JPH0564918B2 - - 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. The present invention relates to a piezoelectric vibrator that can significantly suppress side lobes that occur in connection with an ultrasonic radiation pattern by appropriately forming a pattern and applying an alternating current voltage between both electrodes of the piezoelectric vibrator.

[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 sound pressure above is the strongest, and the sound pressure decreases as the displacement angle θ from the central axis increases. In this case, the sound wave beam on the central axis 4 is called a main lobe M, and the sound wave beams on the sides are called 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 has a directional characteristic. It is important as an indicator to express the

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, a reflected signal related to the side lobe S, for example, a reflected signal from a school of fish, etc., is a 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.

Therefore, before discussing the conventional technical ideas related to this method, in order to further clarify the problems of the conventional technology, we will first explain the basic electrode pattern of a piezoelectric vibrator and its electrode pattern. The relationship with the magnitude of the side lobe S that occurs incidentally 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 the rectangular parallelepiped ultrasonic piezoelectric vibrator is used. 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 the electrical/ultrasonic conversion efficiency.

Therefore, in order to eliminate these drawbacks, a large number of rectangular parallelepiped ultrasonic piezoelectric vibrators are stacked to form vertically symmetrical electrode configurations, and then voltage is applied to each piezoelectric vibrator so as to follow the cos square voltage distribution. Attempts have been made to obtain a multilayer piezoelectric vibrator with a configuration in which the piezoelectric vibrator is supplied, but in such a configuration, it takes time to manufacture the piezoelectric vibrator as a final product, resulting in a new disadvantage of increasing manufacturing costs. is exposed.

[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 vertically symmetrically and approximately.
Excitation electrodes and damping electrodes are arranged in a shape that follows a cos square curve. Therefore, by applying an AC voltage between the two electrodes, it is possible to suppress the side rope S that occurs in the ultrasonic radiation pattern to almost zero, and in addition, the electrodes are extremely easy to form in terms of manufacturing. The purpose of the present invention is to provide an ultrasonic piezoelectric vibrator.

[Means to achieve the purpose]

In order to achieve the above object, the present invention provides a rectangular parallelepiped piezoelectric vibrator that generates ultrasonic waves. An excitation electrode with a vertically symmetrical shape and a plurality of vertically and horizontally symmetrical vibration damping electrodes are arranged with respect to the orthogonal axis passing through the point, and the area of the excitation electrode per unit length in the longitudinal direction of the piezoelectric vibrator is set at the center. The plurality of damping electrodes are formed so as to become gradually narrower from the ends toward both ends, and the area per unit length of the plurality of vibration damping electrodes becomes gradually narrower from the ends toward the center. and is characterized in that it is configured to be electrically coupled to an electrode on the other surface.

[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 FIGS. 5 and 6, reference numeral 10
a and 10b indicate rectangular parallelepiped-shaped piezoelectric vibrators including an electric circuit driving section according to the present invention. The piezoelectric vibrators 10a and 10b have a thin rectangular parallelepiped shape to be precise, and electrodes are formed on two opposing surfaces thereof. In this case, as shown in the figure, a uniform back electrode 14 is formed over the entire surface of the back portion 12. On the other hand, in the front part 16, excitation electrodes 18 and 20 are arranged at the center of the piezoelectric vibrators 10a and 10b in the longitudinal direction. In fact, vibration damping electrodes 22a, 22 are provided at both ends.
b, 24a, and 24b are arranged, and the peripheral surfaces of both electrodes are formed to be insulated.

In this case, the electrode area per unit length in the longitudinal direction of the excitation electrodes 18 and 20 is formed in an area distribution that gradually decreases from the center in the longitudinal direction toward both ends in accordance with a cos square curve. At the same time, vibration damping electrodes 22a, 22b, 24a, 24b
The electrode area per unit length is formed as an area distribution that gradually decreases in proportion to a curve of (1-cos squared) from both ends in the longitudinal direction toward the center. Note that each electrode can be printed and formed by a silk screen method, and therefore, 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 damping electrodes 22a, 22
b, 24a and 24b are electrically connected to each other, and are also connected to the back electrode 14. and,
The excitation electrodes 18, 20 and the damping electrodes 22a, 22
An AC power source E is connected between the common connection point 22c of the damping electrodes 24a, 24b and the back electrode 14, and the common connection point 24c of the damping electrodes 24a, 24b and the back electrode 14, respectively.

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.

In general, 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 10a is , 10b 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 characteristics of the ultrasonic waves are determined by the vibration damping electrodes 22a, 22b, which have the same potential as the back electrode 14 and have a large pattern area per unit length in the longitudinal direction, on both ends of the piezoelectric vibrators 10a, 10b in the longitudinal direction. , 24a, 24b
, the piezoelectric vibrators 10a and 10b operate in such a manner that the vibrations are suppressed at the ends thereof, and the vibrations are more strongly excited toward the center in the longitudinal direction. Therefore, in this case, as described above, the electrode shape of the excitation electrode is oriented from the center in the longitudinal direction to both ends, and is formed so as to be approximately proportional to the cos square characteristic, so that the radiation surface U _S The ultrasonic waves radiated from can have a radiation pattern with almost no side lobes S. In this case, in order to make the directivity pattern of the main lobe M have approximately the same θ _{-3 dB} angle as that of the piezoelectric vibrator with the basic electrode configuration shown in Fig. 2, the length l ₂ in the transverse direction must be Under the condition that it is the same as the basic piezoelectric vibrator, its longitudinal length l ₁
It is preferable to form l ₁ >l.

FIGS. 7 and 8 show other embodiments of the piezoelectric vibrator according to the present invention. In the embodiments shown in FIGS. 7 and 8, substantially the left half of the piezoelectric vibrator is omitted from illustration. In this case, the shape of the left half is symmetrical to the shape of the right half with respect to the central perpendicular. In FIGS. 7 and 8, reference numeral 2
6a and 26b are excitation electrodes arranged on the front part 16, and reference numerals 28a and 28b are vibration damping electrodes. In this case, the back electrode 30a,
30b is formed, and the damping electrode 28 of the front part 10
a, 28b and the back electrodes 30a, 30 of the back part 12
b are electrically connected to each other (not shown). Therefore, the excitation electrodes 26a, 26b and the damping electrode 28
By applying an AC voltage E (not shown) between a and 28b, sound waves are radiated from the radiation surface U _S .
In this case as well, the electrode pattern of the excitation electrodes 26a, 26b is divided into areas proportional to a substantially cos square curve with the center point in the longitudinal direction as the origin and directed toward both ends, and the damping electrodes 28a, 28b are divided in area in the longitudinal direction. An ultrasonic radiation pattern in which side lobes S 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 to 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 by citing preferred embodiments, the present invention is not limited to these embodiments. For example, as shown in FIG. 9, the examples shown in FIGS. Of course, various improvements and changes in design are possible without departing from the spirit of the present invention, such as making the electrodes linearly arranged.

[Brief explanation of drawings]

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.
6 and 6 are perspective explanatory views of a piezoelectric vibrator including an electric circuit drive unit according to the present invention, and FIGS. 7 to 9 are perspective explanatory views showing other embodiments of the piezoelectric vibrator according to the present invention. be. 10a, 10b... piezoelectric vibrator, 12... back part, 14... back electrode, 16... front part, 18,
20... Excitation electrode, 22a, 22b... Damping electrode, 22c... Common connection point, 24a, 24b...
Vibration damping electrode, 24c... Common connection point, 26a, 26
b...excitation electrode, 28a, 28b...damping electrode,
30a, 30b... Back electrode, E... AC power supply,
M...Main lobe, S...Side lobe, U _S
...Ultrasonic radiation surface.

Claims (1)

[Claims] 1. In a rectangular parallelepiped-shaped piezoelectric vibrator that generates ultrasonic waves, at least one of the electrode surfaces that is orthogonal to the harmonic wave radiation surface and faces oppositely has an orthogonal axis that passes through the center point of the surface. An excitation electrode with a vertically symmetrical shape and a plurality of vertically and horizontally symmetrical vibration damping electrodes are arranged, and the area of the excitation electrode per unit length in the longitudinal direction of the piezoelectric vibrator is increased from the center to both ends. The plurality of vibration damping electrodes are formed so as to become gradually narrower in the direction, and the area per unit length of the plurality of vibration damping electrodes becomes gradually narrower in the direction from both ends toward the center. A piezoelectric vibrator configured to be electrically coupled to an electrode. 2. In the piezoelectric vibrator according to claim 1, the narrowing shape of the area per unit length of the excitation electrode and the damping electrode is a non-linear function so that the side rope becomes small in the directional characteristics of the sound wave. A piezoelectric vibrator configured in a shape that follows.