JPS6312438B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transducer for transmitting and receiving ultrasonic waves.

Conventionally, in this type of transducer, in order to obtain directional characteristics, a plurality of transducers were spatially arranged and the difference in the propagation path of sound waves caused by these was utilized. However, this method has the disadvantage that as the frequency becomes lower and the wavelength of the sound wave in the medium becomes longer, the distance between the transducer and the transducer must be increased proportionally, resulting in a larger structure. Ta.

In order to eliminate the above-mentioned drawbacks, a method has been adopted in which pressure gradient type transducers are arranged in four orthogonal directions and directivity is obtained by a combination of these transducers. However, the structure of the transducer obtained by this method is not only complicated due to its bimorph shape, but also has drawbacks such as insufficient mechanical strength because it is held protruding from the housing. Alternatively, piezoelectric materials are arranged in four orthogonal directions on the inner surface of the cylindrical vibrating body,
Some methods obtain directivity by combining the outputs induced by the stress transmitted by the deformation of the vibrating body, but this method also has drawbacks such as a complex structure and insufficient mechanical strength. It was hot.

The purpose of the present invention is to eliminate the drawbacks of the conventional method, and by using a plate-shaped piezoelectric material with an acoustic impedance that is close to the acoustic impedance of the medium, the transmitter and receiver are integrated, and the structure is compact. It is an object of the present invention to provide a transducer which not only has improved mechanical strength but also has unidirectionality.

The transducer of the present invention is constituted by a cylindrical or spherical housing and plate-shaped piezoelectric materials fixed as a pair to at least one opposing surface on the circumference of the housing. Two piezoelectric materials are used as a set, and directivity is obtained by differentially synthesizing the input and output of each.

Next, embodiments according to the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing the structure of a first embodiment of the present invention. In this figure, 1 is a cylindrical metal case, 2-1, 2-2, 2-3, 2
-4 is a plate-shaped piezoelectric material whose acoustic impedance is close to that of the medium bonded to the housing 1. Figure 2 shows the first
FIG. 3 is a plan view of the transducer shown in the figure, viewed from above. In this plan view, (+) of piezoelectric materials 2-1 to 2-4,
The symbol (-) represents the polarity of each piezoelectric material. Those with reversed polarity can be obtained by gluing identical ones with their sides reversed.

The operation of the transducer configured in this way will be explained with reference to the principle diagram of FIG. 3. In addition,
In this figure, only one pair of piezoelectric materials is shown. Since the process of transmitting and receiving waves is exactly the opposite and the principle of operation is the same, only wave reception will be described here. Now, when a sound wave arrives from the direction shown by the arrow in the figure, the housing 1 vibrates back and forth in the direction of travel. Therefore, a compression or expansion force acts on the two piezoelectric materials, and voltages having opposite phases are induced in each of the piezoelectric materials. By combining the differences between these two voltages, this voltage can be doubled.
This voltage decreases to cos θ when the angle of arrival of the sound wave is in the direction of θ. As a result, a so-called figure-eight directivity is obtained. As can be seen from this, when a sound wave arrives from a direction perpendicular to a straight line connecting two piezoelectric materials, voltages of the same phase are induced in each piezoelectric material, so when combining both voltages, The voltage becomes 0.

FIG. 4 is a perspective view showing the structure of a second embodiment of the present invention. In this diagram,
3 is a housing made of a piezoelectric material based on lead zirconate titanate, and is selected to have a larger acoustic impedance than the medium. 4-1, 4-2, 4-3,
4-4 is a polymer piezoelectric material. This iso-piezoelectric material 4-
The polarities of 1 to 4 are selected in the same way as in the first embodiment. Therefore, since this receiver also operates in the same manner as in the first embodiment, a detailed explanation thereof will be omitted. However, when the housing 3 made of piezoelectric material is operated as a wave receiver, the voltage induced therein and the voltage induced in the piezoelectric materials 4-1 to 4-4 are summed or differentially combined. , the directivity of received waves can be made unidirectional. In addition, piezoelectric material 4-1
Since ~4 is close to the acoustic impedance of the medium, the propagation of the arriving sound waves is not inhibited and the sound waves reach the housing 3. Further, when only the housing 3 is operated as a wave transmitter, the wave transmitter vibrates in a zero-order vibration mode, so-called respiratory vibration, and generates a sound wave. In this state, the piezoelectric materials 4-1 to 4 on the outer surface have approximately the acoustic impedance of the medium, so they do not impede vibration or propagation of sound waves.

In the first and second embodiments described above, the housing 1 and the housing 3 made of piezoelectric material are bonded with plate-shaped piezoelectric materials only in four orthogonal directions; This is an example of the minimum number necessary for discrimination. In the present invention, the piezoelectric material is not limited to this, but in order to simply obtain directivity or to obtain a large number of directional beams, the piezoelectric material is arranged in four or less or more perpendicular directions. Needless to say, it may be fixed. for example,
If a spherical casing is used and piezoelectric materials are fixed in six orthogonal directions, two orthogonal planes, more omnidirectional discrimination becomes possible.

The piezoelectric materials used in the above examples have been rapidly developed in recent years, and improvements in piezoelectric constants related to sensitivity, reduction in acoustic impedance, etc.
Alternatively, the performance has been improved due to increased flexibility, etc., and it has come to be expected that the present invention can be effectively utilized in the transducer.

As is clear from the above description, according to the present invention, by fixing a plurality of plate-shaped piezoelectric materials to the casing, not only mechanical strength is obtained and manufacturing is easy, but also the casing By making the body part a piezoelectric material with a large acoustic impedance and making the plate-shaped fixed piezoelectric material almost close to the acoustic impedance of the medium, multiple receivers or these and a transmitter can be integrated. The advantages that can be obtained are significant, such as the ability to easily downsize the structure and easily obtain unidirectivity.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of the first embodiment of the present invention, FIG. 2 is a plan view of the transducer shown in FIG. 1 viewed from above, and FIG. 3 is the transducer shown in FIG. FIG. 4 is a perspective view showing the structure of a second embodiment of the present invention. In the figure, 1 is the housing, 2-1, 2-2, 2-
3, 2-4, 4-1, 4-2, 4-3, and 4-4 are plate-shaped piezoelectric materials, and 3 is a housing made of the piezoelectric material.

Claims (1)

[Scope of Claims] 1. Consisting of a cylindrical or spherical housing and plate-shaped piezoelectric materials fixed as a pair to at least one opposing surface on the circumference of the housing, A transducer characterized by differentially combining the input and output of two piezoelectric materials. 2. In the transducer according to claim 1, the casing is formed of a piezoelectric material having an impedance larger than the acoustic impedance of the medium, and the plate-shaped piezoelectric material has an impedance substantially close to the acoustic impedance of the medium. A transducer characterized by having.