JPH0374797B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an ultrasonic transducer used in an ultrasonic distance measuring device or the like.

The configuration of conventional examples and their problems The frequencies used in conventional aerial ultrasonic distance measuring devices range from 20kHz to 100kHz, and the ultrasonic wavelength is relatively long and the external noise level is high. Therefore, it has been difficult to measure distances with high precision or short distances of 10 cm or less. For this reason, from several hundred kHz to 1k
Attempts have also been made to use ultrasonic transducers that can transmit and receive ultrasonic frequencies on the order of Hz. When using this approximately 1kHz ultrasonic transducer in a distance measurement device, etc., fluctuations in the air due to wind or temperature changes may cause large fluctuations in the ultrasonic transmission and reception signals.
This causes deterioration of measurement accuracy. In particular, when performing fan-shaped scanning with an ultrasonic transducer to measure a wide range, air fluctuations caused by rotation of the ultrasonic transducer become a problem.

Furthermore, as shown in FIG. 1, the conventional ultrasonic transducer consists of a piezoelectric vibrator 1, an acoustic matching body 2 provided on the front surface of the piezoelectric vibrator 1, and a back load 3 provided on the rear surface. ing. As is well known, the properties of the material used for the acoustic matching body 2 are preferably close to the 1/2 power of the respective acoustic impedance values of the piezoelectric vibrator 1 and air, and therefore, the material used for the piezoelectric vibrator 1 is generally used. When a typical piezoelectric ceramic material is used, the acoustic impedance suitable for the acoustic matching body 2 is approximately 0.1 to 1×10 ⁶ Kg/m ² ·s. However, even if values in this vicinity are used, the piezoelectric vibrator 1
Since the acoustic impedance chain of air and air is extremely large, approximately 10 ⁵ :1, the frequency band characteristics of the ultrasonic transducer are narrow, resulting in poor response characteristics.

On the other hand, in a medical ultrasound transducer, a method is well known in which a piezoelectric vibrator that transmits and receives ultrasound of several Hz is mechanically scanned in a fan shape at high speed within an ultrasound cell to obtain an ultrasound tomographic image. However, in this case, the object to which the ultrasonic waves propagate is the human body, and if the ultrasonic waves are emitted into the air as is, the sensitivity will be extremely low, making it difficult to use.

Purpose of the Invention The present invention has been made to solve the problems of the conventional art as described above. The present invention provides an efficient ultrasonic transducer that can operate satisfactorily in a frequency band and can be used in ultrasonic distance measuring devices, ultrasonic imaging devices, and the like.

Structure of the Invention In order to achieve this object, the present invention provides a piezoelectric vibrator and a liquid that controls acoustic matching between the piezoelectric vibrator and a liquid that is an ultrasonic propagation medium. an ultrasonic cell incorporating a first acoustic matching body for acoustic matching, an acoustic window provided in front of the ultrasonic cell, and a second acoustic window provided in front of the ultrasonic cell for efficiently transmitting and receiving ultrasonic waves into the air. The present invention provides an ultrasonic transducer equipped with an acoustic matching body, and with this configuration, even when an ultrasonic beam is scanned at high speed, air fluctuations do not occur and ultrasonic loss is reduced. This makes it possible to sufficiently measure distances even in a high frequency range.

DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view showing an ultrasonic transducer according to an embodiment of the present invention. In the figure, an ultrasonic signal 4 of several hundred kHz emitted from a piezoelectric vibrator 1 made of piezoelectric ceramic or the like is transmitted to a first acoustic matching body provided in front of the piezoelectric vibrator 1 for acoustic matching with the liquid. 5 (for example, a single-layer structure made of tungsten epoxy, or a two-layer structure made of glass and epoxy) can efficiently absorb water, oils such as silicone oil, or fluids such as Dyfloil and Fluorinert (trade name). The ultrasonic wave passes through an ultrasonic propagation medium 6 made of a liquid such as an inert liquid, passes through an acoustic window 8 of an ultrasonic cell 7 made of polyethylene or dimethylpentene, etc., and interacts with a gas provided in front of the acoustic window 8. A second acoustic matching body 9 for achieving acoustic matching (for example, a single layer structure made of a silicone rubber membrane or a silicone rubber membrane containing hollow plastic spheres, or a second acoustic matching body 9 consisting of two layers of silicone rubber or epoxy resin containing hollow spheres with different acoustic impedances) The ultrasonic signal 11 efficiently radiated into the air 10 by the layered structure) is reflected by the object 12, and is received by the piezoelectric vibrator 1 through the same propagation path again. It is used for distance measurement and ultrasonic imaging. Further, when the piezoelectric vibrator 1 performs fan-shaped scanning, the tip of a rotating type or reciprocating vibration system is attached to enable high-speed scanning. When scanning a rotation system, a motor 14 provided in the scanning mechanism 13 is used.
Accordingly, the pulley 16 provided on the piezoelectric vibrator 1 side is rotated via the belt 15, and the piezoelectric vibrator 1 is rotated. Here, 3 is a back load, 17 is a rotation center, and 18 is a sound absorber that absorbs unnecessary ultrasonic signals within the ultrasonic cell 7, and is provided in a portion other than the acoustic window 8.

When the above-described ultrasonic transducer is used, the piezoelectric vibrator 1 is scanned at high speed within the ultrasonic cell 7, which is separated from the air 10, and the first and second acoustic matching bodies 5 and 9, respectively, piezoelectric vibrator 1
Acoustic matching is achieved between the ultrasonic propagation medium 6 and the liquid ultrasonic propagation medium 6, and between the ultrasonic propagation medium 6 and the air 10.

As described above, according to this embodiment, the piezoelectric vibrator 1
Since it is completely separated from the air 10, even if it is mechanically scanned at high speed by the scanning mechanism 13, no air fluctuation occurs. That is, even when ultrasonic signals of several hundred kHz or higher are transmitted and received in the air, distance measurements can be performed relatively stably.

Furthermore, the first and second acoustic matching bodies 5 and 9 can be constructed from easily available matching layer materials by selecting materials 6 for ultrasonic propagation, improving sensitivity and frequency band characteristics, and Ultrasonic waves can be efficiently transmitted and received inside.

Note that the shape of the piezoelectric vibrator 1 may be a concave vibrator or a flat plate vibrator with an acoustic lens attached thereto for focusing, as is generally well known. Further, the shape of the ultrasonic cell is not limited to a cylindrical shape either.

FIG. 3 is a sectional view showing another embodiment of the present invention. A group of piezoelectric vibrating elements 19 arranged adjacent to the ultrasonic transducer and scanned electronically, a first acoustic matching body 20 provided in front thereof in the same manner as in the previous embodiment, and ultrasonic propagation. It is composed of an ultrasonic cell 22 filled with a medium 21, an acoustic window 23 provided on the front side thereof, a second acoustic matching body 24 provided on the front side, a surrounding sound absorber 25, and a rear sound absorber 26. . In such an ultrasonic transducer, the piezoelectric vibrator group 19 is sequentially switched electronically for transmission and reception, thereby eliminating distortion due to vibration and limitations on durability since mechanical scanning is not used. Furthermore,
The acoustic impedance ratio between the piezoelectric vibrating element group 19 and the ultrasonic propagation medium 21 is approximately (10 to 30):1, and the first acoustic matching body 20 provides broadband frequency characteristics. Furthermore, the acoustic impedance ratio between the ultrasonic propagation medium 21 and the acoustic window 23 and air 27 in the second acoustic matching body 24 is the same as that of the ultrasonic propagation medium 2.
1 and the acoustic window 23 having almost the same value, for example, when water and soft polyethylene are combined,
The ratio is approximately 3×10 ³ :1, which is extremely small compared to the ratio in the conventional structure (10 ⁵ :1).
Acoustic matching conditions are also easy to obtain, and broadband characteristics can be obtained. This leads to an improvement in pulse responsiveness, making it possible to transmit and receive short ultrasonic pulse signals, and leading to improved accuracy in ultrasonic distance measurement.

Effects of the Invention In summary, the present invention provides a piezoelectric vibrator installed in an ultrasonic cell filled with an ultrasonic propagation medium, and a first acoustic device provided in front of the piezoelectric vibrator to achieve acoustic matching with a liquid. A matching body, an acoustic window provided in the ultrasonic cell through which the ultrasonic signal passes, and a second acoustic matching body provided on the outer surface of the acoustic window for achieving acoustic matching with the gas. Since the piezoelectric vibrator is separated from the air, no air fluctuation occurs even during high-speed mechanical scanning, and two types of acoustic matching are possible. Since ultrasonic waves can be efficiently emitted into the air by the body, it has advantages such as improved accuracy when used as a transducer for ultrasonic distance measurement or ultrasonic imaging.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional aerial ultrasonic transducer, FIG. 2 is a cross-sectional view of an aerial ultrasonic transducer according to an embodiment of the present invention, and FIG. 3 is another embodiment of the same. FIG. 1... Piezoelectric vibrator, 5, 20... First acoustic matching body, 6, 21... Ultrasonic propagation medium, 7, 22...
...Ultrasonic cell, 8...Acoustic window, 9, 24...Second
acoustic matching body, 13... scanning mechanism, 14... motor, 15... belt, 19... piezoelectric vibrating element group.

Claims (1)

[Claims] 1. A piezoelectric vibrator installed in an ultrasonic cell filled with an ultrasonic propagation medium, and a first acoustic matching provided in front of the piezoelectric vibrator to achieve acoustic matching with a liquid. a second acoustic matching body provided on the outer surface of the acoustic window for achieving acoustic matching with the gas; An ultrasonic transducer featuring: 2. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is mechanically rotated or swing-scanned within the ultrasonic cell. 3. The ultrasonic transducer according to claim 1, wherein the piezoelectric vibrator is composed of a plurality of piezoelectric vibrating element groups, and the piezoelectric vibrating element groups are electronically scanned.