JPS6324799A - Air ultrasonic transducer - Google Patents

Abstract

PURPOSE:To widen the detecting distance scope of an object and to improve reliability by setting the side of a metallic case and the diameter of a piezoelectric vibrator so that the level of the transmitting ringing can be made smaller in a short time. CONSTITUTION:A transducer is composed of a piezoelectric vibrator 22 using the spread vibrating mode of a piezoelectric substrate 21, a 1/4 wavelength acoustic matching layer 23 to increase the emissivity to the air of the spread vibration of the piezoelectric substrate 21 and one edge aperture-shaped metallic case 24. A size (t) and a diameter (w) are set so that a ratio t/w of the size (t) from the junction surface with the 1/4 waveform acoustic matching layer 23 of the metallic case 24 up to other edge surface of the metallic case 24 opposite to it and the diameter (w) of a piezoelectric vibrator can be 0.1<t/w<0.7. Consequently, the level of the transmitting ringing is suppressed and the position of an object can be detected up to a close range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an airborne ultrasonic transducer using a piezoelectric vibrator.

(Prior Art) Generally, aerial ultrasonic transducers are used in various fields such as position detection sensors for products flowing on a conveyor line, back sensors for automobiles, and focus detection for cameras.

Conventionally, this type of aerial ultrasonic transducer
Several 100KH using the spread vibration mode of a piezoelectric vibrator
Some are used in the frequency band of 100 MHz to several MHz.

FIGS. 4 and 5 respectively show longitudinal sections of two examples of such airborne ultrasound transducers.

In the airborne ultrasonic transducer shown in FIG. 4, a circular piezoelectric substrate 1 is spread and placed on one main surface of a piezoelectric vibrator 2 that vibrates. A 4-wavelength acoustic matching layer 3 is bonded, and a ring-shaped support member 4 is bonded to the peripheral edge of this 1/4 wavelength acoustic matching layer 3, as shown in FIG. It is an open type that is supported entirely by. The piezoelectric vibrator 2 has electrodes 5 and 6 formed on the opposing surfaces of the piezoelectric substrate 1, and lead wires 7 and 8 are drawn out from these electrodes 5 and 6, respectively.

On the other hand, in the aerial ultrasonic transducer shown in FIG. 5, a piezoelectric vibrator 2 similar to that shown in FIG.
It is of a resin case type in which lead wires 7 and 8 of the piezoelectric vibrator 2 are soldered to terminals 13 and 14 provided in the piezoelectric vibrator 2, respectively. In this resin case type aerial ultrasonic transducer, the resin case 11 functions as a 1/4 wavelength acoustic matching layer of the aerial ultrasonic transducer.

By the way, in the open type airborne ultrasonic transducer shown in Fig. 4, the piezoelectric vibrator 2 is exposed, so it cannot be used under harsh conditions such as a large amount of dirt and dust floating in the air or high humidity. However, there was a problem that reliability deteriorated and it became unusable.

In addition, in the resin case type shown in FIG. 5, when the piezoelectric substrate 1 of the piezoelectric vibrator 2 spreads and vibrates, the resin case 11 resonates, and even after the ultrasonic wave is emitted, the resin case 11
The vibration continues. This vibration is caught by the piezoelectric vibrator 2 as transmission ringing. Therefore, when measuring the position of a nearby object using the aerial ultrasonic transducer shown in FIG. If the transmission ringing continues even when it returns to the transducer and is received as a reflected wave from the object, the reflected signal from the object will be buried in the transmission ringing, and the position of the nearby object will be lost. There was a problem that it could not be detected.

(Objective of the Invention) An object of the present invention is to provide an airborne ultrasonic transducer that has a wide object detection range, a simple structure, and high reliability.

(Structure of the Invention) Therefore, in the present invention, a 1/4 wavelength acoustic matching layer having a piezoelectric vibrator fixed to an opening at one end of a metal case having an opening at one end is bonded and fixed at its periphery, and the above-mentioned metal Case 1
The ratio t/W of the dimension from the bonding surface with the /4 wavelength acoustic matching layer to the other end surface of the metal case opposing thereto and the diameter W of the piezoelectric vibrator is 0.1<t/w<0.7. It is characterized by being

By setting the above dimensions and the above diameter W so that the above ratio t/w takes a value between 01 and 0.7, the level of transmission ringing can be suppressed and the position of an object can be detected up to a short distance. become.

(Effects of the Invention) According to the present invention, the dimensions of the metal case and the diameter of the piezoelectric vibrator are set so that the level of transmission ringing is reduced in a short time. is not buried in transmission ringing, and therefore objects at close range can be detected with a high S/N ratio. Further, according to the present invention, the metal case is open at one end, and the piezoelectric vibrator is sealed inside the metal case by a quarter-wavelength acoustic plate, so it can be used even under severe environmental conditions. Get a reliable airborne ultrasound transducer.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A vertical cross-sectional view and a perspective view of an embodiment of an airborne ultrasonic transducer according to the present invention are shown in FIGS. 1 and 2, respectively.

The aerial ultrasonic transducer includes a piezoelectric vibrator 22 that utilizes the spreading vibration mode of the piezoelectric substrate 21, and a 1/. a one-wavelength acoustic matching layer 23;
It consists of a metal case 24 with one end open.

The piezoelectric vibrator 22 has electrodes 25 and 26 formed on opposing surfaces of a circular piezoelectric substrate 21 having a diameter of W, respectively. The piezoelectric vibrator 22 is bonded on the electrode 25 side to approximately the center of one main surface of the /4 wavelength acoustic matching layer 23 with an adhesive (not shown).

On the other hand, the 1/4 wavelength acoustic matching layer 23 is formed by mixing hollow glass beads with a diameter of 10 to 200 μm into epoxy resin, for example, and molding the mixture into a disk shape with a diameter of φ()W) and a thickness of X. And its characteristic acoustic impedance is Z=0.1
xlO' to 2.5xlO' is 9/ash 2.S. The quarter wavelength acoustic matching layer 23 is fitted into the opening 24a of the metal case 24.

The metal case 24 is made of a metal material such as aluminum, brass, or stainless steel. Metal case 2 above
The opening 24a of No. 4 has the above-mentioned 1/4 which is fitted into the opening 24a.
It has an inner diameter of (φ+29) so that a gap of g is formed between it and the outer peripheral surface of the wavelength acoustic matching layer 23. Also,
The width of the opening 24a of the metal case 24 is equal to or slightly larger than the thickness X of the 1/4 wavelength acoustic matching layer 23, and the wall 24b surrounding this opening 24a is
It functions as a protective guard for the /4 wavelength acoustic matching layer 23.

The inner diameter of the interior 24c of the metal case 24 following the opening 24a is set to be slightly larger than the diameter of the piezoelectric vibrator 22. That is, the thickness y of the side wall 24d of the metal case 24 surrounding the interior 24c is set to a value within a range where the side wall 24d does not come into contact with the piezoelectric vibrator 22.

Due to such dimension setting inside the metal case 24, a stepped portion 24 is formed between the inside 24c of the metal case 24 and the opening 24a.
e is formed, and the peripheral edge of the 1/4 wavelength acoustic matching layer 23, in which the piezoelectric vibrator 22 is fitted into the opening 24a with the piezoelectric vibrator 22 facing inside the metal case 24, is bonded and fixed to this step 24e. .

Lead wires 27 and 28 are connected to the electrodes 25 and 26 of the piezoelectric vibrator 22, respectively, and these lead wires 27 and 28 are soldered to terminals 31 and 32, respectively, which pass through the bottom of the metal case 24. be done. These terminals 31 and 32 are fixed by penetrating the bottom of the metal case 24 with an insulating resin 29.

In the aerial ultrasonic transducer having the above-described structure, the step portion 24e of the metal case 24 is further provided.
The distance Mt and the diameter W are set so that the ratio of the distance t from The value is set.

This is based on the following experimental results regarding transmission ringing using the above-mentioned aerial ultrasonic transducer by the inventor of the present application.

That is, the inventor of the present application has determined that t/w is 0.0.20
゜0.35, 0.55, 0.62, 0.7, 0.82,
Samples of 0.86° 1.0, 1.05 and 1.20 were prepared and the ringing time with a drop of 40 dH was measured, and the results shown by the curve in FIG. 3 were obtained.

Note that t/w=0 is the case where the metal case 24 is not attached. In FIG. 3, the horizontal axis is L/W, and the vertical axis is 40 decibel drop ringing time (ms).

In FIG. 3 above, the minimum value of the 40 dB drop ringing time is approximately 0.8 m5ec. This 0.8m
The distance that an ultrasonic wave travels in 5ec is the sound speed of 340 m/s
If ec, 340xO, 8XlO-'40.27m
It is. Therefore, the minimum detection distance at this time is the above 0.2
1/2 of 7m. That is, it is about 13.5 cm. By the way, the above minimum detection distance is 15 degrees from the above 13°5 cm.
Considering that approximately 16 ci is sufficient for practical purposes, 4
0 dB drop ringing time 0.8~1,1 m
It can be seen that it is sufficient to set the value to about 5ec.

Therefore, the 40 dB drop ringing time is 0°8~1
, 1 m5ec, it can be seen from FIG. 3 that the value of the above ratio/W should be set in the range of 0/w<0.7.

In addition, in the above embodiment, the l/·1 wavelength acoustic matching layer 2
Ideally, the gap g between 3 and the openings 2 and 1a of the metal case 24 should be filled with no load, but if you want to further reduce the object detection distance or increase the mechanical strength. If desired, the gap g may be filled with silicone rubber, Evoquin, or the like.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of an embodiment of the aerial ultrasonic transducer according to the present invention, FIG. 2 is a perspective view of the aerial ultrasonic transducer of FIG. 1, and FIG. 3 is a view of the aerial ultrasonic transducer of FIG. An explanatory diagram showing the measurement results of a 40 decibel drop ringing time. FIGS. 4 and 5 are longitudinal cross-sectional views of a conventional airborne ultrasonic transducer, respectively. 2I...Piezoelectric substrate, 22...Piezoelectric vibrator, 23/
4-wavelength acoustic matching layer, 24 - Metal case (24a...opening). Patent applicant: Murata Manufacturing Co., Ltd. Agent: Patent attorney: Seihaku Ho, and 2 others @Figure 3 t/w Figure 4 Figure 5

Claims (1)

[Claims] (1) A piezoelectric vibrator that utilizes the spread vibration mode of a circular piezoelectric substrate, and a flat 1/4 wavelength acoustic matching layer that is tightly fixed to approximately the center of one main surface of the piezoelectric vibrator. This 1/4 wavelength acoustic matching layer is made up of a metal case with an open end fixed to an opening at one end at the periphery of the one main surface with the piezoelectric vibrator inside; The ratio t/w of the dimension t from the joint surface with the 1/4 wavelength acoustic matching layer to the other end surface of the metal case opposing thereto and the diameter w of the piezoelectric vibrator is 0.1<t/w<0. 7. An aerial ultrasonic transducer characterized by: