JPS6126399A - Ultrasonic transmitter-receiver - Google Patents

Abstract

PURPOSE:To give a sharp directional characteristic and high transmission/ reception sensitivity characteristic by sticking an annular thin plate to an annular piezoelectric element. CONSTITUTION:An annular piezoelectric element 11 is stuck to an inner bottom of an annular plate having a V-shaped section for including a normal for passing through the center of a circle. Parabolic-surface hones 20 and 21 are provided inside and outside the thin plate 13 through an elastic rubber 22, etc. Then, the titled receiver shows the directional characteristic similar to a circular piston 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 ultra-high wave 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 - Made to be used at the anti-resonance point. Furthermore, since the mechanical impedance of air is significantly smaller than that of piezoelectric ceramics, the bonded piezoelectric element is coupled to the 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′
7 is a terminal, 7 is a case that covers the laminated piezoelectric element 1, etc., 8 is a protective hole formed in the upper part of the case 7, and 9.9' is the laminated piezoelectric element 1. Terminal 6.6
``e'' is a lead wire that is electrically connected. Furthermore, the case 7 is inserted and held in the throat of the parabolic horn 10. The directional characteristics are shown when the driving frequency is 40 kHz and the diameter of the horn 10 is 42 mm.

At this time, in the case of a circular diaphragm that performs piston vibration, the theoretical values of the sound pressure half angle and the first sidelobe are each 1
It is extremely difficult to realize an ultrasonic transducer that exhibits bb at 64° and −17.6 dB (compared to the main lobe), a value close to this theoretical value.

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. But the usage layer! When the skin pressure is increased, the attenuation of sound increases significantly, and the sensitivity of the ultrasonic transducer using a bonded piezoelectric element decreases. Therefore, there is a limit to increasing the frequency used,
I have no choice but to make the sound source louder.

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.

Furthermore, when adding a horn to sharpen the directional characteristics, increasing the size of the diaphragm in order to increase the transmitting and receiving sensitivity not only makes it impossible to achieve sharp directional characteristics, but also increases the transmitting and receiving sensitivity. It was difficult to improve.

Ultrasonic distance measuring devices, especially when used for camera autofocus, have the disadvantage that when the directivity becomes sharp, the distance measuring section is separated from the optical axis of the camera's imaging lens, resulting in glare. .

Furthermore, attempts to improve spatial resolution by creating a thin ultrasonic beam using an annular transducer have already been known, but the transducer had to be made in an annular shape and was difficult to process. Furthermore, the mechanical impedance of the vibrator is significantly larger 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 is directed to bonding an annular thin plate and an annular piezoelectric element,
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 a structure of a wall and a bottom.

The ultrasonic transducer of this invention has a structure in which an annular thin plate and an annular piezoelectric element are bonded together, and transmits ultrasonic signals near resonance and anti-resonance frequencies due to bending vibration of the collapsed structure. It is something that receives waves.

(Description of Embodiment) An embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a cross section of the ultrasonic transducer of this embodiment.

An annular piezoelectric element 1 is disposed at the inner bottom of an annular thin plate 13 whose cross section along a plane including a normal line passing through the center of the annular ring is U-shaped.
1 is attached. Terminals 16 and 16 are connected from the annular piezoelectric element 11 and the annular thin plate 13 to a terminal plate 14 made of an electrical insulator by lead wires 19°19'.
'It is connected to the. Parabolic horns 20 and 21 are connected to the inside and outside of the annular thin plate 13 via elastic combs 22 and the like.
is provided.

Next, Fig. 4 shows the directional characteristics of the ultrasonic transmitter and receiver when placed horizontally. In the figure, the broken line is the directional characteristic exhibited by the annular piston sound source, and the directional coefficient: R (θ) is expressed by the following equation.

Here, Jl is a Bessel function of the first kind, a and b are the outer radius and inner radius of the annular sound source, the wave number is, and θ is the angle with the central axis.

It can be seen from FIG. 4 that the ultrasonic transducer of this embodiment exhibits characteristics almost equivalent to the directivity characteristics of the annular piston sound source. Therefore, compared to the conventional one, it exhibits narrow directivity even when the ultrasonic radiation area is equal. At the same time, the radiated sound pressure level also increased by about 6 dB. It is extremely useful for ultrasonic applied measurements that require sharp directional characteristics, such as distance meters.

[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 directional characteristics, FIG. 3 is a sectional view of an embodiment of the present invention, and FIG. 4 is a diagram showing its directional characteristics. 11... Annular piezoelectric element, 13゛... Annular thin plate, ]
4...Terminal board, 2 (1, 2 horns. Figure 1 Figure 2-4 (J -200dB

Claims (3)

[Claims] (1) An ultrasonic transducer characterized in that it has a structure in which an annular thin plate and an annular piezoelectric element are bonded together, and uses bending vibration of the structure. (2) The ultrasonic transducer according to claim (1), wherein the annular thin plate has a U-shaped cross section in a plane including a normal line passing through the center thereof. (3) The ultrasonic transducer according to claim (1), characterized in that horns are provided on the inside and outside of the annular thin plate.