JPS5829677Y2 - Piezoelectric ceramic electroacoustic transducer - Google Patents

Description

[Detailed Description of the Invention] This invention relates to the structure of an electroacoustic transducer using piezoelectric ceramic.

As is well known, a piezoelectric ceramic acts as a piezoelectric body by applying a DC voltage in the thickness direction of the ceramic to perform a polarization operation that aligns the polarization direction of each domain.

By applying an electric field in the thickness direction of the piezoelectric ceramic, the shape of N changes (particularly expansion and contraction in the direction perpendicular to the thickness direction) and electromechanical conversion is performed.

In order to utilize such a piezoelectric ceramic as an electroacoustic transducer, it is necessary to convert this into vibration in the plane direction, since the conversion efficiency is extremely low when the expansion and contraction occur in the direction perpendicular to the thickness direction.

For this purpose, as shown in FIG. 1a, there is a bimorph type piezoelectric ceramic (hereinafter simply referred to as piezoelectric bimorph), which is made by fixing two piezoelectric ceramic blank plates 1a and 1b with their same polar surfaces facing each other, as shown in FIG. As shown in FIG. 1, there is a structure in which a piezoelectric ceramic plate 1a is fixed to a metal 2 (such as brass) with little expansion and contraction.

In the piezoelectric bimorph type shown in FIG. 1a, when a positive signal is applied to the electrodes formed on the upper surface of the blank plate 1a and the lower surface of 1b, for example, the upper blank plate 1a will extend in the direction of extension, and the lower blank plate 1b will Deforms in the direction of shrinkage.

Due to this opposing deformation, the piezoelectric bimorph is deformed so that its central portion is curved.

(Indicated by a dashed line in the figure).

Conversely, if a negative signal is applied, the opposite expansion and contraction will occur, causing curvature in the opposite direction.

Depending on the magnitude and direction of this curvature, a sound wave corresponding to the input signal is emitted into the atmosphere.

Also, in the case shown in Fig. 1, the piezoelectric ceramic base plate 1a fixed to the metal plate 2, which has extremely low expansion and contraction, expands and contracts in response to the input signal, and as a result, the central part deforms in a curved manner, causing it to leak into the atmosphere. Emit sound waves.

When such a piezoelectric bimorph or a piezoelectric ceramic having a structure fixed to a metal plate is used as a vibrating body, it is usually supported by fixing its peripheral portion as shown in FIG.

However, in such a support structure, for example, a piezoelectric bimorph will be explained (the same applies to the structure shown in FIG. 1).

), the piezoelectric ceramic blank is free to deform in the direction of elongation, but when it deforms in the direction of contraction, its periphery is fixed, so theoretically speaking, it will not shrink and it will curve. This results in no movement.

However, in reality, there is some degree of compliance in the fixed portion, so the rate of curvature is suppressed even though the curving movement is performed.

Therefore, as described above, it can be seen that supporting the peripheral portion in a fixed manner is an undesirable support structure in terms of acoustic radiation efficiency.

This invention solves the above-mentioned drawbacks by supporting the center of the piezoelectric ceramic, and also aims to expand the reproduction band by bringing an elastic body into close contact with the back surface of the piezoelectric ceramic, as shown in Figure 3 below. I will explain in detail.

In FIG. 3, 31 is a disk-shaped piezoelectric bimorph whose center is fixed to a metal support 32 and also electrically connected.

A pedestal 33 having approximately the same diameter as the piezoelectric bimorph 31 is integrally formed at the lower part of the support 32 at an appropriate distance from the piezoelectric bimorph 31 .

- The space between the pedestal 33 and the piezoelectric bimorph 31 is filled with an elastic body 34.

Further, lead wires 35 and 36 for input application are drawn out from the upper surface of the piezoelectric bimorph 31 and the pedestal 34, respectively.

In such a configuration, when a signal is input to the lead wires 35 and 36, the piezoelectric bimorph 31 moves from
The peripheral part vibrates as if swinging up and down, in other words cantilever vibration.

Therefore, since the vibration of the five cantilever beams is free to deform in both directions of expansion and contraction of the piezoelectric ceramic, the amplitude is not suppressed.

Therefore, the following becomes possible.

In other words, the piezoelectric ceramic has the disadvantage that the Q at resonance is extremely high and the reproduction band is extremely narrow, but if the structure of this invention in which the back surface of the piezoelectric bimorph 31 is brought into close contact with the elastic body 34, The reproduction band can be expanded by appropriately suppressing the Q during resonance.

This can be achieved by centrally supporting the piezoelectric bimorph 31, which allows the amplitude to be sufficiently large.

Moreover, since the elastic body 34 can absorb sound waves emitted from the back surface of the piezoelectric bimorph 31, it is extremely useful in practice, such as preventing interference of sound waves emitted from the front and back surfaces of the piezoelectric bimorph.

The above explanation was only about piezoelectric bimorphs\
It goes without saying that similar effects can be obtained with a structure in which a piezoelectric ceramic base plate is fixed to a metal plate.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of the disk-top piezoelectric bimorph and piezoelectric buzzer type ceramic, Figure 2 is a cross-sectional view showing the conventional holding structure, and Figure 3 is one of the piezoelectric ceramic type electroacoustic transducers of this invention. It is a partially cutaway perspective view. 31 is a disk-shaped piezoelectric bimorph, 33 is a pedestal, 32 is a support body, and 34 is an elastic body.

Claims (1)

[Scope of utility model registration request] The center of the disc-shaped piezoelectric bimorph 31 is fixed to a support 32 protruding from the center of a pedestal 33 while maintaining conductivity, and an elastic body 34 is filled between the piezoelectric bimorph 31 and the pedestal 33. A piezoelectric ceramic type electro-acoustic transducer featuring: