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JPH04212054

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DESCRIPTION JPH04212054
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic emission sensor for detecting an acoustic emission.
[0002]
2. Description of the Related Art When a solid breaks or plastically deforms, it releases energy
stored as internal strain as an elastic wave (acoustic wave and ultrasonic wave). The elastic wave
is called AE (abbreviated as AE). Then, by observing the AE wave while applying a load to the
material, a method of complementing the precursor of the occurrence of damage or breakage in
the material, the so-called AE method, "Steel and Steel Handbook", 3rd edition, Volume IV As
described on page 468, it is applied to material fatigue testing and material research.
[0003]
A piezoelectric element as an ultrasonic wave receiving element is usually used as an AE sensor
for detecting an AE wave, but as disclosed in JP-A-51-20890, the piezoelectric element and the
object to be detected are disclosed. By making the contact portion with the sample with an
electrically insulating material and stacking the piezoelectric elements in two stages, it is
resistant to electrical noise and causes a phase difference between AE signals detected by each
piezoelectric element. A balanced AE sensor that has been made difficult has been proposed.
04-05-2019
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[0004]
By the way, when an ultrasonic wave propagates in an object, the longitudinal wave propagates
faster than the transverse wave.
For this reason, if only the longitudinal wave in the AE wave is detected, it is possible to faithfully
detect the change of the AE occurrence intensity in the AE generation source, but in the abovementioned conventional configuration, not only the longitudinal wave but also the transverse
wave is detected Have points.
[0005]
Therefore, a synthetic resin-ceramic composite in which a prismatic ceramic piezoelectric body is
polarized in the height direction so that only longitudinal waves (longitudinal vibration modes) in
AE waves can be detected. It is conceivable to use a piezoelectric element for an AE sensor.
[0006]
However, also in this case, since the frequency range of AE waves that can be detected is narrow
when detecting AE waves, the amount of information is too small to perform various signal
processing, and therefore AE waveform analysis with high accuracy Has the problem of being
unable to
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, in the acoustic
emission sensor of the present invention, a plurality of columnar ceramic piezoelectric members
are arranged such that their height directions are substantially parallel to each other. An acoustic
emission sensor for detecting acoustic emission by a synthetic resin-ceramic composite
piezoelectric element arrayed in a synthetic resin matrix, wherein the synthetic resin matrix has
different heights and has columnar columns polarized in the height direction. It is characterized
in that the ceramic piezoelectric bodies are arranged concentrically.
[0008]
According to the above configuration, since the columnar ceramic piezoelectric material is
polarized in the height direction, the synthetic resin is applied only to the longitudinal vibration
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mode in the AE wave propagating in the height direction. -A potential difference is generated on
both end surfaces of the ceramic composite piezoelectric element.
Thereby, only the longitudinal vibration mode is detected.
Further, since columnar ceramic piezoelectric bodies having different heights are used, resonance
points appear by the type of height, and the detection frequency range of AE waves becomes
wide.
Therefore, the rise time of the AE signal is shortened, the response is improved, and the detection
sensitivity is also improved. Further, since the ceramic piezoelectric members are arranged
concentrically, they are nondirectional, and substantially constant detection sensitivity can be
obtained regardless of the propagation direction of the AE wave.
[0009]
DESCRIPTION OF THE EMBODIMENTS The following will explain one embodiment of the present
invention in reference to FIG. 1 to FIG.
[0010]
The acoustic emission sensor (hereinafter referred to as AE sensor) of the present invention, as
shown in the longitudinal sectional view of FIG. 2, comprises a wave receiving plate 2 for
receiving an AE wave from an object and a wave receiving plate 2 It is mainly composed of a
synthetic resin-ceramic composite piezoelectric element 1 which is provided to convert an AE
wave into an electric signal.
[0011]
The synthetic resin-ceramic composite piezoelectric element 1 has a plurality of columnar
ceramic piezoelectric bodies 3 arranged in the synthetic resin matrix 4 so that their height
directions are almost parallel, and electrodes on both end faces 5 and 6 are provided, and an
electrode 6 'electrically connected to the electrode 6 is provided on the lower outer peripheral
surface, and in each columnar ceramic piezoelectric body 3, the crystal axis of the piezoelectric
crystal particle is It is configured to be oriented in the height direction (vertical direction in FIG.
2) and polarized in that direction.
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[0012]
Further, as shown in the cross sectional view of FIG. 1, the ceramic piezoelectric members 3 are
arranged concentrically in the synthetic resin matrix 4.
Further, on each concentric circle, the heights of the ceramic piezoelectric bodies 3 are
substantially equal, but between the concentric circles, the heights of the ceramic piezoelectric
bodies 3 are not uniform, and the ceramic piezoelectric bodies 3 having different heights are
used. .
In the present embodiment, as shown in FIG. 2, the ceramic piezoelectric body 3 is disposed so as
to be higher as it becomes concentric on the outer peripheral side.
Therefore, although the electrode 6 on the lower end surface is flat, the electrode 5 on the upper
end surface is stepped.
[0013]
The arrangement in the concentric form means that the ceramic piezoelectric bodies 3 are
arranged on the circumference of the concentric circles, and complete concentric circles can not
be formed by arranging the finite ceramic piezoelectric bodies 3. Needless to say. Therefore,
when the ceramic piezoelectric members 3 are arranged concentrically, that is, at substantially
equal distances from the center of the synthetic resin-ceramic composite piezoelectric element 1,
they form a polygon strictly.
[0014]
The electrode 6 on the lower end face of the synthetic resin-ceramic composite piezoelectric
element 1 and the wave receiving plate 2 are bonded by an adhesive.
[0015]
In the above configuration, when the wave receiving plate 2 is brought into close contact with
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the surface of the subject, the AE wave generated inside the subject propagates in the subject and
reaches the surface, and the wave receiving plate 2 and the lower side. The pressure is
transmitted to the synthetic resin-ceramic composite piezoelectric element 2 through the
electrode 6 on the side, and the columnar ceramic piezoelectric body 3 is expanded and
contracted in the height direction.
Then, due to the expansion and contraction, a potential difference is generated at both ends of
the pillar-shaped ceramic piezoelectric members 3.
[0016]
In the AE sensor of the present invention, the columnar ceramic piezoelectric members 3 are
oriented such that the crystal axes are oriented in the height direction and polarized in that
direction. Therefore, only when stretched in the height direction, Although positive and negative
charges are generated at both ends thereof, no charge is generated at both ends even if they are
expanded and contracted in other directions, for example, in a direction orthogonal to the height
direction. That is, the longitudinal vibration component is mainly detected in the AE wave that
reaches the surface from the inside of the subject. Further, since the transverse vibration
component of the ceramic piezoelectric body 3 is rapidly attenuated in the synthetic resin matrix
4, an AE signal with less ringing can be obtained.
[0017]
As a result, the longitudinal wave and the transverse wave caused by the temporally and spatially
different AE are different in propagation velocity, and even if they reach the AE sensor
simultaneously, only the longitudinal vibration component is detected, and the object is
examined. It is possible to faithfully detect the intensity of AE generated inside and its change.
[0018]
By the way, the potential difference generated between the electrodes 5 and 6 of the synthetic
resin-ceramic composite piezoelectric element 1 by the AE wave is an inherent one determined
by the material and shape of the columnar ceramic piezoelectric body 3.
Therefore, if an ultrasonic wave whose intensity is known is received in a preliminary
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experiment, and then the relationship of the potential difference generated between the
electrodes 5 and 6 is determined, this relationship is used to measure in an actual subject The
intensity of the AE wave can be calculated from the potential difference between the electrodes 5
and 6.
[0019]
Further, in the AE sensor of the present embodiment, since the synthetic resin-ceramic composite
piezoelectric element 1 is formed of columnar ceramic piezoelectric bodies 3 of different heights,
it is a so-called resonance dispersion type, It has a different resonance frequency (resonance
point) according to the height of the columnar ceramic piezoelectric material 3. Therefore, the
detection frequency range of the AE sensor is broadened, and sufficient sensitivity characteristics
can be obtained because resonance is used.
[0020]
Further, in the AE sensor of this embodiment, since the ceramic piezoelectric members 3... Are
arranged concentrically in the synthetic resin matrix 4, there is little dependence on the receiving
direction when receiving the AE wave.
[0021]
Specifically, for example, a barium titanate sintered body, a lead titanate sintered body, or a PZT
(lead zirconate titanate) sintered body is used as the material of the columnar ceramic
piezoelectric body 3. Although it is preferable in terms of the detection sensitivity of AE, any one
having piezoelectric characteristics and being polarized in the height direction can be used.
In addition, the shape is a columnar shape, and the ratio of the height to the length of one side of
the bottom surface needs to be 1 or more, preferably 2 or more in terms of AE detection
sensitivity, and this ratio is And 2 to 6 is more preferable. Further, the elastic modulus of the
ceramic piezoelectric body 3 is preferably 6000 kgf / mm 2 or more in view of detection
sensitivity of AE.
[0022]
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The synthetic resin used for the synthetic resin matrix 4 may be anything as long as it can be
integrated with the columnar ceramic piezoelectric body 3 to be integrated. Specifically, for
example, silicone rubber, urethane rubber, butadiene rubber, nitrile rubber, ethylene-propylene
rubber, chloroprene rubber, fluororubber, ethylene-acrylic rubber, polyester elastomer,
epichlorohydrin rubber, acrylic rubber, or chlorinated ethylene rubber However, it is preferable
to use silicone rubber, urethane rubber or butadiene rubber in view of detection sensitivity of AE,
and is preferable to detect only longitudinal vibration mode by largely attenuating the transverse
vibration mode. The elastic modulus of the synthetic resin is preferably 1 to 50 kgf / mm @ 2
from the viewpoint of detection sensitivity of AE, and it is more preferable to match the acoustic
impedance of the AE sensor with the object (FIG. 1). .
[0023]
Further, in the synthetic resin-ceramic composite piezoelectric element 1, the ratio of the volume
of the whole of the columnar ceramic piezoelectric material 3 ... to the volume of the synthetic
resin matrix 22 is in the range of 8/92 to 40/60. It is preferable on the detection sensitivity of
[0024]
Hereinafter, a urethane rubber-PZT (lead zirconate titanate) composite piezoelectric element will
be described as a specific example of the synthetic resin-ceramic composite piezoelectric element
1, and the method of manufacturing the same and the performance of an AE sensor using the
same will be described.
[0025]
A cylindrical (φ10 mm × 6 mm) polarized PZT sintered body (manufactured by Poly Electronic
Corporation, model number HC-50 GS, relative permittivity = 1050, piezoelectric constant g33
==) as a material of the cylindrical ceramic piezoelectric body 3 This is machined using 32 × 103 Vm / N, electromechanical coupling coefficient k33 = 67%, mechanical quality factor Q =
1000), and a cylinder with φ 0.7 mm and height 4 mm, 2 mm, 1 mm A total of 61 pieces were
arranged concentrically on a 2 mm thick PZT disk to obtain an upright PZT microfabric.
The diameters of the respective concentric circles are φ8.5, φ6.4, φ4.3, φ2.1 in order from the
outer circumference side to the inner circumference side, and each concentric circle has a height
of 4 mm × 24, a height 2 mm × 18. It is composed of a cylindrical PZT having a height of 1 mm
× 12 and a height of 1 mm × 6.
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In addition, a 1 mm × 1 cylinder is disposed at the center. For the above processing, an
ultrasonic processing apparatus (type UM-5000 DA, manufactured by Nippon Denshi Kogyo Co.,
Ltd.) equipped with a tool made of S45C (structural carbon steel) was used.
[0026]
The PZT microfabricated product thus obtained is fitted in a silicon molding die, and a urethane
rubber for electrical insulation as a material of the synthetic resin matrix 4 (manufactured by
Sanyu Resin Co., Ltd., trade name SU-2153-9) is put into this molding die. , Hardness of 52,
black) and left at room temperature for 1 day, then curing treatment at 60 ° C. for 5 hours with
a drier to cure the urethane rubber and take it out of the mold, thereby removing the PZT circle.
A urethane rubber-PZT composite in which a urethane rubber-PZT was formed on a plate was
prepared.
[0027]
Next, the PZT disk portion of the urethane rubber-PZT composite is cut off with a diamond blade
(crystal cutter made by Malto Co.), and a cylinder gauge made of PZT of three different heights in
a urethane rubber matrix. Sixty-one pieces were arranged regularly and concentrically to form a
urethane rubber-PZT composite piezoelectric body, and both end faces were polished with sand
paper.
[0028]
Then, silver paste (made by Degussa, trade name DEMETRON 6290-0275) is applied to the end
face on the side with the step and the step near the end face opposite to the step, and the
temperature is raised to 120 ° C., A silver electrode as the electrodes 5 and 6 'was formed by
performing a baking process for a minute.
In addition, a gold electrode as an electrode 6 was formed by sputtering on the other end face
portion without a step.
Then, a 0.2 mm thick alumina thin plate (manufactured by Mitsubishi Mining and Cement Co.,
Ltd., model number MAB-L201K-10φ) as the wave receiving plate 2 was adhered to the gold
electrode surface by an adhesive. Then, lead wires were soldered to the electrodes 5 and 6 'to
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obtain an AE sensor composed of a urethane rubber-PZT composite piezoelectric element.
[0029]
In order to confirm the frequency characteristics of this AE sensor, a mechanical pencil
replacement core of φ 0.5 mm (Pentel Co., hardness 2H) is compressed to generate a pseudo AE
wave, which is received by the above AE sensor. , AE signal voltage was measured.
[0030]
FIG. 3 shows a schematic configuration of the measurement system.
[0031]
The measurement system includes an aluminum plate 8 as a transmission medium, an AE sensor
7 closely attached to the center of the aluminum plate 8, a preamplifier 10 for amplifying the
output of the AE sensor 7, and a memory of the output waveform of the preamplifier 10 Receive
the data stored in the wave memory 12, the termination resistance 11 for impedance matching
provided on the input side of the wave memory 12, and the wave memory 12 through the
interface line 13, and perform Fourier transform It comprises a microcomputer 14 for obtaining
a frequency spectrum.
[0032]
Specifically, for example, a high-strength aluminum alloy (7475 thick plate) having a size of 400
mm × 400 mm × 60 mm is used as the aluminum plate 8.
In addition, a model NF9913S (amplification factor of 20 dB) manufactured by NF Circuit Design
Block Co., Ltd. is used for the preamplifier 10, and a model DL 2120 manufactured by Nippon
Physical Acoustics Co., Ltd. is used for the wave memory 12.
Furthermore, Hewlett Packard model HP 216 was used for the microcomputer 14, and GP-IB
(general purpose interface bus) was used for the interface line 13.
[0033]
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9
In the above construction, the mechanical pencil replacement core 9 is pressed against the lower
surface of the aluminum plate 8 to be compressed, and the pseudo AE wave generated at this
time is received by the AE sensor 7 provided on the upper surface of the aluminum plate 8 Do.
Then, an AE signal as an electric signal is taken out, amplified by the preamplifier 10, and then
taken into the wave memory 12 at a predetermined timing. The AE signal captured in the wave
memory 12 is transferred to the microcomputer 14 through the interface line 13 and Fourier
transform is performed. Thereby, a frequency spectrum indicating the frequency dependency of
the detection signal voltage of the AE sensor 7 is obtained.
[0034]
For comparison of frequency characteristics, as Comparative Example 1, a single resonance type
AE sensor in which the heights of the above-mentioned 61 φ0.7 PZT cylinders are all 4 mm is
the same material as that described above. And it manufactured by the manufacturing method
and performed the same measurement as the above.
[0035]
Also for comparison of frequency characteristics, a commercially available small resonance AE
sensor (trade name PICO manufactured by US Physical Acoustics, size φ 3.5 × 4. The same
measurement as described above was performed using the commercially available wide band AE
sensor (reference standard device for calibration REF10M manufactured by Fuji Ceramics Co.,
Ltd., frequency band 0 to 10 MHz) which is non-resonance type as Comparative Example 3 using
7).
[0036]
The measurement results are shown in FIG. 4 and FIG.
In the figure, the vertical axis is the output voltage ratio of the detection signal of the AE sensor,
and the horizontal axis is the frequency.
[0037]
FIG. 4 compares the frequency spectrum of the resonant dispersive AE sensor with the frequency
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spectrum of the single resonant AE sensor, and the curve 15 shows the resonant dispersive AE
sensor of this embodiment. Curves 16 and 17 show single resonance AE sensors of Comparative
Example 1 and Comparative Example 2, respectively.
[0038]
As is clear from the figure, the frequency at which the output voltage ratio attenuates to -60 dB is
the same for both the AE sensor (Comparative Example 1) and the commercially available AE
sensor (Comparative Example 2), which were manufactured for comparison purposes. Although it
is about 1 MHz, it is about 2 MHz in the AE sensor of this embodiment, and the detectable
frequency band of the AE wave is expanded about twice.
This band broadening is considered to be an effect due to resonance dispersion, and as described
above, in the resonance dispersion type AE sensor, it is considered that the frequency band is
expanded because of having a plurality of different resonance frequencies.
[0039]
FIG. 5 compares the frequency spectrum of the resonance dispersive AE sensor with the
frequency spectrum of the non-resonance AE sensor, and the curve 15 corresponds to the
resonance dispersive AE of this embodiment as in FIG. A sensor is shown, and a curve 18 shows a
non-resonance AE sensor of Comparative Example 3.
[0040]
The frequency at which the output voltage ratio attenuates to -60 dB is approximately equal to
about 2 MHz in both the AE sensor of this embodiment and the commercially available wide
band AE sensor (comparative example 3), but 1 to 2 MHz The decrease in sensitivity in the high
frequency range and the low frequency range below 500 kHz is smaller in the AE sensor of this
embodiment.
[0041]
This difference depends on whether the AE sensor is of the resonance type or the non-resonance
type. In the non-resonance type AE sensor of the comparative example 3, the ceramic
piezoelectric PZT is a damping material made of a resin. The band is broadened by suppressing
04-05-2019
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the resonance point to suppress the resonance point, but this causes not only the high frequency
range but also the sensitivity decrease in the low frequency range.
On the other hand, in the resonance dispersion type AE sensor of the present embodiment, by
using the pillar-shaped ceramic piezoelectric body 3 (FIG. 2) of different heights, the resonance
points respectively in the low, middle and high frequency regions Is placed, so there is less
decrease in sensitivity in any frequency range.
Thereby, a wide and flat detection frequency spectrum is obtained.
Moreover, since the above measurement results are evaluated by the same measurement system
(FIG. 3), the output voltage ratios can be absolutely compared with each other, and the AE sensor
of this embodiment It can be concluded that the sensitivity is higher than that of the AE sensor of
Comparative Example 3.
[0042]
Next, an AE sensor in which a housing is provided to the urethane rubber-PZT composite
piezoelectric element shown in the above specific example is made as a prototype, and frequency
characteristics measured more precisely using this AE sensor are shown in FIGS. It will be as
follows if it explains based on 8.
[0043]
The AE sensor 20 used for the measurement is bonded on the alumina receiving plate 22 for
receiving the AE wave from the subject and the alumina receiving plate 22 as shown in the
longitudinal sectional view of FIG. A urethane rubber-PZT composite piezoelectric element 19 for
converting an AE wave into an electrical signal, and a urethane rubber-PZT composite
piezoelectric element 19 are fixed on the alumina receiving plate 22 so as to cover the entire
surface. A cup-shaped metal housing 21 for protecting the PZT composite piezoelectric element
19, a connector 23 for taking out an AE signal received by the urethane rubber-PZT composite
piezoelectric element 19, and electrodes 5 and 6 of the urethane rubber-PZT composite
piezoelectric element 19. And a lead wire 24 for connecting the connector 23 and the connector
23.
[0044]
Although aluminum is used as the material of the metal housing 21 in this embodiment, stainless
04-05-2019
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steel or the like may be used.
[0045]
Although the alumina receiving plate 22 and the metal housing 21 are fixed by adhesion, they
may be fixed by fitting.
[0046]
In the above configuration, the metal housing 21 not only shields external noise and protects the
urethane rubber-PZT composite piezoelectric element 19, but also the urethane rubber-PZT
composite piezoelectric element 19 through the alumina wave receiving plate 22. It also plays a
role of fixing the patient to the subject.
That is, as described above, the urethane rubber-PZT composite piezoelectric element 19 has
only a size of about φ10 mm × 4 mm, and is very light because of this. Therefore, by providing
the metal housing 21, the alumina receiving plate is provided. When fixing 22 and a subject with
grease etc., it is made difficult to separate.
[0047]
Further, the metal housing 21 attenuates the natural vibration of the alumina wave receiving
plate 22 itself, thereby damping the unnecessary reverberation generated in the urethane
rubber-PZT composite piezoelectric element 19 and the sensitivity characteristic in the high
frequency range. Are also improving.
[0048]
In order to accurately measure the frequency characteristics of the AE sensor 20 having the
metal housing 21 described above, instead of the above-described measurement system for
collapsing a pencil replacement core to generate a pseudo AE wave, it does not depend on the
frequency. A measuring system capable of generating pulses of constant amplitude was used.
[0049]
In this measurement system, as shown in the block diagram of FIG. 7, the pulse generator 27 for
generating electric pulses of various frequencies and the electric pulses output from the pulse
generator 27 are converted into sound pulses of longitudinal waves. Sound source sensor 25, an
04-05-2019
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iron block 26 as a transmission medium, an AE sensor 20 for receiving the sound pulse, a
preamplifier 10 for amplifying the output of the AE sensor 20, and a wave memory 12 for
storing the output waveform of the preamplifier 10 And a termination resistor 11 for impedance
matching provided on the input side of the wave memory 12 and a microcomputer 14 for
receiving data stored in the wave memory 12 via an interface line 13 and obtaining a frequency
spectrum It is configured.
[0050]
The sound source sensor 25 and the AE sensor 20 are disposed to face each other with the iron
block 26 in between.
[0051]
As a transmission medium, an aluminum block may be used instead of the iron block 26.
[0052]
In the above configuration, the frequency is changed in the range of 100 KHz to 2000 KHz from
the pulse generator 27 to generate electric pulses, converted into sound pulses by the sound
source sensor 25, and received by the AE sensor 20. It is possible to obtain a frequency spectrum
showing the frequency dependency of the sensitivity of the AE sensor 20 directly without
conversion.
[0053]
For comparison of frequency characteristics, the above-mentioned commercially available smallsized resonant AE sensor (trade name PICO manufactured by Physical Acoustics, Inc., USA) and
the above-mentioned commercially available broadband AE sensor (calibrated by Fuji Ceramics,
Inc.) The same measurement as the measurement of the above-mentioned AE sensor 20 was
performed using a reference device REF10M (frequency band 0 to 10 MHz).
[0054]
The measurement results are shown in FIG.
[0055]
In the figure, the vertical axis is the output voltage ratio of the detection signal of the AE sensor,
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and the horizontal axis is the frequency.
The vertical axis is determined based on the output voltage measured by replacing the reception
AE sensor 20 (FIG. 7) with the same sensor as the sound source sensor 25.
[0056]
The curve 28 shows the frequency spectrum of the AE sensor 20 having the resonance dispersed
type metal housing 21 (FIG. 6) of the present embodiment, and the curves 29 and 30 respectively
show a commercially available compact resonance AE sensor and a wide band. The frequency
spectrum of the AE sensor is shown.
[0057]
From the comparison of the curves 28 and 29, it can be seen that the AE sensor 20 of the
present embodiment is much broader than the commercially available small resonance type AE
sensor, and at the same high sensitivity.
[0058]
Also, from the comparison of the curve 28 and the curve 30, it is understood that the AE sensor
20 of the present embodiment is 10 to 20 dB more sensitive than the commercially available
wide band AE sensor, and is equally as broadband. .
[0059]
In the above embodiment, although the AE sensor in which the height of the columnar ceramic
piezoelectric body 3 is three types is shown, the height may be any number of types, for example,
the same is true for four types of heights. An effect is obtained.
[0060]
If the number of types is too large, the resonance frequency increases and the entire bandwidth
is broadened, but the number of columnar ceramic piezoelectric bodies 3 per band decreases, so
that the detection sensitivity becomes worse.
[0061]
Further, in the present embodiment, although the ceramic piezoelectric body 3 having a circular
cross-sectional shape is used, the cross-sectional shape is not limited to this, and may be, for
04-05-2019
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example, a square or a hexagonal shape.
[0062]
Further, it may be a curved surface such as an ellipse.
[0063]
As described above, since the AE sensor of the present invention has a wide detection frequency
range, it can be used for qualitative analysis to detect any flaws generated in the subject, and
further, only the longitudinal vibration mode in the AE wave can be obtained. Since it detects
preferentially, it can also be used for quantitative analysis which detects the progress of the said
wound generation.
Further, since the synthetic resin-ceramic composite piezoelectric element 1 excellent in
piezoelectric characteristics is used, the size is small and the detection sensitivity is high.
[0064]
The AE sensor of the present invention can not only be used to detect not only AE waves but also
all elastic waves propagating in gas, liquid and solid, and conversely, to apply an AC voltage from
the outside. Can also generate an elastic wave.
[0065]
According to the acoustic emission sensor of the present invention, as described above, since the
pillar-shaped ceramic piezoelectric material is polarized in the height direction, the longitudinal
direction of the AE wave propagating in the height direction can be obtained. A potential
difference is generated on both end surfaces of the synthetic resin-ceramic composite
piezoelectric element only for the vibration mode.
Thereby, only the longitudinal vibration mode is detected.
Further, since columnar ceramic piezoelectric bodies having different heights are used, resonance
04-05-2019
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points appear by the type of height, and the detection frequency range of AE waves becomes
wide.
Therefore, the rise time of the AE signal is shortened, the response is improved, and the detection
sensitivity is also improved.
Further, since the ceramic piezoelectric members are arranged concentrically, they are
nondirectional, and substantially constant detection sensitivity can be obtained regardless of the
propagation direction of the AE wave.
As described above, it is possible to obtain an acoustic emission sensor capable of sensitively
detecting an AE signal over a wide frequency range necessary for AE waveform analysis.
[0066]
Brief description of the drawings
[0067]
1 is a cross-sectional view of the AE sensor of the present invention.
[0068]
2 is a longitudinal sectional view of the AE sensor of FIG.
[0069]
3 is a block diagram of an apparatus for performing frequency spectrum analysis of the pseudo
AE wave.
[0070]
4 is a frequency spectrum diagram of the AE sensor of the present embodiment and the AE
sensor of Comparative Examples 1 and 2.
[0071]
5 is a frequency spectrum diagram of the AE sensor of the present embodiment and the AE
04-05-2019
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sensor of Comparative Example 3.
[0072]
6 is a longitudinal sectional view showing a schematic configuration of an AE sensor having a
metal housing of the present embodiment.
[0073]
7 is a block diagram of an apparatus for performing frequency spectrum analysis more precisely
using a pulse generator.
[0074]
8 is a frequency spectrum diagram of the AE sensor having a metal housing of the present
embodiment, and a commercially available small resonance AE sensor and a wide band AE
sensor.
[0075]
Explanation of sign
[0076]
1 Synthetic resin-ceramics composite piezoelectric element 3 Ceramics piezoelectric 4 Synthetic
resin matrix
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