WO2024034153A1

WO2024034153A1 - Piezoelectric vibration device

Info

Publication number: WO2024034153A1
Application number: PCT/JP2022/048501
Authority: WO
Inventors: 高志小椋
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2022-08-09
Filing date: 2022-12-28
Publication date: 2024-02-15
Also published as: JP2024024613A

Abstract

A piezoelectric vibration device 100 according to the present disclosure comprises a piezoelectric element 120 and a diaphragm 110 that has a first part 115 to which the piezoelectric element 120 is joined and a second part 116 in the periphery thereof. The piezoelectric element 120 is joined to one surface of the diaphragm 110 in the first part 115 so as to expand and contract under the application of an AC voltage to vibrate the diaphragm 110 and thereby cause sound to be emitted from the diaphragm 110 or so as to expand and contract following the vibration of the diaphragm 110 in a state in which the diaphragm 110 is vibrating to thereby cause a voltage signal to be generated. The piezoelectric vibration device 100 further comprises a rigid layer 118 laminated on one surface of the diaphragm 110 in the second part 116 and bonded to the peripheral surface of the piezoelectric element 120.

Description

piezoelectric vibrator

The present invention relates to a piezoelectric vibrating device including a piezoelectric element and a diaphragm.

As shown in FIG. 10, a thin piezoelectric vibrating device 400 in which a piezoelectric element 420 is bonded to one surface of a diaphragm 410 has been developed (see Patent Document 1). The diaphragm 410 has a three-layer structure in which a resin layer 411 is vertically sandwiched between

metal layers

412 and 413 for the purpose of weight reduction. The piezoelectric element 420 is bonded to a metal layer 412, and this metal layer 412 is used to apply an alternating voltage to the piezoelectric element 420. The other metal layer 413 is provided to position the center of rigidity of the diaphragm 410 at the center of the diaphragm 410 in the thickness direction.

In Patent Document 1, the piezoelectric vibration device 400 is configured as a piezoelectric speaker. Specifically, the piezoelectric vibrating device 400 can reproduce sound by vibrating the diaphragm 410 on the piezoelectric element 420 side and on the opposite side as shown in FIG. Note that in FIG. 11, the shape of the diaphragm 410 when the diaphragm 410 is displaced to the maximum extent toward the piezoelectric element 420 is shown by a solid line. The shape of the diaphragm 410 when the diaphragm 410 is maximally displaced to the side opposite to the piezoelectric element 420 is shown by a dashed line.

If the vibration amplitude of the diaphragm 410 is large, the piezoelectric vibrating device 400 can reproduce a loud sound. Therefore, in order to increase the vibration amplitude of the diaphragm 410, the surrounding part 416 surrounds the diaphragm 410 in the circumferential direction. It is set up like this. Further, in order to fix the piezoelectric vibrating device 400 to another device (for example, a home appliance such as a washing machine when the piezoelectric vibrating device 400 is used as a buzzer), the fixing portion 417 extends around the peripheral portion 416 in the circumferential direction. It is set up to surround.

The surrounding portion 416 is made of the same material as the resin layer 411 of the diaphragm 410 and is formed integrally with this resin layer 411. The fixing part 417 has a central layer 418 made of the same material as the resin layer 411, and the central layer 418 is formed integrally with the peripheral part 416. Further, the fixing portion 417 includes

metal layers

431 and 432 that sandwich the center layer 418 above and below in order to obtain the necessary rigidity for fixing to another device. That is, the fixed part 417 has a three-layer structure similar to the diaphragm 410. On the other hand, unlike the diaphragm 410 and the fixed part 417, the surrounding part 416 has a single layer structure and is more easily deformed than the diaphragm 410 and the fixed part 417.

When reproducing sound using the piezoelectric vibrating device 400, an AC voltage having a frequency that causes the diaphragm 410 to resonate is applied to the piezoelectric element 420. By applying the AC voltage, the piezoelectric element 420 expands and contracts in the direction along the diaphragm 410, and the diaphragm 410 resonates with the expansion and contraction of the piezoelectric element 420, vibrating toward the piezoelectric element 420 side and the opposite side.

The diaphragm 410 is subjected to air resistance while vibrating. The greater the air resistance, the more difficult it becomes for the diaphragm 410 to move. Therefore, under the condition that the piezoelectric element 420 expands and contracts at a constant frequency, the greater the air resistance, the longer the vibration period of the diaphragm 410 becomes, and the piezoelectric vibrator 400 is unable to reproduce low-pitched sounds. Can be done. Air resistance increases as the diaphragm 410 becomes larger, so by making the diaphragm 410 larger, the reproduction range of the piezoelectric vibrating device 400 is expanded to the bass side. Therefore, in Patent Document 1, the diaphragm 410 includes not only the first portion 414 to which the piezoelectric element 420 is bonded, but also the second portion 415 surrounding the first portion 414 in the circumferential direction.

In Patent Document 1, the piezoelectric vibration device 400 is used as a piezoelectric speaker, but the piezoelectric vibration device 400 can also be used as a piezoelectric vibration sensor that detects vibrations of a detection target. That is, if the diaphragm 410 is arranged so as to receive the vibration of the object to be detected, the diaphragm 410 will vibrate in accordance with the vibration of the object to be detected. The piezoelectric element 420 expands and contracts in response to the vibration of the diaphragm 410, and a voltage corresponding to the amount of expansion and contraction of the piezoelectric element 420 is output from the piezoelectric element 420. Therefore, the piezoelectric vibrating device 400 can detect the vibration of the object to be detected. It can function as a detecting sensor (piezoelectric vibration sensor). That is, by monitoring the voltage output from the piezoelectric element 420, the vibration of the object to be detected can be detected and analyzed.

A piezoelectric element 420 is laminated on the first portion 414 of the diaphragm 410, and the first portion 414 and the piezoelectric element 420 constitute a laminated body 419. On the other hand, the piezoelectric element 420 is not stacked on the second portion 415 . Therefore, there is a difference in bending rigidity between the second portion 415 and the laminate 419. Due to this difference in bending rigidity, the second portion 415 bends relative to the laminate 419. This bending of the diaphragm 410 may cause the following problems.

In FIG. 11, a first area surrounded by the diaphragm 410 when the diaphragm 410 is displaced to the maximum extent toward the piezoelectric element 420 side, and the diaphragm 410 when the diaphragm 410 is displaced to the maximum extent to the opposite side. The width corresponds to the amount of air moved by one period of vibration of the diaphragm 410. If the diaphragm 410 is not bent, air corresponding to the second area surrounded by the dotted line in FIG. 11 will be moved by one period of vibration of the diaphragm 410. The second region is wider than the first region, and the bending of the diaphragm 410 causes the air moved by one period of vibration of the diaphragm 410 to be equal to the difference in area between the second region and the first region. It can be seen that the amount of The air resistance that the diaphragm 410 receives while the diaphragm 410 is vibrating becomes smaller by the amount of this decrease in air amount. Therefore, under the condition that the piezoelectric element 420 expands and contracts at a constant frequency, the vibration period of the diaphragm 410 becomes shorter due to the decrease in air resistance that the diaphragm 410 receives, and the piezoelectric vibrating device 400 produces a low sound. It becomes difficult to play.

Further, the above-mentioned difference in bending rigidity directly results in a difference in acoustic impedance between the laminate 419 and the second portion 415. That is, acoustic impedance is expressed as the product of the density of a medium through which sound propagates and the speed of sound. The speed of sound increases as the modulus of elasticity of the medium increases. If the modulus of elasticity of the medium is large, the bending rigidity of the medium and, as a result, the speed of sound will be high. On the other hand, if the modulus of elasticity of the medium is small, the bending rigidity of the medium and, by extension, the speed of sound will be low. Therefore, the speed of sound in the laminate 419, which has a large bending stiffness, and thus the acoustic impedance becomes large, and the speed of sound, and thus the acoustic impedance, in the second portion 415, which has a small bending stiffness, becomes small. These differences in acoustic impedance may cause the following problems, particularly when piezoelectric vibration device 400 is used as a piezoelectric vibration sensor.

When unnecessary vibration components (hereinafter referred to as "noise waves") that propagate along the diaphragm 410 occur in the laminate 419, most of these noise waves are caused by the difference in acoustic impedance described above. It may be reflected at the boundary with the second portion 415. That is, while the number of noise waves propagating to the second portion 415 decreases, the number of noise waves continuing to propagate within the first portion 414 increases. In this case, the influence of the noise waves on the expansion and contraction of the piezoelectric element 420 becomes greater, and the signal output from the piezoelectric element 420 may contain more noise. Further, when the piezoelectric vibrating device 400 is used as a piezoelectric speaker, the sound reproduced by the piezoelectric vibrating device 400 may include a lot of noise.

Japanese Patent Application Publication No. 2003-230193

The present disclosure provides a piezoelectric vibration device that has a wide reproduction band on the bass side and can reduce noise included in reproduced sound, or can output a signal representing the vibration of a detection target with little noise. The purpose is to

The piezoelectric vibration device in the present disclosure is configured to function as a piezoelectric speaker that reproduces sound or a piezoelectric vibration sensor that detects vibration. The piezoelectric vibrating device includes a piezoelectric element, a diaphragm having a first part to which the piezoelectric element is bonded, and a second part around the first part. The piezoelectric element expands and contracts under the application of an alternating current voltage to cause the diaphragm to vibrate between the side to which the piezoelectric element is bonded and the opposite side, thereby generating sound from the diaphragm. The diaphragm is bonded to one surface of the first portion of the diaphragm so that it expands and contracts in accordance with the vibrations of the diaphragm and generates a voltage signal when the diaphragm is vibrating on both sides of the diaphragm. ing. The piezoelectric vibrating device further includes a rigid layer laminated on one surface of the second portion of the diaphragm and bonded to the circumferential surface of the piezoelectric element.

The piezoelectric vibration device described above has a wide reproduction band on the bass side and can reduce the noise contained in the reproduced sound, and can also output a signal representing the vibration of the detection target with less noise.

The objects, features, and advantages of the present disclosure will become more apparent from the following detailed description and accompanying drawings.

Plan view of part of a piezoelectric vibrating device that functions as a piezoelectric speaker A schematic cross-sectional view of the piezoelectric vibrating device along line II-II in FIG. Schematic diagram of the shape of the piezoelectric vibration device during vibration Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-sectional view of other piezoelectric vibrating devices Schematic cross-section of a conventional piezoelectric speaker Schematic diagram of the shape of a conventional piezoelectric speaker during vibration

Hereinafter, embodiments of the piezoelectric vibrating device will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate understanding by those skilled in the art. The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

FIG. 1 is a schematic plan view of a portion of a piezoelectric vibrating device 100 that functions as a piezoelectric speaker. FIG. 2 is a schematic cross-sectional view of the piezoelectric vibrating device 100 (a cross-sectional view taken along line II-II in FIG. 1). The structure of the piezoelectric vibrating device 100 will be explained with reference to FIGS. 1 and 2.

(Structure of piezoelectric vibrator)
The piezoelectric vibrating device 100 includes a substantially square-shaped diaphragm 110, a disc-shaped piezoelectric element 120 joined to the diaphragm 110, and a rectangular frame-shaped peripheral portion 113 surrounding the diaphragm 110 in the circumferential direction. A rectangular frame-shaped fixing part 140 surrounding the peripheral part 113 in the circumferential direction is provided.

The piezoelectric element 120 has a thickness of about 30 μm to 100 μm, and one surface of the piezoelectric element 120 is bonded to the center of the diaphragm 110. Piezoelectric element 120 may be bonded to diaphragm 110 using, for example, an acrylic adhesive.

The piezoelectric element 120 has a characteristic of expanding and contracting in the radial direction when an AC voltage is applied to both sides of the piezoelectric element 120. Furthermore, the piezoelectric element 120 has a characteristic that the larger the voltage applied to both sides of the piezoelectric element 120, the more the piezoelectric element 120 expands and contracts.

In this embodiment, when a positive voltage is applied to one surface (the upper surface in FIG. 2) of the piezoelectric element 120 and a negative voltage is applied to the other surface, the piezoelectric element 120 expands in the radial direction. It has characteristics. Furthermore, when the voltage poles are reversed, the piezoelectric element 120 has a characteristic of contracting in the radial direction. Such a piezoelectric element 120 can be formed using a piezoelectric material such as PZT (lead zirconate titanate), for example.

Note that if the piezoelectric element 120 is inverted vertically and bonded to the diaphragm 110 (that is, if it is electrically bonded in opposite phases), it has an elastic characteristic opposite to the above-mentioned elastic characteristic. That is, with a negative voltage applied to one surface (the upper surface in FIG. 2) of the piezoelectric element 120 and a positive voltage applied to the other surface, the piezoelectric element 120 expands in the radial direction. It has the following characteristics. In this case, the piezoelectric element 120 has a characteristic of contracting in the radial direction due to the polarity reversal of the applied voltage.

The diaphragm 110 is a thin plate-like member (for example, a member with a thickness of about 40 μm) that vibrates on the side to which the piezoelectric element 120 is bonded and the opposite side as the piezoelectric element 120 expands and contracts. The diaphragm 110 is larger than the piezoelectric element 120 in a plan view, and as shown in FIG. It has two parts 116.

The bending rigidity of the laminate of the first part 115 and the piezoelectric element 120 (hereinafter referred to as "first laminate 117") is greater than the bending rigidity of the second part 116 by the bending rigidity of the piezoelectric element 120. ing. These differences in bending rigidity cause the diaphragm 110 to bend and the acoustic impedance within the diaphragm 110 to change rapidly. In order to suppress these adverse effects, a rigid layer 118 is laminated with a substantially constant thickness on the surface of the second portion 116 on the piezoelectric element 120 side, as shown in FIG. (not shown in Figure 1). The rigid layer 118 covers the entire diaphragm 110 except for the first portion 115 to which the piezoelectric element 120 is bonded, and has a substantially square outer shape in plan view. This rigid layer 118 is adhered to the circumferential surface of the piezoelectric element 120.

The thickness and material of the rigid layer 118 are such that the bending rigidity of the first laminate 117 and the flexural rigidity of the laminate of the second portion 116 and the rigid layer 118 (hereinafter referred to as "second laminate 119") are approximately equal. It is set to be. The rigid layer 118 can be formed, for example, by photopolymerizing and curing a liquid resin material (for example, a urethane acrylate resin, an epoxy acrylate resin, or a polyester acrylate resin) on the second portion 116 using ultraviolet rays.

The diaphragm 110 itself may have multiple material layers or may have a single layer structure. In this embodiment, the diaphragm 110 has a two-layer structure and includes a base layer 111 and a conductive layer 112 bonded to the base layer 111 on the piezoelectric element 120 side. A piezoelectric element 120 is bonded to the conductive layer 112. Further, around the piezoelectric element 120, the above-described rigid layer 118 is laminated on the conductive layer 112.

The base layer 111 is made of a material with a lower density than the conductive layer 112. For example, the base layer 111 may be a resin film layer or an aluminum layer. When the base layer 111 is made of resin, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, polyamide, or polyimide may be used. Alternatively, the base layer 111 may be made of styrene-butadiene-based rubber, butadiene-based rubber, butyl-based rubber, or ethylene-propylene-based rubber. These resin materials may have acoustically high internal loss, and this internal loss may contribute to reducing noise contained in reproduced sound.

The material layer constituting the base layer 111 also constitutes the peripheral portion 113. This material layer is a portion that curves and deforms in a convex direction toward the piezoelectric element 120 and in a convex direction in the opposite direction as the piezoelectric element 120 expands and contracts. The thickness of the material layer is set so that a sufficiently large restoring force can be obtained against this curved deformation. For example, this thickness may be 30 μm.

On the other hand, the conductive layer 112 is thinner than the base layer 111 in order to reduce the weight of the diaphragm 110. For example, the thickness of the conductive layer 112 may be about 10 μm. Since the conductive layer 112 is thinner than the base layer 111, it does not affect the internal loss of the entire diaphragm 110 as much as the base layer 111 does. Therefore, the internal loss of the conductive layer 112 may be greater than the internal loss of the base layer 111.

The conductive layer 112 is a part used to supply power to the piezoelectric element 120, and is made of a conductive material. For example, the conductive layer 112 may be a layer of 42 alloy (42Ni-Fe) or a layer of copper (Cu). The conductive layer 112 is bonded to the base layer 111 by van der Waals force. Alternatively, the conductive layer 112 and the base layer 111 may be joined by an adhesive.

The conductive layer 112 has an overall rectangular shape in plan view, but a portion is cut out. A portion of the base layer 111 is exposed in this cutout portion. This notch is used for arranging the electrode 132 for applying voltage to the piezoelectric element 120.

The peripheral portion 113 is made of the material layer that makes up the base layer 111, as described above. In other words, the peripheral portion 113 is made of the same material as the base layer 111, and is formed integrally with the base layer 111 so as to circumferentially surround the base layer 111. If the amount of curved deformation of the peripheral part 113 is large, the diaphragm 110 can vibrate with a large amplitude. Therefore, in order to maintain the ease of deformation of the peripheral part 113, the above-mentioned rigid layer 118 is laminated in the peripheral part 113. It has not been.

The fixing part 140 is a part for fixing the piezoelectric vibrating device 100 to another device 300 (for example, a washing machine). An opening 310 is formed to allow the The fixing part 140 is arranged so as to overlap the device 300 around the opening 310. Note that, at this time, the diaphragm 110 and the surrounding portion 113 are overlapped on the opening 310.

The fixing part 140 includes a fixing layer 141 and a reinforcing layer 142 laminated on the fixing layer 141 to reinforce the fixing layer 141. The fixed layer 141 is made of the same material as the base layer 111 and the peripheral part 113, and is formed integrally with the peripheral part 113 so as to circumferentially surround the peripheral part 113.

As shown in FIG. 1, the reinforcing layer 142 is approximately C-shaped in plan view. In this embodiment, the reinforcing layer 142 is laminated on the surface of the resin layer or aluminum layer that constitutes the peripheral portion 113 and the base layer 111, on which the conductive layer 112 is provided. The reinforcing layer 142 has an opening in the same direction as the cutout portion of the conductive layer 112, and this opening portion is used for arranging the

electrodes

131 and 132 for applying a voltage to the piezoelectric element 120.

The material of the reinforcing layer 142 may be the same as that of the conductive layer 112. Further, the reinforcing layer 142 may have the same thickness as the conductive layer 112, as long as sufficient rigidity is obtained for attachment to the device 300. Note that the reinforcing layer 142 may be thicker than the conductive layer 112 in order to improve the rigidity of the attachment portion to the device 300.

The inner edge of the reinforcing layer 142 is spaced from the outer edge of the conductive layer 112 by a substantially constant distance over its entire length. A portion between the inner edge of the reinforcing layer 142 and the outer edge of the conductive layer 112 is a peripheral portion 113.

As described above, the

electrodes

131 and 132 are arranged using the opening of the fixing part 140 and the cutout of the conductive layer 112. The electrode 131 is formed integrally with the conductive layer 112 and is laminated on the peripheral portion 113 and the fixed portion 140. The electrode 131 is electrically conductive like the conductive layer 112.

On the other hand, the electrode 132 is laminated not only on the peripheral portion 113 and the fixing portion 140 but also on the base layer 111 in the cutout region of the conductive layer 112. The electrode 132 is bonded to the surface of the piezoelectric element 120 opposite to the side to which the conductive layer 112 is bonded using a bonding material that is conductive and stretchable. Since the bonding material has a certain degree of elasticity, the connecting portion between the piezoelectric element 120 and the electrode 132 is less likely to break even under deformation of the piezoelectric element 120. As the bonding material, for example, a silver paste in which a resin material is blended with silver may be used, or a paste material in which a conductor such as copper, gold, nickel, and carbon is further blended as a filler in this silver paste may be used. It's okay. Furthermore, as the resin material of the bonding material, a resin binder having a nitrile group (for example, acryl nitrile rubber), a resin binder containing an epoxy resin, and/or a resin binder containing a urethane resin may be used. good. As another resin material, a thermoplastic polyester-based resin binder may be used. If such a resin binder is used, a flexible bonding material can be obtained.

(Explanation of operation)
When an AC voltage is applied to the

electrodes

131 and 132, the piezoelectric element 120 and the diaphragm 110 vibrate toward the piezoelectric element 120 and the opposite side, as shown in FIG. Note that in FIG. 3, the shapes of the diaphragm 110 and the surrounding portion 113 when the diaphragm 110 is displaced toward the piezoelectric element 120 are schematically shown by solid lines. Furthermore, the shapes of the diaphragm 110 and the surrounding portion 113 when the diaphragm 110 is displaced to the opposite side are schematically shown with chain lines. The area surrounded by the solid line and the chain line corresponds to the volume of air moved by the vibrations of the diaphragm 110 and the surrounding section 113. The wider this region is, the greater the resistance that the diaphragm 110 receives from the air during vibration. When the resistance from the air is large and the piezoelectric element 120 expands and contracts at a constant frequency, the diaphragm 110 tends to be displaced more slowly than when the resistance from the air is small. In other words, the diaphragm 110 easily vibrates at a low frequency. Therefore, the piezoelectric vibrating device 100 can have a wider reproduction band on the bass side as the air resistance that the diaphragm 110 receives increases.

The frequency of the AC voltage applied to the

electrodes

131 and 132 is set to a value that causes the diaphragm 110 and the surrounding section 113 to resonate. That is, if the voltage pole is switched at the timing when the diaphragm 110 and the surrounding area 113 are about to recover from the state in which the diaphragm 110 has been displaced toward the piezoelectric element 120, the diaphragm 110 will be moved to the side opposite to the piezoelectric element 120. Can move quickly. Conversely, if the voltage pole is switched at the timing when the diaphragm 110 and the surrounding area 113 are about to recover from the state in which the diaphragm 110 is displaced to the side opposite to the piezoelectric element 120, the diaphragm 110 is displaced to the side opposite to the piezoelectric element 120. can move vigorously.

Since the bending rigidity of the surrounding part 113 is the smallest in the piezoelectric vibrating device 100, the surrounding part 113 is on the piezoelectric element 120 side with respect to the fixed part 140 when the resonance state shown in FIG. 3 is obtained. and the opposite side can undergo significant bending deformation. Furthermore, since there is a large difference in bending rigidity between the peripheral part 113 and the second laminate 119 adjacent to the peripheral part 113, bending may occur at the boundary between the peripheral part 113 and the second laminate 119. may occur. On the other hand, a rigid layer 118 is laminated on the second portion 116 of the diaphragm 110 so that the difference in bending rigidity between the second laminate 119 and the first laminate 117 is reduced. 119 and the first laminate 117 are less likely to break. Furthermore, the rigid layer 118 of the second laminate 119 is adhered to the outer peripheral surface of the piezoelectric element 120. Therefore, bending is less likely to occur at the boundary between the second laminate 119 and the first laminate 117.

If the rigid layer 118 is not provided, the diaphragm 110 and the surrounding portion 113 will have a shape as shown by the dotted line in FIG. 3. In this case, the bending at the boundary between the first laminate 117 and the second portion 116 becomes large. As a result, the volume of air moved by the vibrations of the diaphragm 110 and the surrounding portion 113 is reduced by the area surrounded by the dotted line and the solid or chain line in FIG. By this volume reduction, the resistance that the diaphragm 110 receives from the air during vibration is reduced. In this case, under the condition that the piezoelectric element 120 expands and contracts at a constant frequency, the diaphragm 110 vibrates with a shorter vibration period than the vibration period of the diaphragm 110 provided with the rigid layer 118. In other words, by providing the rigid layer 118, the diaphragm 110 can vibrate at a lower frequency, and the piezoelectric vibrating device 100 can have a wide reproduction band on the bass side.

(How to use it as a piezoelectric vibration sensor)
Piezoelectric vibration device 100 can also function as a piezoelectric vibration sensor. For example, if the device 300 shown in FIG. 2 vibrates in the vertical direction, the diaphragm 110 and the surrounding portion 113 may vibrate as shown in FIG. 3. In this case, the piezoelectric element 120 expands and contracts in the radial direction. As the piezoelectric element 120 expands and contracts, a potential difference occurs between the

electrodes

131 and 132, and the piezoelectric element 120 can output a voltage signal representing this potential difference. If the

electrodes

131 and 132 are connected to a data collection device such as a computer, time series data regarding the potential difference can be obtained. By analyzing this time-series data, information regarding the vibration intensity and frequency of the device 300 can be obtained.

When the piezoelectric vibration device 100 is used as a piezoelectric vibration sensor, unnecessary vibration components (hereinafter referred to as "noise waves") propagating in the direction along the diaphragm 110 may become a problem, especially in the first laminate 117. . If this noise wave continues to propagate within the first laminate 117, the piezoelectric element 120 forming the first laminate 117 will be affected by the noise wave, and the potential difference data output from the

electrodes

131 and 132 will be , may contain many noise components.

The influence of noise waves on the piezoelectric element 120 can be alleviated by laminating the rigid layer 118 on the second portion 116 of the diaphragm 110. That is, if the rigid layer 118 were not provided, there would be a large difference in bending rigidity between the first laminate 117 and the second portion 116. This difference in bending rigidity directly results in a sudden change in acoustic impedance at the boundary between the first laminate 117 and the second portion 116. Therefore, the noise waves propagating along the diaphragm 110 in the first stacked body 117 are reflected at the boundary between the first stacked body 117 and the second portion 116, and can continue to propagate within the first stacked body 117.

On the other hand, in the configuration in which the second laminate 119 is formed by laminating the rigid layer 118 on the second portion 116, the difference in bending rigidity between the first laminate 117 and the second laminate 119 is reduced. Ru. This difference in bending rigidity directly becomes the difference in acoustic impedance between the first laminate 117 and the second laminate 119, so the acoustic impedance at the boundary between the first laminate 117 and the second laminate 119 is Changes will be smaller. In this case, the noise waves propagating along the diaphragm 110 in the first laminate 117 propagate to the second laminate 119 without being reflected at the boundary between the first laminate 117 and the second laminate 119. obtain.

The difference in bending rigidity is large between the second laminate 119 and the surrounding portion 113, and the acoustic impedance changes rapidly at the boundary between them. Therefore, the noise waves propagating through the second stacked body 119 may be reflected at the boundary between the second stacked body 119 and the peripheral portion 113 and return to the first stacked body 117.

This noise wave can be attenuated while propagating through the second laminate 119 by forming the base layer 111 with a material having high internal loss. Therefore, when the noise waves reflected at the boundary between the second stacked body 119 and the peripheral portion 113 return to the first stacked body 117, they can be sufficiently attenuated.

Such a noise wave attenuation effect is also useful when the piezoelectric vibrating device 100 is used as a piezoelectric speaker. That is, when the piezoelectric vibrating device 100 is used as a piezoelectric speaker, by laminating the rigid layer 118 on the second portion 116, the noise component included in the sound reproduced by the piezoelectric vibrating device 100 can be reduced.

If the thickness of the rigid layer 118 is gradually reduced from the circumferential surface of the piezoelectric element 120 toward the peripheral part 113 as shown in FIG. changes can be suppressed. In the piezoelectric vibrating device 100 shown in FIG. 4, the difference in bending rigidity at the boundary between the peripheral portion 113 and the second laminate 119 is only the bending rigidity of the conductive layer 112. Therefore, changes in acoustic impedance at the boundary between the peripheral part 113 and the second laminate 119 are suppressed, and fewer noise waves are reflected at the boundary between the peripheral part 113 and the second laminate 119. In other words, more noise waves propagate to the surrounding area 113 across the boundary between the surrounding area 113 and the second stacked body 119.

In order to further suppress changes in acoustic impedance at the boundary between the peripheral portion 113 and the second laminate 119, the diaphragm 110 may have a single-layer structure, as shown in FIG. The diaphragm 110 shown in FIG. 5 is made of a conductive material (for example, 42 alloy (42Ni-Fe)) and has a thickness that allows it to vibrate on the piezoelectric element 120 side and on the opposite side. . Note that the rigid layer 118 shown in FIG. 5 is the same as that shown in FIG. 4.

In the piezoelectric vibrating device 100 shown in FIG. 5, there is almost no difference in bending rigidity at the boundary between the peripheral portion 113 and the second laminate 119. Therefore, there is no change in acoustic impedance at the boundary between the peripheral part 113 and the second laminated body 119, and the noise waves are not reflected at the boundary between the peripheral part 113 and the second laminated body 119, and the noise waves are 113.

In the piezoelectric vibrating device 100 shown in FIGS. 4 and 5, by reducing the thickness of the rigid layer 118 toward the peripheral portion 113, changes in acoustic impedance at the boundary between the second laminate 119 and the peripheral portion 113 are reduced. has been reduced. Alternatively, it is also possible to suppress changes in acoustic impedance by forming the rigid layer 118 from multiple types of materials.

For example, the rigid layer 118 may have a first material layer 121 to a third material layer 123, as shown in FIG. The first material layer 121 is adjacent to the piezoelectric element 120 , and the second material layer 122 is formed at a distance from the first material layer 121 and adjacent to the peripheral portion 113 . The third material layer 123 is disposed between the first material layer 121 and the second material layer 122 and is adjacent to the first material layer 121 and the second material layer 122. The first material layer 121 is made of the hardest material among the materials making up the first material layer 121 to the third material layer 123, and the second material layer 122 is made of the hardest material among these materials. Made from the softest material.

In the second laminate 119 shown in FIG. 6, changes in acoustic impedance may occur at the boundary between the first material layer 121 and the third material layer 123 and the boundary between the second material layer 122 and the third material layer 123. , these changes are not very large. Additionally, a certain amount of change in acoustic impedance may occur at the boundary between the second material layer 122 and the surrounding section 113, but this change is due to the change in acoustic impedance at the boundary between the second laminate 119 and the surrounding section 113 shown in FIG. It's not as big as the change.

In the piezoelectric vibrating device 100 shown in FIGS. 1 to 6, a piezoelectric element 120 is laminated on one surface of a diaphragm 110. In addition to this piezoelectric element 120, as shown in FIG. 7, a second piezoelectric element 124 may be laminated on the opposite surface. In this case, a stacked structure that is vertically symmetrical to the stacked structure composed of the conductive layer 112, piezoelectric element 120, and rigid layer 118 in FIG. Ru. That is, the second piezoelectric element 124 and the piezoelectric element 120 are stacked on the first portion 115 so that the diaphragm 110 is sandwiched therebetween. Further, the rigid layer 126 is laminated on the second portion 116 on the second piezoelectric element 124 side and is bonded to the circumferential surface of the second piezoelectric element 124. Rigid layer 126 is the same as rigid layer 118 in shape and material. Further, the second conductive layer 125 is the same in shape and material as the conductive layer 112.

The second piezoelectric element 124 is connected to the vibration plate 110 in an opposite phase to the piezoelectric element 120. Therefore, when an alternating current voltage is applied to the piezoelectric element 120 and the second piezoelectric element 124, their expansion and contraction operations become opposite to each other. That is, when the piezoelectric element 120 is expanding in the radial direction, the second piezoelectric element 124 contracts in the radial direction. Conversely, when the piezoelectric element 120 is contracting in the radial direction, the second piezoelectric element 124 expands in the radial direction. If the piezoelectric element 120 and the second piezoelectric element 124 behave in this manner, the vibration amplitude of the diaphragm 110 becomes large, and the sound pressure sensitivity of the piezoelectric vibrating device 100 can be improved.

In the piezoelectric vibrating device 100 shown in FIG. 7, the first laminate 117 is composed of the first portion 115 of the diaphragm 110, the piezoelectric element 120, and the second piezoelectric element 124. Further, a second laminate 119 is constituted by the second portion 116 of the diaphragm 110 and

rigid layers

118 and 126. Since the rigid layer 126 having a bending rigidity approximately equal to that of the second piezoelectric element 124 is added, the difference in bending rigidity between the first laminate 117 and the second laminate 119 becomes small. . As a result, folding at the boundary between the first laminate 117 and the second laminate 119 is less likely to occur.

The piezoelectric vibrating device 100 shown in FIG. 7 has a structure that is vertically symmetrical about the central portion of the diaphragm 110 in the thickness direction. Therefore, the center of rigidity of the piezoelectric vibrating device 100 is located at the center of the diaphragm 110 in the thickness direction, and the bending rigidity of the piezoelectric vibrating device 100 is symmetrical about the center of the piezoelectric vibrating device 100 in the thickness direction. Become. As a result, the behavior of the piezoelectric vibrating device 100 becomes more symmetrical when the diaphragm 110 is displaced toward the piezoelectric element 120 and when it is displaced toward the opposite side. If such symmetrical behavior is obtained, distortion of the sound reproduced by the piezoelectric vibration device 100 can be suppressed when the piezoelectric vibration device 100 is used as a piezoelectric speaker. Furthermore, when the piezoelectric vibrating device 100 is used as a piezoelectric vibration sensor, the signal output characteristics when the diaphragm 110 is displaced toward the piezoelectric element 120 side and the signal output characteristics when the diaphragm 110 is displaced to the opposite side. Increased symmetry. Therefore, when performing a vibration analysis of the device 300, the process of correcting the asymmetry of the signal output characteristics can be omitted.

Note that the second piezoelectric element 124 and the rigid layer 126 may be omitted from the piezoelectric vibrating device 100 shown in FIG. 7. In this case, the center of rigidity of the piezoelectric vibrating device 100 itself is shifted upward from the center in the thickness direction of the piezoelectric vibrating device 100, but the center of rigidity of the diaphragm 110 is located at the center of the diaphragm 110 in the thickness direction. obtain. Therefore, the symmetry of the behavior of the diaphragm 110 when the diaphragm 110 is displaced toward the piezoelectric element 120 side and when it is displaced toward the opposite side can be improved compared to the piezoelectric vibrating device 100 shown in FIG. 1.

In the piezoelectric vibrating device 100 shown in FIGS. 1 to 7, if the material forming the

rigid layers

118 and 126 does not excessively inhibit the expansion and contraction of the piezoelectric element 120 and the second piezoelectric element 124, the material may cause the piezoelectric element 120 to And the second piezoelectric element 124 may be covered. For example, the piezoelectric vibrating device 100 shown in FIG. 2 can be improved as shown in FIG. 8. The piezoelectric element 120 of the piezoelectric vibrating device 100 shown in FIG. 8 is covered with a protective layer 151 made of the same material as the rigid layer 118. Thereby, the piezoelectric element 120 can be protected by the rigid layer 118 and the protective layer 151 from environmental degrading factors, such as moisture. Moreover, the piezoelectric vibrating device 100 shown in FIG. 7 can be improved as shown in FIG. The piezoelectric element 120 and the second piezoelectric element 124 of the piezoelectric vibrating device 100 shown in FIG. and is covered by. Thereby, the piezoelectric element 120 and the second piezoelectric element 124 can be protected from environmental deterioration factors such as moisture by the

rigid layers

118, 126 and the

protective layers

151, 152. Additionally, since both sides of the second portion 116 are covered with

rigid layers

118, 126, the second portion 116 can also be protected from environmental degrading factors by these

rigid layers

118, 126.

(Effects, etc.)
The piezoelectric vibrating device 100 according to the embodiment described above has the following features and provides the following effects.

The piezoelectric vibration device according to one aspect of the embodiment described above is configured to function as a piezoelectric speaker that reproduces sound or a piezoelectric vibration sensor that detects vibration. The piezoelectric vibrating device includes a piezoelectric element, a diaphragm having a first part to which the piezoelectric element is bonded, and a second part around the first part. The piezoelectric element expands and contracts under the application of an alternating current voltage to cause the diaphragm to vibrate between the side to which the piezoelectric element is bonded and the opposite side, thereby generating sound from the diaphragm. The diaphragm is bonded to one surface of the first portion of the diaphragm so that it expands and contracts in accordance with the vibrations of the diaphragm and generates a voltage signal when the diaphragm is vibrating on both sides of the diaphragm. ing. The piezoelectric vibrating device further includes a rigid layer laminated on one surface of the second portion of the diaphragm and bonded to the circumferential surface of the piezoelectric element.

According to the above configuration, since the rigid layer is laminated on the second part around the first part to which the piezoelectric element is bonded, the bending rigidity of the laminate of the second part and the rigid layer and the first part and the piezoelectric The difference in bending rigidity of the element stack can be reduced. Therefore, bending of the diaphragm due to the difference in bending rigidity between these laminates is suppressed. Furthermore, since the rigid layer is bonded to the circumferential surface of the piezoelectric element, the bonded portion makes it more difficult for the diaphragm to bend. Therefore, the reproduction range on the bass side is less likely to be reduced due to the bending of the diaphragm, and the piezoelectric vibrating device can have a wide reproduction band on the bass side.

Moreover, if the difference in bending rigidity between the above-mentioned laminates is reduced, the difference in acoustic impedance between these laminates is also reduced. Therefore, even if there is an unnecessary vibration component (hereinafter referred to as a "noise wave") propagating from the first part to the second part, the noise wave reflected at the boundary between the first part and the second part can be reduced and the number of noise waves propagating from the first part to the second part can be increased. In this case, the noise waves in the first portion to which the piezoelectric element is joined can be reduced, and when the piezoelectric vibration device is used as a piezoelectric vibration sensor, the noise included in the signal emitted from the piezoelectric element is reduced. Further, when the piezoelectric vibrating device is used as a piezoelectric speaker, noise included in reproduced sound can be reduced.

In the above configuration, the diaphragm includes a conductive layer forming one surface and capable of supplying power to the piezoelectric element, a base layer having laminated conductive layers and having a lower density than the conductive layer, It may have.

According to the above configuration, if one surface of the diaphragm is formed of a conductive layer, by bonding the piezoelectric element to this surface, the conductive layer can be used to supply power to the piezoelectric element. In addition, the weight of the diaphragm can be reduced by configuring the diaphragm by laminating a conductive layer and a base layer with a lower density than the conductive layer, instead of constructing the entire diaphragm only from conductive materials. can.

In the above configuration, the piezoelectric vibrating device circumferentially surrounds the diaphragm and further includes a surrounding portion that bends and deforms between the side to which the piezoelectric element is bonded and the opposite side as the piezoelectric element expands and contracts. It's okay. The rigid layer may not be laminated on the peripheral portion, and may be formed such that the bending rigidity of the rigid layer decreases toward the peripheral portion.

According to the above configuration, the peripheral portion surrounding the diaphragm in the circumferential direction bends and deforms in response to the expansion and contraction of the piezoelectric element between the side to which the piezoelectric element is bonded and the opposite side. can vibrate between the joined side and the opposite side. At this time, since the rigid layer is not laminated on the peripheral part, it does not prevent bending deformation of the peripheral part.

In addition, since the bending stiffness of the rigid layer decreases toward the periphery, a sudden change in bending stiffness at the boundary between the second part and the periphery, and by extension, a sudden change in acoustic impedance, becomes less likely to occur. There is. For this reason, noise waves attempting to propagate from the second portion to the peripheral portion are less likely to be reflected at the boundary between the peripheral portion and the second portion.

In the above configuration, the diaphragm may include a conductive layer forming one surface and capable of supplying power to the piezoelectric element, and a base layer on which the conductive layer is laminated. The base layer may have greater internal loss than the conductive layer.

According to the above configuration, the base layer has a relatively large internal loss, so it easily attenuates noise waves propagating along the diaphragm. That is, the piezoelectric vibration device can function as a piezoelectric vibration sensor that achieves a high S/N ratio. Further, when the piezoelectric vibrating device is used as a piezoelectric speaker, the peak and/or dip of the sound pressure may be reduced due to the large internal loss of the base layer.

In the above configuration, the piezoelectric vibrating device circumferentially surrounds the diaphragm and further includes a surrounding portion that bends and deforms between the side to which the piezoelectric element is bonded and the opposite side as the piezoelectric element expands and contracts. It's okay. The peripheral portion may be formed integrally with the base layer using the same material as the base layer. The rigid layer may not be laminated on the peripheral portion, and may be formed such that the bending rigidity of the rigid layer decreases toward the peripheral portion.

According to the above configuration, the bending rigidity of the rigid layer decreases toward the peripheral portion, so that a sudden change in acoustic impedance is less likely to occur between the peripheral portion and the second portion. Therefore, noise waves attempting to propagate from the second portion to the peripheral portion are less likely to be reflected between the peripheral portion and the second portion, and the number of noise waves propagating through the peripheral portion increases. Since the surrounding part is the same material as the base layer, which has a relatively high internal loss, it is possible to promote the attenuation of noise waves propagated to the surrounding part.

In the above configuration, the piezoelectric vibrating device may further include a protective layer that covers the piezoelectric element so as to protect the piezoelectric element.

According to the above configuration, the piezoelectric element is covered with the protective layer, so it can be protected from environmental deterioration factors such as moisture.

In the above configuration, the piezoelectric vibrating device includes a first piezoelectric element, which is a piezoelectric element, and a second piezoelectric element joined to the first part so as to sandwich the diaphragm in electrically opposite phase to the first piezoelectric element; It may further include another rigid layer laminated on the second portion on the second piezoelectric element side and bonded to the circumferential surface of the second piezoelectric element.

According to the above configuration, the second piezoelectric element is joined to the first part in electrically opposite phase to the first piezoelectric element so as to sandwich the diaphragm between the first piezoelectric element and the first piezoelectric element. It contracts when the first piezoelectric element expands, and expands when the first piezoelectric element contracts. As a result, the amplitude of the diaphragm becomes larger than when only the first piezoelectric element is bonded to the diaphragm. Therefore, when the piezoelectric vibration device is used as a piezoelectric speaker, higher sound pressure sensitivity can be obtained.

Further, another rigid layer is adhered to the circumferential surface of the second piezoelectric element and is laminated on the second portion on the second piezoelectric element side. In this case, the difference in bending rigidity between the first laminate formed at a position corresponding to the first portion of the diaphragm and the laminate formed at a position corresponding to the second portion of the diaphragm is reduced. can be done. Therefore, even if the second piezoelectric element is provided, the diaphragm is less likely to break due to the difference in bending rigidity between the first laminate and the second laminate.

In the above configuration, the piezoelectric vibrating device may further include a protective layer that covers the piezoelectric element so as to protect the first piezoelectric element and the second piezoelectric element.

According to the above configuration, since the first piezoelectric element and the second piezoelectric element are covered with the protective layer, they can be protected from environmental deterioration factors such as moisture. Moreover, since both sides of the second part are also covered with a rigid layer, the second part can also be protected from environmental degrading factors.

The technology in the present disclosure is not limited to the above-described embodiments, but can also be applied to embodiments in which changes, replacements, additions, omissions, etc. are made. Furthermore, it is also possible to create a new embodiment by combining the components described in the above embodiments.

The present disclosure is suitably used in technical fields that require sound generation and technical fields that require vibration detection.

Claims

A piezoelectric vibration device configured to function as a piezoelectric speaker for reproducing sound or a piezoelectric vibration sensor for detecting vibration, the piezoelectric vibration device comprising:
a piezoelectric element;
a diaphragm having a first portion to which the piezoelectric element is bonded, and a second portion surrounding the first portion;
The piezoelectric element expands and contracts under application of an alternating current voltage to cause the diaphragm to vibrate between a side to which the piezoelectric element is bonded and a side opposite thereto, thereby generating sound from the diaphragm, or The first part of the diaphragm is arranged such that when the diaphragm vibrates on the side to which the piezoelectric element is bonded and the opposite side, the diaphragm expands and contracts to generate a voltage signal following the vibration of the diaphragm. It is joined to one side of one part,
The piezoelectric vibrating device further includes a rigid layer laminated on the one surface of the second portion of the diaphragm and bonded to the circumferential surface of the piezoelectric element.
The diaphragm includes a conductive layer forming the one surface and capable of supplying power to the piezoelectric element, and a base layer on which the conductive layer is laminated and having a lower density than the conductive layer. The piezoelectric vibrating device according to claim 1, comprising:
further comprising a peripheral portion that circumferentially surrounds the diaphragm and bends and deforms in response to expansion and contraction of the piezoelectric element between a side to which the piezoelectric element is bonded and a side opposite thereto;
The piezoelectric vibration according to claim 1 or 2, wherein the rigid layer is not laminated on the peripheral part and is formed such that the bending rigidity of the rigid layer decreases toward the peripheral part. Device.
The diaphragm includes a conductive layer forming the one surface and capable of supplying power to the piezoelectric element, and a base layer on which the conductive layer is laminated,
The piezoelectric vibrating device according to claim 1, wherein the base layer has a larger internal loss than the conductive layer.
further comprising a peripheral portion that circumferentially surrounds the diaphragm and bends and deforms in response to expansion and contraction of the piezoelectric element between a side to which the piezoelectric element is bonded and a side opposite thereto;
The peripheral portion is formed integrally with the base layer using the same material as the base layer,
The piezoelectric vibrating device according to claim 4, wherein the rigid layer is not laminated on the peripheral portion and is formed such that the bending rigidity of the rigid layer decreases toward the peripheral portion.
The piezoelectric vibrating device according to claim 1 or 2, further comprising a protective layer that covers the piezoelectric element so as to protect the piezoelectric element.
a second piezoelectric element joined to the first portion so as to sandwich the first piezoelectric element and the diaphragm in electrically opposite phase to the first piezoelectric element;
The piezoelectric vibrating device according to claim 1 or 2, further comprising another rigid layer laminated on the second portion on the second piezoelectric element side and bonded to the peripheral surface of the second piezoelectric element. .
The piezoelectric vibrating device according to claim 7, further comprising a protective layer that covers the piezoelectric element so as to protect the first piezoelectric element and the second piezoelectric element.