JPH0564919B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a piezoelectric vibrator that generates ultrasonic waves using an electrostrictive phenomenon, and more specifically relates to a piezoelectric vibrator that generates ultrasonic waves using an electrostrictive phenomenon. The present invention relates to a piezoelectric vibrator that makes it possible to significantly suppress side lobes generated in connection with an ultrasonic radiation pattern by appropriately forming an electrode pattern and applying an alternating current voltage between the two electrodes.

[Background of the Invention] A piezoelectric vibrator is an electroacoustic transducer that converts an electric signal into a sonic signal, or converts a sonic signal into an electric signal, and has a so-called wave transmitting/receiving function. Among these, piezoelectric vibrators that generate ultrasonic waves have relatively low signal attenuation in liquids, especially underwater, and it is relatively easy to select the size of the sound source to be large compared to the wavelength. Acoustic sounders, because it is possible to sharpen the directionality of sound waves, etc.
In particular, it is widely used in fish finders.

Here, the directional characteristics of sound waves express the characteristics of the range in which sound waves are transmitted from a piezoelectric vibrator that has a wave transmitting and receiving function, and the range in which sound waves are received. It can be said that this is an extremely important factor considering gender.

FIG. 1 shows an example of the directional characteristics of sound waves generated from a piezoelectric vibrator. As can be easily understood from the figure, the central axis 4 is perpendicular to the piezoelectric vibrator 2.
The upper sound pressure is the strongest, and the sound pressure decreases as the displacement angle θ from the central axis 4 increases. In this case, the central axis 4
The upper sound wave beam is called the main lobe M, and the side sound wave beams are called the side lobes S. In addition, when transmitting and receiving using the same piezoelectric vibrator, the directional characteristics increase by a factor of two, so the angle θ _-3dB at which the sound pressure in the main lobe M decreases by 3 dB from the value at the central axis 4 also changes the directional characteristics. It is important as an indicator to represent

By the way, among the directional characteristics of sound waves shown in Figure 1,
The existence of the side lobe S means that when the piezoelectric vibrator that generates the ultrasonic waves is used in a fish finder, the reflected signal related to the side lobe S, for example, the reflected signal from a school of fish, etc., is the reflected signal from the main lobe M. Mistakes may occur. In this case, even if you trust the direction of the school of fish displayed on the display of the fish finder, that is, start casting the net with a misperception of the direction of the school of fish, there will be no school of fish in the casting area, which will reduce operational efficiency. It has been pointed out that there are drawbacks that reduce the

In order to suppress this unnecessary side lobe S, a method is known in which electrode patterns on opposing surfaces of a rectangular parallelepiped ultrasonic piezoelectric vibrator are formed into a special shape.

Before discussing the conventional technical thought related to this measure, in order to further clarify the problems of the conventional technique, we will first explain the basic electrode pattern of a piezoelectric vibrator and the side effects that occur along with the electrode pattern. The relationship with the size of the lobe S will be described.

Usually, the amount of suppression of the sidelobe S is expressed as a sidelobe suppression ratio R; R=201 _pg B/A.
Here, reference numeral A is the maximum sound pressure level of the main lobe M, and reference numeral B is the maximum sound pressure level of the side lobe S (see FIG. 1). Now, as shown in FIG. 2, the electrode pattern of the rectangular parallelepiped piezoelectric vibrator 6 has electrode patterns 8a,
In the most basic case of 8b, on the surface of the ultrasonic radiation surface U _S of the rectangular parallelepiped piezoelectric vibrator 6,
As shown in FIG. 3a, an amplitude characteristic curve is obtained in which the generated sound pressure level has equal amplitude with respect to the long axis l. It is known that the sidelobe suppression ratio R in this case is approximately 13.5 dB. In order to make this sidelobe suppression ratio R infinite, the amplitude characteristic curve related to the sound pressure is, for example, shown in Fig. 3b.
It has been found that it is sufficient to create a characteristic curve that is approximately similar to the cos squared characteristic curve, as shown in .

Next, from this point of view, an example of forming an electrode pattern according to the prior art will be examined. This technical idea is disclosed, for example, in Japanese Patent Publication No. 58-32558. That is, in this example, as shown in FIG. 4, among the electrode patterns on two opposing sides of the rectangular parallelepiped piezoelectric vibrator, the electrode pattern on one side is cut diagonally to form the excitation electrode C and the damping electrode. It is divided into E ₁ and E ₂ and the vibration energy is suppressed at both ends. Therefore, the ultrasonic radiation surface
It is described that the ultrasonic waves radiated from the radiating surface U _S are most intensely radiated from the center of the radiating surface U _S and gradually weaken as they approach the ends.

However, in this case, as is clear from a detailed examination of the pattern shape, the arrangement shape of the excitation electrode C and the damping electrodes E ₁ and E ₂ is linear, so that The effect of suppressing the sidelobe S becomes insufficient. That is, in this prior art, the shape of the amplitude characteristic curve related to the sound pressure is approximately an isosceles triangular shape, so the sidelobe suppression ratio R is approximately 20 dB.
The possibility that a reflected signal from a school of fish or the like related to the side lobe S may be mistakenly recognized as a reflected signal related to the main lobe M has not yet been eliminated.

Furthermore, the shape of the electrode pattern of the piezoelectric vibrator disclosed in the present invention does not satisfy the condition of vertical and horizontal symmetry with respect to the center of the vibrator, which may cause unnecessary vibrations and cause disturbances in the radiation pattern. However, it also exposes various drawbacks such as a decrease in electrical/ultrasonic conversion efficiency.

Therefore, in order to eliminate these drawbacks, a large number of rectangular parallelepiped ultrasonic piezoelectric vibrators are stacked to create a vertically symmetrical electrode configuration, and then voltage is applied to each piezoelectric vibrator so that it follows approximately the cos square voltage distribution. Attempts have been made to obtain a multilayer piezoelectric vibrator configured to supply It shows inconvenience.

[Object of the Invention] The present invention has been made in order to overcome all of the above-mentioned disadvantages, and is to provide electrode patterns on two opposing surfaces of a rectangular parallelepiped piezoelectric vibrator in a vertically symmetrical manner and in a shape that approximately follows a cos square curve. Excitation electrodes and damping electrodes are placed in the center. Therefore, by applying an alternating current voltage between the two electrodes, it is possible to suppress the side lobe S that occurs in the ultrasonic radiation pattern to almost zero, and in addition, it is extremely easy to form the electrodes in terms of manufacturing. The purpose of the present invention is to provide an ultrasonic piezoelectric vibrator.

[Means for Achieving the Object] In order to achieve the above object, the present invention provides a rectangular parallelepiped piezoelectric vibrator that generates ultrasonic waves, in which electrode surfaces are perpendicular to and opposite to the ultrasonic radiation surface. An electrode configuration in which the electrode shape on at least one surface is divided into predetermined lengths in a direction perpendicular to the longitudinal direction,
An electrode including at least an excitation electrode and an electrode including an excitation electrode and a damping electrode are arranged in the predetermined divided electrodes, and the shapes of the excitation electrode and the damping electrode are arranged along orthogonal axes passing through the center point of their surfaces. The area of the excitation electrodes in each predetermined section is defined so as to gradually become narrower from the center in the longitudinal direction toward both ends, and the area of the vibration damping electrode in each predetermined section is It is characterized in that the area is configured to gradually become narrower from both ends in the longitudinal direction toward the center.

[Embodiments] Next, preferred embodiments of the piezoelectric vibrator according to the present invention will be described in detail with reference to the accompanying drawings. Components that are the same as those shown in FIGS. 1 to 4 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 5, reference numeral 10 indicates a rectangular parallelepiped piezoelectric vibrator including an electric circuit driving section according to the present invention. The shape of this piezoelectric vibrator 10 is precisely a thin rectangular parallelepiped shape, and electrodes are formed on two opposing surfaces. In this case, in the figure, a uniform back electrode 14 is formed over the entire surface of the back section 12, while a rectangular parallelepiped piezoelectric vibrator 10 is formed on the front section 16.
Excitation electrodes 18a to 18w and damping electrodes 20a to 20t are arranged in a mosaic pattern in a direction perpendicular to the longitudinal direction of the electrodes, and the peripheral surfaces of both electrodes are insulated. Note that, in order to facilitate understanding, dotted patterns are attached to the vibration damping electrodes 20a to 20t.

In this case, the excitation electrodes 18a to 18w
The electrode areas are formed in an area distribution that gradually decreases in accordance with a cos square curve from the central excitation electrode 18l as the origin toward the ends in the longitudinal direction, and the electrode areas of the damping electrodes 20a to 20t are It is formed as an area distribution that gradually decreases in proportion to a curve of (1-cos squared) from both ends of the direction toward the center. Each of the electrodes formed in this manner can be printed by a silk screen method, so that the accuracy of the curved shape can be maintained and the electrode shape can be made suitable for mass production.

In such a configuration, the excitation electrodes 18a to 18w are electrically connected to each other by a pattern wiring method, and the damping electrodes 20a to 20t are also electrically connected to each other by a pattern wiring method, for example, a two-layer pattern wiring method. At the same time, it is connected to the back electrode 14 by an electric wire or the like. Then, the central excitation electrode 18 of the excitation electrodes 18a to 18w
1, vibration damping electrodes 20a to 20t, and back electrode 1
An AC power source E is connected between the four common connection points 22.

The rectangular parallelepiped piezoelectric vibrator according to the present invention is basically constructed as described above, and its operation and effects will be explained next.

Generally, it is said that a piezoelectric vibrator that utilizes an electrostrictive phenomenon is excited by applying an alternating current voltage, and in reality, the piezoelectric vibrator 10 is emits ultrasonic waves upward from the radiation surface U _S or downward from the surface facing the radiation surface U _S. In this case, the directivity of the ultrasonic wave is determined by the presence of damping electrodes 20a, 20t, etc., which have the same potential as the back electrode 14 and have a large pattern area, on both ends of the piezoelectric vibrator 10 in the longitudinal direction. 10 operates in such a way that the vibration is suppressed at the ends thereof, and the vibration is strongly excited as it approaches the center in the longitudinal direction.

Therefore, in this case, as mentioned above, the electrode width arrangement of the excitation electrode is formed so as to be approximately proportional to the cos square characteristic, so that most of the ultrasonic waves emitted from the radiation surface _U A radiation pattern without lobe S can be obtained. In this case, in order to set the directivity characteristic of the main lobe M to θ _{-3 dB} , which is approximately the same as that of the piezoelectric vibrator with the basic electrode configuration shown in FIG. 2, the length l ₂ in the rectangular direction is Under the condition that it is the same as the vibrator, it is preferable that the length l ₁ in the longitudinal direction is set such that l ₁ >l.

FIG. 6 shows another embodiment of the piezoelectric vibrator according to the present invention. In FIG. 6, reference numerals 24a to 24v are excitation electrodes arranged on the front part 16, and reference numerals 26a to 26t are vibration damping electrodes. In this case, a back electrode 28 is formed on the back part 12, and vibration damping electrodes 26a to 26t on the front part 16 are formed.
and the back electrode 28 of the back part 12 are electrically connected (not shown). Therefore, the excitation electrodes 24a to 2
When an AC power source (not shown) is applied between the damping electrodes 4v and the vibration damping electrodes 26a to 26t, sound waves are radiated from the radiation surface U _S. In this case as well, the electrodes of the excitation electrodes 24a to 24v are divided into areas proportional to a substantially cos squared curve with the central part in the longitudinal direction as the origin and directed toward both ends, and the damping electrodes 26a to 26t are An ultrasonic radiation pattern in which side lobes can be suppressed can be obtained by forming a shape having an area division proportional to a (1-cos squared) curve directed from both ends toward the center.

[Effects of the Invention] As described above, according to the present invention, the excitation electrode and the damping electrode are formed in a vertically and horizontally symmetrical electrode pattern, and the electrode area is formed in a pattern shape that follows a cos square curve. . Therefore, the directivity characteristics of the emitted ultrasonic waves become sharp, and it becomes possible to suppress side lobes generated in the ultrasonic radiation pattern to approximately zero. Furthermore, since the excitation electrode and damping electrode are formed in a symmetrical shape vertically and horizontally with respect to the orthogonal axis passing through the center point of the electrode surface, unnecessary vibration modes will not occur and the radiation pattern will not be disturbed. You can also get the effect of not having any. Furthermore, since the electrodes are formed using a silk screen printing method, it is possible to extremely easily form electrode patterns with complex shapes without increasing manufacturing costs.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments, and various improvements and changes in design are possible without departing from the gist of the present invention. Of course.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the directional characteristics of ultrasonic waves generated from a piezoelectric vibrator, Fig. 2 is a perspective explanatory diagram of a rectangular parallelepiped piezoelectric vibrator having a conventional basic electrode shape, and Fig. 3 a
is an amplitude characteristic curve diagram related to the piezoelectric vibrator shown in FIG. 2, FIG. 3b is a cos square amplitude characteristic curve diagram, FIG.
The figure is an explanatory diagram of a rectangular parallelepiped piezoelectric vibrator including an electric circuit driving section according to the present invention, and FIG. 6 is an explanatory diagram showing another embodiment of the rectangular parallelepiped piezoelectric vibrator according to the present invention. 10... Piezoelectric vibrator, 12... Back part, 14...
...Back electrode, 16...Front part, 18a to 18w...
...Excitation electrode, 20a to 20t...Vibration control electrode, 22
... Common connection point, 24a to 24v ... Excitation electrode,
26a to 26t... Vibration damping electrode, 28... Back electrode, E... AC power supply, M... Main lobe, S...
...Sidelobe, U _S ...Ultrasonic radiation surface.

Claims (1)

[Claims] 1. In a rectangular parallelepiped piezoelectric vibrator that generates ultrasonic waves, the electrode shape of at least one of the electrode surfaces that is orthogonal to the ultrasonic radiation and that faces oppositely is arranged in a direction perpendicular to the longitudinal direction. The electrode structure is divided into sections according to a predetermined length, and among the predetermined sections, an electrode including at least an excitation electrode and an electrode including an excitation electrode and a damping electrode are arranged, and the shapes of the excitation electrode and the damping electrode are arranged. are formed vertically and laterally symmetrically with respect to an orthogonal axis passing through the center point of the surface, and the area of the excitation electrode in each of the predetermined sections is defined so that it gradually narrows from the center in the longitudinal direction toward both ends. In addition, the piezoelectric vibrator is characterized in that the area of the damping electrode for each predetermined section is configured to gradually become narrower from both ends in the longitudinal direction toward the center. 2. In the piezoelectric vibrator according to claim 1, the area narrowing shape of each predetermined section of the excitation electrode and vibration damping electrode is a non-linear shape so that the middle side lobe of the ultrasound directivity becomes small. A piezoelectric vibrator configured in a shape that follows a function.