JPH0564920B2 - - 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 generated 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. Because it is possible to sharpen the directivity of sound waves, it is widely used in acoustic sounders, especially 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 characteristic is multiplied by the square, so the angle θ _-3dB at which the sound pressure in the main lobe M decreases by 3dB from the value at the central axis 4
is also important as an index representing directional characteristics.

By the way, among the directional characteristics of sound waves shown in Figure 1,
The existence of the side lobe S is caused by the misunderstanding that when a piezoelectric vibrator that generates the sound wave 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, is the reflected signal from the main lobe M. There are cases where this happens. In this case, you can rely on the direction of the school of fish shown on the fish finder's display.
That is, even if a cast net is started in a state where the direction of a school of fish is misperceived, there is no school of fish in the casting area, which has been pointed out to be a disadvantage in reducing operational efficiency.

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=20logB/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 should be made similar to the cos square characteristic curve, for example, as shown in FIG. 3b. Good things have been revealed.

Next, from this point of view, let's consider an example of forming an electrode pattern according to the prior art. 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, it is described that the ultrasonic waves emitted from the ultrasonic radiation surface U _S are most intensely radiated from the center of the radiation 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, causing unnecessary vibrations and causing disturbances in the radiation pattern. In addition to the risks involved, various drawbacks are exposed, such as a decrease in electricity-to-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 some inconvenience.

[Object of the Invention] The present invention has been made 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. An excitation electrode and a damping electrode are arranged. 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-shaped piezoelectric vibrator that generates ultrasonic waves, in which electrode surfaces are perpendicular to and opposite to the ultrasonic radiation surface. , formed into an electrode shape that includes one excitation electrode and a pair of damping electrodes that are substantially congruent with each other and symmetrical vertically and horizontally with respect to an axis orthogonal to each other with the center position of each electrode surface as an intersection point. The area of the excitation electrode per unit length in the longitudinal direction of each electrode surface is formed so as to gradually become narrower from the center toward both ends, and the area of the vibration damping electrode per unit length in the longitudinal direction is The area is defined so that it becomes gradually narrower from both ends toward the center, and the damping electrode on one electrode surface is electrically connected to the excitation electrode on the other opposing electrode surface. It is characterized by

[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 designated by 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 electrode patterns are formed on two opposing surfaces in a substantially congruent shape. In this case, in the figure, the front part 12 and the back part 14 each have one excitation electrode 16, 18 extending from the center of the surface to both ends over the entire surface thereof, and one excitation electrode 18 extending from both ends to the center. A pair of damping electrodes 20a, 20b and 22a, 22b extending in a direction are arranged, and the excitation electrodes 16, 18 and the damping electrodes 20a, 20
The peripheral surfaces of b are formed so as to be insulated from each other.

In this case, the electrode area per unit length in the longitudinal direction of the excitation electrodes 16 and 18 is defined in an area distribution that gradually decreases in accordance with a cos square curve, with the origin at the center and oriented toward both ends. At the same time, the electrode area per unit length in the longitudinal direction of the damping electrodes 20a, 20b and 22a, 22b has an area distribution that gradually decreases from both ends to the center in proportion to a curve of (1-cos squared). It is formed as.
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 excitation electrode 16 defined on the front section 12 is electrically connected to the pair of damping electrodes 22a, 22b defined on the back section 14, and the excitation electrode 16 defined on the front section 12 is The pair of damping electrodes 20a, 20b and the excitation electrode 18 defined on the back surface 14 are electrically connected. An AC power source E is connected between the excitation electrode 16 of the front section 12 and the excitation electrode 18 of the rear section 14 .

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 opposing surface of the radiation surface U _S. In this case, the directional characteristics of the ultrasonic waves are such that vibration damping electrodes 20a, 20b and 22a, 22 of the same potential are placed on both ends of the piezoelectric vibrator 10 in the longitudinal direction.
Since the piezoelectric vibrator 10 faces each other, the piezoelectric vibrator 10 operates in such a manner that the vibrations are suppressed at the ends thereof, oriented in the longitudinal direction, and more strongly excited toward the center. In this case, as described above, the electrode area per unit length of the excitation electrodes 16 and 18 is formed so as to be approximately proportional to the cos square characteristic, so the ultrasonic radiation radiated from the radiation surface U _S The sound waves are
A radiation pattern with almost no side lobes S can be obtained. 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 is
It is preferable to form l ₁ >l.

FIG. 6 shows another embodiment of the piezoelectric vibrator according to the present invention. In FIG. 6, reference numeral 24 is an excitation electrode arranged on the front part 12, and reference numeral 2
6a to 26d are vibration damping electrodes. In this case, the excitation electrode 28 and the damping electrodes 30a to 30d are formed on the back surface 14 in a shape substantially congruent with the front surface 12,
The excitation electrode 24 on the front part 12 and the damping electrodes 30a to 30d on the back part 14 are electrically connected, and the damping electrodes 26a to 26d on the front part 12 and the excitation electrode 28 on the back part 14 are electrically connected. connected to. Therefore, the AC power source E is connected between the excitation electrodes 24 and 28.
As a result, sound waves are radiated from the radiation surface U _S . Also in this case, the excitation electrode 24,
The electrode area per unit length in the longitudinal direction of 28 is approximately oriented toward both ends with the center point in the longitudinal direction as the origin.
The area is divided in proportion to the cos squared curve, and on the other hand, for the damping electrodes 26a to 26d, 30a to 30d, the area is proportional to the (1-cos squared) curve from both ends in the longitudinal direction toward the center. It has a shape with distribution. This makes it possible to obtain an ultrasonic radiation pattern in which side lobes can be suppressed.

[Effects of the Invention] As described above, according to the present invention, the excitation electrodes and damping electrodes disposed on the front and back sides of a piezoelectric vibrator are formed into vertically and horizontally symmetrical electrode patterns, and the electrode area is reduced to the cos square. It is formed into a pattern shape that follows a 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 complicated 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.
FIG. 6 is a perspective explanatory view of a piezoelectric vibrator including an electric circuit driving section according to the present invention, and FIG. 6 is a perspective explanatory view showing another embodiment of the piezoelectric vibrator according to the present invention. 10... Piezoelectric vibrator, 12... Front part, 14...
... Back part, 16, 18 ... Excitation electrode, 20a, 2
0b, 22a, 22b... vibration damping electrode, 24... excitation electrode, 26a-26d... vibration damping electrode, 28...
Excitation electrode, 30a to 30d... Damping electrode, E...
AC power supply, M...Main lobe, S...Side lobe, U _S ...Ultrasonic radiation surface.

Claims (1)

[Scope of Claims] 1. In a rectangular parallelepiped-shaped piezoelectric vibrator that generates ultrasonic waves, the electrode surfaces facing each other and perpendicular to the ultrasonic radiation surface have substantially congruent shapes and each The electrode shape is formed to include one excitation electrode and a pair of damping electrodes that are vertically and horizontally symmetrical with respect to an axis orthogonal to each other with the center position of the electrode surface as the intersection point, and The area of the excitation electrode is formed to gradually become narrower from the center to both ends, and the area of the damping electrode per unit length in the longitudinal direction is gradually narrowed from both ends to the center. A piezoelectric vibrator characterized in that the vibration damping electrode on one electrode surface is electrically connected to the excitation electrode on the opposite electrode surface. 2. In the piezoelectric vibrator according to claim 1, the area narrowing shapes of the excitation electrode and vibration damping electrode are configured to follow a non-linear function so that side lobes in the directivity characteristics of ultrasound waves are reduced. A piezoelectric vibrator.