JPH07154898A - Ultrasonic transducer - Google Patents

Abstract

(57) [Summary] [Object] To provide an ultrasonic transducer having a structure capable of further improving reverberation characteristics. [Structure] A piezoelectric element plate 3 is bonded to an upper surface of an acoustic matching plate 2a, and The damping molding layer 7 is carried by the bonded body,
The piezoelectric element plate 3 was embedded in the damping molding layer 7 to shorten the reverberation time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave transmitter / receiver having a function of radiating an ultrasonic wave into the air and, conversely, a function of receiving an ultrasonic wave radiated into the air.

[0002]

2. Description of the Related Art Ultrasonic transducers provided with a conventional acoustic matching layer give priority to sensitivity. However, recently, there has been an increasing demand for a short-distance type ultrasonic wave transmitter / receiver which is applied to detect an object to be detected which is close to the wave transmitting / receiving surface of the ultrasonic wave transmitter / receiver.
In such an application, the most problematic measurement error during distance measurement is the interference between the reverberant wave of the transmitted signal and the received signal. Therefore, at close range,
The reverberation characteristic determines its reliability, and in such applications, the ratio of the received signal to the reverberation voltage is usually 1 /
Those of 10 to 1/100 (20dB to 40dB) are required.

By the way, if the reverberation characteristic is further improved, it becomes possible to detect an object from a nearer position for an ultrasonic proximity switch, which is a weak point of the conventional electrostatic and electromagnetic proximity switches. It is also possible to detect an object at cm ahead. In addition, a sensor that measures the speed of sound and temperature using the propagation time of ultrasonic waves has a problem of reverberation, which makes it difficult to reduce the size. However, the improvement of reverberation characteristics can also improve this problem. It will be.

Correspondingly, as shown in FIG. 7, a piezoelectric element plate c having electrode layers formed on the front and back surfaces on the bottom of an acoustic matching layer made of a bottomed cylindrical case b is bonded. Then, an ultrasonic transducer a having a structure in which the damping layer d is embedded in the case b has been proposed.

[0005]

By the way, when the characteristics of the above-mentioned structure were tested, it was found that the reverberation characteristics were not always sufficiently improved.

An object of the present invention is to provide an ultrasonic wave transmitter / receiver having a structure capable of further improving reverberation characteristics.

[0007]

According to the present invention, a piezoelectric element plate having electrode layers formed on the upper and lower surfaces of an acoustic matching plate is bonded to the upper surface of the acoustic matching plate, and a damping molding layer is carried by the bonded body to form the piezoelectric element. The plate is embedded in a damping molding layer, and the lower surface of the acoustic matching plate is exposed to serve as an ultrasonic wave transmitting / receiving surface.

Further, in the above-mentioned basic structure, a piezoelectric element plate having the same plane shape as the acoustic matching plate is bonded to the upper surface of the acoustic matching plate in a uniform manner, and the damping molded layer is carried by the bonded body. Is proposed.

[0009]

Compared to the structure of FIG. 6, the present invention corresponds to a structure having no peripheral wall of the acoustic matching layer. It was confirmed that the reverberation characteristics were improved because there was no peripheral wall. Furthermore, in a configuration in which a piezoelectric element plate having the same planar shape as the acoustic matching plate is bonded to the upper surface of the acoustic matching plate in a uniform manner, an acoustic matching layer is provided only on the lower surface of the piezoelectric element plate. Furthermore, the reverberation characteristic was improved.

[0010]

The present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention.

In the ultrasonic transmitter / receiver 1a having this structure,
On the upper surface of the disk-shaped acoustic matching plate 2a, electrode layers 4 are formed on the front and back surfaces.
A disk-shaped piezoelectric element plate 3 on which a and 4b are formed is joined. The electrode layer 4a located on the acoustic matching plate 2a side has its electrically drawn end extended to the front surface side, and the conductors 6a and 6b of the lead wire 5 are arranged on the front surface side of the piezoelectric element plate 3 and the electrode layer 4a,
4b, a voltage is applied to the electrode layers 4a, 4b of the piezoelectric element plate 3, and a signal voltage generated between the electrode layers 4a, 4b is taken out. In this structure, the outer diameter of the piezoelectric element plate 3 is smaller than the outer diameter of the acoustic matching plate 2a.

Further, the acoustic matching plate 2a and the piezoelectric element plate 3
The damping molding layer 7 is carried on the bonded body consisting of, the piezoelectric element plate 3 is covered, and the lead wire 5 is drawn out. The lower surface of the acoustic matching plate 2 is exposed to form an ultrasonic wave transmitting / receiving surface f.

In the above structure, the acoustic matching plate 2a is
Foamable plastic materials, materials in which numerous glass balloons are mixed with plastic, etc. are used. Further, the damping molding layer 7 is formed by molding on the bonded body, and is made of lead titanate, lead titanate zirconate titanate, or a material having a large internal friction, such as room sound curing type silicone rubber or urethane resin. It is formed of a material obtained by mixing powders having a large specific gravity such as ceramic powder and metal powder.

The effect of the damping molding layer 7 is that the reverberation time becomes shorter as the acoustic impedance becomes larger (closer to the acoustic impedance of lead zirconate titanate of about 30 × 10 ⁶ ).

Here, FIG. 4 shows the acoustic impedance and
The relationship between reverberation time and receiving sensitivity is shown. As shown in FIG. 5, this reverberation time indicates the time from the rising edge of the transmitted wave to the peripheral edge, and the receiving sensitivity indicates the maximum amplitude of the received wave.

FIG. 2 shows a second embodiment.

In the ultrasonic transmitter / receiver 1b having this structure,
The disk-shaped acoustic matching plate 2b has the same planar shape (outer diameter) as the piezoelectric element plate 3 bonded to the upper surface thereof. The damping molding layer 7 carried on this bonded body is
The piezoelectric element plate 3 has an outer diameter that surrounds the periphery of the bonded body.
It is designed to cover the surrounding surface as well.

FIG. 3 shows a current product according to FIG. 7, a structure according to FIG. 1 (first embodiment) and a structure according to FIG. 2 (second embodiment).
This is a comparison of the sensitivity characteristic of, the receiving sensitivity and the reverberation time.

Here, as case b shown in FIG. 7, a glass balloon having a diameter of 50 microns is added to 75 parts by weight of an epoxy resin.
25 parts by weight mixed composite material (acoustic impedance 1.5 ×
10 ⁶ Ns / m ³ ) formed into a wall thickness H ₂ and used as the acoustic matching plate 2a in FIG. 1 in the form of a disk having an outer diameter D ₃ 10 mm and a thickness H ₄ 2.2 mm made of the same composite material as above. used after molding, as the acoustic matching plate 2b of Figure 2, was used and molded into the outer diameter D ₅ 8 mm, thickness H ₆ 2.2 mm disc-shaped with the same composite material as the.

Further, the damping molding layer d of FIG. 7 and FIG.
As the damping molding layer 7 in FIG. 2, a composite material (acoustic impedance 3 × 10 ⁶ Ns / m) in which 75 parts by weight of lead titanate powder having a diameter of 10 microns is mixed with 25 parts by weight of urethane resin is used.
³⁾ used to fill it into the case in the case of FIG. 7, the outer diameter D ₃ and same size of 10mm the aligning plate in the case of FIG. 1, the height H ₃ 5.8
2 mm, and in the case of FIG. 2, it was molded to have an outer diameter D ₄ 10 mm and a height H ₅ 7 mm.

Further, in FIGS. 7, 1 and 2, the piezoelectric elements c and 3 are 8 mm in diameter and 1 mm thick from lead zirconate titanate.
A disc-shaped product having a diameter of mm was used.

The measurement of the wave transmission / reception sensitivity characteristic was performed using the circuit device shown in FIG.

As can be seen from this figure, each of the above-mentioned configurations has the conventional configuration of FIG. 7 (reception sensitivity 2.1 Vpp, reverberation time 0.25 m).
It can be seen that both the receiving sensitivity and the reverberation time are improved compared to s). In addition, the configuration of Figure 2 (reception sensitivity 4.1Vp
p, reverberation time 0.20 ms) was further improved over the configuration in Fig. 1 (receiver sensitivity 4.1 Vpp, reverberation time 0.10 ms).

In the structure shown in FIGS. 1 and 2, when used in a corrosive gas atmosphere, a film having excellent weather resistance such as polyimide is adhered or coated on the gas contact surface (film thickness 100 μm). ) Will be possible.

[0026]

According to the present invention, the piezoelectric element plate 3 is bonded to the upper surfaces of the acoustic matching plates 2a and 2b, and the damping molding layer 7 is carried by the bonded body, and the piezoelectric element plate 3 is formed on the damping molding layer 7. By embedding it, the receiving sensitivity is improved and the reverberation time is shortened. Therefore, even when used for short-distance measurement, the transmitted signal and the received signal do not interfere with each other, which is optimal for ultrasonic proximity switches. Further, by applying it to a sensor that measures the speed of sound and temperature by using the propagation time of ultrasonic waves, there is an excellent effect that the size can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of a first embodiment of the present invention.

FIG. 2 is a vertical sectional side view of a second embodiment of the present invention.

FIG. 3 is a comparison diagram showing reverberation characteristics.

FIG. 4 is a fluff showing the relationship between acoustic impedance, reverberation time, and receiving sensitivity.

FIG. 5 is a waveform diagram showing a relationship between reverberation time and receiving sensitivity.

FIG. 6 is a circuit diagram for measuring transmission / reception sensitivity.

FIG. 7 is a vertical sectional side view of a conventional configuration.

[Explanation of symbols]

 1a, 1b Ultrasonic wave transmitter / receiver 2a, 2b Acoustic matching plate 3 Piezoelectric element plate 7 Damping forming layer

Claims (2)

[Claims] 1. A piezoelectric element plate having electrode layers formed on the front and back surfaces is joined to the upper surface of an acoustic matching plate, a damping molding layer is carried by the bonded body, and the piezoelectric element plate is embedded in the damping molding layer. An ultrasonic wave transmitter / receiver, wherein the lower surface of the acoustic matching plate is exposed to form an ultrasonic wave transmitter / receiver surface. 2. A piezoelectric element plate having the same plane as the acoustic matching plate is bonded to the upper surface of the acoustic matching plate in a uniform manner, and a damping molding layer is carried by the bonded body. The ultrasonic transmitter / receiver described.