Acoustic Devices

Abstract

To provide an acoustic device capable of improving sound pressure characteristics in a wide frequency band.SOLUTION: An acoustic device 1 arranged on a substrate B includes a vibration unit 2 and a plurality of support members 4a, 4b. The vibration unit 2 has a piezoelectric element 10 and a diaphragm 30 to which the piezoelectric element 10 is joined, and vibrates by expansion and contraction of the piezoelectric element 10. The plurality of support members 4a, 4b supports the vibration unit 2 to the substrate B and vibrates by the vibration of the vibration unit 2. The diaphragm 30 includes a first area 31 where the piezoelectric element 10 is joined and a pair of second areas 32, 33 located on both sides of the first area 31. The support member 4a is arranged in a corresponding second area 32 of the pair of second areas 32, 33. The plurality of support members 4b is arranged in a corresponding second area 33 of the pair of second areas 32, 33. The resonance frequency of the vibration unit 2 is different from the resonance frequencies of the plurality of support members 4a, 4b.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an acoustic device. [Background technology]

[0002] A known acoustic device includes a piezoelectric element and a diaphragm to which the piezoelectric element is bonded (see, for example, Patent Document 1). The acoustic device is disposed on, for example, a substrate. The diaphragm vibrates due to the expansion and contraction of the piezoelectric element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-70100 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one aspect of the present invention is to provide an acoustic device that improves sound pressure characteristics over a wide frequency band. [Means for solving the problem]

[0005] An acoustic device according to one aspect of the present invention is an acoustic device arranged on a substrate, and includes a vibration unit and a plurality of support members. The vibration unit has a piezoelectric element and a vibration plate to which the piezoelectric element is bonded, and vibrates due to expansion and contraction of the piezoelectric element. The plurality of support members support the vibration unit on the substrate, and vibrate due to vibration of the vibration unit. The vibration plate includes a first region to which the piezoelectric element is bonded, and a pair of second regions located on both sides of the first region. The plurality of support members are each arranged in a corresponding one of the pair of second regions. The resonant frequency of the vibration unit is different from the resonant frequency of the plurality of support members.

[0006] In the above aspect, the resonant frequency of the vibration unit is different from the resonant frequency of the multiple support members. Therefore, the sound pressure increases at the resonant frequency of the vibration unit and the resonant frequency of the multiple support members. As a result, the above aspect improves the sound pressure characteristics in a wide frequency band.

[0007] In one of the above aspects, each support member may have a first portion connected to the diaphragm, a second portion connected to the base material, and a third portion located between the first portion and the second portion. The third portion may have a partially smaller cross-sectional area. In a configuration in which each support member has a third portion with a partially small cross-sectional area, the resonant frequency of each support member changes depending on the shape, i.e., the cross-sectional area, of the third portion, and therefore, in this configuration, the resonant frequency of each support member can be easily and reliably adjusted to a desired frequency.

[0008] In one aspect, each support member may have a fourth portion. The fourth portion may be located between the first portion and the second portion and may have a partially smaller cross-sectional area. In a configuration in which each support member has a fourth portion with a partially smaller cross-sectional area, the resonant frequency of each support member varies depending on the shape of the fourth portion, i.e., the cross-sectional area, as well as the shape of the third portion, so that in this configuration, the resonant frequency of each support member can be more easily and reliably adjusted to a desired frequency.

[0009] In the above aspect, the diaphragm may include a main surface to which each of the support members is connected. Each of the support members may extend in a direction intersecting with an imaginary plane including the main surface. A configuration in which each support member extends in a direction intersecting an imaginary plane including the main surface can reduce the size of the acoustic device when viewed in a direction perpendicular to the main surface.

[0010] In the above aspect, the diaphragm may include a main surface to which each of the support members is connected. Each of the support members may extend in a direction parallel to an imaginary plane including the main surface. A configuration in which each support member extends in a direction parallel to an imaginary plane including the main surface can reduce the size of the acoustic device in a direction perpendicular to the main surface.

[0011] In the above aspect, the diaphragm and each of the support members may be made of metal. Effect of the Invention

[0012] One aspect of the present invention provides an acoustic device that improves sound pressure characteristics over a wide frequency range. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing a cross-sectional configuration of an acoustic device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing a cross-sectional configuration of the piezoelectric element according to this embodiment. [Diagram 3] FIG. 3 is a diagram showing frequency characteristics of the acoustic device according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing a cross-sectional configuration of an acoustic device according to a second embodiment. [Diagram 5] FIG. 5 is a diagram showing frequency characteristics of the acoustic device according to the second embodiment. [Figure 6] FIG. 6 is a diagram showing a cross-sectional configuration of an acoustic device according to a third embodiment. [Figure 7] FIG. 7 is a diagram showing a cross-sectional configuration of an acoustic device according to a fourth embodiment. [Figure 8] FIG. 8 is an enlarged view showing each supporting member according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings, the same or corresponding elements are given the same reference numerals, and duplicated description will be omitted as appropriate.

[0015] First embodiment The configuration of an acoustic device 1 according to a first embodiment will be described with reference to Figs. 1 to 3. Fig. 1 is a diagram showing a cross-sectional configuration of the acoustic device 1 according to the first embodiment. Fig. 2 is a diagram showing a cross-sectional configuration of a piezoelectric element 10 according to this embodiment. Fig. 3 is a diagram showing frequency characteristics of the acoustic device 1 according to the first embodiment. The frequency characteristics of the acoustic device 1 refer to the relationship between frequency and amplitude in the acoustic device 1.

[0016] As shown in Fig. 1, the acoustic device 1 is disposed on a base material B. The acoustic device 1 vibrates relative to the base material B to output sound pressure. The acoustic device 1 is used, for example, as a speaker or a buzzer. The acoustic device 1 includes a vibration unit 2 and a plurality of support members 4a, 4b that support the vibration unit 2 on the base material B. In this embodiment, the acoustic device 1 includes a pair of support members 4a, 4b.

[0017] The vibration unit 2 has a piezoelectric element 10 and a vibration plate 30 to which the piezoelectric element 10 is bonded. The piezoelectric element 10 is, for example, a bimorph type piezoelectric element. As shown in Fig. 2, the piezoelectric element 10 has a piezoelectric body 11 and a plurality of external electrodes 13, 14, and 15. In this embodiment, the piezoelectric element 10 has three external electrodes 13, 14, and 15.

[0018] The piezoelectric element 11 has a rectangular parallelepiped shape. The rectangular parallelepiped shape includes, for example, a rectangular parallelepiped shape with chamfered corners and ridges, and a rectangular parallelepiped shape with rounded corners and ridges. The piezoelectric element 11 has a pair of main surfaces 11a, 11b facing each other, and four side surfaces 11c connecting the pair of main surfaces 11a, 11b to each other.

[0019] Each of the principal surfaces 11a, 11b has a rectangular shape having a pair of long sides and a pair of short sides. The length of the piezoelectric body 11 in the direction of the long sides of the principal surface 11a is, for example, 10 mm or more and 70 mm or less. The length of the piezoelectric body 11 in the direction of the short sides of the principal surface 11a is, for example, 10 mm or more and 50 mm or less. The length of the piezoelectric body 11 in the opposing direction of the pair of principal surfaces 11a, 11b is, for example, 0.2 mm or more and 1.0 mm or less.

[0020] The piezoelectric element 11 includes a plurality of stacked piezoelectric layers 12a, 12b, 12c, and 12d. The plurality of piezoelectric layers 12a, 12b, 12c, and 12d are stacked in this order. The stacking direction of the plurality of piezoelectric layers 12a, 12b, 12c, and 12d coincides with the opposing direction of the pair of main surfaces 11a and 11b. Hereinafter, the stacking direction of the plurality of piezoelectric layers 12a, 12b, 12c, and 12d is referred to as the stacking direction. The piezoelectric layer 12a has a main surface 11a. The piezoelectric layer 12d has a main surface 11b. The piezoelectric layers 12b and 12c are located between the piezoelectric layer 12a and the piezoelectric layer 12d. In this embodiment, the thicknesses of the piezoelectric layers 12a, 12b, 12c, and 12d are equal. The equality includes the range of manufacturing error.

[0021] Each of the piezoelectric layers 12a, 12b, 12c, and 12d is made of a piezoelectric material. In this embodiment, each of the piezoelectric layers 12a, 12b, 12c, and 12d is made of a piezoelectric ceramic material. For example, PZT [Pb(Zr, Ti)O3], PT (PbTiO3), PLZT [(Pb, La) (Zr, Ti)O3], or barium titanate (BaTiO3) is used as the piezoelectric ceramic material. Each of the piezoelectric layers 12a, 12b, 12c, and 12d is made of a sintered ceramic green sheet containing the above-mentioned piezoelectric ceramic material, for example. In the actual piezoelectric element 11, each of the piezoelectric layers 12a, 12b, 12c, and 12d is integrated to such an extent that the boundaries between the piezoelectric layers 12a, 12b, 12c, and 12d are not recognizable.

[0022] In the piezoelectric element 10, the external electrodes 13, 14, and 15 are disposed on the main surface 11a. The external electrodes 13, 14, and 15 are arranged along one short side of the main surface 11a in the order of the external electrode 13, the external electrode 14, and the external electrode 15. The external electrodes 13 and 14 are adjacent to each other in the short side direction of the main surface 11a. The external electrodes 14 and 15 are adjacent to each other in the short side direction of the main surface 11a. In the short side direction of the main surface 11a, the distance between the external electrodes 14 and 15 is longer than the distance between the external electrodes 13 and 14. The external electrodes 13, 14, and 15 are spaced apart from all edges of the main surface 11a when viewed from the stacking direction.

[0023] Each of the external electrodes 13, 14 has a rectangular shape when viewed from the stacking direction. In this embodiment, each corner of the rectangular shape is rounded. The external electrode 15 has a square shape when viewed from the stacking direction. The square shape includes, for example, a shape in which each corner is chamfered and a shape in which each corner is rounded. In this embodiment, each corner of the square shape is rounded. Each of the external electrodes 13, 14, 15 is made of a conductive material. For example, Ag, Pd, Pt, or an Ag-Pd alloy is used as the conductive material. Each of the external electrodes 13, 14, 15 is configured as a sintered body of a conductive paste containing the conductive material.

[0024] The piezoelectric element 10 includes a plurality of internal electrodes 16, 17, 18 disposed within the piezoelectric body 11. Each of the internal electrodes 16, 17, 18 is made of a conductive material. For example, Ag, Pd, Pt, or an Ag-Pd alloy is used as the conductive material. Each of the internal electrodes 16, 17, 18 is formed, for example, as a sintered body of a conductive paste containing the conductive material. In this embodiment, the external shape of each of the internal electrodes 16, 17, 18 is rectangular.

[0025] The internal electrodes 16, 17, 18 are laminated in this order. That is, the internal electrodes 16, 17, 18 are arranged in different layers in the lamination direction. The internal electrodes 16, 17, 18 face each other with a gap in the lamination direction. The internal electrodes 16, 17, 18 are not exposed on the surface of the piezoelectric element 11. That is, the internal electrodes 16, 17, 18 are not exposed on the side surfaces 11c. The internal electrodes 16, 17, 18 are separated from all edges of the main surfaces 11a, 11b when viewed from the lamination direction.

[0026] The internal electrode 16 is located between the piezoelectric layer 12a and the piezoelectric layer 12b. The internal electrode 17 is located between the piezoelectric layer 12b and the piezoelectric layer 12c. The internal electrode 18 is located between the piezoelectric layer 12c and the piezoelectric layer 12d.

[0027] The external electrode 13 is electrically connected to the internal electrode 16 and the multiple connecting conductors 21 through multiple via conductors 24. The multiple connecting conductors 21 are located in the same layer as the internal electrodes 17, 18. Specifically, each connecting conductor 21 is located in an opening formed in each internal electrode 17, 18. Each opening is formed at a position corresponding to the external electrode 13 when viewed from the stacking direction. That is, each connecting conductor 21 is surrounded by each internal electrode 17, 18 when viewed from the stacking direction. Each connecting conductor 21 is spaced apart from each internal electrode 17, 18.

[0028] Each connecting conductor 21 faces the external electrode 13 in the stacking direction, and is arranged at a position overlapping with the external electrode 13 when viewed from the stacking direction. Each connecting conductor 21 faces the internal electrode 16 in the stacking direction, and is arranged at a position overlapping with the internal electrode 16 when viewed from the stacking direction. Each of the multiple via conductors 24 is located between the external electrode 13, the internal electrode 16, and the multiple connecting conductors 21, and is arranged at a position overlapping with the external electrode 13 when viewed from the stacking direction. Each of the multiple via conductors 24 penetrates the corresponding piezoelectric layers 12a, 12b, and 12c in the stacking direction.

[0029] The external electrode 14 is electrically connected to the internal electrode 18 and the multiple connection conductors 22 through multiple via conductors 25. The multiple connection conductors 22 are located in the same layer as the internal electrodes 16 and 17. Specifically, each connection conductor 22 is located in an opening formed in each internal electrode 16 and 17. Each opening is formed at a position corresponding to the external electrode 14 when viewed from the stacking direction. That is, each connection conductor 22 is surrounded by each internal electrode 16 and 17 when viewed from the stacking direction. Each connection conductor 22 is spaced from each internal electrode 16 and 17. The connection conductors 21 and 22 located in the same layer as the internal electrode 17 are arranged adjacent to each other in the same opening and are spaced from each other.

[0030] Each connecting conductor 22 faces the external electrode 14 in the stacking direction, and is arranged at a position overlapping with the external electrode 14 when viewed from the stacking direction. Each connecting conductor 22 faces the internal electrode 18 in the stacking direction, and is arranged at a position overlapping with the internal electrode 18 when viewed from the stacking direction. Each of the multiple via conductors 25 is located between the external electrode 14, the internal electrode 18, and the multiple connecting conductors 22, and is arranged at a position overlapping with the external electrode 14 when viewed from the stacking direction. Each of the multiple via conductors 25 penetrates the corresponding piezoelectric layers 12a, 12b, and 12c in the stacking direction.

[0031] The external electrode 15 is electrically connected to the internal electrode 17 and the multiple connecting conductors 23 through multiple via conductors 26. The multiple connecting conductors 23 are located in the same layer as the internal electrodes 16, 18. Specifically, each connecting conductor 23 is located in an opening formed in each internal electrode 16, 18. Each opening is formed at a position corresponding to the external electrode 15 when viewed from the stacking direction. In other words, the entire edge of each connecting conductor 23 is surrounded by each internal electrode 16, 18 when viewed from the stacking direction. Each opening is formed at a position corresponding to the external electrode 15 when viewed from the stacking direction.

[0032] Each connecting conductor 23 faces the external electrode 15 in the stacking direction, and is arranged at a position overlapping with the external electrode 15 when viewed from the stacking direction. Each connecting conductor 23 faces the internal electrode 17 in the stacking direction, and is arranged at a position overlapping with the internal electrode 17 when viewed from the stacking direction. Each of the multiple via conductors 26 is located between the external electrode 15, the internal electrode 17, and the multiple connecting conductors 23, and is arranged at a position overlapping with the external electrode 15 when viewed from the stacking direction. Each of the multiple via conductors 26 penetrates the corresponding piezoelectric layers 12a, 12b, and 12c in the stacking direction.

[0033] Each of the connecting conductors 21 and 22 has a rectangular shape when viewed from the stacking direction. In this embodiment, each corner of the rectangular shape is rounded. Each of the connecting conductors 23 has a square shape when viewed from the stacking direction. In this embodiment, each corner of the square shape is rounded.

[0034] The connection conductors 21, 22, 23 and the via conductors 24, 25, 26 are made of a conductive material. For example, Ag, Pd, Pt, or an Ag-Pd alloy is used as the conductive material. The connection conductors 21, 22, 23 and the via conductors 24, 25, 26 are formed as a sintered body of a conductive paste containing the conductive material. The via conductors 24, 25, 26 are formed by sintering a conductive paste filled in through holes formed in ceramic green sheets for forming the corresponding piezoelectric layers 12a, 12b, 12c.

[0035] No conductor electrically connected to the internal electrodes 16, 17, 18 is disposed on the principal surface 11b of the piezoelectric element 11. In this embodiment, when the principal surface 11b is viewed from the stacking direction, the entire principal surface 11b is exposed. The principal surfaces 11a and 11b are natural surfaces. The natural surfaces are surfaces formed by the surfaces of crystal grains grown by firing.

[0036] No conductor electrically connected to the internal electrodes 16, 17, 18 is disposed on each side surface 11c of the piezoelectric element 11. In this embodiment, when each side surface 11c is viewed from a direction intersecting the stacking direction, the entire side surface 11c is exposed. In this embodiment, each side surface 11c is also a natural surface.

[0037] In the piezoelectric layer 12b, a region sandwiched between the internal electrode 16 connected to the external electrode 13 and the internal electrode 17 connected to the external electrode 15 constitutes a first piezoelectric active region 19. In the piezoelectric layer 12c, a region sandwiched between the internal electrode 18 connected to the external electrode 14 and the internal electrode 17 connected to the external electrode 15 constitutes a second piezoelectric active region 20.

[0038] The first active region 19 and the second active region 20 are polarized in the same direction, for example, by applying voltages of opposite polarities to the external electrodes 13 and 14 while the external electrode 15 is connected to ground. The first active region 19 is polarized, for example, in a direction from the internal electrode 16 to the internal electrode 17, and the second active region 20 is polarized, for example, in a direction from the internal electrode 17 to the internal electrode 18.

[0039] When the piezoelectric element 10 is driven, for example, voltages of the same polarity are applied to the external electrodes 13 and 14, and a voltage of a different polarity from the external electrodes 13 and 14 is applied to the external electrode 15. As a result, a voltage in the same direction as the polarization direction is applied to one of the first active region 19 and the second active region 20, causing it to expand in a direction intersecting the stacking direction, and a voltage in the opposite direction to the polarization direction is applied to the other, causing it to contract in a direction intersecting the stacking direction. The piezoelectric element 10 flexurally vibrates in the stacking direction due to the expansion of one of the first active region 19 and the second active region 20 and the contraction of the other. When an AC voltage is applied to the external electrodes 13 and 14 and the external electrode 15, the polarity of the voltage applied to the external electrodes 13 and 14 and the polarity of the voltage applied to the external electrode 15 are alternately inverted, so that the piezoelectric element 10 flexurally vibrates in the stacking direction.

[0040] In this embodiment, the vibration plate 30 has a plate shape. As shown in FIG. 1, the vibration plate 30 includes a pair of main surfaces 30a, 30b facing each other, and a pair of side surfaces 30c connecting the pair of main surfaces 30a, 30b. In this embodiment, the piezoelectric element 10 is bonded to the vibration plate 30 so that the main surface 11b faces the main surface 30b. For example, the piezoelectric element 10 may face the vibration plate 30 with an adhesive layer sandwiched therebetween. The adhesive layer bonds the piezoelectric element 10 and the vibration plate 30 to each other. The vibration plate 30 is made of metal or resin. The vibration plate 30 is made of aluminum, for example. The vibration plate 30 may be made of stainless steel (for example, SUS304) or Ni-Fe alloy (for example, 42 alloy). The diaphragm 30 may be made of, for example, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), polycarbonate resin, polyacetal resin, or PEEK (polyether ether ketone) resin.

[0041] The vibration unit 2 vibrates in response to the flexural vibration of the piezoelectric element 10. The flexural vibration of the piezoelectric element 10 causes the vibration plate 30 to flexibly vibrate in a direction perpendicular to the main surface 30b. The flexural vibration of the piezoelectric element 10 causes the vibration unit 2 to flexibly vibrate in a direction perpendicular to the main surface 30b. Hereinafter, the direction perpendicular to the main surface 30b is referred to as a first direction D1. In this embodiment, the first direction D1 coincides with the stacking direction.

[0042] The pair of support members 4a, 4b support the vibration unit 2 on the base material B. The pair of support members 4a, 4b are spaced apart from each other. When each of the support members 4a, 4b supports the vibration unit 2 on the base material B, the main surface 30b faces the base material B. Hereinafter, the direction in which the pair of support members 4a, 4b are spaced apart is referred to as a second direction D2. Each of the support members 4a, 4b is made of, for example, metal or resin. Each of the support members 4a, 4b is made of, for example, aluminum. Each of the support members 4a, 4b may be made of, for example, stainless steel (for example, SUS304) or Ni-Fe alloy (for example, 42 alloy). Each of the support members 4a, 4b may be made of, for example, ABS resin (acrylonitrile-butadiene-styrene copolymer resin), polycarbonate resin, polyacetal resin, or PEEK (polyether ether ketone) resin.

[0043] The distance between the main surface 30a and the main surface 30b in the first direction D1 is, for example, 0.1 mm or more and 2 mm or less. This distance is the thickness of the diaphragm 30. The distance between the pair of side surfaces 30c in the second direction D2 is, for example, 30 mm or more and 200 mm or less. The distance between one edge of the pair of main surfaces 30a, 30b and the other edge of the pair of main surfaces 30a, 30b in a direction perpendicular to the second direction D2 as viewed from the first direction D1 is, for example, 10 mm or more and 100 mm or less. Hereinafter, the direction perpendicular to the second direction D2 as viewed from the first direction D1 is referred to as a third direction D3.

[0044] The vibration plate 30 includes a first region 31 to which the piezoelectric element 10 is bonded, and a pair of second regions 32, 33 located on both sides of the first region. The second region 32 includes, for example, one end of the vibration plate 30 in the second direction D2. The second region 33 includes, for example, the other end of the vibration plate 30 in the second direction D2. The support member 4a is disposed in the corresponding second region 32 of the pair of second regions 32, 33. The support member 4b is disposed in the corresponding second region 33 of the pair of second regions 32, 33.

[0045] Each of the support members 4a, 4b has a first portion 41 connected to the diaphragm 30, a second portion 42 connected to the base material B, and a third portion 43 located between the first portion 41 and the second portion 42. The first portion 41 faces the second portion 42 with the third portion 43 interposed therebetween.

[0046] In this embodiment, each of the support members 4a, 4b is connected to the main surface 30b. Each of the support members 4a, 4b extends in a direction intersecting with a virtual plane P1 including the main surface 30b. For example, each of the support members 4a, 4b has a plate shape and extends in a first direction D1. Each of the support members 4a, 4b includes a pair of main surfaces 40a facing each other in the second direction D2 and a pair of side surfaces 40b facing each other in the first direction D1.

[0047] The first portion 41 is connected to the diaphragm 30 at one side surface 40b. The second portion 42 is connected to the base material B at the other side surface 40b. The distance between one main surface 40a and the other main surface 40a in the second direction D2 is, for example, 5 mm or more and 30 mm or less. This distance is the thickness of the first portion 41 and the second portion 42 of each of the support members 4a, 4b. The distance between one side surface 40b and the other side surface 40b in the first direction D1 is, for example, 5 mm or more and 100 mm or less. The distance between one edge of the main surface 40a and the other edge of the main surface 40a in the third direction D3 is, for example, 10 mm or more and 100 mm or less.

[0048] In this embodiment, each of the support members 4a, 4b is located at an end in the second direction D2 of the diaphragm 30. Each of the side surfaces 30c and each of the main surfaces 40a are included in the same imaginary plane (not shown).

[0049] In this embodiment, the length of the diaphragm 30 in the third direction D3 is equal to the length of each of the support members 4a and 4b in the third direction D3. The diaphragm 30 includes a pair of side surfaces (not shown) facing each other in the third direction D3. Each of the support members 4a and 4b includes a pair of side surfaces (not shown) facing each other in the third direction D3. Each of the side surfaces of the diaphragm 30 and each of the side surfaces of the support members 4a and 4b are included in the same imaginary plane (not shown).

[0050] The third portion 43 has a pair of grooves 43a including both ends of each of the support members 4a, 4b in the third direction D3. Each of the main surfaces 40a includes a surface that constitutes the groove 43a. The groove 43a extends from one to the other of a pair of side surfaces that face each other in the third direction D3 of each of the support members 4a, 4b. The pair of grooves 43a are located symmetrically with respect to a virtual plane P2 that is located at an equal distance from one main surface 40a and the other main surface 40a. In the support member 4a, the pair of grooves 43a are formed so that their positions match in the direction in which the first portion 41 and the second portion 42 face each other. In the support member 4b, the pair of grooves 43a are also formed so that their positions match in the direction in which the first portion 41 and the second portion 42 face each other.

[0051] In this embodiment, the surfaces defining the pair of grooves 43a are located symmetrically with respect to the imaginary plane P2. Each groove 43a is formed in the thickness direction of each of the support members 4a and 4b. Each of the main surfaces 40a includes a curved surface 43b defining each of the grooves 43a. The curved surface 43b has a semicircular arc shape when viewed from the third direction D3, for example.

[0052] The third portion 43 has a cross-sectional area that is partially small in a cross section perpendicular to the direction in which the first portion 41 and the second portion 42 face each other. Hereinafter, the cross section perpendicular to the direction in which the first portion 41 and the second portion 42 face each other is referred to as a cross section. The cross-sectional area of ​​the cross section is referred to as a cross-sectional area. In this embodiment, the direction in which the first portion 41 and the second portion 42 face each other coincides with the first direction D1. The third portion 43 has a cross-sectional area that is partially small at the positions of the pair of grooves 43a. The cross-sectional area of ​​the third portion 43 changes depending on the shape of the grooves 43a. The cross-sectional area of ​​the third portion 43 changes depending on the position of the cross section in the direction in which the first portion 41 and the second portion 42 face each other. Specifically, the cross-sectional area of ​​the third portion 43 changes depending on the distance between one curved surface 43b and the other curved surface 43b in the second direction D2. The distance is the thickness of the third portion 43. The minimum value of the thickness of the third portion 43 is, for example, 0.1 mm or more and 3 mm or less. The position in the second direction D2 where the thickness of the third portion 43 is minimum is, for example, 10 mm or more and 50 mm or less away from the main surface 30b. Each of the support members 4a, 4b is deflected and deformed at the third portion 43.

[0053] The pair of support members 4a, 4b vibrate due to the vibration of the vibration unit 2. In this embodiment, the pair of support members 4a, 4b flexibly vibrate in the second direction D2 due to the flexural vibration of the vibration unit 2. When the vibration unit 2 flexibly deforms in the first direction D1, the acoustic device 1 flexibly vibrates such that the pair of support members 4a, 4b flexibly deform toward each other inward in the second direction D2.

[0054] The frequency characteristics of the acoustic device 1 according to the first embodiment will be described with reference to Fig. 3. The horizontal axis of Fig. 3 indicates the frequency (Hz) of vibration, and the vertical axis indicates the amplitude (μm) of vibration. Fig. 3 shows the frequency characteristics of the acoustic device 1 and the frequency characteristics of the vibration unit 2 and the pair of support members 4a, 4b that constitute the acoustic device 1.

[0055] The resonant frequency of the vibration unit 2 is different from the resonant frequency of the pair of support members 4a, 4b. The resonant frequency of the vibration unit 2 and the resonant frequency of the pair of support members 4a, 4b are compared based on their respective lowest resonant frequencies. The lowest resonant frequency of the vibration unit 2 is, for example, 1 kHz. W1 indicates an amplitude peak in a frequency band centered on the lowest resonant frequency of the vibration unit 2. In the frequency band of W1, the sound pressure characteristics of the vibration unit 2 are improved. The lowest resonant frequency of the pair of support members 4a, 4b is, for example, 1.5 kHz. W2 indicates an amplitude peak in a frequency band centered on the lowest resonant frequency of the pair of support members 4a, 4b. In the frequency band of W2, the sound pressure characteristics of the pair of support members 4a, 4b are improved.

[0056] 3, the frequency characteristics of the acoustic device 1 are a combination of the frequency characteristics of the vibration unit 2 and the frequency characteristics of the pair of support members 4a, 4b. Therefore, in the acoustic device 1, the sound pressure characteristics are improved in a frequency band centered on the lowest resonance frequency of the vibration unit 2 and in a frequency band centered on the lowest resonance frequency of the pair of support members 4a, 4b.

[0057] In the acoustic device 1 according to this embodiment, the resonant frequency of the vibration unit 2 is different from the resonant frequency of the pair of support members 4a, 4b. Therefore, the sound pressure increases at the resonant frequency of the vibration unit 2 and the resonant frequency of the pair of support members 4a, 4b. As a result, the acoustic device 1 improves the sound pressure characteristics over a wide frequency band.

[0058] In the acoustic device 1 according to this embodiment, each of the support members 4a, 4b has a first portion 41 connected to the diaphragm 30, a second portion 42 connected to the base material, and a third portion 43 located between the first portion 41 and the second portion 42. The third portion 43 has a partially small cross-sectional area. In a configuration in which each of the support members 4a, 4b has a third portion 43 with a partially small cross-sectional area, the resonant frequency of each of the support members 4a, 4b varies depending on the shape, i.e., the cross-sectional area, of the third portion 43. Therefore, in the acoustic device 1, the resonant frequency of each of the support members 4a, 4b can be easily and reliably adjusted to a desired frequency.

[0059] In the acoustic device 1 according to this embodiment, the diaphragm 30 includes a main surface 30b to which the support members 4a, 4b are connected. The support members 4a, 4b extend in a direction intersecting with an imaginary plane P1 including the main surface 30b. A configuration in which the support members 4a, 4b extend in a direction intersecting the imaginary plane P1 including the main surface 30b can reduce the size of the acoustic device 1 when viewed from the first direction D1.

[0060] In the acoustic device 1 according to this embodiment, each groove 43a is defined by a curved surface 43b. Since each groove 43a is defined by a curved surface 43b, when each support member 4a, 4b undergoes flexural deformation at the third portion 43, stress generated in the third portion 43 is dispersed. Therefore, in the acoustic device 1, the third portion 43 is less likely to undergo plastic deformation.

[0061] Second Embodiment The configuration of an acoustic device 1 according to a second embodiment will be described with reference to Figs. 4 and 5. Fig. 4 is a diagram showing a cross-sectional configuration of the acoustic device 1 according to the second embodiment. Fig. 5 is a diagram showing frequency characteristics of the acoustic device 1 according to the second embodiment. The second embodiment is generally similar to or the same as the first embodiment. The second embodiment differs from the first embodiment in that each of the support members 4a, 4b has a fourth portion 44.

[0062] In this embodiment, each support member 4a, 4b has a third portion 43 located between the first portion 41 and the second portion 42 and having a partially smaller cross-sectional area, and a fourth portion 44 located between the first portion 41 and the second portion 42.

[0063] The fourth portion 44 has a pair of grooves 44a including both ends of each of the support members 4a, 4b in the third direction D3. Each of the main surfaces 40a includes a surface that constitutes the groove 44a. The groove 44a extends from one to the other of a pair of side surfaces of each of the support members 4a, 4b that face each other in the third direction D3. The pair of grooves 44a are located symmetrically with respect to the imaginary plane P2. In the support member 4a, the pair of grooves 44a are formed so that their positions match in the direction in which the first portion 41 and the second portion 42 face each other. In the support member 4b, the pair of grooves 44a are also formed so that their positions match in the direction in which the first portion 41 and the second portion 42 face each other.

[0064] In this embodiment, the surfaces that define the pair of grooves 44a are located symmetrically with respect to the imaginary plane P2. Each groove 44a is formed in the thickness direction of each support member 4a, 4b. Each main surface 40a includes a curved surface 44b that defines each groove 44a. The curved surface 44b has a semicircular arc shape when viewed from the third direction D3, for example.

[0065] The fourth portion 44 has a partially small cross-sectional area at the position of the pair of grooves 44a. In this embodiment, the cross-sectional area of ​​the fourth portion 44 is different from the cross-sectional area of ​​the third portion 43. The cross-sectional area of ​​the fourth portion 44 is larger than the cross-sectional area of ​​the third portion 43. The cross-sectional area of ​​the fourth portion 44 changes according to the shape of the groove 44a. The cross-sectional area of ​​the fourth portion 44 changes according to the position of the cross section. Specifically, the cross-sectional area of ​​the fourth portion 44 changes according to the distance between one curved surface 43b and the other curved surface 43b in the second direction D2. The distance is the thickness of the fourth portion 44. The minimum value of the thickness of the fourth portion 44 is, for example, 0.1 mm or more and 3 mm or less. The position where the thickness of the fourth portion 44 is minimum in the second direction D2 is, for example, 5 mm or more and 40 mm or less away from the position where the thickness of the third portion 43 is minimum. Each of the support members 4a, 4b is deflected and deformed at the third portion 43 and the fourth portion 44.

[0066] The frequency characteristics of the acoustic device 1 according to the second embodiment will be described with reference to FIG. 5. FIG. 5 shows the relationship between frequency and amplitude in the acoustic device 1 according to the second embodiment. The pair of support members 4a, 4b flex and deform in multiple portions, and therefore show multiple amplitude peaks. W3 shows the amplitude peak in a frequency band centered on a resonance frequency different from the lowest resonance frequency of the pair of support members 4a, 4b. The resonance frequency different from the lowest resonance frequency of the pair of support members 4a, 4b is, for example, 1 kHz. In the frequency band of W3, the frequency characteristics of the pair of support members 4a, 4b are improved.

[0067] 5, the frequency characteristics of the acoustic device 1 are a combination of the frequency characteristics of the vibration unit 2 and the frequency characteristics of the pair of support members 4a, 4b. Therefore, in the acoustic device 1, the sound pressure characteristics are improved in a frequency band centered on the lowest resonance frequency of the vibration unit 2, a frequency band centered on the lowest resonance frequency of the pair of support members 4a, 4b, and a frequency band centered on a resonance frequency different from the lowest resonance frequency of the pair of support members 4a, 4b.

[0068] In the acoustic device 1 according to this embodiment, each of the support members 4a, 4b has a fourth portion 44. The fourth portion 44 is located between the first portion 41 and the second portion 42, and has a partially small cross-sectional area. In a configuration in which each of the support members 4a, 4b has a fourth portion 44 with a partially smaller cross-sectional area, the resonant frequency of each of the support members 4a, 4b varies depending on the shape, i.e., the cross-sectional area, of the fourth portion 44 as well as the shape of the third portion 43. Therefore, in the acoustic device 1, the resonant frequency of each of the support members 4a, 4b can be more easily and reliably adjusted to a desired frequency.

[0069] Third embodiment The configuration of an acoustic device 1 according to a third embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing a cross-sectional configuration of an acoustic device 1 according to a third embodiment. The third embodiment is generally similar to or the same as the first embodiment. The third embodiment differs from the first embodiment in that the support members 4a, 4b extend in a direction parallel to a virtual plane P1 including the main surface 30b.

[0070] In this embodiment, the diaphragm 30 includes a main surface 30b to which the support members 4a and 4b are connected, and each of the support members 4a and 4b extends in a direction parallel to a virtual plane P1 including the main surface 30b. For example, each of the support members 4a and 4b has a plate shape and extends in the second direction D2. Each of the support members 4a and 4b includes a pair of main surfaces 40a facing each other in the first direction D1 and a pair of side surfaces 40b facing each other in the second direction D2. The first portion 41 is connected to the diaphragm 30 at one of the main surfaces 40a. One of the side surfaces 40b is connected to the base material B at the second portion 42.

[0071] The pair of support members 4a, 4b vibrate due to the vibration of the vibration unit 2. In this embodiment, the pair of support members 4a, 4b flexibly vibrate in the first direction D1 due to the flexural vibration of the vibration unit 2. In this embodiment, the pair of support members 4a, 4b flexibly vibrate in the first direction D1 due to the flexural vibration of the vibration unit 2. When the vibration unit 2 flexibly deforms in one direction of the first direction D1, the acoustic device 1 flexibly vibrates such that the pair of support members 4a, 4b flexibly deform in one direction of the first direction D1.

[0072] In the acoustic device 1 according to this embodiment, the diaphragm 30 includes a main surface 30b to which the support members 4a, 4b are connected. The support members 4a, 4b extend in a direction parallel to an imaginary plane P1 including the main surface 30b. A configuration in which each of the support members 4a, 4b extends in a direction parallel to the imaginary plane P1 including the main surface 30b can reduce the size of the acoustic device 1 in the first direction D1.

[0073] (Fourth embodiment) 7 is a diagram showing a cross-sectional configuration of an acoustic device 1 according to a fourth embodiment. The fourth embodiment is generally similar or the same as the second and third embodiments. The fourth embodiment differs from the second embodiment in that each of the support members 4a, 4b extends in a direction parallel to a virtual plane P1 including the main surface 30b. The fourth embodiment differs from the third embodiment in that each of the support members 4a, 4b has a fourth portion 44.

[0074] Although the embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0075] (Modification) Fig. 8 is an enlarged view showing a cross-sectional configuration of each of the support members 4a and 4b according to the modified example. Fig. 8 is an enlarged view of the third portion 43. The third portion 43 does not have to have a pair of grooves 43a. In a modification shown in Fig. 8(a), the third portion 43 has one groove 43a including both ends in the third direction D3. Although not shown, the fourth portion 44 may also have one groove 44a including both ends in the third direction D3, similar to the third portion 43. Each of the main surfaces 40a may not include the curved surfaces 43b constituting each of the grooves 43a in the third portion 43. In the modified example shown in (b) of FIG. 8, each of the main surfaces 40a includes, in the third portion 43, a pair of side surfaces 43c opening each of the grooves 43a, a bottom surface 43d constituting the bottom surface of each of the grooves 43a in the second direction D2, and a pair of curved surfaces 43e connecting the pair of side surfaces 43c and the bottom surface 43d to each other, as viewed from the third direction D3. Although not shown, each of the main surfaces 40a may include, in the fourth portion 44, a pair of side surfaces 44c opening each of the grooves 44a, a bottom surface 44d constituting the bottom surface of each of the grooves 44a in the second direction D2, and a pair of curved surfaces 44e connecting the pair of side surfaces 44c and the bottom surface 44d to each other, as viewed from the third direction D3. Each of the main surfaces 40a may not include the curved surface 43e connecting the pair of side surfaces 43c and the bottom surface 43d in the third portion 43. In the modified example shown in Fig. 8(c), each of the main surfaces 40a includes a side surface 43f connecting the pair of side surfaces 43c and the bottom surface 43d in the third portion 43. Although not shown, each of the main surfaces 40a may include a side surface 44f connecting the pair of side surfaces 44c and the bottom surface 44d in the fourth portion 44. The pair of grooves 43a may not reach the ends in the third direction D3 of the third portion 43. The pair of grooves 44a may not reach the ends in the third direction D3 of the third portion 43. The pair of grooves 43a may have different widths in the direction in which the first portion 41 and the second portion 42 face each other. The pair of grooves 43a may have different depths in the thickness direction of each of the support members 4a, 4b.

[0076] The piezoelectric element 10 may be a single-plate piezoelectric element that does not include the multiple internal electrodes 16, 17, and 18. In the piezoelectric element 10 that does not include the multiple internal electrodes 16, 17, and 18, external electrodes may be electrically connected to a pair of main surfaces 11a and 11b. That is, the vibration unit 2 may configure a vibrator with a unimorph structure. The vibration unit 2 may flexurally vibrate in the first direction D1 due to the expansion and contraction of the piezoelectric element 10.

[0077] The cross-sectional area of ​​the fourth portion 44 may be smaller than the cross-sectional area of ​​the third portion 43. The cross-sectional area of ​​the fourth portion 44 may be partially smaller. The cross-sectional area of ​​the fourth portion 44 may be equal to the cross-sectional area of ​​the third portion 43. The cross-sectional area of ​​the fourth portion 44 may be partially smaller.

[0078] Each of the support members 4a, 4b may further have a portion having a locally small cross-sectional area in addition to the third portion 43 and the fourth portion 44. That is, each of the support members 4a, 4b may have three or more portions having a locally small cross-sectional area. In a configuration in which each of the support members 4a, 4b has three or more portions with a partially small cross-sectional area, the resonant frequency of each of the support members 4a, 4b also changes depending on the shape, i.e., the cross-sectional area, of the three or more portions with a partially small cross-sectional area. Therefore, in this configuration, the resonant frequency of each of the support members 4a, 4b can be more easily and reliably adjusted to a desired frequency.

[0079] Each of the support members 4a, 4b may be divided into a plurality of portions in the third direction D3. For example, each of the support members 4a, 4b may be divided into a plurality of column-shaped portions spaced apart from each other in the third direction D3. [Explanation of symbols]

[0080] 1...acoustic device, 2...vibration unit, 4a, 4b...support member, 10...piezoelectric element, 30a, 30b...main surface, 30...diaphragm, 31...first region, 32, 33...second region, 41...first part, 42...second part, 43...third part, 44...fourth part, B...base material, P1, P2...virtual plane.

Claims

1. An acoustic device disposed on a substrate, A vibration unit including a piezoelectric element and a vibration plate to which the piezoelectric element is bonded, the vibration unit vibrating due to the expansion and contraction of the piezoelectric element; a plurality of support members that support the vibration unit on the base material and vibrate due to the vibration of the vibration unit; the vibration plate includes a first region to which the piezoelectric element is bonded, and a pair of second regions located on both sides of the first region, The plurality of support members are each disposed in a corresponding one of the pair of second regions, a resonant frequency of the vibration unit is different from a resonant frequency of the plurality of support members; the diaphragm includes a main surface to which each of the support members is connected; Each of the support members extends in a direction intersecting an imaginary plane including the main surface. Acoustic device.

2. Each of the support members is a first portion coupled to the diaphragm; A second portion coupled to the substrate; a third portion located between the first portion and the second portion and having a partially smaller cross-sectional area; 10. The acoustic device of claim 1, comprising:

3. The acoustic device according to claim 2 , wherein each of the support members has a fourth portion located between the first portion and the second portion and having a partially smaller cross-sectional area.

4. 4. The acoustic device according to claim 1, wherein the diaphragm and each of the support members are made of metal.

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