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DESCRIPTION JPH0614386

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DESCRIPTION JPH0614386
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an
underwater wave receiver such as a marine acoustic measuring instrument, and is an
electroacoustic transducer using a porous piezoelectric ceramic for converting sound pressure
into an electric signal. It is about
[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 which converts sound waves into electric signals. .
Currently, research is being conducted on porous piezoelectric ceramics in which the
piezoelectric g constant of the piezoelectric ceramic is increased, and there are, for example, the
following publications. Literature; Ferroelectrice, 49 (1983) Gordon and Breach, Science
Publishers (US) P.I. No. 265-272 or less The structure of the conventional electroacoustic
transducer is demonstrated, referring FIGS. 2-4. FIG. 2 is a perspective view of a conventional
circular electroacoustic transducer using a piezoelectric ceramic. In this cylindrical
electroacoustic transducer, electrodes 12 and 13 are respectively formed on the inner periphery
and the outer periphery of the cylindrical piezoelectric ceramic 11, and the electrodes 12 and 13
are connected to the terminals 14 and 15, respectively. This electroacoustic transducer utilizes
the sensitivity to the sound pressure mainly due to the change in the peripheral length of the
respiratory vibration. Assuming that the inner diameter of the electroacoustic transducer is a and
the outer diameter is b, and the piezoelectric g constant in the circumferential direction is g31,
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the wave reception sensitivity M is 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 conversion element in which b is
15 (mm), d31 is −198 × 10 −12 (C / N), and ε is 1.59 × 10 −8 (F / m), the receiving
sensitivity M is M = −75 (dB re. V/Pa)
[0003]
FIG. 3 is a cross-sectional view showing a conventional disc-shaped electroacoustic transducer
utilizing thickness resonance. In this disc-shaped electroacoustic transducer, the electrodes 22
and 23 are formed on both sides of the disc-shaped piezoelectric ceramic 21, and the terminals
24 and 25 are connected to the electrodes 22 and 23, respectively. As the piezoelectric ceramic
21, PZT is used.
[0004]
When this electro-acoustic transducer is used at a low frequency below the resonance frequency,
the electro-acoustic transducer receives hydrostatic pressure, so the wave receiving sensitivity M
is gh of piezoelectric g constant of hydrostatic pressure mode and thickness Let t be t, then 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, 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)
[0005]
FIG. 4 is a cross-sectional view showing a conventional disc-shaped electroacoustic transducer
utilizing thickness resonance. This disc-shaped electroacoustic transducer has a transducer
element structure similar to that shown in FIG. 3, and electrodes 32 and 33 are formed on both
sides of the disc-shaped porous piezoelectric ceramic 31, and terminals 34 and 34 are terminals.
, 35 are connected. The porous piezoelectric ceramic 31 is made of, for example, the porous PZT
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described in the aforementioned document. When considering the cross section parallel to the
planes of the electrodes 32 and 33, the area occupied by the PZT is reduced as compared with
the electroacoustic transducer of FIG. Since the amount of charge that occurs and is generated is
equivalent to that of the electroacoustic transducer of FIG. 3, a value equivalent to that of PZT is
adopted.
[0006]
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)
[0007]
However, the electroacoustic transducer of the above construction has the following problems.
(A) The cylindrical electroacoustic transducer shown in 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 in 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. (B) In the disk-shaped electroacoustic
transducer of FIG. 3, since the block-shaped piezoelectric ceramic 21 is used, although the water
pressure is high, the sensitivity is low at a low frequency below the resonance frequency. That is,
the piezoelectric g constant gh (= g33 + g32 + g31) of the piezoelectric ceramic 21 has opposite
signs of g31 and g32 with respect to g33, and the absolute value is about 1/2 (1 / 2g33 ≒ | g31
| ≒ | g32 |) There is a problem that the sensitivity becomes a very small value because there is
one. (C) In the disk-shaped electroacoustic transducer of FIG. 4, since the block-shaped porous
piezoelectric ceramic 31 is used, the water pressure is high and the sensitivity is higher than that
of the electroacoustic transducer of FIG. However, since the dielectric constant is lowered to
increase the piezoelectric g constant, the capacitance is lowered, and the receiving sensitivity by
the cable capacity is lowered, and the problem in the electric circuit by the increase of the
electric impedance is caused. There is.
[0008]
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Therefore, in order to solve such a problem, the inventor of the present application has proposed
an electroacoustic transducer as shown in FIGS. 5 and 6. 5 and 6 are cross-sectional views
showing a disk-shaped electroacoustic transducer proposed by the inventor of the present
invention. The disc-shaped electroacoustic transducer of FIG. 5 has a disc-shaped piezoelectric
ceramic 41 polarized in the thickness direction, and a positive electrode 43 and a negative
electrode 44 are formed on both sides of the piezoelectric ceramic 41. Terminals 45 and 46 are
connected to the positive electrode 43 and the negative electrode 44. A metal cylindrical shell 42
is provided around the piezoelectric ceramic 41.
[0009]
Next, the operation will be described. The disk-shaped electroacoustic transducer of FIG. 5 is
subjected to hydrostatic pressure for a low frequency that is a wavelength 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. (Pb
<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. Let s be 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)
[0010]
Here, it is assumed that PZT for the voltage porcelain 41 and soft iron for the metal cylindrical
shell 42, Ea = 6.10 × 1010 (N / m 2), Eb = 21.14 × 10 10 (N / m 2), .nu.a = .nu.b = 0.3, ra = 12
(mm), rb = 15 (mm), Pa = 1.0 (N / m @ 2), .epsilon. = 1.59.times.10 @ -8 (F / m), d33 = Assuming
that 417 × 10-12 (C / N), d31 = d32 = -198 × 10-12 (C / N), and t = 6 (mm), Pb = 8.64 × 10-1
(N / m 2) dh = 7.46 x 10-11 (C / N) gh = 4.68 x 10-3 (Vm / N) M = -91 (dB re. V/Pa)
[0011]
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The disc-shaped electroacoustic transducer of FIG. 6 has a disc-shaped porous piezoelectric
ceramic 51 polarized in the thickness direction, and a positive electrode 53 and a negative
electrode 54 are formed on both sides thereof. Further, terminals 55 and 56 are connected to the
positive electrode 53 and the negative electrode 54. A metal cylindrical shell 52 is provided
around the porous piezoelectric ceramic 51. The operation of this disc-shaped electro-acoustic
transducer is similar to that of the disc-shaped electro-acoustic transducer of FIG. 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 [email protected] (F / m), [email protected] (C / N), [email protected] (C /
N), and t = 6 (mm) Pb = 7.20 x 10-1 (N / m2) dh = 1. 32 x 10-10 (C / N) gh = 2.98 x 10-2 (Vm /
N) M = -75 (dB re . V/Pa)
[0012]
As described above, in the disk-shaped electroacoustic transducer of FIGS. 5 and 6, since the
metal cylindrical shells 42 and 52 are provided around the piezoelectric ceramic 41 or the
porous piezoelectric ceramic 51, a high water pressure resistance can be obtained. Since the
sensitivity is high and the piezoelectric g constant gh is significantly increased, the thickness can
be reduced and the dielectric constant can be secured. However, the adhesive layer between the
piezoelectric ceramic 41, 51 and the metal cylindrical shell 42, 52 does not have a water
resistant adhesive, so the adhesive layer is softened and peeled off, or the adhesive layer is soft.
There is a problem that the sound pressure leaks and the piezoelectric g constant gh decreases.
The present invention solves the problem that it is difficult to provide a conversion element
having high water pressure, low frequency, high sensitivity, and a large electrostatic capacitance
as a problem of the prior art etc. An electroacoustic transducer of the present invention is
provided.
[0013]
SUMMARY OF THE INVENTION In order to solve the above problems, the present invention
relates to a disc-shaped porous piezoelectric ceramic in an electroacoustic transducer of an
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underwater receiver that converts sound pressure into an electric signal. A cylindrical
piezoelectric ceramic integrally formed around the porous piezoelectric ceramic, a first positive
electrode and a first negative electrode formed on both sides of the porous piezoelectric ceramic,
the first positive electrode, and A second positive electrode and a second negative electrode are
provided on the both sides of the piezoelectric ceramic in the same direction as the first negative
electrode and separated. The porous piezoelectric ceramic and the piezoelectric ceramic form a
disk as a whole, and the porous piezoelectric ceramic and the piezoelectric ceramic are polarized
in the same direction with respect to the thickness direction, and the first positive electrode and
the first positive electrode Two negative electrodes are connected, and the first negative
electrode and the second positive electrode are connected.
[0014]
According to the present invention, since the electroacoustic transducer is configured as
described above, the disk-shaped porous piezoelectric ceramic and the cylindrical piezoelectric
ceramic provided around the disk-shaped porous disk are generally disk-shaped. Thus, high
water pressure resistance can be improved. In the porous piezoelectric ceramic and the
piezoelectric ceramic polarized in the same direction with respect to the thickness direction, the
positive electrode of the porous piezoelectric ceramic and the negative electrode of the
piezoelectric ceramic are connected among the positive and negative electrodes provided on both
surfaces thereof. Since the negative electrode of the porous piezoelectric ceramic and the positive
electrode of the piezoelectric ceramic are connected, characteristics of high sensitivity at low
frequency can be obtained, and an increase in capacitance can be achieved. Therefore, the
problem can be solved.
[0015]
FIG. 1 is a cross-sectional view of a disk-shaped electroacoustic transducer showing an
embodiment of the present invention. This disc-shaped electroacoustic transducer has a discshaped porous piezoelectric ceramic 61 with a thickness t and a radius ra, and a cylindrical
piezoelectric ceramic 62 is integrally molded around it. The piezoelectric ceramic 62 has a disk
shape as a whole along with the porous piezoelectric ceramic 61 with an inner radius ra, an outer
radius rb, and a thickness t. For example, the porous piezoelectric ceramic 61 is formed of
porous PZT, and the piezoelectric ceramic 62 is formed of PZT, and they are polarized in the
same direction with respect to the thickness direction. The positive electrode 63 and the negative
electrode 64 are formed on both sides of the disk-shaped porous piezoelectric ceramic 61, and
the positive electrode 65 and the negative electrode 66 are also formed on both sides of the
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cylindrical piezoelectric ceramic 61. The positive electrode 63 and the negative electrode 66 are
commonly connected to the terminal 67, and the negative electrode 64 and the positive electrode
65 are commonly connected to the terminal 68.
[0016]
Next, the operation will be described. The disc-shaped electroacoustic transducer 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. In the
thickness direction of the porous PZT (61), the stress Pa is applied by the sound pressure Pa, but
in the electrode surface direction of the porous PZT (61), the sound is produced by the
cylindrical PZT (62) integrally formed on the periphery. The pressure Pa is braked and the stress
Pb is applied. Assuming that the Young's modulus of the porous PZT (61), the Poisson's ratio are
Ea, aa, the Young's modulus of the PZT (62), and the Poisson's ratio is Eb, νb, Pb is obtained.
Therefore, the charge Qa generated on the positive electrode 63 of the disk-shaped porous PZT
(61) has an electrode area of the porous PZT (61) Sa, a piezoelectric d constant in the
polarization direction d33, and a direction perpendicular to the polarization direction Assuming
that the piezoelectric d constant of this is d31 and d32, Qa = (Pa · d33 + Pb · d32 + Pb · d31) ×
Sa (C)
[0017]
On the other hand, in the negative electrode 66 of the cylindrical PZT (62), when the thickness
(rb -ra) becomes thinner, the stress in the direction perpendicular to the electrode surface is
more influenced by the stress in the circumferential direction. , Positive charge is generated. The
charge Qb generated at the negative electrode 66 of the cylindrical PZT (62) is Sb 2 for the
electrode area of the cylindrical PZT (62), d33 for the piezoelectric d constant in the polarization
direction, and d33 for the piezoelectric d constant in the direction perpendicular to the
polarization direction. Assuming that d31 and d32 (note that the piezoelectric d constants of the
porous PZT (61) and the PZT (62) are the same for the reason described in the conventional FIG.
4). Therefore, the total charge amount Qt generated on the positive electrode 63 of the
electroacoustic transducer is such that Qt = Qa + Qb (C) because these electrodes 63 and 66 are
connected. Further, assuming that the dielectric constant εt of the electroacoustic transducer
and the capacitance Ct are εa of the porous PZT (61) and εb of the PZT (62), εt = (εa · Sa +
εb · Sb ) / (Sa + Sb) (F / m) Ct = .epsilon.t (Sa + Sb) / t (F). From the above, the piezoelectric d
constant dh, the piezoelectric g constant gh, and the receiving sensitivity M of the electroacoustic
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transducer are dh = Qt / {| Pa (Sa + Sb)} (C / N) gh = dh / εtM = 20 x log (| gh | · t) (dB re.
V/Pa)となる。 Here, Ea = 1.75 × 1010 (N / m 2), Eb = 6.10 × 10 10 (N / m 2), aa = νb =
0.3, ra = 12 (mm), rb = 15 (mm) , Pa = 1.0 (N / m 2), ε a = 4.43 × 10 −9 (F / m), ε b = 1.59 ×
10 −8 (F / m), d 33 = 417 × 10 −12 C / N), [email protected] (C / N), and t = 6
(mm), so [email protected] (N / m @ 2) Qa = 3.39 X 10-14 (C) Qb = 1.91 x 10-14 (C) Qt = 5.30
x 10-14 (C) ε t = 8.85 x 10-9 (F / m) Ct = 1010 (pF ) Dh = 7.50 × 10 11 (C / N) gh = 8.75 × 10
−3 (Vm / N) M = −86 (dB re. V/Pa)
[0018]
The present embodiment has the following advantages (i) to (v). (I) Compared with the
conventional cylindrical electroacoustic transducer of FIG. 2, since the air layer and the balance
structure are not required inside, the electroacoustic transducer of this embodiment has a simple
structure and high water pressure resistance. Can be realized. (Ii) 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 with the cylindrical electroacoustic transducer of the
conventional FIG. The example electroacoustic transducer is 6.6 times better. However, since the
dielectric constant of the porous PZT (61) is smaller than that of the PZT (62), the capacitance
according to the present embodiment decreases, but the thickness t of the electroacoustic
transducer of the present embodiment is When the thickness t is reduced to 3.2 (mm) when the
capacitance is reduced so as to have the same outer diameter and the same capacitance as the
electroacoustic transducer of No. 3, the receiving sensitivity in this case is -91 (dB re.
V/Pa)となる。 Therefore, the receiving sensitivity is 3.5 times better than that of the
conventional electroacoustic transducer of FIG. 3 even with the same outer diameter and the
same capacitance.
[0019]
(iii) Comparing the electroacoustic transducer according to this embodiment with the same outer
diameter and the same thickness as that of the conventional FIG. 4 with the disk-shaped
electroacoustic transducer of the conventional FIG. The electroacoustic transducer according to
the example is 1.8 times better. Also, even in comparison with the capacitance, the capacitance in
the conventional FIG. 4 is t = 6 (mm), radius 15 (mm), dielectric constant ε = 4.43 × 10 -9 (F /
m) Therefore, it is 522 (pF), and the capacitance is also 1.9 times better. (Iv) Comparing the
electroacoustic transducer according to the present embodiment with the same outer diameter
and the same thickness as that of the related proposal of FIG. 5 with the disc type electroacoustic
transducer of FIG. The electroacoustic transducer according to the example is 1.9 times better. In
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addition, since the capacitance of this embodiment is smaller than that of FIG. 5, the thickness t
of the electroacoustic transducer of this embodiment is reduced so as to have the same outer
diameter and capacitance. Then, when the sensitivity is compared, the thickness t of the
electroacoustic transducer according to the present embodiment is 5 (mm), and the sensitivity in
this case is −87 (dB re. V/Pa)となる。 Therefore, even with the same outer diameter and
the same capacitance, the wave receiving sensitivity is 1.6 times better than that of the
electroacoustic transducer of FIG. Furthermore, in the electro-acoustic transducer of this
embodiment, since the porous PZT (61) and the PZT (62) are integrally molded, the space
between the piezoelectric ceramic 41 and the cylindrical shell 42 of metal as shown in FIG. It is
possible to prevent the peeling of the adhesive and the reduction of the piezoelectric g constant
gh due to the leakage of sound waves into the adhesive.
[0020]
(V) Comparing the electroacoustic transducer according to the present embodiment with the
same outer diameter and the same thickness as that of the related proposal of FIG. 6 with the
electroacoustic transducer of FIG. The constant gh is about 3/10 of the piezoelectric g constant
gh in FIG. 6, but the capacitance of the present embodiment is a large value compared to that of
FIG. When the sensitivity t is compared by reducing the thickness t of the electroacoustic
transducer of this example so as to obtain capacitance, t = 15 (mm), and the sensitivity in this
case is −78 (dB re. V/Pa)となる。 Therefore, in the case of the same outer diameter and
the same capacitance, the receiving sensitivity is 3 (dB re. V / Pa) It becomes inferior. However,
since the electro-acoustic transducer of this embodiment integrally molds the porous PZT (61)
and the PZT (62), the porous piezoelectric ceramic 51 as shown in FIG. It is possible to prevent
the peeling of the adhesive during and the reduction of the piezoelectric g constant gh due to the
sound wave leaking into the adhesive. The present invention is not limited to the above
embodiment. For example, even if the porous piezoelectric ceramic 61 is formed of a material
other than porous PZT, or the piezoelectric ceramic 62 is formed of a material other than PZT,
compared with the prior art. Thus, it is possible to provide a high-performance electro-acoustic
transducer. Moreover, the disk-shaped electroacoustic transducer of FIG. 1 may change the
whole structure into shapes and structures other than FIG.
[0021]
As described above in detail, according to the present invention, since the whole has a disk shape,
not only high water pressure resistance can be realized with a simple structure, but also high
sensitivity at low frequency and further A conversion element with a large capacitance can be
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realized. Moreover, since the disc-shaped porous piezoelectric ceramic and the cylindrical
piezoelectric ceramic are integrally molded, it is possible to prevent the peeling between them
and the decrease of the piezoelectric g constant due to the leakage of the sound wave to the
portion. .
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