (Pinus resinosa), and
loblolly pine (Pinus taeda). With the exception o f loblolly pine, all wood species were
locally harvested and logs were bucked into 6-ff lengths for transport. Relatively small
diameter (*10 in. dbh) trees were harvested to minimize processing requirements. Log
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202
ends were painted with Anchorseal™ wax coating (UC Coatings: Buffalo, NY) to control
end-grain moisture loss and the log bolts were stored in an unheated warehouse until
needed. Each log bolt was manually debarked with two surfaces processed on a wood
jointer. A planer was then used to square and dress size the green material into surfacedfour-sides dimension 4 in. x 4 in. stock. Stock lengths were cut into two final sizes (4 in.
x 4 in. x 4 in. +/- 1/8 in. tolerance or 4 in. x 4 in. x 1 in. +/- 1/16 in. tolerance) with a
radial arm saw. These dimensions were chosen because they are representative o f actual
components used in pallets. Finished cubes and the 4 in. x 4 in. x 1 in. material samples
were then bagged in plastic and frozen to maintain their moisture content and inhibit
deterioration. These processed materials represented largely heartwood with some minor
sapwood content mixture.
Native poplar species were chosen for all experiments conducted in China
because poplar is the second most common wood used in wooden packing materials in
China and it was readily available. Pine, which is used the most often, is not a host o f
ALB, which is our target pest. The following four species were supplied for the
experiments: Populus cathayana Rehd, Populus beijingemis,W. Y. Hsu, Populus
dakuanensis, and Populus nigra L. var. thevestina (Dode) Bean. However, it was not
possible to identify which o f these four wood species was used in a given experiment.
The poplar trees were felled within 3 days o f the commencement o f experiments and
were stored outdoors. For the lumber experiments, each log was debarked, planed, and
cut to finished dimensions (4 in x 4 in. x 4 in. +/- 1/8 in. tolerance or 4 in. x 4 in. x 1 in.
+/- 1/16 in. tolerance). Finished cubes and 1-in. sections were then bagged in plastic to
maintain their moisture content. All cubes were used in experiments within three days. A
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203
mix o f heartwood and sapwood, primarily around the pith region o f the tree, was
obtained. For the natural infested experiments, some of the logs were cut into 5- to 6-in.
long sections, whereas other logs were processed into lumber as previously described
before being treated with microwave energy. For the dry wood experiments, the poplar
cubes and 1-in. sections were placed in an oven set at 110 °C for 48 hours.
Characterization o f moisture content (MC) and specific gravity (SG) was
conducted on test samples o f each wood species in accordance with ASTM Standard D
2395 following Method A procedures23 [4-14,4-15]. Typical moisture content and
specific gravity for the four domestic wood species according to the Wood Handbook24
are delineated in Table 4-7.
4.4.2.2 Larval Sources
Larvae and pupae o f Asian longhomed beetle and the surrogate cottonwood borer
were used in these studies. The cottonwood borer larvae were provided by the USFS
rearing facility in E. Lansing, Michigan, and the ALB larvae and pupae were collected
from natural sources in China (experiments using ALB were performed in China only).
All larvae weighed between 0.35 and 2.2 g. Length ranged from % in. to 2 in.
4.4.2.2.1 Collection o f Asian Longhomed Beetles in China
ALB infested trees were harvested from Chinese forests. As the logs were split,
live larvae and pupae were collected for use in the microwave trials. The insects were
kept in moist sawdust until needed.
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Table 4-7: Wood Handbook25 typical moisture content
and specific gravity for aspen, Eastern white
pine, red pine and loblolly pine
WOOD SPECIES
Aspen
Eastern White Pine
Red Pine
Poplar (China)
Loblolly Pine
%MOISTURE
CONTENT
(typical species
average) heartwood
/sapwood
95/113
32/134
n/a
33/110
SPECIFIC
GRAVITY
(typical species
average)
0.35-0.36
0.34
0.41
n/a
0.47
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205
4.4.2.2.2 Laboratory Rearing of the Cottonwood Borer Beetle,
Plectrodera scalator (Fabricius) (Coleoptera: Cerambycidae)
The cottonwood borer (CWB) was chosen as a surrogate for the Asian longhomed
beetle (ALB) because it is similar in size and is in the same family as ALB. The CWB
colony was established from adults collected in Michigan and Mississippi in 2000 and
2002. Adult pairs were maintained in growth chambers. Eggs were collected daily and
placed in a separate growth chamber. Once neonates hatched, larvae were then
maintained at 24 °C with a modified Prionus artificial diet in plastic diet cups. Some
larvae were then subjected to an 8 °C chill (diapause). Before microwave trials, larvae
were transferred to 8 oz. diet jars at 3 to 4 weeks old (Figure 4-11). Larvae were then
maintained for 2 to 3 months at room temperature until needed. Both pre- and postchill
larvae were used in the microwave studies. Chilling only affects developmental rate
(time to pupation), but has no effect on response to microwave energy.
4.4.2.3 Microwave Systems
A common kitchen multimode microwave oven with a nonuniform field
distribution (Galanz model #WD900) was used in all ALB experiments conducted in
China (Figure 4-12). The maximum microwave power output was 900 kW.
Except for the scale-up experiment equipment discussed below, cottonwood
borer experiments conducted in the United States were also conducted with a similar
multimode microwave oven with a nonuniform field distribution (Sears, Kenmore Model
#565.69401890, maximum input o f 1000 W) (Figure 4-13). The wood samples were
placed on a 1-in. high plastic box in the center o f the microwave chamber after the
turntable was removed.
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206
8 oz. Diet
Jar
- 4 -
CWB
D iet-
\
CWB Larva
Figure 4-11: CWB larva next to 8 oz. diet jar
Figure 4-12: Galanz microwave oven used in ALB experiments
conducted in China
Figure 4-13: Inside and outside o f the 1100 W microwave oven used in
CWB experiments conducted in the U.S.
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207
For the scale-up experiments, a 6 kW 2.45 GHz Microwave Generator (Cober
Electronics) was connected to a 2 ft. x 2 ft. x 1.5 ft. chamber (Figure 4-14 a and b) by S
band waveguides (284). Two or three flexible fiberoptic probes (Lumitherm) were
placed through small holes in the top o f the chamber and into small holes drilled in the
wood samples or on the surface o f the wood. The probes were then connected in turn to
the single channel Lumitherm temperature readout device (Figure 4-14 c and d). In order
to reduce the tendency o f the probes to snap when they were connected and disconnected
to the single channel throughout the experiments, the probes were threaded through small
flexible plastic tubing. On the stationary turntable inside the chamber, the wood samples
were placed on a 1-in. thick plastic box in order to bring the sample closer to the center o f
the microwave chamber (Figure 4-14 e).
All microwave systems used in these studies were tested for radiation leakage
with a Rahman Radiation meter and a Rahman Probe (General Microwave Corp, Model #
48IB and Model #82 respectively) or a Holladay Industries microwave leakage meter
(Model #HI1501: 0.1 to 100 mW/cm2 at 2450 MHz).
4.4.2.4 Insect Status Procedure
Once the insect was irradiated, it was visually checked for movement and
dehydration. If the larva was dehydrated and not moving despite repeated prodding, it
was considered dead. If the larva was moving, it was deemed alive and was placed on
water-dampened filter paper in the bottom o f a plastic petri dish. If the larva was not
moving and not dehydrated, it was also placed in a petri dish. The filter paper was
checked daily for ffass production, a physiological parameter o f live vs. dead. If no frass
was produced in 24 hours, then the larva was either dead (no movement with prodding)
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Fiberoptic probes
Single
channel
port
Figure 4-14: Photographs o f a) 6 kW Cober microwave generator, b) microwave
chamber, c) fiberoptic probe threaded through holes in port window,
d) Lumitherm7 measuring device, and e) fiberoptic probes placed
in drilled holes in the wood samples
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209
or deemed nonviable. All pupae were placed on damp filter paper in petri dishes and
visually inspected daily. If a pupa was not moving and dehydrated or had changed color,
it was deemed dead.
4.4.2.5 Irradiation of Asian Longhomed Beetles in China
Microwave experiments (2.45 GHz) using ALB larvae were conducted using both
artificially infested poplar lumber and naturally infested poplar logs and lumber. By
artificially inserting a known number o f live larvae (2 to 3) into known locations and
plugging the hole with wood o f the same moisture content, condition o f the larvae after
treatment could be positively made. Wood moisture content was varied, as well as
microwave power and time. In order to confirm these findings, naturally infested logs
and lumber o f approximately the same dimensions were treated with microwave energy.
4.4.2.5.1 Artificially Inserted ALB in Green Poplar
Blocks of two different dimensions (4 in. x 4 in. x 4 in. and 4 in. x 4 in. x 1in.)
were seeded with two larvae each, one in the center of the block and one off-center (see
Figure 4-15). Since the wood was riddled with holes from ALB infestations, density
could not be determined or was understated. In addition, the holes were drilled either
with the grain or across the grain, depending on the configuration o f the ALB tunnels
already present in the wood samples. The larvae were placed in the holes and a wood
cork of the same species covered the holes. Two different lots o f green poplar (50 and
121 blocks) and one lot o f 1-month air-dried (25 blocks) poplar were used. All
irradiation was carried out at 100% o f power (output 900 W). For the dry wood
experiments, the poplar 4-in. cubes and 1-in. sections were placed in an oven set at
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Larvae
a
b
Figure 4-15: Larvae configuration for a) 4 in. x 4 in. x 4 in. and b) 4 in. x 4 in. x 1 in.
blocks used in the ALB and CWB microwave experiments
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21 1
110 °C for 48 hours.
4.4.2.5.2 ALB Naturally Infested Log and Lumber Trial
Poplar samples (air dried for 1 month) that were naturally infested with ALB were
irradiated at 100% power (900 W) for 3 minutes. The round log samples (19) were
between 316 and 6 in. in diameter, and the rectangular samples (12) had average
dimensions o f 4 in. x 4 in. x 5 in.
To determine the likelihood that a larvae would be found dead in a log before
microwave treatment, untreated naturally infested logs were split and the total number of
live vs. dead larvae were counted. Over 200 larvae were found and all o f them were
alive.
4.4.2.6 Artificially Inserted Cottonwood Borer Beetle Study
The ALB experiments carried out in China used fairly small sample sizes (n=25
to n=100). Therefore, additional experiments using the surrogate CWB were conducted
on 4-in. cube blocks o f aspen (134 larvae), Eastern white pine (90 larvae), red pine (52
larvae), loblolly pine (48 larvae). Combining these experiments with the ALB trials in
China brought the sample population up to 446. Other than increasing the sample size, a
second goal o f this set o f experiments was to compare the lethal effects of 9000 to 1100
W o f microwave irradiation o f larvae infesting different wood species for 5-minute
periods. A separate set o f trials was conducted to find the moisture content at which
volatiles were released from the wood irradiated under the same microwave conditions.
This is important because of the risk o f fire. In addition, scale-up concerns such as wood
surface area, chamber volume, power/time variance, and energy to wood volume issues
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212
were then addressed. The goal is to figure out what parameters would need to be
delineated in microwave schedules that could be proposed to regulatory authorities for
use by commercial wooden packaging material manufacturers. To determine if
microwave energy selectively heats the larvae infesting the wood, a final set o f trials
comparing in situ larval temperature to surrounding wood temperature was completed.
4.4.2.6.1 Lethal Microwave Power/Time in Various Wood Species
All 4-in. wood sample blocks were artificially seeded with two larvae, one in the
center o f the block and one off-center (Figure 4-8). Wooden plugs o f the same wood
species were used to close the holes. Four different species (red pine, loblolly pine,
aspen, and Eastern white pine) with moisture contents ranging from 15% to 137% were
tested. The blocks were individually placed in a 2.45 GHz microwave oven (Figure 4-13)
and were subjected to 1000 W o f microwave energy for 5 minutes (330,000 J). Viability
of the larvae was checked after microwave treatment was completed.
4.4.2.6.2 Critical Moisture Content
At some critical moisture content volatiles will begin to be released when
subjected to high enough microwave energy exposure. A series o f experiments were done
with red pine and aspen to determine the moisture content at which volatiles were
released. Wood samples were air-dried to various moisture contents before being
subjected to microwave treatment. All 4-in. cube samples were irradiated with 330,000 J
o f 2.45 GHz microwave energy (5 minutes at 1100 W) (Figure 4-13). If at any time
during the 5 minutes volatiles emerged, then treatment was stopped.
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213
4.4.2.6.S Surface Area
An investigation o f the effect o f surface area on lethal doses o f 2.45 GHz
microwave radiation was undertaken using red pine. The theory was that thickness o f the
material would be the deciding factor for the amount o f microwave energy necessary to
a 3
kill larvae inside the wood. The red pine volume was kept constant at 64 in. Three
different surface areas were chosen —96 in.2 (4 in. x 4 in. x 4 in.), 108 in.2 (2 in. x 6 in. x
5.3 in.), and 160 in.2 (1 in. x 6.5 in. x 9.8 in.). Green weight for each block was
obtained. Moisture content o f 63% was targeted. Two larvae were place in each 4 in. x 4
in. x 4 in. block as shown in Figure 4-16a. Three larvae were placed in each o f the other
blocks (Figure 4-16b and c). Using the 1 kW system (Figure 4-13), microwave energy o f
1000 W was applied for 3 minutes (180,000 J).
After treatment, the status o f the larva
was checked. Wood blocks were weighed after microwave treatment. Dry wood weight
was also measured.
4.4.2.6.4 Chamber Volume
Similar experiments in the 6 kW chamber (Figure 4-14) were then conducted with
irradiation of 180,000 J o f 2.45 GHz energy to determine if the chamber volume to
sample size ratio affected the outcome. Depending on the material, this ratio can be
important when scaling up manufacturing. The same three surface areas were chosen o f
96 in2 (4 in. x 4 in. x 4 in.), 108 in2 (2 in. x 6 in. x 5.3 in.), and 160 in2 (1 in. x 6.5 in. x
9.8 in.). Wood temperature near the larva was measured with a fiberoptic temperature
monitoring system. Block configuration for both larvae and fiberoptic probes are shown
in Figure 4-17.
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214
Larvae
9
b
Figure 4-16: Larvae configuration for (a) 4 in. x 4 in. x 4 in., (b) 1 in. x 6.5 in. x 9.8 in.,
and (c) 2 in. x 6 in. x 5.3 in. blocks used in the CWB microwave experiments
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215
Fiberoptic
probes
o
Larvae
Figure 4-17: Fiberoptic/larvae configuration for a) 4 in. x 4 in. x 4 in., b) 1 in. x 6.5 in.
x 9.8 in., and c) 2 in. x 6 in. x 5.3 in. blocks used in the CWB microwave experiments
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216
4.4.2.6.5 Input Power/Time Variance
These trials were designed to investigate whether power per volume is a
parameter that should be included in regulatory schedules. The overall power (3000 W)
and sample volume (64 in.3) were held constant. The input power was increased from
1000 W to 1500 W and 3000 W with a corresponding decrease in processing time o f 3, 2,
and 1 minute, respectively. Surface area was varied, while target wood moisture content
was approximately 60%. The wood dimensions chosen were 4 in. x 4 in. x 4 in. (96 in2),
2 in. x 6 in. x 5.3 in. (108 in2), and 1 in. x 6.5 in. x 9.8 in. (160 in2). Wood temperature
near the larva was measured with a fiberoptic temperature monitoring system. Block
configurations for both larvae and fiberoptic probes are shown in Figure 4-10.
4.4.2.6.6 Energy vs. Wood Volume
In order to test the theoiy that the energy to volume ratio (2,812.5 J/in3) can be
directly applied to a larger volume o f the same moisture content, 1000 W o f 2.45 GHz
input power irradiated a 6-in. red pine cube for 10 minutes (216 in. ). The 6 kW
microwave unit was used. Block configuration for the larvae and fiberoptic devices are
shown in Figure 4-18.
4.4.2.6.7 Temperature Dependence o f Lethal Microwave Irradiation
Combining the experiments in sections 4.4.6.3 to 4.4.6.S, which measured wood
temperature with the fiberoptic system, an analysis o f the wood temperature surrounding
the live larvae during microwave treatment was completed.
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Fiberoptic
probes
o
Larvae
*
m
Figure 4-18: Six-in. cube red pine block configuration for larvae and
fiberoptic temperature probes
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218
4.4.2.6.8 Critical Larva vs. Wood Temperature
The 6 kW microwave system was used for this trial (Figure 4-14). Red pine samples (4
in. x 4 in. x 4 in.) with one larva embedded in a center hole and plugged with wood o f the
same type were used. The fiberoptic temperature measurement device was threaded
through a small hole in the wooden plug until it touched the larva in the hole. During the
trial, the temperature o f the larva was directly measured every 30 seconds. In addition, a
hole in the surrounding wood was drilled within Vg in. of the larva and a fiberoptic probe
was placed in this hole (Figure 4-19). The red pine samples were exposed to 1000 W o f
2.45 GHz microwave exposure for 3 minutes.
4.4.3 Experimental Results and Discussion
4.4.3.1 ALB Trial Results
4.4.3.1.1 Artificially Inserted
For trials using 1-month air-dried poplar, moisture content ranged from 26 to 45%
o f dry weight with an average moisture content o f 37%. After 3 minutes o f irradiation at
full power (900 W), all 50 larvae in 4 in. x 4 in. x 4 in. blocks (25 blocks) were dead.
Fifty 4 in. x 4 in. x 1 in. blocks were irradiated for 30 seconds. One o f the 100 larvae was
barely moving, but still alive after treatment. This larva died within 48 hours.
For green poplar Lot 1, moisture content figures were not available for the first
shipment o f green poplar used in the study. Twenty-five blocks o f 4 in .x 4 in .x 4 in .
were each seeded with two larvae, one in the center position and one in the off-center
position. These blocks were irradiated at 100% power for 3 minutes. Eight o f 48 larvae
were still alive after the 3-minute microwave treatment. Twenty-five additional blocks
were then treated at 100% power for 4 minutes. All 47 o f the larvae were dead.
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219
Fiberoptic
probes
Empty hole o
Larvaefilled hole
-
Figure 4-19: Critical larval and wood temperature red pine sample configuration
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220
The second shipment of green poplar Lot 2 was received one day after felling and
had moisture contents ranging from 128 to 191%. After 1 week wrapped in plastic the
moisture contents in this lot dropped to between 103 and 109%. The 4 in. x 4 in. x 4 in.
blocks were irradiated for 4 and 5 minutes, respectively. The 4 in. x 4 in. x 1 in. blocks
were irradiated for 1 and 2 minutes, respectively. The length o f the ALB larvae ranged
from 0.5 in. to 2.0 in. Four minutes o f 900 W irradiation with 2.45 GHz was not
sufficient to kill all o f the larvae in the very green, wet wood. Seven o f the 52 larvae in
this trial survived. However when the microwave treatment was increased to 5 minutes a
significantly higher proportion o f the larvae died (chi-square = 14.4, P < 0.0001). The
average moisture content for this group was only 109%. Two minutes o f irradiation with
900 W produced 100% mortality (N=40 larvae) in 103% moisture content poplar with
dimensions o f 4 in. x 4 in. x 1 in. but did not kill significantly more larvae than did
irradiation for 1 minute (chi-square = 1.71, P = 0.19). Detailed results are shown in
Table 4-8.
Larvae placed in dry wood died more quickly than in the moist wood (Table 4-9).
Larvae placed in center holes o f 4 in. x 4 in. x 1 in. poplar blocks died in 5 seconds at 720
W. Larvae placed in the center hole o f 4 in. x 4 in. x 4 in. blocks were killed in 5 seconds
at 900 W. This is probably because the only major absorber o f microwave energy in the
dry samples is the water inside the larva itself. As was mentioned in section 4.2, dry
wood absorbs very little microwave energy; instead, most o f it is transmitted. In contrast,
irradiation o f moist wood may shield the larva because the microwave energy is absorbed
first by water in the outer sections o f the wood sample. Therefore, there may be a time
lag before either the surrounding wood temperature creates lethal temperatures in the
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221
Table 4-8: Detailed results for green poplar artificially seeded
with ALB larvae
# of larvae
irradiated
Size Range
oflarvae
%
Mortality
4 in. x 4 in. x 4 in.
4 min
26 blocks
52
87%
4 in. x 4 in. x 4 in.
5 min
51 blocks
102
100%
109
4 in. x 4 in. x 1 in.
1 min
24 blocks
48
95.8%
128
4 in. x 4 in. x 1 in.
2 min
20 blocks
40
1 in. (6),
1.25 in. (21),
1.5 in. (24),
1.75 in.(l),
0.75 in. (2)
1 in. (6),
1.125 in. (5)
1.25 in. (24),
1.375 in. (3)
1.5 in. (43),
1.75 in. (17),
2.00 in. (2)
1 in. (6),
1.25 in. (21),
1.5 in. (24),
1.75 in. (1),
1 in. (4),
1.125 in. (1)
1.25 in. (11),
1.5 in. (18),
1.75 in. (6),
Average Wood
Moisture
Content
(%)
191
100%
103
Irradiation Time (min)/
# of samples
Table 4-9: Detailed results for dry poplar artificially seeded with ALB larva
Time Irradiated
% of Maximum
Power (900 W)
Status of
Larvae or
Pupae
No. of
Replicates
Under the
Same
Conditions
100
100
100
dead
dead
dead
1
1
2
80
80
dead
dead
5
5
4 in. x 4 in. x 4 in. Block
1 la r v a in c e n te r h o le
30 seconds
15 seconds
5 seconds
4 in. x 4 in. x 1 in. Block
1 la rv a in c e n te r h o le
30 seconds
5 seconds
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222
insect or the microwave energy interacts with the physiology of the larva sufficiently to
kill it.
4.4.3.1.2 Irradiation o f ALB in Naturally Infested Logs and Lumber
After 3 minutes o f 900 W o f irradiation, 91 larvae (86 ALB and 5 unknown
species) were found in both the round debarked logs and the rectangular lumber. All 91
larvae were dead after irradiation.
4.4.3.2 Irradiation o f Cottonwood Borer
4.4.3.2.1 Efficacy Results
As can be noted in Table 4-10 below, all CWB and ALB larvae (446) placed in 4
in. x 4 in. x 4 in. cubes (64 in3 volume) died regardless of wood type and moisture
content (up to 137%) when irradiated with 270,000 to 330,000 J (5 minutes o f irradiation
at 900 W or 1100 W, 4,218 to 5,156 J/in) of microwave energy.
4.4.3.2.2
Critical Moisture Content Study Results
4.4.3.2.2.1
Volatile release. The critical minimum moisture content for red pine
was between 27% and 32% (see Table 4-11). At this moisture content, some wood
blocks released volatiles and some did not. Above 41% moisture content, however, none
o f the red pine samples released volatiles under these microwave conditions.
Aspen, on the other hand, when irradiated for 5 minutes at 1100 W did not release
volatiles until the moisture content o f the 4-in. cube dropped below 20% (see Table 412). All larvae inserted into the aspen blocks in this study died.
A. 4.3.2.2.2 Moisture content effect on larval mortality. Comparing 4 in. cubes of
poplar at two different moisture contents, it was found that at 900 W o f power none o f the
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223
Table 4-10: Detailed results various wood species cut to 4 in. x 4 in. x 4 in.
dimensions and artificially seeded with either cottonwood borer
or Asian longhomed beetle larvae
Wood
Type
Energy
(J)
Moisture
Content
#of
Wood
Samples
10
51
45
Output
Power
Time
(min)
ALB
900 W
900 W
5
5
270,000
270,000
CWB
CWB
1100 W
1100 W
5
5
330,000
330,000
109%
64%
30% to
137%
15% to 91%
Pine
CWB
1100 W
5
330,000
11% to 75%
26
Loblolly
Pine
Total
CWB
1100 W
5
330,000
69% to 94%
24
Poplar
Poplar
Eastern
White Pine
Aspen
Larval
Species
ALB
#of
Larvae/
mortality
20/20
102/102
90/90
67
134/134
R ed
52/52
48/48
446/446
223
Table 4-11: Red pine volatile release after 5 minutes of
2.45 GHz irradiation at 1100 W (330,000 J)
Red Pine
(4 in. cube)
Moisture
Content
41% to 75%
# of Blocks
Volatile Status
# of Larvae/
mortality
11
22/22
30% to 32%
2
27% to 29%
5
NONE
Released
Volatiles
NONE
Released
Volatiles
3 Released
Volatiles
11% to 26%
8
ALL Released
Volatiles
16/16
Observations
4/4
10/10
Volatiles were
noticed @ ~4
minutes
Volatiles were
noticed ~3 to 4
minutes into
the treatment
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224
Table 4-12: Volatile release as a function of moisture content for 4-in. cubes of
aspen irradiated with 330,000 J of 2.45 GHz energy
Aspen (4” cube)
Moisture Content
59% to 98%
# of Wood Blocks
Volatile Status
26
19% to 44%
9
13% to 17%
10
NOME Released
Volatiles
NONE Released
Volatiles
Two Released Volatiles
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#of Larvae/
mortality
52/52
18/18
20/20
225
50 larvae artificially inserted in samples with 37% moisture content survived 3 minutes
o f irradiation, and 7 o f the 52 larvae artificially inserted in samples with 190% moisture
content survived 4 minutes of irradiation. This leads us to conclude that moisture content
is a major factor in larval mortality.
One theory is that higher moisture content may absorb the available microwave
energy near the surface o f the wood, thus effectively reducing the microwave energy
reaching the larva and moisture deep inside the wood. As discussed in section 2.4.2, the
microwave depth o f penetration [2.61] through a homogenous material is dependent on
the dielectric loss and the dielectric constant o f the material, as well as the frequency o f
the wave itself. The depth o f penetration26 of a 2.45 GHz wave through water at 25 °C is
expected to be 1.4 cm. Increasing the water temperature to 95 °C, the expected depth of
penetration also increases to 5.7 cm. Dry wood, on the other hand, has a much larger
depth o f penetration, 8 to 350 cm. Wood containing moisture content is not a
homogenous material. However, one can deduce that microwave penetration of a block
o f wood with high water content at room temperature will be less than microwave
penetration of the same block heated to 95 °C or higher. One can also deduce that
microwave penetration o f a dry block of wood will be much greater than the same block
containing moisture. This supports the theory that moisture content can provide a
temporary shielding effect to larva deep inside the sample.
Not all the larvae present inside high moisture content samples survive, however.
This could be due to the ability o f some larva to survive better than others under the same
microwave conditions. Other reasons could include variation in local moisture content
and local heat transfer.
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226
4.4.3.2.3 Surface Area Results
Moisture content of the green wood before microwave treatment was difficult to
control since the oven-dry weight of wood samples was needed to calculate moisture
content. Although moisture content o f 63% was targeted, actual moisture content varied
by +/-19%. Experiments in the 1000 W kitchen multimode microwave showed that for
red pine, 3 minutes o f irradiation was lethal regardless of differences in surface area
when moisture content ranged between 44% and 83% (see Table 4-13).
4.4.3.2.4 Chamber Volume to Sample Size Results
Similar experiments in the larger 6 kW chamber at 180,000 J o f 2.45 GHz energy
were then conducted to determine if the chamber volume to sample size ratio (the fill
factor) affected the outcome. The results (Table 4-14) showed that the larger chamber
volume had no effect on mortality, although moisture content did.
4.4.3.2.5 Input Power/Time Variance
When the energy and sample volume was held constant as the power was
increased and the time decreased, 100% mortality was still attained both at 1500 W and
3000 W (Tables 4-15 and 4-16).
4.4.3.2.6
Energy to Wood Volume Ratio Results
In order to test the theory that the energy to volume ratio (2,812.5 J/in3) can be
directly applied to a larger volume of the same moisture content, larval mortality in a 6in. cube was found to be 100% for moisture contents between 60 and 78% (Table 4-17).
For moisture contents above 92%, one larva out o f four survived, but this was not
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227
Table 4-13: Mortality of larvae as a function of sample surface area after
exposure to 180,000 J o f 2.45 GHz microwave energy in a
modified, multimode, 1 kW microwave oven
Red Pine
1000 W 3min
180,000J
1 kW MW
4 in. x 4 in. x 4 in.
Volume
(in.3)
Surface
Area
(in.2)
64
96
1 in. x 6.5 in. x 9.8 in.
64
160
2 in. x 6 in. x 5.3 in.
64
108
Moisture
Content
Range
(%)
33%
39-41%
46%-56%
119%-122%
67%-81%
99-111%
45%-61%
131%-132%
#of
Wood
Expts
#of
Larvae/
Mortality
1
2
3
2
4
2
4
2
2/2
6/6
6/6
6/6
12/12
2/1
12/12
4/3
Table 4-14: Mortality o f larvae as a function of sample surface area after
exposure to 180,000 J o f 2.45 GHz microwave energy in a
6 kW multimode microwave chamber
Red Pine
1000 W 3min
180,0001
6 kW MW
4 in. x 4 in. x 4 in.
Volume
(in3)
Surface
Area
(in2)
64
96
1 in. x 6.5 in. x 9.8 in.
64
160
2 in. x 6 in. x 5.3 in.
64
108
Moisture
Content
Range
(%)
40-44%
49-63%
46-83%
85-106%
46-79.1%
#of
Wood
Expts
# of Larvae/
Mortality
6
9
3
4
6
6/6
14/14
9/9
12/10
18/18
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228
Table 4-15: Mortality o f larvae as a function o f sample surface area after exposure
to 180,000 J of 2.45 GHz microwave energy (1500 W for 2 minutes)
in a 6 kW multimode microwave chamber
Red Pine
1500 W 2min
180,000J
6 kW MW
4 in. x 4 in. x 4 in.
1 in. x 6.5 in. x 9.8 in.
Volume
(in3)
Surface
Area (in2)
64
64
96
160
2 in. x 6 in. x 5.3 in.
64
108
Moisture
Content
Range
(%)
60-76%
21%
46%
31.7%
53-67%
# of
Wood
Expts
# of Larvae/
Mortality
5
1
1
1
4
10/10
3/3
3/3
3/3
12/12
Table 4-16: Mortality o f larvae as a function o f sample surface area after exposure
to 180,000 J o f 2.45 GHz microwave energy (3000 W for 1 minute)
in a 6 kW multimode microwave chamber
Red Pine
3000 W Imin
180,000 J
6 kW MW
4 in. x 4 in. x 4 in.
2 in. x 6 in. x 5.3 in.
Volume
(in3)
Surface
Area
(in2)
64
64
96
108
Moisture
Content
Range
(%)
45-78%
59-81%
#of
Wood
Expts
# of Larvae/
Mortality
5
4
10/10
12/12
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229
Table 4-17: Mortality o f larvae after exposure o f 6-in. cubes to
607,500 J (2,812.5 J/in3) of 2.45 GHz microwave energy
(1000 W for 10 minutes) in a 6 kW multimode,
microwave chamber
Red Pine
1000 W
10 min
607,500 J
6 kWMW
6 in .x 6 in .x 6 in.
Volume
(in3)
Surface
Area (in2)
Moisture
Content
Range
(%)
#of
Wood
Expts
# of
Larvae/
Mortality
216
216
61-78%
93-96%
7
2
14/14
4/1
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230
significantly different from mortality in wood with 60-78% moisture content (chi-square
= 1.3, P - 0.245).
4.4.3.2.7 Temperature Dependence of Lethal Microwave Irradiation
The wood temperature of red pine surrounding larvae that survived irradiation (5
o f 180 larvae) ranged from 44 °C to 61 °C (error range +/-2 °C). However, significantly
more larvae (175 out o f 180 larvae) did not survive at these temperatures (chi-square =
4.5, P = 0.0299). All larvae that experienced higher temperatures died.
4.4.3.2.8 Critical Larva vs. Wood Temperature Results
Using the fiberoptic temperature measurement device, the temperature of each
larva was directly measured, as well as the surrounding wood temperature to a distance
within 1/8 in. o f the larva (Table 4-18). No consistent trends were noticed. In some
cases, the larval temperature was higher than the wood temperature during portions o f the
cycle, and in other cases the opposite was true. One explanation could be that
microwave energy is interacting with the water in the larva in a similar manner to the
water in the wood surrounding the insect. However, wood of markedly different
moisture contents (e.g., moisture content > 100% or <20%) may produce different
results.
The larva temperature data in Table 4-18 imply that thermal effects may be the
cause of death as the temperatures o f all the larvae were between 90 and 100.4 °C at the
end of 3 minutes o f 1000 W irradiation. However, there was no way o f knowing if the
larva died at an earlier point in the cycle when the temperature was lower.
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231
Table 4-18: Temperature comparison of larvae and surrounding wood
MW
Exp
Time
0
30s
lm
lm30s
2m
2m30s
3m
4 in. x 4 in. x 4 in. Red Pine (6 kW MW Oven)
1000 W microwave exposure for 3 min.
Expt#60
Expt #58
Expt #59
(43%mc)
(41%mc)
(56%mc)
Larva
Wood
Wood
Larva
Wood
Larva
Temp
Temp
Temp
Temp
Temp
Temp
(°Q
(°C)
(°C)
(°C)
(°Q
(°C)
15.5
15.9
16.3
16.1
16.9
16.6
24.2
23.5
20.8
31.8
28.9
39.4
33.4
42.2
32.5
51.7
52.1
37.2
50.2
52.5
62.0
61.5
69.9
40.9
75.4
64.7
81.7
56.8
81.7
70.6
89.9
90.9
97.2
68.6
90.5
85.8
99.1
99.8
99.2
100.0
86.9
94.5
Expt #61
(41%mc)
Larva Wood
Temp Temp
(°C)
(°C)
21.5
20.6
32.5
30.4
36.3
57.7
59.9
78.6
87.1
95.9
95.7
99.6
100.1 99.2
MW
Exp
Time
0
30s
lm
lm30s
2m
2m30s
3m
Expt #62
(55%mc)
Larva
Wood
Temp
Temp
(°C)
(°C)
23.1
23.1
32.3
32.6
51.2
38.7
56.6
57.9
76.0
67.3
85.0
91.9
99.7
99.0
Expt #63
(51%me)
Wood
Larva
Temp
Temp
(°Q
(°C)
19.6
19.9
40.4
33.6
51.0
58.4
73.2
71.3
83.2
96.3
99.2
100.0
99.3
100.4
Expt #67
(41%mc)
Wood
Larva
Temp
Temp
(°C)
(°C)
18.9
18.9
26.6
41.3
42.1
52.2
52.8
77.3
75.8
93.3
98.6
89.3
100.1
99.6
Expt #68
(42%mc)
Larva Wood
Temp Temp
(°C)
(°Q
18.5
18.6
37.9
28.1
34.5
74.3
91.5
51.1
98.2
59.8
100.0 81.1
90.5
99.1
MW
Exp
Time
0
30s
lm
lm30s
2m
2m30s
3m
Expt #69
(44%me)
Wood
Larva
Temp
Temp
(°C)
(°C)
16.6
16.8
34.0
49.4
57.7
63.0
94.3
77.0
99.2
99.6
99.6
99.3
99.7
99.3
Expt #70
(56%mc)
Wood
Larva
Temp
Temp
CO
(°C)
16.3
16.2
24.2
25.7
29.0
43.4
44.3
52.7
67.9
52.0
63.5
77.6
69.2
90.0
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232
4.4.4
Lethal Microwave Experiment Conclusions
Eradication o f cerambycid larval infestations in laboratory-size pine and poplar
lumber o f 216 in.3 or less with 2.45 GHz microwave energy is feasible. Wood moisture
content is an important factor in determining the lethal dose of microwave energy
required for 100% eradication. Preferential larval absorption of microwave energy
probably occurs in dry wood environments since dry wood does not absorb energy well.
However, in moist wood environments, this does not hold true. Wood of high moisture
content obviously contains more water molecules for microwave energy to interact with,
reducing the depth of penetration and potentially shielding the larvae in the center of the
sample. This shielding mechanism is one explanation for the need for additional
microwave power as wood moisture content increases in order to assure a lethal dose has
been administered. On a more local scale, however, microwave energy likely interacts
with the water molecules inside the larvae in approximately the same manner as the
neighboring water molecules in the surrounding wood, resulting in larval temperatures
that mimic those in the surrounding wood.
Five minutes of 1100 W irradiation produced 100% mortality o f larvae infesting 4
in. x 4 in. x 4 in. blocks o f red pine, loblolly pine, Eastern white pine, aspen, and other
poplar species (moisture content range o f 30% to 137%). At this power level, volatiles
were released in some aspen or red pine samples with moisture contents less than 30%.
Several microwave parameters were tested to determine their effect on larval
survival. Volume was more important than surface area when moisture content was held
constant. In addition, the energy-to-volume ratio was an acceptable parameter to predict
lethal microwave doses as long as wood moisture content was held constant. The
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233
chamber size to sample size ratio was not important for these microwave system and
wood dimensions.
In addition to demonstrating the feasibility of eradicating cerambycids infesting
wood with microwave energy, these experiments provide a more than sufficient
justification to begin industrial scale-up experiments. For example, the proposed energyto-volume ratio for up to 78% moisture content wood samples is 2,812.5 J/in3. Using this
figure, expected lethal microwave doses could be calculated for various volumes of
commercial lumber. Experiments in industrial microwave ovens could then verify this
energy to volume ratio. It would also be expected that chamber-size to sample-size ratios
do not affect larval mortality; however, this hypothesis requires further experimentation
for verification.
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234
4.5 References
^ an ag an MT. Microwave Dielectric Properties of Antiferroelectric Lead Zirconate, PhD
Thesis. University Park, PA: The Pennsylvania State University; May 1987.
2Ibid.
3Ligthart LP. A fast computational technique for accurate permittivity determination
using transmission line methods. IEEE Trans. On Microwave Theory and Tech 1983;
MTT-31(3):249-254.
4Torgovnikov GI. Dielectric Properties of Wood and Wood-based Materials. Heidelberg,
Germany: Springer -Verlag; 1993:15.
5Ibid.
6Torgovnikov GI. Dielectric Properties o f Wood and Wood-based Materials. Heidelberg,
Germany: Springer -Verlag; 1993:77.
7Von Hippel AR. Dielectrics and Waves. New York, NY: John Wiley 1959.
8Rosenburg VI. Scattering and Attenuation o f Electromagnetic Radiation by the
Atmospheric Particles. Leningrad, Russia: Gydrometizdat; 1979.
9Torgovnikov GI. Dielectric Properties o f Wood and Wood-based Materials. Heidelberg,
Germany: Springer -Verlag; 1993:175.
10Ibid.
nDube DC, Lanagan MT, Kim JH, Jang SJ. Dielectric measurements on substrate
materials at microwave frequencies using a cavity perturbation technique. Journal of
Applied Physics 1988; 63(7):2466-2468.
12Bethe HA, Schwinger J. Perturbation theory for cavities. NDRC, Washington, D.C.,
Rept. No. Dl-117; 1943.
13Spencer EG, LeCraw RC, Ault LA. Note on cavity perturbation theory. Journal of
Applied Physics 1957; 28: 130.
14Waldron RA, Perturbation theory o f resonant cavities. Proc. Inst. Elec. Eng. 1960;
107c:272.
15Altschuler HM. Handbook o f Microwave Measurements. Sucher M, Fox J (eds). New
York, NY; Brooklyn Poltechnic Press 1963; 2:530.
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235
16Bimbaun G, Franeau J. Measurement of the dielectric constant and loss of solids and
liquids by a cavity perturbation method. Applied Physics 1949; 20:817.
17Ibid.
18Lanagan MT. Microwave Dielectric Properties of Antiferroelectric Lead Zirconate,
PhD Thesis. University Park, PA: The Pennsylvania State University; May 1987; 52,
101-106.
19American Society for Testing Materials. Standard test methods for specific gravity o f
wood and wood-based materials. West Conshohocken, PA: Ann. Book of ASTM
Standards 1996; Vol. 4.10 ASTM Standard D2395.
20Torgovnikov GI. Dielectric Properties of Wood and Wood-based Materials. Heidelberg,
Germany: Springer -Verlag; 1993:175.
21Ibid.
22Ibid.
23American Society for Testing Materials. Standard test methods for specific gravity o f
wood and wood-based materials. West Conshohocken, Pa: Ann. Book of ASTM
Standards 1996; Vol. 4.10 ASTM Standard D2395.
24Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material.
Agriculture Handbook 72. Washington, DC: U.S. Department o f Agriculture, Forest
Service 1987.
25Ibid.
26Peushchner Microwaves. http://www. pueschner.com/engl/basics/calculations_en.html.
May 7, 2003.
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5
TREATMENT OPERATING COST COMPARISONS
Operating cost comparisons of three different solid wood packing material
treatments (heat treatment, methyl bromide fumigation, and microwave treatment) will be
made for the United States. Cost comparison of fumigation vs. microwave treatments will
also be made for China. Slat and stabilizer configurations o f wooden pallets vary,
depending on the expected loads. However, for the purposes of this analysis, all
estimates o f the wood content of pallets were taken from the following picture o f typical
pallets used for exports in China (Figure 5-1). Each pallet has 14 slats (1 in. x 4 in. x 48
in.) and 8 stabilizer blocks (4 in. x 4 in. x 4 in.). The pallet dimensions are approximately
6 in. x 48 in. x 48 in.
5.1
Methyl Bromide Fumigation
In the United States, most fumigation orders completed commercially are for
loaded pallets stacked one or two layers high in 42 ft. long trailers. In this analysis,
however, the costs of two extremes were used in the following estimates, including (1) a
2700-cubic ft. trailer folly packed with unloaded pallets and (2) the same trailer with
loaded pallets stacked two layers high. When outside temperatures are lower than 40 °F,
the trailers must be preheated in order for the methyl bromide to work. Consequently,
costs are higher in colder weather. The following assumptions were made in this analysis
using the 2002 industry fees for methyl bromide fumigation o f a 2700-cubic ft. trailer
containing loaded pallets:1
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Figure 5-1: Photograph of typical Chinese pallet
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238
For unloaded pallets
2700 ft.3trailer fully packed with 4 ft. x 4 ft. x 0.5 ft. pallets (8 ft.3 per pallet)
Total number o f pallets in trailer: 337
Cost at plant: $300 for outside temperatures above 70 °F
Cost at customer site: $600 for outside temperatures above 70 °F
Premium for outside temperatures between 40 °F and 69 °F: $78.00
$7.24/ lb. x 2 lb./l 000ft.3x 2700 ft.3x 2 (for profit)
estimated by Mary Fleming from per pound cost of methyl bromide
Treatment time: 16 hours
Pallet configuration:
8 - 4 in. x 4 in. x 4 in. stabilizers per pallet (0.04 ft.3 * 8 == 0.32 ft.3)
14 - 48 in. x 4 in. x 1 in. slats per pallet (0.11 f t.3 * 14 =1.54 ft.3)
Total cubic feet of wood per pallet: 1.86 ft.3
Given these assumptions, cost per pallet for methyl bromide fumigation is
estimated to be between 89 cents per pallet (48 cents per cubic foot o f wood) and $1.78
per pallet (96 cents per cubic foot of wood) for warm weather fumigation, and the cost o f
colder weather (between 40 °F and 70 °F) can be estimated to fall within the range o f
$1.12 to $2.01 per pallet (60 cents/ft.3 to $1.08 / ft.3). Cost of fumigation at temperatures
lower than 40 °F would be even higher. Expected throughput is 337 pallets in 16 hours.
For loaded pallets
2700 ft.3trailer (8 ft. wide by 8 ft. tall x 42 ft. long) with loaded pallets
stacked two high
Total number of pallets in the trailer: 42 (21 on floor x 2 high)
Cost at plant: $300 for outside temperatures above 70 °F
Cost at customer site: $600 for outside temperatures above 70 °F
Premium for outside temperatures between 40 °F and 69 °F: $78.00
$7.24/ lb. x 2 lb./l000 ft.3 x 2700 ft.3 x 2 (for profit)
estimated by Mary Fleming from per pound cost of methyl bromide
Treatment time: 16 hours
Pallet configuration:
8 - 4 in. x 4 in. x 4 in. stabilizers per pallet (0.04 ft.3 * 8 = 0.32 ft.3)
1 4 - 4 8 in. x 4 in. x 1 in. slats per pallet (0.11 ft.3 * 14 =1.54 ft.3)
Total cubic feet of wood per pallet: 1.87 f t.3
Given these assumptions, cost per pallet for methyl bromide fumigation is
estimated to be between $7.14 per pallet ($3.82 per cubic foot of wood) and $14.28 per
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239
pallet ($7.64 per cubic foot o f wood) for warm weather fumigation (above 70 °F),
whereas the cost o f colder weather (between 40 °F and 60 °F) can be estimated to fall
within the range o f $9.00 to $16.14 per pallet ($4.83 to $8.68 per cubic foot of wood). Of
course, cost o f fumigation at temperatures lower than 40
°Fwould be even higher.
Expected throughput is 42 pallets in 16 hours.
In China, two main methods of fumigation occur. Loaded freight containers from
the interior regions o f China are fumigated at the coastline ports. Unloaded pallets are
also fumigated separately before loading when the manufacturers are located closer to the
ports. In China, the cost2 to fumigate one loaded, freight container is approximately
US$50. Assuming there are 42 loaded pallets in the freight container, cost per pallet to
fumigate with methyl bromide is approximately $1.19. Assuming 337 pallets in an
unloaded trailer, the cost per pallet is estimated to be 15 U.S. cents.
5.2 Heat Treatment
In the United States, Brunner-Hildebrand3 is a manufacturer o f natural gas kilns
used for heat treatment. For steam heat treatment a 3- to 4-hour cycle is required to bring
wood in pallets up to 56 °C for 30 minutes. With Brunner-Hildebrand equipment, the
company estimates that energy costs for the heat treatment of pallets ranges from 5 to 10
cents per pallet depending on the moisture content of the wood and local natural gas
prices.
In China,4 sawdust rather than gas is used to produce heat for conventional
treatment. Consequently, energy costs are very difficult to estimate.
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240
5.3
Microwave Treatment
Although the necessary technology is available, the microwave process
discussed in this dissertation is not yet scaled-up to commercial dimensions nor has
commercial equipment been developed. Consequently, capital costs will be neglected in
this analysis. Labor costs and throughput are also difficult to assess due to the lack of
commercial equipment. In addition, estimates o f energy-operating costs do not reflect
economies of scale or the energy needs that might occur in a larger scale operation.
Energy and labor cost estimates were made however. In order to account at least in part
for profit, energy and labor estimates will be multiplied by 2. These estimates are
reported below for the United States.
Although electricity costs vary considerably by region in the United States, the
following electricity costs were obtained from Utah Power/Pacific Corp as of March 24,
2003:5 for Utah 6.3 cents/kW-hour and for Oregon 3.7 cents/kW-hour. The definition of a
kilowatt-hour is the number o f kilowatts used in 1 hour. As with the treatments above,
each pallet was assumed to have 14 slats o f dimension 4 in. x 1 in. x 48 in. and 8
stabilizers of dimension 4 in. x 4 in. x 4 in. A microwave treatment o f 1000 W for 5
minutes (0.083 hours) was chosen for the 4 in. x 4 in. x 4 in. blocks. The dimensions
used for the 1-in. thick samples in the laboratory were 4 in. x 1 in. x 4 in. Energy
requirements for these samples were estimated as 900 W for 2 minutes (.033). Twelve
samples of these dimensions would be equivalent to 1 pallet slat. The analysis is
summarized in Table 5-1. The electricity cost per pallet would equal approximately 39
cents in Utah and 24 cents in Oregon.
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241
Table 5-1: Energy/cost analysis for the microwave treatment of one pallet
For Single
Sample
in the U.S.
4 in. x 4 in.
x 4 in.
4 in. x 4 in.
x 1 in.
Power
(KW)
MW
Duration
(hours)
Energy
Used
(kWhour)
Utah
Electricity
Rate
(cents/
kW-hour)
Oregon
Electricity
Rate
(cents/
kW-hour)
Electricity
Cost in
Utah
(cents)
Electricity
Cost in
Oregon
(cents)
1
.083
.083
6.3
3.7
0.522
0.307
0.9
.033
.0297
6.3
3.7
0.187
0.110
31.4
18.5
4.18
2.46
35.58
20.96
For One
Pallet in the
U.S.
14 slats
(1 slat = 12
1 in.
samples)
8 blocks
Total
Energy
Cost per
Pallet
1
0.083
CHINA
High
Range
(U.S.
cents)
0.083
30
0.9
0.033
0.0297
For Single
Sample
in China
4 in. x 4 in.
x 4 in.
4 in. x 4 in.
x 1 in.
For One
Pallet in
China
14 slats
(1 slat= 12
1 in.
samples)
8 blocks
Total
Energy
Cost per
Pallet
Low
Range
(U.S.
cents)
20
High
Range
(U.S.
cents)
2.49
Low
Range
(U.S.
cents)
1.66
30
20
0.891
0.594
149.69
99.79
19.92
13.28
169.61
113.07
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242
Estimated labor to load and unload board is 5 minutes per pallet. Assuming the
hourly U.S. labor charge is $7.00/hour, the cost per pallet would be 58 cents per pallet.
Thus, the estimated energy and labor cost per pallet is 94 cents in Utah and 79 cents in
Oregon. Doubling these estimates to account for profit, cost to the end-user is estimated
at $1.88 per pallet in Utah and $1.58 in Oregon.
In China,6 the cost o f electricity ranges between 20 and 30 cents per kilowatt
hour. The energy cost per pallet for microwave treatment is estimated to be between 113
and 170 cents per pallet. Assuming that the labor and other operating costs are
considerably less in China than in the United States (US$3.00/day or 38 cents per hour)
and 5 minutes o f labor per pallet is required, labor is projected to cost 3 cents per pallet.
Profit requirements are assumed also to be less at 20%. Operating costs per pallet
including profit is estimated to be 139 cents to 207 cents.
5.4. Conclusions
In the United States, energy costs for microwave treatment o f one pallet are
estimated to be in the range o f 21 to 36 cents. This is more expensive than the energy
cost estimates for heat treatment o f 5 to 10 cents per pallet. Cost o f methyl bromide
fumigation for loaded pallets to the exporter is markedly higher than for microwave
estimates (per pallet). When pallet material is fumigated before pallets are loaded, the
methyl bromide cost drops to $0.89 from $2.01 per pallet - equal to or lower than the
microwave treatment cost-to-exporter estimates.
In China, projected fumigation costs for loaded pallets are comparable to
microwave estimates per pallet. However, cost o f fumigating unloaded pallets are much
less than microwave projections.
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In conclusion, microwave treatment of wooden pallet material appears to be
competitive with methyl bromide fumigation in the United States, as well as with loaded
container fumigation in China. Heat treatment energy costs are less than microwave
treatment energy costs in the United States. Given these estimates, additional microwave
research to industry-size loads is warranted. More accurate energy, operating, and capital
cost estimates can be made once the microwave process has been scaled up to industry
dimensions.
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244
5.5 References
1 Mueller D. Fumigation Service and Supply. Westfield, IN: personal communication.
Jan. 30, 2003.
2Wang, Y. Director and Professor of the Quarantine Treatment Research Division,
Animal and Plant Quarantine Institute, General Administration of Quality Supervision,
Inspection and Quarantine o f the People's Republic of China (AQSIQ). Beijing, China:
personal communication. Jan. 30,2003.
3Juergen R. Brunner-Hildebrand Company. South Carolina: www.brunnerhildebrand.com. personal communication. March 28, 2003.
4Wang, Y. Director and Professor o f the Quarantine Treatment Research Division,
Animal and Plant Quarantine Institute, General Administration o f Quality Supervision,
Inspection and Quarantine o f the People's Republic of China (AQSIQ). Beijing, China:
personal communication. Jan. 30,2003.
5Utah Power/Pacific Corp. Business Customer Service. Portland, Oregon: personal
communication. March 24,2003.
6Wang, Y. Director and Professor o f the Quarantine Treatment Research Division,
Animal and Plant Quarantine Institute, General Administration of Quality Supervision,
Inspection and Quarantine o f the People's Republic of China (AQSIQ). Beijing China:
personal communication. Jan. 30,2003.
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6 FUTURE RESEARCH
6.1 Microwave
6.1.1
Alternative Microwave Techniques
Alternative microwave techniques, which should be tested on a laboratory scale,
include pulsed microwave and steam/microwave hybrid systems, as well as 915 MHz
frequency systems. Pulsed microwave treatments may reduce the microwave energy
requirements for lethal doses. The addition o f steam to the microwave system may
reduce the microwave energy requirements, as well as the fire risk for dry wood. The
915 MHz system has a greater depth of penetration than the 2.45 GHz system Therefore,
the 915 MHz system may be more appropriate for larger wood loads. Similar
experiments to those reported in this dissertation should be conducted for all o f these
systems to determine which systems are the most practical.
6.1.2
Commercializing Microwave Processing o f Wooden
Packing Materials
Commercialization o f this microwave process requires two major areas of
research. The first is to scale up the process to industry-size loads, testing the lethalness
o f the pertinent parameters such as energy density and moisture content on the
cerambycid larvae used in the current study. In conjunction with these data, testing the
efficacy of microwave treatment for the eradication of other pests infesting wooden
packing material is also important in order for the international regulatory bodies to adopt
microwave as a valid treatment process. The next step required for the commercialization
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246
o f the microwave processing of wooden packing materials is to develop equipment that is
specifically designed for this application.
6.1.3
Cause of Larval Death
The cause o f larval death was not investigated in the microwave research
presented here. An understanding o f this phenomenon could provide information on the
effect o f 2.45 GHz microwave energy on living organisms and might change the
proposed treatment schedule approach. Potential causes o f death include changes in the
larval cell structure or physiological changes as a consequence of exposure to
electromagnetic radiation and/or internal heating. Depending on the moisture content o f
the surrounding environment, the major cause of death may be different. In addition,
there may be a distinct difference between the microwave electric field and the magnetic
field contribution to mortality.
Thermal effects generated by the microwave treatment may be the cause of larval
death. Wood temperatures o f 60 °C for 30 minutes have been shown to be lethal to the
ALB larvae as reported by Mack et al.1 In a microwave environment, any moisture
content in the field interacts with the microwave energy by a rotation o f water molecule
dipoles. Water is found both within the larva itself and in the wood sample.
Consequently, heat can be generated inside the larva, as well as in the moist wood
surrounding the larva. Cerambycid larval cell damage from microwave energy is not
addressed in the literature. However, cell damage to other organisms by microwave
radiation has been studied. The reported results were mixed. For example, Woo et al2
placed Escherichia coli cells in suspension before microwave radiation. The E. coli cells
sustained severe surface damage (viewed by scanning electron microscopy), whereas
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247
Bacillus subiilis cells did not. Lai and Singh3 reported that DNA strands in rat brain cells
were affected when exposed to pulsed 2.45 GH microwave energy. On the other hand,
Malyapa et al4 did not find DNA strand damage in cultured mammalian cells after
exposure to 2.45 GHz radiation.
Electromagnetic radiation consists of both an electric field and a magnetic field
contribution. Regardless of the material, most microwave research in the past focused on
the electric field contribution of dipole alignment, while neglecting the magnetic field
contribution, which is not at all well understood. Roy et al5 have begun to study the
magnetic field contribution to microwave/material interaction. They found that ferric
oxides such as FesCh form noncrystalline materials when placed in a pure magnetic field
node in a single-mode 2.45 GHz microwave field. Under electric field node conditions,
these ferric oxide pellets form crystalline materials o f a single phase. The effect o f the
microwave magnetic field on living organisms has not yet been addressed.
Two sets o f experiments to better understand the cause o f larval death under
microwave field exposure are thus proposed. Using a 2.45 GHz multimode microwave
system and various samples with different moisture contents, the microwave power can
be varied. During all treatments, larval temperature and surrounding wood temperature
should be monitored using fiber optic temperature monitoring devices. After each
microwave treatment method, the DNA, the permeability of cell membranes (light
microscopy) and the surface condition o f the cerambycid larval cells (scanning electron
microscopy) for both the larvae that survive and the larvae that died during treatment
should be analyzed to determine changes in physical structure. Thermal modeling o f the
energy conversion and mapping of the temperature profiles during microwave processing
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248
o f the wood sample can provide a framework for this work. For the electric and magnetic
field experiments, cerambycid larvae are too big to fit inside the 2.45 GHz single-mode E
and H field nodes. However, a 915 MHz microwave system has larger nodal regions and
could be used to study the separate effects of these fields on larvae. Temperature o f the
larva and the surrounding air in the chamber should be recorded. The DNA o f both the
surviving and dead larvae should be analyzed, the permeability of cell membrane should
be determined, and the surface condition o f the cerambycid larval cells should also be
observed under scanning electron microscopes.
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249
6.2 References
*Mack RG, Xu Zhixin. Heating in a kiln as a regulatory treatment for Anoplophora
glabripennis in solid wood packing. First Annual Asian Longhomed Beetle Research and
Development Review Nov. 6-8, 2001 Annapolis, MD. USD A Forest Service, USDA
Agriculture Research Service, & USDA Animal & Plant Health Inspection Service 2001;
67.
2Woo IS, Rhee IK, Park HD. Differential damage in bacterial cells by microwave
radiation on the basis o f cell wall structure. Applied Environmental Microbiology 2000;
66(5): 2243-47.
3Lai H, Singh NP. Acute low intensity microwave exposure increases DNA single-strand
breaks in rat brain cells. Bioelectromagnetics 1995;16(3):207-10.
4Malyapa RS, Ahem EW, Straube WL, et al. Measurement ofDNA damage after
exposure to 2450 MHz electromagnetic radiation. Radiation Research 1997; 148(6):608617.
5Roy R, Peelamedu R, Hurtt L, et al. Definitive experimental evidence for microwave
effects: radically new effects o f separated E and H fields, such as decrystallization of
oxides in seconds. Material Research Innovations 2002; 6:128-140.
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APPENDIX A
NONCONTACT ULTRASOUND FIXED TRANSDUCER
VARIED FREQUENCY GRAPHS
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RP3 Noncontact Frequency Comparison
Frozen
Moisture Content 29%
-50
-70 -80 -90 -100
-
100 KHz
500 KHz
Position
Room Temperature
Moisture Content 22%
- * — 100 KHZ
- • —200 KH z
—• — 500 KH z
Position
10-Hour Dry
Moisture Content 3.4%
- * - 1 0 0 KHz
—®—200 KHz
—* —500 KHz
Position
25-Hour Dry
Moisture Content 0.1%
—•— 100 KHz
—■—200 KHz
-100 J----------------------------Position
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RP9 Noncontact Frequency Comparison
Frozen
Moisture Content 22.7%
-50
200 KHz
500 KHz
-100
Position
10-Hour Dry
Moisture Content
1%
-50
-60
—
-70
100 KHz
- * - 2 0 0 KHz
-80
—®— 500 KHz
-90
-100
Position
25-Hour Dry
Moisture Content 0.2%
-50
-60
- * - 1 0 0 KHz
-70
- * - 2 0 0 KHz
-80
- * - 5 0 0 KHz
-9 0
-100
Position
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RP10 Noncontact Frequency Comparison
Frozen
Moisture Content 31.1%
-40
100 KHz
500 KHz
H
.90 -100 J---------------------------Position
Room Temperature
Moisture Content 23%
.§
^
§
H
-40
-50
-60
-70
-80
-90
-100 KHz
-2 0 0 KHz
-5 0 0 KHz
-100
Position
10-Hour Dry
Moisture Content 0.7%
-40
-50
-60 -7 0 -8 0 -90
100 KHz
-® —200 KHz
- • — 500 KHz
-100
Position
25-Hour Dry
Moisture Content 0%
-6 0 H B - 200 KHz
§
-8 0 -
-® — 500 KHz
-100
Position
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RP12 Noncontact Frequency Comparison
Frozen
Moisture Content 16.7%
100 K H z
- * - 2 0 0 KHz
- * - 5 0 0 KH z
-too J— ------------- —
Position
10-Hour Dry
Moisture Content 1.1%
-4 0 i
-50 —*—100 KHz
-6 0 -
- * - 2 0 0 KHz
-8 0 -90 -
-100 -1
- * —500 KHz
Position
25-Hour Dry
Moisture Content 0.1%
-4 0 •,--------------------------
—
- * - 2 0 0 KHz
- * - 5 0 0 KH z
-100 J---------------------Position
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RP13 Noncontact Frequency Comparison
Frozen
Moisture Content 28%
- * - 1 0 0 kHz
—®—500 kHz
-too -L----- —------------Position
Room Temperature
Moisture Content 22%
-50
—* —lOOKHz
- * - 2 0 0 KHz
- * - 5 0 0 KHz
-100 J---------------------Position
10-Hour Dry
Moisture Content 0.7%
-50
-60
—• — lOOKHz
-70
- * - 2 0 0 KHz
-80
- * - 5 0 0 KHz
-90
-100
Position
25-Hour Dry
Moisture Content 0%
-50
-60
-70
—is—200 KHz
-80
—*—500 KHz
-9 0
-100
Position
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RP14 Noncontact Frequency Comparison
Frozen
Moisture Content 27%
20
a
.s02 -20
-40 -
-lOOKHz
-200 KHz
-60 -
- 500 KHz
-
(5 -80-
-100 -1
Position
Room Temperature
Moisture Content 23%
g
-40
-50
-60 -
1 $
-70
§
H
100 KHz
-® - 200 KHz
-80
-90
-100
500KHz
Position
10-Hour Dry
Moisture Content 4%
-40
-50 -60 -
—
9
lOOKHz
- ® - 200 KHz
-80 -90 -100 J
- s - 500 KHz
Position
25-Hour Dry
Moisture Content 0%
100 KHz
-60 -70 -
-®—200 KHz
500 KHz
Position
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RP16 Noncontact Frequency Comparison
Frozen
Moisture Content 28%
§L -20 -
a
.2
J
lOOKHz
-4 0 -
200 KHz
-60 -
500 KHz
H
-80 -
-100
Position
Room Temperature
Moisture Content 20%
S3
1
J
-5 0
-60
-lOOKHz
-70
-2 0 0 KHz
-80
-90
-5 0 0 KHz
-100
10-Hour Dry
Moisture Content 5%
-50
s
■S
-60
-lOOKHz
-70
-80
-2 0 0 KHz
-5 0 0 KHz
-90
-100
Position
25-Hour Dry
Moisture Content 0%
C
h
.2
-50
-60 -70 -
-200 KHz
-5 0 0 KHz
-90 -
-100 -1
Position
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RP19 Noncontact Frequency Comparison
Frozen
Moisture Content 31%
c
.9
CO
—#—100KHz
.S9
*33
C
500KHz
-100
Position
Room Temperature
Moisture Content 22%
c
•I
i f
-70
-lOOKHz
-80
-200 KHz
F
-90
-500 KHz
-60
-100
Position
10-Hour Dry
Moisture Content 3%
^
-50
-...... --r ............ t-------"T ............ r ..........
-60 Sh
.9
1
2
3
4
-70 -
5
100 KHz
- * - 2 0 0 KHz
1 '80
1 '90 "
- * - 5 0 0 KHz
H -100
Position
25-Hour Dry
Moisture Content 0%
-50
-60
-70
-80
-90
-100
-I
-
-2 0 0 KHz
-5 0 0 KHz
-
Position
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RP21 Noncontact Frequency Comparison
Frozen
Moisture Content 28%
-50
ffl
lOOKHz
200 KHz
500 KHz
-80 -
H
-90 -
-100
Position
Room Temperature
Moisture Content 17%
-50
n
-o
-60 -
lOOKHz
200 KHz
500 KHz
-80 -90 -
-100 J
Position
10-Hour Dry
Moisture Content 2%
^ -50 i
ffl
3 . -60 -
-lOOKHz
-200 KHz
-80 -
-500 KHz
-90 -100
-
Position
25-Hour Dry
Moisture Content 0%
-50
-60 -
-100 KHz
-200 KHz
-500 KHz
-80 -
-100
Position
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RP24 Noncontact Frequency Comparison
Frozen
Moisture Content 41%
I
-40
-50
-60
-70
-80
-90
-100 KHz
-500 KHz
-100
Position
Room Temperature
Moisture Content 19%
-40
— 100 KHz
—•—200 KHz
-100 J-----------------------------
Position
10-Hour Dry
Moisture Content 2.4%
-4U
— 100 KHz
-• - 2 0 0 KHz
-*—500 KHz
Position
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APPENDIX B
NONCONTACT ULTRASOUND FIXED TRANSDUCER
VARIED COUPLANT GRAPHS
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262
RP3 200 kHz Couplant Comparison
Room Temperature
Moisture Content 22%
§
-20 i
I f
P
H
-40'
-60
-80
- air-coupled
- diy-coupled
-100
Position
10-Hour Dry
Moisture Content 3.4%
o
air-coupled
dry-coupled
- 100 J----------------------------Position
25-Hour Dry
Moisture Content 0.1%
-20
-
air-coupled
dry-coupled
Position
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RP9 200 kHz Couplant Comparison
Room Temperature
Moisture Content 22.7%
—®— air-coupled
dry-coupled
Position
10-Hour Dry
Moisture Content 1%
air-coupled
—* —dry-coupled
H
-8 0 -
^
-too J----------------------Position
25-Hour Dry
Moisture Content 0.2%
— *—
air-coupled
dry-coipled
Position
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RP10 200 kHz Couplant Comparison
Room Temperature
Moisture Content 23%
0
-20
1
3
2
4
5
■
u
-40
- sir-contact
-60
-dry-contact
-SO
-100
Position
10-Hour Dry
Moisture Content 0.7%
—
air-contact
-m —
dry-contact
-100 J---------------------------
Position
25-Hour Dry
Moisture Content 0%
0
C
-20
!§ ,
&
-40 -60
-80
.9
-
—s—air-coupled
dry-coipled
-100
Position
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RP12 200 kHz Couplant Comparison
Room Temperature
Moisture Content 16.7%
- air-coupled
- dry-coupled
- gel-coupled
9
Poston
10-Hour Dry
Moisture Content 1.1%
—.......-'"i..............r
e
.a
II
-
i
f
5
—®—air-coupled
diy-coupled
gel-coupled
-40
H
-100
Poston
25-Hour Dry
Moisture Content 0.1%
- air-coupled
-dry-coupled
- gel-coupled
I 9
-100
Poston
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RP13 200 kHz Couplant Comparison
Room Temperature
Moisture Content 22%
air-coupled
dry-coupled
19
Position
10-Hour Dry
Moisture Content 0.7%
0
S3
.9
H
-20
-40
-60
-80
1
2
68... --- —
3
4
5
- air-coupled
- dry-coupled I
-100
Position
25-Hour Dry
Moisture Content 0%
.§
-air-coupled
- dry-coupled
H
Position
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RP14 200 kHz Couplant Comparison
Frozen
Moisture Content 27%
.5
0
#
1
It
.......
2
H
r
5
4
3
-30 H
- air-coupled
- dry-coupled
£
-60
Position
Room Temperature
Moisture Content 23%
..
1
S3
-S
2
3
-4
5
-air-coupled
-60
-80
- dry-coupled
-100
Position
25-Hour Dry
Moisture Content 0%
- air-coupfed
-diy-coupled
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268
RP16 200 kHz Couplant Comparison
Room Temperature
Moisture Content 20%
air-coupled
'§ ffi
dry-coupled
-100
Position
10-Hour Dry
Moisture Content 5%
air-coupled
—a— dry-coupled
Position
25-Hour Dry
Moisture Content 0%
—
air-coupled
—■— dry-coupled
Position
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RP19 200 kHz Couplant Comparison
Frozen
Moisture Content 31%
o
-20
-40
- air-coupled
-60
- dry-coupled
-80
-100
P osition
Room Temperature
Moisture Content 22%
o
S3
.a
-i---------- 1---------- 1---------- r
-20 H
-40
-air-coupfed
-60 -|
- dry-corpfed
-80
-100
Position
10-Hour Dry
Moisture Content 3%
-ar-coupled
- diy-coupled
IS
Position
o
S3
.a
-20
25-Hour Dry
Moisture Content 0%
---- 1------ 1------ 1--- -—i---1
2
3
5
- air-coupled
-diy-coupled
-40
-60
-80
-100
4
Position
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RP21 200 kHz Couplant Comparison
Frozen
Moisture Content 28%
— air-coupied
—^—dry-coupled
Poskion
Room Temperature
Moisture Content 17%
- air-coupled
- dry-coipledl
H
Position
10-Hour Dry
Moisture Content 2%
—»—air-coupled
diy-coupled
Position
25-Hour Dry
Moisture Content 0%
0
.q
Xfl
M /*N
I t
H
-20
-
-40 -60 -80 -100
-
Poskion
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
RP24 200 kHz Couplant Comparison
Frozen
Moisture Content 41%
pa
T5
-20 1
air-coupled
dry-coupled
-40 H
gel-coupled
-60
Position
Room Temperature
Moisture Content 19%
-30 H
—#— air-coupled
dry-coupled
-70
A
—
gel-coupfed
Position
10-Hour Dry
Moisture Content 2.4%
0
—e—air-coupled
-®—dry-coupled
-g>—gel-coupled
-100
J —
—
- —
—
-
Position
25-Hour Dry
Moisture Content 0%
-20
-
—♦ — air-coupled
dry-coupled
-® — get-coupled
Poskion
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APPENDIX C
NONCONTACT ULTRASOUND C-SCANS
100 kHz BEST RANGE
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NCA 1000 Settings for all 100 kHz Experiments
NCA Sellings
Frequency:
1 1 3 .0 0
tJcBs)
B an d w id th :
22.00
(M is)
( %)
C h irp
S tep
A:
(%)
C h irp
Step
B :
8
o
o
50.00
&
<n
a
o
o
Ampl i t u d e :
(%)
Im age
S iz e :
(51,51)
Step
Size:
1.00
( mam)
Frozen Wood Dimension:
4 in. x 4 in. x 1in.
Scan Dimensions:
50 mm x 50 mm x 50 mm x 50 mm
as marked by arrows on photograph
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274
Red Pine Sample 3
100 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Content: 22.2%
No bowing, no cracking
Moist Content:28.7 %
N o cracks, no knots
i
■9.55
*
-16
-4.37
21.8
10.2
Color Scale (dB)
-4.98
-7.27
-2.69
Color Scale (dB)
-
25-Hour Dry
Moist. Content: 0.1%
No bowing, no cracking
16-Hour Dry
Moist. Content: 3.4%
No bowing, no cracking
K
Not Available
-0 2 7
|
025
-0.001
0.51
Color Scale (dB)
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0.77
275
Red Pine Sample 9
1 0 0 KHz c-scan image
Best Range
Photo not available
Room Temperature
Frozen Wood
Moist Content: 22.7%
N o bowing, no cracking
Moist Content: 30.6 %
No cracks, no knots
-8.23
!
-3.45
1
I
1.34
5.84
-1.06
Color Scale (dB)
-10.2
-2.97
-6.57
0.62
Color Scale (dB)
25-Hour Dry
10-Hour Dry
Moist. Content: 1.0%
No bowing, no cracking
Not Available
-5.37
--------- i----------1.71
-3.54
0.11
Color Scale (dB)
1.94
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4.22
276
Red P in e Sample 10
100 K H z c-scan im age
Best Range
Room Temperature
Frozen Wood
Moist Cont: 23%
N o bowing, no cracking
Moist Cont: 31.1%
No cracks, no knots
IHfajM]
inNMM
is
-3.72
-0.45
-2.08
1.19
Color Scale (dB)
2.82
-4.32
-0.38
-2.35
1.59
Color Scale (dB)
3.56
25-Hour Dry
10-Hour Dry
Moist. Cont: <0.0%
N o bowing, no cracking
Moist. Cont: 0.7%
N o bowing, no cracking
!-----------
-2.27
1.08
-0.60
2.75
Color Scale (dB)
4.43
-1.04
-0.19
0.61
0.23
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
0.66
277
Red Pine Sample 12
100 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 28.2%
N o cracks, no knots
Not Available
-4
-0.06
-2.03
1.91
Color Scale (dB)
3.88
25-Hour Dry
10-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
Moist. Cont: 1.1%
No bowing, no cracking
-0.10
3.64
1.77
5.51
Color Scale (dB)
7.38
-0.06
2.03
1.91
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
3.88
278
Red Pine Sample 13
100 K H z c-scan im age
Best Range
Photo not available
Frozen Wood
Room Temperature
Moist Cont: 27.7 %
No crack, no knots
Moist Cont: 21.9%
No bowing, no cracking
----------- i-----------
•10.7
-0.18
-5.41
-8.03
-2.79
Color Scale (dB)
-10.2
25-Hour Dry
10-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
Moist. Cont: 0.7%
N o bowing, no cracking
-8.6
-4.63
-6.62
-2.65
Color Scale (dB)
1.57
-4.32
-7.26
-1.38
Color Scale (dB)
-
0.66
-0.19
0.33
0.07
0.59
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
0.85
279
Red Pine Sample 14
100 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 22.5 %
Bowed up, no cracking
Not Available
1-----------
-7.14
6.94
-0.10
-3.62
3.42
Color Scale (dB)
25-Hour Dry
10-Hour Dry
Moist. Cont: 0 %
Bowed up, no cracking
Moist. Cont: 4.4 %
Bowed up, no cracking
S 25
if!)
-Til
_____
5
-12.5
■12.5
10
15
Displacement (mm)
-2.92
30
I
1.86
-2.92
-7.69
1.86
Color Scale (dB)
6.64
T
-1.44
0.22
-0.61
-
1.02
0.20
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-
280
Red Pine Sample 16
100 KHz c-scan image
Best Range
Frozen Wood
Room Temperature
Moist Cont: 27.8 %
No crack, no knots
Moist Cont: 20.4%
No bowing, no cracking
15
is p la c e m errt (m m )
-1.27
-12.5
-18.1
2C
-6.88
4.34
-12.5
-1.27
Color Scale (dB)
-10.4
4.78
I
-2.81
-6.61
-0.98
Color Scale (dB)
25-Hour Dry
10-Hour Dry
Moist. Cont: 0%
N o bowing, no cracking
Moist. Cont: 4.5%
No bowing, no cracking
K' s a w
-14.3
-5.45
-9.87
-1.02
Color Scale (dB)
3.4
-1.12
-0.50
0.81
-0.19
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
0.12
281
Red Pine Sample 19
100 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 22.4%
bowed up, no cracking
Moist Cont: 30.5%
No cracks, no knots
i
10
15
20
pispfocernertt (m m l
-3.18
-24.5
3.94
-10.3
-17.4
-3.18
Color Scale (dB)
■13.1
Moist. Cont: 0%
Bowed up, no cracking
Moist. Cont:3.2 %
bowed up, no cracking
kj
V
\
jjpl
IlylpSlf'■
s$i&
sca
mmm flPfl
.4■
t;
i
ft
{
i
5.67
25-Hour Dry
10-Hour Dry
V
■
-3.69
-8.38
0.99
Color Scale (dB)
i
id
1
-11.7
-1.64
-6.65
3.37
Color Scale (dB)
8.38
-1.19
3.6
1.21
5.99
Color Scale (dB)
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout perm ission.
8.39
282
Red Pine Sample 21
100 K H z c-scan im age
Best Range
Room Temperature
Frozen Wood
Moist Cont: 17.3%
No bow ing, no cracking
if
Not Available
-2.23
2.82
0.30
5.35
Color Scale (dB)
7.88
25-Hour Dry
10-Hour D ry
Moist. Cont:0%
Bowed down, nc
Moist. Cont: 1.7%
Bowed down, no cracking
■
%
(-----------
-2.55
3.09
0 27
5 92
’ Color Scale (dB)'
!-----------
8.74
-1.24
3.73
1.24
6.21
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
8.7
283
Red Pine Sample 24
100 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 41.0 %
N o cracks, no knots
Not Available
0
:
15
20
25
--s . - p - frnm)
-6.41
-21.4
-21.4
4.62
-8.41
-14.9
-1.89
Color Scale (dB)
25-Hour Dry
10-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
Moist. Cont: 2.4%
Bowed up, no cracking
" F in sc " --—
i
**
10
15
20
D i^ p lsce m a n t fm m l
■
-6.59
-11.5
-1.67
-6.59
3.25
Color Scale (dB)
■
8.18
8.18
j-----------
-1.23
3.85
1.31
6.39
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
8.93
APPENDIX D
NONCONTACT ULTRASOUND C-SCANS
100 kHz COMMON RANGE
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
NCA 1000 Settings for all 100 kHz Experiments
NCA Settings
Frequency:
Ban dw i d th .:
Antpl i t u d e :
C h i r p S t e p A:
Chirp S t e p B :
Im age
Size:
S tep
Siz e :
119.00
22.00
(kHz)
(kHz)
50.00
(%)
45.00
( %)
45.00
( %)
(51,51)
1.00 (mm)
Frozen Wood Dimension:
4 in. x 4 in. x 1 in.
Scan Dimensions:
50 mm x 50 mm x 50 mm x 50 mm
as marked by arrows on photograph
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
286
Red Pine Sample 3
100 KHz c-scan image
C om m on R ange
Room Temperature
Frozen Wood
Moist Cont: 22.2%
No bowing, no cracking
Moist Cont: 28.7%
No cracks, no knots
-22
-11.7
I
-16.8
-6.5
Color Scale (dB)
10-Hour Dry
-1.33
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
Not Available
|
-11.7
16.8
-6
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
287
Red Pine Sample 9
100 KHz c-scan image
Common Range
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 22.7%
No bowing, no cracking
Moist Cont: 30.6%
No cracks, no knots
-22
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 1.0%
No bowing, no cracking
Moist. Cont: 0.2%
No bowing, no cracking
Not Available
-22
-11.7
■ |
16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
288
Red Pine Sample 10
100 KHz c-scan image
C om m on R ange
Room Temperature
Frozen Wood
Moist Cont: 23%
No bowing, no cracking
Moist Cont: 31.1%
No cracks, no knots
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
i
1-------1-------r~
|
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
10-Hour Dry
Moist. Cont: 0.7%
No bowing, no cracking
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
289
Red Pine Sample 1 2
100 KHz c-scan image
C om m on R ange
Room Temperature
Frozen Wood
Moist Cont: 28.2%
No cracks, no knots
■
tM
Not Available
-22
|
ML7
|
-16.8
-6.5
Color Scale (dB)
-L33
25-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
10-Hour Dry
Moist. Cont: 1.1%
No bowing, no cracking
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
■1.33
290
Red Pine Sample 13
100 KHz c-scan image
C om m on R ange
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 21.9%
No bowing, no cracking
Moist Cont: 27.7%
No cracks, no knots
-22
-11.7
16.8
-6.5
Color Scale (dB)
-1.33
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
■1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 0.7%
No bowing, no cracking
Moist. Cont:0%
No bowing, no cracking
!----------
-22
|
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
291
Red Pine Sample 14
100 KHz c-scan image
C om m on Mange
Room Temperature
Frozen Wood
Moist Cont: 22.5%
Bowed up, no cracking
Not Available
-22
15
arpeititmofl
-1.33
25-Hour Dry
Moist. Cont: 0%
Bowed up, small crack
10-Hour Dry
Moist. Cont: 4.4%
Bowed up, no cracking
tO
I
-11.7
-16.8
-6.5
Color Scale (dB)
20
i---------------1---22
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
292
Red Pine Sample 16
100 KHz c-scan image
C om m on R ange
Room Temperature
Frozen Wood
Moist Cont: 27.8%
No cracks, big knots
Moist Cont: 20.4%
No bowing, no cracking
9
r
■:
is
20
P iB p la c B frie rl fm m l
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
Moist. Cont: 4.5%
Bowed down, no cracking
,
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: o%
Bowed down, no cracking
10-Hour Dry
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
|
,
I
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
293
Red Pine Sample 19
100 KHz c-scan image
C om m on R ange
Room Temperature
Moist Cont: 22.4%
Bowed up, no cracking
Frozen Wood
Moist Cont: 30.5%
No cracks, no knots
i£.j
V 'v
E
_
10
IS
20
Displacement f m m t
25
_
-16.8
-22
-11.7
16.8
-6.5
Color Scale (dB)
-1.33
-22
up
V
M
-1.33
25-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
10-Hour Dry
Moist. Cont: 3.2%
Bowed up, no cracking
■
-11.7
j
16.8
-6.5
Color Scale (dB)
'
■ U
1
-22
!
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
,
-1.33
l
-22
!
l
I
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
l
-1.33
294
Red Pine Sample 21
100 K H z c-scan im age
Common Range
.j
(
I
Frozen Wood
Room Temperature
Moist Cont: 17.3%
No bowing, no cracking
Not Available
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
10-Hour Dry
Moist. Cont: 1.7%
Bowed down, no cracking
25-Hour Dry
Moist. Cont: 0%
Bowed down, no cracking
|
-11.7
|
-16.8
-6.5
Color Scale (dB)
|
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
-1.33
295
Red Pine Sample 24
100 KHz c-scan image
C om m on R ange
Room Temperature
Frozen Wood
Moist Cont: 41%
No cracks, no knots
Not Available
1
-1.33
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 2.4%
Bowed up, no cracking
5
10
'5
20
Moist. Cont: 0%
Bowed up, no cracking
25
D isplacem ent fmml
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
APPENDIX E
NONCONTACT ULTRASOUND C-SCANS
200 kHz BEST AND COMMON RANGE
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
NCA 1000 Settings for all 200 kHz Experiments
NCA Sellings
Frequency:
(kHz)
202.00
o
o
i
Dl
e»
id th :
ftropl i t m d e :
C h i r p S t e p A:
50.00
( %)
45.00
(%)
C h ir p
45.00
( %)
£ andw
S tep
£:
Im age
S i z e :
S tep
S i s e :
(kHz)
(51,51)
1.00
( mm)
Frozen Wood Dimension:
4 in. x 4 in. x 1 in.
Scan Dimensions:
50 mm x 50 mm x 50 mm x 50 mm
As marked by arrows on photograph
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
298
Red Pine Sample 3
200 KHz c-scan image
Best and Common Range
Room Temperature
Moist Cont: 22.2%
No bowing, no cracking
Frozen Wood
Moist Cont: 28.7%
No cracks, no knots
l
-22
|
l
I
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
I
-1.33
------------ 1-------------j-------------.-----------
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
10-Hour Dry
Moist. Cont: 3.4%
No bowing, no cracking
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-1117
|
16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
-1.33
299
Red Pine Sample 9
200 KHz c-scan image
Best and Common Range
Photo not available
Room Temperature
Moist Cont: 22.7%
No bowing, no cracking
Frozen Wood
Moist Cont: 30.6%
No cracks, no knots
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
■1.33
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
25-Hour Dry
10-Hour Dry
Moist. Cont: 1.0%
No bowing, no cracking
Not Available
-22
-11.7
16.8
-6.5
Color Scale (dB)
-1.33
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission
-1.33
300
Red Pine Sample 10
200 KHz c-scan image
Best and Common Range
Room Temperature
Frozen Wood
Moist Cont: 31.1%
No cracks, no knots
i
-22
Moist Cont: 23%
No bowing, no cracking
---------- 1---------- r~
-11.7
I -1.33
-16.8
-6.5
Color Scale (dB)
Moist. Cont: 0.7%
No bowing, no cracking
-11.7
|
-16.8
-6.5
Color Scale (dB)
!
|
-11.7
|
-16.8
-6.5
Color Scale (dB)
!
-1.33
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
10-Hour Dry
-22
-22
-1.33
I---------- 1---------- 1---------- !---------1
-22
I
-11.7
I -1.33
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited without perm ission.
301
Red Pine Sample 12
200 KHz c-scan image
Best and Common Range
Room Temperature
Frozen Wood
Moist Cont: 28.2%
No cracks, no knots
Moist Cont: 16.7%
No bowing, no cracking
1------------ 1—
-22
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
Moist. Cont: 0.1%
No bowing, no cracking
Moist. Cont: 1.1%
No bowing, no cracking
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited without perm ission.
-1.33
302
Red Pine Sample 13
200 KHz c-scan image
Best and Common Range
Photo unavailable
Room Temperature
Frozen Wood
Moist Cont: 21.9%
No bowing, no cracking
Moist Cont: 27.7%
No cracks, no knots
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
■1.33
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 0.7%
No bowing, no cracking
Moist. Cont: 0%
No bowing, no cracking
-16.8
-6.5
Color Scale (dB)
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
303
Red Pine Sample 14
200 KHz c-scan image
Best and Common Range
Room Temperature
Frozen Wood
Moist Cont: 22.5%
Bowed up, no cracking
Moist Cont: 27.2%
No cracks, big knot
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: %
Bowed up, no cracking
Moist. Cont: 0%
Bowed up, small crack
H H
1
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
•1.33
304
Red Pine Sample 16
200 KHz c-scan image
Best and Common Range
■B
Iwmm
Room Temperature
Moist Cont: 20.4%
No bowing, no cracking
Frozen Wood
Moist Cont: 27.8%
No cracks, big knot
-22
l
-11.7
i
|
16.8
-6.5
Color Scale (dB)
i
-1.33
10-Hour Dry
Moist. Cont: 4.5%
Bowed down, no cracking
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
25-Hour Dry
Not Available
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
305
Red Pine Sample 19
200 KHz c-scan image
Best and Common Range
Room Temperature
Moist Cont: 22.4%
Bowed up, no cracking
Frozen Wood
Moist Cont: 30.5%
No cracks, no knots
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
Moist. Cont: 3.2%
Bowed up, no cracking
I
-22
-11.7
16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
-1.33
306
Red Pine Sample 21
200 KHz c-scan image
Best and Common Range
I
Room Temperature
Frozen Wood
Moist Cont: 28.2%
No cracks, no knots
Moist Cont: 17.3%
No bowing, no cracking
1
-22
-11.7
16.8
-6.5
Color Scale (dB)
■1.33
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
Moist. Cont: 1.7%
Bowed down, no cracking
25-Hour Dry
Moist. Cont:0%
Bowed down, no cracking
-16.8
-6.5
Color Scale (dB)
-11.7
|
16.8
-6.5
Color Scale (dB)
10-Hour Dry
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
Red Pine Sample 24
200 KHz c-scan image
Best and Common Range
Room Temperature
Frozen Wood
Moist Cont: 41.0%
No cracks, no knots
Not Available
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 2.4%
Bowed up, no cracking
Not Available
-22
-11.7
I
-16.8
-6.5
Color Scale (dB)
■1.33
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
APPENDIX F
NONCONTACT ULTRASOUND C-SCANS
500 kHz BEST RANGE
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
NCA 1000 Settings for all 500 kHz Experiments
NCA Settings
Fr
e q p ie n c y :
480.00
(kH z)
B and™ i d th .:
180.00
(kH z)
A w p litu d e:
5 0 .0 0
(%)
A:
S tep B :
4 5.00
(%)
45.0 0
(%)
C hirp
C hirp
Step
Im age
5 i z e :
Step
S i s e :
(5 1 ,5 1 }
1 .0 0
( man)
Frozen Wood Dimension:
4 in. x 4 in. x 1 in.
Scan Dimensions:
50 mm x 50 mm x 50 mm x 50 mm
As marked by arrows on photograph
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
310
Red Pine Sample 3
500 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 28.7%
No cracks, no knots
1
23
Moist Cont: 22.2%
No bowing, no cracking
" 1....
-13.2
|
-3.48
-8.36
-1 8.1
Color Scale (dB)
-31.3
22.1
|
-13
|
-26.7
-17.5
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
10-Hour Dry
Moist. Cont: 3.4 %
No bowing, no cracking
n
27.6
-16
1
-1 0.2
-21.8
Color Scale (dB)
-4.37
-28.4
i
-16.4
-22.4
-10.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-4.53
311
Red Pine Sample 9
500 KHz c-scan image
Best Range
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 22.7%
No bowing, no cracking
m
Not Available
-32.6
25-Hour Dry
Moist. Cont: 0.2%
Slight bowing, no cracking
10-Hour Dry
Moist. Cont: 1.0%
No bowing, no cracking
-25.8
-13.7
19.7
-7.63
Color Scale (dB)
-16.5
-24.5
-28.5
-2 0.5
Color Scale (dB)
-1.58
-23
-1.33
-12.2
-17.6
-6.76
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
312
Red Pine Sample 10
500 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 23%
No bowing, no cracking
Moist Cont: 31.1%
No cracks, no knots
-14.9
|
-5.06
|
4.77
-9.98
-0.15
Color Scale (dB)
-28
|
-18.1
|
-8.24
-23
-13 2
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
10-Hour Dry
Moist. Cont: 0.7%
No bowing, no cracking
I
-12.9
I
-2.76
|
-7.81
2.3
Color Scale (dB)
7.35
-3.32
|
5.28
-7.61
0.98
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
313
Red Pine Sample 12
500 KHz c-scan image
Best Range
Frozen Wood
Room Temperature
Not Available
Not Available
10-Hour Dry
Moist. Cont: 1.1%
No bowing, no cracking
25-Hour Dry
-1L8
|
^A08
|
163
-7.93
-0.22
Color Scale (dB)
Moist. Cont: 0.1%
No bowing, no cracking
I---------- 1---------- 1---------- !---------1
-14.5
I
-5.23
I 4.01
-9.84
-0.61
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
314
Red Pine Sample 1 3
500 KHz c-sean image
Best Range
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 27.7%
No cracks, no knots
l
-28.6
|
l
I
l
I
-17.2
|
-5.71
-22.9
-11.4
Color Scale (dB)
10-Hour Dry
Moist Cont: 21.9%
No bowing, no cracking
I---------- 1---------- 1---------- 1---------1
-32.1
|
-22.7
I -13.3
-27.4
-18
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
Not Available
I
-30.8
|
I
1
l
I
-18.5
I -6.22
-24.7
-12.4
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
315
Red Pine Sample 14
500 KHz c-scan image
Best Range
Room Temperature
Frozen Wood
Moist Cont: 27.2%
No cracks, big knot
Moist Cont: 22.5%
Bowed up, no cracking
J
-19.2
I
-5.7
I 7.79
-12.4
1.05
Color Scale (dB)
10-Hour Dry
Moist. Cont: 4.4%
Bowed up, no cracking
-19.3
8.6
-5.33
-12.3
1.63
Color Scale (dB)
-26.1
-13.2
I -0.23
-19.7
-6.71
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0%
Bowed up, small crack
-24.3
-8.74
I 6.84
-16.5
-0.95
Color Scale (dB)
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout perm ission.
316
Red Pine Sample 16
500 KHz c-scan image
Best Range
Room Temperature
Moist Cont: 20.4%
No bowing, no cracking
Frozen Wood
Moist Cont: 27.8%
No cracks, big knot
-29.1
-
-3.9
I
-16.5
22.8
10.2
Color Scale (dB)
-30
I
-21
I -12.1
-25.5
-16.6
Color Scale (dB)
-
10-Hour Dry
Moist. Cont: 4.5%
Bowed down, no cracking
25-Hour Dry
Moist. Cont: 0%
Bowed down, no cracking
1
-24.1
I
-14.8
|
-5.49
-19.4
-10.1
Color Scale (dB)
-30.4
-20.5
10.6
-25.5
-15.6
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-
317
Red Pine Sample 19
500 KHz c-scan image
Best Range
Frozen Wood
Moist Cont: 30.5%
No cracks, no knots
Room Temperature
Moist Cont: 22.4%
Bowed up, no cracking
PI
-27.7
I
-16.1
I -4.6
-21.9
-10.4
Color Scale (dB)
10-Hour Dry
Moist. Cont: 3.2%
Bowed up, no cracking
r
-21.5
T
0.36
|
-10.6
-16.1
-5.12
Color Scale (dB)
I---------- 1---------- 1---------- p
-29.8
I
-20.6
I
-25.2
-16
Color Scale (dB)
-11.5
25-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
I------------ 1------------ 1------------ 1---------- 1
-25.3
I
-13.4
I -1.4
-19.3
-7.38
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
318
Red Pine Sample 2 1
500 KHz c-scan image
Best Range
Frozen Wood
Moist Cont: 28.2%
No cracks, no knots
Room Temperature
Moist Cont: 17.3%
No bowing, no cracking
1%
-16.7
-7.22
|
2.24
-11.9
-2.49
Color Scale (dB)
10-Hour Dry
Moist. Cont: 1.7%
Bowed down, no cracking
-13.6
|
-1.57
-7.56
4.42
Color Scale (dB)
-28.5
I
-19
I -9.45
-23.7
-14.2
Color Scale (dB)
25-Hour Dry
Moist. Cont: 0%
Bowed down, no cracking
-2.38
-7.27
2.51
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
319
Red Pine Sample 24
500 KHz c-scan image
Best Range
Frozen Wood
Room Temperature
Not Available
Not Available
25-Hour Dry
10-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
Moist. Cont: 2.4%
Bowed up, no cracking
-20.7
-8.88
|
2.96
-14.8
-2.96
Color Scale (dB)
r
-25.4
T
3.82
I
-10.8
-18.1
-3.49
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
APPENDIX G
NONCONTACT ULTRASOUND C-SCANS
500 kHz COMMON RANGE
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
NCA 1000 Settings for all 500 kHz Experiments
NCA Settings
Tr e q m e n c y :
Ba n d w i d t h :
A m p li t u d e :
C h ir p S t e p A:
480.00
(kH z)
180.00
(kHz)
C hirp
Step
B :
Im a g e S i z e :
S te p Size:
50.00
(%)
45.00
( %)
45.00
( %)
(51,51)
1.00
(mm)
Frozen Wood Dimension:
4 in. x 4 in. x 1 in.
Scan Dimensions:
50 mm x 50 mm x 50 mm x 50 mm
As marked by arrows on photograph
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited without perm ission.
322
Red Pine Sample 3
500 KHz c-scan image
Common Range
Room Temperature
Moist Cont: 22.2%
No bowing, no cracking
Frozen Wood
Moist Cont: 28.7%
No cracks, no knots
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
Moist. Cont: 3.4%
No bowing, no cracking
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0.1%
No bowing, no cracking
10-Hour Dry
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
323
Red Pine Sample 9
500 KHz c-scan image
Common Range
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 22.7%
No bowing, no cracking
Moist Cont: 30.6%
No cracks, no knots
-22
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
Moist. Cont: 0.2%
Bowed up, no cracking
Moist. Cont: 1.0%
No bowing, no cracking
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
324
Red Pine Sample 10
500 KHz c-scan image
Common Range
Room Temperature
Frozen Wood
Moist Cont: 31.1%
No cracks, no knots
-22
-11.7
-16.8
-6.5
Color Scale (dB)
Moist Cont: 23%
No bowing, no cracking
-1.33
-22
10-Hour Dry
Moist. Cont: 0.7%
No bowing, no cracking
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
I
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
325
Red Pine Sample 12
500 KHz c-scan image
Common Mange
Room Temperature
Frozen Wood
Not Available
Not Available
25-Hour Dry
10-Hour Dry
Moist. Cont: 1.1 %
No bowing, no cracking
Moist. Cont: 0.1%
No bowing, no cracking
III
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
-16.8
-6.5
Color Seale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
326
Red Pine Sample 13
500 KHz c-scan image
Common Range
Photo not available
Room Temperature
Frozen Wood
Moist Cont: 21.9%
No bowing, no cracking
Moist Cont: 27.7%
No cracks, no knots
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
10-Hour Dry
-1.33
-22
|
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0%
No bowing, no cracking
Not Available
1--I----------------22
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
327
Red Pine Sample 14
500 KHz c-scan image
Common Range
Room Temperature
Frozen Wood
Moist Cont: 22.5%
Bowed up, no cracking
Moist Cont: 27.2%
No cracks, big knot
-22
-11.7
|
-16.8
-6.5
Color Scale (dB)
-1.33
l
-22
-1.33
25-Hour Dry
Moist. Cont: 0%
Bowed up, small crack
10-Hour Dry
Moist. Cont: 4.4%
Bowed up, no cracking
I---------- 1---------- 1--------22
I
-11.7
-16.8
-6.5
Color Scale (dB)
I
l
I
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
328
Red Pine Sample 16
500 KHz c-scan image
Common Range
jrfs
Room Temperature
Moist Cont: 20.4%
No bowing, no cracking
Frozen Wood
Moist Cont: 27.8%
No cracks, big knot
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 4.5%
Bowed down, no cracking
Moist. Cont: 0%
Bowed down, no cracking
I
-22
I
-11.7
-16.8
-6.5
Color Scale (dB)
■1.33
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited without perm ission.
-1.33
329
Red Pine Sample 19
500 KHz c-scan image
Common Range
Room Temperature
Frozen Wood
Moist Cont: 22.4%
Bowed up, no cracking
Moist Cont: 30.5%
No cracks, no knots
----------------------------------
-22
1----------- j—
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
10-Hour Dry
Moist. Cont: 3.2%
Bowed up, no cracking
-22
|
-11.7
-16.8
-6.5
Color Scale (dB)
Moist. Cont: 0%
Bowed up, no cracking
-1.33
-22
-11.7
I
16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited without perm ission.
-1.33
330
Red Pine Sample 21
500 KHz e-scan image
Common Range
Room Temperature
Frozen Wood
Moist Cont: 17.3%
No bowing, no cracking
Moist Cont: 28.2%
No cracks, no knots
-22
-11.7
-16.8
-6.5
Color Scale (dB)
-1.33
-22
-11.7
16.8
-6.5
Color Scale (dB)
-1.33
25-Hour Dry
Moist. Cont: 0%
Bowed down, no cracking
10-Hour Dry
Moist. Cont: 1.7%
Bowed down, no cracking
-22
-11.7
I
16.8
-6.5
Color Scale (dB)
-1.33
I------------ 1------------ 1------------ 1---------- 1
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
-1.33
331
Red Pine Sample 24
KHz c-scan image
Common Range
500
Frozen Wood
Room Temperature
Not Available
Not Available
25-Hour Dry
Moist. Cont: 0%
Bowed up, no cracking
10-Hour Dry
Moist. Cont: 2.4%
Bowed up, no cracking
I----------- 1----------- 1------------1----------1
-22
I
-11.7
I
-16.8
-6.5
Color Scale (dB)
-1.33
I
-22
:-------1-------------1-------------1-----------1
I
-11.7
|
-16.8
-6.5
Color Scale (dB)
R ep ro d u ced with p erm ission o f th e copyright ow ner. Further reproduction prohibited w ithout perm ission.
-1.33
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