JP7781652B2 - Vibration device - Google Patents

Description

This disclosure relates to a vibration device.

An example of a conventional vibration device is the vibration device described in Patent Document 1. This vibration device includes a piezoelectric element and a wiring member. The piezoelectric element has a piezoelectric body with a rectangular main surface and an external electrode arranged on the main surface. The wiring member is located on the external electrode and is electrically connected to the external electrode. When viewed from a direction perpendicular to the main surface of the piezoelectric body, the wiring member has a rectangular first region that overlaps with the main surface. The first region includes a second region that is bonded to the piezoelectric element so as to cover the external electrode. When viewed from the perpendicular direction, the second region is arranged near one of the corners of the first region.

International Publication No. 2020/100824

Vibration devices such as those described above are used as acoustic devices such as speakers and buzzers. For this reason, there is a demand for flat acoustic characteristics in specific frequency bands depending on the application.

This disclosure has been made to solve the above problem, and aims to provide a vibration device that can achieve flat acoustic characteristics in a specific frequency band.

A vibration device according to one aspect of the present disclosure comprises a piezoelectric portion including a piezoelectric element, a housing that holds the piezoelectric portion, and a wiring member electrically connected to the piezoelectric portion. The housing has a holding wall that holds the piezoelectric portion on a first surface side, and a first space-forming portion on the first surface side and a second space-forming portion on a second surface side opposite the first surface, which are separated by the holding wall surface. The first space-forming portion has a first opening that connects to the outside, and the second space-forming portion has a second opening that connects to the outside independently of the first opening.

In this vibration device, vibrations on the holding wall surface on which the piezoelectric portion is arranged can be output independently from the first opening of the first space-forming portion and the second opening of the second space-forming portion. Therefore, by adjusting the spatial volume of the first space-forming portion and the second space-forming portion, and the opening shape and orientation of the first opening and the second opening, it is possible to easily adjust the acoustic characteristics and output directivity. Therefore, this vibration device can achieve flattening of acoustic characteristics in specific frequency bands depending on the application.

The second space forming portion may be formed so as to surround the first space forming portion when viewed from the normal direction of the retaining wall surface. In this case, the spatial volume of the second space forming portion can be sufficiently secured, further flattening the acoustic characteristics.

The retaining wall surface may be made of metal. In this case, the vibration of the piezoelectric portion can be efficiently transmitted to the first space forming portion and the second space forming portion, further flattening the acoustic characteristics.

The second space forming portion may have an opposing wall surface that faces the holding wall surface. In this case, vibrations from the piezoelectric portion can be transmitted to the second space forming portion more efficiently, further flattening the acoustic characteristics.

The opposing wall surface may be made of metal. In this case, vibrations from the piezoelectric portion can be transmitted to the second space-forming portion more efficiently, resulting in even flatter acoustic characteristics.

The housing may be constructed by combining two or more different materials, making it even easier to adjust the acoustic characteristics.

The spatial volume created by the second space forming portion may be equal to or greater than the spatial volume created by the first space forming portion. This configuration further flattens the acoustic characteristics.

The first opening and the second opening may open in different directions. This makes it easier to adjust the output directivity.

This disclosure makes it possible to achieve flat acoustic characteristics in specific frequency bands.

1 is a perspective view of a vibration device according to a first embodiment of the present disclosure. FIG. 2 is a cross-sectional view of the vibration device shown in FIG. 1 . FIG. 10 is a cross-sectional view of a vibration device according to a second embodiment of the present disclosure. FIG. 10 is a cross-sectional view of a vibration device according to a third embodiment of the present disclosure. FIG. 10 is a cross-sectional view of a vibration device according to a modified example. FIG. 10 is a cross-sectional view of a vibration device according to another modified example. 10 is a graph showing the results of an evaluation test of the acoustic characteristics of the vibration devices of Example 1 and the comparative example. 10 is a graph showing the results of an evaluation test of the acoustic characteristics of the vibration devices of Example 2 and the comparative example.

Hereinafter, preferred embodiments of a vibration device according to one aspect of the present disclosure will be described in detail with reference to the drawings.
[First embodiment]

Figure 1 is a perspective view showing a vibration device according to a first embodiment of the present disclosure. Vibration device 1A is an acoustic device used, for example, as a speaker or buzzer. As shown in Figure 1, vibration device 1A is configured to include a piezoelectric portion 2, a housing 3, and a wiring member 4.

The piezoelectric unit 2 includes a piezoelectric element 5. The piezoelectric element 5 includes a piezoelectric body and a pair of external electrodes. The piezoelectric element 5 has a rectangular parallelepiped shape that is flat in the thickness direction. The rectangular parallelepiped shape may include a shape in which the corners and ridges are chamfered or a shape in which the corners and ridges are rounded. The piezoelectric body is formed by a laminate of multiple piezoelectric layers. Each piezoelectric layer is formed of a piezoelectric material such as a piezoelectric ceramic. Examples of piezoelectric ceramic materials include PZT [Pb(Zr,Ti) _O3 ], PT ( _PbTiO3 ), PLZT [(Pb,La)(Zr,Ti) _O3 ], and barium titanate ( _BaTiO3 ).

Each piezoelectric layer is composed of a sintered ceramic green sheet containing, for example, the piezoelectric ceramic described above. In an actual piezoelectric element, the piezoelectric layers are integrated to the extent that the boundaries between the layers are indistinguishable. Multiple internal electrodes (not shown) are arranged within the piezoelectric element. Each internal electrode is made of a conductive material. Examples of conductive materials include Ag, Pd, and Ag-Pd alloys.

The piezoelectric section 2 may be a combination of a piezoelectric element 5 and a diaphragm. The diaphragm is a plate-shaped member made of, for example, a metal material. Examples of metal materials that can be used to make the diaphragm include Ni-Fe alloy, Ni, brass, and stainless steel. The diaphragm is, for example, rectangular. The diaphragm is placed on the bottom surface (the surface facing the housing 3) of the piezoelectric element 5 and can be fixed to the piezoelectric element 5 and housing 3 using, for example, adhesive, double-sided tape, etc.

The housing 3 is a member that holds the piezoelectric portion 2. The housing 3 is formed, for example, from a molded body of a resin material, and has an overall flat rectangular parallelepiped shape. Examples of resin materials that can be used to form the housing 3 include ABS resin, PBT resin, PPS resin, LCP resin, acrylic resin, and vinyl chloride resin. The housing 3 has a holding wall surface 11 that holds the piezoelectric portion 2, and multiple side wall surfaces 12 that are arranged around the edges of the holding wall surface 11 to surround the piezoelectric portion 2.

The wiring member 4 is a member that electrically connects the piezoelectric portion 2 to an external device. The wiring member 4 is, for example, a flexible printed circuit (FPC). One end of the wiring member 4 is electrically connected to each of a pair of external electrodes of the piezoelectric element 5. An anisotropic conductive adhesive, for example, can be used to connect one end of the wiring member 4 to the external electrodes of the piezoelectric element 5. The other end of the wiring member 4 (not shown) is electrically connected to an external device.

Next, the configuration of the housing 3 and the arrangement of the piezoelectric portion 2 will be described in more detail with reference to Figures 1 and 2. Figure 2 is a cross-sectional view of the vibration device shown in Figure 1. For ease of explanation, the wiring member 4 (and the notch 18 described below) have been omitted from Figure 2.

As shown in Figures 1 and 2, the housing 3 is configured to include the above-mentioned holding wall surface 11, side wall surface 12, and opposing wall surface 13. The holding wall surface 11 is rectangular in plan view, with a pair of long sides 11A, 11B and a pair of short sides 11C, 11D. The holding wall surface 11 has, in the thickness direction of the holding wall surface 11, a first surface 15A and a second surface 15B opposite to the first surface 15A. The above-mentioned piezoelectric part 2 is fixed to the first surface 15A of the holding wall surface 11.

In this embodiment, the piezoelectric portion 2 has a rectangular shape in a plan view, with a pair of long sides 2A, 2B and a pair of short sides 2C, 2D. The planar shape of the piezoelectric portion 2 is the planar shape of the piezoelectric element 5 when the piezoelectric portion 2 is composed only of the piezoelectric element 5, and is the planar shape of the diaphragm when the piezoelectric portion 2 is composed of the piezoelectric element 5 and a diaphragm. The piezoelectric portion 2 is disposed approximately in the center of the first surface 15A of the retaining wall surface 11. The long sides 2A, 2B of the piezoelectric portion 2 face the long sides 11A, 11B of the retaining wall surface 11, and the short sides 2C, 2D of the piezoelectric portion 2 face the short sides 11C, 11D of the retaining wall surface 11.

The side wall surfaces 12 are provided on the edge of one long side 11A and the edge of a pair of short sides 11C and 11D of the retaining wall surface 11. The side wall surface 12 has three first side wall surfaces 12A on the first surface 15A side of the retaining wall surface 11 and three second side wall surfaces 12B on the second surface 15B side of the retaining wall surface 11. The three first side wall surfaces 12A and the retaining wall surface 11 form a first space forming portion 16A on the first surface 15A side. The three second side wall surfaces 12B, the retaining wall surface 11, and the opposing wall surface 13 form a second space forming portion 16B on the second surface 15B side. The first space forming portion 16A and the second space forming portion 16B are separated by the retaining wall surface 11.

In the first space forming portion 16A, the piezoelectric part 2 held on the first surface 15A of the holding wall surface 11 is surrounded by the first side wall surface 12A from three directions excluding the long side 11B side. The height of the first side wall surface 12A from the first surface 15A of the holding wall surface 11 is greater than the thickness of the piezoelectric part 2. As a result, a vibration space of a certain volume is formed around the piezoelectric part 2 in the housing 3.

The first space forming portion 16A has a first opening S1 that connects to the outside. In this embodiment, to form the first opening S1, a joining member such as double-sided tape is placed on the top surfaces 12a of the three first side wall surfaces 12A. Using this joining member, the vibration device 1A can be attached to an external device K, as shown in FIG. 2. In this case, the first space forming portion 16A and the second space forming portion 16B are arranged in order from closest to the external device K.

When the vibration device 1A is attached to an external device K, the top surface 12a of the first side wall surface 12A is blocked by the external device K. As a result, a rectangular first opening S1 is defined on the long side 11B of the holding wall surface 11 by the holding wall surface 11, the two first side wall surfaces 12A, 12A on the short sides 11C, 11D of the holding wall surface 11, and the external device K. When the vibration device 1A is attached to an external device, the first opening S1 functions as an outlet for extracting vibrations generated by the piezoelectric portion 2 to the outside.

In the first space forming portion 16A, a rectangular cutout 18 (see Figure 1) is provided on the top surface 12a of the first side wall surface 12A on the long side 11A side of the holding wall surface 11. When the vibration device 1A is attached to an external device K, the wiring member 4 can be pulled out to the outside of the housing 3 by passing it through this cutout 18.

In the second space forming portion 16B, the second surface 15B on which the piezoelectric portion 2 is not disposed is surrounded by the second side wall surface 12B on three sides excluding the long side 11B side. The top side of the second side wall surface 12B is also blocked by the opposing wall surface 13. This creates a vibration space in the housing 3 that is independent of the vibration space around the piezoelectric portion 2. In other words, the vibration space formed by the second space forming portion 16B is not connected to the vibration space formed by the first space forming portion 16A.

In this embodiment, the height of the second side wall surface 12B from the second surface 15B of the retaining wall surface 11 is equal to or greater than the height of the first side wall surface 12A from the first surface 15A of the retaining wall surface 11. Therefore, the spatial volume (volume of the vibration space) defined by the second space forming portion 16B is equal to or greater than the spatial volume (volume of the vibration space) defined by the first space forming portion 16A.

The second space forming portion 16B has a second opening S2 that is independent of the first opening S1 and connects to the outside. The second opening S2 is defined in a rectangular shape on the long side 11B side of the holding wall surface 11 by the holding wall surface 11, two second side wall surfaces 12B, 12B on the short side 11C, 11D sides of the holding wall surface 11, and the opposing wall surface 13. The second opening S2 functions as an outlet, separate from the first opening S1, for extracting vibrations generated by the piezoelectric portion 2 to the outside.

In the vibration device 1A described above, vibrations on the holding wall surface 11 on which the piezoelectric portion 2 is arranged can be output independently from the first opening S1 of the first space forming portion 16A and the second opening S2 of the second space forming portion 16B. Therefore, by adjusting the spatial volume of the first space forming portion 16A and the second space forming portion 16B, and the opening shape and opening orientation of the first opening S1 and the second opening S2, the acoustic characteristics and output directivity can be easily adjusted. Therefore, the vibration device 1A can achieve flat acoustic characteristics in specific frequency bands depending on the application.

In the vibration device 1A, the second space forming portion 16B has an opposing wall surface 13 that faces the holding wall surface 11. This arrangement of the opposing wall surface 13 allows the vibration of the piezoelectric portion 2 to be transmitted to the second space forming portion 16B more efficiently, thereby further flattening the acoustic characteristics. Furthermore, in the vibration device 1A, the spatial volume of the second space forming portion 16B is equal to or larger than the spatial volume of the first space forming portion 16A. This configuration further flattens the acoustic characteristics.
Second Embodiment

Figure 3 is a cross-sectional view of a vibration device according to a second embodiment of the present disclosure. As shown in Figure 3, the vibration device 1B according to the second embodiment differs from the first embodiment in that the second space forming portion 16B is formed to surround the first space forming portion 16A when viewed from the normal direction of the holding wall surface 11.

Specifically, in the vibration device 1B, the distance between the two second side wall surfaces 12B, 12B on the short sides 11C, 11D side that constitute the second space forming portion 16B is greater than the distance between the two first side wall surfaces 12A, 12A on the short sides 11C, 11D side that constitute the first space forming portion 16A. Furthermore, the height of the second side wall surface 12B from the opposing wall surface 13 is the height of the second side wall surface 12B in the first embodiment plus the thickness of the retaining wall surface 11 and the height of the first side wall surface 12A. As a result, the vibration space formed by the second space forming portion 16B is also formed between the first side wall surface 12A and the second side wall surface 12B, and is expanded to sandwich the first space forming portion 16A in the direction connecting the short sides 11C, 11D of the retaining wall surface 11.

In the vibration device 1B, similar to the vibration device 1A, vibrations at the holding wall surface 11 on which the piezoelectric portion 2 is arranged can be output independently from the first opening S1 of the first space forming portion 16A and the second opening S2 of the second space forming portion 16B. Therefore, it is possible to achieve flattening of acoustic characteristics in a specific frequency band according to the application. Furthermore, in the vibration device 1B, the second space forming portion 16B is formed to surround the first space forming portion 16A when viewed from the normal direction of the holding wall surface 11. Therefore, it is possible to ensure a sufficient spatial volume of the second space forming portion 16B, thereby further flattening of acoustic characteristics.
[Third embodiment]

Figure 4 is a cross-sectional view of a vibration device according to a third embodiment of the present disclosure. As shown in Figure 4, the vibration device 1C according to the third embodiment differs from the first embodiment in that the housing 3 is made of a combination of two or more different materials.

More specifically, in the vibration device 1C, the retaining wall surface 11 and the opposing wall surface 13 are made of metal, and the first side wall surface 12A and the second side wall surface 12B are made of resin. Examples of metal materials that make up the retaining wall surface 11 and the opposing wall surface 13 include stainless steel, aluminum, and 42Ni alloy. The metal material that makes up the retaining wall surface 11 and the metal material that makes up the opposing wall surface 13 may be the same or different. As in the first embodiment, examples of resin materials that make up the first side wall surface 12A and the second side wall surface 12B include ABS resin, PBT resin, PPS resin, LCP resin, acrylic resin, and vinyl chloride resin. The resin material that makes up the first side wall surface 12A and the resin material that makes up the second side wall surface 12B may be the same or different.

In this vibration device 1C, as in the vibration device 1A, vibrations on the holding wall surface 11 on which the piezoelectric portion 2 is arranged can be output independently from the first opening S1 of the first space forming portion 16A and the second opening S2 of the second space forming portion 16B. Therefore, it is possible to achieve flat acoustic characteristics in a specific frequency band depending on the application.

In the vibration device 1C, the housing 3 is constructed by combining two or more different materials. This makes it even easier to adjust the acoustic characteristics. Furthermore, in the vibration device 1C, the holding wall surface 11 and the opposing wall surface 13 are constructed from metal. This allows the vibration of the piezoelectric portion 2 to be transmitted to the second space forming portion 16B even more efficiently, further flattening the acoustic characteristics.

4, both the retaining wall surface 11 and the opposing wall surface 13 are made of metal, but one of the retaining wall surface 11 and the opposing wall surface 13 may be made of metal and the other may be made of resin. Also, at least one of the first side wall surface 12A and the second side wall surface 12B may be made of metal.
[Modification]

The present disclosure is not limited to the above-described embodiments. For example, in each of the above-described embodiments, the vibration space formed by the second space forming portion 16B is hollow, but the vibration space may be filled with a filler material such as resin. Examples of resin materials that make up the filler include ABS resin, PBT resin, PPS resin, and LCP resin. Increasing the amount of filler lowers the resonance frequency, and decreasing the amount of filler raises the resonance frequency. Therefore, it is possible to adjust the acoustic characteristics more precisely by adjusting the amount of filler.

In each of the above embodiments, the first opening S1 and the second opening S2 both open in the same direction (toward the long side 11B of the holding wall surface 11). However, the first opening S1 and the second opening S2 may open in different directions. In this case, it is easier to adjust the output directivity. For example, as shown in FIG. 5 , the first opening S1 may open toward the long side 11B of the holding wall surface 11, while the second opening S2 may open toward the short side 11C of the holding wall surface 11. Contrary to the example in FIG. 5 , the second opening S2 may open toward the short side 11D of the holding wall surface 11.
6, the first opening S1 may open to the long side 11B of the holding wall surface 11, while the second opening S2 may open to the long side 11A of the holding wall surface 11. Although Fig. 5 and Fig. 6 illustrate modified examples of the configuration of the vibration device 1A according to the first embodiment, the configuration in which the first opening S1 and the second opening S2 open in different directions from each other can also be applied to the vibration device 1B according to the second embodiment and the vibration device 1C according to the third embodiment.
[Evaluation test of acoustic characteristics]

An evaluation test of the acoustic characteristics of the vibration device according to the present disclosure will now be described. In this evaluation test, the frequency characteristics of the output sound pressure were measured for the vibration devices of the example and comparative example. As the example, a sample of a vibration device having a configuration equivalent to that of the first embodiment (Example 1) and a sample of a vibration device having a configuration equivalent to that of the second embodiment (Example 2) were prepared. Additionally, as a comparative example, a sample of a vibration device whose housing only has a first space forming portion was prepared.

Figure 7 is a graph showing the results of an evaluation test of the acoustic characteristics of the vibration devices of Example 1 and the comparative example. Furthermore, Figure 8 is a graph showing the results of an evaluation test of the acoustic characteristics of the vibration devices of Example 2 and the comparative example. In Figures 7 and 8, the horizontal axis represents frequency (Hz) and the vertical axis represents sound pressure (dBA/10 cm). As shown in Figures 7 and 8, in the comparative example, the sound pressure gradually increases toward the higher frequency side, but it can be seen that a valley (gap) in the sound pressure level occurs between 5,000 Hz and 10,000 Hz.

In contrast, as shown in Figure 7, in Example 1, the valley (gap) in the sound pressure level between 5,000 Hz and 10,000 Hz is eliminated, and the acoustic characteristics in that range are flattened. Furthermore, as shown in Figure 8, in Example 2, the valley (gap) in the sound pressure level near 10,000 Hz is eliminated, and the acoustic characteristics in that range are flattened. These results confirm that the configuration of the vibration device disclosed herein contributes to flattening the acoustic characteristics in specific frequency bands depending on the application.

1A-1C...Vibration device, 2...Piezoelectric portion, 3...Housing, 4...Wiring member, 5...Piezoelectric element, 11...Retaining wall surface, 13...Opposite wall surface, 15A...First surface, 15B...Second surface, 16A...First space forming portion, 16B...Second space forming portion, S1...First opening, S2...Second opening.

Claims (7)

a piezoelectric portion including a piezoelectric element;
a housing that holds the piezoelectric portion;
a wiring member electrically connected to the piezoelectric portion,
the housing has a holding wall surface that holds the piezoelectric portion on a first surface side, and a first space forming portion on the first surface side and a second space forming portion on a second surface side opposite to the first surface, which are partitioned by the holding wall surface;
the first space forming portion has a first opening connected to the outside, and the second space forming portion has a second opening connected to the outside independently of the first opening ,
the first space forming portion has a first side wall surface extending in a direction intersecting with the holding wall surface, and the second space forming portion has a second side wall surface extending in a direction intersecting with the holding wall surface and surrounding the first side wall surface;
A vibration device , wherein the vibration space formed by the second space forming portion includes a portion located between the first side wall surface and the second side wall surface . The vibration device according to claim 1 , wherein the holding wall surface is made of metal. The vibration device according to claim 1 or 2 , wherein the second space forming portion has an opposing wall surface that faces the holding wall surface. The vibration device according to claim 3 , wherein the opposing wall surface is made of metal. The vibration device according to any one of claims 1 to 4 , wherein the housing is made of a combination of two or more different materials. The vibration device according to any one of claims 1 to 5 , wherein a spatial volume defined by the second space forming portion is equal to or larger than a spatial volume defined by the first space forming portion. The vibration device according to any one of claims 1 to 6 , wherein the first opening and the second opening are open in different directions.