JPH0634558B2 - Piezoelectric vibrator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezoelectric vibrator that generates an ultrasonic wave by utilizing an electrostriction phenomenon, and more specifically, electrodes on two opposite surfaces of a rectangular parallelepiped piezoelectric vibrator. The present invention relates to a piezoelectric vibrator capable of remarkably suppressing side lobes generated in association with an ultrasonic wave radiation pattern by appropriately forming a pattern and applying an AC voltage between the electrodes.

BACKGROUND OF THE INVENTION A piezoelectric vibrator is an electroacoustic conversion element having a so-called wave transmission / reception function of converting an electric signal into a sound wave signal or converting a sound wave signal into an electric signal. Among them, piezoelectric oscillators that generate ultrasonic waves have relatively little signal attenuation when ultrasonic waves are in liquid, especially in water, or it is relatively easy to select a large sound source size compared to the wavelength. It is widely used in acoustic sounding machines, especially in fish finder because it can sharpen the directivity of sound waves.

Here, the directional characteristic of a sound wave represents a characteristic of which range the sound wave is transmitted from and received by the piezoelectric vibrator having a transmission / reception function. It can be said that this is an extremely important factor in view of the gender.

FIG. 1 shows an example of directional characteristics of sound waves generated from the piezoelectric vibrator. As can be easily understood from the figure, the sound pressure on the central axis 4 in the direction orthogonal to the piezoelectric vibrator 2 is the strongest,
The sound pressure decreases as the displacement angle θ from the central axis 4 increases.
In this case, the acoustic wave beam on the central axis 4 is referred to as a main lobe M, and the lateral acoustic wave beam is referred to as a side lobe S. Also, when transmitting and receiving using the same piezoelectric vibrator,
Since the directional characteristics are squared, the angle θ _-3 dB at which the sound pressure in the main lobe M decreases by 3 dB from the value of the central axis 4 is also important as an index representing the directional characteristics.

[Problems to be Solved by the Invention] In the directional characteristics of sound waves shown in FIG. 1, the presence of the side lobes S causes the side lobes S to appear when the piezoelectric vibrator that generates the sound waves is used in a fish finder. There is a case where the reflection signal, for example, the reflection signal from the school of fish or the like is mistaken as the reflection signal from the main lobe M. In this case, trusting the orientation of the school of fish displayed on the display of the fish finder, that is, even if the casting net is started in a state where the orientation of the school of fish is misidentified, there is no school of fish in the casting area and the operating efficiency is improved. It has been pointed out that there are drawbacks that reduce it.

In order to suppress this unnecessary side lobe S, there is known a method of forming an electrode pattern on the opposing surface of the rectangular parallelepiped ultrasonic piezoelectric vibrator in a special shape.

Before describing the conventional technical idea related to this measure, first, in order to further clarify the location of the problems of the conventional technology, first, the basic electrode pattern of the piezoelectric vibrator and the side that accompanies the electrode pattern are generated. The relationship with the size of the lobe S will be described.

Usually, the suppression amount of the side lobe S is expressed as a side lobe suppression ratio R; R = 20logB / A. Here, the reference symbol A is the maximum sound pressure level of the main lobe M, and the reference symbol B is the maximum sound pressure level of the side lobe S (first).
See figure). Now, the electrode pattern of the rectangular parallelepiped piezoelectric vibrator 6 is
As shown in FIG. 2, in the most basic case where the two opposing surfaces are all electrode patterns 8a and 8b, the ultrasonic radiation surface U _s of the piezoelectric vibrator 6 has a surface shown in FIG. As shown in (1), an amplitude characteristic curve in which the generated sound pressure level is equal in amplitude to the major axis 1 is obtained. It is known that the side lobe suppression ratio R in this case is approximately 13.5 dB. In order to make the side lobe suppression ratio R infinite, the amplitude characteristic curve relating to the sound pressure is set to, for example,
It has been clarified that a characteristic curve similar to the substantially cos square characteristic curve may be used as shown in FIG.

Next, from this viewpoint, let us verify an example of forming an electrode pattern according to the related art. This technical idea is disclosed in, for example, Japanese Patent Publication No. 58-32558. That is,
In this example, as shown in FIG. 4, the electrode pattern on one surface of the two opposite electrode patterns of the rectangular parallelepiped piezoelectric vibrator is cut in an oblique direction so that the excitation electrode C and the damping electrode E ₁ , E ₂ and the vibration energy is suppressed at both ends. Therefore, the ultrasonic radiation surface U
ultrasound emitted from _s is most strongly emitted from the center of the radiation surface U _s, is described as being gradually weakens as radiation toward the end.

However, in this case, as is clear from a detailed examination of the pattern shape, since the arrangement shape of the excitation electrode C and the damping electrodes E ₁ and E ₂ is linear, the rectangular parallelepiped ultrasonic piezoelectric vibrator is related. The effect of suppressing the side lobe S becomes insufficient. That is, in this conventional technique, since the shape of the amplitude characteristic curve related to the sound pressure is a shape of an isosceles triangle, the sidelobe suppression ratio R is about 20 dB, and the reflection signal of the fish school or the like related to the sidelobe S is about 20 dB. The possibility of erroneously recognizing as a reflected signal related to the main lobe M has not been eliminated.

Furthermore, since the electrode pattern shape 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, it may cause unnecessary vibration and disturb the radiation pattern. However, it has various drawbacks in that the efficiency of converting electricity to ultrasonic waves is reduced.

Therefore, in order to eliminate these drawbacks, a large number of rectangular parallelepiped ultrasonic piezoelectric vibrators are stacked to form a vertically symmetrical electrode configuration, and the voltage is applied to each piezoelectric vibrator so as to follow a substantially cos square voltage distribution. Attempts have been made to obtain a multi-layered piezoelectric vibrator having a structure for supplying a piezoelectric vibrator. However, in such a structure, it takes time to manufacture a piezoelectric vibrator as a final product, and eventually a new manufacturing cost is increased. Revealing inconvenience.

[Object of the Invention] The present invention has been made in order to overcome the above-mentioned inconveniences, and the electrode patterns are vertically symmetrically arranged on the two opposing surfaces of the rectangular parallelepiped piezoelectric vibrator, and further, the electrode patterns are arranged in a shape that substantially follows a cos square curve. It is an object of the present invention to provide a piezoelectric vibrator in which the excitation electrode and the damping electrode are arranged and the side lobes generated in the radiation pattern of ultrasonic waves are suppressed to substantially zero.

[Means for Achieving the Object] In order to achieve the above-mentioned object, the present invention relates to a rectangular parallelepiped piezoelectric vibrator that generates an ultrasonic wave, and an electrode surface that is substantially orthogonal to the ultrasonic wave radiation surface and faces each other. The electrodes on at least one surface of the excitation electrode and the damping electrode are alternately divided in the direction orthogonal to the longitudinal direction of the piezoelectric vibrator, and the electrode area of each excitation electrode electrode is from the central portion in the longitudinal direction to both ends. It is formed so that it gradually narrows toward the center, and the electrode area of each damping electrode is gradually narrowed from both ends in the longitudinal direction toward the center, and it is electrically connected to the electrodes on the other surface. And applying the same voltage in the same phase to each of the excitation electrodes.

[Embodiment] Next, preferred embodiments of the piezoelectric vibrator according to the present invention will be given and described in detail below with reference to the accompanying drawings. The same components as those shown in FIGS. 1 to 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 5, reference numeral 10 indicates a rectangular parallelepiped piezoelectric vibrator including an electric circuit driving unit according to the present invention. The shape of the rectangular parallelepiped piezoelectric vibrator 10 is exactly a thin rectangular parallelepiped shape, and electrodes are formed on two opposing surfaces thereof. In this case, in the figure, the back surface 12 is formed with a uniform back electrode 14 over the entire surface thereof, while the front surface 16 is provided with excitation electrodes 18a through 18a in a direction orthogonal to the longitudinal direction of the rectangular parallelepiped piezoelectric vibrator 10. 18i and damping electrode
20a to 20j are alternately arranged in a strip shape, and the peripheral surfaces of both electrodes thereof are formed to be insulated.

In this case, the electrode widths of the excitation electrodes 18a to 18i are defined in an area distribution that is directed toward the longitudinal end of the piezoelectric vibrator 10 with the central excitation electrode 18e as the origin and gradually decreases corresponding to the cos square curve. At the same time, the electrode width of the damping electrodes 20a to 20j is directed from the both ends in the longitudinal direction toward the center (1-cos
It is formed as an area distribution that gradually decreases in proportion to the curve of (square). The respective electrodes can be formed by printing by the silk screen method, and therefore the electrode shape suitable for mass production can be obtained while maintaining the accuracy.

In such a configuration, the excitation electrodes 18a to 18i are electrically connected to each other, while the damping electrodes 20a to 20j are electrically connected to each other and are also connected to the back electrode 14.
An AC power source E is connected between the common connection point 22a of the excitation electrodes 18a to 18i and the common connection point 22b of the damping electrodes 20a to 20j and the back electrode 14.

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

In general, it is said that a piezoelectric vibrator using the electrostriction phenomenon is excited by a method of applying an AC voltage. In practice, the piezoelectric vibrator 10 emits radiation when an AC power source E having a resonance frequency is applied. Ultrasonic waves are emitted upward from the surface U _s or downward from a surface facing the radiation surface U _s . in this case,
Since the directional characteristics of ultrasonic waves have damping electrodes 20a, 20j and the like having the same potential as the back electrode 14 and a large pattern area on both end sides in the longitudinal direction of the piezoelectric vibrator 10, the piezoelectric vibrator 10 has The vibration is damped on the end side, is oriented in the longitudinal direction, and is strongly excited toward the center. Therefore, in this case, as described above, since the electrode width arrangement of the excitation electrodes 18a to 18i is formed so as to be in proportion to, for example, the cos square characteristic, the ultrasonic wave emitted from the radiation surface U _s is The radiation pattern can be almost free of the side lobes S. At this time, in order to make the directional pattern of the main lobe M substantially the same θ _{-3 dB} angle as the piezoelectric vibrator having the basic electrode configuration shown in FIG.
Under the condition that ₂ is the same as the basic piezoelectric vibrator, it is preferable to form the length l ₁ in the longitudinal direction as 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 portion 16, and reference numeral 26 is a damping electrode. In this case, a back electrode 28 is formed on the back portion 12, and the damping electrode 26 of the front portion 16 and the back electrode 28 of the back portion 12 are electrically connected. Therefore, sound waves are radiated from the radiation surface U _s by the AC power source between the excitation electrode 24 damping electrode 26 (not shown) is applied. Also in this case, the electrode pattern of the excitation electrode 24 is directed toward both end portions with the central point in the longitudinal direction as the origin, and the area section is proportional to the approximately cos square curve. From the side toward the center (1
An ultrasonic radiation pattern capable of suppressing side lobes can be obtained by adopting a shape having an area section proportional to the −cos square) curve.

[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 according to the cos square curve. . Therefore, the side lobes generated in the radiation pattern of the ultrasonic waves are suppressed to substantially zero, and it is possible to prevent the generation of reflected signals due to the side lobes.

Furthermore, since the side lobes are suppressed to almost zero,
The effect is that a clear reflection image can be obtained. Moreover, since the electrode forming method is the silk screen printing method, it is possible to form an electrode pattern having a complicated shape very easily without increasing the manufacturing cost.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment,
For example, as shown in FIG. 7, the vertical symmetry is sacrificed, but unlike the example of FIG. 6, the excitation electrode outlet is arranged on the end face of the rectangular parallelepiped shape. Needless to say, various improvements and design changes can be made without departing from the scope.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of directivity of ultrasonic waves generated from a piezoelectric vibrator, FIG. 2 is a perspective explanatory view of a conventional piezoelectric vibrator having a basic electrode shape, and FIG. 3a is a piezoelectric vibrator shown in FIG. Amplitude characteristic curve diagram relating to the vibrator, FIG. 3b is a cos square amplitude characteristic curve diagram, FIG. 4 is a perspective explanatory view of a piezoelectric vibrator according to the prior art, and FIG. 5 shows an electric circuit driving unit according to the present invention. FIGS. 6 and 7 are perspective explanatory views of a piezoelectric vibrator including the piezoelectric vibrator according to another embodiment of the present invention. 10 ... Piezoelectric vibrator, 12 ... Rear part 14 ... Rear electrode, 16 ... Front part 18a-18i ... Excitation electrode, 20a-20j ... Damping electrode 22a, 22b ... Common connection point 24 ... Excitation electrode, 26 ... Damping electrode 28 ... Back electrode, E ... AC power supply M ... Main lobe, S ... Side lobe _Us, ... Ultrasonic radiation surface

Claims (3)

[Claims] 1. A rectangular parallelepiped piezoelectric vibrator for generating ultrasonic waves, the electrodes being orthogonal to an ultrasonic radiation surface, and at least one of the opposing electrode surfaces being orthogonal to the longitudinal direction of the piezoelectric vibrator. The excitation electrode and the damping electrode are alternately divided in the direction, and the electrode area of each excitation electrode is formed so that it gradually narrows from the central part in the longitudinal direction to both ends. The electrode area of the electrode is formed so as to become gradually narrower from both ends in the longitudinal direction toward the central portion, and is electrically connected to the electrode on the other surface as well, and has the same phase and the same for each of the excitation electrodes. A piezoelectric vibrator characterized by applying a voltage. 2. The piezoelectric vibrator according to claim 1, wherein, among the electrodes divided alternately, the excitation electrodes are connected to each other along the longitudinal axis thereof, and the damping electrodes are arranged on the long side. Piezoelectric vibrators that are connected to each other and are also electrically connected to the electrodes on the other surface. 3. The piezoelectric vibrator according to claim 1 or 2, wherein the narrowing shape of the area of the excitation electrode and the damping electrode is to reduce side lobes in the directivity characteristic of the sound wave. , A piezoelectric vibrator configured to have a shape that follows a non-linear function.