Piezoelectric vibration device

Abstract

A piezoelectric vibration device (100) according to the present disclosure is provided with: a piezoelectric element (120); and a vibrating plate (110) having a first portion (115) joined to the piezoelectric element (120), and a second portion (116) located at the periphery of the first portion (115). The piezoelectric element (120) is joined to one surface of the first portion (115) of the vibrating plate (110) such that, when an AC voltage is applied, the piezoelectric element (120) expands and contracts and vibrates the vibrating plate (110), thereby generating sound from the vibrating plate (110), and the piezoelectric element (120) is joined to the other surface of the first portion (115) of the vibrating plate (110). Alternatively, in a state where the diaphragm (110) vibrates, the voltage signal is generated by expanding and contracting in accordance with the vibration of the diaphragm (110). The piezoelectric vibration device (100) further includes a rigid layer (118) that is laminated on one surface of the second portion (116) of the vibration plate (110) and that is bonded to the peripheral surface of the piezoelectric element (120).

Description

Technical Field

[0001] The present invention relates to a piezoelectric vibration device including a piezoelectric element and a vibration plate. Background Art

[0002] like Fig.10 As shown in the figure, a thin piezoelectric vibration device 400 has been developed in which a piezoelectric element 420 is bonded to one side of a vibration plate 410 (see Patent Document 1). In order to reduce the weight, the vibration plate 410 has a three-layer structure in which a resin layer 411 is sandwiched between metal layers 412 and 413. The piezoelectric element 420 is bonded to the metal layer 412, and the metal layer 412 is used to apply an AC voltage to the piezoelectric element 420. The metal layer 413 on the other side is provided so that the rigid center of the vibration plate 410 is located at the center in the thickness direction of the vibration plate 410.

[0003] In Patent Document 1, a piezoelectric vibration device 400 is configured as a piezoelectric speaker. Specifically, the piezoelectric vibration device 400 is configured such that a vibration plate 410 is formed. Fig.11 As shown in the figure, the piezoelectric element 420 vibrates and vibrates in the opposite direction to generate sound. Fig.11 In FIG. 1 , the solid line shows the shape of the vibration plate 410 when the vibration plate 410 is displaced to the piezoelectric element 420 to the maximum extent. The dashed-dotted line shows the shape of the vibration plate 410 when the vibration plate 410 is displaced to the opposite side of the piezoelectric element 420 to the maximum extent.

[0004] The larger the vibration amplitude of the vibration plate 410, the larger the sound that the piezoelectric vibration device 400 can produce. Therefore, in order to increase the vibration amplitude of the vibration plate 410, the peripheral portion 416 is provided to surround the vibration plate 410 in the circumferential direction. In addition, in order to fix the piezoelectric vibration device 400 to other devices (for example, household appliances such as washing machines when the piezoelectric vibration device 400 is used as a buzzer), the fixing portion 417 is provided to surround the peripheral portion 416 in the circumferential direction.

[0005] The peripheral portion 416 is made of the same material as the resin layer 411 of the vibration plate 410 and is formed integrally with the resin layer 411. The fixed portion 417 has a central layer 418 made of the same material as the resin layer 411 and formed integrally with the peripheral portion 416. In addition, in order to obtain the rigidity required for being fixed to other devices, the fixed portion 417 has metal layers 431 and 432 that sandwich the central layer 418 from top to bottom. That is, the fixed portion 417 has the same three-layer structure as the vibration plate 410. On the other hand, the peripheral portion 416 is different from the vibration plate 410 and the fixed portion 417 and has a single-layer structure, which is easier to deform than the vibration plate 410 and the fixed portion 417.

[0006] When the piezoelectric vibration device 400 is used to reproduce sound, an AC voltage having a frequency that resonates the vibration plate 410 is applied to the piezoelectric element 420. Based on the application of the AC voltage, the piezoelectric element 420 expands and contracts in the direction along the vibration plate 410, and the vibration plate 410 resonates with the expansion and contraction of the piezoelectric element 420, thereby vibrating toward the piezoelectric element 420 and the opposite side thereof.

[0007] The vibration plate 410 is subjected to air resistance during vibration. The greater the air resistance, the more difficult it is for the vibration plate 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 vibration plate 410, thereby enabling the piezoelectric vibration device 400 to play bass. The larger the vibration plate 410, the greater the air resistance, and therefore, by increasing the size of the vibration plate 410, the playback range of the piezoelectric vibration device 400 can be expanded toward the bass side. Therefore, in Patent Document 1, the vibration plate 410 includes not only the first portion 414 to which the piezoelectric element 420 is joined, but also the second portion 415 surrounding the first portion 414 in the circumferential direction.

[0008] 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 for detecting the vibration of the detection object. That is, if the vibration plate 410 is configured to bear the vibration of the detection object, the vibration plate 410 vibrates in accordance with the vibration of the detection object. The piezoelectric element 420 expands and contracts in accordance with the vibration of the vibration plate 410, and a voltage corresponding to the expansion and contraction amount of the piezoelectric element 420 is output from the piezoelectric element 420, so that the piezoelectric vibration device 400 can function as a sensor (piezoelectric vibration sensor) for detecting the vibration of the detection object. That is, by monitoring the voltage output from the piezoelectric element 420, the vibration of the detection object can be detected and analyzed.

[0009] The piezoelectric element 420 is stacked on the first portion 414 of the vibration plate 410, and the first portion 414 and the piezoelectric element 420 constitute a stacked 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 stacked body 419. Due to the difference in bending rigidity, the second portion 415 is bent relative to the stacked body 419. The bending of the vibration plate 410 may cause the following problems.

[0010] exist Fig.11In the figure, the area of ​​the first region surrounded by the vibration plate 410 when the vibration plate 410 is displaced to the piezoelectric element 420 side at the maximum limit and the vibration plate 410 when the vibration plate 410 is displaced to the opposite side of the piezoelectric element 420 at the maximum limit is equivalent to the amount of air driven by one cycle of vibration of the vibration plate 410. If no bending occurs in the vibration plate 410, Fig.11 In the figure, the amount of air corresponding to the second area surrounded by the dotted line is driven based on one cycle of vibration of the vibration plate 410. The second area is wider than the first area, and it can be seen that the bending of the vibration plate 410 reduces the amount of air driven based on one cycle of vibration of the vibration plate 410 by the area difference between the second area and the first area. During the vibration of the vibration plate 410, the air resistance borne by the vibration plate 410 is reduced by an amount corresponding to the reduction in the amount of air. Therefore, under the condition that the piezoelectric element 420 expands and contracts at a constant frequency, the vibration period of the vibration plate 410 becomes shorter due to the reduction in air resistance borne by the vibration plate 410, and the piezoelectric vibration device 400 becomes difficult to play bass.

[0011] In addition, the above-mentioned difference in bending rigidity is directly attributed to the difference in acoustic impedance between the stack 419 and the second part 415. That is, the acoustic impedance is represented by the product of the density of the medium that propagates sound and the speed of sound. The larger the elastic modulus of the medium, the higher the sound speed. If the elastic modulus of the medium is large, the bending rigidity of the medium is high, and thus the sound speed is also high. On the other hand, if the elastic modulus of the medium is small, the bending rigidity of the medium is low, and thus the sound speed is also low. Therefore, the sound speed in the stack 419 having large bending rigidity is large, and thus the acoustic impedance is also large, and the sound speed in the second part 415 having small bending rigidity is small, and thus the acoustic impedance is also small. The above-mentioned difference in acoustic impedance, especially when the piezoelectric vibration device 400 is used as a piezoelectric vibration sensor, will cause the following problems.

[0012] When an unnecessary vibration component (hereinafter referred to as "noise wave") propagating along the vibration plate 410 is generated in the stack 419, most of the noise wave is reflected at the boundary between the stack 419 and the second portion 415 based on the above-mentioned difference in acoustic impedance. That is, the noise wave propagating to the second portion 415 decreases, while the noise wave continuing to propagate in the first portion 414 increases. In this case, the noise wave has a great influence on the expansion and contraction of the piezoelectric element 420, and the noise in the signal output from the piezoelectric element 420 increases. In addition, when the piezoelectric vibration device 400 is used as a piezoelectric speaker, the noise contained in the sound played by the piezoelectric vibration device 400 increases.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Publication No. 2003-230193 Summary of the invention

[0016] An object of the present invention is to provide a piezoelectric vibration device that can have a wide reproduction frequency band on the bass side and can reduce noise contained in the reproduced sound; or can output a signal representing the vibration of a detection object in a state with less noise.

[0017] The piezoelectric vibration device disclosed in the present invention functions as a piezoelectric speaker for playing sound or a piezoelectric vibration sensor for detecting vibration. The piezoelectric vibration device includes: a piezoelectric element; and a vibration plate having a first part joined to the piezoelectric element, and a second part located around the first part. The piezoelectric element is joined to one surface of the first part of the vibration plate in such a manner that: when an alternating voltage is applied, the vibration plate is expanded and contracted and vibrates toward the side to which the piezoelectric element is joined and toward the opposite side, thereby generating sound from the vibration plate; or, in a state where the vibration plate vibrates toward the side to which the piezoelectric element is joined and toward the opposite side, the vibration plate expands and contracts following the vibration of the vibration plate, thereby generating a voltage signal. The piezoelectric vibration device also includes: a rigid layer, which is stacked on one surface of the second part of the vibration plate and is bonded to the peripheral surface of the piezoelectric element.

[0018] The piezoelectric vibration device described above can have a wide reproduction frequency band on the bass side and can reduce noise included in the reproduction sound, and can output a signal indicating vibration of a detection target object in a state with less noise.

[0019] The objects, features and advantages of the present disclosure will become more apparent from the following detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a partial plan view of a piezoelectric vibration device that functions as a piezoelectric speaker.

[0021] Figure 2 is along Figure 1 A simplified cross-sectional view of the piezoelectric vibration device taken along line II-II.

[0022] Figure 3 This is a schematic diagram of the shape of a piezoelectric vibration device when it vibrates.

[0023] Figure 4 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0024] Figure 5 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0025] Figure 6 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0026] Figure 7 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0027] Figure 8 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0028] Fig. 9 This is a schematic cross-sectional view of another piezoelectric vibration device.

[0029] Fig.10 This is a schematic cross-sectional view of a conventional piezoelectric speaker.

[0030] Fig.11 This is a schematic diagram showing the shape of a conventional piezoelectric speaker when it vibrates. DETAILED DESCRIPTION

[0031] Hereinafter, an embodiment of the piezoelectric vibration device will be described in detail with reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted sometimes. For example, detailed descriptions of well-known matters or repeated descriptions of substantially the same structure may be omitted sometimes. This is to avoid the following description from becoming unnecessarily lengthy so that it is easy for those skilled in the art to understand. In addition, the drawings and the following descriptions are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the scope of protection of the claims.

[0032] Figure 1 It is a schematic plan view of a part of the piezoelectric vibration device 100 that functions as a piezoelectric speaker. Figure 2 is a schematic cross-sectional view of the piezoelectric vibration device 100 (along the Figure 1 sectional view of line II-II). Figure 1 and Figure 2 The structure of the piezoelectric vibration device 100 will be described.

[0033] (Structure of Piezoelectric Vibration Device)

[0034] The piezoelectric vibration device 100 includes a substantially square vibration plate 110 , a disc-shaped piezoelectric element 120 joined to the vibration plate 110 , a rectangular frame-shaped peripheral portion 113 circumferentially surrounding the vibration plate 110 , and a rectangular frame-shaped fixing portion 140 circumferentially surrounding the peripheral portion 113 .

[0035] 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 vibration plate 110. The piezoelectric element 120 may be bonded to the vibration plate 110 using, for example, an acrylic adhesive.

[0036] The piezoelectric element 120 has a characteristic of expanding or contracting in the radial direction when an AC voltage is applied to both surfaces of the piezoelectric element 120. The piezoelectric element 120 has a characteristic of expanding or contracting more as the voltage applied to both surfaces of the piezoelectric element 120 increases.

[0037] In this embodiment, the piezoelectric element 120 has a positive voltage applied to one surface of the piezoelectric element 120 ( Figure 2 The piezoelectric element 120 has a characteristic that it stretches in the radial direction when a negative voltage is applied to the other surface. In addition, if the voltage pole is reversed, the piezoelectric element 120 has a characteristic that it contracts in the radial direction. Such a piezoelectric element 120 can be formed using a piezoelectric material such as PZT (lead zirconate titanate).

[0038] Furthermore, if the piezoelectric element 120 is reversed upside down and joined to the vibration plate 110 (i.e., joined in an electrically reverse phase), it has a stretching characteristic opposite to the above-mentioned stretching characteristic. That is, when a negative voltage is applied to one surface of the piezoelectric element 120 ( Figure 2 When the positive voltage is applied to the other surface, the piezoelectric element 120 has a characteristic of stretching in the radial direction. In this case, by reversing the electrode to which the voltage is applied, the piezoelectric element 120 has a characteristic of contracting in the radial direction.

[0039] The vibration plate 110 is a thin plate-like member (e.g., a member having a thickness of about 40 μm) that vibrates toward the side to which the piezoelectric element 120 is bonded and the side opposite to the side as the piezoelectric element 120 expands and contracts. The vibration plate 110 is larger than the piezoelectric element 120 in a plan view. Figure 2 As shown, it has: a first portion 115 joined to the piezoelectric element 120 ; and a second portion 116 forming a peripheral area of ​​the first portion 115 .

[0040] The bending rigidity of the stack of the first portion 115 and the piezoelectric element 120 (hereinafter referred to as "the first stack 117") is greater than the bending rigidity of the second portion 116 by an amount corresponding to the bending rigidity of the piezoelectric element 120. The difference in their bending rigidity causes the bending of the vibration plate 110 and the rapid change in the acoustic impedance in the vibration plate 110. In order to suppress these adverse effects, Figure 2 As shown in FIG. 1 , a rigid layer 118 is stacked with a substantially constant thickness on the surface of the second portion 116 on the piezoelectric element 120 side (in Figure 1 The rigid layer 118 is not shown in the figure. The rigid layer 118 covers the entire vibration plate 110 except for the first portion 115 to which the piezoelectric element 120 is bonded, and has a substantially square shape in a plan view. The rigid layer 118 is bonded to the peripheral surface of the piezoelectric element 120.

[0041] The thickness and material of the rigid layer 118 are set so that the bending rigidity of the first laminate 117 is substantially equal to the bending rigidity of the laminate of the second portion 116 and the rigid layer 118 (hereinafter referred to as the "second laminate 119"). The rigid layer 118 can be formed, for example, by photopolymerizing and curing a liquid resin material (e.g., urethane acrylate resin, epoxy acrylate resin, or polyester acrylate resin) on the second portion 116 using ultraviolet rays.

[0042] The vibration plate 110 itself may have a plurality of material layers or a single-layer structure. In the present embodiment, the vibration plate 110 has a two-layer structure, which is composed of a bottom layer 111 and a conductive layer 112 bonded to the bottom layer 111 on the side of the piezoelectric element 120. The piezoelectric element 120 is bonded to the conductive layer 112. In addition, the above-mentioned rigid layer 118 is stacked on the conductive layer 112 around the piezoelectric element 120.

[0043] The bottom layer 111 is formed of a material having a lower density than the conductive layer 112. For example, the bottom layer 111 may be a resin film layer or an aluminum layer. When the bottom layer 111 is made of resin, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, polyamide or polyimide may be used. Alternatively, the bottom layer 111 may be made of styrene butadiene rubber, butadiene rubber, butyl rubber or ethylene propylene rubber. These resin materials may have acoustically high internal loss, which may help reduce noise contained in the played sound.

[0044] The material layer constituting the bottom layer 111 also constitutes the peripheral portion 113. The material layer is a portion that is bent and deformed in a direction that becomes convex toward the piezoelectric element 120 side and in a direction that becomes convex in the opposite direction thereof as the piezoelectric element 120 expands and contracts. The thickness of the material layer is set in a manner that a sufficiently large restoring force can be obtained with respect to the bending deformation. For example, the thickness may be 30 μm.

[0045] On the other hand, in order to reduce the weight of the vibration plate 110, the conductive layer 112 is thinner than the bottom layer 111. For example, the thickness of the conductive layer 112 can be about 10 μm. Since the conductive layer 112 is thinner than the bottom layer 111, its influence on the internal loss of the vibration plate 110 as a whole is not as great as that of the bottom layer 111. Therefore, the internal loss of the conductive layer 112 can be greater than the internal loss of the bottom layer 111.

[0046] The conductive layer 112 is a portion for supplying power to the piezoelectric element 120 and is formed of a conductive material. For example, the conductive layer 112 may be a 42# alloy (42# Ni-Fe) layer or a copper (Cu) layer. The conductive layer 112 is bonded to the bottom layer 111 based on van der Waals force. Alternatively, the conductive layer 112 and the bottom layer 111 may be bonded by an adhesive.

[0047] The conductive layer 112 is rectangular in shape as a whole when viewed from above, but a portion is cut out to form a notch. In the notch, a portion of the base layer 111 is exposed. The notch is used to arrange an electrode 132 for applying a voltage to the piezoelectric element 120.

[0048] As described above, the peripheral portion 113 is formed of a material layer constituting the base layer 111. 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 in a manner of surrounding the base layer 111 in the circumferential direction. If the bending deformation amount of the peripheral portion 113 is large, the vibration plate 110 can vibrate with a large amplitude, so in order to maintain the deformation ease of the peripheral portion 113, the above-mentioned rigid layer 118 is not laminated on the peripheral portion 113.

[0049] The fixing portion 140 is a portion for fixing the piezoelectric vibration device 100 to another device 300 (for example, a washing machine), and an opening 310 is formed in the device 300 to allow the vibration plate 110 to vibrate toward the piezoelectric element 120 side and the opposite side. The fixing portion 140 is configured to overlap with the device 300 at the peripheral portion of the opening 310. At this time, the vibration plate 110 and the peripheral portion 113 are overlapped on the opening 310.

[0050] The fixing portion 140 includes a fixing layer 141 and a reinforcing layer 142 stacked on the fixing layer 141 to reinforce the fixing layer 141. The fixing layer 141 is made of the same material as the base layer 111 and the peripheral portion 113 and is formed integrally with the peripheral portion 113 so as to surround the peripheral portion 113 in the circumferential direction.

[0051] like Figure 1 As shown in FIG. 1 , the reinforcing layer 142 is substantially C-shaped in a plan view. In this embodiment, the reinforcing layer 142 is laminated on the surface of the resin layer or aluminum layer constituting the peripheral portion 113 and the bottom layer 111 on which the conductive layer 112 is provided. The reinforcing layer 142 is opened in the same direction as the notch portion of the conductive layer 112, and the opening portion is used as the electrodes 131 and 132 configured to apply a voltage to the piezoelectric element 120.

[0052] The material of the reinforcing layer 142 may be the same as that of the conductive layer 112. In addition, if sufficient rigidity can be obtained when mounted on the device 300, the reinforcing layer 142 may also have the same thickness as that of the conductive layer 112. In addition, in order to improve the rigidity of the mounting portion on the device 300, the reinforcing layer 142 may also be thicker than the conductive layer 112.

[0053] The inner edge of the reinforcing layer 142 is separated from the outer edge of the conductive layer 112 by a substantially constant distance over the entire length. The portion between the inner edge of the reinforcing layer 142 and the outer edge of the conductive layer 112 is a peripheral portion 113 .

[0054] As described above, electrodes 131 and 132 are arranged using the opening of fixing portion 140 and the notch of conductive layer 112. Electrode 131 is formed integrally with conductive layer 112 and is stacked on peripheral portion 113 and fixing portion 140. Electrode 131 has conductivity similarly to conductive layer 112.

[0055] On the other hand, the electrode 132 is not only laminated on the peripheral portion 113 and the fixed portion 140, but also laminated on the bottom layer 111 in the notch area of ​​the conductive layer 112. The electrode 132 is bonded to the surface of the piezoelectric element 120 on the opposite side to the side bonded with the conductive layer 112 through a bonding material having conductivity and elasticity. Since the bonding material has a certain degree of elasticity, even if the piezoelectric element 120 is deformed, it is difficult for the connection part between the piezoelectric element 120 and the electrode 132 to break. As a bonding material, for example, a silver paste made by mixing a resin material in silver can be used, and a paste material made by further mixing a conductor such as copper, gold, nickel and carbon as a filler in the above-mentioned silver paste can also be used. In addition, as a resin material of the bonding material, a resin binder having a nitrile group (such as acrylonitrile rubber), a resin binder containing an epoxy resin and / or a resin binder containing a polyurethane resin can be used. As other resin materials, a resin binder having a thermoplastic polyester system can be used. By using such a resin adhesive, a flexible bonding material can be obtained.

[0056] (Action description)

[0057] If an AC voltage is applied to the electrodes 131 and 132, the piezoelectric element 120 and the vibration plate 110 will Figure 3 As shown in the figure, the piezoelectric element 120 vibrates and vibrates in the opposite direction. Figure 3In FIG. 1 , the shapes of the vibration plate 110 and the peripheral portion 113 when the vibration plate 110 is displaced toward the piezoelectric element 120 are schematically indicated by solid lines. In addition, the shapes of the vibration plate 110 and the peripheral portion 113 when the vibration plate 110 is displaced to the opposite side are schematically indicated by dot-dash lines. The area surrounded by the solid line and the dot-dash line corresponds to the volume of the air driven by the vibration of the vibration plate 110 and the peripheral portion 113. The wider the area, the greater the resistance from the air to which the vibration plate 110 is subjected when vibrating. When the resistance from the air to which the vibration plate 110 is subjected becomes larger, and under the condition that the piezoelectric element 120 expands and contracts at a constant frequency, the vibration plate 110 becomes easier to displace slowly compared to the case where the resistance from the air to which the vibration plate 110 is subjected is smaller. In other words, the vibration plate 110 becomes easier to vibrate at a low frequency. Therefore, the greater the air resistance to which the vibration plate 110 is subjected, the wider the reproduction frequency band of the piezoelectric vibration device 100 can be on the bass side.

[0058] The frequency of the AC voltage applied to the electrodes 131 and 132 is set to a value that resonates the vibration plate 110 and the peripheral portion 113. That is, if the voltage pole is switched when the vibration plate 110 and the peripheral portion 113 are about to recover from the state of being displaced from the vibration plate 110 to the piezoelectric element 120 side, the vibration plate 110 can move to the side opposite to the piezoelectric element 120 side with good momentum. Conversely, if the voltage pole is switched when the vibration plate 110 and the peripheral portion 113 are about to recover from the state of being displaced from the vibration plate 110 to the side opposite to the piezoelectric element 120 side, the vibration plate 110 can move to the piezoelectric element 120 side with good momentum.

[0059] The bending rigidity of the peripheral portion 113 is the smallest in the piezoelectric vibration device 100. Therefore, the peripheral portion 113 is Figure 3 In the resonant state shown, the piezoelectric element 120 can be greatly bent and deformed toward the piezoelectric element 120 side and the opposite side relative to the fixed portion 140. In addition, a large difference in bending rigidity is generated between the peripheral portion 113 and the second stack 119 adjacent to the peripheral portion 113, so that bending occurs at the boundary portion between the peripheral portion 113 and the second stack 119. On the other hand, in order to reduce the difference in bending rigidity between the second stack 119 and the first stack 117, the rigid layer 118 is stacked on the second portion 116 of the vibration plate 110, so that bending at the boundary portion between the second stack 119 and the first stack 117 is difficult to occur. Moreover, the rigid layer 118 of the second stack 119 is in a state of being bonded to the outer peripheral surface of the piezoelectric element 120. Therefore, bending is more difficult to occur at the boundary portion between the second stack 119 and the first stack 117.

[0060] If the rigid layer 118 is not provided, the vibration plate 110 and the peripheral portion 113 become Figure 3In this case, the bend at the boundary between the first stack 117 and the second portion 116 becomes larger. As a result, the volume of air driven by the vibration of the vibration plate 110 and the peripheral portion 113 is reduced. Figure 3 The volume of the area surrounded by the dotted line and the solid line or the dashed line in FIG. The resistance from the air to which the vibration plate 110 is subjected during vibration is reduced by the amount of the reduction in volume. In this case, and under the condition that the piezoelectric element 120 expands and contracts at a constant frequency, the vibration plate 110 vibrates at a vibration period shorter than the vibration period of the vibration plate 110 provided with the rigid layer 118. In other words, by providing the rigid layer 118, the vibration plate 110 can vibrate at a lower frequency, and the piezoelectric vibration device 100 can have a wide playback frequency band on the bass side.

[0061] (Usage as a piezoelectric vibration sensor)

[0062] The piezoelectric vibration device 100 can also function as a piezoelectric vibration sensor. Figure 2 The device 300 shown in the figure vibrates in the vertical direction, and the vibration plate 110 and the peripheral part 113 are as follows. Figure 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 is generated between the electrodes 131 and 132, and the piezoelectric element 120 can output a voltage signal representing the potential difference. If the electrodes 131 and 132 are connected to a data collection device such as a computer, time series data on the potential difference can be obtained. By analyzing the time series data, information on the intensity and frequency of the vibration of the device 300 can be obtained.

[0063] When the piezoelectric vibration device 100 is used as a piezoelectric vibration sensor, the unnecessary vibration component (hereinafter referred to as "noise wave") propagating in the direction along the vibration plate 110 in the first stack 117 becomes a problem. If the noise wave continues to propagate in the first stack 117, the piezoelectric element 120 constituting the first stack 117 is affected by the noise wave, and the potential difference data output from the electrodes 131 and 132 contains a large amount of noise components.

[0064] The influence of noise waves on the piezoelectric element 120 can be reduced by laminating the rigid layer 118 on the second portion 116 of the vibration plate 110. That is, if there is no rigid layer 118, a large difference in bending rigidity will occur between the first stack 117 and the second portion 116. This difference in bending rigidity directly leads to a sharp change in acoustic impedance at the boundary between the first stack 117 and the second portion 116. Therefore, the noise wave propagating along the vibration plate 110 in the first stack 117 is reflected at the boundary between the first stack 117 and the second portion 116, and continues to propagate in the first stack 117.

[0065] In contrast, in the configuration in which the rigid layer 118 is stacked on the second portion 116 to form the second stack 119, the difference in bending rigidity between the first stack 117 and the second stack 119 is reduced. Since the difference in bending rigidity directly becomes the difference in acoustic impedance between the first stack 117 and the second stack 119, the change in acoustic impedance at the boundary between the first stack 117 and the second stack 119 becomes smaller. In this case, the noise wave propagating along the vibration plate 110 in the first stack 117 is not reflected at the boundary between the first stack 117 and the second stack 119, but can be propagated to the second stack 119.

[0066] The difference in bending rigidity between the second stack 119 and the peripheral portion 113 is large, and the acoustic impedance changes sharply at their boundary. Therefore, noise waves propagating in the second stack 119 may be reflected at the boundary between the second stack 119 and the peripheral portion 113 and return to the first stack 117.

[0067] Since the base layer 111 is made of a material having high internal loss, the noise wave is attenuated while propagating in the second stack 119. Therefore, the noise wave reflected at the boundary between the second stack 119 and the peripheral portion 113 is sufficiently attenuated when returning to the first stack 117.

[0068] Such a noise wave attenuation effect is also useful when the piezoelectric vibration device 100 is used as a piezoelectric speaker. That is, when the piezoelectric vibration device 100 is used as a piezoelectric speaker, if the rigid layer 118 is stacked on the second portion 116, the noise component contained in the sound reproduced by the piezoelectric vibration device 100 can be reduced.

[0069] like Figure 4 As shown in FIG. 1 , if the thickness of the rigid layer 118 is gradually reduced from the peripheral surface of the piezoelectric element 120 toward the peripheral portion 113, changes in acoustic impedance at the boundary between the peripheral portion 113 and the second stack 119 can be suppressed. Figure 4 In the piezoelectric vibration device 100 shown, the difference in bending rigidity at the boundary between the peripheral portion 113 and the second stack 119 is an amount corresponding to the bending rigidity of the conductive layer 112. Therefore, the change in acoustic impedance at the boundary between the peripheral portion 113 and the second stack 119 is suppressed, and the noise wave reflected at the boundary between the peripheral portion 113 and the second stack 119 decreases. In other words, the noise wave that crosses the boundary between the peripheral portion 113 and the second stack 119 and propagates toward the peripheral portion 113 increases.

[0070] In order to further suppress the change in acoustic impedance at the boundary between the peripheral portion 113 and the second stack 119, as shown in FIG. Figure 5As shown, the vibration plate 110 may have a single-layer structure. Figure 5 The vibration plate 110 shown is formed of a conductive material (for example, 42# alloy (42# Ni—Fe)) and has a thickness that allows it to vibrate toward the piezoelectric element 120 side and the opposite side. Figure 5 The rigid layer 118 is shown with Figure 4 Same as shown.

[0071] exist Figure 5 In the piezoelectric vibration device 100 shown, there is almost no difference in bending rigidity at the boundary between the peripheral portion 113 and the second stack 119. Therefore, there is no change in acoustic impedance at the boundary between the peripheral portion 113 and the second stack 119, and noise waves are not reflected at the boundary between the peripheral portion 113 and the second stack 119 and can propagate toward the peripheral portion 113.

[0072] exist Figure 4 and Figure 5 In the piezoelectric vibration device 100 shown, the thickness of the rigid layer 118 decreases toward the peripheral portion 113, thereby reducing the change in acoustic impedance at the boundary between the second stack 119 and the peripheral portion 113. Alternatively, the change in acoustic impedance can also be suppressed by forming the rigid layer 118 with a plurality of materials.

[0073] For example, Figure 6 As shown, the rigid layer 118 may include a first material layer 121 to a third material layer 123. The first material layer 121 is adjacent to the piezoelectric element 120, and the second material layer 122 is formed at a position away from the first material layer 121 and adjacent to the peripheral portion 113. The third material layer 123 is provided between the first material layer 121 and the second material layer 122 and adjacent to the first material layer 121 and the second material layer 122. The first material layer 121 is formed of the hardest material among the materials constituting the first material layer 121 to the third material layer 123, and the second material layer 122 is formed of the softest material among these materials.

[0074] exist Figure 6 In the second stacked body 119 shown, changes in acoustic impedance may occur at the boundaries between the first material layer 121 and the third material layer 123 and at the boundaries between the second material layer 122 and the third material layer 123, but these changes will not become too large. In addition, changes in acoustic impedance may also occur to a certain extent at the boundary between the second material layer 122 and the peripheral portion 113, but the changes are not as large as Figure 2 The degree of change in acoustic impedance at the boundary between the second stacked body 119 and the peripheral portion 113 is large.

[0075] exist Figures 1 to 6In the piezoelectric vibration device 100 shown in FIG. 1 , the piezoelectric element 120 is stacked on one surface of the vibration plate 110. Figure 7 In this case, the second conductive layer 125, the second piezoelectric element 124 and the rigid layer 126 constitute the same as the Figure 2 The stacked structure composed of the conductive layer 112, the piezoelectric element 120 and the rigid layer 118 is a stacked structure that is symmetrical from top to bottom. That is, the second piezoelectric element 124 and the piezoelectric element 120 are stacked on the first part 115 in a manner of clamping the vibration plate 110. In addition, the rigid layer 126 is stacked on the second part 116 on the side of the second piezoelectric element 124 and is bonded to the peripheral surface of the second piezoelectric element 124. The rigid layer 126 is the same as the rigid layer 118 in shape and material. In addition, the second conductive layer 125 is the same as the conductive layer 112 in shape and material.

[0076] The second piezoelectric element 124 is connected to the vibration plate 110 in a phase opposite to that of the piezoelectric element 120. Therefore, if an AC voltage is applied to the piezoelectric element 120 and the second piezoelectric element 124, their expansion and contraction actions are opposite to each other. That is, when the piezoelectric element 120 is extended in the radial direction, the second piezoelectric element 124 is contracted in the radial direction. Conversely, when the piezoelectric element 120 is contracted in the radial direction, the second piezoelectric element 124 is extended in the radial direction. If the piezoelectric element 120 and the second piezoelectric element 124 act in this way, the vibration amplitude of the vibration plate 110 will increase, and the sound pressure sensitivity of the piezoelectric vibration device 100 can be improved.

[0077] exist Figure 7 In the piezoelectric vibration device 100 shown, the first stack 117 includes the first portion 115 of the vibration plate 110, the piezoelectric element 120, and the second piezoelectric element 124. In addition, the second stack 119 includes the second portion 116 of the vibration plate 110, and rigid layers 118 and 126. Since the rigid layer 126 having a bending rigidity substantially equal to that of the second piezoelectric element 124 is added, the difference in bending rigidity between the first stack 117 and the second stack 119 is reduced. As a result, bending is less likely to occur at the boundary between the first stack 117 and the second stack 119.

[0078] Figure 7The piezoelectric vibration device 100 shown has a structure that is vertically symmetrical about the center portion in the thickness direction of the vibration plate 110. Therefore, the rigidity center of the piezoelectric vibration device 100 is located at the center in the thickness direction of the vibration plate 110, and the bending rigidity of the piezoelectric vibration device 100 is symmetrical about the center in the thickness direction of the piezoelectric vibration device 100. As a result, the symmetry of the action of the piezoelectric vibration device 100 when the vibration plate 110 is displaced to the piezoelectric element 120 side and when it is displaced to the opposite side is high. If such symmetrical action can be obtained, when the piezoelectric vibration device 100 is used as a piezoelectric speaker, the distortion of the sound reproduced by the piezoelectric vibration device 100 can be suppressed. In addition, when the piezoelectric vibration device 100 is used as a piezoelectric vibration sensor, the symmetry of the signal output characteristics when the vibration plate 110 is displaced to the piezoelectric element 120 side and the signal output characteristics when the vibration plate 110 is displaced to the opposite side is high. Therefore, when performing vibration analysis of the device 300, the process of correcting the asymmetry of the signal output characteristics can be omitted.

[0079] In addition, you can also Figure 7 The second piezoelectric element 124 and the rigid layer 126 are omitted in the piezoelectric vibration device 100 shown. In this case, the rigid center of the piezoelectric vibration device 100 itself is shifted to the upper side relative to the center in the thickness direction of the piezoelectric vibration device 100, but the rigid center of the vibration plate 110 can be located at the center in the thickness direction of the vibration plate 110. Therefore, the symmetry of the movement of the vibration plate 110 when the vibration plate 110 is displaced to the piezoelectric element 120 side and when it is displaced to the opposite side is compared with Figure 1 The piezoelectric vibration device 100 shown is improved.

[0080] exist Figures 1 to 7 In the piezoelectric vibration device 100 shown, if the material forming the rigid layers 118 and 126 does not excessively hinder the expansion and contraction of the piezoelectric element 120 and the second piezoelectric element 124, the piezoelectric element 120 and the second piezoelectric element 124 may be covered with the material. Figure 2 The piezoelectric vibration device 100 shown can be Figure 8 Improved as shown. Figure 8 The piezoelectric element 120 of the piezoelectric vibration device 100 shown is covered by a protective layer 151 formed of the same material as the rigid layer 118. Thus, the piezoelectric element 120 can be protected by the rigid layer 118 and the protective layer 151 from environmental deterioration factors such as moisture. Figure 7 The piezoelectric vibration device 100 shown can be Fig. 9 Improved as shown. Fig. 9The piezoelectric element 120 and the second piezoelectric element 124 of the piezoelectric vibration device 100 shown are covered by a protective layer 151 formed of the same material as the rigid layer 118 and a protective layer 152 formed of the same material as the rigid layer 126. Thus, 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. In addition, since both surfaces of the second portion 116 are covered by the rigid layers 118, 126, the second portion 116 can also be protected from environmental deterioration factors by these rigid layers 118, 126.

[0081] (Effects, etc.)

[0082] The piezoelectric vibration device 100 according to the above-described embodiment has the following features and has the following effects.

[0083] The piezoelectric vibration device involved in one aspect of the above-mentioned embodiment functions as a piezoelectric speaker that plays sound or a piezoelectric vibration sensor that detects vibration. The piezoelectric vibration device includes: a piezoelectric element; and a vibration plate having a first part joined to the piezoelectric element and a second part located around the first part. The piezoelectric element is joined to one surface of the first part of the vibration plate in the following manner: when an AC voltage is applied, the vibration plate is expanded and contracted and vibrates toward the side to which the piezoelectric element is joined and to the opposite side, thereby generating sound from the vibration plate; or, when the vibration plate vibrates toward the side to which the piezoelectric element is joined and to the opposite side, it expands and contracts following the vibration of the vibration plate, thereby generating a voltage signal. The piezoelectric vibration device also includes: a rigid layer, which is stacked on one surface of the second part of the vibration plate and is bonded to the peripheral surface of the piezoelectric element.

[0084] According to the above-mentioned structure, since the rigid layer is stacked on the second part around the first part joined with the piezoelectric element, the difference in bending rigidity between the stacked body of the second part and the rigid layer and the stacked body of the first part and the piezoelectric element can be reduced. Therefore, the bending of the vibration plate caused by the difference in bending rigidity between these stacked bodies can be suppressed. Moreover, the rigid layer is bonded to the peripheral surface of the piezoelectric element, so it is more difficult for the vibration plate to bend based on the bonding portion. Therefore, it is difficult to reduce the playback sound range on the bass side due to the bending of the vibration plate, and the piezoelectric vibration device can have a wide playback frequency band on the bass side.

[0085] In addition, if the difference in bending rigidity between the above-mentioned stacked bodies becomes smaller, the difference in acoustic impedance between these stacked bodies is also reduced. Therefore, if there is a useless vibration component (hereinafter referred to as "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 also be reduced, and the noise wave propagating from the first part to the second part can be increased. In this case, the noise wave in the first part joined with the piezoelectric element will become less, and when the piezoelectric vibration device is used as a piezoelectric vibration sensor, the noise contained in the signal emitted from the piezoelectric element can be reduced. In addition, when the piezoelectric vibration device is used as a piezoelectric speaker, the noise contained in the played sound can be reduced.

[0086] In the above configuration, the vibration plate may include: a conductive layer forming one surface and formed so as to be able to supply power to the piezoelectric element; and a base layer on which the conductive layer is stacked and which has a lower density than the conductive layer.

[0087] According to the above configuration, if one surface of the vibration plate is formed by a conductive layer, the conductive layer can be used to supply power to the piezoelectric element by bonding the piezoelectric element to the surface. In addition, the vibration plate is not formed entirely of conductive materials, but is formed by stacking a conductive layer and a bottom layer having a lower density than the conductive layer, thereby reducing the weight of the vibration plate.

[0088] In the above configuration, the piezoelectric vibration device may further include: a peripheral portion that surrounds the vibration plate in the circumferential direction and is bent and deformed toward the side to which the piezoelectric element is connected and toward the opposite side thereof in response to the expansion and contraction of the piezoelectric element. The rigid layer may not be stacked on the peripheral portion, and may be formed in such a manner that the bending rigidity of the rigid layer decreases as it goes toward the peripheral portion.

[0089] According to the above configuration, the peripheral portion surrounding the vibration plate in the circumferential direction is bent and deformed toward the side connected to the piezoelectric element and the opposite side thereof in response to the expansion and contraction of the piezoelectric element, so that the vibration plate can vibrate toward the side connected to the piezoelectric element and the opposite side thereof. At this time, the rigid layer is not laminated on the peripheral portion and thus does not hinder the bending deformation of the peripheral portion.

[0090] In addition, since the bending rigidity of the rigid layer decreases toward the peripheral portion, it is difficult to produce a sharp change in bending rigidity at the boundary between the second portion and the peripheral portion, and further, it is difficult to produce a sharp change in acoustic impedance. Therefore, the noise wave that is intended to propagate from the second portion to the peripheral portion is difficult to be reflected at the boundary between the peripheral portion and the second portion.

[0091] In the above configuration, the vibration plate may include: a conductive layer forming one surface and being formed to be able to supply power to the piezoelectric element; and a bottom layer on which the conductive layer is stacked. The bottom layer may have a larger internal loss than the conductive layer.

[0092] According to the above configuration, since the bottom layer has a relatively large internal loss, the noise wave propagating along the vibration plate is easily attenuated. That is, the piezoelectric vibration device can function as a piezoelectric vibration sensor that achieves a high S / N ratio. In addition, when the piezoelectric vibration device is used as a piezoelectric speaker, the peak and / or valley value of the sound pressure can be reduced due to the large internal loss of the bottom layer.

[0093] In the above-mentioned configuration, the piezoelectric vibration device may further include: a peripheral portion that surrounds the vibration plate in the circumferential direction and is bent and deformed toward the side to which the piezoelectric element is connected and toward the opposite side thereof in response to the expansion and contraction of the piezoelectric element. The peripheral portion may be formed integrally with the bottom layer from the same material as the bottom layer. The rigid layer may not be laminated on the peripheral portion, and may be formed in such a manner that the bending rigidity of the rigid layer decreases as it goes toward the peripheral portion.

[0094] According to the above configuration, since the bending rigidity of the rigid layer decreases toward the peripheral portion, it is difficult to generate a sharp change in acoustic impedance between the peripheral portion and the second portion. Therefore, the noise wave that is intended to propagate from the second portion to the peripheral portion is difficult to be reflected between the peripheral portion and the second portion, and the noise wave propagating in the peripheral portion increases. Since the peripheral portion is made of the same material as the bottom layer having a relatively high internal loss, it is possible to promote the attenuation of the noise wave propagating to the peripheral portion.

[0095] In the above structure, the piezoelectric vibration device may further include: a protective layer covering the piezoelectric element to protect the piezoelectric element.

[0096] According to the above configuration, since the piezoelectric element is covered with the protective layer, it can be protected from environmental deterioration factors such as moisture.

[0097] In the above-mentioned structure, the piezoelectric vibration device may also include: a second piezoelectric element, which is joined to the first part in a manner of clamping the vibration plate with the first piezoelectric element as the piezoelectric element and is electrically opposite to the first piezoelectric element; and other rigid layers, which are stacked on the second part on the side of the second piezoelectric element and are bonded to the peripheral surface of the second piezoelectric element.

[0098] According to the above configuration, the second piezoelectric element is bonded to the first portion in a manner that the second piezoelectric element sandwiches the vibration plate with the first piezoelectric element and is electrically opposite to the first piezoelectric element, so that it contracts when the first piezoelectric element expands and expands when the first piezoelectric element contracts. As a result, the amplitude of the vibration plate becomes larger than when only the first piezoelectric element is bonded to the vibration plate. Therefore, when the piezoelectric vibration device is used as a piezoelectric speaker, a higher sound pressure sensitivity can be obtained.

[0099] In addition, the other rigid layer is bonded to the peripheral surface of the second piezoelectric element and is stacked on the second portion on the second piezoelectric element side. In this case, the difference in bending rigidity between the first stack formed at a position corresponding to the first portion of the vibration plate and the stack formed at a position corresponding to the second portion of the vibration plate can be reduced. Therefore, even if the second piezoelectric element is provided, it is difficult to cause bending of the vibration plate due to the difference in bending rigidity between the first stack and the second stack.

[0100] In the above configuration, the piezoelectric vibration device may further include a protective layer covering the piezoelectric element to protect the first piezoelectric element and the second piezoelectric element.

[0101] According to the above-mentioned structure, the first piezoelectric element and the second piezoelectric element are covered by the protective layer, so they can be protected from environmental deterioration factors such as moisture. In addition, since the two surfaces of the second part are also covered by the rigid layer, the second part can also be protected from environmental deterioration factors.

[0102] The technology disclosed in the present invention is not limited to the above-mentioned embodiments, and can be applied to embodiments in which changes, substitutions, supplements, omissions, etc. are made. In addition, each component described in the above-mentioned embodiments can be combined to form a new embodiment.

[0103] Industrial Applicability

[0104] The present disclosure can be well used in the technical field where sound needs to be generated and the technical field where vibration needs to be detected.

Claims

1. A piezoelectric vibration device, characterized in that: Functions as a piezoelectric speaker that plays sound or a piezoelectric vibration sensor that detects vibration, and includes: a piezoelectric element; and A vibration plate having a first portion joined to the piezoelectric element and a second portion located around the first portion; wherein, The piezoelectric element is bonded to one surface of the first portion of the vibration plate in the following manner: when an alternating voltage is applied, the piezoelectric element expands and contracts and causes the vibration plate to vibrate toward the side to which the piezoelectric element is bonded and toward the opposite side, thereby generating sound from the vibration plate; or, when the vibration plate vibrates toward the side to which the piezoelectric element is bonded and toward the opposite side, the piezoelectric element expands and contracts following the vibration of the vibration plate, thereby generating a voltage signal, The piezoelectric vibration device also includes: The rigid layer is laminated on the one surface of the second portion of the vibration plate and is bonded to the peripheral surface of the piezoelectric element.

2. The piezoelectric vibration device according to claim 1, characterized in that: The vibration plate has: a conductive layer forming the one surface and being formed so as to be able to supply power to the piezoelectric element; and The bottom layer is stacked with the conductive layer and has a lower density than the conductive layer.

3. The piezoelectric vibration device according to claim 1 or 2, characterized in that Also includes: The peripheral portion surrounds the vibration plate in the circumferential direction and is bent and deformed toward the side to which the piezoelectric element is joined and toward the opposite side thereof in response to the expansion and contraction of the piezoelectric element; wherein, The rigid layer is not laminated on the peripheral portion, and is formed so that the bending rigidity of the rigid layer decreases toward the peripheral portion.

4. The piezoelectric vibration device according to claim 1, wherein: The vibration plate has: a conductive layer forming the one surface and being formed so as to be able to supply power to the piezoelectric element; and A bottom layer, stacked with the conductive layer; wherein, The bottom layer has a greater internal loss than the conductive layer.

5. The piezoelectric vibration device according to claim 4, characterized in that Also includes: The peripheral portion surrounds the vibration plate in the circumferential direction and is bent and deformed toward the side to which the piezoelectric element is joined and toward the opposite side thereof in response to the expansion and contraction of the piezoelectric element; wherein, The peripheral portion is formed integrally with the bottom layer and made of the same material as the bottom layer. The rigid layer is not laminated on the peripheral portion, and is formed so that the bending rigidity of the rigid layer decreases toward the peripheral portion.

6. The piezoelectric vibration device according to claim 1 or 2, characterized in that Also includes: The protective layer covers the piezoelectric element to protect the piezoelectric element.

7. The piezoelectric vibration device according to claim 1 or 2, characterized in that Also includes: a second piezoelectric element joined to the first portion in a manner that the second piezoelectric element sandwiches the vibration plate with the first piezoelectric element and is electrically opposite to the first piezoelectric element; as well as, Another rigid layer is stacked on the second portion on the second piezoelectric element side and bonded to the periphery of the second piezoelectric element.

8. The piezoelectric vibration device according to claim 7, characterized in that Also includes: The protective layer covers the piezoelectric element to protect the first piezoelectric element and the second piezoelectric element.

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