JP2985916B2 - Electroacoustic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for underwater receivers such as marine acoustic measuring instruments and the like, and 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 Conventionally, piezoelectric ceramics such as barium titanate and zirconate / lead titanate (PZT) have been used as a material for an electroacoustic transducer of an underwater receiver for converting sound waves into electric signals. . At present, research is being conducted on porous piezoelectric ceramics in which the piezoelectric g constant of the piezoelectric ceramic is increased, and for example, there is one described in the following literature. Literature; Ferroelectrice, 49 (1983) Gordon and B
reach, Science Publishers (US) 265-272 Hereinafter, the configuration of the conventional electroacoustic transducer will be described with reference to FIGS. 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 formed on the inner and outer circumferences of a cylindrical piezoelectric ceramic 11, respectively.
2 and 13 are connected to terminals 14 and 15, respectively.
This electro-acoustic transducer utilizes sensitivity to sound pressure mainly due to a change in the circumference of respiratory vibration. Assuming that the inner diameter of the electroacoustic transducer is a and the outer diameter is b, and that a / b ≒ 1, and that the piezoelectric g constant in the peripheral direction is g ₃₁ , M = 20 × log (| g ₃₁ | · B) (dB re.
V / Pa). Here, g ₃₁ is the piezoelectric d constant in the peripheral direction d
₃₁ and the dielectric constant is ε, then g ₃₁ = d ₃₁ / ε (Vm / N). b is 15 (mm), d ₃₁ is -198 × 10 ^-12
In the case of a cylindrical conversion element having (C / N) and ε of 1.59 × 10 ⁻⁸ (F / m), the receiving sensitivity M is M = −75 (dB re.V / Pa).

FIG. 3 is a sectional view showing a conventional disc-shaped electroacoustic transducer utilizing thickness resonance. In this disc-shaped electroacoustic transducer, electrodes 22 and 23 are formed on both surfaces of a disc-shaped piezoelectric ceramic 21, respectively.
3, terminals 24 and 25 are connected. PZT is used as the piezoelectric ceramic 21.

When the electro-acoustic transducer is used at a low frequency lower than the resonance frequency, the electro-acoustic transducer receives a hydrostatic sound pressure. _h, and the thickness and t, M = 20 × log ( | g h | · t) (dB r
e. V / Pa). Here, if the piezoelectric g constant in the polarization direction is g ₃₃ , the piezoelectric g constants in the direction perpendicular to the polarization are g ₃₁ and g _32, and the corresponding piezoelectric d constants are d ₃₃ , d ₃₁ and d ₃₂ , g is _{h = g 33 + g 32 +} g 31 = d 33 / ε + d 32 / ε + d 31 / ε = d h / ε (Vm / N). PZT is used for the piezoelectric ceramic 21. t
There 6 (mm), d ₃₃ is ^{417 × 10 -12 (C / N} ), d
_31, d ₃₂ is ^{-198 × 10 -12 (C / N} ), the dielectric constant ε is a ^{1.59 × 10 -8 (F / m} ), the piezoelectric g constant g _h, reception sensitivity M is, g _h = 1.32 × 10 ⁻³ (Vm / N) M = −102 (dB re. V / Pa)

FIG. 4 is a 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 of FIG.
Electrodes 32 and 33 are provided on both sides of the disc-shaped porous piezoelectric ceramic 31.
Are formed, and terminals 34 and 35 are connected to the electrodes 32 and 33, respectively. The porous piezoelectric ceramic 31 is made of, for example, porous PZT described in the above-mentioned document. Porous P
When the piezoelectric d constant of ZT is considered to be a cross section parallel to the planes of the electrodes 32 and 33, the area occupied by PZT is smaller than that of the electroacoustic transducer of FIG. Since the amount of electric charge generated in the electrodes 32 and 33 is equivalent to that of the electroacoustic transducer of FIG. 3, a value equivalent to PZT is adopted. The dielectric constant ε is smaller than that of PZT due to the gap.

T is 6 (mm) and d ₃₃ is 417 × 10 ^-12
(C / N), d ₃₁ and d ₃₂ are −198 × 10 ⁻¹² (C / N
N), the dielectric constant ε is a ^{4.43 × 10 -9 (F / m} ), the piezoelectric g constant g _h, reception sensitivity M ^{_{is, g h = 4.74 × 10 -3}} (Vm / N) M = -91 (dB re.V / P
a)

[0007]

However, the electroacoustic transducer having the above configuration has the following problems. (A) The cylindrical electro-acoustic transducer shown in FIG. 2 has a high wave receiving sensitivity, but has a problem that it has a low water pressure and cannot be used at a deep depth because it has an air layer inside. Also,
There is also a balance system in which oil or the like is put inside to provide water pressure resistance, but there are problems such as a decrease in sensitivity and a complicated structure.

(B) The disc-shaped electro-acoustic transducer shown in FIG. 3 has a high water pressure resistance because the block-shaped piezoelectric ceramic 21 is used, but has low sensitivity at low frequencies below the resonance frequency.
That is, the piezoelectric g constant g _h of the piezoelectric ceramic 21 (= g ₃₃ + g ₃₂ +
g ₃₁ ) is different from g _{33 in} that g ₃₁ and g ₃₂ have different signs and the absolute value is about １ ／ (１ ／ g ₃₃ ≒ | g ₃₁ ≒ | g ₃₂ ）). Is a very small value.

(C) The disc-shaped electro-acoustic transducer shown in FIG. 4 uses the block-shaped porous piezoelectric ceramic 31, and therefore has a higher water pressure and higher sensitivity than the electro-acoustic transducer shown in FIG. However, since the dielectric constant is reduced in order to increase the piezoelectric g constant, the capacitance is reduced, and the receiving sensitivity is reduced due to the cable capacitance, and the inconvenience in the electric circuit due to the increase in the electrical impedance is caused. There is. Then, in order to solve such a problem, the present inventor proposed an electroacoustic transducer as shown in FIGS.

FIGS. 5 and 6 are sectional views showing a disc-shaped electro-acoustic transducer proposed by the present inventors. The disc-shaped electroacoustic transducer shown in 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 surfaces of the piezoelectric ceramic 41. Positive electrode 43
Also, terminals 45 and 46 are connected to the negative electrode 44. A metal cylindrical shell 42 is provided around the piezoelectric ceramic 41.

Next, the operation will be described. The disc-shaped electro-acoustic transducer shown in FIG. 5 receives a hydrostatic sound pressure at a low frequency having a wavelength sufficiently longer than the dimension of the transducer. When the sound pressure (the hydrostatic pressure) and P _a, the sound pressure P _a is applied to the entire surface of the electroacoustic transducer. Although applied stress P _a by the sound pressure P _a in the thickness direction of the piezoelectric ceramic 41, the electrode surface direction of the piezoelectric ceramic 41, the sound pressure P _a of a cylindrical shell 42 of metal provided on the circumference is subjected to braking , so that the stress _{P b (P b <P a} ) is applied. The Young's modulus and Poisson's ratio of the piezoelectric ceramic 41 are E _a and ν _a , and the Young's modulus and Poisson's ratio of the metal are E _b and ν.
_{Assuming b} , P _b is

(Equation 1) Becomes Therefore, the piezoelectric d constant d _h , the piezoelectric g constant g _h , and the wave receiving sensitivity M of the electroacoustic transducer are d ₃₃ for the piezoelectric d constant in the polarization direction of the piezoelectric ceramic 41 and d for the piezoelectric d constant in the direction perpendicular to the polarization.
_31, d _32, when the dielectric constant _{ε, d h = (P a} · d 33 + P b · d 32 + P b · d 31) / | P a | (C / N) g h = d h / ε ( Vm / N) M = 20 × log (| g h | · t) becomes a (dB re.V / Pa).

Here, it is assumed that PZT is used for the voltage porcelain 41 and soft iron is used for the metal cylindrical shell 42, and E _a = 6.10 × 10 ¹⁰
(N / m ² ), E _b = 21.14 × 10 ¹⁰ (N / m ² )
m ² ), ν _a = ν _b = 0.3, r _a = 12 (mm), r
_{b = 15 (mm), P} a = 1.0 (N / m 2), ε =
1.59 × 10 ⁻⁸ (F / m), d ₃₃ = 417 × 10 ⁻¹²
(C / N), d ₃₁ = d ₃₂ = −198 × 10 ⁻¹² (C / N
N), When t = 6 (mm), P b = 8.64 × 10 -1 (N / m 2) d h = 7.46 × 10 -11 (C / N) g h = 4.68 × 10 ⁻³ (Vm / N) M = −91 (dB re. V / P
a)

The disc-shaped electro-acoustic transducer shown in FIG.
It has a disk-shaped porous piezoelectric ceramic 51 polarized in the thickness direction, on both surfaces of which a positive electrode 53 and a negative electrode 54 are formed.
6 are connected. Around the porous piezoelectric ceramic 51,
A metal cylindrical shell 52 is provided. The operation of the disc-shaped electro-acoustic transducer is the same as that of the disc-shaped electro-acoustic transducer shown in FIG. That is, the porous piezoelectric ceramic 51 is made of porous PZ.
T, assuming that soft iron is used for the metal cylindrical shell 52, the porous PZ
Assuming that the piezoelectric d constant in the polarization direction of T is d ₃₃ , the piezoelectric d constant in the direction perpendicular to the polarization is d ₃₁ , d ₃₂ , and the dielectric constant is ε, the stress P _b between the porous PZT-metal of the electroacoustic transducer, The piezoelectric d constant d _h , the piezoelectric g constant g _h , and the receiving sensitivity M are E _a = 1.7.
5 × 10 ¹⁰ (N / m ² ), E _b = 21.14 × 10
¹⁰ (N / m ² ), v _a = v _b = 0.3, r _a = 13 (m
_{m), r b = 15 (} mm), P a = 1.0 (N /
m ² ), ε = 4.43 × 10 ⁻⁹ (F / m), d ₃₃ = 41
7 × 10 ⁻¹² (C / N), d ₃₁ = d ₃₂ = −198 × 10
⁻¹² (C / N) and t = 6 (mm), P _b = 7.20 × 10 ⁻¹ (N / m ² ) d _h = 1.32 × 10 ⁻¹⁰ (C / N) g _h = 2.98 × 10 ⁻² (Vm / N) M = −75 (dB re.V / P
a)

As described above, in the disc-shaped electroacoustic transducer shown in FIGS. 5 and 6, the piezoelectric ceramic 41 or the porous piezoelectric ceramic 5 is used.
Since metal cylindrical shells 42 and 52 are provided around 1,
A high water pressure resistance, good sensitivity, since the further piezoelectric g constant g _h is greatly increased, it is possible to reduce the thickness, can be secured even dielectric constant. However, since the adhesive layer between the piezoelectric ceramics 41, 51 and the metal cylindrical shells 42, 52 does not have a water-resistant adhesive, the adhesive layer softens and peels off, or the adhesive layer is soft. the piezoelectric g constant g _h leak sound pressure there is a problem such as a decrease. SUMMARY OF THE INVENTION The present invention provides an underwater receiver which solves the problems of the prior art and the like that it is difficult to provide a conversion element having a high water pressure resistance, a high sensitivity at a low frequency, and a large capacitance. The present invention is to provide an electroacoustic transducer of the present invention.

[0015]

According to the present invention, there is provided an electroacoustic transducer for an underwater receiver for converting sound pressure into an electric signal, which comprises: a disc-shaped porous piezoelectric ceramic; It comprises a cylindrical piezoelectric ceramic integrally molded around the porous piezoelectric ceramic, and positive and negative electrodes formed on both surfaces of the porous piezoelectric ceramic and the piezoelectric ceramic. The porous piezoelectric ceramic and the piezoelectric ceramic form a disc shape as a whole, and the porous piezoelectric ceramic and the piezoelectric ceramic are polarized in directions opposite to the thickness direction.

[0016]

According to the present invention, since the electro-acoustic transducer is constructed as described above, the disc-shaped porous piezoelectric ceramic and the cylindrical piezoelectric ceramic provided around the same are entirely disc-shaped. Therefore, it is possible to improve the high water pressure resistance. The porous piezoelectric ceramic and the piezoelectric ceramic polarized in the direction opposite to the thickness direction improve the sensitivity at a low frequency and increase the capacitance. Therefore, the above problem can be solved.

[0017]

FIG. 1 is a sectional view of a disc-shaped electroacoustic transducer according to an embodiment of the present invention. This disc-shaped electro-acoustic transducer has a disc-shaped porous piezoelectric ceramic 61 having _a thickness t and a radius ra, and _a cylindrical piezoelectric ceramic 62 is integrally formed therearound. The piezoelectric ceramic 62, the inner radius r _a, an outer radius r _b, and the thickness t, and forms a disc-shaped throughout with porous piezoelectric ceramic 61. For example, the porous piezoelectric ceramic 61 is formed of porous PZT, and the piezoelectric ceramic 62 is formed of PZT, and they are respectively polarized in directions opposite to the thickness direction. A positive electrode 63 and a negative electrode 64 are formed on both sides of the porous piezoelectric ceramic 61 and the piezoelectric ceramic 62, and the positive electrode 63 and the negative electrode 64 are connected to terminals 65 and 66, respectively.

Next, the operation will be described. This disc-shaped electro-acoustic transducer receives a hydrostatic sound pressure at a low frequency, which is a wavelength sufficiently longer than the dimension of the transducer. When the sound pressure (the hydrostatic pressure) and P _a, the sound pressure P _a is applied to the entire surface of the electroacoustic transducer. The thickness direction of the porous PZT (61), the sound pressure P _a by the stress P _a is applied to the electrode surface direction of the porous PZT (61), integrally molded cylindrical PZT the periphery (62) the sound pressure P _a is subjected to braking, so that the applied stress P _b by. Porous PZT (6
The Young's modulus and Poisson's ratio of 1) are E _a , ν _a , PZT (6
If the Young's modulus and Poisson's ratio of 2) are E _b and ν _b , P
_b is

(Equation 2) Becomes Therefore, the charge Q _a generated in the positive electrode 63 by the disc-shaped porous PZT (61) is porous PZT
The electrode area of the (61) S _a, the porous PZT (61)
Assuming that the piezoelectric d constant in the polarization direction is d ₃₃ and the piezoelectric d constants in the direction perpendicular to the polarization direction are d ₃₁ and d ₃₂ , Q _a = (P _a d ₃₃ + P _b d ₃₂ + P _b d ₃₁ ) × S _a (C).

On the other hand, the electric charge generated on the positive electrode 63 on the cylindrical PZT (62) has a smaller stress (r _b -r _a ) than a stress in a direction perpendicular to the electrode surface when the thickness (rb−ra) is thin. And the polarization direction becomes porous PZT (6
Since it is the reverse of 1), a positive charge is generated. Charge Q generated on positive electrode 63 on cylindrical PZT (62)
_{As for b} , assuming that the electrode area on the cylindrical PZT (62) is S _b , the piezoelectric d constant in the polarization direction is d ₃₃ , and the piezoelectric d constants in the direction perpendicular to the polarization direction are d ₃₁ and d ₃₂ (note that the porous material is porous). PZT (6
The piezoelectric d constants of 1) and PZT (62) are the same for the reason described with reference to FIG.

(Equation 3) Becomes Therefore, total charge Q _t that occurs in the positive electrode 63 of electroacoustic transducer becomes _{Q t = Q a + Q b} (C). Further, the permittivity ε _t and the capacitance C _t of the electroacoustic transducer are obtained by setting the permittivity of the porous PZT (61) to ε _a , PZ
Assuming that the permittivity of T (62) is ε _b , ε _t = (ε _a · S _a + ε _b · S _b ) / (S _a + S _b ) (F / m) C _t = ε _t · (S _a + S _b ) / t (F). From the above, the piezoelectric d constant d _h , the piezoelectric g constant g _h , and the receiving sensitivity M of the electroacoustic transducer are: d _h = Q _t / {| P _a | · (S _a + S _b )} (C / _{N) g h = d h /} ε t M = 20 × log (| g h | · t) becomes a (dB re.V / Pa). Here, E _a = 1.75 × 10 ¹⁰ (N /
m ² ), E _b = 6.10 × 10 ¹⁰ (N / m ² ), ν _a =
ν _b = 0.3, r _a = 12 (mm), r _b = 15 (m
m), P _a = 1.0 (N / m ² ), ε _a = 4.43 × 1
0 ^-9 (F / m), ε _b = 1.59 × 10 ^-8 (F / m),
d ₃₃ = 417 × 10 ⁻¹² (C / N), d ₃₁ = d ₃₂ = −1
Since 98 × 10 ^-12 (C / N) and t = 6 (mm), P _b = 8.64 × 10 ^-1 (N / m ² ) Q _a = 3.39 × 10 ^-14 (C) ^{_{Q b = 1.91 × 10 -14 (}} C) Q t = 5.30 × 10 -14 (C) ε t = 8.85 × 10 -9 (F / m) C t = 1010 (pF) d h = 7.50 a ^{× 10 -11 (C / N)} g h = 8.75 × 10 -3 (Vm / N) M = -86 (dB re.V / Pa).

The present embodiment has the following advantages (i) to (i).
(V). (I) Compared with the conventional cylindrical electroacoustic transducer of FIG. 2, since no air layer or balance structure is required inside, the electroacoustic transducer of this embodiment has a simple structure and a high water pressure resistance. Can be realized. (Ii) and electro-acoustic transducer according to the present embodiment of the conventional FIG. 3 and the same outer diameter and the same thickness, when compared with the cylindrical electroacoustic transducer of the conventional FIG. 3, a piezoelectric g constant g _h, the The electroacoustic transducer according to the embodiment is improved by 6.6 times.
However, the dielectric constant of the porous PZT (61) is PZT (6).
2), the capacitance according to the present embodiment decreases, but the thickness t of the electroacoustic transducer of the present embodiment is set to the same outer diameter and the same capacitance as the conventional electroacoustic transducer of FIG. When the thickness is reduced so as to have a capacity, the thickness t is 3.2 (mm), and the receiving sensitivity in this case is -91 (dB re.V / P).
a). Therefore, even with the same outer diameter and the same capacitance, the receiving sensitivity is 3.5 times better than the conventional electroacoustic transducer of FIG.

(Iii) A comparison between the conventional electroacoustic transducer of the present embodiment having the same outer diameter and the same thickness as that of FIG. 4 and the conventional disc-shaped electroacoustic transducer of FIG. _h
Thus, the electroacoustic transducer according to the present embodiment is 1.8 times better. Also in comparison with the capacitance, the conventional capacitance in FIG. 4 is t = 6 (mm), radius 15 (mm), and dielectric constant ε = 4.43 × 10 ⁻⁹ (F / m). So 522 (p
F), and the capacitance is 1.9 times better.

(Iv) A comparison between the electroacoustic transducer of the present embodiment having the same outer diameter and the same thickness as FIG. 5 of the related proposal and the disc-shaped electroacoustic transducer of FIG.
_h , the electroacoustic transducer according to the present embodiment is 1.9 times better. Further, since the capacitance of the present embodiment is smaller than that of FIG. 5, the thickness t of the electroacoustic transducer of the present embodiment is reduced so as to have the same outer diameter and the same capacitance. Comparing the sensitivities, the thickness t = 5 (mm) of the electroacoustic transducer according to the present embodiment is obtained, and the sensitivity in this case is -87 (dB re.V / Pa). Therefore, even with the same outer diameter and the same capacitance, the receiving sensitivity is 1.6 times better than that of the electroacoustic transducer of FIG. Further, in the electroacoustic transducer of this embodiment, the porous PZT
Since (61) and PZT (62) are integrally molded, the adhesive between the piezoelectric ceramic 41 and the metal cylindrical shell 42 as shown in FIG. the reduction of the piezoelectric g constant g _h by write can be prevented.

(V) A comparison between the electroacoustic transducer of the present embodiment having the same outer diameter and the same thickness as that of FIG. 6 of the related proposal and the electroacoustic transducer of FIG. 3 of the piezoelectric g constant g _h of the piezoelectric g constant g _h in FIG. 6
/ 10, but the capacitance of the present embodiment is shown in FIG.
Since this value is larger than that of the electroacoustic transducer of the present embodiment, the thickness t of the electroacoustic transducer of the present embodiment is reduced so that the same outer diameter and the same capacitance are obtained. mm), and the sensitivity in this case is -78 (dB re. V / P
a). Therefore, when the same outer diameter and the same capacitance are used, the receiving sensitivity is 3 (d) as compared with the electroacoustic transducer of FIG.
Bre. V / Pa). However, the electro-acoustic transducer of this embodiment is different from the porous PZT (61)
Since the ZT (62) is integrally formed, the adhesive between the porous piezoelectric ceramic 51 and the metal cylindrical shell 52 as shown in FIG. 6 is peeled off, or the sound wave leaks into the adhesive. thereby preventing the deterioration of the piezoelectric g constant g _h. The present invention is not limited to the above embodiment. For example, even if the porous piezoelectric ceramic 61 is made of a material other than porous PZT, or the piezoelectric ceramic 62 is made of a material other than PZT, And an electroacoustic transducer with good performance can be provided. Further, the entire structure of the disc-shaped electro-acoustic transducer of FIG. 1 may be changed to a shape or structure other than that of FIG.

[0024]

As described in detail above, according to the present invention, since the whole is disk-shaped, not only high water pressure resistance can be realized with a simple structure, but also high sensitivity at low frequencies and high sensitivity. A conversion element having a large capacitance can be realized. In addition, since the disc-shaped porous piezoelectric ceramic and the cylindrical piezoelectric ceramic are integrally formed, separation between the two and reduction of the piezoelectric g constant due to leakage of sound waves into the portion can be prevented. .

[Brief description of the drawings]

FIG. 1 is a sectional view of a disc-shaped electroacoustic transducer showing an embodiment of the present invention.

FIG. 2 is a perspective view of a conventional disc-shaped electroacoustic transducer.

FIG. 3 is a sectional view of a conventional disc-shaped electroacoustic transducer.

FIG. 4 is a cross-sectional view of a conventional disc-shaped electroacoustic transducer.

FIG. 5 is a cross-sectional view of a related disk-shaped electroacoustic transducer.

FIG. 6 is a cross-sectional view of a disk-shaped electro-acoustic transducer proposed in a related art.

[Explanation of symbols]

 61 Porous piezoelectric ceramic 62 Piezoelectric ceramic 63 Positive electrode 64 Negative electrode

Claims (1)

(57) [Claims] 1. An electroacoustic transducer for an underwater receiver for converting sound pressure into an electric signal, comprising: a disc-shaped porous piezoelectric ceramic; and a cylindrical piezoelectric ceramic integrally formed around the porous piezoelectric ceramic. A porcelain, comprising a positive electrode and a negative electrode formed on both surfaces of the porous piezoelectric ceramic and the piezoelectric ceramic, the porous piezoelectric ceramic and the piezoelectric ceramic form a disc shape as a whole,
An electroacoustic transducer in which the porous piezoelectric ceramic and the piezoelectric ceramic are polarized in directions opposite to the thickness direction.