JPH01190100A - Aerial ultrasonic transducer - Google Patents

Abstract

PURPOSE:To shorten reverberation time and to identify a shorter distance by arranging a tubulous body composed of a material which can be deformed elastically so that the tubulous body can surround a piezoelectric element, strongly pressing an acoustic matching layer by this tubulous body and giving a moderate load for the acoustic matching layer. CONSTITUTION:An aerial ultrasonic transducer 10 includes an acoustic matching layer 12 and a case 14 which are resin molded in a body. A piezoelectric element 18 is fixed onto the internal surface of the acoustic matching layer 12. In the internal part of the case 14, a tubulous body 26, which is a cylindrical body formed with the material, which can be deformed elastically, and made to have a length longer than that of the lower edge surface of the case 14, namely, the upper edge surface of a terminal plate 22, for a constant length L, is arranged so that the tubulous body 26 can surround the piezoelectric element 18, and one edge of the tubulous body 26 can contact on the acoustic matching layer 12, the tubulous body 26 is pressed and fitted into the case 14 under an elastically deformed state into a barrel shape by pushing up the other edge of the tubulous body 26 by the terminal plate 22 and fixing the terminal plate 22 onto the lower edge surface of the case 14, and in the internal surface of the acoustic matching layer 12, omparatively strong pressurized contact force is received around the piezoelectric element 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an airborne ultrasonic transducer, and in particular, for example, a disk-shaped or ring-shaped piezoelectric ceramic is fixed to a disk-shaped acoustic matching layer, and its wave transmission/reception. The present invention relates to an airborne ultrasonic transducer that measures the distance to, for example, an object by wave timing.

[Prior art]

Examples of this type of airborne ultrasonic transducer are, for example,
The application was published on the date of Utility Model Application No. 9-1643.
No. 98 and Japanese Utility Model Application Publication No. 60-163899.

[Problem that the invention seeks to solve]

Conventional technology that transmits and receives ultrasonic waves using the same piezoelectric element uses a pulse (tone burst)
Reverberation occurs during input, and if the transmitted signal is buried in the reverberation, it becomes difficult to distinguish between them, and distance measurement becomes impossible. Conventionally known devices have a problem in that such reverberation times are relatively long and therefore shorter distances cannot be measured or detected.

Therefore, a primary objective of this invention is to provide an airborne ultrasound transducer that can discriminate shorter distances.

[Means for solving problems]

In this invention, a cylindrical body made of an elastically deformable material such as felt, which is slightly longer than the length of the case, is placed in the case so as to surround the piezoelectric element, and one end of the cylindrical body is placed in contact with the acoustic matching layer. This is an airborne ultrasonic transducer that is press-fitted with its lower end or other end typically in contact with a lid member such as a terminal plate.

[Effect]

When the cylindrical body is press-fitted with the lid member, the cylindrical body undergoes elastic deformation and strongly presses against the acoustic matching layer.

Therefore, an appropriate load is applied to the acoustic matching layer, and the generation of spurious components in the acoustic matching layer is suppressed. In addition,
Since the cylindrical body has elasticity, the ultrasonic vibration itself caused by the piezoelectric element is not hindered.

[Effects of the Invention] According to the present invention, since spurious in the acoustic matching layer is suppressed, the reverberation time becomes shorter than that of the conventional one, and thus it becomes possible to identify a shorter distance.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

〔Example〕

FIG. 1 is an illustrative cross-sectional view showing one embodiment of the present invention.

In this embodiment, the aerial ultrasonic transducer 10 includes an acoustic matching layer 12 and a case 14 that are integrally molded with resin.
including. However, it goes without saying that the acoustic matching J112 and the case 14 may be configured as separate entities and then integrated by being glued together.

Inside the acoustic matching layer 12, there are particles having a predetermined particle size, for example, 10 to 10.
Glass microballoons 16 having a diameter of 200 μm are dispersed. This acoustic matching F! The acoustic impedance of i12 is determined by the acoustic impedance in the air and the piezoelectric element 18.
It has an intermediate acoustic impedance between the two, and thus serves to match the acoustic impedances of both.

A known disk-shaped or ring-shaped piezoelectric element 18 is adhered or fixed to the inner surface of the acoustic matching layer 12. This piezoelectric element 18 includes a ceramic unit such as PZT, and vibrating electrodes formed on both surfaces thereof, and each of the vibrating electrodes is connected to a corresponding external terminal 24 provided on a terminal plate 22 by a lead 20. connected to. When a tone burst wave is applied to the piezoelectric element 18 through the external terminal 24, a predetermined ultrasonic signal is transmitted from the piezoelectric element 18, and the ultrasonic wave returned from the reflector is received by the piezoelectric element 18. Then, the distance to the reflector can be determined based on the time difference between the wave transmission and reception timing and the speed of sound.

What should be noted is that a cylindrical body 26 is disposed inside the case 14. This cylindrical body 26 is a cylindrical body formed of an elastically deformable material, typically felt, and its length is as large as the length of the case 26, as can be clearly seen from FIG.
4, that is, the upper end surface of the terminal plate 22, by a certain length. Such a cylindrical body 26 surrounds the piezoelectric element 18 and is arranged such that one end thereof contacts the acoustic matching Ji12. Then, as shown in FIG. 2, by pushing up the other end of the cylindrical body 26 with the terminal plate 22 and fixing the terminal plate 22 to the lower end surface of the case 14, the cylindrical body 26 as shown in FIG. It is press-fitted into the case 14 in a state where it is elastically deformed into a barrel-shaped cross section.

Due to the elasticity of the cylindrical body 26 press-fitted in this way,
The inner surface of the acoustic matching layer 12 receives a relatively strong pressure force around the piezoelectric element 18 .

The pressure contact force applies an appropriate load to the acoustic matching layer 12, thereby suppressing spurious components that may occur in the acoustic matching N12. Therefore, the acoustic matching layer 1
2, the overall reverberation time is relatively short.

According to experiments conducted by the inventors, in a conventional airborne ultrasonic transducer, the reverberation time is approximately 1 msec at 110 kHz, and therefore the minimum discernible distance is 25 cm. In contrast, the airborne ultrasonic transducer according to the present invention has a reverberation time of 0.6 m.
The distance has become shorter to about 5 ec, and therefore the minimum distinguishable distance has also become much shorter, for example to 15 cm.

The material for the cylindrical body 26 is preferably a material that also has a sound absorbing function, such as glass wool, such as the above-mentioned felt, but it is also possible to use anisotropic rubber or isotropic silicone rubber that does not have a sound absorbing function. be.

[Brief explanation of the drawing]

FIG. 1 is an illustrative cross-sectional view showing one embodiment of the present invention. FIG. 2 is an illustrative cross-sectional view showing the relationship between the lengths of the cylindrical body and the case of this embodiment. In the figure, 10 is an airborne ultrasonic transducer, 12
14 is an acoustic matching layer, 14 is a case, 18 is a piezoelectric element, 22 is a terminal plate, and 26 is a cylindrical body. Patent Applicant Murata Manufacturing Co., Ltd. Representative Patent Attorney Yama 1) Yoshi Personnel Figure 1 Figure 2

Claims (1)

[Claims] A piezoelectric element is fixed to a plate-shaped acoustic matching layer, and a case of a predetermined length is formed on the same side as the fixed surface of the acoustic matching layer,
In an airborne ultrasonic transducer whose case is sealed by a lid member, a cylindrical body made of an elastically deformable material and whose length is longer than the length of the case is disposed in the case so as to surround the piezoelectric element. An airborne ultrasonic transducer, characterized in that the cylindrical body is press-fitted so that one end of the cylindrical body contacts the fixed surface of the acoustic matching layer and the other end abuts against the lid member.