Acoustic device

Abstract

To provide an acoustic device in which the sound pressure characteristics in a desired frequency bandwidth can be easily adjusted.SOLUTION: An acoustic device AD includes a housing 1 and a piezoelectric element 20. The housing 1 includes: a bottom plate part 3; a top plate part 5 including a surface 6 facing the bottom plate part 3; and a side plate part 7 connecting the bottom plate part 3 and the top plate part 5 to each other. The piezoelectric element 20 is fixed to a surface 6 of the top plate part 5, away from the top plate part 5. The bottom plate part 3, the top plate part 5, and the side plate part 7 define a space S1, the top plate part 5 and the piezoelectric element 20 define a space S2. The top plate part 5 is provided with a plurality of opening parts OP leading to at least one of the space S1 and the space S2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an acoustic device including a piezoelectric element.

Background Art

[0002] Known acoustic devices include a housing, a diaphragm disposed within the housing, and a piezoelectric element disposed on the diaphragm (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One aspect of the present invention aims to provide an acoustic device in which sound pressure characteristics in a desired frequency band can be easily adjusted.

Means for Solving the Problems

[0005] An acoustic device according to one aspect of the present invention includes a housing and a piezoelectric element. The housing includes a bottom plate portion, a top plate portion including a surface facing the bottom plate portion, and side plate portions connecting the bottom plate portion and the top plate portion. The piezoelectric element is fixed away from the top plate portion on the surface included in the top plate portion. The bottom plate portion, the top plate portion, and the side plate portions define a first space, and the top plate portion and the piezoelectric element define a second space. A plurality of openings communicating with at least one of the first space or the second space are formed in the top plate portion.

[0006] In the above aspect, each of the first space and the second space functions as a resonance space. The above aspect includes a plurality of resonance spaces. Therefore, in one aspect, sound pressure characteristics in a desired frequency band can be easily adjusted.

[0007] In the above-described one aspect, the piezoelectric element may have a rectangular shape including a pair of first side edges facing each other and a pair of second side edges facing each other in a plan view. The piezoelectric element may be fixed to the above-described surface along each of the pair of first side edges. In the configuration where the piezoelectric element having the above-described rectangular shape is fixed to the above-described surface along each of the pair of first side edges, it is difficult to inhibit the displacement of the piezoelectric element, and the displacement of the piezoelectric element is surely transmitted to the top plate portion.

[0008] In the above-described one aspect, the first space and the second space may communicate with each other through a gap between the above-described surface included in the top plate portion and the pair of second side edges. In the configuration where the first space and the second space communicate with each other, the sound pressure characteristics in a desired frequency band can be adjusted more easily. The configuration in which the first space and the second space communicate with each other through the above-described gap easily realizes the configuration in which the first space and the second space communicate with each other.

[0009] In the above-described one aspect, the first space and the second space may communicate with each other. In the configuration where the first space and the second space communicate with each other, the sound pressure characteristics in a desired frequency band can be adjusted more easily.

[0010] In the above-described one aspect, the top plate portion may include a region facing the piezoelectric element. The plurality of openings may include the openings formed in the above-described region included in the top plate portion. The above-described openings formed in the region may communicate with the first space through the second space. In the configuration where the openings formed in the region included in the top plate portion and facing the piezoelectric element communicate with the first space through the second space, the sound pressure characteristics in a desired frequency band can be adjusted more easily.

[0011] In the above-described one aspect, the second space may be smaller than the first space. In the configuration where the second space is smaller than the first space, for example, the sound pressure characteristics in a desired low frequency band can be enhanced.

[0012] In the above one aspect, the plurality of openings may include an opening directly communicating with the first space and an opening directly communicating with the second space. In a configuration where the plurality of openings include an opening directly communicating with the first space and an opening directly communicating with the second space, the sound pressure characteristics in a desired frequency band can be adjusted more easily.

[0013] In the above one aspect, it may further include a wiring body electrically connected to the piezoelectric element. An opening through which the wiring body is inserted may be formed in the side plate portion. In a configuration where an opening through which the wiring body is inserted is formed in the side plate portion, the wiring body electrically connected to the piezoelectric element disposed in the housing can be surely disposed without interfering with the housing.

[0014] In the above one aspect, the housing may be composed of a first member including a bottom plate portion and a side plate portion and having a box shape with an opening, and a second member including a top plate portion and having a plate shape. The configuration in which the housing is composed of the above-described first member and second member realizes the housing simply and at low cost.

Effect of the Invention

[0015] One aspect of the present invention provides an acoustic device in which the sound pressure characteristics in a desired frequency band can be easily adjusted.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals will be used for the same elements or elements having the same function, and redundant descriptions will be omitted.

[0018] With reference to FIGS. 1 to 3, the configuration of the acoustic device AD according to the present embodiment will be described. FIG. 1 is a perspective view of the acoustic device according to the present embodiment. FIGS. 2 and 3 are diagrams showing the cross-sectional configuration of the acoustic device according to the present embodiment. The acoustic device AD includes a housing 1, a piezoelectric element 20, and a wiring body 50. The piezoelectric element 20 is disposed within the housing 1. The wiring body 50 is electrically and physically connected to the piezoelectric element 20.

[0019] The housing 1 includes a bottom plate portion 3, a top plate portion 5, and side plate portions 7. The top plate portion 5 includes a surface 6 facing the bottom plate portion 3. The side plate portions 7 connect the bottom plate portion 3 and the top plate portion 5. The housing 1 has, for example, a rectangular parallelepiped shape. The housing 1 may have a cylindrical shape or a disc shape in plan view. The rectangular parallelepiped shape includes, for example, a rectangular parallelepiped shape with chamfered corners and edges, or a rectangular parallelepiped shape with rounded corners and edges. In the configuration where the housing 1 has a rectangular parallelepiped shape, the bottom plate portion 3 and the top plate portion 5 have a rectangular shape, and the side plate portion 7 has a rectangular frame shape. The top plate portion 5 has a rectangular shape including a pair of long sides and a pair of short sides in plan view. The side plate portion 7 includes four walls 8. The bottom plate portion 3 and the side plate portion 7 are, for example, integrally formed with each other. The top plate portion 5 and the side plate portion 7 may be integrally formed with each other. The rectangular shape includes, for example, a shape with chamfered corners or a shape with rounded corners. The planar dimensions of the housing 1 are, for example, 25 mm × 15 mm. The thickness of the housing 1 is, for example, 2 mm.

[0020] As also shown in FIG. 4, the housing 1 is composed of, for example, a plurality of members 11, 13. The housing 1 is composed of, for example, a pair of members 11, 13. The member 11 has a box shape with an opening 11a. The member 13 has a plate shape. The member 11 includes the bottom plate portion 3 and the side plate portion 7. The member 13 includes the top plate portion 5. For example, when the member 11 includes a first member, the member 13 includes a second member. The member 13 covers the opening 11a. FIG. 4 is an exploded perspective view of the housing.

[0021] The housing 1, that is, the plurality of members 11, 13, is made of, for example, resin. The housing 1, that is, the plurality of members 11, 13, is made of, for example, acrylic resin or epoxy resin. The housing 1 (the plurality of members 11, 13) may be made of, for example, plastic. The member 11 and the member 13 may be made of the same resin as each other or may be made of different resins from each other. The plurality of members 11, 13 may be made of, for example, metal. The member 11 may be made of resin and the member 13 may be made of metal. The metal includes, for example, Ni - Fe alloy, Ni, brass, or stainless steel. The pair of members 11, 13 are adhered to each other. The member for adhering the pair of members 11, 13 is made of, for example, resin. The member for adhering the pair of members 11, 13 is made of, for example, acrylic resin or epoxy resin. The member for adhering the pair of members 11, 13 may be made of, for example, plastic.

[0022] As shown in FIGS. 5 and 6, the piezoelectric element 20 includes a piezoelectric body 21, a plurality of electrode layers 31, 32, 33, 34 disposed within the piezoelectric body 21, and a plurality of external electrodes 47, 49 disposed on the piezoelectric body 21. The piezoelectric element 20 includes, for example, four electrode layers 31, 32, 33, 34. The piezoelectric element 20 includes, for example, a pair of external electrodes 47, 49. The piezoelectric element 20 includes, for example, a stacked piezoelectric element. The piezoelectric element 20 includes, for example, a unimorph-type piezoelectric element. The piezoelectric element 20 may include a bimorph-type piezoelectric element. FIG. 5 is a diagram showing a cross-sectional configuration of the piezoelectric element. FIG. 6 is an exploded perspective view of the piezoelectric element.

[0023] The piezoelectric body 21 has, for example, a rectangular parallelepiped shape. The piezoelectric body 21 includes a pair of main surfaces 21a, 21b facing each other, a pair of side surfaces 21c facing each other, and a pair of side surfaces 21e facing each other. Each of the main surfaces 21a, 21b has a rectangular shape. Each of the main surfaces 21a, 21b has a rectangular shape having a pair of long sides and a pair of short sides. In plan view, the piezoelectric element 20 has a rectangular shape including a pair of end sides 22a facing each other and a pair of end sides 22b facing each other. The end side 22a corresponds to the short side of the main surface 21b, and the end side 22b corresponds to the long side of the main surface 21b. The end side 22a may correspond to the short side of the main surface 21a. The end side 22b may correspond to the long side of the main surface 21a. The pair of end sides 22a face each other in the direction in which the pair of side surfaces 21e face each other. The pair of end sides 22b face each other in the direction in which the pair of side surfaces 21c face each other. For example, when each end side 22a includes a first end side, each end side 22b includes a second end side.

[0024] The pair of side surfaces 21c and the pair of side surfaces 21e connect the pair of main surfaces 21a and 21b. The length of the piezoelectric element 21 in the direction in which the pair of side surfaces 21c face each other is, for example, 10 mm. The length of the piezoelectric element 21 in the direction in which the pair of side surfaces 21e face each other is, for example, 20 mm. The length of the piezoelectric element 21 in the direction in which the pair of main surfaces 21a and 21b face each other, that is, the thickness of the piezoelectric element 21 is, for example, 0.5 mm. Each of the main surfaces 21a and 21b and each of the side surfaces 21c and 21e may be indirectly adjacent to each other. In this case, a ridge portion is located between each of the main surfaces 21a and 21b and each of the side surfaces 21c and 21e.

[0025] The piezoelectric element 21 is configured by laminating a plurality of piezoelectric layers 23a, 23b, 23c, 23d, and 23e. The piezoelectric element 21 includes the plurality of laminated piezoelectric layers 23a, 23b, 23c, 23d, and 23e. In the present embodiment, the piezoelectric element 21 includes five piezoelectric layers 23a, 23b, 23c, 23d, and 23e. In the piezoelectric element 21, the plurality of piezoelectric layers 23a, 23b, 23c, 23d, and 23e are laminated in the direction in which the pair of main surfaces 21a and 21b face each other. The piezoelectric layer 23a includes the main surface 21a. The piezoelectric layer 23e includes the main surface 21b. The piezoelectric layers 23b, 23c, and 23d are located between the piezoelectric layer 23a and the piezoelectric layer 23e. The length of each of the piezoelectric layers 23a, 23b, 23c, 23d, and 23e in the direction in which the pair of main surfaces 21a and 21b face each other, that is, the thickness of each of the piezoelectric layers 23a, 23b, 23c, 23d, and 23e is, for example, 35 μm.

[0026] Each of the piezoelectric layers 23a, 23b, 23c, 23d, 23e is made of a piezoelectric ceramic material. The piezoelectric element 21 is made of a piezoelectric ceramic material. The piezoelectric ceramic material includes, for example, PZT [Pb(Zr,Ti)O3], PT (PbTiO3), PLZT [(Pb,La)(Zr,Ti)O3], PZN [Pb(Zn,Nb)O3], or barium titanate (BaTiO3). Each of the piezoelectric layers 23a, 23b, 23c, 23d, 23e is composed of, for example, a sintered body of a ceramic green sheet containing the above-described piezoelectric ceramic material. In the actual piezoelectric element 21, each of the piezoelectric layers 23a, 23b, 23c, 23d, 23e is integrated to such an extent that the boundaries between the piezoelectric layers 23a, 23b, 23c, 23d, 23e cannot be recognized.

[0027] The plurality of electrode layers 31, 32, 33, 34 are arranged at different positions (layers) in the direction in which the pair of main surfaces 21a, 21b face each other. The main surface 21a and the electrode layer 31 face each other with a gap in the direction in which the pair of main surfaces 21a, 21b face each other. The electrode layer 31 and the electrode layer 32 face each other with a gap in the direction in which the pair of main surfaces 21a, 21b face each other. The electrode layer 32 and the electrode layer 33 face each other with a gap in the direction in which the pair of main surfaces 21a, 21b face each other. The electrode layer 33 and the electrode layer 34 face each other with a gap in the direction in which the pair of main surfaces 21a, 21b face each other. The electrode layer 34 and the main surface 21b face each other with a gap in the direction in which the pair of main surfaces 21a, 21b face each other.

[0028] The electrode layer 31 is located between the piezoelectric layer 23a and the piezoelectric layer 23b. The electrode layer 32 is located between the piezoelectric layer 23b and the piezoelectric layer 23c. The electrode layer 33 is located between the piezoelectric layer 23c and the piezoelectric layer 23d. The electrode layer 34 is located between the piezoelectric layer 23d and the piezoelectric layer 23e. Each of the electrode layers 31, 32, 33, 34 is not exposed on the surface of the piezoelectric element 21. Each of the electrode layers 31, 32, 33, 34 is separated from the side surfaces 21c and 21e and is not exposed on the side surfaces 21c and 21e. Each of the electrode layers 31, 32, 33, 34 is separated from all the edges of the main surfaces 21a, 21b, that is, the four sides of the main surfaces 21a, 21b, when viewed in the direction in which the pair of main surfaces 21a, 21b face each other.

[0029] When viewed in the direction in which the pair of main surfaces 21a, 21b face each other, each of the electrode layers 31, 32, 33, 34 has a rectangular shape. When viewed in the direction in which the pair of main surfaces 21a, 21b face each other, each of the electrode layers 31, 32, 33, 34 has a rectangular shape having a pair of long sides and a pair of short sides. The long side direction of each of the electrode layers 31, 32, 33, 34 coincides with the direction in which the pair of side surfaces 21e face each other. The short side direction of each of the electrode layers 31, 32, 33, 34 coincides with the direction in which the pair of side surfaces 21c face each other. When viewed in the direction in which the pair of main surfaces 21a, 21b face each other, the outer edges of the electrode layers 31, 32, 33, 34 have the same shape as each other and coincide with each other. When viewed in the direction in which the pair of main surfaces 21a, 21b face each other, the four corners of each of the electrode layers 31, 32, 33, 34 are rounded and have a so-called R shape. The rounded corners do not mean corners formed by the intersection of two straight lines, but curved corners formed by connecting the ends of two straight lines with a curve.

[0030] Each of the electrode layers 31, 32, 33, 34 includes an internal electrode. Each of the electrode layers 31, 32, 33, 34 is made of a conductive material. The conductive material includes, for example, Ag, Pd, or an Ag-Pd alloy. Each of the electrode layers 31, 32, 33, 34 is configured, for example, as a sintered body of a conductive paste containing the above conductive material.

[0031] The plurality of external electrodes 47 and 49 are disposed on the main surface 21a. The external electrode 47 and the external electrode 49 are arranged in the direction in which a pair of side surfaces 21e face each other. The external electrode 47 and the external electrode 49 are adjacent to each other in the direction in which a pair of side surfaces 21e face each other. Each of the external electrodes 47 and 49 is separated from all the edges of the main surface 21a, that is, the four sides of the main surface 21a, when viewed in the direction in which the pair of main surfaces 21a and 21b face each other. Each of the external electrodes 47 and 49 has a rectangular shape when viewed in the direction in which the pair of main surfaces 21a and 21b face each other.

[0032] The pair of external electrodes 47 and 49 have the same shape as each other when viewed in the direction in which the pair of main surfaces 21a and 21b face each other. When viewed in the direction in which the pair of main surfaces 21a and 21b face each other, the short side direction of each of the external electrodes 47 and 49 corresponds to the direction in which a pair of side surfaces 21c face each other, and the long side direction of each of the external electrodes 47 and 49 corresponds to the direction in which a pair of side surfaces 21e face each other. Each of the external electrodes 47 and 49 is made of a conductive material. The conductive material includes, for example, Ag, Pd, or an Ag-Pd alloy. Each of the external electrodes 47 and 49 is configured, for example, as a sintered body of a conductive paste containing the above conductive material.

[0033] The external electrode 47 is electrically connected to the connection conductor 35 through the via conductor 39. The connection conductor 35 is located in the same layer as the electrode layer 31. The connection conductor 35 is located inside the electrode layer 31. An opening is formed in the electrode layer 31 at a position corresponding to the external electrode 47 when viewed in the direction in which the pair of main surfaces 21a and 21b face each other. The connection conductor 35 is located within the opening formed in the electrode layer 31. When viewed in the direction in which the pair of main surfaces 21a and 21b face each other, the entire edge of the connection conductor 35 is surrounded by the electrode layer 31.

[0034] The connection conductor 35 is located between the piezoelectric layer 23a and the piezoelectric layer 23b. The electrode layer 31 and the connection conductor 35 are separated from each other. The connection conductor 35 faces the external electrode 47 in the direction in which the pair of main surfaces 21a, 21b face each other. The via conductor 39 is connected to the external electrode 47 and is also connected to the connection conductor 35. The connection conductor 35 is electrically connected to the electrode layer 32 through the via conductor 40. The connection conductor 35 faces the electrode layer 32 in the direction in which the pair of main surfaces 21a, 21b face each other. The via conductor 40 is connected to the connection conductor 35 and is also connected to the electrode layer 32.

[0035] The electrode layer 32 is electrically connected to the connection conductor 36 through the via conductor 40. The connection conductor 36 is located in the same layer as the electrode layer 33. The connection conductor 36 is located inside the electrode layer 33. An opening is formed in the electrode layer 33 at a position corresponding to the external electrode 47 (connection conductor 35) when viewed in the direction in which the pair of main surfaces 21a, 21b face each other. The connection conductor 36 is located within the opening formed in the electrode layer 33. When viewed in the direction in which the pair of main surfaces 21a, 21b face each other, the entire edge of the connection conductor 36 is surrounded by the electrode layer 33.

[0036] The connection conductor 36 is located between the piezoelectric layer 23c and the piezoelectric layer 23d. The electrode layer 33 and the connection conductor 36 are separated from each other. The connection conductor 36 faces the electrode layer 32 in the direction in which the pair of main surfaces 21a, 21b face each other. The via conductor 41 is connected to the electrode layer 32 and is also connected to the connection conductor 36. The connection conductor 36 is electrically connected to the electrode layer 34 through the via conductor 42. The connection conductor 36 faces the electrode layer 34 in the direction in which the pair of main surfaces 21a, 21b face each other. The via conductor 42 is connected to the connection conductor 36 and is also connected to the electrode layer 34.

[0037] The external electrode 49 is electrically connected to the electrode layer 31 through the via conductor 43. The electrode layer 31 faces the external electrode 49 in the direction in which the pair of main surfaces 21a, 21b face each other. The via conductor 43 is connected to the external electrode 49 and is also connected to the electrode layer 31.

[0038] The electrode layer 31 is electrically connected to the connection conductor 37 through the via conductor 44. The connection conductor 37 is located in the same layer as the electrode layer 32. The connection conductor 37 is located inside the electrode layer 32. An opening is formed in the electrode layer 32 at a position corresponding to the external electrode 49 when viewed in the direction in which the pair of main surfaces 21a and 21b face each other. The connection conductor 37 is located within the opening formed in the electrode layer 32. When viewed in the direction in which the pair of main surfaces 21a and 21b face each other, the entire edge of the connection conductor 37 is surrounded by the electrode layer 32.

[0039] The connection conductor 37 is located between the piezoelectric layer 23b and the piezoelectric layer 23c. The electrode layer 32 and the connection conductor 37 are separated from each other. The connection conductor 37 faces the electrode layer 31 in the direction in which the pair of main surfaces 21a and 21b face each other. The via conductor 44 is connected to the electrode layer 31 and is also connected to the connection conductor 37. The connection conductor 37 is electrically connected to the electrode layer 33 through the via conductor 45. The connection conductor 37 faces the electrode layer 33 in the direction in which the pair of main surfaces 21a and 21b face each other. The via conductor 45 is connected to the connection conductor 37 and is also connected to the electrode layer 33.

[0040] The electrode layer 33 is electrically connected to the connection conductor 38 through the via conductor 46. The connection conductor 38 is located in the same layer as the electrode layer 34. The connection conductor 38 is located inside the electrode layer 34. An opening is formed in the electrode layer 34 at a position corresponding to the external electrode 49 when viewed in the direction in which the pair of main surfaces 21a and 21b face each other. The connection conductor 38 is located within the opening formed in the electrode layer 34. When viewed in the direction in which the pair of main surfaces 21a and 21b face each other, the entire edge of the connection conductor 38 is surrounded by the electrode layer 34.

[0041] The connection conductor 38 is located between the piezoelectric layer 23d and the piezoelectric layer 23e. The electrode layer 34 and the connection conductor 38 are separated from each other. The connection conductor 38 faces the electrode layer 33 in the direction in which the pair of main surfaces 21a and 21b face each other. The via conductor 46 is connected to the electrode layer 33 and is also connected to the connection conductor 38.

[0042] The external electrode 47 is electrically connected to the via conductor 39, the connection conductor 35, the via conductor 40, the electrode layer 32, the via conductor 41, the connection conductor 36, the via conductor 42, and the electrode layer 34. The external electrode 49 is electrically connected to the via conductor 43, the electrode layer 31, the via conductor 44, the connection conductor 37, the via conductor 45, the electrode layer 33, the via conductor 46, and the connection conductor 38.

[0043] The connection conductors 35 to 38 and the via conductors 39 to 46 are made of a conductive material. The conductive material includes, for example, Ag, Pd, or an Ag-Pd alloy. The connection conductors 35 to 38 and the via conductors 39 to 46 are configured, for example, as a sintered body of a conductive paste containing the above conductive material. The connection conductors 35 to 38 exhibit a rectangular shape when viewed from the direction in which the pair of main surfaces 21a and 21b face each other. The via conductors 39 to 46 are formed by sintering a conductive paste filled in through holes formed in a ceramic green sheet for forming the corresponding piezoelectric layers 23a, 23b, 23c, and 23d.

[0044] On the main surface 21b of the piezoelectric element 21, there are no conductors electrically connected to the electrode layers 31 and 33 and no conductors electrically connected to the electrode layers 32 and 34. For example, when the main surface 21b is viewed from the direction in which the pair of main surfaces 21a and 21b face each other, the entire main surface 21b is exposed. On each of the side surfaces 21c and 21e of the piezoelectric element 21, there are no conductors electrically connected to the electrode layers 31 and 33 and no conductors electrically connected to the electrode layers 32 and 34. For example, when each side surface 21c is viewed from the direction in which the pair of side surfaces 21c face each other, the entire side surface 21c is exposed. When each side surface 21e is viewed from the direction in which the pair of side surfaces 21e face each other, the entire side surface 21e is exposed.

[0045] The regions sandwiched between the electrode layer 31 and the electrode layer 32 in the piezoelectric layer 23b, the regions sandwiched between the electrode layer 32 and the electrode layer 33 in the piezoelectric layer 23c, and the regions sandwiched between the electrode layer 33 and the electrode layer 34 in the piezoelectric layer 23d include piezoelectrically active regions. In the piezoelectric element 21, active regions are formed between the electrode layer 31 and the electrode layer 32, between the electrode layer 32 and the electrode layer 33, and between the electrode layer 33 and the electrode layer 34. When viewed from the direction in which the pair of main surfaces 21a and 21b face each other, the outer edges of the electrode layers 31, 32, 33, and 34 serve as the boundaries between the active regions and the piezoelectrically inactive regions.

[0046] For example, the active regions are positioned so as to surround the plurality of external electrodes 47 and 49 when viewed from the direction in which the pair of main surfaces 21a and 21b face each other. The regions where the external electrodes 47 and 49 are disposed include inactive regions when viewed from the direction in which the pair of main surfaces 21a and 21b face each other. When viewed from the direction in which the pair of main surfaces 21a and 21b face each other, the piezoelectric element 21 includes active regions in the regions located between the external electrode 47 and the external electrode 49. When viewed from the direction in which the pair of main surfaces 21a and 21b face each other, the piezoelectric element 21 includes active regions outside the regions where the external electrodes 47 and 49 are located.

[0047] The piezoelectric element 20 is fixed to the surface 6 included in the top plate portion 5. The piezoelectric element 20 is fixed to the surface 6, for example, such that the main surface 21b and the surface 6 face each other. The piezoelectric element 20 is fixed to the housing 1. The piezoelectric element 20 is fixed only to the top plate portion 5 of the housing 1. The piezoelectric element 20 is not fixed to the bottom plate portion 3 and the side plate portion 7 of the housing 1. As shown in FIG. 7, the top plate portion 5 includes a region 5a facing the piezoelectric element 20 and a region 5b not facing the piezoelectric element 20. The region 5a is located inside the region 5b. When the top plate portion 5 is viewed from the direction in which the pair of main surfaces 21a and 21b face each other, the entire region 5a is surrounded by the region 5b. The fixing of the piezoelectric element 20 (main surface 21b) to the top plate portion 5 (surface 6) includes detachable fixing. FIG. 7 is an exploded perspective view showing the top plate portion, the piezoelectric element, and the wiring body.

[0048] The piezoelectric element 20 is fixed to the surface 6 along each of a pair of end sides 22a. The piezoelectric element 20 is fixed to the surface 6 by, for example, a plurality of fixing portions 17. The piezoelectric element 20 is fixed to the surface 6 by, for example, a pair of fixing portions 17. Each of the pair of fixing portions 17 is arranged along the corresponding end side 22a among the pair of end sides 22a. The pair of fixing portions 17 is located between the piezoelectric element 20 and the top plate portion 5 (surface 6). The fixing portion 17 includes, for example, a double-sided pressure-sensitive adhesive tape. The fixing portion 17 may be made of, for example, resin. The fixing portion 17 may be made of, for example, an acrylic resin or an epoxy resin. The fixing portion 17 may be made of, for example, plastic.

[0049] The piezoelectric element 20 is fixed to the surface 6 by, for example, only a pair of fixing portions 17. The main surface 21b includes a region covered by the pair of fixing portions 17 and a region exposed from the pair of fixing portions 17. The main surface 21b is exposed from the pair of fixing portions 17 except for the region covered by the pair of fixing portions 17. The region included in the main surface 21b and exposed from the pair of fixing portions 17 faces the surface 6 directly. In the piezoelectric element 20, the main surface 21b is fixed to the surface 6 by a plurality of fixing portions 17. In the piezoelectric element 20, the main surface 21a is not fixed to the surface 6. The main surface 21a is not fixed to the housing 1. The main surface 21a faces the bottom plate portion 3. The piezoelectric element 20 is fixed to the housing 1 only on the side of the main surface 21b. The piezoelectric element 20 is separated from the top plate portion 5 (surface 6). A gap GA is formed between each of the pair of end sides 22b and the surface 6. The gap GA extends in the direction in which the pair of side surfaces 21e face each other. The fixing portion 17 is located between each of the pair of end sides 22a and the surface 6. Therefore, it is difficult to form a gap between each of the pair of end sides 22a and the surface 6.

[0050] The audio device AD includes a plurality of spaces S1, S2 within the housing 1. For example, the audio device AD includes two spaces S1, S2 within the housing 1. The bottom plate portion 3, the top plate portion 5, and the side plate portion 7 define the space S1. The housing 1 defines the space S1. The top plate portion 5 and the piezoelectric element 20 define the space S2. The space S2 is located between the surface 6 and the main surface 21b. In the audio device AD, not only the top plate portion 5 and the piezoelectric element 20 but also a pair of fixing portions 17 define the space S2. In this case, the space S2 is located between the surface 6 and the region included in the main surface 21b and exposed from the pair of fixing portions 17. For example, when the space S1 includes the first space, the space S2 includes the second space. The space S2 is defined within the space S1. The space S1 and the space S2 communicate with each other. For example, the space S1 and the space S2 communicate with each other through the gap GA. The space S2 is smaller than the space S1.

[0051] A plurality of openings OP are formed in the top plate portion 5. The plurality of openings OP penetrate the top plate portion 5, that is, the member 13. Each of the plurality of openings OP includes a through hole. When viewed from a direction orthogonal to the member 13, each of the plurality of openings OP has, for example, a circular shape. When viewed from a direction orthogonal to the member 13, each of the plurality of openings OP may have a polygonal shape. The plurality of openings OP are arranged in a matrix with intervals in, for example, the direction in which a pair of side surfaces 21e face each other and the direction in which a pair of side surfaces 21c face each other. The plurality of openings OP may be arranged in a staggered pattern with intervals in, for example, the direction in which a pair of side surfaces 21e face each other and the direction in which a pair of side surfaces 21c face each other. The plurality of openings OP may be arranged irregularly.

[0052] As also shown in FIG. 7, the plurality of openings OP include a plurality of openings OP1 formed in region 5a and a plurality of openings OP2 formed in region 5b. The plurality of openings OP communicate with at least one of space S1 or space S2. The plurality of openings OP1 communicate directly with space S2. The plurality of openings OP1 communicate indirectly with space S1 through space S2. The plurality of openings OP2 communicate directly with space S1. The number of each of the openings OP1 and OP2 may not be plural and may be one.

[0053] The wiring body 50 includes a plurality of conductors 53 and 55. For example, the wiring body 50 includes a pair of conductors 53 and 55. The wiring body 50 includes a base material and a cover in addition to the plurality of conductors 53 and 55. The wiring body 50 includes, for example, a flexible printed circuit board (FPC). The wiring body 50 is arranged so as to intersect the long sides of each of the main surfaces 21a and 21b. The direction in which the wiring body 50 extends intersects the direction in which the pair of side surfaces 21e face each other. For example, the wiring body 50 is arranged so as to be orthogonal to the long sides of each of the main surfaces 21a and 21b. The direction in which the wiring body 50 extends is orthogonal to the direction in which the pair of side surfaces 21e face each other. The wiring body 50 extends in the direction in which the pair of side surfaces 21c face each other. The wiring body 50 includes one end that is electrically and physically connected to the piezoelectric element 20 and the other end that is electrically and physically connected to an electronic device (not shown) on which the acoustic device AD is mounted.

[0054] The base material has electrical insulation. The base material is made of resin. The base material is made of, for example, polyimide resin. Each of the conductors 53 and 55 is arranged on the base material. Each of the conductors 53 and 55 is joined to the base material by, for example, an adhesive layer. Each of the conductors 53 and 55 extends in the direction in which the wiring body 50 extends. Each of the conductors 53 and 55 is separated in a direction intersecting the direction in which each of the conductors 53 and 55 extends. Each of the conductors 53 and 55 is made of, for example, copper. Each of the conductors 53 and 55 has a rectangular shape having a pair of long sides and a pair of short sides in plan view.

[0055] The cover is disposed on each of the conductors 53, 55 so as to cover a part of each of the conductors 53, 55. For example, each of the conductors 53, 55 is exposed from the cover at one end and the other end of the wiring body 50. The cover is joined to each of the conductors 53, 55 by, for example, an adhesive layer. The base material and the cover are joined to each other in a region exposed from each of the conductors 53, 55. The cover is made of resin. The cover is made of, for example, polyimide resin. The regions of each of the conductors 53, 55 that are exposed from the cover are subjected to, for example, nickel plating and gold flash plating. The wiring body 50 includes, for example, a reinforcing member 59. The reinforcing member 59 is disposed at the other end of the wiring body 50. The reinforcing member 59 is disposed on the base material. The reinforcing member 59 is joined to the base material by, for example, an adhesive layer. The reinforcing member 59 has electrical insulation and has a plate shape. The reinforcing member 59 is made of, for example, polyimide resin.

[0056] An opening 9 through which the wiring body 50 is inserted is formed in one wall 8 included in the side plate portion 7. The opening 9 includes a through hole. The wiring body 50 is inserted through the opening 9 and includes a portion located inside the housing 1 and a portion located outside the housing 1. The portion of the wiring body 50 located inside the housing 1 is electrically and physically connected to the piezoelectric element 20. The piezoelectric element 20 and the wiring body 50 are electrically and physically connected to each other by a connection material (not shown). The connection material includes a connection material that electrically and physically connects the external electrode 47 and the conductor 53 to each other, and a connection material that electrically and physically connects the external electrode 49 and the conductor 55 to each other. The connection material includes, for example, a resin layer and a plurality of metal particles included in the resin layer. The resin layer includes, for example, a thermosetting elastomer. The metal particles include, for example, gold-plated particles. Each of the external electrodes 47, 49 and each of the conductors 53, 55 corresponding to each other are electrically connected through the metal particles. The connection material is formed, for example, by curing an anisotropic conductive paste or an anisotropic conductive film.

[0057] For example, when drive voltages with different polarities are applied to the external electrodes 47 and 49 through the conductors 53 and 55, an electric field is generated between the electrode layers 31, 33 and the electrode layers 32, 34. Displacement occurs in each active region, that is, the region sandwiched between the electrode layer 31 and the electrode layer 32 in the piezoelectric layer 23b, the region sandwiched between the electrode layer 32 and the electrode layer 33 in the piezoelectric layer 23c, and the region sandwiched between the electrode layer 33 and the electrode layer 34 in the piezoelectric layer 23d. When an AC signal is applied to the external electrodes 47 and 49, for example, the piezoelectric element 20 repeats expansion and contraction according to the frequency of the applied AC signal. Since the piezoelectric element 20 is fixed to the top plate portion 5, the top plate portion 5 bends and vibrates integrally with the piezoelectric element 20 according to the repeated expansion and contraction in the piezoelectric element 20. The acoustic device AD emits a sound pressure signal based on the bending vibration of the top plate portion 5.

[0058] In the acoustic device AD, each of the spaces S1 and S2 functions as a resonance space. The acoustic device AD includes a plurality of resonance spaces. Therefore, in the acoustic device AD, the sound pressure characteristics in a desired frequency band can be easily adjusted. For example, by controlling the size of each of the spaces S1 and S2, the sound pressure characteristics in a desired frequency band are improved.

[0059] In the acoustic device AD, the piezoelectric element 20 has a rectangular shape including a pair of end sides 22a and a pair of end sides 22b in plan view. The piezoelectric element 20 is fixed to the surface 6 included in the top plate portion 5 along each of the pair of end sides 22a. Therefore, the acoustic device AD hardly inhibits the displacement of the piezoelectric element 20 and reliably transmits the displacement of the piezoelectric element 20 to the top plate portion 5.

[0060] In the acoustic device AD, the space S1 and the space S1 communicate with each other. Therefore, in the acoustic device AD, the sound pressure characteristics in a desired frequency band can be adjusted even more easily. In the acoustic device AD, the space S1 and the space S2 communicate with each other through the gap GA between the surface 6 included in the top plate portion 5 and the pair of end sides 22b. The audio device AD easily realizes a configuration in which the space S1 and the space S2 communicate with each other.

[0061] In the audio device AD, the top plate portion 5 includes a region 5a facing the piezoelectric element 20. The plurality of openings OP includes the opening OP1 formed in the region 5a. The opening OP1 communicates with the space S1 through the space S2. Therefore, in the audio device AD, the sound pressure characteristics in a desired frequency band can be adjusted more easily.

[0062] In the audio device AD, the space S2 is smaller than the space S1. Therefore, the audio device AD can enhance, for example, the sound pressure characteristics in a desired low frequency band.

[0063] In the audio device AD, the plurality of openings OP includes the opening OP2 directly communicating with the space S1 and the opening OP1 directly communicating with the space S2. Therefore, in the audio device AD, the sound pressure characteristics in a desired frequency band can be adjusted more easily.

[0064] In the audio device AD, an opening 9 through which the wiring body 50 is inserted is formed in the side plate portion 7. The wiring body 50 is physically and electrically connected to the piezoelectric element 20. Therefore, in the audio device AD, the wiring body 50 is surely arranged without interfering with the housing 1.

[0065] In the audio device AD, the housing 1 includes a member 11 having a box shape and a member 13 having a plate shape. The member 11 includes the bottom plate portion 3 and the side plate portion 7. The member 11 has an opening 11a. The member 13 includes the top plate portion 5. The audio device AD realizes the housing 1 simply and at low cost.

[0066] In the audio device AD, the piezoelectric element 20 is directly fixed to the top plate portion 5 without being fixed to a diaphragm different from the top plate portion 5. Therefore, the audio device AD can reduce the height of the housing 1. The top plate portion 5 can amplify the vibration of the piezoelectric element 20.

[0067] Next, in the audio device AD, based on the examples and comparative examples, it will be described that the sound pressure characteristics in a desired frequency band can be easily adjusted. In the example, the sound pressure characteristics of the above-described audio device AD were confirmed. The audio device according to the example, as described in the above-described embodiment, has the top plate portion 5 vibrating integrally with the piezoelectric element 20 and includes a plurality of resonance spaces. In the comparative example, it is an audio device in which only the piezoelectric element 20 vibrates substantially and includes only one resonance space. In the audio device according to the comparative example, as shown in FIG. 8, the piezoelectric element 20 is not substantially fixed to the top plate portion 5 in which a plurality of openings OP are formed, and is disposed in one space defined by the housing 1. In the audio device according to the comparative example, the piezoelectric element 20 is fixed to the bottom plate portion 3. The sizes of the housing 1 and the piezoelectric element 20 are the same in the example and the comparative example. FIG. 8 is a diagram showing a cross-sectional configuration of the audio device according to the comparative example.

[0068] The sound pressure levels of the audio devices according to the examples and comparative examples were confirmed as follows. A predetermined alternating voltage was applied to each of the audio devices according to the examples and comparative examples, and the sound pressure signal emitted by the audio device was detected with a microphone. The sound pressure level of the detected sound pressure signal was obtained. The distance between the microphone and the audio device is 0.1 m. The alternating voltage to be applied is a sine wave. The frequency of the alternating voltage was changed in the range of 100 to 4000 Hz. The amplitude of the alternating voltage is ±3 V.

[0069] The confirmation results are shown in FIG. 9. FIG. 9 is a diagram showing the sound pressure characteristics of the audio device. The sound pressure characteristics are, for example, the frequency characteristics of the sound pressure level. In FIG. 9, the sound pressure characteristics in the above example are shown by a solid line, and the sound pressure characteristics in the above comparative example are shown by a broken line. As can be understood from FIG. 9, the embodiment enhances the sound pressure characteristics in a desired low frequency band compared to the comparative example. Specifically, the embodiment enhances the sound pressure characteristics in a frequency band of 1500 Hz or less compared to the comparative example.

[0070] As described above, the embodiments of the present invention have been described. However, the present invention is not necessarily limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

[0071] The plurality of openings OP may include only the plurality of openings OP1. The plurality of openings OP may include only the plurality of openings OP2. The space S1 and the space S2 may not communicate with each other. For example, in a configuration where the plurality of openings OP include the opening OP1 and the opening OP2, the space S1 and the space S2 may not communicate with each other. The wiring body 50 may be inserted into a gap formed between the member 11 and the member 13. In a configuration where the wiring body 50 is inserted into a gap formed between the member 11 and the member 13, the opening 9 may not be formed in the side plate portion 7. The member 11 may have a plate shape and the member 13 may have a box shape. In a configuration where the member 11 has a plate shape and the member 13 has a box shape, the member 13 may include a side plate portion 7 and a top plate portion 5. In this configuration, the member 11 may include a bottom plate portion 3.

[0072] As can be understood from the description of the above-described embodiments, this specification includes the disclosure of the following aspects. (Appendix 1) A housing including a bottom plate portion, a top plate portion including a surface facing the bottom plate portion, and a side plate portion connecting the bottom plate portion and the top plate portion, A piezoelectric element fixed away from the top plate portion on the surface included in the top plate portion, The bottom plate portion, the top plate portion, and the side plate portion define a first space, The top plate portion and the piezoelectric element define a second space, An acoustic device in which a plurality of openings communicating with at least one of the first space or the second space are formed in the top plate portion. (Appendix 2) The piezoelectric element has a rectangular shape including a pair of first end sides facing each other and a pair of second end sides facing each other in a plan view, and is fixed to the surface along each of the pair of first end sides. The acoustic device according to Supplementary Note 1. (Supplementary Note 3) The first space and the second space communicate with each other through a gap between the surface included in the top plate portion and the pair of second end sides. The acoustic device according to Supplementary Note 2. (Supplementary Note 4) The first space and the second space communicate with each other. The acoustic device according to any one of Supplementary Notes 1 to 3. (Supplementary Note 5) The top plate portion includes a region facing the piezoelectric element. The plurality of openings include openings formed in the region included in the top plate portion. The openings formed in the region communicate with the first space through the second space. The acoustic device according to Supplementary Note 3 or 4. (Supplementary Note 6) The second space is smaller than the first space. The acoustic device according to any one of Supplementary Notes 1 to 5. (Supplementary Note 7) The plurality of openings include openings directly communicating with the first space and openings directly communicating with the second space. The acoustic device according to any one of Supplementary Notes 1 to 6. (Supplementary Note 8) The acoustic device further includes a wiring body electrically connected to the piezoelectric element. An opening through which the wiring body is inserted is formed in the side plate portion. The acoustic device according to any one of Supplementary Notes 1 to 7. (Supplementary Note 9) The housing includes a first member including the bottom plate portion and the side plate portion and having a box shape with an opening, and a second member including the top plate portion and having a plate shape. The acoustic device according to any one of Supplementary Notes 1 to 8.

Explanation of Reference Numerals

[0073] 1…housing, 3…bottom plate portion, 5…top plate portion, 5a, 5b…regions included in the top plate portion, 6…surface included in the top plate portion, 7…side plate portion, 9…opening through which the wiring body is inserted, 11, 13…members, 20…piezoelectric element, 50…wiring body, AD…acoustic device, GA…gap, OP, OP1, OP2…openings, S1, S2…spaces.

Claims

1. A housing including a bottom plate portion, a top plate portion including a surface facing the bottom plate portion, and side plate portions connecting the bottom plate portion and the top plate portion. A piezoelectric element fixed away from the top plate portion on the surface included in the top plate portion. The bottom plate portion, the top plate portion, and the side plate portions define a first space. The top plate portion and the piezoelectric element define a second space. An acoustic device, wherein a plurality of openings communicating with at least one of the first space or the second space are formed in the top plate portion.

2. The piezoelectric element has a rectangular shape including a pair of first end sides facing each other and a pair of second end sides facing each other in plan view, and is fixed to the surface along each of the pair of first end sides. The acoustic device according to claim 1.

3. The first space and the second space communicate with each other through a gap between the surface included in the top plate portion and the pair of second end sides. The acoustic device according to claim 2.

4. The first space and the second space communicate with each other. The acoustic device according to claim 1.

5. The top plate portion includes a region facing the piezoelectric element. The plurality of openings include openings formed in the region included in the top plate portion. The openings formed in the region communicate with the first space through the second space. The acoustic device according to claim 3 or 4.

6. The second space is smaller than the first space. The acoustic device according to claim 1.

7. The plurality of openings include openings directly communicating with the first space and openings directly communicating with the second space. The acoustic device according to claim 1.

8. further comprising a wiring body electrically connected to the piezoelectric element, The acoustic device according to claim 1, wherein an opening through which the wiring body is inserted is formed in the side plate portion.

9. The housing includes a first member having a box shape including the bottom plate portion and the side plate portion and having an opening, and a second member including the top plate portion and having a plate shape, the acoustic device according to claim 1.

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