JP2014039094A - Acoustic generator, acoustic generating device, and electric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sound pressure on a low frequency region.SOLUTION: An acoustic generator includes: a film 3; a frame member 5 provided in a peripheral part of the film 3; a piezoelectric element 1 provided in the film 3 within the frame member 5; and a resin layer 20 filled within the frame member 5 so that the piezoelectric element 1 is embedded. The resin layer 20 has an uneven pattern on a surface. Thereby, rigidity of the resin layer 20 is lowered compared with a case where the surface of the resin layer 20 is flat and smooth; a first resonance frequency that a vibration body, which is composed of the film 3 and the resin layer 20, united with the piezoelectric element 1, has is reduced.

Description

  The present invention relates to a sound generator, a sound generator, and an electronic apparatus.

  Conventionally, an acoustic generator typified by a piezoelectric speaker has been known as a small-sized, low-current driving acoustic device using a piezoelectric body as an electroacoustic transducer, for example, a small electronic device such as a mobile computing device. It is used as an integrated sound generator.

  In general, an acoustic generator using a piezoelectric body as an electroacoustic transducer has a structure in which a piezoelectric element in which an electrode made of a silver thin film or the like is attached to a metal diaphragm. The sound generation mechanism of an acoustic generator using a piezoelectric body as an electroacoustic transducer generates a shape distortion in the piezoelectric element by applying an AC voltage to both sides of the piezoelectric element, and the shape distortion of the piezoelectric element is made of a metal diaphragm. The sound is generated by transmitting to and vibrating.

  However, an acoustic generator having a structure in which a piezoelectric element is bonded to a metal diaphragm generates an area bending vibration by restraining a piezoelectric element that spreads and vibrates with a metal plate whose area does not change. It has been difficult to provide sound pressure characteristics with low conversion efficiency, small size, and low resonance frequency.

  In response to such a problem, the present applicant has proposed an acoustic generator in which a resin film is used as a diaphragm instead of a metal diaphragm (see, for example, Patent Document 1).

  In this acoustic generator, a bimorph-type laminated piezoelectric element is sandwiched between a pair of resin films in the thickness direction, and this resin film is fixed to a frame member in a tensioned state. Thereby, acoustic conversion efficiency is improved, and generation | occurrence | production of a high sound pressure is enabled.

JP 2010-177867 A

  However, in the above-described acoustic generator, the primary resonance frequency having the lowest frequency among the plurality of resonance frequencies of the vibration body is lowered by enlarging the vibration body made of a film integrated with the piezoelectric element. However, there is a problem that miniaturization is difficult.

  This invention is made | formed in view of the above, Comprising: It aims at providing the sound generator, sound generator, and electronic device which can improve the sound pressure in a low frequency range.

  An acoustic generator according to the present invention includes a film, a frame member provided on an outer peripheral portion of the film, a piezoelectric element provided on the film in a frame of the frame member, and the piezoelectric element embedded therein. And a resin layer filled in the frame of the frame member, and the resin layer has an uneven pattern on the surface.

  According to one aspect of the sound generator according to the present invention, there is an effect that the sound pressure in the low frequency region can be improved without increasing the size.

FIG. 1A is a plan view showing a sound generator of a first form. FIG. 1B is a cross-sectional view illustrating a sound generator according to the first embodiment. FIG. 2 is a diagram schematically showing the particle structure of the resin layer. FIG. 3 is a diagram schematically showing the particle structure of the resin layer.

  Hereinafter, embodiments of a sound generator, a sound generator, and an electronic device according to the present invention will be described in detail with reference to the drawings. Note that this embodiment does not limit the present invention. And each form illustrated below as embodiment can be suitably combined in the range which does not contradict the shape and dimension of each member which comprise an acoustic generator.

(1) 1st form [structure of a sound generator]
First, the 1st form of an acoustic generator is demonstrated based on FIG. 1A and FIG. 1B. FIG. 1A is a plan view showing a sound generator of the first form, and FIG. 1B is a cross-sectional view showing the sound generator of the first form. 1B shows a cross-sectional view along the line AA shown in FIG. 1A. Moreover, in FIG. 1B, in order to facilitate understanding, the thickness direction (y direction) of the multilayer piezoelectric element 1 is shown enlarged.

  1A and 1B includes a laminated piezoelectric element 1 on the upper surface of a film 3 that serves as a support plate and is sandwiched between a pair of frame-shaped frame members 5. ing. In other words, as shown in FIG. 1B, the sound generator of the first form is configured such that the film 3 is held in the first and second frame members 5a and 5b by holding the film 3 in a tensioned state. The laminated piezoelectric element 1 is disposed on the upper surface of the film 3 and is fixed to the second frame members 5a and 5b.

  Among these, the piezoelectric element 1 is formed in a plate shape, and upper and lower main surfaces are formed in a square shape, a rectangular shape, or a polygonal shape. The piezoelectric element 1 includes a laminate 13 in which piezoelectric layers 7 made of four ceramic layers and three internal electrode layers 9 are alternately laminated, and surface electrodes formed on both upper and lower surfaces of the laminate 13. The layers 15a and 15b and a pair of external electrodes 17 and 19 provided at both ends in the longitudinal direction x of the laminate 13 are included.

  The external electrode 17 is connected to the surface electrode layers 15a and 15b and one internal electrode layer 9b. The external electrode 19 is connected to the two internal electrode layers 9a and 9c. The piezoelectric layer 7 is polarized as shown by an arrow in FIG. 1B. When the piezoelectric layers 7a and 7b contract, the piezoelectric layers 7c and 7d extend, or the piezoelectric layers 7a and 7b extend. In this case, a voltage is applied to the external electrodes 17 and 19 so that the piezoelectric layers 7c and 7d contract.

  Upper and lower end portions of the external electrode 19 are extended to the upper and lower surfaces of the multilayer body 13 to form folded external electrodes 19a, respectively. These folded external electrodes 19a are surface electrodes formed on the surface of the multilayer body 13. A predetermined distance is extended between the surface electrode layers 15a and 15b so as not to contact the layers 15a and 15b.

  The four piezoelectric layers 7 and the three internal electrode layers 9 are fired at the same time in a stacked state, and the surface electrode layers 15 a and 15 b are the stacked bodies 13. Thereafter, the paste is applied and baked.

  Further, in the piezoelectric element 1, the main surface on the film 3 side and the film 3 are joined by an adhesive layer 21. The thickness of the adhesive layer 21 between the piezoelectric element 1 and the film 3 is 20 μm or less. In particular, the thickness of the adhesive layer 21 is preferably other than 10 μm. Thus, when the thickness of the adhesive layer 21 is 20 μm or less, the vibration of the laminated body 13 is easily transmitted to the film 3.

  As the adhesive for forming the adhesive layer 21, known ones such as an epoxy resin, a silicon resin, and a polyester resin can be used. As a method for curing the resin used for the adhesive, the vibrating body can be produced by using any method such as thermosetting, photocuring or anaerobic curing.

  Furthermore, in the acoustic generator of the first form, the resin layer 20 is formed by filling the inside of the frame member 5a with the resin so that the piezoelectric element 1 is embedded. In FIG. 1A, the resin layer 20 is not shown for easy understanding.

  The resin layer 20 can employ an epoxy resin, an acrylic resin, a silicon resin, rubber, or the like. The resin layer 20 is preferably applied in a state of completely covering the piezoelectric element 1 from the viewpoint of suppressing spurious. Further, since the film 3 serving as a support plate also vibrates integrally with the piezoelectric element 1, the region of the film 3 that is not covered with the piezoelectric element 1 is similarly covered with the resin layer 20.

  As described above, in the acoustic generator of the first embodiment, by embedding the piezoelectric element 1 with the resin layer 20, it is possible to induce an appropriate damping effect against the peak dip associated with the resonance phenomenon of the piezoelectric element 1. Such a damping effect can suppress the resonance phenomenon and suppress the peak dip. As a result, the frequency dependence of the sound pressure can be reduced.

  As the piezoelectric layer 7, existing piezoelectric ceramics such as lead-free piezoelectric materials such as lead zirconate (PZ), lead zirconate titanate (PZT), Bi layered compounds, and tungsten bronze structure compounds can be used. . The thickness of the piezoelectric layer 7 is set to 10 to 100 μm from the viewpoint of low voltage driving.

  The internal electrode layer 9 desirably includes a metal component composed of silver and palladium and a material component constituting the piezoelectric layer 7. By including the ceramic component constituting the piezoelectric layer 7 in the internal electrode layer 9, the stress due to the difference in thermal expansion between the piezoelectric layer 7 and the internal electrode layer 9 can be reduced, and the piezoelectric element 1 without stacking failure can be obtained. Can do. The internal electrode layer 9 is not particularly limited to a metal component composed of silver and palladium, but may be another metal component, and is limited to a material component constituting the piezoelectric layer 7 as a ceramic component. It may be other ceramic components.

  The surface electrode layers 15a and 15b and the external electrodes 17 and 19 preferably contain a glass component in a metal component made of silver. By containing the glass component in this way, a strong adhesion can be obtained between the piezoelectric layer 7 and the internal electrode layer 9 and the surface electrode layer 15 or the external electrodes 17 and 19.

  As shown in FIG. 1B, the frame member 5 has a rectangular shape, and is formed by bonding two rectangular frame-shaped frame members 5a and 5b, and the film 3 is interposed between the frame members 5a and 5b. Are fixed in a state where a tension is applied. The frame members 5a and 5b are made of stainless steel having a thickness of 100 to 1000 μm, for example. The material of the frame members 5a and 5b is not limited to stainless steel and may be any material that is more difficult to deform than the resin layer 20. For example, hard resin, plastic, engineering plastic, ceramics, etc. can be used. In the form, the material and thickness of the frame members 5a and 5b are not particularly limited. Furthermore, the frame shape is not limited to a rectangular shape, and part or all of the inner peripheral portion or the outer peripheral portion may be circular or elliptical, or the inner peripheral portion or the outer peripheral portion may be rhombus.

  The film 3 is fixed to the frame members 5a and 5b in a state where the film 3 is tensioned in the surface direction by sandwiching the outer peripheral portion of the film 3 between the frame members 5a and 5b, and the film 3 serves as a diaphragm. Plays. The thickness of the film 3 is, for example, 10 to 200 μm, and the film 3 is made of, for example, a resin such as polyethylene, polyimide, polypropylene, polystyrene, or tenn, or paper made of pulp, fiber, or the like. The peak dip can be suppressed by using these materials.

[Surface structure of resin layer]
Then, the surface structure of the resin layer which the acoustic generator of the 1st form of this embodiment has is demonstrated. In this embodiment, the surface structure is compared between the resin layer 20 having a concavo-convex pattern on the surface and the resin layer 20 having a smooth surface, but the resin capable of forming a concavo-convex pattern on the surface. If so, the same result can be obtained.

  Here, in the acoustic generator of the first form, for example, the resin layer 20 is formed by a film in which an indefinite shape resin is connected. That is, in the acoustic generator of the first embodiment, the first resonance frequency f0 of the vibrating body is lowered by enlarging the vibrating body made up of the film 3 and the resin layer 20 in which the piezoelectric element 1 is integrated. Instead, an approach is adopted in which the first resonance frequency f0 is lowered by giving the resin layer 20 forming the vibrating body physical properties that are easily deformable. The “first resonance frequency” mentioned here refers to the lowest resonance frequency among the plurality of resonance frequencies of the vibrating body.

  2 and 3 are diagrams schematically illustrating the particle structure of the resin layer 20. FIG. 2 schematically shows the microstructure of the resin layer 20 having a smooth surface, and FIG. 3 schematically shows the microstructure of the resin layer 20 having an uneven pattern on the surface. Is shown. The resin layer 20 shown in FIG. 2 is formed of a film having a smooth surface, such as a glass film. On the other hand, the resin layer 20 shown in FIG. 3 is formed of a matrix having a structure in which amorphous resins are partially bonded to each other. In addition, the shape of the surface of the resin layer 20 can be changed by the difference in the main agent, the solvent, the type of the reaction initiator, or the curing conditions contained in the resin. In this case, the shrinkage behavior when the above components such as the main component contained in the resin are cured is affected, and an uneven pattern is generated on the surface of the resin layer 20. In this case, an epoxy resin is preferable as the resin in that a large number of irregularities can be formed per unit area on the surface of the resin layer 20.

  Thus, when the surface of the resin layer 20 has an uneven pattern, since there are many thin portions in the resin layer 20, the resin layer 20 is compared with the case where the surface of the resin layer 20 is smooth. The rigidity of 20 can be lowered. Due to the reduction in rigidity, the vibration generated from the piezoelectric element 1 can be relaxed in the resin layer 20, and as a result, the primary resonance frequency of the vibrating body can be lowered.

  Therefore, according to the acoustic generator of the first embodiment, the sound pressure in the low frequency region can be improved.

[Production method]
A method for producing the acoustic generator of the present invention will be described.

  First, the bimorph type piezoelectric element 1 is prepared. In the piezoelectric element 1, a binder, a dispersant, a plasticizer, and a solvent are kneaded with a piezoelectric material powder to produce a slurry. As the piezoelectric material, any of lead-based and non-lead-based materials can be used.

  Next, the slurry can be formed into a sheet shape to obtain a green sheet, and an internal electrode paste is printed on the green sheet to form an internal electrode pattern, and the green sheet on which the electrode pattern is formed 3 Laminated sheets are laminated, and only a green sheet is laminated on the uppermost layer to produce a laminated molded body.

  Next, the laminated body 13 can be obtained by degreasing and firing the laminated molded body and cutting it to a predetermined size. The laminated body 13 processes the outer peripheral part as necessary, prints the paste of the surface electrode layers 15a and 15b on the main surface in the lamination direction of the piezoelectric layer 7 of the laminated body 13, and then continues in the longitudinal direction of the laminated body 13 The bimorph piezoelectric element 1 shown in FIGS. 1A and 1B can be obtained by printing the external electrodes 17 and 19 on both end faces of x and baking the electrodes at a predetermined temperature.

  Next, in order to impart piezoelectricity to the bimorph type piezoelectric element 1, a DC voltage is applied through the surface electrode layers 15 a and 15 b or the external electrodes 17 and 19, so that the piezoelectric layer 7 of the bimorph type piezoelectric element 1 Perform polarization. Such polarization is performed by applying a DC voltage so as to be in the direction indicated by the arrow in FIG. 1B.

  Next, the film 3 which becomes a support is prepared, the outer peripheral portion of the film 3 is sandwiched between the frame members 5a and 5b, and the film 3 is fixed in a tensioned state. Thereafter, an adhesive is applied to the film 3, the surface electrode layer 15a side of the bimorph type piezoelectric element 1 is pressed onto the film 3, and then the adhesive is cured by irradiation with heat or ultraviolet rays. . Then, a specific resin is poured inside the frame member 5a, the bimorph type piezoelectric element 1 is completely embedded, and the resin layer 20 is cured under a predetermined condition to obtain the first form of the sound generator. it can.

  In the acoustic generator configured as described above, the resin layer 20 having an uneven pattern on the surface is formed. Thus, the resin layer 20 having a concavo-convex pattern on the surface can reduce the rigidity of the resin layer 20 as compared with the resin layer 20 having a smooth surface. Due to such a reduction in rigidity, the vibration generated from the piezoelectric element 1 can be relaxed in the resin layer 20. As a result, the primary resonance frequency of the vibrating body can be lowered, and the sound pressure in the low frequency range can be improved.

(2) Second Embodiment The embodiments of the present invention have been described so far. However, the present embodiment may be implemented in various different forms other than the above-described embodiments. Therefore, hereinafter, other modes included in the present embodiment will be described.

[Scope of application]
For example, in the first embodiment, the bimorph type piezoelectric element is exemplified, but the present invention is not limited to this. That is, the present invention is not limited to the case where the piezoelectric element is a bimorph type. Even if the piezoelectric element is a unimorph type, the same effect can be obtained by adopting a resin layer having a concavo-convex pattern on the surface as in the first embodiment. Can be obtained.

[Speaker device]
Further, the sound generator described in the first embodiment can be configured as a sound generator, so-called “speaker device”, by being housed in a housing that houses the sound generator, a so-called resonance box. For example, if it can be configured as a large-sized speaker device used for televisions, personal computers, etc., it can be a medium-sized or small-sized device mounted on mobile terminals such as smartphones, mobile phones, PHS (Personal Handyphone System), and PDA (Personal Digital Assistants). It can also be configured as a speaker device. In addition, a speaker apparatus is not limited to said use, It can comprise as a speaker apparatus mounted in arbitrary electronic devices, such as a vacuum cleaner, a washing machine, and a refrigerator.

[Electronics]
Furthermore, the sound generator described in the first embodiment includes at least an electronic circuit connected to the sound generator, and a housing that houses the electronic circuit and the sound generator. It can also be configured as an electronic device having a function of generating sound from the sound. Examples of such electronic devices include televisions and personal computers, and various mobile terminals.

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 3 Film 5, 5a, 5b Frame member 7, 7a, 7b, 7c, 7d Piezoelectric layer 9, 9a, 9b, 9c Internal electrode layer 13 Laminated body 15a, 15b Surface electrode layer 17, 19 External electrode 20 Resin Layer x Longitudinal direction of laminate y Thickness direction of piezoelectric element

Claims (4)

With film,
A frame member provided on the outer periphery of the film;
A piezoelectric element provided on the film in the frame of the frame member;
A resin layer filled in the frame of the frame member so as to embed the piezoelectric element;
The acoustic generator according to claim 1, wherein the resin layer has an uneven pattern on a surface.   The acoustic generator according to claim 1, wherein the resin layer is an epoxy resin. The sound generator according to claim 1 or 2,
And a housing for housing the sound generator. The sound generator according to claim 1 or 2,
An electronic circuit connected to the acoustic generator;
A housing for housing the electronic circuit and the acoustic generator,
An electronic apparatus having a function of generating sound from the sound generator.