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JPH0257099

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DESCRIPTION JPH0257099
[0001]
The present invention relates to a composite piezoelectric vibrator used for an ultrasonic probe
such as f′i , a sonar for detecting a target in water, etc., and an ultrasonic diagnostic
apparatus for diagnosing a living body. 2. Related Art Conventionally, as a piezoelectric
transducer material used for ultrasonic probes such as sonars and ultrasonic diagnostic devices
intended for water and living bodies, PZT based or lead titanate (Pb Ti 03) based ceramics Has
been used because of its high electromechanical coupling coefficient. However, these
piezoelectric vibrator materials have an acoustic impedance of 25 to 35 × 106 kg / m ′ ′-s
tee, which is significantly higher than that of water or biological (7) acoustic impedance, about
15 × 106 kg / m ′ ′ @ S, There is a problem that mismatching occurs-it is easy and inefficient.
Therefore, recently, as a piezoelectric vibrator material having a high electromechanical coupling
coefficient and a small acoustic impedance, that is, a piezoelectric vibrator material close to the
acoustic impedance of water or a living body, a so-called composite piezoelectric vibrator
material complexed with piezoelectric ceramics Has been done. In addition, on the other hand,
studies are also being made to obtain the above characteristics by making the piezoelectric
ceramic porous. The above-mentioned composite piezoelectric vibrator and Cite-ha, W, A, Smith
et al: Proc, IEEF3 1985 Ultrasonics Symp, 642-647 and Technical Report of IEICE. No. 160 US
83-3011C is known. Hereinafter, the conventional composite piezoelectric vibrator will be
described with reference to the drawings. As shown in FIG. 7, a PZT-based piezoelectric ceramic
5 and an organic polymer 52 such as silicone rubber or epoxy resin are respectively connected in
one and three dimensions to a piezoelectric ceramic 5 of PZT type. A so-called 1-3 type
composite piezoelectric vibrator 53 is configured. In order to manufacture this composite
piezoelectric vibrator 53, usually, a sheet of piezoelectric ceramic is cut into a mesh shape by a
dicing machine or the like, and the organic polymer 52 made of silicone rubber is filled in the
gaps of the piezoelectric ceramic 51 generated by the cutting. Do. At this time, by adjusting the
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thickness of the blade for cutting the piezoelectric ceramic 51 and the cutting pitch, the volume
fraction of the piezoelectric ceramic 51 can be adjusted to obtain desired characteristics. The
electromechanical coupling coefficient of the composite piezoelectric vibrator 53 configured in
this way has almost the same direct characteristic as R33 'of the electromechanical coupling
coefficient of the piezoelectric ceramic alone, and the acoustic impedance is higher than that of
the piezoelectric ceramic alone. It becomes smaller.
For example, when the volume ratio of the piezoelectric ceramic 51 is 25 and the organic
polymer 52 made of silicone rubber is 75, the acoustic impedance of the composite piezoelectric
vibrator 53 is about 8.8 X I 06 kg / m "ms. And raw 6 =-. The matching with the acoustic
impedance of the body is considerably better than that of the piezoelectric ceramic alone, and the
transmission and reception efficiency of ultrasonic waves can be improved. As another
conventional example of a piezoelectric vibrator using a porous piezoelectric ceramic, a
configuration described in Japanese Patent Application Laid-Open No. 63-78700 is known. In
this composite piezoelectric vibrator, a piezoelectric ceramic such as PZT is formed in a porous
manner, and the density is reduced to reduce the acoustic impedance. Then, for example, a
dispersion is prepared from a ceramic powder of PZT, a water-soluble acrylic resin as a binder,
and PVA, and the dispersion is molded into a sheet, which is then fired to obtain a porous
ceramic having a porosity of 43%. obtain. A porous piezoelectric vibrator is obtained by
polarizing the porous ceramic. The acoustic impedance of this porous piezoelectric vibrator is
about 6 × 10 6 kg / s · S, the electromechanical coupling coefficient is about 63%, and the
acoustic matching with water or a living body is as good as the above composite piezoelectric
vibrator And ultrasound transmission and reception efficiency 7 / <. It has the feature that it can
be improved. Problems to be Solved by the Invention However, in the former among the abovedescribed conventional examples, since the former is a composite of the piezoelectric ceramic 51
and the organic polymer 52, there is a limit in bringing the acoustic impedance close to the
acoustic impedance of water or a living body. That is, although the acoustic impedance is a
product of density and sound velocity, actually, changing the density more than the sound
velocity has a high degree of contribution in adjusting the acoustic impedance, and the density of
the piezoelectric ceramic 51 is about 7 to 8 kf / Since the density of the organic polymer 52 such
as silicone rubber is about 1 k19 / ail, the acoustic impedance is about 7 × 10 6 kg / m even if
the volume ratio of the piezoelectric ceramic 51 is reduced! S is the limit. If this is to be further
reduced, the volume ratio of the organic polymer 52 must be increased, the electromechanical
coupling coefficient decreases, and the overall characteristics deteriorate. Therefore, although the
acoustic impedance can be brought closer to water or a living body as compared with the case of
the piezoelectric ceramic alone, it still has a problem that sufficiently good acoustic matching can
not be taken.
On the other hand, in the latter case, the acoustic impedance can be reduced by increasing the
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porosity of the porous piezoelectric ceramic, but when it reaches the porosity on a certain plate,
the mechanical strength is extremely weak, and breakage is not easy. In addition, since the
dielectric constant is also extremely small, the electrical impedance is high, which makes it
difficult to achieve electrical matching. Therefore, it is difficult to make the acoustic impedance
smaller than a certain value, and it is impossible to obtain a value sufficiently close to the
acoustic impedance of water or living body as in the above-mentioned conventional example, and
a sufficiently good acoustic matching is taken. Have the problem of being unable to The present
invention solves the above problems of the prior art, has a high electromechanical coupling
coefficient, and can therefore improve the strength, and can be used as the value of acoustic
impedance of water or a living body. It can be as close as possible, thus enabling good acoustic
matching with water and living bodies, improving the efficiency of ultrasonic transmission /
reception and increasing the resolution in the depth direction. It is an object of the present
invention to provide a composite piezoelectric vibrator which can be improved and whose
frequency band can be expanded. Means for Solving the Problems In order to achieve the above
object, the technical means of the present invention comprises piezoelectric ceramics and an
organic substance to form pores. Then, the piezoelectric ceramic is formed in a columnar shape,
and the piezoelectric ceramic in the columnar shape is two-dimensionally arrayed and fixed with
an organic substance to form pores in the gaps of the piezoelectric ceramic in the columnar
shape or two-dimensionally arrayed. The organic substance mixed with hollow bodies that
become pores is filled in the gaps of the columnar piezoelectric ceramics, or the expandable
organic substance is filled in the gaps of columnar piezoelectric ceramics arranged in two
dimensions to form pores in the organic substance It is preferable to use a foamable
polyurethane resin and a foamable silicone rubber as the foamable organic substance. In
addition, porous piezoelectric ceramics and organic substances 10 = -7, and holes are formed.
Then, the above-mentioned porous piezoelectric ceramic is formed in a columnar shape, the
columnar and porous piezoelectric ceramics are two-dimensionally arranged, the space between
the columnar and porous piezoelectric ceramic is filled with an organic substance, and the above
columnar and porous The piezoelectric ceramic of the present invention has pores, and as the
organic substance, any one of synthetic rubber, epoxy resin, polyurethane resin, foamable
polyurethane resin, foamable silicone rubber, or columnar and porous arranged in two
dimensions The piezoelectric ceramic of the present invention is fixed with an organic substance,
and while the above-mentioned columnar and porous piezoelectric ceramic has pores, the gaps of
the columnar and porous piezoelectric ceramic are made to be pores or two-dimensionally
arranged columnar An organic substance mixed with a hollow body is filled in a gap of the
porous piezoelectric ceramic, and the above-mentioned columnar, porous piezoelectric ceramic is
a void And having, in which as a hollow body of the organic material is pores.
Operation The present invention has the following operations 11 / and -7 by the above technical
means. A composite piezoelectric vibrator comprising a piezoelectric ceramic and an organic
substance, in which the density can be reduced by forming the pores, and hence the acoustic
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impedance can be reduced, which is close to the acoustic impedance of water or a living body It
can be a value. In addition, by using a porous piezoelectric ceramic, the density of the
piezoelectric ceramic can be reduced to about a half of the conventional density, and hence the
acoustic impedance can be reduced, which is close to the acoustic impedance of water or a living
body Can be Further, by forming pores among the piezoelectric ceramics in addition to the pores
of the porous piezoelectric ceramic, the density can be further reduced, so that the acoustic
impedance can be reduced, and water and biological It can be close to the acoustic impedance. In
addition, the electromechanical coupling coefficient is the same as in the case of the piezoelectric
ceramic alone. EXAMPLES Examples of the present invention will be described below. First, the
first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view
showing a composite piezoelectric vibrator according to a first embodiment of the present
invention. As shown in FIG. 1, one PZT ceramic sheet of a desired thickness is cut in a mesh
shape and divided, and a large number of columnar piezoelectric ceramics 1 are arranged in two
dimensions. Both end faces of the piezoelectric ceramic 1 are covered with a film-like selfadhesive epoxy resin which is an organic polymer material, and the film-like self-adhesive epoxy
resin 2 is heated in a pressurized state to form a columnar piezoelectric material. It is bonded to
the ceramic 1 and hardened. Since the film-like self-adhesive epoxy resin 2 is of a type that
softens and adheres, the piezoelectric ceramic 1 is fixed without flowing into the gap of the
columnar piezoelectric ceramic 1. Therefore, the gap of the columnar piezoelectric ceramic 1 is
kept in the state of the air holes 3. Electrodes 4 made of Al, Ag, Au, etc. are vapor-deposited or
plated on the outer surface of each film-like self-adhesive epoxy resin. A lead (not shown) is taken
out of a part of the electrode 13 page 4. Also, although not shown, if necessary, a back load
material is provided on the surface of one of the electrodes 4 and an acoustic lens for focusing an
acoustic matching layer and a sound wave is provided on the surface of the other electrode 4
that emits ultrasonic waves. . For example, using the PZT-based material C-6 (density: 7.4 kg / m
′ ′) of 0.5 mm in thickness as the piezoelectric ceramic 1, the gaps cut and divided in a mesh
shape, that is, the pores The volume ratio of 3 and the columnar piezoelectric ceramic 1 is set to
7596.25q6, and both end faces of the columnar piezoelectric ceramic 1 are bonded with a 100
mm film-like self-adhesive epoxy resin 2. The density ρ of the composite piezoelectric vibrator is
expressed by the following equation (1).
Vl = v 1 L L + V 2 2+ 2 + v 3 3 3 ° (1) where vl, ll are the piezoelectric ceramic 10 volume ratio
and density, v2. ρl is a film-like self-adhesive epoxy resin 20 volume ratio and density, v3. Let
ρ3 be the volume ratio and density of air holes (air) 3. From the above equation (1), the density i
of the composite piezoelectric vibrator becomes about 1.63 kg / m ′ ′ and 14 ···. On the other
hand, the speed of sound is slower than that of the composite piezoelectric vibrator (the speed of
sound is 3 to 4 km / s) by the conventional piezoelectric ceramics and epoxy resin because air (0,
344 km / s) is contained. It will be back and forth. Accordingly, the acoustic impedance of the
composite piezoelectric vibrator of this embodiment is 3 to 4 × 10 kg / lr · ′ ′ · S,
considerably close to the value of acoustic impedance of water or a living body, and the
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transmission / reception efficiency of ultrasonic waves is high Moreover, the reflection with
water or a living body can be reduced, the resolution in the depth direction can be improved, and
a composite piezoelectric vibrator having a wide wave number band can be obtained. Next, a
second embodiment of the present invention will be described. FIG. 2 is a cross-sectional view
showing a composite piezoelectric vibrator according to a second embodiment of the present
invention. As shown in FIG. 2, one piezoelectric ceramic plate of a PZT system having a desired
thickness is cut in a mesh shape and divided, and a large number of columnar piezoelectric
ceramics 1 are two-dimensionally arranged. After the resin 5 which is an organic polymer
material is poured into the gaps of the columnar piezoelectric ceramics 1 and filled with resin
and hardened, the 15 hems / portions of the resin 5 are cut in the same manner as above. At this
time, the resin 5 is cut so that a part thereof remains at one end side of the columnar
piezoelectric ceramic 1. A film-like self-adhesive epoxy resin 3 which is an organic polymer
material is provided on the surface of the columnar piezoelectric ceramic 1 opposite to the
remaining part of the resin 5 and is heat-cured. The electrode 4 is provided on the surface of the
columnar piezoelectric ceramic 1 on the resin 5 side and the outer surface of the film-like selfadhesive epoxy resin in the same manner as in the first embodiment to form a composite
piezoelectric vibrator. The other configuration is the same as that of the first embodiment. Also in
the present embodiment, it is possible to obtain a composite piezoelectric vibrator having the
same characteristics as those of the first embodiment described above; As the piezoelectric
ceramic 1 of the second embodiment, a porous one can be used, and in this case, the acoustic
impedance can be further reduced by the pores of the porous piezoelectric ceramic itself in
addition to the pores 3 . Next, a third embodiment of the present invention will be described.
FIG. 3 is a cross-sectional view showing a composite piezoelectric vibrator according to a third
embodiment of the present invention. As shown in FIG. 3, one piezoelectric ceramic plate of a
PZT system having a desired thickness is cut in a mesh shape and divided, and a large number of
columnar piezoelectric ceramics 1 are two-dimensionally arranged. The resin 7 mixed with the
microballoon (hollow body) 6 is poured into the gap of the columnar piezoelectric ceramics 1 by
filling and hardened. Electrodes 4 are provided on both end faces of the columnar piezoelectric
ceramic 1 to constitute a composite piezoelectric vibrator. The other configuration is the same as
that of the first embodiment. For example, Muromachi mixed with 8 parts by weight ratio of
plastic micro balloon F30E of Matsumoto Oil & Fats Co., Ltd. as micro balloon 6 using PZT
system C-6 (density 7.4 kg / kg) of Fuji Ceramics as piezoelectric ceramic 1 An epoxy resin
(density: 0.54 kg / m ′ ′; sound velocity: 1.7 km / s) 7 of Epotech 301 manufactured by
Chemical Co., is filled in the gap of the columnar piezoelectric ceramic 1 and heat cured.
Assuming that the volume ratio at this time is 25 for the piezoelectric ceramic 17 and 25 for the
epoxy resin 7 in which the microballoon 6 is mixed, the density of the composite piezoelectric
vibrator at this time is about 2.26 k177 m 3 . Further, since the microballoons 6 are formed in
the epoxy resin 7 to form pores, the sound velocity is also slower than the sound velocity (2, 5 to
3 km / s) of the epoxy resin 7 alone, so that the conventional piezoelectric ceramics and It will be
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slower than the composite piezoelectric vibrator with epoxy resin only. Therefore, the acoustic
impedance of the composite piezoelectric vibrator of this embodiment is about 5 × 10 kg / m ′
′ · S, and can be about 20 times smaller than that of a conventional piezoelectric ceramic and
silicone rubber composite piezoelectric vibrator. Since the acoustic impedance of water or a
living body can be further approximated, it is possible to obtain a composite piezoelectric
transducer with high transmission / reception efficiency of ultrasonic waves. The other
characteristics are the same as those of the first embodiment. In this embodiment, an epoxy resin
is used as the resin 7 filled in the gap of the columnar piezoelectric ceramic 1. However, the
polymer material such as this pond, polyurethane, and synthetic rubber is also the same. It is
obvious that it can be applied. In addition to the pores of the microballoon 6, the acoustic
impedance can be further reduced by the pores of the porous piezoelectric ceramic itself.
Also, instead of plastic microballoons, various microballoons such as glass, carbon and shirasu
can be used. Next, a fourth embodiment of the present invention will be described. FIG. 4 is a
cross-sectional view showing a composite piezoelectric vibrator according to a fourth
embodiment of the present invention. As shown in FIG. 4, one piezoelectric ceramic plate having
a desired thickness is cut in a mesh shape and divided, and a large number of columnar
piezoelectric ceramics 1 are two-dimensionally arranged. The epoxy resin 8 which is an organic
polymer material is poured into the gap of the columnar piezoelectric ceramic 1, filled and cured,
and then the epoxy resin 8 is cut and removed from both sides, and the epoxy resin 8 is a
columnar piezoelectric ceramic 1 A part is left in the central part of. Both end surfaces of the
columnar piezoelectric ceramic 2 are not broken 191,-. The film-like self-adhesive epoxy resin is
heated in a pressurized state and bonded to the columnar piezoelectric ceramic 1, and is film-like
self-adhesive with the epoxy resin 8. A void 3 is formed between the mold and the epoxy resin 2.
Electrodes 4 are provided on the outer surface of each film-like self-adhesive epoxy resin 2 to
constitute a composite piezoelectric vibrator. The other configuration is the same as that of the
first embodiment. Also in this embodiment, the same characteristics as those of the first
embodiment can be obtained, and the piezoelectric ceramic 1 is reinforced by being bridged by
the epoxy resin 8, so that the mechanical strength of the composite piezoelectric vibrator is also
improved. You can get a reliable one. In this example, the case of using the epoxy resin 8 as the
organic substance for filling a part of the gap of the columnar piezoelectric ceramic 1 was
described in this example, but in addition to this, the organic substance such as polyurethane,
foamable epoxy resin, foamable polyurethane It is clear that it can be implemented for Also, a
porous one can be used as the piezoelectric ceramic, and in this case, it is possible to further
reduce the acoustic impedance by the pores of the porous piezoelectric ceramic itself in addition
to the pores 3. Next, a fifth embodiment of the present invention will be described. FIG. 5 is a
cross-sectional view showing a composite piezoelectric vibrator according to a fifth embodiment
of the present invention. As shown in FIG. 5, one piezoelectric ceramic plate of the PZT system is
cut into a desired thickness and divided into a network, and a large number of piezoelectric
ceramics 1 are arranged in a two-dimensional manner. Foamable polyurethane resin 9 such as
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ECCO (MM li "PH / 12-10H (density is 0.22 m at 97 m ') made by Brace Japan Co., Ltd.) is poured
into the gaps of the columnar piezoelectric ceramic 1 by filling and hardening. It is done.
After curing, the foamable polyurethane resin 9 has pores 10 formed therein. Electrodes 4 are
provided on both end surfaces of the columnar piezoelectric ceramic 1 and the polyurethane
resin 9 to constitute a composite piezoelectric vibrator. The other configuration is the same as
that of the first embodiment. 21 · · · In this embodiment, since the foamable polyurethane resin 9
is used, the density can be reduced by the holes 1o. Accordingly, the acoustic impedance can also
be reduced, so that it is possible to obtain a composite piezoelectric transducer with high
efficiency of transmission and reception of ultrasonic waves. The other characteristics are the
same as those of the first embodiment. Similarly, in the present embodiment, the case of using
the foamable polyurethane resin 9 has been described, but in addition to this, a foamable silicone
rubber, such as Tosform 5300 (density 0.25 kg / m 3) of Toshiba Silicone Co., Ltd., etc. It is clear
that foamable polymeric materials can also be used. Also, it is possible to use a porous one as the
piezoelectric ceramic, in which case the acoustic impedance can be further reduced by the pores
of the porous piezoelectric ceramic itself in addition to the pores 10 of the foamable epoxy resin
9 is there. Next, a sixth embodiment of the present invention will be described. FIG. 6 is a crosssectional view showing a composite piezoelectric vibrator according to a sixth embodiment of the
present invention. -22 of PZT system of desired thickness as shown in FIG. A sheet of porous
piezoelectric ceramic plates is cut into a mesh shape and divided, and a large number of
columnar and porous piezoelectric ceramics 11 are arranged in a two-dimensional array. An
epoxy resin 12 which is an organic substance is filled in a gap between the columnar and porous
piezoelectric ceramics 11 and hardened. Electrodes 4 are provided on both end surfaces of a
columnar, porous piezoelectric ceramic 11 and an epoxy resin 12 so that a composite
piezoelectric vibrator in which the porous piezoelectric ceramic 11 itself has holes 13 is
configured. The other configuration is the same as that of the first embodiment. The density of
the porous piezoelectric ceramic 11 can be adjusted by the porosity. For example, when the
porosity is about 40 in PZT-based ceramics, the density is about 3.8 kg / m 3 and the acoustic
impedance is about 6 X It will be 106 kg / m · S. When the volume ratio of such porous
piezoelectric ceramic 11 and epoxy resin 12 is 25% and 75%, the density of the composite
piezoelectric vibrator is about 1.78 kg / m '. Therefore, the acoustic impedance is 97 m-5 or less
at 5 X 106, and is smaller than that of the conventional piezoelectric vibrator of porous
piezoelectric ceramic alone, and is closer to the acoustic impedance value of water and living
body 23 /. Thus, it is possible to obtain a composite piezoelectric transducer with high efficiency
of transmission and reception of ultrasonic waves.
The other characteristics are the same as those of the first embodiment. In the present
embodiment, the case of using an epoxy resin as a material filled in the gaps of the columnar
porous ceramic 11 has been described, but in addition to the above, organic rubber such as
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synthetic rubber and polyurethane, and expandable epoxy resin or It is apparent that the present
invention can be practiced using foamable organic substances such as foamable polyurethane.
Effects of the Invention As is apparent from the above description, according to the present
invention, the piezoelectric ceramic and the organic substance are provided to form pores. Then,
the piezoelectric ceramic is formed in a columnar shape, the columnar piezoelectric ceramics are
arrayed in two dimensions, fixed with an organic substance, and holes are formed in the gaps of
the columnar piezoelectric ceramic, or columnar arrayed in two dimensions An organic substance
in which hollow bodies that become pores are mixed in the gaps of the piezoelectric ceramics is
filled in the gaps of the piezoelectric ceramics, or a void in the columnar piezoelectric ceramics
arranged in two dimensions is filled with the foamable organic substance. It forms a void. In
addition, porous piezoelectric ceramics and an organic substance are provided to form pores.
Then, the above-mentioned porous piezoelectric ceramic is formed in a columnar shape, and this
columnar, porous piezoelectric ceramic is two-dimensionally arranged, and the space between
the columnar, porous piezoelectric ceramic is filled with an organic substance, and the porous
piezoelectric ceramic Form pores, and as the organic substance, a synthetic rubber, an epoxy
resin, a polyurethane resin, a foamable polyurethane resin, a foamable silicone rubber, an organic
substance mixed with a hollow body, etc. The porous piezoelectric ceramic is fixed to the organic
substance so that the porous piezoelectric ceramic has pores and the gaps thereof become pores.
Therefore, the density can be reduced, and the acoustic impedance can be reduced. Therefore,
the acoustic impedance of water 25 l <-> or a living body can be made as close as possible to the
value as much as possible. The ultrasonic probe can be used to transmit and receive ultrasonic
waves with high efficiency. In addition, the electromechanical coupling coefficient also has a high
straightness almost unchanged from that of the piezoelectric ceramic alone. Further, as described
above, the acoustic impedance is close to water or a living body, the reflection between the
composite piezoelectric vibrator and water or a living body is reduced, the resolution in the depth
direction can be improved, and the frequency band is broadened. it can. By using such a
composite piezoelectric vibrator for an ultrasonic probe for an ultrasonic diagnostic apparatus, it
is possible to obtain an ultrasonic image with high efficiency and high resolution.
[0002]
Brief description of the drawings
[0003]
FIGS. 1 to 6 are sectional views showing composite piezoelectric vibrators according to the first
to sixth embodiments of the present invention, and FIG. 7 is a perspective view showing a
conventional composite pressure transducer.
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DESCRIPTION OF SYMBOLS 1 ... Piezoelectric ceramics, 2 ... Self-adhesive-type epoxy resin of a
film form 3 ... Vacancy, 4 ... Electrode, 5 .. 8 ... epoxy resin, 9191 foamable urethane resin, 11 ...
porous piezoelectric ceramics, 12 ... epoxy resin, 13 ... pores.
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