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JPH0614385

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DESCRIPTION JPH0614385
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an
underwater receiver such as a marine acoustic measuring instrument, and is a high water
pressure resistant, low frequency, high sensitivity electroacoustic system for converting sound
waves into electrical signals. It relates to a conversion element.
[0002]
2. Description of the Related Art Heretofore, piezoelectric ceramics such as barium titanate,
zirconate and lead titanate (PZT) and the like have been used as materials for an electroacoustic
transducer of an underwater wave receiver. In recent years, for example, as described in the
following documents, research has also been conducted on porous piezoelectric ceramics in
which the piezoelectric g constant of the piezoelectric ceramic is increased. Hereinafter, a
conventional electroacoustic transducer will be described with reference to the drawings.
Literature; Ferroelectrics, 49 (1983) Gordon and Breach, Science Publishers (US) P. et al. 265272 FIG. 2 is a perspective view of a conventional cylindrical electroacoustic transducer using a
piezoelectric ceramic. This cylindrical electroacoustic transducer mainly utilizes the sensitivity to
the sound pressure due to the change in the peripheral length of the respiratory vibration, and
has the cylindrical piezoelectric ceramic 11 and the electrodes on the inner and outer peripheries
thereof. 12 and 13 are formed respectively, and the electrodes 12 and 13 are connected to the
terminals 14 and 15, respectively. Assuming that the inner diameter of the piezoelectric ceramic
11 is a and the outer diameter is b, and the piezoelectric g constant in the circumferential
direction is g31, the wave receiving sensitivity M of this cylindrical electroacoustic transducer is
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M = 20. × log (| g31 | · b) (dB re. V / Pa). Here, assuming that the piezoelectric d constant in the
circumferential direction is d31 and the dielectric constant is ε, g31 is g31 = d31 / ε (Vm / N).
In the case of a cylindrical electroacoustic transducer in which b is 15 (mm), d31 is −198 × 10
−12 (C / N), and ε is 1.59 × 10 −8 (F / m), the wave receiving sensitivity M is M = −75 (dB
re. V/Pa)
[0003]
FIG. 3 is a cross-sectional view of a conventional disk-shaped electroacoustic transducer utilizing
thickness resonance. This disc-shaped electroacoustic transducer has a disc-shaped piezoelectric
ceramic 21, and positive and negative electrodes 22 and 23 are formed on both sides thereof,
and the positive and negative electrodes 22 and 23 are terminals 24 and 25. Connected to each
other. When this disc-shaped electroacoustic transducer is used at a low frequency equal to or
lower than the resonance frequency, the transducer receives a hydrostatic sound pressure, so the
wave receiving sensitivity M is the thickness g of the piezoelectric g constant of hydrostatic
pressure mode. M = 20 × log (| gh | · t) (dB re. V / Pa). Here, assuming that the piezoelectric g
constant in the polarization direction is g33, the piezoelectric g constants in the direction
perpendicular to the polarization are g31, g32, and the piezoelectric d constants corresponding
thereto are d33, d31, d32, then gh = g33 + g32 + g31 = d33 / ε + d32 It is / (epsilon) + d31 /
(epsilon) = dh / (epsilon) (Vm / N). PZT is used for the piezoelectric ceramic 21. t is 6 (mm), d33
is 417 × 10-12 (C / N), d31 and d32 are −198 × 10-12 (C / N), and the dielectric constant ε
is 1.59 × 10-8 (F / Assuming that m), the piezoelectric g constant gh and the receiving
sensitivity M are as follows: gh = 1.32 × 10 −3 (Vm / N) M = −102 (dB re. V/Pa)
[0004]
FIG. 4 is a cross-sectional view of a disk-shaped electroacoustic transducer using thickness
resonance as in FIG. This disc-shaped electro-acoustic transducer has a porous piezoelectric
ceramic 31 substantially in the same manner as in FIG. 3, and a positive electrode 32 and a
negative electrode 33 are formed on both sides thereof. Terminals 34 and 35 are connected
respectively. The porous piezoelectric ceramic 31 is made of porous PZT as described in the
above-mentioned document. When considering the cross section parallel to the electrode surface,
the area occupied by PZT is reduced compared to the conventional FIG. 3, but the concentration
of stress occurs in the PZT, and the amount of charge generated occurs. Is the same as that of the
conventional FIG.
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[0005]
t is 6 (mm), d33 is 417 × 10-12 (C / N), d31 and d32 are −198 × 10-12 (C / N), and the
dielectric constant ε is 4.43 × 10-9 (F / Assuming that m), the piezoelectric g constant gh and
the receiving sensitivity M are as follows: gh = 4.74 × 10 −3 (Vm / N) M = −91 (dB re.
V/Pa)
[0006]
However, the conventional electroacoustic transducer has the following problems (i) to (iii) and it
is difficult to solve it. (I) The cylindrical electroacoustic transducer of FIG. 2 has high sensitivity
to receiving waves, but has an air layer inside, so it has a problem that the water pressure
resistance is low and it can not be used to a deep depth. There is also a balance method in which
oil or the like is internally added in order to provide water pressure resistance, but there are
problems such as a decrease in sensitivity and a complicated structure. (Ii) The electroacoustic
transducer using the block-shaped disc-shaped piezoelectric ceramic 21 shown in FIG. 3 has high
water pressure resistance but low sensitivity at low frequencies below the resonance frequency.
That is, the piezoelectric g constant gh (= g33 + g32 + g31) of the piezoelectric ceramic has
different signs of g31 and g32 with respect to g33, and the absolute value is about 1/2 (1 / 2g33
≒ | g31 | ≒ | g32 |) Therefore, there is a problem that it becomes a very small value. (iii) The
electroacoustic transducer using the block-shaped disc-shaped porous piezoelectric ceramic 31
of FIG. 4 has high water resistance and is more sensitive than the conventional electroacoustic
transducer of FIG. Since the dielectric constant is lowered to increase the capacitance, there is a
problem that the capacitance is lowered, the receiving sensitivity by the cable capacity is
lowered, the inconvenience in the electric circuit by the increase of the electric impedance, and
the like. The present invention solves the problem that it is difficult to obtain an electroacoustic
transducer having high water pressure resistance and high sensitivity at low frequency as a
problem of the prior art, and an electroacoustic transducer element of an underwater receiver. It
is provided.
[0007]
According to a first aspect of the present invention, there is provided an electroacoustic
transducer of an underwater wave receiver for converting sound pressure into an electric signal,
wherein the disc polarized in the thickness direction is provided. And a positive electrode and a
negative electrode formed on both sides of the piezoelectric ceramic, and a hard shell provided
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around the piezoelectric ceramic. In a second aspect of the invention, an electroacoustic
transducer of an underwater wave receiver for converting sound pressure into an electric signal,
formed on both sides of a disc-shaped porous piezoelectric ceramic polarized in the thickness
direction and the porous piezoelectric ceramic. And a hard shell provided around the porous
piezoelectric ceramic.
[0008]
In the third invention, the hard shell of the first or second invention is constituted by a cylindrical
shell made of metal or hard resin. In a fourth aspect of the present invention, an electroacoustic
transducer of an underwater wave receiver for converting sound pressure into an electric signal
is formed on both sides of a disc-shaped porous piezoelectric ceramic polarized in the thickness
direction and the porous piezoelectric ceramic. And a shell of ceramic material integrally molded
around the porous piezoelectric ceramic. In the fifth invention, the shell of the porcelain material
of the fourth invention is constituted by a cylindrical shell.
[0009]
According to the first aspect of the invention, since the electroacoustic transducer is configured
as described above, the hard shell provided around the disk-shaped piezoelectric ceramic is
stressed in the electrode surface direction of the piezoelectric ceramic. And reduce the
piezoelectric g constant in the hydrostatic pressure mode. According to the second invention, the
hard shell provided around the disk-shaped porous piezoelectric ceramic reduces the stress
applied in the electrode surface direction of the porous piezoelectric ceramic, and the
piezoelectric g in the hydrostatic pressure mode It works to increase the constant. By increasing
the piezoelectric g constant, the thickness can be reduced and the capacitance can be increased.
According to the third invention, the cylindrical shell made of metal or hard resin has a function
of reducing the stress applied in the electrode surface direction of the piezoelectric ceramic, as in
the first and second inventions.
[0010]
According to the fourth aspect of the present invention, the shell of the ceramic material
integrally molded around the disc-shaped porous piezoelectric ceramic has stress applied in the
electrode surface direction of the porous piezoelectric ceramic in substantially the same manner
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as the second aspect of the present invention. It serves to reduce, to increase the piezoelectric g
constant in the hydrostatic pressure mode, and to further increase the capacitance. In addition,
the shell integrally formed has a function of suppressing the separation between the porous
piezoelectric ceramic and the shell, and the decrease of the piezoelectric g constant due to the
sound pressure leakage. According to the fifth invention, the cylindrical shell reduces the stress
applied in the electrode surface direction of the porous piezoelectric ceramic in substantially the
same manner as the fourth invention, and increases the piezoelectric g constant in the
hydrostatic pressure mode, It has the function of increasing the capacity, and the function of
suppressing the peeling between the porous piezoelectric ceramic and the leakage of sound
waves. Therefore, the problem can be solved.
[0011]
First Embodiment FIG. 1 is a cross-sectional view of a disk-shaped electro-acoustic transducer
showing a first embodiment of the present invention. The disc-shaped electroacoustic transducer
has a disc-shaped piezoelectric ceramic 41 of thickness t and radius ra. The piezoelectric ceramic
41 is polarized in its thickness direction, and a positive electrode 43 and a negative electrode 44
are formed on both sides thereof, and the positive electrode 43 and the negative electrode 44 are
connected to the terminals 45 and 46, respectively. A metal cylindrical shell 42 having a
thickness t, an inner radius ra and an outer radius rb is provided around the disc-shaped
piezoelectric ceramic 41.
[0012]
Next, the operation will be described. The disk-shaped electroacoustic transducer of FIG. 1
receives hydrostatic pressure for low frequencies that are wavelengths sufficiently longer than
the dimensions of the transducer. Assuming that the sound pressure (hydrostatic pressure) is Pa,
the sound pressure Pa is applied to the entire surface of the electroacoustic transducer. The
stress Pa is applied in the thickness direction of the piezoelectric ceramic 41 by the sound
pressure Pa, but in the direction of the electrode surface of the piezoelectric ceramic 41, the
sound pressure Pa is braked by the metal cylindrical shell 42 provided on the circumference, and
the stress Pb is applied. (<Pa) will be added. If the Young's modulus, Poisson's ratio of the
piezoelectric ceramic 41 is Ea, νa, the Young's modulus of metal, and the Poisson's ratio are Eb,
νb, Pb is obtained. Therefore, the piezoelectric d constant dh, the piezoelectric g constant gh and
the wave receiving sensitivity M of the electroacoustic transducer are d33 for the piezoelectric d
constant in the polarization direction of the piezoelectric ceramic 41 and d31 and d32 for the
piezoelectric d constant in the direction perpendicular to the polarization. Assuming that the rate
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is ε, dh = (Pa · d33 + Pb · d32 + Pb · d31) / | Pa | (C / N) gh = dh / ε (Vm / N) M = 20 × log (|
gh | · t) (dB re. V / Pa) = 20 x log (gh · t)-120 (dB re. V / μPa). Here, it is assumed that PZT for
the voltage porcelain 41 and soft iron for the cylindrical shell 42 of metal, Ea = 6.10 × 1010 (N
/ m 2), Eb = 21.14 × 10 10 (N / m 2), aa = νb = 0.3, ra = 12 (mm), rb = 15 (mm), Pa = 1.0 (N /
m2), ε = 1.59 x 10-8 (F / m), d33 = 417 x 10 Assuming that -12 (C / N), d31 = d32 = -198 x 1012 (C / N) and t = 6 (mm), Pb = 8.64 x 10-1 (N / m2) dh = 7 .46 x 10-11 (C / N) gh = 4.68 x 10-3
(Vm / N) M = -91 (dB re. V/Pa)=−211 (dB re. V / μPa)
[0013]
The first embodiment has the following advantages. (I) As compared with the conventional diskshaped electroacoustic transducer of FIG. 3 having the same outer diameter and the same
thickness, the disk-shaped electroacoustic transducer of this embodiment is a conventional one
as can be seen from the piezoelectric g constant gh. The piezoelectric g constant is about 3.5
times better than that of FIG. (Ii) In the electro-acoustic transducer of this example, the electrode
area is smaller if the outer diameter is the same as in the conventional one shown in FIG.
However, if the thickness t of the electroacoustic transducer of this embodiment is reduced so
that the sensitivity is the same as that of the conventional one shown in FIG. 3, the receiving
sensitivity is proportional to the thickness t. (Mm), and since the radius is 12 (mm) and ε = 1.59
× 10 -8 (F / m), the capacitance is 4230 (pF). The conventional disc-shaped electroacoustic
transducer of FIG. 3 has a radius of 15 (mm), a thickness of 6 (mm), and ε = 1.59 × 10 −8 (F /
m). pF). Therefore, if the electroacoustic transducer according to the present embodiment has the
same sensitivity and the same outer diameter, it can be seen that the capacitance is increased by
2.3 times.
[0014]
As described above, in the disk-shaped electroacoustic transducer of this embodiment, the stress
applied in the electrode surface direction of the piezoelectric ceramic 41 can be reduced as
compared with the conventional one shown in FIG. It is possible to increase the piezoelectric g
constant gh in hydrostatic pressure mode more than one. Furthermore, when compared with the
cylindrical electroacoustic transducer of FIG. 2, since an air layer and a balance structure are not
required inside, a high water pressure resistant transducer can be realized with a simple
structure. If the cylindrical shell of hard resin is provided instead of the metal cylindrical shell 42
shown in FIG. 1 or a shell other than the cylindrical shell is provided, substantially the same
effect as described above can be obtained.
04-05-2019
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[0015]
Second Embodiment FIG. 5 is a cross-sectional view of a disk-shaped electro-acoustic transducer
showing a second embodiment of the present invention. This disc-shaped electroacoustic
transducer has a disc-shaped porous piezoelectric ceramic 51 of thickness t and radius ra. The
porous piezoelectric ceramic 51 is polarized in the thickness direction, and the positive electrode
53 and the negative electrode 54 are formed on both surfaces thereof, and the terminals 55 and
56 are connected to the positive electrode 53 and the negative electrode 54, respectively. There
is. Around the porous piezoelectric ceramic 51, a metal cylindrical shell 52 of thickness t, inner
radius ra and outer radius rb is provided.
[0016]
The operation of this disc-shaped electroacoustic transducer is substantially the same as that of
the first embodiment. That is, assuming that porous PZT is used as the porous piezoelectric
ceramic 51 and soft iron is used as the metal cylindrical shell 52, the piezoelectric d constant in
the polarization direction of the porous PZT is d33, and the piezoelectric d constant in the
direction perpendicular to the polarization is d31, d32, Assuming that the dielectric constant is
ε, the stress Pb between porous PZT and metal of the electroacoustic transducer, the
piezoelectric d constant dh, the piezoelectric g constant gh, and the receiving sensitivity M are Ea
= 1.75 × 1010 (N / m 2) , Eb = 21.14 x 1010 (N / m2), aa = νb = 0.3, ra = 13 (mm), rb = 15
(mm), Pa = 1.0 (N / m2), ε = 4 Because 43.times.10@-9 (F / m), d33=417.times.10@12 (C / N),
d31=d32=-198.times.10@12 (C / N), and t = 6 (mm) Pb = 7.20 x 10-1 (N / m2) dh = 1. 32 x 1010 (C / N) gh = 2.98 x 10-2 (Vm / N) M = -75 (dB re . V/Pa)
[0017]
The second embodiment has the following advantages. (A) Comparing the disk-shaped
electroacoustic transducer according to the present embodiment with the same outer diameter
and thickness as in the conventional FIG. 3 with that in the conventional FIG. Although the
electroacoustic transducer is improved by 22.6 times, the capacitance of the electroacoustic
transducer of this example is lowered because the dielectric constant of the porous PZT used is
smaller than that of PZT. However, when the thickness t of the electroacoustic transducer of this
embodiment is reduced to have the same outer diameter and the same capacitance as the
conventional electroacoustic transducer of FIG. 3, the thickness t is 1.3 (mm). , The receiving
04-05-2019
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sensitivity is −88 (dB re. V/Pa)となる。 Therefore, the reception sensitivity is increased by
five times as compared with the conventional electroacoustic transducer of FIG. (B) Comparing
the electroacoustic transducer according to this embodiment with the same outer diameter and
thickness as that of the conventional FIG. 4 with that of the conventional FIG. The element is
excellent by 6.3 times, but if the electro-acoustic transducer of the present embodiment has the
same outer diameter, the electrode area is reduced by the metal cylindrical shell 52 provided on
the circumference, the static area is reduced. The capacitance decreases. However, when the
thickness t of the electroacoustic transducer of this embodiment is reduced to have the same
outer diameter and the same sensitivity as the conventional electroacoustic transducer of FIG. 4,
the thickness t is 0.9 (mm) The capacitance is 2612 (pF). The capacitance of the conventional
FIG. 4 is 522 (pF) because t = 6 (mm), radius 15 (mm), ε = 4.43 × 10 −9 (F / m), and thus the
static The capacitance has increased by five times.
[0018]
As described above, in the disk-shaped electroacoustic transducer of this embodiment, the stress
applied in the electrode surface direction of the porous piezoelectric ceramic (for example,
porous PZT) 51 can be reduced by the metal cylindrical shell 52. Thus, the piezoelectric g
constant gh in the hydrostatic pressure mode can be increased as compared with the
conventional electroacoustic transducer of FIGS. 3 and 4. In addition, since the piezoelectric g
constant gh is increased, the thickness can be reduced, and an increase in capacitance can also
be achieved. Furthermore, compared with the conventional cylindrical electroacoustic transducer
of FIG. 2, since an air layer and a balance structure are not required inside, a highly water
resistant electroacoustic transducer can be achieved with a simple structure. If the cylindrical
shell of hard resin is provided instead of the metal cylindrical shell 52 shown in FIG. 5 or a shell
other than the cylindrical shell is provided, substantially the same effect as described above can
be obtained.
[0019]
Third Embodiment FIG. 6 is a cross-sectional view of a disk-shaped electro-acoustic transducer
showing a third embodiment of the present invention. This disc-shaped electroacoustic
transducer has a disc-shaped porous piezoelectric ceramic 61 with a thickness t and a radius ra.
The porous piezoelectric ceramic 61 is made of, for example, porous PZT and is polarized in the
thickness direction, and a positive electrode 63 and a negative electrode 64 are formed on both
sides of the porous piezoelectric ceramic 61. Terminals 65 and 66 are connected. A cylindrical
shell 62 made of a porcelain material (for example, PZT) is integrally molded around the porous
04-05-2019
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piezoelectric ceramic 61. The cylindrical shell 62 has a thickness t, an inner radius ra, and an
outer radius rb, and is formed of, for example, PZT having a larger Young's modulus than porous
PZT.
[0020]
The operation of this embodiment is substantially the same as that of FIG. 1 showing the first
embodiment. That is, Ea = 1.75 × 1010 (N / m 2), Eb = 6.10 × 1010 (N / m 2), aa = νb = 0.3, ra
= 12 (mm), rb = 15 (mm), Pa = 1.0 (N / m 2), dielectric constant of porous PZT ε = 4.43 × 10
−9 (F / m), piezoelectric d constant of porous PZT d 33 = 417 × 10 −12 (C / N , D31=d32=198.times.10@-12 (C / N), t = 6 (mm), Pb=8.64.times.10@1 (N/m@2)dh=7.50.times.10@-11 (C /
N) gh = 1.69 × 10 -2 (Vm / N) M = -80 (dB re. V/Pa)
[0021]
The third embodiment has the following advantages (1) to (5). (1) Compared with the
conventional cylindrical electroacoustic transducer of FIG. 2, since an air layer and a balance
structure are not required inside, a high water pressure resistant electroacoustic transducer can
be realized with a simple structure. (2) Comparing the electroacoustic transducer according to
the present embodiment with the same outer diameter and the same thickness as that of the
conventional FIG. 3 and the electroacoustic transducer of the conventional FIG. The sound
conversion element is 12.8 times better. However, since the dielectric constant of the porous PZT
is smaller than that of PZT, the capacitance of the present embodiment is lowered. However, the
thickness t of the electro-acoustic transducer of the present embodiment is set to the
conventional electroacoustic transducer shown in FIG. In the case of the same outer diameter and
the same capacity, the thickness t is 1.1 (mm), and in this case, the receiving sensitivity is −95
(dB re. V/Pa)となる。 Therefore, if the same outer diameter and the same capacity, the
wave receiving sensitivity is increased by 2.4 times as compared with the conventional
electroacoustic transducer of FIG. (3) Comparing the electroacoustic transducer according to the
present embodiment with the same outer diameter and the same thickness as that of the
conventional FIG. 4 with the electroacoustic transducer of the conventional FIG. The
electroacoustic transducer is 3.6 times better. However, in the electro-acoustic transducer of the
present embodiment, since the electrode area is reduced by the cylindrical shell 62 of the
circumference if the outer diameter is the same, the capacitance is reduced, but the thickness of
the electro-acoustic transducer of the present embodiment When the thickness t is reduced to
have the same outer diameter and the same sensitivity as the conventional electroacoustic
transducer of FIG. 4, the thickness t is 1.7 (mm) and the capacitance is 1178 (pF). . The
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capacitance of the conventional FIG. 4 is 522 (pF) because t = 6 (mm), radius 15 (mm), ε = 4.43
× 10 −9 (F / m), and thus the static The capacitance increases 2.3 times.
[0022]
(4) Comparing the electroacoustic transducer according to the present embodiment with the
same outer diameter and the same thickness as that of FIG. 1 showing the first embodiment with
the electroacoustic transducer of FIG. The electroacoustic transducer of the embodiment is 3.6
times better. Further, in FIG. 1, when the piezoelectric ceramic 41 and the metal cylindrical shell
42 are bonded with an adhesive, for example, the adhesive is softened and peeled off, or the
adhesive is soft and the sound pressure leaks. There is a possibility that the piezoelectric g
constant gh will decrease. On the other hand, since the electroacoustic transducer of this
embodiment is integrally molded, the piezoelectric g constant due to peeling between the
piezoelectric ceramic 41 and the metal cylindrical shell 42 as shown in FIG. It is possible to
properly prevent the possibility of a decrease in gh. (5) Comparing the electroacoustic transducer
according to the present embodiment with the same outer diameter and the same thickness as
that of FIG. 5 showing the second embodiment with the electroacoustic transducer of FIG. The
piezoelectric g constant gh of the element is about 3⁄5 of the piezoelectric g constant gh of FIG.
However, since the electroacoustic transducer of this embodiment is integrally molded, the
piezoelectric g constant gh due to peeling between the porous piezoelectric ceramic 51 and the
metal cylindrical shell 52 in FIG. It is possible to prevent the decline properly. In FIG. 6, even if
the cylindrical shell 62 is made of a shell of a ceramic material other than the cylindrical shell,
the same effect as described above can be obtained.
[0023]
As described above in detail, according to the first invention, since the hard shell is provided
around the disk-shaped piezoelectric ceramic, the stress applied in the electrode surface direction
of the piezoelectric ceramic can be reduced Can be reduced by Therefore, the piezoelectric g
constant in the hydrostatic pressure mode can be increased compared to the conventional
electroacoustic transducer of the disk-shaped piezoelectric ceramic. Furthermore, compared with
the conventional cylindrical electroacoustic transducer, since an air layer and a balance structure
are not required inside, a highly water resistant electroacoustic transducer can be realized with a
simple structure. According to the second invention, since the hard shell is provided around the
disk-shaped porous piezoelectric ceramic, the electrode surface direction of the porous
piezoelectric ceramic is substantially the same as the first invention by the hard shell. The stress
applied to the above can be reduced, and the piezoelectric g constant in the hydrostatic pressure
04-05-2019
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mode can be increased compared to an electroacoustic transducer composed of a conventional
disk-shaped piezoelectric ceramic. In addition, since the piezoelectric g constant is increased, the
thickness can be reduced, and an increase in capacitance can also be achieved. Also, as in the
first invention, compared to the conventional cylindrical electroacoustic transducer, an air layer
and a balanced structure are not required inside, so a high water pressure resistant
electroacoustic transducer with a simple structure. Can be achieved.
[0024]
According to the third invention, since the hard shell is constituted by a cylindrical shell made of
metal or hard resin, substantially the same effect as in the first and second inventions can be
obtained. According to the fourth invention, since the shell of the porcelain material is integrally
molded around the disc-shaped porous piezoelectric ceramic, it has high water resistance and
good sensitivity, as in the first and second inventions. Furthermore, since the piezoelectric g
constant significantly increases, the thickness can be reduced, and an increase in capacitance can
also be achieved. Furthermore, compared with the first invention, the piezoelectric g constant is
several times better in the present invention. In addition, since the electroacoustic transducer of
the present invention is integrally molded, it is possible to properly prevent the problems such as
peeling between the porous piezoelectric ceramic and the shell around it and the decrease of the
piezoelectric g constant due to the sound pressure leakage. . Further, compared with the second
invention, the piezoelectric g constant according to the present invention is smaller than the
piezoelectric g constant of the second invention, but since the electroacoustic transducer of the
present invention is integrally molded, porous piezoelectric It is possible to properly prevent the
problems such as peeling between the porcelain and the shell around it and the decrease of the
piezoelectric g constant due to the sound pressure leakage. According to the fifth invention, since
the shell of the porcelain material is formed of a cylindrical shell, substantially the same effect as
that of the fourth invention can be obtained.
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