JPS5888000A - Damper construction of piezoelectric converter - Google Patents

Abstract

PURPOSE:To make the frequency characteristics of a diaphragm flat, by adhering a hard elastic body to a diaphragm made of a piezoelectric bimorph disc, adhering a solft elastic body and performing damping of the diaphrgam. CONSTITUTION:A piezoelectic element disc 12 is sticked to a metallic disc 11 to form a piezoelectric bimorph diaphragm and the assembly is supported in a ring shape with a comparatively hard elastic body 13 such as silicon rubber. Further, the elastic body 13 is supported with an elastic body 14 made of a softer substance such as sponge and foamed plastic than that of the elastic body 13 and closely adhered to a bottom plate 15. Oscillating parts 11-14 are covered with a frame 16 and a protecting plate 17 having small holes. Thus, even when a piezoelectric bimorph diaphragm is made small in size, an excellent damping characteristic can be provided, the frequency characteristics can be made flat and the diaphragm can simply be manufactured with an inexpensive material.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state damping method particularly suitable for small piezoelectric transducers using a piezoelectric bimorph circular diaphragm.

FIG. 1 shows a configuration example of a braking method used in a conventional piezoelectric transducer. 1 is a metal disk, and 2 is a piezoelectric element disk, both of which are bonded together by adhesive to form a piezoelectric bimorph diaphragm. 6 is a first back air chamber, 4 is a plurality of small holes for air leakage provided in the frame 9, and 5 is a second back air chamber.
In the back air chamber, 6 is a bottom plate, 7 is a protection plate, and 8 is a plurality of sound holes provided in the protection plate.

In this way, the conventional braking method uses a so-called two-degree-of-freedom acoustic vibration system consisting of the diaphragm, first back air chamber, leakage hole, and second back air chamber to brake the diaphragm. . When actually used in a telephone, etc., a earpiece (or mouthpiece) (not shown) is provided on the front surface of the protection plate 7, and an acoustic vibration system with a degree of freedom can be transmitted through the small holes provided in the front surface of the protection plate 7. In the case of a handset, the frequency characteristics of the output sound pressure with respect to the electrical input to the diaphragm are flat, and in the case of a transmitter, the frequency characteristics of the electrical output with respect to the acoustic input to the diaphragm are flat. It is designed to.

FIG. 2 shows an example of the output sound pressure frequency characteristic of a conventional telephone receiver (in the case of a six-degree-of-freedom acoustic vibration system).

In the case of a telephone, the upper limit frequency of the band is approximately 3400 Hz, and it is preferable that the output sound pressure decreases in the frequency band above this G). If we use the above 6 degrees of freedom acoustic vibration system,
It is known that the effective frequency band can be expanded to approximately JS times the resonance frequency of the diaphragm. Therefore, the resonant frequency f1 of the diaphragm may be approximately 3400 Hz/-fY; In order to flatten the frequency characteristics, it is necessary to uniquely determine the dimensions of the first back air chamber 6, second back air chamber 5, small air leakage hole 4, etc. regarding the mechanical impedance of the diaphragm. 0 When trying to downsize the piezoelectric transducer as described above, it is first necessary to reduce the outer diameter of the diaphragm. Since there is a manufacturing limit to reducing the thickness of the piezoelectric diaphragm, reducing the outer diameter of the diaphragm increases the mechanical impedance of the diaphragm. Therefore, it becomes necessary to reduce the dimensions of the first back air chamber 6, the second back air chamber 5, the small air leakage hole 4, etc. Usually, the frame 9 shown in Fig. 1, the earpiece (or mouthpiece) (not shown), etc. are often made of plastic molded products, and the back air chambers and small holes become extremely small in the early stages of molding. becomes.

In addition, if the outer diameter of the diaphragm becomes smaller and its resonant frequency becomes equal to the required band - upper limit frequency, damping due to acoustic vibration, etc. described above (or band expansion will occur, which is undesirable. Therefore, the diaphragm It is necessary to devise measures such as damping the resonance by another method.

The present invention is intended to provide a solid damping structure directly connected to a diaphragm as a damping structure suitable for downsizing the piezoelectric transducer, and will be described below with reference to the drawings.

FIG. 6 shows an embodiment of the present invention, in which 11 is a metal disk;
2 is a piezoelectric element disk, and the piezoelectric bimorph diaphragm is constructed by bonding the two together.

16 is a relatively hard elastic body made of silicone rubber, 14 is a softer elastic body than the elastic body 13 made of sponge, foamed plastic, etc., 15 is a bottom plate, 16 is a frame, and 17 is a protection plate. be.

The elastic body 16 has an annular upper part, and 6- This portion is in close contact with the piezoelectric element 12.

In addition, the lower part has a wide circular flat surface, and the elastic body 1
4 and is in close contact with the entire surface. The elastic body 14 is in the shape of a disk, and by pressing it down with the bottom plate 15, the two elastic bodies 16 and 14 maintain an appropriate state of rotation and form a sandwich-like structure between the bottom plate 15 and the piezoelectric bimorph diaphragm. It is composed of

FIG. 4 shows the damping effect of the output sound pressure according to the present invention, and is an example of the characteristics of the receiver when the resonant frequency f2 of the diaphragm becomes equal to the upper limit frequency of the required band due to miniaturization.

Curve A is the output sound pressure frequency characteristic in an unbraked state without the elastic bodies 15 and 14. Curve B is an example in which the elastic body 14 is removed and only the elastic body 16 is fixed to the bottom plate for braking, and there is almost no braking effect, and the stiffness of the hard elastic body 13 is added, causing the resonance frequency to decrease. As the value increases, the output sound pressure of low frequencies decreases. Note that when braking is performed only with the soft elastic body 14 (not shown), it is the same as when no braking is performed (5rrJ = 4 - curve A), or as the pressing force by the bottom plate is increased. The curve is close to curve B, and there is almost no braking effect. Curve C is the case when both elastic bodies 13 and 14 are used as shown in FIG. 6, and by appropriately adjusting the pressing force of the bottom plate 15, a good result can be obtained without reducing the output sound pressure at low frequencies. The braking effect can be changed.

In addition, if the diaphragm resonance frequency is lower than the required upper limit frequency, it is of course possible to extend the band by providing an appropriate earpiece in front of the protection plate 17 to configure a so-called two-degree-of-freedom acoustic vibration system. be. In this embodiment, the bottom plate 15 and the frame 16 are made up of separate parts, but they are made into an integrated cup-shaped structure, into which the elastic bodies 14 and 13 are inserted to form a piezoelectric bimorph diaphragm (11 , 12) may be applied to achieve an appropriate compression state.

FIG. 5 shows another embodiment of the present invention, in which the upper part of the hard elastic body 18 is made into a circular part, and this part is tightly attached to the piezoelectric bimorph diaphragm (11, 12). By appropriately selecting the dimensions of the circular portion 18a and the pressing force exerted by the bottom plate, the same braking effect as described above can be achieved.

FIG. 6 shows another embodiment of the present invention, in which a large number of protrusions 19a are provided on the upper part of the hard elastic body 19, and the protrusions 19a are brought into close contact with the diaphragm (11, 12). be.

FIG. 7 shows another embodiment of the present invention, in which the piezoelectric element disk 12 of the piezoelectric bimorph diaphragm is oriented upward, that is, the metal disk 11 and the hard elastic body 13 are in close contact with each other.

As explained above, according to the present invention, it is possible to provide good damping even when the piezoelectric bimorph diaphragm is downsized, and it is possible to achieve good damping without configuring a complicated acoustic imaging system unlike the conventional one. It has the advantage that the diaphragm can be easily braked using inexpensive damping materials, and the thickness of the transducer can be made smaller than that of conventional ones.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a braking structure used in a conventional piezoelectric transducer, Fig. 2 is a characteristic diagram showing the braking effect of a conventional telephone handset, and Fig. 5 is a longitudinal cross-sectional view showing the braking structure of the present invention. figure,
Figure 4 is a characteristic diagram showing the braking effect of the present invention, Figures 5 and 6.
7 are longitudinal cross-sectional views of main parts showing other embodiments of the present invention. 1.11 Metal disk, 2, 12 Piezoelectric element disk, 6 First back air chamber, 4 Small air leak hole, 5 Second back air chamber, 6
, 15 Bottom plate, 7, 17 Protective plate, 8 Sound hole, 9, 16
・Frame, 13.18.19・Hard elastic body, 14
・Soft elastic body. Patent applicant Daisuke Higo, President and CEO of Daiko Electric Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. In a piezoelectric transducer using a diaphragm made of a piezoelectric bimorph disk, a hard elastic body is brought into close contact with the above-mentioned imaging plate and used as a first damping material, and a fixed part and the above-mentioned first
Braking of a piezoelectric transducer characterized in that an elastic body softer than the first damping material is brought into close contact between the damping material and the second damping material, and the diaphragm is damped by these damping materials. Composition.