WO2006025138A1

WO2006025138A1 - Piezoelectric electroacoustic transducer

Info

Publication number: WO2006025138A1
Application number: PCT/JP2005/009746
Authority: WO
Inventors: Tetsuo Takeshima; Masakazu Yamauchi; Muneyuki Daidai; Manabu Sumita
Original assignee: Murata Manufacturing Co., Ltd.
Priority date: 2004-08-30
Filing date: 2005-05-27
Publication date: 2006-03-09

Abstract

[PROBLEMS] To provide a piezoelectric electroacoustic transducer having high sound pressure over a wide range. [MEANS FOR SOLVING PRPBLEMS] The piezoelectric electroacoustic transducer is manufactured by sticking a piezoelectric diaphragm (A) smaller than a resin film (B) to the central part on one side of the resin film, and supporting the peripheral part of the resin film (B) on the case. The piezoelectric diaphragm (A) is formed by bonding upper and lower piezoelectric elements (1, 10), having an intermediate layer (20) sandwiches in between. Each piezoelectric element has a piezoelectric ceramics layer polarized in the thickness direction, and electrodes are provided on the front and rear major surfaces of each piezoelectric element. Each piezoelectric element elongates/contracts reversely in the plane direction when an AC signal is applied between these electrodes, and the piezoelectric diaphragm generates bending vibration as a whole. Sound pressure of secondary resonance is increased by the intermediate layer (20) and high sound pressure can be obtained over a wide band.

Description

Specification

Piezoelectric electroacoustic transducer

Technical field

[0001] The present invention relates to a piezoelectric electroacoustic transducer such as a piezoelectric resono piezoelectric sounder or a piezoelectric speaker.

Background art

Conventionally, piezoelectric electroacoustic transformation is widely used as a piezoelectric sounder or a piezoelectric receiver that generates an alarm sound or an operation sound in electronic devices, home appliances, mobile phones, and the like.

The conventional piezoelectric electroacoustic transducer has a problem that the resonance frequency becomes high because the piezoelectric diaphragm is accommodated in the case and the periphery of the piezoelectric diaphragm is fixed to the case. In order to reduce the resonance frequency, the size of the piezoelectric diaphragm must be increased, and the case becomes larger. In addition, there is a large drop in sound pressure between the primary resonance frequency and the secondary resonance frequency, and an almost flat sound pressure characteristic cannot be obtained over a wide band! /.

[0003] Therefore, the applicant of the present application has proposed a piezoelectric electroacoustic transducer that can achieve both a reduction in size and a low frequency, a large amount of displacement, and a substantially flat sound pressure characteristic in a wide band (patent) Reference 1). In this electroacoustic transformation, a piezoelectric element having a smaller laminated structure is attached to one surface or both surfaces of a resin film, and the outer peripheral portion of the resin film is supported by a casing. A piezoelectric element consists of two piezoelectric ceramic layers stacked with internal electrodes in between, and the polarization direction of each ceramic layer is the same direction, and an AC signal is generated between the main surface electrode provided on the front and back surfaces of the piezoelectric element and the inside. Is applied to generate flexural vibration.

Thus, by supporting the piezoelectric element through the resin film, it is possible to obtain a low resonance frequency and a substantially flat sound pressure characteristic in a wide band.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-7400

[0004] In the above-described piezoelectric electroacoustic transducer, a piezoelectric element having a two-layer structure is used. To increase the sound pressure, a method of increasing the number of layers can be considered. However, by simply increasing the number of layers, electrical sound with a high sound pressure in a wide band where the effect of improving the sound pressure characteristics near the secondary resonance is small. It was difficult to get Hibiki.

Disclosure of the invention

Problems to be solved by the invention

[0005] Therefore, an object of the present invention is to provide a piezoelectric electroacoustic change with a wide and high sound pressure in a band.

Means for solving the problem

In order to achieve the above object, the invention according to claim 1 is characterized in that a piezoelectric diaphragm smaller in size than the resin film is attached to the center of one surface of the resin film, and the peripheral part of the resin film is enclosed in a housing. A piezoelectric electroacoustic transducer supported by the body! The piezoelectric diaphragm is formed by laminating and bonding two piezoelectric elements with an intermediate layer therebetween, and each piezoelectric element has a single or a plurality of piezoelectric ceramic layers polarized in the thickness direction. Each piezoelectric element has electrodes on the front and back main surfaces or inside, and by applying an AC signal between these electrodes, the two piezoelectric elements expand and contract in opposite directions in the plane direction, and the piezoelectric diaphragm as a whole vibrates and vibrates. A piezoelectric type electroacoustic transducer characterized by generating the above is provided.

The piezoelectric diaphragm has a structure in which two piezoelectric elements are stacked with an intermediate layer therebetween, and each piezoelectric element expands and contracts in the opposite direction in the plane direction by an applied AC signal. Therefore, the piezoelectric diaphragm generates bending vibration as a whole. A piezoelectric diaphragm is affixed to the resin film, and the periphery of the resin film is supported by the housing, so that the vibration of the piezoelectric diaphragm is not obstructed and has an almost flat sound pressure characteristic over a wide band. Acoustic variation is obtained.

In addition, since the piezoelectric diaphragm is formed by laminating and bonding two piezoelectric elements with an intermediate layer in between, a high-order (secondary resonance) mode is greatly excited. As a result, high sound pressure electroacoustic transformation can be obtained in a wide band.

As the intermediate layer of the present invention, a resin adhesive having a smaller Young's modulus and density than the ceramic constituting the piezoelectric element is generally used. The intermediate layer should have a uniform thickness.

[0008] As in claim 2, the intermediate layer may be a resin adhesive containing a spherical filler having a uniform diameter.

In this case, since the diameter of the filler determines the thickness of the intermediate layer, the intermediate layer has a uniform thickness. Can be obtained.

[0009] As in claim 3, the intermediate layer is made by impregnating a fibrous sheet such as paper with a resin adhesive.

Also in this case, the thickness is almost determined by the fibrous sheet, and the upper and lower piezoelectric elements are bonded and fixed by the resin adhesive impregnated therein.

[0010] As a structure of the piezoelectric diaphragm, as in claim 4, each of the two piezoelectric elements has a single piezoelectric ceramic layer, and main surface electrodes are provided on the front and back surfaces of the single piezoelectric ceramic layer. An AC signal may be applied between the front and back main surface electrodes. As in claim 5, each of the two piezoelectric elements has a plurality of piezoelectric ceramic layers, and the surface of the plurality of piezoelectric ceramic layers. The main surface electrode and the internal electrode are provided between the back surface and each piezoelectric ceramic layer, and the polarization directions of the adjacent piezoelectric ceramic layers are opposite to each other, and between the main surface electrode and the internal electrode on the front and back surfaces. An AC signal may be applied.

In either case, a large flexural vibration can be generated in the piezoelectric diaphragm.

The invention's effect

As is apparent from the above description, according to the invention of claim 1, a laminated piezoelectric vibration plate that generates flexural vibration is attached to one surface of the resin film, and the outer peripheral portion of the film is enclosed by a housing. Since it is supported by the body, the vibration of the piezoelectric diaphragm is not hindered, and an electroacoustic transducer having a broad and substantially flat sound pressure characteristic can be obtained.

In addition, since the piezoelectric diaphragm is made by laminating and bonding two piezoelectric elements with an intermediate layer in between, the higher-order (resonance) mode is greatly excited, and electroacoustic change with high sound pressure is achieved over a wide band. Obtainable.

Brief Description of Drawings

FIG. 1 is a perspective view of an example of piezoelectric electroacoustic transformation according to the present invention.

2 is an exploded perspective view of the piezoelectric electroacoustic transducer shown in FIG.

FIG. 3 is an exploded perspective view of a piezoelectric diaphragm used in the piezoelectric electroacoustic transducer shown in FIG. 1.

4 is a schematic cross-sectional view of a piezoelectric diaphragm used in the piezoelectric electroacoustic transducer shown in FIG. FIG. 5 is a sound pressure characteristic diagram of a piezoelectric diaphragm having an intermediate layer and a piezoelectric diaphragm having no intermediate layer.

[Fig. 6] A diagram showing the relationship between the thickness of the intermediate layer and the sound pressure obtained by the finite element method simulation.

FIG. 7 is a diagram showing the relationship between the intermediate layer thickness, resonance frequency fr, and electromechanical coupling coefficient K obtained by finite element method simulation.

FIG. 8 is a partial cross-sectional view of a second embodiment of a piezoelectric diaphragm.

FIG. 9 is a cross-sectional view of a third embodiment of a piezoelectric diaphragm including a resin film.

FIG. 10 is a cross-sectional view of a fourth embodiment of a piezoelectric diaphragm including a resin film.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described with reference to examples.

Example 1

FIGS. 1 to 4 show examples of the piezoelectric force that is the first embodiment of the piezoelectric electroacoustic transformation according to the present invention.

This embodiment includes a piezoelectric diaphragm A, a resin film B on which the piezoelectric diaphragm A is pasted, and a housing that stores the resin film B. Here, the housing has a lower cover 30 having a large number of sound emission holes 30a, a frame-shaped lower case 31, a U-shaped upper case 32, and a number of sound emission holes 33a, similar to the lower cover 30. It consists of an upper cover 33.

[0015] As shown in Figs. 3 and 4, the piezoelectric diaphragm A is formed by laminating and bonding two piezoelectric elements 1 and 10 with an intermediate layer 20 therebetween, and is formed in a rectangular shape as a whole. Yes. The upper piezoelectric element 1 is formed by laminating two piezoelectric ceramic layers la and lb. Main surface electrodes 2 and 3 are formed on the front and back main surfaces of the piezoelectric element 1, and between the ceramic layers la and lb. An internal electrode 4 is formed on the substrate. The two ceramic layers la and lb are polarized in opposite directions in the thickness direction as indicated by an arrow P. The lower piezoelectric element 10 has the same structure as the upper piezoelectric element 1, but the polarization direction P is opposite. That is, two piezoelectric ceramic layers 10a and 10b are laminated, main surface electrodes 12 and 13 are formed on the front and back main surfaces, and an internal electrode 14 is formed between the ceramic layers 10a and 10b. The two ceramic layers 10a and 10 are polarized in the opposite direction in the thickness direction as indicated by the arrow P !. Here, as the ceramic layers la, lb, 10a and 10b, rectangular PZT ceramics having an outer dimension of 24 × 12 mm and a thickness of one layer of 15 m were used.

The intermediate layer 20 in this example uses a fibrous sheet such as Japanese paper impregnated with epoxy resin. Its thickness is about 40 m. The intermediate layer 20 should have a Young's modulus and density smaller than ceramics. Specifically, the Young's modulus is 1 X 10 ² to 1 X 10 ⁴ MPa, and the density is 0.8 to 2. Okg / m ³ Good thing. The piezoelectric ceramic used in this example had a Young's modulus of 6.3 × 10 ⁴ MPa and a density of 7.8 × 10 ³ kg / m ³ .

[0017] The front-side main surface electrode 2 and the back-side main surface electrode 3 of the piezoelectric element 1, and the front-side main surface electrode 12 and the back-side main surface electrode 13 of the piezoelectric element 10 are one end face of the piezoelectric elements 1 and 10. And they are connected to each other through an end face electrode 5 formed on one end face of the intermediate layer 20. The internal electrode 4 of the piezoelectric element 1 and the internal electrode 14 of the piezoelectric element 10 are connected to the other end face of the piezoelectric elements 1 and 10 and the end face electrode 6 formed on the other end face of the intermediate layer 20. A part of the main surface electrode 2 of the upper piezoelectric element 1 is cut off, and an auxiliary electrode 7 connected to the end face electrode 6 is formed in the cut portion. In FIG. 3, the end face electrodes 5 and 6 are shown separated by the piezoelectric elements 1 and 10 and the intermediate layer 20, but in actuality, the piezoelectric elements 1 and 10 and the intermediate layer 20 are laminated and bonded continuously. Formed.

When an AC signal is applied between the end face electrodes 5 and 6, one piezoelectric element expands in the plane direction, and the other piezoelectric element contracts in the plane direction. That is, since both the piezoelectric elements 1 and 10 expand and contract in the direction opposite to the plane direction, the piezoelectric diaphragm A can be flexibly vibrated as a whole.

[0018] The front and back surfaces of the piezoelectric diaphragm A are covered with resin layers 8 and 9, as shown in FIG. The resin layers 8 and 9 have a role as a protective layer for preventing the piezoelectric elements 1 and 10 from cracking due to a drop impact, and are provided as necessary. At both corners of one short side of the front-side resin layer 8, a notch 8a where a part of the main surface electrode 2 is exposed and a notch 8b where the auxiliary electrode 7 is exposed are formed. In addition, similar notches 9a and 9b are formed in the backside resin layer 9, but these notches are provided to eliminate directionality and can be omitted.

[0019] The piezoelectric diaphragm A is affixed to a substantially central portion of the surface of the rectangular resin film B having a larger size. As the pressure-sensitive adhesive, for example, a silicone-based or acrylic-based pressure-sensitive adhesive is used. However, it is not limited to adhesion, and adhesion or heat welding may be used. The resin film B is thinner than the piezoelectric diaphragm A and is formed of a resin material having a Young's modulus of 1 to 200 MPa. Specifically, a resin material such as ethylene propylene rubber or styrene butadiene rubber is used.

Here, ethylene propylene rubber having an outer dimension of 31.2 X 15.5 mm and a thickness of 70 m was used.

[0020] The upper and lower surfaces of the peripheral portion of the resin film B are bonded and supported by upper and lower cases 31, 32. Instead of adhesion, adhesion or heat welding may be used. The cases 31 and 32 are formed of a metal plate or a resin plate having a thickness (for example, 0.25 to 0.35 mm) that can secure the vibration space of the piezoelectric diaphragm A. In addition to the piezoelectric diaphragm A, a terminal portion 34 is attached to the upper surface of the resin film B, and the terminal portion 34 is exposed on the side portion of the upper cover 33. The terminal portion 34 is provided with terminal electrodes 35 and 36 for connecting the outside and the piezoelectric diaphragm A on an insulating substrate such as a glass epoxy substrate. The electrodes 2 and 7 exposed from the layer 8 are connected to each other through force leads 37 and 38. The lead portions 37 and 38 may be thin film electrodes or thick film electrodes. An electric signal is input to the piezoelectric diaphragm A via the terminal portion 34.

In this embodiment, since the terminal portion 34 is provided on one end side of the resin film B, the upper case 32 is formed in a U shape with one end side opened. However, when the terminal portion 34 is provided on both end sides of the resin film B, In addition, the upper case 32 can be constituted by a pair of parallel walls.

[0021] In this embodiment, a resin film B with a piezoelectric diaphragm A attached thereto is bonded and supported by frame-like cases 31, 32 from above and below, and the openings of these cases 31, 32 are covered with a thin plate. Since it is configured to close at 30, 33, it is possible to configure a thin (less than lmm) electroacoustic transformation as a whole. Since the terminal portion 34 is provided on one end side of the electroacoustic transducer, the external connection can be made from one direction.

In the above description, the structure of the piezoelectric electroacoustic transformation unit has been described. However, in actual production, a plurality of piezoelectric diaphragms A and terminal portions 34 are formed on a wide-area resin film B. Glue the adhesive film case B to the upper and lower surfaces of the resin film B, and then cover the upper and lower sides of the aggregate board state cover 30, 33, and then separate it into a single piezoelectric electroacoustic transformation. It can also be mass-produced by cutting. FIG. 5 shows the sound pressure characteristics of a piezoelectric electroacoustic transducer using a piezoelectric diaphragm having an intermediate layer, and a piezoelectric electroacoustic transducer using a piezoelectric diaphragm without an intermediate layer! This is shown in contrast with the sound pressure characteristics of. The piezoelectric diaphragm used here has two piezoelectric ceramic layers on one side in the same way as in FIG. 4, and the intermediate layer is 40 m thick and paper is impregnated with grease.

As can be seen from Fig. 5, the sound pressure rises not only at the primary resonance near lOOOHz, but also at the secondary resonance around 3000-4000Hz. In particular, the increase in sound pressure at the secondary resonance indicated by X in Fig. 5 is remarkable.

[0024] Table 1 is a table comparing dimensions and sound pressure characteristics of a piezoelectric diaphragm having an intermediate layer and a piezoelectric diaphragm having no intermediate layer. The piezoelectric diaphragm used here is the same as in FIG. As can be seen from Table 1, the average sound pressure is increased by 4.9 dB in the piezoelectric diaphragm with the intermediate layer compared to the piezoelectric diaphragm without the intermediate layer.

[0025] [Table 1]

[0026] Fig. 6 shows the relationship between the thickness of the intermediate layer and the sound pressure by finite element simulation. Fig. 7 shows the relationship between the thickness of the intermediate layer, the resonance frequency fr, and the electromechanical coupling coefficient K. It was obtained by finite element method simulation.

However, the resin film used here is a circle with a diameter of 20 mm, and the piezoelectric diaphragm is formed by laminating a circular ceramic layer with a diameter of 18 mm and a thickness of 15 m on two sides. The Young's modulus of the intermediate layer lOOMPa The density was 1. Okg / m ³ .

Fig. 6 Thickness of the middle layer SOmm, 0.02mm, O.04mm, O.06mm, 0.08m, 0.1mm It can be seen that the sound pressure is higher in the primary resonance and the secondary resonance in the case of having the intermediate layer than in the case of having no intermediate layer. Karu.

As shown in Fig. 7, the resonance frequency increases as the thickness of the intermediate layer increases, but the rate of increase of the secondary resonance frequency is greater than that of the primary resonance frequency.

In addition, regarding the electromechanical coupling coefficient K, it can be seen that as the thickness of the intermediate layer increases, the K of the primary resonance decreases while the K of the secondary resonance increases. When the thickness of the intermediate layer is 0.07 mm or less, the primary resonance K is larger than the secondary resonance K, but when it exceeds 0.07 mm, the secondary resonance K is larger than the K of the secondary resonance.

In general, electroacoustic transducers are often used in the region where K of primary resonance is larger than K of secondary resonance, and the product of resonance frequency and electromechanical coupling coefficient affects sound pressure.

In order to obtain a nearly flat and high sound pressure in a wide band, the thickness of the intermediate layer is 0.02 to 0.0.

It should be used in the range of 6 mm, more preferably in the range of 0.03 to 0.05 mm.

Example 2

FIG. 8 shows a cross-sectional structure of a second embodiment of the piezoelectric diaphragm.

In this embodiment, an intermediate layer 21 in which a spherical filler 23 having a diameter of 30 μm is dispersed and mixed in a resin adhesive 22 such as an epoxy resin is used. The filler 23 may be an insulating material or a metal material.

In this case, since the filler 23 does not overlap vertically, when the upper and lower piezoelectric elements 1 and 10 are pressure-bonded with the intermediate layer 21 in between, the thickness of the intermediate layer 21 is limited by the diameter of the filler 23, and the uniform thickness (about 40 μm) of intermediate layer 21 can be obtained.

Example 3

FIG. 9 shows a third embodiment of the piezoelectric diaphragm.

In the piezoelectric diaphragm A of the first embodiment, the piezoelectric elements 1 and 10 bonded with the intermediate layer 20 in between have been described as having two piezoelectric ceramic layers, but the piezoelectric diaphragm A1 of the third embodiment In this case, the piezoelectric elements 1 and 10 bonded with the intermediate layer 20 therebetween have one piezoelectric ceramic layer la and 10a. Arrow P indicates the direction of polarization.

In this embodiment, the main surface electrodes 2 and 3 are provided on the front and back surfaces of the piezoelectric ceramic layers la and 10a, and the front surface main surface electrode 2 of the piezoelectric element 1 and the back surface main surface electrode 13 of the piezoelectric element 10 form the end surface electrode 6. The back side main surface electrode 3 of the piezoelectric element 1 and the front side main surface electrode 12 of the piezoelectric element 10 are connected to each other. It is connected via the end face electrode 5.

Also in this case, when an AC signal is applied between the end face electrodes 5 and 6, when one piezoelectric element expands in the plane direction, the other piezoelectric element contracts in the plane direction. That is, since both the piezoelectric elements 1 and 10 expand and contract in the direction opposite to the plane direction, the piezoelectric diaphragm A1 can be flexibly vibrated as a whole.

Example 4

FIG. 10 shows a fourth embodiment of the piezoelectric diaphragm.

The piezoelectric diaphragm A2 of this example has piezoelectric ceramic layers la to lc and 10a to 10c of piezoelectric elements 1, 10 force S3 layers bonded with the intermediate layer 20 therebetween. Arrow P indicates the direction of polarization.

In this embodiment, the main surface electrode and the internal electrode are alternately drawn out to different end portions and connected to the end surface electrodes 5 and 6. Since the number of piezoelectric ceramic layers constituting the piezoelectric elements 1 and 10 is increased, the sound pressure is higher than that of the piezoelectric diaphragm shown in FIGS. 4 and 9, and the presence of the intermediate layer 20 causes the secondary resonance sound. The pressure also increases, and an electroacoustic transducer with a wide band and high sound pressure can be obtained.

[0030] The present invention is not limited to the above-described embodiments, but can be modified without departing from the spirit of the present invention.

The structure of the housing is not limited to a frame type case and a flat plate cover that are bonded to the upper and lower surfaces of the resin film as in the embodiment. For example, the frame type case and the flat plate cover are integrated. It is also possible to adhere the concave case to the upper and lower surfaces of the resin film! / Since it is composed of a concave case that contains the resin film and a flat cover that covers the opening on the upper surface. Good.

Claims

The scope of the claims

[1] A piezoelectric electroacoustic transducer in which a piezoelectric diaphragm smaller than the resin film is attached to the center of one surface of the resin film, and the periphery of the resin film is supported by a housing. The diaphragm is made by laminating and bonding two piezoelectric elements with an intermediate layer in between, and each of the piezoelectric elements has a single or a plurality of piezoelectric ceramic layers polarized in the thickness direction.

Each piezoelectric element has electrodes on the front and back main surfaces or inside, and by applying an AC signal between these electrodes, the two piezoelectric elements expand and contract in opposite directions in the plane direction, and the piezoelectric diaphragm as a whole undergoes bending vibration. A piezoelectric electroacoustic transducer characterized by being generated.

[2] The piezoelectric electroacoustic transducer according to [1], wherein the intermediate layer is a resin adhesive containing a spherical filler having a uniform diameter.

3. The piezoelectric electroacoustic transducer according to claim 1, wherein the intermediate layer is a fibrous sheet such as paper impregnated with a resin adhesive.

[4] Each of the two piezoelectric elements has a single piezoelectric ceramic layer,

Main surface electrodes are provided on the front and back surfaces of the piezoelectric ceramic layer,

4. The piezoelectric electroacoustic transducer according to claim 1, wherein an AC signal is applied between the front and back main surface electrodes.

[5] Each of the two piezoelectric elements has a plurality of piezoelectric ceramic layers,

A main surface electrode and an internal electrode are provided between the front and back surfaces of the plurality of piezoelectric ceramic layers and the piezoelectric ceramic layers of each layer,

The direction of polarization of adjacent piezoelectric ceramic layers is opposite,

2. An AC signal is applied between the front and back main surface electrodes and the internal electrode. The piezoelectric electro-acoustic deformation described in 3 or 3 is ^^.