JPH0622396A - Piezoelectric element and hydrophone using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] A polymer piezoelectric element having a substantially cylindrical shape, excellent in flexibility and impact resistance, and suitable for transmitting and receiving sound waves, and deformation noise is reduced by using the polymer piezoelectric element. A hydrophone that retains excellent wave receiving sensitivity and flexibility is provided. A flexible strip-shaped piezoelectric element 10 having electrode layers 2a, 2b facing each other on both sides of a strip-shaped polymer piezoelectric body 1 is spirally wound around a certain central axis O to form a cylinder as a whole. Use an approximate arrangement structure. The counter electrode layer is
A plurality of pairs may be provided so as to be separated from each other in the lengthwise direction of the strip-shaped piezoelectric body.
In order to form the hydrophone, it is preferable to use a pair of strip-shaped polymer piezoelectric bodies and stack them with a central metal layer interposed so that their polarization directions are opposite to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element having a cylindrical structure in which a flexible band-shaped polymer piezoelectric material is spirally wound around a certain central axis, and the piezoelectric element is used.
In particular, the present invention relates to a flexible hydrophone having excellent applicability as a towed sonar.

[0002]

2. Description of the Related Art A towed sonar is known as an example of a cylindrical piezoelectric element (JP-A-55-76962).
No. 57-60992, JP-A-2-278178, etc.). This is a hydrophone linear array that is suitable for the frequency band of transmitted sound waves by arranging a number of hydrophone receivers in a straight line at predetermined intervals in order to mainly receive engine sounds, screw sounds, cavitation sounds, etc. emitted by ships. In order to detect the target vessel by phasing the output phase of each receiver, this hydrophone linear array is usually towed by the vessel via a rope with electric wires. Take the form.

Conventionally, as a sound wave detecting element used in such a towed sonar, a ceramic piezoelectric element formed in a hollow cylindrical shape, for example, a PZT piezoelectric element has been used.

When a hollow cylindrical piezoelectric element of this kind is used as a sound wave transmitter, the sound wave is radiated isotropically in the radial direction regardless of the frequency, that is, at an equal sound pressure,
On the other hand, as the wave receiver, the receiving sensitivity does not change even if the element is rotated around the central axis in the longitudinal direction. In other words,
There is no directivity in the transmission / reception sensitivity in the radial direction.

On the other hand, in the field of ultrasonic machining, an electrostrictive element such as barium titanate magnet has been used in a cylindrical shape to obtain a large displacement. Also, US Pat. No. 2,497
No. 108 discloses a relay using a bimorph formed by spirally cutting a hollow cylinder of a ceramic piezoelectric body.

[0006]

The above-mentioned conventional cylindrical ceramic piezoelectric element achieves isotropic sensitivity characteristics as a sound wave transmitter / receiver regardless of the frequency of the sound wave, and a large displacement occurs in the electrostrictive element. Although it has the advantage of being obtained, it includes the following problems. (1) Although it has rigidity, it is weak against impact and is troublesome to handle. For example, since it is poor in flexibility, it is not easy to store it in a long device. (2) It is not easy to manufacture a large diameter and long product. (3) In the structure in which a large number of wave receivers are linearly arranged like the hydrophone linear array, mechanical characteristics such as bending and strength and specific gravity are non-uniform due to the joints. The characteristics of the towed vehicle may be deteriorated due to the shock caused by the motion of the towed vehicle transmitted via the rope, the bending stress caused by the water flow, and the like.

There is also a problem that the operability when unwinding or winding up the hydrophone linear array together with the rope is extremely poor.

It is possible to solve the above-mentioned problems of the hollow-cylindrical ceramic piezoelectric element, in particular, the problems caused by the rigidity of the ceramic by a polymer piezoelectric element having excellent flexibility. However, since it is difficult to form electrodes on the polymer piezoelectric body, it is not easy to form a seamless cylindrical piezoelectric element, and even a polymer piezoelectric body has a flexible cylindrical shape. Does not improve so much. On the other hand, the conventional spiral element cut out from the hollow cylinder made of ceramics has a drawback that it is weak and vulnerable to impact, in addition to the fact that it is not easy to manufacture a large-diameter and long-sized one, and the flexibility is low. Is several steps inferior to the polymer piezoelectric material.

It is an object of the present invention to provide a piezoelectric element, which is improved with respect to the problems of the conventional hollow cylindrical ceramic piezoelectric element, and a flexible hydrophone using the same.

[0010]

According to the research conducted by the present inventors, a flexible band-shaped piezoelectric element is spirally wound to have a shape close to a cylinder, thereby maintaining the isotropy of sensitivity. At the same time, it has been found that a significant improvement over the problems of the hollow cylindrical ceramic piezoelectric element described above can be obtained.

That is, according to the present invention, a flexible band-shaped polymer piezoelectric material having electrode layers facing each other on its surface is spirally wound around a certain central axis, and the surface electrode layer is extended from the central axis. The present invention provides a piezoelectric element having a structure arranged substantially parallel to the direction.

Further, according to the present invention, a band-shaped piezoelectric element obtained by laminating a pair of band-shaped polymer piezoelectric materials with a central electrode layer sandwiched therebetween such that the polarization directions thereof are opposite to each other is spirally wound and arranged. The present invention provides a hydrophone having a structure capable of taking out an electric output generated between a surface electrode formed on both surfaces of the strip piezoelectric element and the central electrode layer.

[0013]

As described above, the piezoelectric element of the present invention is formed into a substantially cylindrical shape by winding the band-shaped piezoelectric element. Therefore, in addition to having good isotropic sensitivity characteristics, Significant improvements are obtained over the lack of flexibility and impact resistance that were the major problems with cylindrical ceramic piezoelectric elements.

Deformation associated with the output in the piezoelectric body constituting the polymer piezoelectric element includes expansion and contraction in the plane direction (biaxial), thickness change (uniaxial), and volume compression / expansion change. Of these, the noise generated by mechanical stress applied to the towed sonar and the like is the cause of noise due to expansion and contraction in the surface direction, and in the hydrophone of the present invention, noise due to such expansion and contraction in the surface direction. Is effectively offset by the use of a strip-shaped piezoelectric element obtained by laminating a pair of polymer piezoelectric bodies so that their polarization directions are opposite to each other via a central electrode layer, and substantially no harmful noise occurs. On the other hand, by adopting a cylindrical structure in which such a band-shaped piezoelectric element is wound and arranged in a spiral shape, the flexibility as a whole is not impaired, and the sound pressure of the sound wave from the measured object is equal to that of the polymer piezoelectric material. It is effectively detected as deformation in the thickness direction or volumetric compression / expansion change.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a piezoelectric element and a hydrophone of the present invention will be described with reference to the drawings for preferred embodiments thereof.
Further details will be described.

FIG. 1 is a partially cutaway front view of a spiral piezoelectric element according to an embodiment of the present invention configured as a wave receiver (hydrophone) of a towed sonar, and FIG. 2 is shown in FIG. It is a thickness direction cross section of the piezoelectric element taken along the notch plane II-II.

With reference to FIGS. 1 and 2, a strip-shaped piezoelectric element 10 constituting this spiral piezoelectric element has surface electrodes 2a and 2b formed on both sides of a flexible strip-shaped piezoelectric body 1. The spiral piezoelectric element according to the present invention has a shape in which the strip piezoelectric element 10 is spirally wound around a certain central axis O. Then, the lead wires 8a and 8b are respectively connected to the surface electrodes 2a and 2b by soldering 7, and an electric output generated between the surface electrodes when receiving a sound wave is provided at the right end of the spiral piezoelectric element. Terminals A and B so that they can be taken out between terminals AB and when transmitting sound waves.
Is configured so that a voltage can be applied to the piezoelectric body 1.

The width (d) and the spiral pitch (p) of the strip-shaped piezoelectric element 10 are appropriately selected according to the characteristics required of the piezoelectric element, but generally the width is about 2 to 50 mm, preferably 5 to 20 mm, and 1 The range of <p / d ≦ 3 is preferable. If the width is less than 2 mm, cutting is likely to occur during spiral winding, and if it exceeds 50 mm, it becomes difficult to shape it into a spiral shape. If p / d ≦ 1, electrical noise may occur due to the strip-shaped piezoelectric elements 10 partially overlapping each other or due to contact between the surface electrodes 2a or between 2a-2b. On the other hand, if p / d> 3, the area efficiency of the device decreases. The number of turns of the spiral forming the spiral piezoelectric element is preferably 1 or more, particularly 3 or more so as to ensure the above-mentioned isotropic sensitivity characteristic.

Explaining the material of each part, in order to give good flexibility as a whole of the spiral piezoelectric element or to form a long spiral piezoelectric element, the flexible piezoelectric body 1 of the present invention is made of polymer piezoelectric material. Consists of the body. Such a polymer piezoelectric body 1 can be easily formed into a spiral shape as shown in FIG. 1 by winding the polymer piezoelectric body 1 into a strip having surface electrodes 2a and 2b.

The polymer piezoelectric material 1 is optionally composed of a generally known polymer piezoelectric material, but is a VD composed of vinylidene fluoride (VDF) homopolymer or copolymer.
An F-based piezoelectric material or a vinylidene cyanide-vinyl acetate copolymer having a relatively high heat resistance is preferably used. After being formed into a film by melt extrusion or the like, these polymer piezoelectric materials are optionally subjected to uniaxial stretching or heat treatment at a softening temperature or lower, and polarization treatment by applying an electric field at a softening temperature or lower. The polymer piezoelectric body 1 can generally take the form of a film or sheet, and its thickness is 20 to 2
It is preferably selected in the range of about 000 μm, particularly 100 to 1000 μm. The thickness of the piezoelectric polymer is 20
If it is less than μm, sufficient wave receiving sensitivity cannot be obtained.
When the thickness is more than μm, the flexibility of the film is impaired, and a high voltage is required for polarization, so that edge discharge occurs and polarization becomes extremely difficult.

The surface electrodes 2a and 2b are formed on the surface of the piezoelectric body 1 by silver, without impairing the flexibility of the entire spiral piezoelectric element.
It can be formed in a thickness range of 0.02 μm to 200 μm by vapor deposition, thermal spraying, plating (especially electroless plating) of a conductive material such as copper, aluminum, zinc or the like, adhesive bonding of a metal foil, and the like. Above all, in the combination with the polymer piezoelectric material, in order to provide good solderability and excellent wave transmission / reception sensitivity while maintaining good flexibility, the counter electrodes 2a and 2b are
It is preferably formed as a sprayed electrode layer having a thickness of 10 to 100 μm, particularly 20 to 50 μm.

The electrodes 2a, 2b of the spiral piezoelectric element of the present invention
It is preferable to apply an insulating coating to the surface of the. As shown in FIG. 3, which corresponds to FIG.
It is also possible to form the insulating coating layers 5a and 5b which selectively cover b, but more preferably, as shown in FIG. 1, the entire spiral piezoelectric element is embedded in the insulator 11 to form a solid (or hollow) material. It is preferable to form it in a cylindrical shape to improve the robustness and handleability of the device. Such an insulating cover 5
a, 5b or 11 is plastic, ceramic,
It can be selected from elastomers and the like according to the usage situation. Among them, with respect to the insulator 11, it is preferable to use an elastomer such as urethane rubber, silicone rubber or butyl rubber in order to maintain the flexibility as the whole spiral piezoelectric element in addition to the robustness.

The external shape of the buried cover 11 is a cylinder.
The shape is not limited to the above, and may be another shape as long as the directionality does not occur in the sensitivity. For example, the embedded coating may be formed into an elliptic cylinder (cylindrical) shape to give direction to the bending stress. . In addition to the electric wires, electric parts such as a preamplifier, a strength member, and a filling material may be buried in the central portion of the buried cover, or a cavity may be formed to dispose them. it can.

The surface electrodes 2a and 2b need not be provided over the entire surface of the long strip piezoelectric body 1. For example, as shown in FIG. 4 corresponding to FIG. 1, the surface electrodes 2a (and 2b—not shown) are provided along the length direction of the strip-shaped piezoelectric body 1 so as to be spaced apart from each other, and the piezoelectric body is provided in the intermediate blank portion. It is also possible to have a structure in which 1 is exposed. As a result, functionally, two spiral piezoelectric elements 10a and 10b are formed in each region where the surface electrode 2a (2b) is present. Of these elements 10a and 10b, the front and back electrodes 2a and 2b of 10a are connected to terminals A1 and B1 via lead wires 81a and 81b connected by solder 7, respectively, so that an electrical output generated between both electrodes is generated. It is taken out between terminals A1 and B1. On the other hand, the front and back electrodes 2a, 2 of the element 10b
b is connected to the terminals A2 and B2 via the soldered lead wires 82a and 82b, respectively, and the birth of the element 10b is taken out between the terminals A2 and B2. Lead wire 8
It is preferable that 1 and 82 are passed through a portion close to the central axis of the spiral piezoelectric element (inside the spiral) as shown in the drawing. The hydrophone having such a configuration is not limited to two, but a larger number of unit elements are functionally independent and structurally linearly connected to form a hydrophone linear array, which is a sound wave of a wide frequency band. The conformity with is secured. Also, since these connecting elements are integrally molded, bending,
It has a characteristic that mechanical characteristics such as strength and specific gravity are uniform, and even if it has a plurality of functions, it has an advantage that it can be handled in the same manner as one element in terms of structural handling. Since the piezoelectric elements are functionally independent of each other, the coupling element can transmit and receive at different frequencies, and one of them can be used as a transmitter and the other as a receiver.

Next, another preferred embodiment of the present invention will be described.

FIG. 5 is a partially cutaway front view of one embodiment of the hydrophone of the present invention, and FIG. 6 is a cutout surface V of FIG.
It is a thickness direction schematic cross section of the piezoelectric element taken along I-VI. In these drawings, parts similar to those shown in FIGS. 1 to 4 are indicated by similar reference numerals.

Referring to FIGS. 5 and 6, a strip-shaped piezoelectric element 50 constituting this hydrophone has a pair of strip-shaped polymer piezoelectric bodies 1a and 1b arranged so that their polarization directions p are opposite to each other. , And is attached to the central electrode layer 3 via the adhesive layers 4a and 4b. Moreover, these polymer piezoelectric bodies 1a and 1b have surface electrodes 2a and 2b on the surface opposite to the central electrode layer 3, respectively.

In the hydrophone of the present invention, such a strip-shaped piezoelectric element 50 is spirally wound around a certain central axis O as shown in FIG. 5, and the surface electrodes 2a on both sides thereof are arranged.
And the outputs from 2b (output terminals A and C) are short-circuited,
It has a configuration in which the voltage output between the output from the central electrode layer 3 (output terminal B) can be taken out by the detection means 5.

In order to prevent the noise due to the expansion and contraction stress in the surface direction as described above, and to secure good detection characteristics of sound waves and excellent flexibility as a whole, the strip-shaped piezoelectric element is
The central electrode layer 3 located in the center has a layer configuration in which stress deformation is vertically symmetrical with respect to the neutral axis. For example, the central electrode layer 3 is a metal foil electrode that controls the rigidity of the entire strip-shaped piezoelectric element. It is preferred to form the surface electrodes 2a and 2b by flexible vapor deposition electrodes or especially metal sprayed electrodes.

In this second embodiment, the central electrode layer 3
Is, for example, copper, which has higher rigidity than the polymer piezoelectric bodies 1a and 1b and the surface electrodes 2a and 2b, as described above.
Thickness of aluminum, tin, zinc, gold, silver, platinum, etc. is 6 ~
It is preferably formed of a metal foil having a thickness of about 200 μm, particularly 20 to 120 μm. However, as described above, the central electrode layer 3 serves as a neutral point, and a layer configuration in which the upper and lower polymer piezoelectric bodies are deformed symmetrically with respect to bending stress is preferably adopted. Other than the above-mentioned metal foil can also be used.

The adhesive layers 4a and 4b can be formed of a conductive adhesive in which conductive particles are dispersed,
Even when a layer having a thickness of about 5 to 40 μm is formed with an adhesive such as an epoxy resin, a urethane resin, a polyester resin, a butadiene resin, or an acrylic resin, which has more excellent adhesive strength, the output characteristics are maintained well.

In the present embodiment, the surface electrodes 2a, 2b of the piezoelectric element 50 are made of silver, copper, aluminum, zinc or the like and have a thickness of 10 to 100 μm, preferably 20 to 50 μm, or 0.02 to 0. It is preferable to form a vapor deposition electrode of about 1 μm and maintain good flexibility. With this configuration, even when a metal foil electrode having a relatively high rigidity is used as the central electrode layer 3, good flexibility is maintained as the entire band-shaped piezoelectric element 50, and the spiral winding as shown in FIG. Structure is possible. Then, in combination with the spirally wound structure shown in FIG. 5, a cylindrical piezoelectric element 50 having good flexibility as a whole is obtained. This element has no significant difference in flexibility in the radial direction, and has excellent operability during deployment and storage of the sonar.

Also, when the laminated polymer piezoelectric material is used as in this embodiment, the surface electrodes 2a and 2b do not need to be provided over the entire surface of the long strip piezoelectric element 50, and in the example of FIG. As described above, the piezoelectric elements 50 can be formed discontinuously with the electrode blank portions at predetermined intervals in the length direction. The hydrophone formed by spirally winding the strip-shaped piezoelectric element 50 is a hydrophone linear array in which a large number of element units shown in FIG. 5 are linearly connected, and compared to a conventional hydrophone array. Since it is integrally molded, it has a characteristic that mechanical properties such as bending, elongation, strength, etc. and specific gravity are uniform. Therefore, for example, the durability against tensile impact becomes excellent.

In the hydrophone of the present invention, similarly to the embodiments shown in FIGS. 1 to 4, the belt-shaped piezoelectric element 50 as described above is provided on the electrically insulating support body which gives the central axis O, for example, rubber elasticity. It is also possible to have a structure in which a body rod or a cylinder is spirally wound and an insulating coating is applied to the outer surface thereof. However, in order to prevent the stress applied to the strip-shaped piezoelectric element from remaining and to improve the measurement sensitivity, the strip-shaped piezoelectric element is once wound around a rigid or elastic rod-shaped body and then spirally shaped. It is preferable that the rod-shaped body is removed and the strip-shaped piezoelectric element 50 formed in a spiral shape is embedded in the elastomer coating 11 made of urethane rubber, silicon rubber, butyl rubber, or the like. Thus, a cylindrical rod-shaped hydrophone as shown in FIG. 5 having good flexibility as a whole and good wave receiving sensitivity is obtained.

On the other hand, the outer shape of the covering 11 is preferably cylindrical, but may be other shapes, for example, the covering 11 may be formed into an elliptic cylinder to give directionality to bending stress. It is possible. Further, in the center of the covering body 11, electric wires such as signal lines and power supply lines and electric parts such as a depth gauge and an azimuth gauge, a strength member, and a filling material are embedded, or a cavity is formed to dispose them. You can also do it.

The strip piezoelectric element 50 generally has a width of 2 to 50.
mm, preferably 5 to 20 mm, and having a desired length, for example, with a spacing of 1 to 20 mm (preferably spacing / width ≦ 1), a winding number of 1 or more, and a winding diameter of 8 to 50 mm. A hydrophone is obtained.

The individual hydrophone elements thus obtained are sequentially connected at intervals that are changed so as to be compatible with sound waves in a desired wavelength range, thereby making the hydrophone suitable for use as a towed sonar. An array is obtained.

In the above, the piezoelectric body 1 is a single layer or two.
Although the case of layers has been illustrated, the piezoelectric body 1 may have a structure in which a larger number of piezoelectric bodies are laminated, and in this case, an intermediate electrode layer may be interposed between the respective piezoelectric body layers.

Further, in the above, the spiral piezoelectric element of the present invention has been mainly described with respect to a wave receiver of a towed sonar which is a preferred embodiment thereof. However, the spiral piezoelectric element using the band-shaped piezoelectric element 10 of the present invention is not limited to this, but as a probe of an ultrasonic flaw detector or an ultrasonic thickness gauge for a cylindrical inspection object such as a pipe, or It can also be used as an oscillating (receiving) element such as a probe of a sonic cleaner. At this time, the lead wires (signal wires) 8a, 8b, 8c shown in FIG. 1, FIG. 4 or FIG.
81a, 81b, 82a, 82b etc. will be used as a feeder.

When the spiral piezoelectric element of the present invention is used as a probe for inspecting a cylindrical inspection object,
In order to maintain good acoustic contact between the object to be inspected and the piezoelectric element, it is preferable to seal the periphery of the element with a flexible tube or balloon, and to provide a means for sucking and discharging liquid inside the element. .

[0041]

Example 1 A hydrophone was manufactured according to the embodiment shown in FIGS.

First, a vinylidene fluoride (VDF) / trifluoroethylene (TrFE) copolymer having a molar ratio of 75/25 (number average molecular weight = 1.75 × 10 ⁵ , manufactured by Kureha Chemical Industry Co., Ltd.) was diced. Sheet extrusion at a temperature of 265 ° C, 1
After heat treatment at 25 ° C. for 13 hours, under an electric field of 75 MV / m,
A holding time of 5 minutes at 123 ° C and a polarization treatment of 1 hour including the ascending / descending time were performed to obtain a polymer piezoelectric film with a thickness of 500 μm. After surface treatment, electro-spraying type thermal spraying machine (manufactured by Kato Metallikon Co., DK type metal spraying machine E)
Type) and sprayed under conditions of an air pressure of 5 kg / cm ² and a voltage of 15 V, and a zinc sprayed electrode 2 having a thickness of about 40 μm each 2
a and 2b were formed.

Next, from the piezoelectric element having the laminated structure shown in FIG. 2 obtained above, a machine direction (M
D) Slitting was performed to obtain the strip piezoelectric element 10.

This strip-shaped piezoelectric element 10 was wound around a brass rod having a diameter of 7 mm, wound with tape and fixed, and then 70
After heat treatment at 1 ° C for 1 hour, the material was gradually cooled to room temperature, spirally attached to the belt-shaped piezoelectric element, and the brass rod was removed. The brass rod used in this blunting process preferably has a smaller diameter than the brass rod used in the next shaping process.

Subsequently, a shaping tool in which a plate-shaped screw blade is spirally attached to a brass bar having a diameter of 10 mm with a pitch of 15 mm is prepared, and the spiral piezoelectric element having the above-mentioned curl is attached to the tool at a constant interval (about (5 mm) and immediately wound, and allowed to stand at room temperature for 10 minutes or more to mold. Thus, a shaped spiral piezoelectric element having a length of 120 mm was obtained, and then the shaping tool was taken out leaving about half of the element, and axially aligned using a jig in a Teflon mold frame having a diameter of 20 mm. Fully degassed after being inserted by using "TYPE3318 / 2 manufactured by Nippon Zeon Co., Ltd."
(023 / DOA = 50/40/10 ”(weight ratio)) was poured to about half of the mold frame, and after heat curing at 60 ° C. for 6 hours, the jig, the mold frame and the shaping tool were removed.
Then, the lead wires 8a and 8b connected to the terminals A and B are joined to one end of the spiral piezoelectric element by the solder 7, and then returned to the mold frame and the polyurethane resin is cast on the remaining uncoated portion. By curing, a hydrophone (about 135 mm in length) was obtained in which the strip-shaped piezoelectric element 10 spirally wound and shaped as shown in FIG. 1 was embedded in the insulating coating 11.

In order to test the performance of the thus obtained hydrophone as a wave receiver, the slit-shaped piezoelectric element having slits and the hydrophone obtained by shaping the slit-shaped piezoelectric element in a spiral shape and embedded in a urethane elastomer were used. The hydrostatic piezoelectric strain constant d _h was measured and the two were compared.

The measurement results are shown in Table 1 below. From the table, it is understood that the piezoelectric element of the present invention maintains the wave receiving sensitivity before shaping even after shaping. Here, hydrostatic piezoelectric constant d _h was determined by the following method.

Immerse the sample in silicon oil placed in a pressure resistant container.
Pickle and pressure P (Newton (N) from the nitrogen gas source into the container.
/ M² ) Is added to the sample, the charge amount Q (Coulomb
(C)) is measured. And gauge pressure 2Kg / cm²
The amount of charge increase dQ with respect to the pressure increase dP in the vicinity is obtained,
It was calculated by the following formula.

D _h = (dQ / dP) / A The unit is C / N. Where A is the electrode area (m ² )
Is.

[0050]

[Table 1]

This hydrophone can be easily bent by hand, and after repeated bending several times with a radius of curvature of about 8 cm and then re-measured, the d _h constant did not change. Thus, it can be seen that the piezoelectric element of the present invention has excellent flexibility.

Example 2 A hydrophone was manufactured according to the embodiment shown in FIGS. 5 and 6.

First, in the same manner as in Example 1, the thickness 500
A μm polymer piezoelectric film was obtained, and one surface thereof was roughened.

Separately, a polyester adhesive (Toron Co., Ltd. “Byron 30SS” and Nippon Polyurethane Co., Ltd. “Coronate L” 99: 1 (weight ratio) mixture) to thickness 1
After coating at 0 μm, a pair of piezoelectric films cut out from the polymer piezoelectric film obtained above were attached so that their polarization characteristics were opposite to each other, and the temperature was kept at 50 ° C. for 2
The adhesive was cured under the condition of 0 kg / cm ² to obtain a laminated body of 1a / 4a / 3 / 4b / 1b excluding the surface electrodes 2a and 2b of FIG.

Then, both surfaces of the laminate obtained above were roughened by sand blasting with an alumina-based abrasive having a grain size of # 60, and then electro-spraying type thermal spraying machine (manufactured by Kato Metallikon Co., D
Air pressure 5kg / c using K type metal sprayer E type)
Thermal spraying is performed under the conditions of m ² and voltage of 15 V, and the thickness is about 40 μm.
The zinc sprayed electrodes 2a and 2b were formed.

Then, from the piezoelectric element having the laminated structure shown in FIG. 6 obtained above, a machine direction (M
The strip-shaped piezoelectric element 50 was obtained by slitting into D).

Example 1 of this strip-shaped piezoelectric element 50
120mm in length with the same curling and patterning as
The shaped spiral piezoelectric element 50 is obtained, and thereafter, it is embedded and molded in polyurethane in the same manner as in Example 1, and spirally wound as shown in FIG.
A hydrophone (length: about 135 mm) having a form embedded in the urethane elastomer coating 11 was obtained.

The electrode take-out portion (right end in FIG. 5) of the hydrophone thus obtained was shaken with a hand in a pendulum shape between terminals A and B and between terminals AC and B (as shown in FIG. 6). The output in AC was short-circuited was measured by a digital oscilloscope (DL-2240 type, Yokogawa Electric Corp.). An oscillograph chart of the output waveform is shown in FIG. 7 (between terminals AB) and FIG. 8 (end AC-B), respectively.
Between). In the figure, the vertical axis is the output (20 mV / div.),
The horizontal axis represents time (0.5 sec / div.).

As is clear from the comparison between FIG. 7 and FIG.
It can be seen that in the output between the terminals AC and B (FIG. 8) according to the structure of the present invention, the deformation noise due to the expansion and contraction of the hydrophone is effectively canceled.

Further, the hydrostatic piezoelectric strain constant d _h of the slit strip piezoelectric element and the hydrophone in which the slit was formed in a spiral shape and embedded in a urethane elastomer was measured in the same manner as in Example 1, The two were compared. The measurement results are shown in Table 2 below. From the table, as in Example 1, the wave receiving sensitivity before shaping is maintained even after shaping.

[0061]

[Table 2]

Subsequently, when the hydrophone was fixed to a radius of curvature of 10 cm by a jig and the same measurement was carried out, d
There was no change in the _h constant.

[0063]

As described above, according to the present invention, since the flexible strip-shaped piezoelectric body is spirally wound, the flexibility and the flexibility significantly improved as compared with the cylindrical piezoelectric element can be obtained. A piezoelectric element having impact resistance and suitable as a sound wave transmitting / receiving element is provided.

Further, by adopting a strip-shaped piezoelectric element having a structure in which a pair of strip-shaped polymer piezoelectric bodies are bonded to each other on the opposite side, and a spirally wound structure of the strip-shaped piezoelectric elements, while maintaining the flexibility as a whole, Provided is a hydrophone which prevents generation of noise due to the application of dynamic stress and has a good receiving sensitivity.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a hydrophone according to an embodiment of the piezoelectric element of the present invention, as viewed from the front.

2 is a schematic cross-sectional view in the thickness direction of the strip-shaped piezoelectric element taken along the cutout surface II-II in FIG.

3 is a schematic cross-sectional view in the thickness direction of a strip-shaped piezoelectric element having an insulating coating layer corresponding to FIG.

FIG. 4 is a perspective view of a hydrophone having a connecting element structure according to another embodiment of the piezoelectric element of the present invention, viewed from the front.

FIG. 5 is a partially cutaway perspective view of an embodiment of the hydrophone of the present invention as viewed from the front.

6 is a schematic cross-sectional view in the thickness direction of a strip-shaped piezoelectric element taken along the cutout surface VI-VI in FIG.

FIG. 7 is an oscillograph chart showing a noise generation state due to mechanical deformation in a hydrophone using a polymer piezoelectric element according to a comparative example (AB output extraction structure).

FIG. 8 is an oscillograph chart showing a noise generation state due to mechanical deformation in a hydrophone using a polymer piezoelectric element according to an example (AC-B output extraction structure).

[Explanation of symbols]

1, 1a, 1b: band-shaped polymer piezoelectric material, 2a, 2b: surface electrode layer, 3: central electrode layer, 4a, 4b: adhesive layer, 5a, 5b: insulating coating layer, 6: voltage output detecting means, 7: Solder, 8a, 8b, 8c, 81a, 81b, 82a, 82b:
Lead wire, 10, 10a, 10b, 50: Piezoelectric element wound in a spiral shape, 11: Cover, O: Central axis, A, B, A1, B1, A2, B2: Terminal.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuyuki Yoshitake 1-34-5 Eharacho, Nakano-ku, Tokyo (72) Inventor Taku Sato 183-1 Nishikimachi Harada, Iwaki, Fukushima Prefecture (72) Inventor Kazumoto Suzuki Fukushima 1-9-3 Honcho, Ueda-cho, Iwaki, Japan (72) Inventor Kenichi Nakamura 32, 4 Sakuta, Shizawa, Nakoso-cho, Iwaki-shi, Fukushima Prefecture

Claims (6)

[Claims] 1. A strip-shaped polymer piezoelectric material having electrode layers provided facing each other on its surface is spirally wound around a central axis, and the surface electrode layers are arranged substantially parallel to the extension direction of the central axis. A piezoelectric element having the above structure. 2. The piezoelectric element according to claim 1, wherein a plurality of pairs of the surface electrode layers are provided at intervals in the extension direction of the polymer piezoelectric material. 3. The polymer piezoelectric material is a pair of polymer piezoelectric materials laminated with a central electrode layer interposed therebetween.
Alternatively, the piezoelectric element described in 2. 4. The piezoelectric element according to claim 1, wherein the outer surface of the surface electrode layer is insulation-coated. 5. A strip-shaped piezoelectric element obtained by stacking a pair of strip-shaped polymer piezoelectric bodies with a central electrode layer sandwiched therebetween such that the polarization directions of the strip-shaped polymer piezoelectric bodies are opposite to each other. A hydrophone excellent in flexibility having a structure capable of taking out an electric output generated between a surface electrode formed on both surfaces of a piezoelectric element and the central electrode layer. 6. The hydrophone according to claim 5, wherein the strip-shaped piezoelectric element wound and arranged in a spiral shape is embedded in an elastomer coating to form a cylindrical rod shape as a whole.