JP3270616B2 - Wave receiving piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wave receiving type piezoelectric element having improved sound wave receiving sensitivity.

[0002]

2. Description of the Related Art Microphones that are typically used to receive sound waves propagating in air or gas, as well as those that are used to receive sound waves propagating in water or liquids. 2. Description of the Related Art A receiving type piezoelectric element such as a hydrophone which is used by being placed inside is known.

[0003] receiving sensitivity of acoustic waves in these piezoelectric elements, when the size of the piezoelectric element is sufficiently smaller than the wavelength of the acoustic wave is represented by the hydrostatic piezoelectric constant (d _h constant), naturally d _h constants The larger the value, the better the sensitivity.

Generally, the d _h constant of a piezoelectric material is given by the following equation as the sum of the contribution in the polarization direction (d ₃₃ ) and the contribution in two directions perpendicular to the polarization direction (d ₃₁ and d ₃₂ ).

D _h = d ₃₁ + d ₃₂ + d _{33 In} a generally used sheet-like piezoelectric material, the polarization direction is often taken in the thickness direction because of the ease of polarization. in the thickness direction contributes (d ₃₃₎
And the contributions in two directions (d ₃₁ and d ₃₂ ) orthogonal thereto are often opposite in sign, that is, have opposite actions.

[0006] Focusing on the characteristics of such a sheet-like piezoelectric element, the effects of sound pressure from the side of the sheet-shaped piezoelectric body is blocked by the frame, except for the d ₃₁ and d ₃₂ contributions, thickness It is by out take the contribution d ₃₃ directions of deformation preferentially, device structure to reduce the increase in resulting in d _h constant has been proposed (JP 62-220099). According to the study of the present inventors, at this time, if the sheet-like piezoelectric member is sandwiched between a pair of rigid members having a larger area, the area ratio between the pair of rigid members and the sheet-like piezoelectric member (pressure amplification). depending on the rate), has also been found that a piezoelectric element showing a d _h constants of apparent excess of d ₃₃ constant of the sheet-like piezoelectric element is obtained in comparison with the sound pressure to act.

However, the sheet-like piezoelectric element as described above in the thickness direction primarily utilizing a piezoelectric constant d _33, in particular of a sheet-like piezoelectric element both surfaces of a pair of large-area more through the electrode provided on the both surfaces In a piezoelectric element having a structure sandwiched by rigid members, the electrode area of the piezoelectric element must be reduced in order to increase the pressure amplification factor by using a rigid member having a certain size. Therefore, in addition to making it difficult to take out the lead wire, the capacitance of the piezoelectric element is reduced and the internal impedance is increased. A detection circuit that extracts a voltage output from such an element is required to have an input impedance that is higher than the internal impedance of the element. Therefore, the detection circuit has a disadvantage that it must be configured to take measures against the influence of noise such as electromagnetic waves, the circuit is likely to be unstable, and the lead wire cannot be long.

[0008]

The object of the invention to be solved solved] The present invention, while eliminating the problems of device configuration, including the detection circuit and the like found in a piezoelectric element utilizing d ₃₃ constant of the sheet-like piezoelectric element as described above, the constant An object of the present invention is to realize a wave receiving piezoelectric element having higher sensitivity from a piezoelectric body.

[0009]

According to the study of the present inventors, in order to achieve the above-mentioned object, even when a piezoelectric material polarized in the thickness direction is used, the d ₃₃ constant is not sufficient. Not
It d ₃₁ or d ₃₂ contributions constants be positively used by an element structure, it is effective to particularly substantially form such device structure using a hollow cylindrical piezoelectric body rather perpendicular thereto Was found.

That is, the wave receiving type piezoelectric element of the present invention has an outer surface and an inner surface constituting two main surfaces sandwiching a certain thickness, and two side surfaces substantially orthogonal to and opposed to the two surfaces. A cross-sectional shape corresponding to the wall thickness is a closed annular shape or a spiral shape, and the entire shape is a substantially cylindrical shape. And a pair of rigid members which sandwich the cylindrical piezoelectric body between two opposite side surfaces thereof and have a larger area than the side surfaces, and which act on outer surfaces of the pair of rigid members. The pressure is converged as a stress that changes the distance between two opposing side surfaces of the piezoelectric body.

As described above, in order to converge the sound pressure as a stress that changes the distance between the two opposing sides of the substantially cylindrical piezoelectric body, a pair of rigid members are moved in the axial direction of the cylindrical piezoelectric body by the sound pressure. Displaceable without hindering displacement,
It is preferable to dispose a rigid member so that the effect of sound pressure on at least one of the inner and outer surfaces of the cylindrical piezoelectric body is substantially cut off. In particular, the pair of rigid members sandwich the cylindrical piezoelectric body. It is preferable to form an airtight internal space by the inner surface of the portion that protrudes outward without being used.

In the present invention, the outer surface area (effective operating area) of a rigid member on which sound pressure can be used by converging as a plane direction (axial direction) deformation stress of the piezoelectric body is:
It is not the outer surface area itself in a general sense, but the projected area of the outer surface of the rigid member on a plane perpendicular to the direction in which the rigid member presses the piezoelectric body (pressing direction). In the case where sound pressure acts on the surface, the area of the inner surface on which the sound pressure acts (similarly, the projected area on a plane perpendicular to the pressing direction) is subtracted.
In the case of a cylindrical piezoelectric body, the above-mentioned “plane perpendicular to the direction in which the piezoelectric body is pressed” is generally a plane parallel to the side surface of the piezoelectric body, that is, a plane perpendicular to the axial direction of the cylindrical piezoelectric body. .

The sound wave in the present invention should be interpreted as a pressure vibration wave, and is not limited to an audible sound wave. More precisely, the sound wave of the present invention is a wave of pressure vibration whose wavelength is longer than that of the rigid member. The sound pressure is the pressure of the vibration.

[0014]

As described above, according to the present invention, two opposite sides of a cylindrical piezoelectric body having a certain area are sandwiched between a pair of rigid members having a larger area to deform the cylindrical piezoelectric body in the axial direction. By increasing the effective working area of the sound pressure that contributes to the above, the apparent d _h constant can be significantly increased.
The electrode area of the element can be changed by changing the axial length of the cylindrical piezoelectric body independently of the pressure amplification rate determined by the effective working area of the rigid member / the area of the cylindrical piezoelectric body side surface. Accordingly, the internal impedance of the element can be arbitrarily set. Furthermore, performed for pressure amplification by the rigid member, blocking the sound pressure to the rigid member surface, in many cases, of the d _h constant of the piezoelectric body,
The contribution of the component in the thickness direction (d ₃₃ component) having an action opposite to the component orthogonal to the polarization direction of the piezoelectric material (d ₃₁ or d ₃₂ component of the piezoelectric material polarized in the thickness direction), that is, the thickness of the piezoelectric material It also has the effect of blocking the action of the sound pressure in the vertical direction, and it is understood that this also contributes to the apparent increase of the d _h constant.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the wave receiving piezoelectric element of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals used in the description of different embodiments indicate similar parts.

FIG. 1A is a partially cutaway perspective view of an embodiment of a wave receiving type piezoelectric element (hereinafter, simply referred to as "piezoelectric element") of the present invention, and FIG. It is a front sectional view. FIGS. 2A and 2B are an enlarged plan view and a front view, respectively, of the cylindrical piezoelectric element used in this embodiment. Referring to these drawings, this piezoelectric element 10
Outer surface 2a constituting two main surfaces sandwiching a certain thickness t
And two side surfaces 2c and 2d (upper and lower surfaces in the figure) opposed to the inner surface 2b at right angles to the two surfaces 2a and 2b.
A piezoelectric body 2 having a polarization p in the thickness direction, the cross-sectional shape corresponding to the thickness being a closed annular shape (annular shape in this example), and having a generally cylindrical shape; Piezoelectric element 1 having electrodes 3a and 3b respectively provided on
And a pair of rigid members 4 and 5 sandwiching the cylindrical piezoelectric body 2 between two opposing side surfaces 2c and 2d and having a larger area than the side surfaces. 5 is converged as a stress that changes (decreases) the distance between two opposing side surfaces 2c and 2d of the cylindrical piezoelectric body 2.

In this example, the cylindrical piezoelectric body 2 has two opposing side surfaces 2c and 2d sandwiched between a pair of bowl-shaped (bowl-shaped) rigid members 4, 5 having a circular horizontal shape. The rigid members 4 and 5 each have a curved outer surface 4.
a, 5a, outwardly protruding portions 4 not involved in holding the piezoelectric body 2
b, 5b. The rigid members 4 and 5 abut against the surfaces of the flat side surfaces 2c and 2d of the cylindrical piezoelectric body 2 uniformly, and in some cases, their pressing surfaces (bottom surfaces) 4c and 5c are flat so as to be bonded. It has been processed. A pair of rigid members 4 and 5 for holding the cylindrical piezoelectric body 2 (and thus the cylindrical piezoelectric element 1 including the same) are housed in a rigid cylinder 6, and its side surfaces 4d and 5d and the cylinder 6 are connected to each other. Are sealed with the elastomer resin 7.

In this embodiment, the pair of rigid members 4 and 5 have an effective working area (not the outer surfaces 4a and 5a forming the curved surfaces of the rigid members,
A sound pressure sp corresponding to an area projected on a horizontal plane parallel to the side surfaces 2c and 2d of the cylindrical piezoelectric body acts, and this sound pressure is converged on the side surface of the cylindrical piezoelectric body having a smaller area. The ratio between the effective working area and the area of the side surface of the cylindrical piezoelectric body is the pressure amplification rate.

Further, the elastomer resin 7 used in the present embodiment is composed of inner surfaces 4e, 5e of a pair of rigid members 4, 5.
And the internal space 8 defined by the inner surface of the rigid cylinder 6
This structure satisfies the requirement that the airtight space is cut off from the direct action of p and that the displacement of the pair of rigid members 4 and 5 for causing the axial dimensional change of the cylindrical piezoelectric body 2 is not hindered. Thus, the rigid members 4 and 5 having such rigidity that they are not deformed by the sound pressure and the similarly rigid cylinder 6
The pressure in the content space 8 partitioned is kept substantially constant by, outward protrusion inner surface 4e of the rigid member, 5e and the outer peripheral or the thickness t of d ₃₃ contributes to constant piezoelectric element 1 of the piezoelectric element 1 The effect of the sound pressure sp in the changing direction is substantially cut off. In order to enhance or control the sound pressure blocking action in the internal space 8, the interior space is evacuated,
Alternatively, an arbitrary gas may be filled, or an arbitrary buffer material such as a foamed resin may be filled.

FIG. 3 is a front sectional view of another embodiment of the wave receiving type piezoelectric element of the present invention. The cylindrical piezoelectric element 1 used in the piezoelectric element 20 is the same as the example in FIG. 1, but uses rigid members 14 and 15 having different shapes. That is, rigid plate members 14 and 15 having a U-shaped cross section and having convex surfaces 14f and 15f formed on the periphery are used. The rigid plate 1 as the rigid member of the present invention corresponds to the rigid members 4 and 5 in FIG.
4 and 15 are outer surfaces 14a and 15a,
4b, 15b, pressing surfaces 14c, 15c, side surfaces 14d, 1
5d and the protrusion inner surfaces 14e, 15e. The gap between the inner surfaces 14f and 15f of the rigid plate members 14 and 15 protruding in a U-shape is
Reference numeral 15 is sealed with an elastomer resin 17 so as to be displaceable in the axial direction of the cylindrical piezoelectric body 2 by sound pressure. As in the previous example, the interior space 18 thus formed is filled with gas, foamed resin, or the like, and can be evacuated. Note that any material having a deformation rate greater than the compression deformation rate of the piezoelectric body 2 can be used instead of the elastomer resin 17 that seals the void or the foamed resin that fills the internal space 18.

Also in the embodiment shown in FIG. 3, the pressing direction is a direction perpendicular to the side surface of the piezoelectric body (the axial direction of the cylindrical piezoelectric body 2), and the inner surface facing the outer surfaces 14a and 15a of the plate members 14 and 15 is also used. Sound pressure cutoff is achieved for all regions. Therefore, the entire outer surfaces 14a and 15a are used as the effective working area of the sound pressure.

At the ends of a pair of rigid members, they are joined,
Further, in order to seal the space therebetween, a member having both rigidity and elasticity, such as a bellows and a leaf spring, may be used instead of filling the elastomer resin 17 as in this embodiment.

FIG. 4 is a front sectional view of another embodiment of the piezoelectric element of the present invention. The cylindrical piezoelectric element 1 used in the piezoelectric element 30 is the same as that used in the example of FIG. 1 (shown in FIG. 2). The rigid members used in this example are a pair of flat rigid plate members 24 and 25, and their pressing surfaces 24e and 25e correspond to a pair of side surfaces (upper and lower surfaces) 2c and 2d of the cylindrical piezoelectric body 2. The inner space 2e of the cylindrical piezoelectric body 2 is made airtight by being in contact with and preferably being bonded. Thus, the inner surfaces of the pair of rigid members including the pressing surfaces 24e and 25e are not affected by the sound pressure, and the entire area of the outer surfaces 24a and 25a of the rigid members 24 and 25 is reduced to the effective working area of the sound pressure. As a result, a pressure amplification factor corresponding to the ratio of the area of the pressed surfaces 2c and 2d of the smaller cylindrical piezoelectric body can be obtained. However, the piezoelectric element 3 of this example
In the case of 0, the element configuration is simple, but FIG.
Since the effective working area of the pair of rigid members does not increase so much as compared with the piezoelectric element of the above, effective pressure amplification cannot be expected, and the d ₃₃ constant of the hydrostatic pressure sp acting on the outer peripheral surface of the piezoelectric body 2 The contribution is d ₃₁ as intended by the present invention.
Or there is a disadvantage that it can not suppress the effect of offsetting the output of the d ₃₂ constant.

The ceramic piezoelectric element 2 is a cylindrical piezoelectric element 1 having electrodes provided on both sides of a hollow cylindrical piezoelectric element 2 having a polarization direction p in the thickness direction as used in each of the above-described examples shown in FIG. Those used are commercially available (for example, a cylindrical PZT piezoelectric element manufactured by Tokin Co., Ltd.) and are suitably used in the present invention. On the other hand, when a polymer piezoelectric element is used, for example, as shown in a sectional view of FIG. 5, a film or sheet-like piezoelectric film having electrodes 13a and 13b on both surfaces of a polymer piezoelectric film 12 having polarization p in the thickness direction. The element is wound around a certain axis by using its flexibility, and as shown in FIG. 6 ((a) is a plan view, (b) is a front view), both ends of the film are epoxy resin 27 or the like. By bonding, the polymer-based piezoelectric element 11 having a function similar to that of the ceramic-based piezoelectric element 1 in FIG. 2 can be formed. It is desirable to perform heat setting after winding as necessary to fix the cylindrical shape.

As the polymer piezoelectric material, a vinylidene cyanide-vinyl acetate copolymer having relatively high heat resistance is preferably used, and a vinylidene fluoride resin piezoelectric material having excellent piezoelectric properties is preferable. Compared to vinylidene fluoride (VDF) homopolymer, which requires uniaxial stretching for β-type crystallization suitable for piezoelectricity development, VDF copolymer ( For example, a copolymer of a superior amount of VDF and an inferior amount of vinyl fluoride (VF), trifluoroethylene (TrFE) or tetrafluoroethylene (TFE) is preferable, and a superior amount (particularly 70 to 80 mol%) is preferable. VDF and inferior amount (especially 3
(0 to 20 mol%) of a copolymer with TrFE is most preferably used.

These polymer piezoelectric materials are formed into a film by melt extrusion or the like, and then subjected to a uniaxial stretching or a heat treatment at a temperature lower than the softening temperature and a polarization treatment by applying an electric field at a temperature lower than the softening temperature, if necessary, to form a film or sheet 12. Is formed as In the polymer-based piezoelectric material used in the present invention, these films or sheets can be used as a single layer, or the same polarization direction is used, or two or more layers are stacked in the opposite direction via an intermediate electrode layer. It is used as a laminate of a degree.

As can be seen from the above examples, the rigid member of the present invention having the function of converging the sound pressure received on the outer surface of the large area to the side surface of the cylindrical piezoelectric body having a relatively small area is used as the sound pressure amplifier. Can also be considered as In this case, one measure of the amplification factor is the ratio between the effective working area of the rigid member defined above and the area of the side surface (pressed surface) of the piezoelectric body. Of course, the amplification factor or area ratio is a value exceeding 1, but the upper limit is preferably selected within a range in which the stress (amplified sound pressure) applied to the piezoelectric material does not cause plastic deformation of the piezoelectric material.

As another aspect, in the piezoelectric element of the present invention, the sound pressure received on the outer surface of the large-sized rigid member is amplified and converged on the side surface of the cylindrical piezoelectric element having a small area. Therefore,
For d ₃₁ or d ₃₂ amplification works effectively is (a pressure amplification factor, to improve the piezoelectric characteristics (d _h constant) are coincident), the sound pressure converging the above amplification of the cylindrical piezoelectric body It must be effectively converted to a compressive deformation stress in the plane direction (or axial direction). That is, it is desirable to avoid as far as it is capable possible in a variant to increase the contribution of the d ₃₃ component, such as bending or swelling in the thickness or radial direction of the cylindrical piezoelectric element.

From such a viewpoint, when the above-mentioned polymer-based piezoelectric material 12 is wound to form the cylindrical piezoelectric element 11, the thickness t may be increased by adopting a laminated structure as necessary. preferable. In order to suppress the thickness or radial deformation of the obtained cylindrical piezoelectric element using a polymer piezoelectric material, vapor deposition electrodes 13a and 13b generally used on both surfaces of the piezoelectric material 12 as shown in FIG. In place of the general polymer piezoelectric element provided with
58844 and 4-203160. As shown in FIG. 7, a piezoelectric element in which a porous sheet-like electrode such as a net-like or perforated plate is embedded in the surface of a piezoelectric sheet is used. Utilizing the reinforcing effect in a range that maintains the property; furthermore, the sheet-like piezoelectric element shown in FIG. 5 or FIG.
It is preferable that the piezoelectric element 21 has a spiral cross section (planar shape) as shown in FIG.

As the electrodes 3a, 3b, 13a, 13b (23a, 23b) forming the cylindrical piezoelectric element used in the present invention, a vapor deposition electrode, a foil electrode stuck with an adhesive, or Japanese Patent Application No. 3-356668. A metal spray electrode as described in the specification can be used. However, preferably,
(1) those which do not inhibit the compressive deformation of the piezoelectric body in the plane direction due to the amplified sound pressure; and (2) in the case of a polymer piezoelectric body, those which satisfy requirements such as easy cylindrical or spiral shaping.
For example, an electrode capable of ensuring flexibility such as a vapor deposition electrode, a coated conductive paint, and the above-described porous sheet electrodes 23a and 23b is preferable.

The piezoelectric body of the present invention is constantly subjected to compressive deformation stress in the plane direction. Therefore, it is more preferable that the electrode has a strong delamination strength between the electrode and (3) the piezoelectric body. In this sense, the above-mentioned porous sheet-like electrode, and among them, the mesh-like electrode is particularly preferable.

[0032]

Production Examples Hereinafter, production examples and comparative production examples of hydrophones as specific examples of the wave receiving piezoelectric element of the present invention will be described.

With respect to the manufactured measurement sample and hydrophone, the hydrostatic pressure piezoelectric strain constant (d _h
Constant). The sample is immersed in an electrically insulating liquid such as silicon oil in a pressure-resistant container, and the charge amount Q (coulomb (C)) of the sample is applied to the container while applying a pressure P (Newton (N) / m ² ) from a nitrogen gas source. ) Is measured. Then, the charge increase dQ with respect to the pressure rise dP near the gauge pressure of 2 kg / cm ² was obtained, and was calculated by the following equation.

D_h= (DQ / dP) / A The unit is C / N. Here, A is the electrode area (m^Two )
It is.

Further, d of the measurement sample piece₃₁And d₃₂Set
The number was determined by measuring according to the following method. That is, dynamic viscosity
Elasticity / piezoelectricity measuring device (Leo manufactured by Toyo Seiki Seisaku-sho, Ltd.)
The specimen in the longitudinal direction using
It was clamped at a lamp distance of 18 mm. One side of the clamp
The (fixed side) is on the load cell and the other (moving side) is on the measuring device.
Connected to the shaker. First, add 0.35 kg
A static load is applied, followed by a frequency of 0.8 Hz by a shaker
Was superimposed and applied. Then, charge the sample
The variation of the charge induced between the poles △ Q (C) and the load cell
Of the tension per unit cross-sectional area due to m
^Two) Was calculated by the following equation.

D ₃₁ or d ₃₂ = (△ Q / △ T) / A The unit is C / N.

Here, the measurement sample piece was prepared by forming an aluminum vapor-deposited film having a thickness of 0.03 μm on both sides of the polymer piezoelectric film, and cutting out a strip sheet having a width of 5 mm and a length of 25 mm. The slit sheet is so longitudinal direction parallel to the stretching direction (MD) of the piezoelectric film (d ₃₁ direction) or perpendicular (d ₃₂ direction), cut out respectively, were prepared two kinds.

Comparative Example 1 First, a VDF homopolymer ("KF" manufactured by Kureha Chemical Industry Co., Ltd.)
# 1000 ”) at a die temperature of 265 ° C., and while being uniaxially stretched at a sheet temperature of 80 to 120 ° C. (drawing ratio of about 4), 50 to 90 V / μm by corona discharge.
The electric field was applied to perform a polarization treatment to obtain a polymer piezoelectric film having a thickness of 250 μm. The piezoelectric constant of the measurement sample piece prepared from this polymer piezoelectric film is d _h
= -11.5 pC / N, d ₃₁ = + 16.6 pC / N, d
₃₂ = + 1.5 pC / N.

Next, a conductive nickel paint (“Shintron E-63” manufactured by Shinto Chemitron Co., Ltd.) was sprayed on both surfaces of the polymer piezoelectric film to form electrodes having a thickness of 30 to 40 μm. the so that the width direction is MD direction (d ₃₁ direction), it was cut to a width 20 mm, length 80 mm, to obtain a strip-like piezoelectric element showing a sectional structure in FIG.

Separately, as shown in FIG.
Mold 101a, 101 having a cylindrical inner surface
b, the strip-shaped piezoelectric element obtained above is spirally wound in the longitudinal direction, inserted into both the molds 101a and 101b, and connected and held by bolt holes 103 (both ends of the spiral piezoelectric element). Is open inside the mold). And
The mold was placed in a dryer at 70 ° C., held for 24 hours, heat-fixed, taken out of the mold, and the height h (roll width) = 20.
8 and a cross-sectional area (pressed surface area) of 20 mm ² as shown in FIG. 8 to obtain a spiral-shaped piezoelectric element (outer diameter is about 20 mmφ), and confirm that the inner and outer surfaces of the spiral-shaped piezoelectric element are not in contact with each other. confirmed. Further, both electrodes 13 are formed by using a conductive instant adhesive (“Sycolon” manufactured by Atsugi Central Research Institute Co., Ltd.).
The lead wires were connected to a and 13b to complete the cylindrical piezoelectric element 21. D _h constant of the cylindrical piezoelectric element 21 -11.
It was 3 pC / N.

Embodiment 1 Subsequently, a piezoelectric element 10 (including a piezoelectric element 21 shown in FIG. 8 instead of the piezoelectric element 1) substantially as a hydrophone as shown in FIG. Obtained.

First, the cylindrical piezoelectric element 2 obtained in Comparative Example 1
An adhesive was applied to the end face in the axial direction of No. 1. Then, the cylindrical piezoelectric element 21 to which the adhesive is applied is sandwiched between a pair of rigid plate members 4 and 5 having a circular horizontal cross-sectional shape and a bowl shape (bowl shape) and adhered and fixed to each other. Is 52 mm in length,
It was housed in a vinyl chloride resin cylinder 6 having an inner diameter of 80 mm and a thickness of 5 mm. Further, the gap between the rigid members 4 and 5 and the cylinder 6 was filled with a urethane rubber adhesive 7 to fix them, and the internal space 8 was sealed to obtain the piezoelectric element 10. Actually, the bowl-shaped rigid plate members 4 and 5 include the pressing surface 4
A plastic lens molded product made of acrylic resin obtained by flattening e and 5e was used, the thickness was 5 mm, and the diameter of the horizontal cross section of the side surfaces 4d and 5d was 75 mmφ (4420 mm ² as a pressure receiving area). The lead wires connected to the cylindrical piezoelectric element 21 were separately drawn out through holes provided through the rigid members 4 and 5, respectively, and the holes were thereafter sealed. The d _h constant of the piezoelectric element 10 was + 1,160pC / N.

Comparative Example 2 The same electrode was formed using the same polymer piezoelectric film as in Comparative Example 1, and then cut into a width of 20 mm and a length of 140 mm to obtain a plate-like piezoelectric element having a sectional structure shown in FIG. Was. Then, the height h was increased by the same spiral shaping operation as in Comparative Example 1.
= 20 mm, and a cylindrical spiral-shaped piezoelectric element (outer diameter of about 30 mmφ) 21 having a cross-sectional area (pressed surface area) of 35 mm ² was completed. D _h constant of the cylindrical piezoelectric element 21 -11.
It was 3 pC / N.

Example 2 A piezoelectric element 10 was obtained in the same manner as in Example 1, except that a cylindrical spiral piezoelectric element 21 similar to that obtained in Comparative Example 2 was used. The d _h constant of the piezoelectric element 10 is +6
It was 90 pC / N.

Comparative Example 3 First, a VDF / TrFE (75/25 molar ratio) copolymer (manufactured by Kureha Chemical Industry Co., Ltd.) was extruded in a sheet at a die temperature of 265 ° C., and after a heat treatment at 125 ° C. for 13 hours, 60 V /
A polarization treatment was performed under a μm electric field for a total of 1 hour including a holding time at 123 ° C. for 5 minutes and a heating time to obtain a polymer piezoelectric film having a thickness of 500 μm. The piezoelectric constant of the measurement sample piece prepared from this polymer piezoelectric film is d _h
= -12.4 pC / N, d ₃₁ = + 13.2 pC / N, d
₃₂ = + 13.0 C / N.

Next, acetone at 30 ° C. was applied to both surfaces of the polymer piezoelectric film and held for 30 seconds, and then 300 mesh (twill weave, 45 μm mesh, 40 μm wire diameter, 27.8% aperture ratio) was applied to the acetone-treated surface. Put the phosphor bronze wire mesh
These laminates were subjected to a temperature of 90 ° C. and a pressure of 50 kg / c.
The metal wire electrode was embedded in the surface layer of the polymer piezoelectric film by pressure bonding under conditions of m ² and time of 2 minutes. Then, the piezoelectric film on which the electrodes are formed as described above is made to have a width of 20 mm and a length of 14 mm.
By cutting to 0 mm, a band-shaped piezoelectric element having a sectional structure shown in FIG. 7 was obtained. Next, by the same spiral shaping operation as in Comparative Example 1, the height was 20 mm, and the cross-sectional area (pressed surface area) was 35 mm ^2.
Cylindrical spiral element (outer diameter is about 30 mmφ) 2
1 was completed. The d _h constant of this piezoelectric element 21 is -1.
2.1 pC / N.

Example 3 A piezoelectric element 10 was obtained in the same manner as in Example 1 except that a cylindrical spiral piezoelectric element 21 similar to that obtained in Comparative Example 3 was used. The d _h constant of the piezoelectric element 10 is +6
It was 30 pC / N.

Comparative Example 4 Inner diameter 12.3 mmφ, outer diameter 16.3 mmφ, length 10 m
Thickness-polarized cylindrical PZT with dimensions of m
Piezoelectric element (manufactured by Tokin Co., Ltd., cross-sectional area 90 mm ² , d ₃₃
= + 302 pC / N, d ₃₁ = d ₃₂ = −133 pC / N)
A lead wire is connected to the electrodes formed on the inner and outer surfaces of the cylinder by using the same conductive instant adhesive as in Comparative Example 1, and FIG.
The completed cylindrical piezoelectric element 1 as shown in FIG. D _h constant of the cylindrical piezoelectric element 1 was + 26.7pC / N.

Example 4 An axial end face of a cylindrical piezoelectric element 1 similar to that obtained in Comparative Example 4 was coated with an acrylic resin disk having an outer diameter of 17 mmφ and a thickness of 2 mm (a pressure receiving area of 209 mm ² ) using an adhesive. Then, a piezoelectric element 30 as shown in FIG. 4 was obtained. The d _h constant of the piezoelectric element 30 was -550pC / N.

Example 5 A cylindrical piezoelectric element 1 similar to that obtained in Comparative Example 4 was used by using a pair of rigid plate members 4 and 5 and a cylinder 6 similar to those in Example 1.
A piezoelectric element 10 was obtained in the same manner as in Example 1. The d _h constant of the piezoelectric element 10 was -6,480pC / N.

The above measurement results show that the piezoelectric constant of the wave-receiving piezoelectric element of the present invention actually increases to a value several hundred times larger than that of a blank (piezoelectric element in which no rigid member is disposed). ing. Further, since the rate of increase of the piezoelectric constant has a strong correlation with the so-called area ratio, it is important to pay attention to the above-described deformation in the width direction of the piezoelectric body, and if the area ratio is further increased, a larger increase rate can be obtained. Suggests.

After all, if the rigid member is carefully designed and arranged so that it can be displaced in the surface direction of the piezoelectric body with a small force and the action of sound pressure on the surface of the piezoelectric body is effectively cut off. It can be understood that the sound pressure received on the outer surface of the large-area rigid member can be efficiently converged on the side surface of the piezoelectric body, and as a result, the piezoelectric constant can be significantly increased.

[0053]

As described above, according to the present invention, the end face of the piezoelectric body polarized in the thickness direction and having a constant _dh constant, which is perpendicular to the axis, is sandwiched between a pair of rigid members having a larger area. , by increasing the effective active area contributing sound pressure in the axial direction deformation of the piezoelectric body (d ₃₁ or d ₃₂ variations), without causing an increase in internal impedance, achieving a significant increase of the apparent d _h constants Thus, it is possible to obtain a wave-receiving piezoelectric element that is effective for microphones, hydrophones, and the like in which the reception sensitivity of sound waves is significantly improved.

[Brief description of the drawings]

FIG. 1A is a partially cutaway perspective view and FIG. 1B is a front sectional view of an embodiment of a wave receiving type piezoelectric element according to the present invention.

FIG. 2 is an enlarged (a) plan view and (b) front sectional view of the cylindrical piezoelectric element shown in FIG.

FIG. 3 is a front sectional view of another embodiment of the wave receiving piezoelectric element of the present invention.

FIG. 4 is a front sectional view of another embodiment of the wave receiving piezoelectric element of the present invention.

FIG. 5 is a schematic cross-sectional view of an example of a sheet-shaped polymer piezoelectric element before being shaped into a cylindrical piezoelectric element used in the present invention.

6A is a plan view and FIG. 5B is a front view of a cylindrical piezoelectric element obtained by shaping the sheet piezoelectric element of FIG.

FIG. 7 is a schematic cross-sectional view of another example of a sheet-shaped polymer piezoelectric element before being shaped into a cylindrical piezoelectric element used in the present invention.

8 (a) is a plan view of a cylindrical spiral piezoelectric element obtained by shaping the sheet-like piezoelectric element of FIG. 5 or FIG. 7, and FIG.
Front view.

FIG. 9 is a cross-sectional view of a mold used for shaping a cylindrical piezoelectric element having a spiral cross section in the embodiment.

[Explanation of symbols]

 1, 11, 21: cylindrical piezoelectric element 2, 12: (cylindrical) piezoelectric body 3a, 3b, 13a, 13b: electrode 4, 5, 14, 15, 24, 25: rigid member 6: rigid cylinder 7: seal Material 8, 18: Internal space 10, 20, 30: Receiving piezoelectric element p: Polarization direction sp: Sound pressure

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-309799 (JP, A) US Patent 5,267,223 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04R 17 / 00 330 G01S 7/521 H04R 1/44 330

Claims (6)

(57) [Claims] An outer surface and an inner surface constituting two main surfaces sandwiching a certain thickness, and two side surfaces substantially orthogonal to and opposed to the two surfaces, and a cross-sectional shape corresponding to the thickness is provided. A cylindrical piezoelectric element comprising a closed-circular or vortex-shaped, generally cylindrically-polarized piezoelectric body having a generally cylindrical shape, and electrodes provided on the two surfaces, respectively; And a pair of rigid members having a larger area than the side surfaces of the piezoelectric member, and applying a sound pressure acting on the outer surfaces of the pair of rigid members to the two opposite side surfaces of the piezoelectric body. A wave receiving type piezoelectric element configured to converge as a stress for changing an inter-distance. 2. A belt-shaped piezoelectric body made of a polymer, wherein the cylindrical piezoelectric element has two main surfaces sandwiching a certain thickness and side surfaces substantially orthogonal to the two surfaces, and the polarization direction is the thickness direction. 2. The wave receiving piezoelectric element according to claim 1, wherein the piezoelectric element is wound around a certain axis together with electrodes provided on the two surfaces and shaped into a cylindrical or spiral shape. 3. 3. The cylindrical piezoelectric element has an outer surface and an inner surface constituting two main surfaces sandwiching a certain thickness, and a side surface substantially orthogonal to the two surfaces, and the polarization direction is the thickness direction. 2. The wave receiving piezoelectric element according to claim 1, wherein electrodes are provided on the two surfaces of a certain ceramic cylindrical piezoelectric body. 4. An airtight internal space is defined and formed by an inner surface of an outwardly protruding portion of the pair of rigid members, which is not used for holding a cylindrical piezoelectric body. 4. A resin filled with any one of the resins.
The piezoelectric element according to any one of the above. 5. The wave receiving piezoelectric element according to claim 1, which functions as a hydrophone that receives a sound wave propagating in a liquid. 6. The wave receiving piezoelectric element according to claim 1, which functions as a microphone that receives a sound wave propagating in a gas.