JPH0564293A - Acoustic transducer - Google Patents

Abstract

PURPOSE:To provide the acoustic transducer which can obtain wide directional width even when the cross sectional area of a piezoelectric oscillator is enlarged. CONSTITUTION:Electrodes 2a, 2b are provided through piezoelectric ceramics cylinder 1b to a piezoelectric ceramics cylinder 1a at a piezoelectric oscillator 3a, a phase shift board 4 as a first layer is joined to the side of the electrode 2a, a delay board 5 as a second layer is joined to the phase shift board 4, and the joint face of the phase shift board 4 and the delay board 5 is made spherical. A bagging 6a is joined to the side of the electrode 2b at the piezoelectric oscillator 3a, a sound cut-off board 7a is joined onto the outer peripheral face of the piezoelectric oscillator 3 and the bagging 6a, the electrodes 2a, 2b are respectively equipped with lead wires 8a, 8b, and the surfaces of the piezoelectric oscillator 3, phase shift board 4, delay board 5, bagging 6 and sound cut-off board 7a are molded by mold resin 9a so as to be electrically insulated from the water of an external medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency acoustic transducer (hereinafter referred to as a transducer) used for a sensor.

[0002]

2. Description of the Related Art Conventionally, in order to transmit at a high frequency, a transducer of this type is provided with electrodes 2c and 2d via a piezoelectric ceramic cylinder 1b as shown in FIG. The piezoelectric vibrators 3b are resonantly vibrated in the longitudinal direction, and a sound insulating plate 7b made of a sound insulating material such as cork is joined to the outer peripheral surface of the piezoelectric ceramic cylinder 1b to form the piezoelectric ceramic cylinder 1b.
The backing 6b was joined to one of the end faces of the to shield the sound, and efficient electroacoustic conversion was performed.

[0003]

However, in the conventional acoustic transducer, the effective radiation solid angle of the sound wave, that is, the directivity width is inversely proportional to the diameter of the piezoelectric vibrator and is inversely proportional to the frequency. As a result, the diameter of the piezoelectric vibrator for increasing the frequency while obtaining a constant directivity width must be inversely reduced. This means that when the resonance frequency in the thickness direction of the piezoelectric vibrator is used efficiently, the thickness of the piezoelectric vibrator must be thinned in inverse proportion to the frequency. There has been a problem that the volume is decreased in inverse proportion to the cube of the frequency, and as a result, when the frequency is increased, the converted power, that is, the output sound pressure is significantly reduced. An object of the present invention is to provide an acoustic transducer capable of obtaining a wide directional width even if the cross-sectional area of the piezoelectric vibrating body is increased.

[0004]

According to the present invention, a piezoelectric ceramic body having a first surface and a second surface facing each other, and a first ceramics body bonded to the first and second surfaces, respectively. An acoustic transducer having a second electrode, a first layer having a flat surface for bonding to the surface of the first electrode and a non-planar surface for the other surface, and a non-flat surface of the first layer. A second layer having a non-planar joint surface with a flat surface, the sound velocity passing through the second layer is slower than the sound velocity passing through the first layer, and the thickness of the first layer is 3/8 or less of the wavelength of the vibration wave propagating inside the first layer,
Moreover, an acoustic transducer is obtained in which the thickness of the second layer is 3/8 or less of the wavelength of the vibration wave propagating inside the second layer. In the acoustic transducer, it is possible to obtain an acoustic transducer having a second layer in which the bonding surface between the first layer and the second layer is a spherical surface and the other surface is a flat surface.

[0005]

Embodiments of the present invention will be described below with reference to FIGS. In FIG. 1, a piezoelectric ceramic cylinder 1a
The phase shift plate 4, which is the first layer, is bonded to the electrode 2a side of the piezoelectric vibrator 3a in which the electrodes 2a and 2b are provided via the piezoelectric ceramic cylinder 1a, and the delay plate 5, which is the second layer, is joined. Is bonded to one of the end faces of the phase shift plate 4, and the bonding surface of the phase shift plate 4 and the delay plate 5 is spherical. A backing 6a is bonded to the electrode 2b side of the piezoelectric vibrator 3a, and a sound insulating plate 7a is bonded to the outer peripheral surfaces of the piezoelectric vibrator 3 and the backing 6a to block radiation sound in unnecessary directions. Lead wires 8a and 8b are provided on the electrodes 2a and 2b, respectively, and the lead wires 8a and 8b serve as terminals for inputting electrical signals. The piezoelectric vibrator 3, the phase shift plate 4, the delay plate 5, the backing 6, and the sound insulating plate 7 configured as described above.
The surface of a is covered with a mold resin 9a to electrically insulate it from water as an external medium.

FIG. 2 is a diagram showing the operation of the embodiment according to the present invention. When an electric signal having the same frequency as the thickness resonance frequency of the piezoelectric vibrator 3a is applied to the lead wires 8a and 8b of FIG. 2A, the plane at the position equally divided in the length direction of the piezoelectric vibrator 3 becomes a node, and the electrode The primary vibrations occur in the opposite directions on the surface of 2a and the surface of the electrode 2b.
It exhibits a half-wavelength distribution as shown in (b). The phase shift plate 4 is driven with an even distribution from the joint surface with the piezoelectric vibrator 3a, and its vibration propagates in the phase shift plate at a sound velocity determined by the material, and its propagation time is shown in FIG. 2 (c). As described above, the primary vibration wave has a long center point C / L of the propagation path while passing through the phase shift plate 4.
Takes longer than the propagation time on the outer peripheral surface, that is, at the position of r = a. Further, this vibration is transmitted to the delay plate 5 and propagates at a sound velocity determined by the material of the delay plate, but since the sound velocity is lower than that of the phase shift plate, the inclination becomes smaller as shown in the graph of FIG. 2C, The time difference distribution over the outer peripheral surface of the delay plate 5 from the joint surface of the phase shift plate 4 and the delay plate 5 is increased.
This time difference distribution is the emission surface of the underwater sound wave, that is, the delay plate 5.
The phase shift difference distribution on the outer surface of the radiating surface relaxes the concentration of sound waves in the vertical direction of the radiating surface, that is, the direction of the acoustic center axis. As a result, a wide directional width characteristic as shown in FIG. be able to.

When there is no phase difference distribution, sound waves are concentrated in the direction of the central axis of the sound, resulting in a characteristic having a narrow directivity width as shown in FIG. 3B. If the phase difference distribution that gives a wide directional width characteristic also becomes 180 degrees or more, an antiphase region occurs, and distortion occurs in the directivity pattern or a dent in the acoustic center axis direction.
The range of distribution is 180 degrees or less, that is, 1 / wavelength of the underwater sound wave.
It becomes 2 or less. To satisfy this condition, depending on the ratio of the thicknesses of the phase shift plate and the delay plate in the lengthwise direction, at least one of them must be about 3/8 or less of the wavelength in the material.

The shape of the non-planar joint between the first layer and the second layer has a degree of freedom in selection, and the acoustic center axis is inclined from the vertical direction of the radiation surface, or the directivity width is narrowed. Can be selected according to its purpose (not shown).

[0009]

As described above, according to the present invention, it is possible to obtain a wide directional width characteristic even if a piezoelectric vibrator having a large cross section is used.

[Brief description of drawings]

FIG. 1 is a perspective view showing a partial cross section of an acoustic transducer according to the present invention.

FIG. 2 is a diagram showing the operation of the acoustic transducer according to the present invention.

FIG. 3 is a diagram showing characteristics of directivity width of a conventional acoustic transducer.

FIG. 4 is a perspective view showing a partial cross section of a conventional acoustic transducer.

[Explanation of symbols]

 1a, 1b Piezoelectric ceramics cylinder 2a, 2b, 2c, 2d Electrodes 3a, 3b Piezoelectric vibrator 4 Phase shift plate 5 Delay plate 6a, 6b Backing 7a, 7b Sound insulation plate 8a, 8b, 8c, 8d Lead wire 9a, 9b Mold resin

Claims (2)

[Claims] 1. An acoustic transducer having a piezoelectric ceramic body having a first surface and a second surface facing each other, and first and second electrodes respectively bonded to the first and second surfaces. A first surface having a flat surface for joining with the surface of the first electrode and a non-flat surface for the other surface.
And a second layer having a non-planar joining surface between the first layer and the non-planar surface, and the sound velocity passing through the second layer is lower than the sound velocity passing through the first layer. And the thickness of the first layer is 3 times the wavelength of the vibration wave propagating inside the first layer.
/ 8 or less, and the thickness of the second layer is the second
The acoustic transducer is characterized by having a wavelength of 3/8 or less of a vibration wave propagating inside the layer. 2. The acoustic transducer according to claim 1, further comprising a second layer in which a bonding surface between the first layer and the second layer is a spherical surface and the other surface is a flat surface. Acoustic transducer.