JPS642320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic transducer having sharp directivity characteristics and improved pulse characteristics.

Bonded piezoelectric elements made of piezoelectric ceramics are often used as transmitters and receivers for ultrasonic waves in the air.
It is made to be used at the resonance point and anti-resonance point of the bending vibration of the bonded piezoelectric element. Furthermore, since the mechanical impedance of air as a medium 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.
This involves penetrating and fixing a coupling shaft 2 to the center of the bonded piezoelectric element 1, attaching a diaphragm 3 to the coupling shaft 2, and directing the vibration nodes of the bonded piezoelectric element 1 to the tip of the support base 4. It was fixed with an elastic adhesive 5. 6 and 6' are terminals, 7 is a case that covers the bonded piezoelectric element, 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 terminal 6,
This is a lead wire that electrically connects 6'.

FIG. 2 shows the pulse characteristics of the ultrasonic transducer having the above structure, and shows the transmission waveform when driven with a plurality of pulses. Due to the high mechanical Q of piezoelectric ceramics, the rise and fall times were slow, reaching more than 2 milliseconds.

For example, when measuring the distance of a moving object, when using such a conventional ultrasonic transducer, it is necessary to obtain measurement information at short time intervals, and the rise and fall times are extremely long, so the received signal is It takes time to reach the peak value. Alternatively, the next signal may be received before the received signal falls, causing interference and making it impossible to obtain accurate measurement information.

In addition, when transmitting and receiving waves using a single element,
Until it becomes ready to receive after transmitting a wave,
It took a considerable amount of time, during which time no measurement information could be obtained.

Furthermore, in order to increase the resolution of the object to be measured, sharp directional characteristics are required.
As is well known, sharp directional characteristics can be achieved by increasing the size of the sound source and raising the frequency used, but as the frequency used increases, the attenuation of sound increases significantly, so there is a limit to increasing the frequency. can be,
It is necessary 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, and the support base that supports the bonded piezoelectric element become significantly large. Even if a large diaphragm was used, it was extremely difficult to achieve uniform piston vibration, and the directional characteristics were generally not as sharp as the sound source was made larger.

On the other hand, when trying to sharpen the directional characteristics by using a horn, it was not easy to add a horn to a conventional ultrasonic transceiver to lower the mechanical Q and improve the pulse characteristics. .

Therefore, the present invention provides a diaphragm at 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. By adding a thin plate with an opening in the front and a horn, an ultrasonic transducer having sharp directional characteristics and good pulse characteristics is provided.

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 3 is a sectional view of this embodiment.

A diaphragm 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 13 is
It is elastically fixed to the inner surface of the cylindrical case 17 via a buffer material 20 such as elastic rubber formed in an annular shape so as to suppress mechanical vibrations. A sound absorbing material 21 is attached to the bottom of the case 17.
In front of the diaphragm 13, there is a circular opening 22 centered on a straight line passing through the coupling shaft 12;
A thin plate 23 having another opening 22' provided on a concentric circumference is installed, and the case 17 and the thin plate 23 are fitted into the throat of the parabolic horn 24. Lead wires 19 and 19' electrically connect the bonded piezoelectric element 11 and the terminals 16 and 16'.

The shape of the openings 22, 22' of the thin plate 23 changes depending on the size of the bonded piezoelectric element 11, the size of the diaphragm 13, the inner diameter of the cushioning material 20, etc. This is shown in Figures 1 to 16. In both figures, a is a plan view and b is a sectional view.

Next, FIG. 17 shows the pulse characteristics of the ultrasonic transducer having the structure of the present invention. This clearly shows that the pulse rise and fall times are less than 0.3 milliseconds.

FIG. 18 shows changes in the half-reduction angle of sound pressure, wave transmission sensitivity, and rise time when the inner diameter of the buffer material 20 is changed. As the inner diameter of the buffer material 20 decreases, the rise time decreases, but the sound pressure half-decrease angle increases slightly and the wave transmission sensitivity also decreases. If the inner diameter is further reduced, the side lobes also increase (not shown). Therefore, it can be seen that the inner diameter of the cushioning material 20 has an optimum value once the sizes and thicknesses of the bonded piezoelectric element 11 and the diaphragm 13 are determined. Note that the diameter of the bonded piezoelectric element 11 is 9.1
mm, the thickness is approximately 0.6 mm, and the diameter of the bottom of the diaphragm 13 is
Conical shape of about 17mm, diameter of horn 24 is about 55mm
mm and thin plate 23 are experimental values for the one shown in FIG.

FIG. 19 shows that the diameter of the bonded piezoelectric element 11 is approximately 9.1 mm, and when the thickness is changed, the half-reduction angle of the sound pressure,
Changes in transmission sensitivity, rise time, and drive frequency (frequency at which sensitivity is maximized) are shown, respectively.
As the thickness of the bonded piezoelectric element 11 increases, the drive frequency increases and the half-reduction angle of sound pressure decreases, but the wave transmission sensitivity decreases and the rise time also increases.

As the diameter of the diaphragm 23 increases, the wave transmission sensitivity increases, but the rise time also increases, so the diameter may be determined depending on the application. When spatially uniform directivity (for example, vertically, horizontally, and horizontally) is required, the diaphragm 13 is preferably of a conical shape, a lattice shape, a bowl shape, or the like.

FIG. 20a shows the directivity characteristics of the device of the present invention when the thin plate 23 is installed in front of the diaphragm 13. Figure b shows the directivity characteristics before installation. It can be seen that according to the present invention, the sidelobes are greatly reduced. It has become possible to obtain spatially almost uniform directional characteristics.

In addition, by integrating the case 17 and the thin plate 23, it is not only possible to obtain more spatially uniform directivity characteristics, but also the variation in characteristics is reduced, making assembly easier and mass production easier. .

Furthermore, noise resistance was improved by making the integrally formed case 17 and thin plate 23 conductive and connecting them to ground.

As described above, according to the present invention, it has sharp directivity characteristics and good pulse characteristics, and it has become possible to obtain accurate measurement information at short time intervals. Therefore, the ultrasonic transducer of the present invention is extremely useful for ultrasonic applied measurements that require sharp directivity characteristics, such as distance meters using sound waves.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a conventional ultrasonic transducer, and FIG. 2 is a diagram showing its pulse characteristics.
FIG. 3 is a cross-sectional view of one embodiment of the ultrasonic transducer of the present invention, and FIGS. 4 to 16 show the structure of a typical example of the thin plate thereof, in which figure a is a front view and figure b is a front view. A cross-sectional view, FIG. 17 is a diagram showing an example of the pulse characteristics of the ultrasonic transducer of the present invention, and FIG. 18 is a diagram showing the inner diameter of the buffer material, half-sound pressure angle, and wave transmission sensitivity of the ultrasonic transducer of the present invention. , Figure 19 shows the relationship between the rise time and the thickness of the bonded piezoelectric element and the sound pressure half angle,
FIG. 20, which is a diagram showing the relationship between wave transmission sensitivity, rise time, and drive frequency, is also a diagram showing the effect of a thin plate. 11... Bonded piezoelectric element, 13... Vibration plate, 17... Case, 20... Cushioning material, 21...
Sound absorbing material, 22, 22'... opening, 23... thin plate,
24...Horn.

Claims (1)

[Claims] 1. A bonded piezoelectric element having a diaphragm in the center, a case enclosing the bonded piezoelectric element,
a cushioning material attached so as to be in contact with the periphery of the diaphragm and the inner surface of the case; a thin plate with an opening disposed in front of the bonded piezoelectric element;
and an ultrasonic transducer characterized in that it has at least a horn that seals and fixes the case and the thin plate in the throat, and the diaphragm is elastically fixed to the case by the cushioning material. 2. The ultrasonic transducer according to claim 1, characterized in that the thin plate, the case, and the horn are integrally formed.