JPS6055798A - Ultrasonic wave transmitting and receiving device - Google Patents

Abstract

PURPOSE:To improve both transient and transmission/reception sensitive characteristics by setting the resonance frequency of a pasted piezoelectric element containing a diaphragm within a prescribed range. CONSTITUTION:A diaphragm 13 is attached at the center part of a pasted piezoelectric element 11, and the peripheral part of the diaphragm 13 is fixed to the inner side surface of a case 17 via a buffer 20 such as the elastic rubber, etc. In addition, a thin film 23 having opening parts 20, 20' and 20'' is provided at the front part of the diaphragm 13. The resonance frequency which is decided by each opening part of the film 23, the capacity between the film 23 and the diaphragm 13, etc. is set in a range between the resonance frequency of the element 11 and its antiresonance frequency. Thus both transient and transmission/reception sensitive characteristics can be improved by setting the resonance frequency within a prescribed range.

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 configurations and their problems Many piezoelectric ceramic bonded elements are used in devices that transmit and receive ultrasonic waves in the air. 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. I'm trying.

The structure and characteristics of a conventional ultrasonic transducer are shown in Figures 1 and 2.
Each is shown in the figure. As shown in FIG. 1, a coupling shaft 2 is fixed through the center of the bonded piezoelectric element 1, and a diaphragm 3 is attached to this coupling shaft 2. The vibration nodes of the laminated piezoelectric element 1 are fixed to the tip of the support base 4 with an elastic adhesive 5. In addition, 6, 6' are terminals,
7 is a case that covers the bonded piezoelectric element 1, etc.; 8 is a retention mesh attached to a through hole formed in the upper part of the case 7; 9 and 9' are the bonded piezoelectric element 1 and the terminal 6; 6
This is the lead wire that electrically connects .

Figure 2 shows the transmission and reception waveforms when the ultrasonic transducer with the above structure is driven with multiple pulses.
The fall time was slow, reaching more than 2 milliseconds.

When it is necessary to obtain measurement information at short time intervals using such a conventional ultrasonic transducer, the signal received by the receiver has long rise and fall times, so the received signal is It takes time to reach the peak value. Or the next signal is received before the received signal falls, etc.
Accurate measurement information could not be obtained.

In addition, when transmitting and receiving waves using a single element, it takes a considerable amount of time until the wave can be immediately received after transmitting the wave, and during that time, no measurements can be made.

Furthermore, when ultrasonic transducers using piezoelectric ceramics are required to have sharp directivity characteristics, there is a drawback that the diaphragm, the bonded piezoelectric element, and the support base for supporting the bonded piezoelectric element become significantly large. . Even if a large diaphragm is used, it is difficult to cause the piston to vibrate, so it has been impossible to make the directivity characteristics extremely sharp.

Therefore, when trying to sharpen the directional characteristics by using a horn, it became even more difficult to reduce the mechanical Q and improve the pulse characteristics.

OBJECTS OF THE INVENTION The present invention seeks to provide an ultrasonic transducer with good transient characteristics and wave transmitting/receiving sensitivity characteristics.

Structure of the Invention The present invention provides a diaphragm in the center of a bonded piezoelectric element, and elastically fixes the periphery of the diaphragm to a case with an elastic material such as elastic rubber so as to suppress mechanical vibration. We have achieved an ultrasonic transducer with sharp transient characteristics, and improved the transmitting/receiving sensitivity characteristics and temperature characteristics.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a sectional view of the ultrasonic transducer of this embodiment.

A vibration plate 13 made of metal or resin is attached to a coupling shaft 12 arranged at the center of the bonded piezoelectric element 11. The periphery of the diaphragm 130 (is a cushioning material 2 such as elastic rubber formed in an annular shape to suppress mechanical vibrations)
0, and is elastically fixed to the inner surface of the cylindrical case 17.

A sound absorbing material 21 is provided at the bottom of the case 17. In front of the diaphragm 13 is a thin plate 23 having a circular opening 22 in the center and other openings 22', 22' provided on a concentric circumference centered on a straight line passing through the coupling shaft 12. is installed. A case 17 that covers the thin plate 23, the bonded piezoelectric element 11, etc. is fitted into the throat of the parabolic horn 24 and held there. 19.19' is bonded piezoelectric element 1
1 and terminals 1e and 16'.

The openings 22, 22' and 22'' of the thin plate 23 depend on the size and thickness of the bonded piezoelectric element 11, the size, thickness and central angle of the diaphragm 13, the inner diameter of the cushioning material 20, etc. , the optimum shape is different. A typical one is shown in FIG.

The size and shape of the openings 22, 22' and 22'' of the thin plate 23, the thickness of the thin plate 23, and the thin plate 23 and the diaphragm 13
Resonant frequency f determined by the volume between. is set to a value in the range from the resonant frequency fr of the bonded piezoelectric element 11 having the diaphragm 13 elastically fixed to the buffer material 2o at the center to the anti-resonant frequency.

Next, FIG. 5 shows the transient characteristics of the ultrasonic transducer having the structure of the present invention. Pulse rise/fall time is 0.2
Now indicates milliseconds or less.

FIG. 6 shows the resonant frequency fl + anti-resonant frequency fa of the bonded piezoelectric element 11 having the diaphragm 13 in the center which is elastically fixed by the buffer material 20, and the opening 22, 22'.
, 22', shows the frequency characteristics of the transmitted sound pressure level and reception sensitivity of the ultrasonic transducer when the relationship between the resonance frequency fo determined by the same volume of the thin plate 23 and the diaphragm 13 is changed. .

f<fr'! , or f. >, the transmitted sound pressure level was approximately 123 dB and the receiving sensitivity was approximately -sei dB at each maximum frequency.

It has become clear that by setting fo so that fr≦fc≦fa, the transmitted sound pressure level reception sensitivity is increased.

Furthermore, the frequency characteristics of the transmitted sound pressure level and the receiving sensitivity change with changes in the ambient temperature.

This change is caused by openings 22, 22', 22'', thin plates 23
The wavelength λ that resonates due to the capacitance between the diaphragm 130 and the diaphragm 130. is almost constant regardless of temperature, whereas the sound speed ■ changes, so its resonant frequency fo is f0=■/λ0
This is because it changes according to the formula shown below.

However, as is clear from Fig. 6(-), The temperature characteristics of pressure level and reception sensitivity have been significantly improved. Note that curves A and B in the figure indicate the transmitted sound pressure level, and curves C and D indicate the receiving sensitivity, respectively.

Effects of the Invention As described above, the ultrasonic transducer of the present invention has good transient characteristics and high wave transmitting and receiving sensitivity characteristics, and is extremely useful for ultrasonic applied measurements such as distance meters using sound waves. It is.

[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 transient characteristics, and FIG. 3 is a sectional view showing an embodiment of the ultrasonic transducer of the present invention. Fig. 4 is a front view showing an example of the thin plate of the ultrasonic transducer, Fig. 6 is a diagram showing the transient characteristics of the ultrasonic transducer, and Fig. 6 is the sensitivity of the ultrasonic transducer. Temperature change in frequency characteristics and resonance frequency f. FIG. . 11... Bonded piezoelectric element, 13...
- Vibration plate 20...Buffer material, 21...Sound absorbing material, 22, 2i. 22'...opening, 23...thin plate, 2
4...Horn. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 5

Claims (3)

[Claims] (1) It has an electroacoustic transducer including at least a laminated piezoelectric element provided with a diaphragm and a case enclosing the laminated piezoelectric element, and has An ultrasonic transducer characterized in that the resonant frequency determined by the volume of the front surface of the diaphragm is set within a range from the resonant frequency to the anti-resonant frequency of the electroacoustic transducer. (2) A thin plate having a plurality of openings is installed in front of the electroacoustic converter, and the electroacoustic converter and the thin plate are embedded in the horn.
Ultrasonic transducer described in section. (3) The electroacoustic transducer connects the diaphragm to the diaphragm using the cushioning material so as to suppress mechanical vibrations using the cushioning material disposed so as to contact the peripheral portion of the diaphragm and the inner surface of the case. 3. The ultrasonic transducer according to claim 2, wherein the ultrasonic transducer is elastically fixed to the case.