Piezoelectric Vibration Device

Abstract

To provide a long life piezoelectric vibration device.SOLUTION: A disclosed piezoelectric vibration device 100 includes: a piezoelectric element 120; a diaphragm 110 joined to the piezoelectric element 120; a first protective layer 151 coating the piezoelectric element 120 and the diaphragm 110 on the side where piezoelectric element 120 is joined; and a second protective layer 152 coating the diaphragm 110 on the side opposite to the first protective layer 151. The diaphragm 120 has a base layer 111 and a surface layer 112 laminated on the base layer 111 and bonded to the piezoelectric element 120.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] 9(a) and 9(b), a thin piezoelectric speaker 400 has been developed in which a disc-shaped piezoelectric element 420 is bonded to a conductive, flat diaphragm 410. An electrode 431 is attached to the surface of the piezoelectric element 420 opposite to the surface bonded to the diaphragm 410. In addition, another electrode 432 is attached to the diaphragm 410.

[0003] In piezoelectric speaker 400 shown in Fig. 9(a), a positive voltage is applied to electrode 431, while a negative voltage is applied to electrode 432. This voltage application causes piezoelectric element 420 to expand in the radial direction. At this time, diaphragm 410 elastically curves so as to be convex toward piezoelectric element 420. When the voltage applied to electrodes 431 and 432 is removed, diaphragm 410 restores its original flat shape.

[0004] 9(b), the polarity of the voltage applied to electrodes 431 and 432 is opposite to that of the voltage shown in FIG. 9(a). In this state, piezoelectric element 420 contracts in the radial direction, and diaphragm 410 elastically curves so as to convex on the side opposite piezoelectric element 420.

[0005] 9(b) are repeated by applying an AC voltage to electrodes 431 and 432. That is, diaphragm 410 vibrates by repeatedly bending convexly toward piezoelectric element 420 and bending convexly away from piezoelectric element 420. When diaphragm 410 is vibrating in this manner, if the polarity of the voltage is switched at the timing when diaphragm 410 returns to its original flat plate shape, diaphragm 410 enters a resonant state, and the amplitude of diaphragm 410 increases. If diaphragm 410 vibrates with a large amplitude, piezoelectric speaker 400 can produce a loud sound.

[0006] In order to further increase the vibration amplitude of diaphragm 410 under the same energy, it is conceivable to reduce the weight of diaphragm 410. By reducing the thickness of diaphragm 410, diaphragm 410 becomes lighter, but the restoring force when diaphragm 410 returns from a curved and deformed state to a flat plate shape becomes smaller, and the vibration of diaphragm 410 shown in Figures 9(a) and 9(b) cannot be obtained. For this reason, in Patent Document 1, as shown in Figures 10(a) and 10(b), the weight of diaphragm 410 is reduced while maintaining the thickness required for vibration of diaphragm 410.

[0007] Specifically, diaphragm 410 of piezoelectric speaker 400 of Patent Document 1 has a three-layer structure, with the central layer being base layer 411, which has a lower density than the other layers. The thickness of base layer 411 is set so that diaphragm 410 has a certain degree of restoring force. Surface layer 412 is laminated on the surface of base layer 411 facing piezoelectric element 420. Surface layer 412 is made of a conductive material with a higher density than base layer 411, and piezoelectric element 420 is bonded to surface layer 412. Piezoelectric element 420 is bonded to base layer 411 via surface layer 412 for the following reasons.

[0008] Because the base layer 411 has a low density, it is prone to deformation in which the molecules constituting the base layer 411 move closer to each other, i.e., contraction of the base layer 411. For this reason, if the piezoelectric element 420 contracts while directly bonded to the base layer 411, only the portion bonded to the piezoelectric element 420 will contract in accordance with the contraction of the piezoelectric element 420, and the amount of bending deformation of the base layer 411 may be small. Therefore, in Patent Document 1, a surface layer 412 having a higher density than the base layer 411 is provided, and the piezoelectric element 420 is bonded to this surface layer 412.

[0009] Another surface layer 413 is laminated on base layer 411 on the side opposite surface layer 412. Another surface layer 413 is made of the same material as surface layer 412 and has approximately the same thickness as surface layer 412. This makes the bending rigidity of diaphragm 410 symmetrical on the surface layer 412 side and the surface layer 413 side, and the vibration amplitude of diaphragm 410 on the piezoelectric element 420 side and the vibration amplitude on the opposite side are approximately equal. By making these vibration amplitudes approximately equal, distortion of the sound emitted from piezoelectric speaker 400 is suppressed.

[0010] 9(a) to 10(b), a piezoelectric vibration sensor that detects vibrations of an object to be detected can be configured. That is, if the diaphragm 410 is disposed so as to receive vibrations of the object to be detected, the diaphragm 410 vibrates. The piezoelectric element 420 expands and contracts in response to this vibration, and a voltage having a magnitude corresponding to the amount of expansion and contraction of the piezoelectric element 420 is output from the piezoelectric element 420, so that the sensor can function as a vibration detection sensor. By monitoring the voltage output from the piezoelectric element 420, the vibrations of the object to be detected can be detected and analyzed. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-230193 Summary of the Invention [Problem to be solved by the invention]

[0012] 9(a) to 10(b) is thin and can be mounted in various devices (e.g., a smartphone or a washing machine), but the lifespan of the device in which the piezoelectric speaker 400 is mounted may be shortened depending on the environment in which the device is placed. For example, if the piezoelectric speaker 400 of FIG. 9(a) to 10(b) is mounted in a washing machine, the lifespan of the piezoelectric speaker 400 may be shortened due to humidity. A similar problem may also occur in a piezoelectric vibration sensor.

[0013] An object of the present invention is to provide a technique for extending the life of a piezoelectric vibration device that can function as a piezoelectric speaker and a piezoelectric vibration sensor. [Means for solving the problem]

[0014] The piezoelectric vibration device of the present disclosure includes a diaphragm, a piezoelectric element bonded to one surface of the diaphragm so as to expand and contract under application of an AC voltage, thereby bending and deforming the diaphragm and vibrating the diaphragm to generate sound, or so as to expand and contract in response to the vibration of the diaphragm while the diaphragm is vibrating and bending, thereby generating a voltage signal; a first protective layer that covers the piezoelectric element and one surface of the diaphragm to protect the piezoelectric element and the diaphragm; and a second protective layer that covers the other surface of the diaphragm opposite the first protective layer to protect the diaphragm. The first and second protective layers are capable of bending and deforming together with the diaphragm. The diaphragm has a base layer that has a thickness that generates a restoring force to restore the diaphragm from a bent and deformed state, and a surface layer that is bonded to the surface of the base layer facing the first protective layer and to the piezoelectric element and is made of a material with a higher density than the base layer. The second protective layer is bonded to the base layer without being bonded to the surface layer. [Effects of the Invention]

[0015] The piezoelectric vibration device described above has a long life. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a plan view of a portion of a piezoelectric vibration device that functions as a piezoelectric speaker; [Figure 2] 2 is a schematic cross-sectional view of the piezoelectric vibration device taken along line II-II in FIG. 1; [Figure 3] Schematic diagram showing the bending deformation of a diaphragm [Figure 4] A plan view of a portion of a piezoelectric vibration device [Figure 5] 5 is a schematic cross-sectional view of the piezoelectric vibration device taken along line VV in FIG. 4. [Figure 6] Schematic cross-sectional view of a piezoelectric vibration device [Figure 7]Schematic cross-sectional view of a piezoelectric vibration device [Figure 8] Schematic cross-sectional view of a piezoelectric vibration device functioning as a piezoelectric vibration sensor. [Figure 9] Schematic cross-sectional view of a conventional piezoelectric speaker [Figure 10] Schematic cross-sectional view of a conventional piezoelectric speaker DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, the first and second embodiments will be described in detail with reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that 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.

[0018] (First embodiment) Fig. 1 is a schematic plan view of a portion of a piezoelectric vibration device 100 that functions as a piezoelectric speaker. Fig. 2 is a schematic cross-sectional view of the piezoelectric vibration device 100 (a cross-sectional view taken along line II-II in Fig. 1). The structure of the piezoelectric vibration device 100 will be described with reference to Figs. 1 and 2.

[0019] (Structure of piezoelectric vibration device) The piezoelectric vibration device 100 comprises an approximately square vibration plate 110, a flat piezoelectric element 120 bonded to the vibration plate 110, a surrounding layer 113 surrounding the vibration plate 110 in the circumferential direction, and a rigid layer 140 laminated on the surrounding layer 113.

[0020] Piezoelectric element 120 is a circular plate having a thickness of about 30 μm to 50 μm, and one surface of piezoelectric element 120 is bonded to diaphragm 110. Piezoelectric element 120 may be bonded to diaphragm 110 using, for example, an acrylic adhesive. Piezoelectric element 120 has the property of expanding and contracting in the radial direction when an AC voltage is applied to both surfaces of piezoelectric element 120. Furthermore, piezoelectric element 120 has the property of expanding and contracting more as the voltage applied to both surfaces of piezoelectric element 120 increases.

[0021] 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 has a characteristic of expanding in the radial direction, as shown in FIG. 3(a). Also, when the polarity of the voltage is reversed from the state in FIG. 3(a), the piezoelectric element 120 has a characteristic of contracting in the radial direction, as shown in FIG. 3(b). Such a piezoelectric element 120 can be formed using a piezoelectric material such as PZT (lead zirconate titanate).

[0022] If the piezoelectric element 120 is inverted and bonded to the diaphragm 110, it will have expansion and contraction characteristics opposite to those shown in Figures 3(a) and 3(b). That is, when a negative voltage is applied to one surface (the upper surface in Figure 2) of the piezoelectric element 120 and a positive voltage is applied to the other surface, the piezoelectric element 120 will have a characteristic of expanding in the radial direction. In this case, reversing the polarity of the applied voltage will cause the piezoelectric element 120 to contract in the radial direction.

[0023] Diaphragm 110 is a thin plate-like member (for example, a member with a thickness of about 40 μm) that curves and deforms in response to expansion and contraction of piezoelectric element 120. Diaphragm 110 has a two-layer structure and is composed of a base layer 111 and a surface layer 112 bonded onto base layer 111 on the piezoelectric element 120 side. Piezoelectric element 120 is bonded to surface layer 112.

[0024] The base layer 111 is formed from a material with a lower density than the surface 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 from styrene-butadiene rubber, butadiene rubber, butyl rubber, or ethylene-propylene rubber.

[0025] The base layer 111 has a thickness that provides a restoring force for returning the base layer 111 from the curved state shown in Figures 3(a) and 3(b) to the flat state shown in Figure 2 when the voltage application to the piezoelectric element 120 is removed, and is thicker than the surface layer 112. For example, the base layer 111 has a thickness of 30 µm, while the surface layer 112 has a thickness of approximately 10 µm. In this way, the base layer 111 is thicker than the surface layer 112, but as described above, the base layer 111 is made of a material with a lower density than the surface layer 112, and therefore an increase in the weight of the diaphragm 110 is suppressed.

[0026] The surface layer 112 is formed from a conductive material and is used to apply a voltage to the piezoelectric element 120. The surface layer 112 is formed from a material with a higher density than the base layer 111. For example, the surface layer 112 may be a layer of 42 alloy (42Ni-Fe) or a layer of copper (Cu). The surface layer 112 is bonded to the base layer 111 by van der Waals forces. Alternatively, the surface layer 112 and the base layer 111 may be bonded by an adhesive.

[0027] The surface layer 112 has an overall rectangular shape in a plan view, but is partially cut out. In this cutout, a part of the base layer 111 is exposed from the surface layer 112. This cutout is used to arrange an electrode 132 for applying a voltage to the piezoelectric element 120.

[0028] The surface layer 112 is made of a material with a higher density than the base layer 111, and when the piezoelectric element 120 expands and contracts in the radial direction, it is curved and deformed in a direction convex toward the piezoelectric element 120 and in a direction convex in the opposite direction, as shown in Figures 3(a) and 3(b). Following this curved deformation of the surface layer 112, the base layer 111 bonded to the surface layer 112 is also curved and deformed.

[0029] 2, the surface layer 112 is bonded only to the surface of the base layer 111 on the piezoelectric element 120 side, and is not provided on the opposite side of the piezoelectric element 120. Therefore, the diaphragm 110 has high rigidity on the surface layer 112 side and low rigidity on the opposite side.

[0030] The surrounding layer 113 is formed integrally with the base layer 111 so as to surround the base layer 111 in the circumferential direction. That is, the material of the surrounding layer 113 is the same as that of the base layer 111, and the surrounding layer 113 and the base layer 111 form a single resin or aluminum layer. As shown in FIG. 2 , when the piezoelectric vibration device 100 is placed with the vibration plate 110 overlapping a rectangular opening 310 provided in the device 300, the surrounding layer 113 is the portion that overlaps the device 300 around the opening 310. In this state, the surrounding layer 113 is fixed to the device 300 together with other layers (a third protective layer 153 and a fourth protective layer 154 described below) that protect the surrounding layer 113.

[0031] The surrounding layer 113 itself is made of the same low-density material as the base layer 111, and therefore may not have sufficient rigidity as a portion attached to the device 300. For this reason, the rigid layer 140 is laminated on the surrounding layer 113 to increase the rigidity of the laminated portion. In other words, by laminating the rigid layer 140 on the surrounding layer 113, the rigidity suitable for the portion attached to the device 300 is obtained.

[0032] The rigid layer 140 has a substantially C-shape in plan view, and is laminated so as to surround the diaphragm 110 in the circumferential direction. In this embodiment, the rigid layer 140 is laminated on the surface of the resin layer or aluminum layer constituted by the surrounding layer 113 and the base layer 111, on which the surface layer 112 is provided. The rigid layer 140 has an opening in the same direction as the notched portion of the surface layer 112, and this opening is used for arranging electrodes 131 and 132 for applying a voltage to the piezoelectric element 120.

[0033] The rigid layer 140 may be made of the same material as the surface layer 112. Furthermore, if sufficient rigidity is obtained for attachment to the device 300, the rigid layer 140 may have the same thickness as the surface layer 112. Note that the rigid layer 140 may be thicker than the surface layer 112 to improve the rigidity of the attachment portion to the device 300. As shown in FIGS. 3(a) and 3(b), when the piezoelectric vibration device 100 is attached to the device 300, the rigid layer 140 may be arranged so as to overlap the periphery of the opening 310 over the entire length, and may be fixed to the device 300 in this state.

[0034] The inner edge of the rigid layer 140 is spaced at a substantially constant distance from the outer edge of the surface layer 112 along its entire length. Therefore, an inner edge portion 114 of the peripheral layer 113 that follows the outer edge of the base layer 111 appears between the inner edge of the rigid layer 140 and the outer edge of the surface layer 112. In other words, the rigid layer 140 is laminated to the peripheral layer 113 outside the inner edge portion 114 of the peripheral layer 113.

[0035] Neither the surface layer 112 nor the rigid layer 140, which have relatively high rigidity, are laminated on the inner edge portion 114 of the surrounding layer 113. Therefore, when the diaphragm 110 is curved and deformed as shown in Figures 3(a) and 3(b), the inner edge portion 114 is allowed to deform significantly in accordance with this curved deformation.

[0036] Furthermore, inner edge portion 114 of surrounding layer 113 has a substantially constant width. Therefore, diaphragm 110 is not in a state in which it is likely to vibrate specifically in any one direction in the radial direction of piezoelectric element 120. In other words, inner edge portion 114 of surrounding layer 113 is designed to be able to expand and contract substantially evenly on all four sides of diaphragm 110, which is substantially square in shape.

[0037] As described above, the electrodes 131 and 132 are arranged by utilizing the openings in the rigid layer 140 and the notches in the surface layer 112. The electrode 131 is formed integrally with the surface layer 112 and is laminated on the surrounding layer 113. The electrode 131 is conductive like the surface layer 112.

[0038] Meanwhile, the electrode 132 is laminated not only on the surrounding layer 113 but also on the base layer 111 in the notched region of the surface layer 112. The electrode 132 is bonded to the surface of the piezoelectric element 120 opposite to the surface layer 112 by a conductive and elastic bonding material. The bonding material has a certain degree of elasticity, making it less likely for the connection between the piezoelectric element 120 and the electrode 132 to break even when the piezoelectric element 120 is deformed. For example, a silver paste containing silver and a resin material may be used as the bonding material. Alternatively, a paste material containing a conductor such as copper, gold, nickel, or carbon as a filler may be used in addition to the silver paste. Furthermore, a resin binder containing a nitrile group (e.g., acrylonitrile rubber), a resin binder containing an epoxy resin, and / or a resin binder containing a urethane resin may be used as the resin material for the bonding material. Another resin material may be a thermoplastic polyester-based resin binder. The use of such a resin binder makes it possible to obtain a flexible bonding material.

[0039] 2, first to fourth protective layers 151 to 154 are provided to protect diaphragm 110, piezoelectric element 120, rigid layer 140, and electrodes 131, 132 from environmental deteriorating factors such as moisture. First to fourth protective layers 151 to 154 may be formed from an acrylic resin, an epoxy resin, or a urethane resin that is polymerized and hardened by thermal drying. Alternatively, first to fourth protective layers 151 to 154 may be formed from a material that is photopolymerized and hardened by ultraviolet light (for example, a urethane acrylate resin, an epoxy acrylate resin, or a polyester acrylate resin).

[0040] The first protective layer 151 is provided to protect the surface layer 112 and the piezoelectric element 120 of the diaphragm 110. That is, the first protective layer 151 is provided so as to be laminated on the surface layer 112 and the piezoelectric element 120 on the side of the surface layer 112 and the piezoelectric element 120, covering them. The third protective layer 153 is formed so as to surround the first protective layer 151 in the circumferential direction so as to form a single resin layer together with the first protective layer 151, and is laminated on the surrounding layer 113. The third protective layer 153 is provided to protect the rigid layer 140 and the electrode 131, covering them. The other electrode 132 is covered by the first protective layer 151 and the third protective layer 153.

[0041] Second protective layer 152 is provided on the opposite side of first protective layer 151 in the thickness direction of diaphragm 110 (the vertical direction in FIG. 2), and covers base layer 111. That is, second protective layer 152 is bonded to base layer 111 without being bonded to surface layer 112. Furthermore, fourth protective layer 154 is formed to surround second protective layer 152 in the circumferential direction so as to form a single resin layer together with second protective layer 152, and is laminated on the surface of surrounding layer 113 opposite to third protective layer 153. As a result, base layer 111 and surrounding layer 113 are protected by second protective layer 152 to fourth protective layer 154.

[0042] The thicknesses of the resin layers constituting the first protective layer 151 to the fourth protective layer 154 are set so that the first protective layer 151 to the fourth protective layer 154 can bend and deform in accordance with the bending deformation of the vibration plate 110 and the piezoelectric element 120 shown in Figures 3(a) and 3(b).

[0043] The second protective layer 152 is formed from the same material as the first protective layer 151, but is thicker than the first protective layer 151 so as to have higher rigidity than the first protective layer 151. The thickness of the second protective layer 152 may be set so that the bending rigidity of the second protective layer 152 is close to the bending rigidity of the laminate made up of the first protective layer 151 and the surface layer 112. In other words, the bending rigidities of the two layers sandwiching the base layer 111 (i.e., the layer of the laminate made up of the first protective layer 151 and the surface layer 112, and the second protective layer 152) may be approximately equal.

[0044] (Explanation of operation) When an AC voltage is applied to the electrodes 131 and 132, the piezoelectric element 120 and the diaphragm 110 vibrate by repeatedly undergoing bending deformation as shown in FIGS. 3(a) and 3(b).

[0045] 3(a), a positive voltage is applied to one surface (upper surface) of the piezoelectric element 120 through the electrode 132, and a negative voltage is applied to the other surface (lower surface) of the piezoelectric element 120 through the electrode 131 and the surface layer 112. In the state shown in FIG. 3(b), a negative voltage is applied to one surface (upper surface) of the piezoelectric element 120 through the electrode 132, and a positive voltage is applied to the other surface (lower surface) of the piezoelectric element 120 through the electrode 131 and the surface layer 112.

[0046] 3(a) and 3(b), a potential difference occurs between the two surfaces of the piezoelectric element 120, and this potential difference causes the piezoelectric element 120 to expand and contract. In the state shown in FIG. 3(a), the potential difference between the two surfaces of the piezoelectric element 120 causes the piezoelectric element 120 to expand in the radial direction, and the diaphragm 110 is curved so as to be convex on the side facing the piezoelectric element 120. On the other hand, in the state shown in FIG. 3(b), the potential difference between the two surfaces of the piezoelectric element 120 causes the piezoelectric element 120 to contract in the radial direction, and the diaphragm 110 is curved so as to be convex on the side opposite to the piezoelectric element 120.

[0047] 3(a) and 3(b) are alternately repeated at a predetermined frequency, the diaphragm 110 enters a state of vibrating at the predetermined frequency. As a result of the vibration of the diaphragm 110, the air around the diaphragm 110 vibrates, generating a sound corresponding to the vibration frequency of the diaphragm 110. By changing the frequency of the AC voltage applied to the piezoelectric element 120, the vibration frequency of the diaphragm 110 changes, and it becomes possible to change the frequency of the sound generated by the piezoelectric vibration device 100.

[0048] When a voltage is applied as shown in FIG. 3(a) and then removed, the diaphragm 110 returns to the flat state shown in FIG. 2. At this time, when the polarity of the voltage is switched as shown in FIG. 3(b), the direction of deformation of the diaphragm 110 due to the restoring force of the base layer 111 coincides with the direction of deformation of the diaphragm 110 due to the contraction of the piezoelectric element 120, allowing the diaphragm 110 to undergo large curvature deformation. In this way, if the frequency of the AC voltage applied to the piezoelectric element 120 is adjusted so that the direction of deformation of the diaphragm 110 due to the restoring force of the base layer 111 coincides with the direction of deformation of the diaphragm 110 due to the expansion and contraction of the piezoelectric element 120, the diaphragm 110 enters a resonant state. In this state, the diaphragm 110 vibrates with a large amplitude, and the piezoelectric vibration device 100 can produce a loud sound.

[0049] 3(a) and 3(b), when the diaphragm 110 is vibrating, the inner edge portion 114 of the surrounding layer 113 also flexes and deforms in the vertical direction in Fig. 2 in response to the vibration of the diaphragm 110. As a result, the vibration amplitude of the diaphragm 110 increases by the amount of deformation of the inner edge portion 114 of the surrounding layer 113, and the piezoelectric vibration device 100 can produce a loud sound.

[0050] In the above embodiment, the first protective layer 151 and the second protective layer 152 protect the vibration plate 110, the piezoelectric element 120, and the rigid layer 140, so that the piezoelectric vibration device 100 has a long life.

[0051] In the above-described embodiment, the surface layer 112 is provided on only one surface of the base layer 111. Therefore, the number of steps for forming the surface layer 112 is reduced compared to the conventional diaphragm 410 (diaphragm 410 in which the base layer 411 is sandwiched between a pair of surface layers 412 and 413) shown in Figures 10(a) and 10(b).

[0052] As a result of providing the surface layer 112 on only one surface of the base layer 111, the diaphragm 110 has high bending rigidity on the surface layer 112 side and low bending rigidity on the opposite side. Due to this distribution of bending rigidity, the bending ease of the diaphragm 110 itself differs between the direction convex toward the piezoelectric element 120 and the direction convex toward the opposite side. Even if the first protective layer 151 and the second protective layer 152, which have the same bending rigidity, are laminated on the diaphragm 110, the difference in bending ease described above is not resolved. Therefore, the vibration amplitude of the laminate of the diaphragm 110, the first protective layer 151, and the second protective layer 152 differs between the direction convex toward the piezoelectric element 120 and the direction convex toward the opposite side. This difference in vibration amplitude can cause sound distortion.

[0053] On the other hand, in the above-described embodiment, the bending rigidity of the second protective layer 152 is higher than the bending rigidity of the first protective layer 151 and is close to the bending rigidity of the laminate of the first protective layer 151 and the surface layer 112. That is, the bending rigidities of the two layers sandwiching the base layer 111 (i.e., the layers of the laminate of the first protective layer 151 and the surface layer 112 and the second protective layer 152) are approximately equal. As a result, the bending ease of the laminate of the diaphragm 110, the first protective layer 151, and the second protective layer 152 is approximately equal in the direction convex toward the piezoelectric element 120 and the direction convex toward the opposite side. In other words, the vibration amplitude of the laminate of the diaphragm 110, the first protective layer 151, and the second protective layer 152 is approximately equal in these directions, thereby suppressing sound distortion.

[0054] In the above-described embodiment, the first protective layer 151 and the second protective layer 152 are made of the same material. Alternatively, the second protective layer 152 may be made of a material harder than the material making up the first protective layer 151. In this case, even if the thickness of the second protective layer 152 is less than the thickness of the first protective layer 151, the condition that the bending rigidity of the second protective layer 152 is approximately equal to the bending rigidity of the laminate made up of the first protective layer 151 and the surface layer 112 can be satisfied. Therefore, by forming the second protective layer 152 using a relatively hard material, it is possible to reduce the thickness of the piezoelectric vibration device 100.

[0055] 4 and 5, the rigid layer 140 may be laminated on the surrounding layer 113 on the surface opposite to the piezoelectric element 120. In the piezoelectric vibration device 100 shown in FIGS. The rigid layer 140 is laminated on the lower surface of the surrounding layer 113, while the electrodes 131 and 132 are laminated on the upper surface of the surrounding layer 113, and there is no interference between the rigid layer 140 and the electrodes 131 and 132. For this reason, the rigid layer 140 does not need to have an opening region for arranging the electrodes 131 and 132, and may be formed to completely surround the diaphragm 110. For example, as shown in Figures 4 and 5, the rigid layer 140 may be formed in a substantially square frame shape in plan view instead of a C-shape.

[0056] In the piezoelectric vibration device 100 shown in Figures 4 and 5, the rigid layer 140 is laminated on the lower surface of a resin or aluminum layer composed of the surrounding layer 113 and the base layer 111, while the surface layer 112 is laminated on the upper surface of the resin or aluminum layer. In this case, the rigid layer 140 may be formed in a lamination process separate from the lamination process for laminating the base layer 111 and the surface layer 112. When a lamination process separate from the lamination process for the surface layer 112 is provided for forming the rigid layer 140, the amount of effort required to form the surface layer 112 and the rigid layer 140 does not change significantly even if the rigid layer 140 is formed from a different material than the surface layer 112. Therefore, the rigid layer 140 may be formed to be harder than the surface layer 112, for example.

[0057] 4 and 5, the third protective layer 153 that protects the rigid layer 140 is provided so as to form a single resin layer together with the second protective layer 152. That is, the third protective layer 153 is formed so as to surround the second protective layer 152 in the circumferential direction, and is laminated on the surrounding layer 113. On the other hand, the fourth protective layer 154 is laminated on the surrounding layer 113 so as to surround the first protective layer 151 in the circumferential direction, and forms a single resin layer together with the first protective layer 151.

[0058] In the piezoelectric vibration device 100 shown in FIGS. 1 to 5 , the first to fourth protective layers 151 to 154 entirely cover both sides of the resin or aluminum layer formed by the base layer 111 and the surrounding layer 113. In this case, the first to fourth protective layers 151 to 154 can provide excellent protection for the piezoelectric vibration device 100 while also suppressing deformation of the inner edge portion 114 of the surrounding layer 113. To reduce this suppression effect, the resin layers of the first to fourth protective layers 151 to 154 may be formed so as not to constrain the inner edge portion 114. For example, as shown in FIG. 6 , gaps 155 may be formed between the first to third protective layers 153 and between the second to fourth protective layers 152 and 154. In this case, the gaps 155 are formed at positions corresponding to the inner edge portion 114 of the surrounding layer 113, so that the inner edge portion 114 is not constrained by the first to fourth protective layers 151 to 154. The piezoelectric vibration device 100 shown in FIG. 6 has the same configuration as the piezoelectric vibration device 100 shown in FIGS. 1 and 2, except that a gap 155 is formed.

[0059] 6, the inner edge portion 114 is not covered by the first to fourth protective layers 151 to 154, and therefore deformation of the inner edge portion 114 is not prevented by the first to fourth protective layers 151 to 154. Therefore, the diaphragm 110 can vibrate with a larger amplitude than when the gap 155 is not formed.

[0060] In the piezoelectric vibration device 100 shown in Fig. 6, the gap 155 is formed both between the first protective layer 151 and the third protective layer 153 and between the second protective layer 152 and the fourth protective layer 154. Alternatively, the gap 155 may be formed on only one side, as long as the difference in amplitude of the vibration plate 110 between the piezoelectric element 120 side and the opposite side does not become excessively large. In this case, the vibration amplitude of the vibration plate 110 may be smaller than the vibration amplitude of the piezoelectric vibration device 100 shown in Fig. 6, but the protective effect provided by the first protective layer 151 to the fourth protective layer 154 may be enhanced.

[0061] The void 155 may be formed in the piezoelectric vibration device 100 shown in Figures 4 and 5. Even when the void 155 is formed in the piezoelectric vibration device 100 shown in Figures 4 and 5, the vibration amplitude of the vibration plate 110 can be increased.

[0062] 1 to 6 includes a rigid layer 140. Alternatively, as shown in Fig. 7, the piezoelectric vibration device 100 does not need to include the rigid layer 140, as long as the laminate of the surrounding layer 113, the third protective layer 153, and the fourth protective layer 154 has sufficient rigidity for attachment to the device 300. The piezoelectric vibration device 100 shown in Fig. 7 has the same configuration as the piezoelectric vibration device 100 shown in Figs. 1 and 2, except that it does not include the rigid layer 140.

[0063] A piezoelectric vibration device 100 according to one aspect of the above-described embodiment includes a diaphragm 110, a piezoelectric element 120 bonded to one surface of the diaphragm 110 so as to expand and contract under application of an AC voltage to cause the diaphragm 110 to vibrate and curve and deform, thereby generating sound, or to expand and contract in response to the vibration of the diaphragm 110 when the diaphragm 110 is vibrating and curved, thereby generating a voltage signal, a first protective layer 151 that covers the piezoelectric element 120 and one surface of the diaphragm 110 to protect the piezoelectric element 120 and the diaphragm 110, and a second protective layer 152 that covers the other surface of the diaphragm 110 opposite to the first protective layer 151 to protect the diaphragm 110. The first protective layer 151 and the second protective layer 152 are capable of curving and deforming together with the diaphragm 110. The diaphragm 110 has a base layer 111 having a thickness that generates a restoring force for restoring the diaphragm 110 from a curved and deformed state, and a surface layer 112 that is bonded to the surface of the base layer 111 facing the first protective layer 151 and to the piezoelectric element 120 and is made of a material with a higher density than the base layer 111. The second protective layer 152 is bonded to the base layer 111 without being bonded to the surface layer 112.

[0064] According to the above-described configuration, when an AC voltage is applied to the piezoelectric element 120, the piezoelectric element 120 vibrates the diaphragm 110 while curving and deforming it, thereby generating sound, and therefore the piezoelectric vibration device 100 can function as a piezoelectric speaker. On the other hand, if the piezoelectric element 120 expands and contracts in response to the vibration of the diaphragm 110 while the diaphragm 110 is vibrating while curving and deforming, the piezoelectric element 120 generates a voltage signal, and therefore the piezoelectric vibration device 100 can function as a piezoelectric vibration sensor that detects vibrations.

[0065] The piezoelectric element 120 and the vibration plate 110 are protected by being covered with the first protective layer 151 and the second protective layer 152, and the piezoelectric vibration device 100 has a long life. Furthermore, the second protective layer 152 is bonded to the base layer 111 without being bonded to the surface layer 112, and the surface layer 112 is not interposed between the second protective layer 152 and the base layer 111. Therefore, there are fewer steps for forming the surface layer 112 than in a conventional vibration plate in which the base layer 111 is sandwiched between a pair of surface layers 112, and the manufacturing process for the piezoelectric vibration device 100 can be simplified.

[0066] In the above-described configuration, the bending rigidity of the second protective layer 152 may be greater than the bending rigidity of the first protective layer 151.

[0067] When a relatively high-rigidity surface layer 112 is laminated on only one side of the base layer 111, the diaphragm 110 has high rigidity on the surface layer 112 side and low rigidity on the opposite side. Due to this rigidity distribution, the diaphragm 110 itself bends differently when bending toward the surface layer 112 side and when bending toward the opposite side. Even if a first protective layer 151 and a second protective layer 152, each with the same bending rigidity, are laminated on such a diaphragm 110, the difference in bending ease described above cannot be resolved. This difference in bending ease manifests itself as a difference in amplitude between the diaphragm 110 bending toward the surface layer 112 side and the diaphragm 110 bending toward the opposite side. If the piezoelectric vibration device 100 is used as a piezoelectric speaker in this state, distortion may occur in the sound emitted by the piezoelectric vibration device 100. Furthermore, if the piezoelectric vibration device 100 is used as a piezoelectric vibration sensor, the vibration detection accuracy may differ between when the vibration plate 110 is curved toward the surface layer 112 and when it is curved toward the opposite side.

[0068] For this reason, in the above-described configuration, the bending rigidity of second protective layer 152 laminated on diaphragm 110 is set higher than the bending rigidity of first protective layer 151. In this case, it is possible to reduce the difference in bending rigidity between the laminate of first protective layer 151 and surface layer 112 and second protective layer 152. That is, the bending rigidities of the two layers sandwiching base layer 111 (i.e., the layer of the laminate of first protective layer 151 and surface layer 112 and second protective layer 152) become close to each other, and differences in bendability depending on the curvature direction of diaphragm 110 are suppressed.

[0069] In the above-described configuration, the material of the second protective layer 152 may be the same as that of the first protective layer 151. The second protective layer 152 may be thicker than the first protective layer 151.

[0070] According to the above-described configuration, the first protective layer 151 and the second protective layer 152 are made of the same material, which can facilitate the manufacture of the piezoelectric vibration device 100. In this case, by making the second protective layer 152 thicker than the first protective layer 151, the bending rigidity of the second protective layer 152 can be made higher than the bending rigidity of the first protective layer 151.

[0071] In the above-described configuration, the second protective layer 152 may be made of a material harder than the first protective layer 151 and may have a thickness less than that of the first protective layer 151.

[0072] According to the above-described configuration, second protective layer 152 is formed from a material harder than first protective layer 151. Therefore, even if second protective layer 152 has a thickness less than that of first protective layer 151, the bending rigidity of the layer of the laminate of first protective layer 151 and surface layer 112 and second protective layer 152 can be close to each other.

[0073] In the above-described configuration, the piezoelectric vibration device 100 may further include a surrounding layer 113 that is configured to surround the base layer 111 in the circumferential direction using the same material as the base layer 111 and is formed integrally with the base layer 111, a rigid layer 140 that is laminated on the surface of the surrounding layer 113 facing the same direction as one side or the other side of the vibration plate 110, thereby increasing the rigidity around the vibration plate 110 and enabling the piezoelectric vibration device 100 to be attached to another device 300, and a third protective layer 153 that protects the rigid layer 140 by covering it.

[0074] According to the above-described configuration, the portion of the surrounding layer 113 where the rigid layer 140 is laminated has high rigidity, and can therefore be used to attach the piezoelectric vibration device 100 to another device 300. The rigid layer 140 is protected by being covered with the third protective layer 153.

[0075] In the above-described configuration, the surrounding layer 113 may have an inner edge portion 114 that follows the outer edge of the base layer 111. The rigid layer 140 may be laminated to the surrounding layer 113 on the outside of the inner edge portion 114 so as to allow the inner edge portion 114 to deform in response to the vibration of the diaphragm 110. The third protective layer 153 may cover the rigid layer 140 so as not to restrict the inner edge portion 114.

[0076] According to the above-described configuration, the surrounding layer 113 is formed from the same material as the base layer 111, and therefore has a relatively low density. Therefore, the inner edge portion 114 of the surrounding layer 113, which is located along the outer edge of the base layer 111, can deform in response to the vibration of the diaphragm 110. If the inner edge portion 114 of the surrounding layer 113 deforms significantly in response to the vibration of the diaphragm 110, the vibration amplitude of the diaphragm 110 can be increased. If the diaphragm 110 vibrates with a large amplitude, a louder sound can be generated from the diaphragm 110 when the piezoelectric vibration device 100 is used as a piezoelectric speaker. Furthermore, if the piezoelectric vibration device 100 functions as a piezoelectric vibration sensor, a larger voltage signal can be generated, thereby improving the vibration detection accuracy. Therefore, the positions of the rigid layer 140 and the third protective layer 153 are determined so as to enable a large deformation of the inner edge portion 114 of the surrounding layer 113. That is, since rigid layer 140 of surrounding layer 113 is laminated on surrounding layer 113 outside inner edge portion 114 of surrounding layer 113, inner edge portion 114 of surrounding layer 113 can deform in response to the vibration of diaphragm 110 without being hindered by rigid layer 140. Furthermore, since third protective layer 153 covers rigid layer 140 so as not to constrain inner edge portion 114 of surrounding layer 113, inner edge portion 114 can deform in response to the vibration of diaphragm 110 without being hindered by third protective layer 153.

[0077] (Second embodiment) The piezoelectric vibration device 100 shown in FIGS. 1 to 7 can also function as a piezoelectric vibration sensor that detects vibrations of an object to be detected. That is, when vibrations of an object to be detected are transmitted to the vibration plate 110, the vibration plate 110 vibrates. When the vibration plate 110 vibrates, the piezoelectric element 120 bonded to the vibration plate 110 expands and contracts, and a potential difference corresponding to the amount of expansion and contraction of the piezoelectric element 120 can be generated in the piezoelectric element 120. By detecting the potential difference generated in the piezoelectric element 120, the vibration of the object to be detected can be detected. In the second embodiment, a case where the piezoelectric vibration device 100 shown in FIGS. 1 and 2 functions as a piezoelectric vibration sensor will be described with reference to FIG. 8.

[0078] The piezoelectric vibration device 100 is attached to a device 300 (for example, a washing machine) that is the detection target. The device 300 has a substantially square opening 310 that is wider than the vibration plate 110 so as not to interfere with the vibration of the vibration plate 110.

[0079] Piezoelectric vibration device 100 is fixed to device 300 such that rigid layer 140 overlaps the portion of device 300 around opening 310, while the entire inner area of ​​rigid layer 140 overlaps opening 310. In this state, when device 300 vibrates, the vibration is transmitted to piezoelectric vibration device 100, causing diaphragm 110 and inner edge portion 114 inside rigid layer 140 to vibrate as well. As a result, diaphragm 110 can deform as shown in Figures 3(a) and 3(b).

[0080] In the state shown in FIG. 3(a), the diaphragm 110 is curved and deformed in a direction that convexly faces the piezoelectric element 120. Following this curved deformation, the piezoelectric element 120 expands in the radial direction, and a potential difference occurs between both surfaces of the piezoelectric element 120. Furthermore, the greater the amount of curved deformation of the diaphragm 110, the greater the amount of expansion of the piezoelectric element 120, and the greater the potential difference occurring across the piezoelectric element 120. On the other hand, as shown in FIG. 3(b), if the diaphragm 110 is curved and deformed in the opposite direction, the piezoelectric element 120 contracts. In this case, the greater the amount of curved deformation of the diaphragm 110, the greater the amount of contraction of the piezoelectric element 120, and the greater the potential difference occurring across the piezoelectric element 120.

[0081] In the state shown in FIG. 3(a), one surface (top surface) of the piezoelectric element 120 has a positive potential, and the other surface (bottom surface) of the piezoelectric element 120 has a negative potential. On the other hand, in the state shown in FIG. 3(b), the other surface (bottom surface) of the piezoelectric element 120 has a positive potential, and one surface (top surface) of the piezoelectric element 120 has a negative potential. Since electrodes 131 and 132 are connected to both surfaces of the piezoelectric element 120, information about the potential difference generated in the piezoelectric element 120 is output from the electrodes 131 and 132 as a voltage signal. The electrodes 131 and 132 may be electrically connected to a vibration analyzer (e.g., a microcomputer). In this case, the vibration analyzer can obtain information about the vibration frequency of the piezoelectric vibration device 100, and ultimately the device 300, based on the frequency at which the voltage signal switches between positive and negative polarities. Furthermore, from the magnitude of the voltage signal, the vibration analyzer can obtain information regarding the vibration amplitude of the piezoelectric vibration device 100, and therefore the device 300.

[0082] 6, a void 155 is formed in the first protective layer 151 and the second protective layer 152. In the region where the void 155 is formed, the surrounding layer 113 can deform significantly, causing the vibration plate 110 to vibrate with a larger amplitude, increasing the amount of expansion and contraction of the piezoelectric element 120. In this case, under the condition that the vibration amplitude of the object to be detected (the device 300) is the same, when the void 155 is formed, a larger voltage signal is output in response to the vibration amplitude of the object to be detected than when the void 155 is not formed. Therefore, the formation of the void 155 makes it possible to detect the vibration amplitude of the object to be detected with higher accuracy.

[0083] A piezoelectric vibration device 100 according to one aspect of the second embodiment, like the first embodiment, includes a diaphragm 110, a piezoelectric element 120 bonded to one surface of the diaphragm 110 so as to expand and contract under application of an AC voltage, thereby curving and deforming the diaphragm 110 and vibrating the diaphragm 110 to generate sound, or to expand and contract in response to the vibration of the diaphragm 110 while the diaphragm 110 is vibrating and curving, thereby generating a voltage signal, a first protective layer 151 that covers the piezoelectric element 120 and one surface of the diaphragm 110 to protect the piezoelectric element 120 and the diaphragm 110, and a second protective layer 152 that covers the other surface of the diaphragm 110 opposite to the first protective layer 151 to protect the diaphragm 110. The first protective layer 151 and the second protective layer 152 are capable of curving and deforming together with the diaphragm 110. The diaphragm 110 has a base layer 111 having a thickness that generates a restoring force for restoring the diaphragm 110 from a curved and deformed state, and a surface layer 112 that is bonded to the surface of the base layer 111 facing the first protective layer 151 and to the piezoelectric element 120 and is made of a material with a higher density than the base layer 111. The second protective layer 152 is bonded to the base layer 111 without being bonded to the surface layer 112.

[0084] In the above-described configuration, the bending rigidity of the second protective layer 152 may be greater than the bending rigidity of the first protective layer 151, similar to the first embodiment.

[0085] In the above-described configuration, the material of the second protective layer 152 may be the same as that of the first protective layer 151, as in the first embodiment. The second protective layer 152 may be thicker than the first protective layer 151.

[0086] In the above-described configuration, the second protective layer 152 may be formed of a material harder than the first protective layer 151 and may have a thickness less than that of the first protective layer 151, as in the first embodiment.

[0087] In the above-described configuration, the piezoelectric vibration device 100, as in the first embodiment, is configured to surround the base layer 111 in the circumferential direction using the same material as the base layer 111, and may further include a surrounding layer 113 formed integrally with the base layer 111, a rigid layer 140 that is laminated on the surface of the surrounding layer 113 facing the same direction as one side or the other side of the vibration plate 110, thereby increasing the rigidity around the vibration plate 110 and enabling the piezoelectric vibration device 100 to be attached to another device 300, and a third protective layer 153 that protects the rigid layer 140 by covering it.

[0088] In the above-described configuration, similarly to the first embodiment, the surrounding layer 113 may have an inner edge portion 114 that follows the outer edge of the base layer 111. The rigid layer 140 may be laminated on the surrounding layer 113 outside the inner edge portion 114 so as to allow the inner edge portion 114 to deform in response to the vibration of the diaphragm 110. The third protective layer 153 may cover the rigid layer 140 so as not to restrict the inner edge portion 114.

[0089] (Effects, etc.) The piezoelectric vibration device 100 according to the above embodiment has the following features and provides the following effects.

[0090] A piezoelectric vibration device according to one aspect of the above-described embodiment includes a diaphragm, a piezoelectric element bonded to one surface of the diaphragm so as to expand and contract under application of an AC voltage, thereby bending and deforming the diaphragm and vibrating the diaphragm to generate sound, or to expand and contract in response to the vibration of the diaphragm while the diaphragm is vibrating and bending, thereby generating a voltage signal, a first protective layer that covers the piezoelectric element and one surface of the diaphragm to protect the piezoelectric element and the diaphragm, and a second protective layer that covers the other surface of the diaphragm opposite the first protective layer to protect the diaphragm. The first protective layer and the second protective layer are capable of bending and deforming together with the diaphragm. The diaphragm includes a base layer having a thickness that generates a restoring force to restore the diaphragm from a bent and deformed state, and a surface layer bonded to the surface of the base layer facing the first protective layer and to the piezoelectric element, and made of a material with a higher density than the base layer. The second protective layer is bonded to the base layer without being bonded to the surface layer.

[0091] According to the above-described configuration, when an AC voltage is applied to the piezoelectric element, the piezoelectric element vibrates the diaphragm while curving and deforming it, thereby generating sound, so that the piezoelectric vibration device can function as a piezoelectric speaker. On the other hand, if the piezoelectric element expands and contracts in response to the vibration of the diaphragm while the diaphragm is vibrating while curving and deforming, the piezoelectric element generates a voltage signal, so that the piezoelectric vibration device can function as a piezoelectric vibration sensor that detects vibrations.

[0092] The piezoelectric element and vibration plate are protected by being covered with the first protective layer and the second protective layer, and the piezoelectric vibration device has a long life. Furthermore, the second protective layer is bonded to the base layer without being bonded to the surface layer, and no surface layer is interposed between the second protective layer and the base layer. Therefore, compared to conventional vibration plates in which the base layer is sandwiched between a pair of surface layers, the number of steps for forming the surface layer is reduced, and the manufacturing process for the piezoelectric vibration device can be simplified.

[0093] In the above-described configuration, the bending rigidity of the second protective layer may be greater than the bending rigidity of the first protective layer.

[0094] When a relatively high-rigidity surface layer is laminated on only one side of the base layer, the diaphragm has high rigidity on the surface layer side and low rigidity on the opposite side. Due to this rigidity distribution, the diaphragm itself bends differently when bent toward the surface layer and when bent toward the opposite side. Even if a first protective layer and a second protective layer with equal bending rigidity are laminated on such a diaphragm, the difference in bendability described above cannot be resolved. This difference in bendability manifests itself as a difference in amplitude between the diaphragm bent toward the surface layer and the diaphragm bent toward the opposite side. If a piezoelectric vibration device is used as a piezoelectric speaker in this state, distortion may occur in the sound emitted by the piezoelectric vibration device. Furthermore, if a piezoelectric vibration device is used as a piezoelectric vibration sensor, the vibration detection accuracy may differ between the diaphragm bent toward the surface layer and the opposite side.

[0095] For this reason, in the above-described configuration, the bending rigidity of the second protective layer laminated on the diaphragm is set higher than that of the first protective layer. In this case, the difference in bending rigidity between the laminate of the first protective layer and the surface layer and the second protective layer can be reduced. That is, the bending rigidities of the two layers sandwiching the base layer (i.e., the layer of the laminate of the first protective layer and the surface layer and the second protective layer) become close to each other, and the difference in ease of bending depending on the curvature direction of the diaphragm is suppressed.

[0096] In the above-described configuration, the material of the second protective layer may be the same as that of the first protective layer, and the second protective layer may be thicker than the first protective layer.

[0097] According to the above-described configuration, the first protective layer and the second protective layer are made of the same material, which can facilitate manufacturing of the piezoelectric vibration device. In this case, by making the second protective layer thicker than the first protective layer, the bending stiffness of the second protective layer can be made higher than the bending stiffness of the first protective layer.

[0098] In the above-described configuration, the second protective layer may be made of a material harder than the first protective layer and may have a thickness less than that of the first protective layer.

[0099] According to the above-described configuration, the second protective layer is formed from a material harder than the first protective layer, so even if the second protective layer has a thickness less than that of the first protective layer, the bending rigidity of the laminate layer of the first protective layer and the surface layer and the bending rigidity of the second protective layer can be close to each other.

[0100] In the above-described configuration, the piezoelectric vibration device may further include a peripheral layer that is configured to surround the base layer circumferentially using the same material as the base layer, and is formed integrally with the base layer, a rigid layer that is laminated on the surface of the peripheral layer facing the same direction as one or the other surface of the vibration plate, thereby increasing the rigidity around the vibration plate and enabling the piezoelectric vibration device to be attached to other devices, and a third protective layer that protects the rigid layer by covering it.

[0101] According to the above-described configuration, the portion of the surrounding layer where the rigid layer is laminated has high rigidity, and can be used for attaching the piezoelectric vibration device to other devices. The rigid layer is protected by being covered with the third protective layer.

[0102] In the above-described configuration, the peripheral layer may have an inner edge portion that follows the outer edge of the base layer. The rigid layer may be laminated on the peripheral layer outside the inner edge portion to allow the inner edge portion to deform in response to vibration of the diaphragm. The third protective layer may cover the rigid layer so as not to constrain the inner edge portion.

[0103] According to the above-described configuration, the peripheral layer is formed from the same material as the base layer, and therefore has a relatively low density. Therefore, the inner edge portion of the peripheral layer, which follows the outer edge of the base layer, can deform in response to the vibration of the diaphragm. If the inner edge portion deforms significantly in response to the vibration of the diaphragm, the vibration amplitude of the diaphragm can increase. If the diaphragm vibrates with a large amplitude, the piezoelectric vibration device can generate a louder sound when used as a piezoelectric speaker. If the piezoelectric vibration device functions as a piezoelectric vibration sensor, the voltage signal can be increased, thereby improving the vibration detection accuracy. Therefore, the positions of the rigid layer and the third protective layer are set to enable large deformation of the inner edge portion of the peripheral layer. That is, the rigid layer is laminated on the peripheral layer outside the inner edge portion of the peripheral layer, so that the inner edge portion of the peripheral layer can deform in response to the vibration of the diaphragm without being hindered by the rigid layer. Furthermore, the third protective layer covers the rigid layer so as not to constrain the inner edge portion, so that the inner edge portion of the peripheral layer can deform in response to the vibration of the diaphragm without being hindered by the third protective layer.

[0104] As described above, the first and second embodiments have been described as examples of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to these and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made. Furthermore, it is also possible to combine the components described in the first and second embodiments to create new embodiments. [Industrial Applicability]

[0105] The present disclosure is suitably used in technical fields where sound generation is required and vibration detection is required. [Explanation of symbols]

[0106] 100 Piezoelectric vibration device 110...Diaphragm 111... Base layer 112...Surface layer 113... Surrounding layer 114... Inner edge part 120 Piezoelectric element 140...Rigid layer 151...1st protective layer 152...Second protective layer 153...Third protective layer 300...equipment

Claims

1. A diaphragm and a piezoelectric element bonded to one surface of the diaphragm so as to expand and contract under application of an AC voltage, thereby vibrating the diaphragm while curving and deforming it, thereby generating sound, or so as to expand and contract in response to the vibration of the diaphragm while the diaphragm is vibrating while curving and deforming, thereby generating a voltage signal; a first protective layer that covers the piezoelectric element and the one surface of the vibration plate to protect the piezoelectric element and the vibration plate; a second protective layer that protects the diaphragm by covering the other surface of the diaphragm opposite to the first protective layer, the first protective layer and the second protective layer are capable of bending and deforming together with the diaphragm, the diaphragm has a base layer having a thickness that generates a restoring force for restoring the diaphragm from a curved and deformed state, and a surface layer that is bonded to the surface of the base layer facing the first protective layer and to the piezoelectric element and is made of a material with a higher density than the base layer; The piezoelectric vibration device, wherein the second protective layer is bonded to the base layer without being bonded to the surface layer.

2. The piezoelectric vibration device according to claim 1 , wherein the second protective layer has a bending rigidity greater than that of the first protective layer.

3. the second protective layer is made of the same material as the first protective layer; The piezoelectric vibration device according to claim 2 , wherein the second protective layer is thicker than the first protective layer.

4. The piezoelectric vibration device according to claim 2 , wherein the second protective layer is made of a material harder than the first protective layer and has a thickness less than that of the first protective layer.

5. a peripheral layer made of the same material as the base layer, surrounding the base layer in a circumferential direction, and integrally formed with the base layer; a rigidity layer that is laminated on a surface of the surrounding layer that faces the same direction as the one surface or the other surface of the vibration plate, thereby increasing the rigidity around the vibration plate and enabling the piezoelectric vibration device to be attached to another device; The piezoelectric vibration device according to claim 1 , further comprising: a third protective layer that covers the rigid layer to protect the rigid layer.

6. the peripheral layer has an inner edge portion that follows the outer edge of the base layer; the rigid layer is laminated on the peripheral layer outside the inner edge portion so as to allow the inner edge portion to deform in response to vibration of the diaphragm; The piezoelectric vibration device according to claim 5 , wherein the third protective layer covers the rigid layer so as not to constrain the inner edge portion.

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