JPS6126397A - Ultrasonic transmitter-receiver - Google Patents

Abstract

PURPOSE:To give a sharp directional characteristic and high transmission/ reception sensitivity characteristic by jointing plural piezoelectric elements to an annular diaphragm. CONSTITUTION:An annular diaphragm 13 made of metal or resin is fitted to a joint axis 12 disposed at the center of plural sticking-type piezoelectric elements 11. A vibrating node of the element 11 is supported at the top of a support stand 14 by and elastic adhesive 15. Parabolic-surface hones 20 and 21 are provided inside and outside an annular case 17. With this constitution the titled receiver shows the directional characteristic similar to a circular peak sound source. As a result, it shows the narrower directivity compared with a conventional one even if a ultrasonic wave emitting area is equal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ultrasonic transducer necessary for ultrasonic applied measurement in the air.

(Conventional structure and its problems) For ultrasonic transducers in the air, laminated piezoelectric elements made of piezoelectric ceramics are often used, and the resonance point of the bending vibration of the laminated piezoelectric element is Designed for use at anti-resonance points. However, the mechanical impedance of air is significantly smaller than that of piezoelectric ceramics, so a bonded piezoelectric element is combined with a diaphragm to reduce the mechanical impedance.

The structure of a conventional ultrasonic transducer is shown in FIG.

A coupling shaft 2 is fixed through the center of the bonded piezoelectric element 1, and a diaphragm 3 is attached to the coupling shaft 2.

The vibration nodes of the bonded piezoelectric element 1 are supported by an elastic adhesive 5 at the tip of the support base 4. In addition, 6,6′
is a terminal, 7 is a case that covers the bonded piezoelectric element 1, etc., 8 is a protective mesh attached to a through hole formed in the upper part of the case 7, and 9 and 9' are the bonded piezoelectric element 1 and the terminal 6. ,6
This is the lead wire that electrically connects . Furthermore, the case 7 is inserted and held in the throat of the parabolic horn 10.

FIG. 2 shows the directivity characteristics of the ultrasonic transducer having the above structure. However, the directivity characteristics are when the driving frequency is 40 kHz and the diameter of the horn 10 is 42 mm.

After this, in the case of a circular diaphragm that performs piston vibration, the theoretical values of the sound pressure half angle and the first side rope are each 1
64° and -17.6 dB (compared to the main lobe), and it is extremely difficult to realize an ultrasonic transducer that exhibits values near these theoretical values.

Increasing the resolution of the object to be measured requires even sharper directivity. The sharp directivity is
As is well known, this can be achieved by increasing the size of the sound source and increasing the frequency used. However, when the operating frequency is increased, the attenuation of sound increases significantly, and the sensitivity of the ultrasonic transducer employing the bonded piezoelectric element decreases.

Therefore, there is a limit to increasing the frequency used, and the sound source must be made larger.

When an ultrasonic transducer using piezoelectric ceramics is required to have sharp directivity characteristics, there is a drawback that the diaphragm, the bonded piezoelectric element, the support base for supporting the bonded piezoelectric element, etc. become significantly large.

1. When trying to make the directional characteristics sharp by adding a horn, it is not foolish to make the diaphragm louder in order to increase the transmitting and receiving sensitivity. It has been difficult to improve the transmitting and receiving sensitivity.

When using an ultrasonic distance measuring device, particularly for automatic focusing of a camera, when the directivity becomes sharp, there is a drawback that variation occurs because the optical axis of the camera's imaging lens and the distance measuring section are separated.

Furthermore, attempts to improve the azimuth resolution by producing a thin ultrasonic beam using a circular transducer are already known, but this requires the transducer to be produced in a circular shape and is difficult to process. Ta. Furthermore, the mechanical impedance of the vibrator is significantly higher than that in the air, and as a result, the degree of conversion into acoustic energy is low.

(Object of the invention) The present invention combines a plurality of piezoelectric elements to an annular diaphragm,
It is an object of the present invention to provide an ultrasonic transducer having sharp directivity characteristics and high wave transmission/reception sensitivity characteristics.

(Structure of the Invention) In order to achieve the above object, the present invention is characterized by having the following structure.

The ultrasonic transducer of the present invention has a configuration in which a plurality of piezoelectric elements each having a coupling shaft provided in the center are coupled to an annular diaphragm via the coupling shaft, and the plurality of piezoelectric elements and the It transmits and receives ultrasonic signals near the resonance and anti-resonance frequencies determined by the annular diaphragm.

(Description of Embodiment) An embodiment of the present invention will be described with reference to FIGS. 3 and 4.

A coupling shaft 1 arranged at the center of a plurality of bonded piezoelectric elements 11
An annular diaphragm 13 made of metal or resin is attached to 2, and the vibration node of each bonded piezoelectric element 11 is supported at the tip of a support base 14 with an elastic adhesive 15. Parabolic horns 20 and 21 are provided on the inside and outside of the annular case 17 that covers the bonded piezoelectric element 11 and the like.
is provided. 18 is a protective mesh attached to a through hole formed in the upper part of the case 17; 19, 19';
is a lead wire electrically connecting the bonded piezoelectric element 11 and the terminals 16 and 16'. Note that the plurality of bonded piezoelectric elements 11 are connected in series or in parallel depending on the purpose, peripheral circuit, etc.

Next, the directivity characteristics of the ultrasonic transducer with the above structure are determined by the fifth
As shown in the figure. In the figure, the broken line is the directional characteristic exhibited by the annular piston sound source, and the directional coefficient: R (expressed by a quadratic equation).

a2-b2 k-b-sin θ where Jl is the Bessel function of the first kind, a r b is the outer radius and inner radius of the annular sound source, k is the wave number, and θ is the angle with the central axis.

It can be seen that the ultrasonic transducer of this example exhibits characteristics almost equivalent to the directivity characteristics of the annular piston sound source shown in FIG. Therefore, compared to the conventional one, it exhibits narrow directivity even when the ultrasonic radiation area is equal. In this case, the transmitted sound pressure level was also improved by 6 dB.

As a result of measuring various shapes of the annular diaphragm 13,
The best directivity characteristics were obtained when the annular diaphragm 13 had a V-shaped cross section in a plane including the normal passing through its center.

Another embodiment of the invention is shown in FIG. An annular diaphragm 13 made of metal or resin is attached to a coupling shaft 12 arranged at the center of a plurality of bonded piezoelectric elements 11. The peripheral portion of the annular diaphragm 13 is elastically fixed to the inner surface of the case 17 via a buffer material 22 such as an elastic comb formed in an annular shape so as to suppress mechanical vibration. Parabolic horns 20 and 21 are provided inside and outside the annular case 17.

The directivity characteristics of the ultrasonic transducer in this embodiment are the same as those in the previous embodiment (FIG. 5). Furthermore, the ultrasonic transducers of these embodiments realize steep transient characteristics as shown in FIG. 7(b).

Therefore, the transmitted and received signals have a peak value of 1
This reduces the time required for measurement and improves measurement accuracy.

(Effects of the Invention) As described above, the ultrasonic transducer of the present invention not only has sharp directivity characteristics and high transmitting and receiving sensitivity characteristics, but also can realize steep transient characteristics, making it possible to transmit sound waves. It is extremely useful for ultrasonic applied measurements that require sharp directional characteristics, such as the distance meter used.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a conventional ultrasonic transducer;
FIG. 2 is a diagram showing its directivity characteristics, FIG. 3 is a sectional view of an embodiment of the present invention, FIG. 4 is a perspective view of the electroacoustic transducer, and FIG. 5 is a diagram showing the same. This is a diagram showing directional characteristics, No. 6
This figure is a sectional view of another embodiment of the present invention, and FIG. 7 is a diagram showing its transient characteristics. 11... Bonded piezoelectric element, 13 Annular diaphragm, 14
Support stand, 15-Elastic adhesive, 20.2 Tohon, 22
Buffer material. Patent applicant Matsushita Electric Industrial Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 1 Figure 4 Figure 5 Figure 6

Claims (5)

[Claims] (1) Ultrasonic wave transmission and reception characterized by comprising a plurality of piezoelectric elements each having a coupling axis in the center and an annular diaphragm coupled to each of the plurality of piezoelectric elements via the coupling axis. vessel. (2) The ultrasonic transducer according to claim (1), characterized in that horns are provided inside and outside the annular diaphragm. (3) The ultrasonic transducer as set forth in claim (1), wherein the annular diaphragm has a V-shaped cross section in a plane including a normal passing through the center of the annular diaphragm. (4) A patent claim characterized in that the peripheral portion of the annular diaphragm is elastically fixed to the inner surface of a case housing the annular diaphragm and a plurality of piezoelectric elements via a cushioning material. The ultrasonic transducer according to the range (1) above. (5) The ultrasonic transducer according to claim (2), wherein the case and the horn are integrally formed.