JPH08256395A - Ultrasonic wave transmitter-receiver - Google Patents

Abstract

PURPOSE: To reduce dispersion in the characteristic without suppression of the main vibration mode by using a seat base having a recessed part so that the user cannot be in contact with an electrode of a piezoelectric porcelain vibrator and fixing the vibrator only at the outer circumferential part. CONSTITUTION: A circular or rectangular opposed electrode 9 opposite to a piezoelectric porcelain plate 1 nearly in the middle in the broadwise direction and a couple of lead electrodes 10a, 10b led in different directions so as not to be opposed to each other in the broadwise direction from the opposed electrode 9 are formed. Lead wires 6a, 6b are connected to the lead electrodes 10a, 10b to be polarized and stimulated. A recessed part 12 is provided to the seat base 2 in a range where the opposed electrode 9 is located so that the user cannot be directly in contact with the opposed electrode 9. Only the outer circumferential part of the piezoelectric vibrator 1 is adhered to the seat base 2 and water-resistance structure is provided by molding. Thus, the dispersion in the characteristic by assembling is less without dumping the vibration in the broadwise direction and the transmitter-receiver suitable for transmission reception of a high frequency ultrasonic wave is easily obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an ultrasonic wave transmitter / receiver which is a sensor portion for transmitting / receiving ultrasonic waves in water to detect an object.

[0002]

2. Description of the Related Art In a vehicle that moves at high speed in water, an ultrasonic transducer is embedded in the vehicle so that an acoustic window for transmitting and receiving ultrasonic waves is flush with the surface of the vehicle. However, the laminar flow containing cavitation small bubbles or flow noise generated during navigation had a bad influence on the acoustic performance of the ultrasonic transducer. In order to reduce these influences, structural measures such as the shape of the navigation vehicle or the treatment of the outer surface are taken, while many measures are being taken for the transducers as well. This is an effective means for the transmitter / receiver, and the ultrasonic transmitter / receiver using the frequency in the megahertz band is being put into practical use.

Conventionally, a transducer used in a frequency band of several hundreds of kHz to several MHz utilizes the vibration in the thickness direction of a piezoelectric ceramic oscillator having a disk or rectangular plate shape, and is used for positioning and fixing the oscillator. In general, the structure is such that it is adhered and fixed to a pedestal or the like, and a waterproof structure is provided by a method such as molding with a rubber-like elastic body.

[0004]

By the way, in a piezoelectric ceramic vibrator utilizing vibration in the thickness direction, metal electrodes made of silver, nickel, or the like are formed on substantially the entire opposite surfaces in the thickness direction. Polarization and transmission / reception of electric signals are performed, and vibration in the thickness direction is uniformly excited in the entire vibrator. When using such a vibrator to handle higher frequencies, the thickness of the vibrator decreases in inverse proportion to the resonance frequency.
In addition, in order to maintain the directivity width, which is the performance of the transducer, the outer diameter of the transducer or the dimension in the width and length directions must be reduced, resulting in a reduction in the volume of the transducer. There has been a problem of increasing factors that increase variations in the characteristics of the assembled product, such as deterioration of workability in bonding and assembling.

This is a phenomenon that is often seen in vibrators that utilize vibration in the thickness direction.
For example, there is a problem that higher-order mode resonance of vibration in the radial direction, width, or length direction is likely to appear as parasitic vibration.
If the frequency is about 200 to 300 kHz, the influence is prevented by processing the slit to a depth of about two-thirds of the thickness of the vibrator and making the resonance frequency of parasitic vibration higher than the resonance frequency of thickness-direction vibration. However, since the thickness of the vibrator becomes 1 to 2 mm or less when the frequency is increased to the MHz band, it is difficult to take similar measures in terms of processing and strength. Furthermore, when the dimensions such as the outer diameter or width of the vibrator, which are determined by the requirements for directional characteristics, and the dimensions in the thickness direction of the oscillator approach a specific dimensional ratio, which is determined by the material constants and shape of the oscillator, vibration in the thickness direction occurs. Coupled vibrations between parasitic vibrations are likely to occur. When the coupled vibration occurs, the vibration in the thickness direction, which is the originally used vibration mode, cannot be effectively excited, and at the same time, a transition of the resonance frequency occurs and it becomes difficult to use the vibration at the intended frequency.

Further, as the frequency of sound wave propagation is shortened by increasing the frequency, the influence of the thickness of the adhesive layer for adhering and fixing the vibrator can be seen. When used at low frequencies, the adhesive layer thickness of 0.1-0.2 mm is
The wavelength ratio is about several tenths, and the low mechanical sharpness Qm of the adhesive can be ignored, but the wavelength becomes 1
When it is shortened to about 2 mm, the thickness of the adhesive layer cannot be ignored, and because of its low Qm, it functions as a damping factor for the vibration of the vibrator, and at the same time the adhesive that sticks out to the outer peripheral part of the vibrator and hardens It becomes a braking factor.

Furthermore, although a lead wire for transmitting and receiving a signal is connected to the electrode surface of the vibrator, the mass, rigidity, or elasticity of the lead wire cannot be ignored, and in many cases, like the adhesive, vibration of the vibrator is affected. It has a braking effect.

All of these are obstacles to the excitation of the thickness direction vibration, which is the main vibration mode of the vibrator, and have been the cause of characteristic defects such as a decrease in sensitivity of the transducer.

Further, a transducer having stable characteristics such as the presence of a lead wire and a soldering point for connecting the same on the electrode surface which is the acoustic surface of the vibrator, which causes a disturbance of the directional characteristics, is provided. Was very difficult to get.

The present invention is intended to solve the above-mentioned problems associated with increasing the frequency of an underwater ultrasonic transmitter / receiver, and to provide a transmitter / receiver with a small variation in characteristics by a simple method.

[0011]

DISCLOSURE OF THE INVENTION Circular or rectangular counter electrodes facing each other in the thickness direction at approximately the center of a circular or rectangular piezoelectric ceramic plate, and different directions so as not to face the counter electrode in the thickness direction. An extraction electrode is formed on the extraction electrode, an electric wire for exchanging an electric signal is connected to the extraction electrode to perform polarization and excitation, and the counter electrode is provided with a recessed portion at least in a range where the counter electrode is located. Consists of a pedestal with a structure that does not touch directly, and the oscillator is fixed by adhering only the outer peripheral part of the oscillator to the pedestal so that the counter electrode of the oscillator is located in the recessed part of the pedestal. It is characterized in that a waterproof structure is provided by a method such as molding.

[0012] As a measure for reducing the adverse effect of the ultrasonic wave transmitter / receiver provided on the underwater vehicle in high-speed traveling, increasing the operating frequency of the wave transmitter / receiver is an effective means. We are trying to put into practical use an ultrasonic transducer that uses band frequencies. However, the piezoelectric ceramic vibrator using the vibration in the thickness direction, which is used in this ultrasonic transmitter / receiver, has the following problems as the frequency becomes higher.
Not only the thickness of the vibrator but also the area of the vibrating surface must be reduced due to the requirement of directional characteristics, which leads to an increase in variations in characteristics due to deterioration of workability in bonding and assembling. Parasitic vibration peculiar to thickness direction vibration is likely to occur, and due to the directional characteristics, when the dimension of the vibrating surface and the dimension ratio in the thickness direction approach a specific dimension ratio, coupled vibration between the thickness direction vibration and the parasitic vibration occurs. When the vibration occurs, the thickness direction vibration cannot be effectively excited, and further, the target resonance frequency transition occurs. The thickness of the adhesive layer cannot be ignored, and becomes a braking factor for the vibration of the vibrator. The mass, rigidity, or elasticity of the lead wire cannot be ignored, and becomes a braking factor for the vibration of the vibrator. The lead wire on the electrode surface and the soldering point for connecting it are
This contributes to the disturbance of the directional characteristics. Therefore, in order to overcome these problems, the structural measures described above were taken and solved.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 4 (a) is a top perspective view and FIG. 4 (b) is a schematic cross-sectional view showing an example of the structure of a conventional transducer. Rectangular piezoelectric ceramic oscillator 1 with electrodes on both sides in the thickness direction
The lead wires 26a and 26b are connected to both electrodes by soldering, and the rear surface of the vibrator 21 is fixed to the pedestal 22 with an adhesive. In the through hole of the case 23, the lead wire 26a,
After passing through 26b and adhering the pedestal 22 and the case 23,
The lead wire is connected to the airtight terminals 28a and 28b, and the airtight terminal is bonded to a predetermined position of the housing 25. Case 2
3 is adhered to the housing 25, and a filler 27 such as an epoxy resin is injected into the space formed behind the case 23 to prevent deformation or damage when water pressure is applied, and after curing, the exposed side of the vibrator 21. A rubber-like elastic body 24 is molded into a watertight structure.

Now, the shape and size of the vibrator will be examined. The thickness of the vibrator when utilizing the thickness direction vibration is, for example, about 1.2 m when the resonance frequency is 1.5 MHz.
m and the resonance frequency is 3.0 MHz, it is about 0.6 mm. Further, when the outer diameter dimension of the vibrator is calculated from the requirement of the directional characteristics with the thickness of the vibrator being 1, in the case of the rectangular plate-shaped vibrator, if the -6 dB directivity width is 10 degrees, the side length of the rectangular plate is If the directional width is about 5 and -6 dB and the angle is 20 degrees, the side length is about 2.5. Therefore, if an attempt is made to obtain a -6 dB directivity width of 20 degrees at a frequency of 1.5 MHz, a rectangular plate-shaped vibrator will have a thickness of about 1.2 mm and a side length of about 3.0 mm square. If the frequency is raised to 3.0 MHz while maintaining the same value, the thickness is about 0.6 mm and the side length is about 1.5 mm square.
That is, the oscillator is significantly downsized as the frequency is increased so that the volume becomes approximately one fourth.

FIG. 5 shows the characteristics of a square plate-shaped thickness direction oscillator designed for manufacturing the transducer having the configuration of FIG. 4 on the assumption that it is used in the vicinity of 3 MHz. 5A shows the admittance frequency characteristic of the vibrator alone, and FIG. 5B shows the same characteristic before the rubber-like elastic body 24 is molded.

As a problem in the conventional method, the parasitic vibration is likely to be generated in the vibrator, but in the characteristic of FIG. 5A, in addition to the resonance f _{A in} the thickness direction vibration, f _B , f _C
And resonance of parasitic vibration is seen. If the resonance of vibration in the thickness direction is relatively low and the volume of the vibrator is large, the vibration in the thickness direction should be effectively used by damping the parasitic vibration such as the higher-order mode resonance of the width direction vibration by adhering to the pedestal. However, in such a small vibrator, the influence of the thickness of the adhesive layer or the lead wire connection cannot be ignored.

As shown in FIG. 5 (b), by virtue of the bonding of the vibrator 21 to the pedestal 22 and the attachment of the lead wires 26a and 26b, the originally necessary vibration in the thickness direction is damped, and the admittance value of f _A. Is reduced to the same level as the other parasitic vibrations f _B and f _C. The admittance is the reciprocal of the impedance, which means that the impedance at f _A becomes large and the excitation becomes difficult. It can be easily inferred that it is difficult to obtain the desired performance even if the transducer is assembled in this state. If the changes in characteristics due to assembly are uniform, it is possible to suppress variations in characteristics by taking measures such as reviewing the oscillator specifications or reviewing the assembly method, but this change is not uniform, and similar Even when a change tendency is shown, the amount of change varies greatly and cannot be easily controlled.Therefore, it is customary to allow a situation in which there is a large variation in characteristics, or to produce a large number and select and use them according to characteristics. It was

FIGS. 1 and 2 show an example of the structure according to the present invention. FIG. 1 shows an assembled structure of a vibrator and a pedestal, (a) is a top view and (b) is a sectional view, and FIG. The schematic sectional drawing of a container is shown. A circular counter electrode 9 is formed substantially at the center of the rectangular plate-shaped vibrator 1, and extraction electrodes 10a and 10b are formed on the front surface and the back surface of the vibrator in directions different by 180 degrees from the counter electrode. Lead wires are connected to the ends of 10b by soldering. The vibrator 1 is coated with the adhesive 11 only on the outer peripheral portion and is bonded and fixed to the pedestal 2. The pedestal 2 is provided with a recessed portion 12 that is larger than the range in which the counter electrode 9 is located, so that the counter electrode on the back surface of the vibrator 1 does not directly contact the pedestal.
After configuring in this way, the lead wires 6a and 6b are passed through the through holes of the case 3, and then the pedestal 2 and the case 3 are bonded and assembled, and the lead wires 6a and 6b are connected to the airtight terminals 8a and 8b. The terminal is adhered to the housing 5 at a predetermined position. The case 3 is adhered to the housing 5, and the filling material 7 is injected into the space behind the case 3 and cured, and then the rubber-like elastic body 4 is formed.
Is molded on the exposed surface side of the vibrator 1 to form a watertight structure.

A vibrator which has an electrode structure as shown in FIG. 1 and excites vibration in the thickness direction is generally known as an energy confinement vibrator. In such a vibrator, the vibration in the thickness direction is strongly excited in the counter electrode portion, and as the distance from the counter electrode is increased, the vibration is exponentially attenuated, and as a result, the vibration is confined in the vicinity of the counter electrode portion. Show. Utilizing these characteristics,
By virtue of bonding and fixing only the peripheral portion of the vibrator 1 in which vibration in the thickness direction is hardly excited, and connecting a lead wire to the end of the vibrator 1, the vicinity of the counter electrode 9 located in the substantially central portion of the vibrator 1 It is possible to configure the wave transmitter / receiver without dampening the vibration of.

However, if it is assumed that the vibrator is used in the air, a sufficient effect can be obtained only by using such a vibrator. However, when the vibrator is used in water, it is necessary to consider the situation of applying water pressure. . When water pressure is applied in such a configuration that the counter electrode part comes into direct contact with the pedestal, the contact condition between the counter electrode and the pedestal will change from time to time due to the pressure. Means to do. If this impedance changes, the acoustic energy propagating toward the pedestal changes, resulting in a change in sensitivity as a transducer, which is not preferable. Therefore, in order to effectively utilize the characteristics of the vibrator 1, it is necessary to adopt a configuration in which the impedance behind the vibrator 1 hardly changes with changes in water pressure.
As the method, it is most effective to provide a void, and this can be easily achieved by providing the dented portion 12 in the pedestal 2 by spot facing or the like. It is obvious that the formation range of the recessed portion 12 needs to be at least as large as that of the counter electrode 9, and it is desirable to form the recessed portion 12 in a wider area than the counter electrode 9 in practical use. Since the portion excluding the vibrator 1 and the pedestal 2 has substantially the same configuration as the conventional wave transmitter / receiver, it can be easily improved only by replacing this portion.

FIG. 3 shows the characteristics of the transmitter / receiver having the structure shown in FIG. 1, which is manufactured on the assumption that it is used in the vicinity of 3 MHz.
(A) is the admittance frequency characteristic of the oscillator alone, FIG.
(B) shows a plurality of the same characteristics before the rubber-like elastic body 4 is molded.

In FIG. 3 (a), resonances f _b , f _C, etc. of parasitic vibration are seen as in the case of the conventional vibrator having the entire surface electrode, but it is smaller than the conventional case when compared with the vibration f _{A in} the thickness direction. And approaches a single resonance of vibration in the thickness direction.
In FIG. 3B, the parasitic vibrations of f _b and f _C disappear,
This indicates that by bonding and fixing only the outer peripheral portion of the vibrator 1, a damping effect appears in parasitic vibration such as higher-order mode resonance of widthwise vibration. On the other hand, in the thickness direction vibration f _a , there is little change in the admittance value, and the vibration ‘
As shown in the characteristic example, there is no extreme change such that the admittance value is reduced to about 1/5 of that of the vibrator alone, and the thickness direction vibration is well excited. The five transducers are assembled in a state in which the resonance frequency and the shape of the admittance characteristic are fairly well aligned without the disturbance of the characteristic change as seen in the conventional configuration.

[0024]

As described above, according to the present invention,
In the excitation of the thickness direction vibration used as the main vibration mode of the vibrator when transmitting and receiving ultrasonic waves corresponding to the higher frequency of the transducer, without damaging the thickness direction vibration, It is possible to easily obtain a transducer with little variation.

[Brief description of drawings]

1A and 1B are views showing an assembly structure of a pedestal portion of an underwater ultrasonic transducer according to the present invention, FIG. 1A being a top view and FIG. 1B.
Is a cross-sectional view.

FIG. 2 is a cross-sectional view showing a schematic configuration of a wave transceiver according to the present invention.

FIG. 3 is a diagram showing characteristics of a piezoelectric ceramic oscillator used in the present invention, FIG. 3 (a) is a admittance characteristic of a single unit, and FIG.
(B) shows the admittance characteristics of the assembly before molding.

4A and 4B are schematic configuration diagrams of a conventional underwater ultrasonic transducer, FIG. 4A is a top perspective view, and FIG. 4B is a cross-sectional view.

FIG. 5 is a diagram showing characteristics of a piezoelectric ceramic oscillator used in a conventional configuration, FIG. 5 (a) is a admittance characteristic of a single unit, and FIG.
(B) shows the admittance characteristics of the assembly before molding.

[Explanation of symbols]

 1,21 Piezoelectric ceramic or piezoelectric ceramic oscillator 2,22 Pedestal 3,23 Case 4,24 Rubber-like elastic body 5,25 Housing 6a, 6b, 26a, 26b Lead wire 7,27 Filler 8a, 8b, 28a, 28b Airtight terminal 9 Counter electrodes 10a, 10b Lead-out electrode 11 Adhesive 12 Recessed part

Claims (1)

[Claims] 1. A circular or rectangular counter electrode facing in the thickness direction at approximately the center of a circular or rectangular plate-shaped piezoelectric ceramic, and a pair of electrodes in different directions so as not to face the counter electrode in the thickness direction. An extraction electrode is formed, a vibrator configured to perform polarization and excitation by connecting an electric wire for exchanging an electric signal to the extraction electrode, and the counter electrode provided with a recessed portion in a range where the counter electrode is located. Consists of a pedestal with a structure that does not directly touch, and only the outer peripheral portion of the vibrator is adhered and fixed to the pedestal so that the counter electrode is located in the recessed portion of the pedestal, and a waterproof structure by a mold is provided. An underwater ultrasonic transducer.