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JP2005086797

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DESCRIPTION JP2005086797
The present invention provides a serpentine coil type electromagnetic ultrasonic transducer
which has high sensitivity, less random noise and is not easily damaged. In a meandering coil
type electromagnetic ultrasonic transducer including a meandering coil for generating an
alternating magnetic field and a magnet for forming a static magnetic field, a linear circuit made
of a conductive material is periodically formed on one side of an insulating sheet to conduct
these. A composite serpentine sheet coil is used in which a plurality of serpentine coils, all of
which are equally spaced apart in parallel straight portions on one side of a single insulating
sheet, bonded with a conductive material. Alternatively, a multi-layered composite serpentine
sheet coil is used in which a plurality of the above-mentioned composite serpentine sheet coils
are stacked and joined together by conductive external leads. Alternatively, a metal plate or alloy
plate having an electrical resistivity of greater than 40 × 10 Ωcm and a thickness of 0.01 mm or
more and 1 mm or less is provided on the surface of the meandering sheet coil on the measured
material side to protect the meander sheet coil. Further, the ground side terminal of the
serpentine sheet coil is bonded to the metal plate or the alloy plate with a conductive material.
[Selected figure] Figure 1
Electromagnetic ultrasonic transducer
[0001]
The present invention relates to an electromagnetic ultrasonic transducer for detecting flaws on
or in the surface of a conductive material, measuring residual stress, and measuring material
properties.
[0002]
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FIG. 2 is a view showing a schematic configuration of a conventional meandering coil type
electromagnetic ultrasonic transducer.
Fig.2 (a) is the figure seen from the bottom side, FIG.2 (b) is the figure seen from the side. As
shown in FIG. 2, the meandering coil type electromagnetic ultrasonic transducer arranges a
meandering coil 2 made of a conductive material on a flat plate-like steel plate 1 which is an
object to be measured, and forms a static magnetic field on the top 3 is arranged. The spacings of
the parallel lines that make up the serpentine coil must all be equal. Also, electromagnets are
used instead of permanent magnets. The electrically insulating material 4 (ceramics, mica, heat
resistant plastic, etc.) protects the meandering coil 2.
[0003]
When a high frequency current is applied to the meandering coil 2 of such a meandering coil
type electromagnetic ultrasonic transducer, induced high frequency currents in opposite
directions flow alternately on the surface of the flat steel plate 1 directly below the meandering
coil 2. The induced high frequency current and the static magnetic field of the permanent magnet
3 interact to generate the Lorentz force. Since this Lorentz force occurs at the same interval as
the interval of the parallel lines of the serpentine coil 2 and occurs in the opposite direction to
each other, the surface of the steel plate 1 has a wavelength of twice the interval of the parallel
lines of the serpentine coil 2 Sound waves are generated. The ultrasonic wave propagates in a
direction perpendicular to the parallel line of the serpentine coil 2. This ultrasonic wave is
reflected on the end face of the steel plate 1, a surface or internal flaw, a grain boundary, a
surface where acoustic impedance such as a change in structure becomes discontinuous. This
reflected wave can be detected by a meandering coil type electromagnetic ultrasonic transducer
or a meandering coil type electromagnetic ultrasonic transducer of the same structure provided
separately. The principle of detection can be described as the reverse process of the principle of
generation. A method of generating and detecting such ultrasonic waves is also described in
"Ultrasonic Handbook", edited by the Ultrasonic Handbook Editorial Board, Maruzen Co., Ltd.,
published on Aug. 30, 1999, p. 133-140.
[0004]
By analyzing the reflected wave thus detected, it is possible to detect a flaw on the surface or
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inside, measure a residual stress, and measure a material property. However, it is well known that
the electromagnetic ultrasonic method is inefficient in emitting and receiving ultrasonic waves in
principle because the efficiency of electric / acoustic energy conversion is low. In addition, the
electrically insulating material 4 and the meandering coil 2 often contact the surface of the flat
steel plate 1 as the object to be measured, resulting in breakage. Such breakage can be largely
prevented if the distance between the electrically insulating material 4 and the surface of the
object to be measured is several millimeters or more, but in the case of the electromagnetic
ultrasonic method, ultrasonic waves are emitted and received when the distance is increased. It is
known that the efficiency rapidly deteriorates. In order to compensate for this, it is necessary to
use a large amplification amplifier to amplify a small ultrasonic signal. Since an amplifier with a
large amplification factor simultaneously amplifies minute random noise, a target reflected wave
tends to be buried in the random noise, which is the largest cause of false detection.
[0005]
In order to solve the above-mentioned drawbacks, Japanese Patent Application Laid-Open No. 9166584 proposes an invention for improving the transmission / reception performance of a
serpentine coil type electromagnetic ultrasonic transducer. The first is disclosed in claims 2 and
3 of JP-A-9-166584 and FIG. 4 of JP-A-9-166584, and meandering coils made of a conductive
material are provided on both sides of the insulation sheet through the insulation sheet. It is a
meandering sheet coil arranged to face each other. No. 2 is disclosed in FIG. 1 of JP-A-9-166584,
and three meandering coils are formed on one side of the insulating sheet.
[0006]
The inventions disclosed in claim 2, 3 and 4 of the above-mentioned JP-A-9-166584 require that
serpentine coils must be formed on both sides of the insulating sheet, and the manufacturing
process is complicated and the manufacturing cost is large. There was a drawback of that.
[0007]
There is also a drawback in the invention of forming three meandering coils disclosed in FIG. 1 of
JP-A-9-166584 on one side of the insulating sheet.
In order to explain this drawback, a diagram of FIG. 1 of JP-A-9-166584 is shown in FIG. 3 of the
present invention. In FIG. 3, three meandering coils of the meandering coil 5, the meandering coil
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6, and the meandering coil 7 are formed on one side of the insulating sheet so as not to be in
electrical contact with each other. As can be seen immediately from FIG. 3, it is inevitable that the
meandering coil 5 and the meandering coil 7 can have two types of spacing between parallel
lines. As described in paragraph 0002 of the present invention, the intervals of the parallel lines
of the serpentine coil must all be equal, and therefore, if there are two large and small intervals
between the parallel lines, the transmission / reception performance will be impaired. There is a
drawback that the expected transmission and reception performance can not be obtained.
[0008]
In order to prevent the meandering coil from breaking due to contact with the unevenness which
sometimes exists on the surface of the object to be measured, the thin plate-like material having
heat insulation resin, mica, ceramics, etc. Although it is usual to set it between the surface of the
object to be measured, these electrically insulating protective materials are generally weak to
mechanical impact and can not sufficiently prevent breakage of the serpentine coil. Using a metal
plate that is strong and excellent in toughness as a protective material is ideal as a failure
prevention method, but the so-called electromagnetic skin effect of the metal plate on the high
frequency electromagnetic field causes an electromagnetic coupling between the serpentine coil
and the object surface Is generally considered to be significantly inhibited, which in turn
significantly reduces the transmission and reception performance of ultrasound.
[0009]
In order to solve the above-mentioned problems, the invention according to claim 1 is a
meandering coil type electromagnetic ultrasonic transducer comprising a meandering coil for
generating an alternating current magnetic field and a magnet for forming a static magnetic field.
A metal plate or alloy plate having a thickness of greater than 40 × 10 <-6> Ωcm and a
thickness of 0.01 mm or more and 1 mm or less is provided on the surface of the meandering
coil on the side of the material to be measured. So far, it has generally been considered that the
so-called electromagnetic skin effect of the metal plate on the high frequency electromagnetic
field significantly inhibits the electromagnetic coupling between the meandering coil and the
surface of the object to be measured and thus significantly reduces the transmission and
reception performance of ultrasonic waves. The However, the inventor of the present invention
significantly reduces the generation and reception performance of ultrasonic waves if the metal
plate or alloy plate has an electrical resistivity of 40 × 10 <-6> Ωcm and a thickness of 0.01 mm
or more and 1 mm or less. It has been discovered that it can be used to protect meandering coils
without
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[0010]
The invention according to claim 2 is a meandering coil type electromagnetic ultrasonic
transducer comprising a meandering coil for generating an alternating magnetic field and a
magnet for forming a static magnetic field, wherein two meandering sheet coils having a
meandering coil formed on one side of an insulating sheet The sheet is characterized in that the
number of sheets is five or less, and these are connected by a conductive external lead wire.
[0011]
In the electromagnetic ultrasonic transducer having a coil for generating an alternating magnetic
field and a magnet for forming a static magnetic field, a linear circuit made of a conductive
material is periodically formed on one side of the insulating sheet. It is characterized by using a
composite serpentine sheet coil in which these are connected by a conductive material to form 2
to 6 serpentine coils all having the same distance between parallel straight portions on one side
of one insulating sheet. Do.
[0012]
The invention according to claim 4 uses a multi-layered composite serpentine sheet coil in which
the composite serpentine sheet coil according to claim 3 is folded in two or more and five or less,
and these are joined by a conductive outer lead wire. It is characterized by
[0013]
In order to protect the meandering sheet coil according to claim 2 or claim 3 or claim 4
according to the invention described in claim 5, the electrical resistivity is larger than 40 × 10 <6> Ω cm and the thickness is A metal plate or alloy plate of 0.01 mm or more and 1 mm or less
is provided on the surface of the meandering sheet coil on the side of the material to be
measured.
[0014]
In the invention according to claim 6, the electrical resistivity provided for protection of the
ground side terminal of the meandering sheet coil according to claim 1 or 5 is greater than 40 ×
10 <-6> Ωcm and the thickness is It is characterized in that it is bonded to a metal plate or alloy
plate of 0.01 mm or more and 1 mm or less by a conductive material.
[0015]
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The best mode for carrying out the invention is an electromagnetic ultrasonic transducer
comprising a coil for generating an alternating magnetic field and a magnet for forming a static
magnetic field according to claim 6.
[0016]
Embodiments of the invention will be described based on examples and with reference to the
drawings.
FIG. 4 is a schematic view showing an outline of an electromagnetic ultrasonic inspection
apparatus according to an embodiment of the present invention.
In FIG. 4, 8 is a thick steel plate to be inspected, 9 is a small surface defect (length 1.5 cm, depth
0.3 mm), 10 is a burst wave transmitter, 11 is an electromagnetic ultrasonic wave for surface
wave transmission. Transducer 12 is a short distance (9 cm) from the electromagnetic ultrasonic
transducer 11 for surface wave transmission. The electromagnetic ultrasonic transducer for
surface wave reception 13 is an amplifier 14 is an AD converter. 15 is a data storage. 16 is a
computing unit, and 17 is an output device.
The data storage 15 is constituted by the IC memory of the computer, but may be a hard disk of
the computer instead of the IC memory.
The 11 and 12 electromagnetic ultrasonic transducers have the same structure, and FIG. 5 is a
schematic representation of this structure.
FIG. 5 (a) is a bottom view of the surface acoustic wave transmitting or receiving electromagnetic
ultrasonic transducer, and FIG. 4 (b) is a side view of the same electromagnetic ultrasonic
transducer showing the relationship with the thick steel plate 8 as the object. FIG.
In FIG. 5, 19 is a permanent magnet, 20 is a ceramic plate for protection, and 21 is a multilayer
composite serpentine sheet coil to be described in detail later. A waveform arrow 18 in FIG. 4
indicates how a surface wave transmitted by the electromagnetic ultrasonic transducer 11 for
transmitting a surface wave propagates on the surface of the steel and is reflected even if it is
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reflected by the small surface defect 9.
[0017]
The burst wave transmitter 10 transmits a burst wave current having a frequency of 1 MHz, a
wave number of 15, and a repetition frequency of 100 Hz to the electromagnetic ultrasonic
transducer 11 for surface wave transmission. Then, a surface wave is generated on the surface of
the thick steel plate 8. In FIG. 4, this surface wave first propagates to the right and is received as
a direct surface wave by the surface acoustic wave receiving electromagnetic ultrasonic
transducer 12 provided at a distance of 9 cm from the surface acoustic wave transmitting
electromagnetic ultrasonic transducer 11. Further, it propagates to the right and is reflected by
the surface defect 9 at a distance of 71 cm from the electromagnetic ultrasonic transducer 11 for
surface wave transmission and propagates to the left and the defect surface wave by the
electromagnetic ultrasonic transducer 12 for surface wave reception As received. The amplifier
13 amplifies direct surface waves and defect surface waves.
[0018]
FIG. 6 shows the result of detection of a small surface defect 9 (length 1.5 cm, depth 0.3 mm). In
FIG. 6, reference numeral 22 denotes an electric signal generated by electromagnetic induction
spaced apart by a burst wave current for ultrasonic wave transmission. 23 is a direct surface
wave, 24 is a defect surface wave, and 25 is random noise. Small surface defects 9 are clearly
detected as defect surface waves 24.
[0019]
The multi-layered composite serpentine sheet coil 21 is formed by stacking two sheets of the
composite serpentine sheet coil shown in FIG. 1 so as to completely overlap each other, and
further connecting them by a conductive outer lead wire. FIG. 7 is an enlarged view of a portion
surrounded by a two-dot chain line 26 in FIG. 8 is a cross-sectional view of the composite
serpentine sheet coil taken along the alternate long and short dash line A-B in FIG. The black
trapezoidal portion 27 in FIG. 8 is a cross section of a serpentine coil made of electrolytic copper
foil and has a thickness of 18 μm. 28, 29 are polyimides, which are one type of plastic, having a
thickness of 25 μm. 30 is an adhesive. The structure of the composite serpentine sheet coil will
now be described with reference to FIGS. 1, 7 and 8. As shown in FIGS. 1, 7 and 8, three linear
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copper foils 0.1 mm wide and 18 μm thick are arranged in parallel to each other at a spacing of
0.1 mm, and there are 32 sets is there. These 32 sets of linear copper foils are disposed parallel
to each other at a distance of 1.4 mm. All of these linear copper foils are disposed on one side of
the insulating sheet 31 of FIG. These are combined as shown in FIG. 1, but all the parts
represented by dotted lines as represented by dotted line 32 and dotted line 33 in FIG. 1 or
dotted line 32 and dotted line 33 in FIG. These linear copper foils are bonded to the back surface
of the insulating sheet 31 via The portions shown by solid lines are all arranged on one side of
the insulating sheet 31. When coupled in this manner, three meandering coils electrically isolated
from one another are formed on one side of the insulating sheet 31. The spacings of the parallel
straight portions of the three serpentine coils are all the same and 1.4 mm. The first of the three
meandering coils is connected to the terminals 34 and 35, the second is connected to the
terminals 36 and 37, and the third is connected to the terminals 38 and 39. Further, the terminal
35 and the terminal 36 are connected, and the terminal 37 and the terminal 38 are respectively
joined by the thin copper foil 40 and the thin copper foil 41. In this way, a composite serpentine
sheet coil having the terminals 34 and 39 as two terminals on one side of the insulating sheet 31
is completed. The composite serpentine sheet coil having such a structure can be manufactured
by the existing flexible circuit (printed circuit) technology, so the details of its manufacturing
method will be omitted. Further, two composite serpentine sheet coils made in this way are
stacked so as to completely overlap each other, and when these are joined with a conductive
external lead wire, a multilayer composite serpentine sheet coil 21 is completed.
[0020]
A composite serpentine sheet coil in which more than three serpentine coils are formed on one
side and these are electrically coupled can further improve performance, but since the space on
one side is limited, the serpentine coil can be formed on one side. The limit is up to six. In
addition, the performance is further improved if a multi-layer composite serpentine sheet coil in
which two or more composite serpentine sheet coils are stacked and joined is combined, but the
impedance increases in a multi-layered composite serpentine sheet coil. It was found by
experiments that the performance is deteriorated and the limit is a limit of five stacked multilayered composite serpentine sheet coils.
[0021]
In the second embodiment of the present invention, an example using an electromagnetic
ultrasonic transducer different from that of the first embodiment is shown. FIG. 9 shows an
electromagnetic ultrasonic transducer used in Example 2, but this has a 0.2 mm thick evanome
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plate 42 as a protective plate in place of the ceramic plate 20 for protection of FIG. 5 used in
Example 1. It is Evanome, also referred to as EVANOHM, is a nickel-based alloy containing
chromium, manganese, aluminum, and silicon, and is a commercially available material. The
electrical resistivity of the evanome is as large as 137 × 10 <-6> Ωcm. The other apparatus and
the test object used the same thing as what was used in Example 1.
[0022]
FIG. 10 shows the result of detection of a small surface defect 9 (length 1.5 cm, depth 0.3 mm).
In FIG. 10, reference numeral 43 denotes an electric signal generated by electromagnetic
induction spaced apart by a burst wave current for ultrasonic wave transmission. 44 is a direct
surface wave, 45 is a defect surface wave, and 46 is random noise. Small surface defects 9 are
about 50% less sensitive than in Example 1 but are clearly detected as defect surface waves 45.
Further, the experiment was conducted by electrically connecting the ground side terminal 47 of
the multilayer composite serpentine sheet coil 21 of the above-mentioned electromagnetic
ultrasonic transducer to the above-mentioned evanome plate 42 for protection with a copper
wire 48. It was also found that the% decreased and the practically important S / N ratio (signal to
noise ratio) improved and the effect was large. That is, the protective plate has the effects of
protection of a meandering coil and reduction of random noise by one stone and two birds.
[0023]
As Example 3 of the present invention, an example using a metal protection plate different from
Example 2 is shown. A 0.2 mm thick titanium plate was used as a protective plate. The electrical
resistivity of titanium is also large, about 40 × 10 <-6> Ωcm. The other apparatus and the test
object used the same thing as what was used in Example 2.
[0024]
FIG. 11 shows the result of detection of a small surface defect 9 (length 1.5 cm, depth 0.3 mm).
In FIG. 11, reference numeral 49 denotes an electric signal generated by electromagnetic
induction spaced apart by a burst wave current for ultrasonic wave transmission. 50 is a direct
surface wave, 51 is a defect surface wave, and 52 is random noise. Small surface defects 9 are
about 40% less sensitive than Example 2, but are clearly detected as defect surface waves.
Furthermore, the ground side end of the multilayer composite type serpentine sheet coil 21 of
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the above-mentioned electromagnetic ultrasonic transducer was connected to the abovementioned protective titanium plate by a copper wire, but random noise was reduced by about
20%, which is important for practical use It is also found that the S / N ratio (signal to noise ratio)
is improved and the effect is large.
[0025]
As the fourth embodiment of the present invention, an example using an electromagnetic
ultrasonic transducer different from the first embodiment, the second embodiment and the third
embodiment is shown. In Example 4, an electromagnetic ultrasonic transducer having a threelayered double-layered serpentine sheet coil formed by stacking three serpentine sheet coils in
which one serpentine coil is formed on one side of the insulating sheet was used. A detailed view
of one of these three serpentine sheet coils is shown in FIG. Also by this, a small surface defect 2
(length 1.5 cm, depth 0.3 mm) could be detected clearly.
[0026]
As the fifth embodiment of the present invention, an example using an electromagnetic ultrasonic
transducer different from the first embodiment, the second embodiment, the third embodiment
and the fourth embodiment is shown. In Example 5, an electromagnetic ultrasonic transducer
used in Example 4 with an evanome plate or a titanium plate attached as a protective plate was
used. Also by this, a small surface defect 2 (length 1.5 cm, depth 0.3 mm) could be detected
clearly. Furthermore, the ground side end of the meander sheet coil of the above-mentioned
electromagnetic ultrasonic transducer was tested by bonding it with a copper wire to the abovementioned protective evanome plate or titanium plate, but random noise was reduced by about
20%, which is important for practical use It is also found that the S / N ratio (signal to noise ratio)
is improved and the effect is large.
[0027]
An example using an electromagnetic ultrasonic transducer different from the first embodiment,
the second embodiment, the third embodiment, the fourth embodiment and the fifth embodiment
is shown as the sixth embodiment of the present invention. In the sixth embodiment, the
evanome plate used in the electromagnetic ultrasonic transducer used in the fifth embodiment,
or one in which the thickness of the titanium plate is changed is used. As a result, if the thickness
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is less than 0.01 mm, the effect as a protective plate is small, and if the thickness is 1 mm or
more, the sensitivity is too low and the surface defect 2 (length 1.5 cm, depth 0.3 mm) It could
not be detected clearly. Accordingly, it has been found that a metal plate or alloy plate having an
electrical resistivity of greater than 40 × 10 <-6> Ωcm and a thickness of 0.01 mm or more and
1 mm or less is suitable as the protective plate.
Effect of the invention
[0028]
As described above, according to the present invention, the following excellent effects can be
obtained. An electromagnetic ultrasonic inspection apparatus using any one of the
electromagnetic ultrasonic transducers according to claims 1, 2, 3, 4, 5, 6 realizes an
electromagnetic ultrasonic inspection method with high sensitivity and no damage easily.
Therefore, detection of flaws on or in the surface of the conductive material, measurement of
residual stress, and measurement of material characteristics can be realized with high reliability.
[0029]
In the steel industry and the aluminum industry, it can be used for detecting flaws on the surface
or inside of steel plates and aluminum plates, measuring residual stress, and measuring material
characteristics. The electromagnetic ultrasonic transducer according to the present invention can
be manufactured according to the surface shape of the material to be measured, so it can be used
not only for plate-like materials but also for measurement of steel pipes, aluminum pipes or
rolling rollers.
[0030]
It is a figure which shows the structure of the composite-type meander sheet coil used for the
meander coil type | mold electromagnetic ultrasonic transducer of this invention. It is a figure
which shows schematic structure of the conventional meandering coil type | mold
electromagnetic ultrasonic transducer, the figure (a) is the figure seen from the bottom side, and
the figure (b) is the figure seen from the side. It is a schematic diagram of what formed the three
meandering coils currently disclosed by FIG. 1 of Unexamined-Japanese-Patent No. 9-166584 on
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the single side | surface of an insulation sheet. It is a figure for demonstrating the measurement
principle of a meandering coil type | mold electromagnetic ultrasonic transducer. FIG. 1 is a
schematic view of a meandering coil type electromagnetic ultrasonic transducer using a
multilayer composite type meandering sheet coil 21 and a ceramic plate 20 for protection
according to the present invention. The figure (a) is a figure seen from the bottom side, and the
figure (b) is a figure seen from the side. It is a figure which shows the measurement result by the
meandering-coil type | mold electromagnetic ultrasonic transducer using the multilayer
composite type meandering sheet coil 21 of this invention, and the ceramic board 20 for
protection. It is an enlarged view of the part enclosed with the dashed-two dotted line 26 of FIG.
It is the dashed-dotted line AB sectional drawing of FIG. FIG. 1 is a schematic view of a
meandering coil type electromagnetic ultrasonic transducer using a multilayer composite type
meandering sheet coil 21 and an evanome plate 42 for protection according to the present
invention. The figure (a) is a figure seen from the bottom side, and the figure (b) is a figure seen
from the side. It is a figure which shows the measurement result by the meander coil type | mold
electromagnetic ultrasonic transducer which used the multilayer composite type meandering
sheet coil 21 of this invention, and the evanome board 42 for protection. It is a figure which
shows the measurement result by the meander coil type | mold electromagnetic ultrasonic
transducer which used the multilayer composite type meandering sheet coil 21 of this invention,
and the titanium plate for protection. It is a figure which shows the structure of the meandering
sheet coil used for the meandering coil type | mold electromagnetic ultrasonic transducer of this
invention.
Explanation of sign
[0031]
Reference Signs List 1 flat steel plate 2 meandering coil 3 permanent magnet 4 electrically
insulating material 5 meandering coil 6 meandering coil 7 meandering coil 8 thick steel plate to
be inspected 9 small surface defect 10 burst wave transmitter 11 electromagnetic wave for
surface wave transmission Ultrasonic Transducers 12 Electromagnetic Ultrasonic Transducers
for Receiving Surface Waves 13 Amplifiers 14 AD Converters 15 Data Storage 16 Calculator 17
Output Device 18 Waveform Arrows Depicting Ultrasonic Propagation 19 Permanent Magnets
20 Ceramic Plates for Protection 21 Multilayer composite serpentine sheet coil 22 Electric signal
generated by electromagnetic induction separated by space by burst wave current for ultrasonic
wave generation 23 direct surface wave 24 defect surface wave 25 random noise 26 for showing
enlarged part Two-dotted line 27 Cross section 28 plastic of serpentine coil made of electrolytic
copper foil Polyimide 29 which is one of the following: polyimide 30 which is one of the plastics
30 adhesive 31 insulation sheet 32 electrically connected part of the back side of the insulation
sheet 31 33 electrically connected part of the back side of the insulation sheet 31 34 terminal 35
terminal 36 terminal 37 terminal 38 terminal 39 terminal 40 thin copper foil 41 thin copper foil
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42 evanome plate 43 electric signal generated by electromagnetic induction separated by space
by burst wave current for ultrasonic wave transmission 44 direct surface acoustic wave 45 defect
surface wave 46 random noise 47 ground side terminal 48 copper wire 49 electric signal
generated by electromagnetic induction separated by space by burst wave current for ultrasonic
wave transmission 50 direct surface wave 51 defect surface wave 52 random noise
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