JPS63251000A - Piezo-electric vibrator - Google Patents

Abstract

PURPOSE:To improve the utility efficiency of a vibrator by forming driving electrodes and damping electrodes which are arranged in confronting two surfaces of the piezo-electric vibrator in substantially congruence graphics into the electrode patterns of vertical and horizontal symmetry, forming the electrode areas into pattern shapes following cos square curves and connecting high resistances with the damping electrodes. CONSTITUTION:The electrode areas per unit length in the longitudinal direction of the driving electrodes 26 and 28 are formed into areal distributions which gradually decrease from a center which is an origin towards both end parts and which correspond to cos square curves, and the electrode areas per unit length in the longitudinal direction of the damping electrodes 30a, 20b, 32a and 32b are formed into areal distribution which gradually decrease in proportion to (1-cos square) curves from both end parts toward the center. In such a constitution, high resistances R1 and R2 of more than 100kOMEGA are respectively connected from the common connection points 34a and 34b of the damping electrodes 30a, 30b, 32a and 32b to the driving electrodes 26 and 28. An AC power source E2 is connected between the common connection points 36a and 36b of the high resistances P1 and R2 and the driving electrodes 26 and 28.

Description

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

[Background of the Invention] A piezoelectric vibrator is an electro-speech transducer that converts an electric signal into a sonic signal or 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 sounding 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 sound pressure on the central axis 4 in the direction perpendicular to the piezoelectric vibrator 2 is strongest;
As the displacement angle θ from the central axis 4 increases, the sound pressure decreases.

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. Also, when transmitting and receiving using the same piezoelectric vibrator,
Since the directivity multiplier is squared, the angle θ- at which the sound pressure in the main lobe M is less than 3dB'o3 than the value of the central axis 4 is
3 dB is also important as an index representing directional characteristics.

By the way, in the directional characteristics of the sound waves shown in Fig. 1, the presence of side lobes S means that when a piezoelectric vibrator that generates the sound waves is used in a fish finder, reflected signals related to the side lobes S,
For example, there may be a case where a reflected signal from a school of fish or the like is mistakenly thought to be a reflected signal from the main lobe M. In this case, even if you trust the direction of the school of fish displayed on the display of the fish finder, that is, you start casting the net after misperceiving 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 method, in order to further clarify the problems of the conventional technique, first of all,
The relationship between the basic electrode pattern of a piezoelectric vibrator and the size of the side lobe S generated along with the electrode pattern will be described.

Normally, the amount of suppression of the sidelobe S is the sidelobe suppression ratio R
; expressed as R=201og 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 is such that the entire surface of two opposing surfaces are electrode patterns 8a,
8b, the sound pressure level generated on the surface of the ultrasonic radiation surface U of the rectangular parallelepiped piezoelectric vibrator 6 is equal to the long axis l, as shown in FIG. 3a. An amplitude characteristic curve, which is the amplitude, is obtained. It is known that the sidelobe suppression ratio R in this case is approximately 13.5 dB. In addition, in order to make this sidelobe suppression ratio R infinite, the amplitude characteristic curve related to the sound pressure is changed, for example, to
As shown in FIG. 3, it has been found that a characteristic curve approximately similar to the cos square characteristic curve can be used.

Next, from this point of view, an example of forming an electrode pattern according to the prior art will be described. This technical idea is, for example,
It is disclosed 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 10a and the damping electrode. Insulated between 12a and 12b: a14 a, 14 b
The damping electrodes 12a and 12b are connected to the excitation electrode 10b on the other side so that the vibration energy is suppressed at both ends, and an AC power source E is supplied. Therefore, the ultrasonic waves radiated from the ultrasonic radiation surface U.

It is most strongly radiated from the center of the vibration damping electrodes 12a, 12.
It is described that due to the effect of b, the radiation is gradually weakened as it approaches the end.

However, in this case, as is clear from a detailed examination of the pattern shape, the arrangement shape of the excitation electrode 10a and the damping electrodes 12a, 12b is linear, so that The effect of suppressing the sidelobe S becomes insufficient. That is, in this prior art, since the shape of the amplitude characteristic curve related to the sound pressure is approximately an isosceles triangular shape, the sidelobe suppression ratio R is approximately 20d.
B, and 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 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.

Furthermore, as can be easily understood from the electrical connection diagram shown in FIG.
Since a high voltage is applied to the insulating grooves 14a and 14b existing between the insulating grooves 14a and 14b, it is necessary to ensure a sufficient creeping distance, and it has also been pointed out that the efficiency of using the piezoelectric vibrator is reduced.

Moreover, such a driving voltage application configuration is applicable to the excitation electrode 10.
Since electric charge is stored between a and the vibration damping electrodes 12a and 12b, there is also an inherent drawback that the electricity-to-ultrasonic conversion efficiency is reduced due to this.

[Object of the Invention] The present invention has been made in order to overcome all of the above-mentioned disadvantages, and the electrode patterns are arranged vertically symmetrically on two opposing surfaces of a rectangular parallelepiped piezoelectric vibrator. An excitation electrode and a damping electrode are arranged in a shape that follows a curve. , -, it is possible to suppress the side lobe S generated in the ultrasonic radiation pattern to approximately zero by applying an alternating voltage between the two electrodes, and in addition,
It is an object of the present invention to provide an ultrasonic piezoelectric vibrator whose electrodes are extremely easy to manufacture.

[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 opposing electrode surfaces have substantially congruent shapes with each other. In addition, the electrodes are formed in an electrode shape including one excitation electrode and a pair of vibration damping electrodes that are vertically and horizontally symmetrical with respect to an axis orthogonal to the center of each surface, and the excitation electrode per unit length in the longitudinal direction of each surface is The area of the damping electrode is formed so that it gradually becomes narrower from the center to both ends, and the area of the damping electrode per unit length in the longitudinal direction becomes gradually narrower from both ends to the center. Further, a damping electrode on one surface is electrically connected to a damping electrode on the other electrode surface facing this damping electrode, and a resistor is connected to the two damping electrodes. It is characterized in that the resistor is configured to be connected to a drive voltage source connected to the excitation electrode.

[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 5 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 6, reference numeral 20 indicates a rectangular parallelepiped-shaped piezoelectric vibrator including an electric circuit driving section according to the present invention. The shape of this piezoelectric vibrator 20 is precisely a thin rectangular parallelepiped shape, and electrode patterns are formed on two opposing faces in a substantially congruent shape.

In this case, in the figure, the front part 22 and the back part 24 each have one excitation electrode 26, 28 extending over the entire surface from the center of the surface to both ends, and one excitation electrode 26, 28 extending from both ends to the center. Two pairs of damping electrodes 30a, 30b extending toward
and 32a, 32b are arranged, and the circumferential surfaces of the excitation electrode 26.28, the damping electrodes 30a, 30b, and 32a, 32b are formed so as to be insulated from each other by insulating grooves 31a, 31b, and 332.33b. has been done.

In this case, the electrode area per unit length in the longitudinal direction of the excitation electrodes 26, 28 is defined in an area distribution that gradually decreases corresponding to a cos square curve, with the center as the origin and directed toward both ends. In addition, vibration damping electrodes 30a and 30b
The electrode area per unit length in the longitudinal direction of 32a and 32b is formed as an area distribution that gradually decreases from both ends toward the center in proportion to a curve of (1-cos squared). Note that each electrode can be formed by printing by a silk screen method, and therefore, it is possible to maintain the shape of the curved shape and to make the electrode shape suitable for mass production.

In such a configuration, the vibration damping electrode 30a.

30b and 32a, 32b are connected in common, and from the common connection point 34a, 34b, for example, 100
The high resistances R, , R2 of approximately Ω or more are connected to the excitation electrodes 26 .
28. An AC power source E1 is connected between the common connection points 36a and 36b of the high resistances R, , R2 and the excitation electrodes 26, 28. Here, the AC power source E1 is a voltage source having a frequency that resonates with the ultrasonic waves generated from the piezoelectric vibrator 20. Incidentally, an electric circuit wiring diagram related to the above-mentioned connection explanation is shown in FIG.

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.

The piezoelectric vibrator 20 emits ultrasonic waves upward from the radiating surface U or downward from the opposing surface of the radiating surface Us by applying the AC power source E1 having a resonant frequency. In this case, the directivity of the ultrasonic wave is determined by the vibration damping electrodes 30a, 30b and 32a, 32 having the same potential on both ends of the piezoelectric vibrator 20 in the longitudinal direction.
b exist facing each other, the piezoelectric vibrator 20 operates in such a way that the vibration is suppressed at the ends thereof, directed in the longitudinal direction, and more strongly (excited) toward the center.In this case, As mentioned above, since the electrode area per radial length of the excitation electrodes 26 and 28 is formed so as to be approximately proportional to the cosine square characteristic, most of the ultrasonic waves radiated from the radiation surface U5 are , it is possible to obtain a radiation pattern without side lobes.In this case, the directivity pattern of the main lobe M is set to a θ-3 dB angle, which is approximately the same as that of the piezoelectric vibrator with the basic electrode configuration shown in Fig. 2. In order to do this, under the condition that the length 12 in the lateral direction is the same as that of the basic piezoelectric vibrator, it is preferable that the length !!1 in the longitudinal direction be set as j21>β.

On the other hand, as can be easily understood from the electric circuit diagram shown in FIG.
), only a voltage of E,/2 rV] is applied under the partial pressure action of 81? m31 a, 3
1b, 33a, and 33b may be formed to have a dielectric strength that is half that of the conventional one. In other words, the creepage distance can be reduced to approximately half the value.

Furthermore, electric charges stored between the excitation electrode 26 and the damping electrodes 30a, 3Ob and the charges stored between the excitation electrode 28 and the damping electrodes 32a, 3Ob
Since the electric charge stored between 2b and 2b is discharged through the resistors R and R2 every cycle of the AC power source E1,
It is also possible to prevent a decrease in electricity/ultrasonic conversion efficiency due to charge storage.

FIG. 8 shows another embodiment of the piezoelectric vibrator according to the present invention. In FIG. 8, reference numeral 40 is an excitation electrode arranged on the front part 22, and reference numerals 42a and 42b are vibration damping electrodes. In this case, an excitation electrode 44 and damping electrodes 46a and 46b are formed on the back surface 24 in a shape substantially congruent with the front surface 22. Electrically, the vibration damping electrodes 42a, 4
2b and 463.46b are commonly connected, and high resistances R, RZ are connected to the excitation electrodes 40.44 from the common connection points 48a and 48b, respectively. Therefore, the high resistance R
+, common connection point 48a of Rz and excitation electrode 40.44,
Ultrasonic waves can be radiated from the radiation surface U by connecting the driving power source E between the radiating surfaces 48b and 48b. In this case as well, the electrode area per unit length in the longitudinal direction of the excitation electrode 40.44 is divided into area proportions that are approximately proportional to a cos square curve with the center point in the longitudinal direction as the origin and directed toward both ends. The vibrating electrodes 42a, 42b and 46a, 46b are oriented from both 6Mj portions in the longitudinal direction toward the center (1-cos
An ultrasonic radiation pattern in which side lobes can be suppressed can be obtained by using a shape having an area distribution proportional to the squared curve.

[Effects of the Invention] As described above, according to the present invention, the excitation electrodes and the damping electrodes, which are arranged in substantially congruent shapes on two opposing surfaces of a piezoelectric vibrator, are arranged in vertical and horizontal symmetrical electrode patterns. Furthermore, the electrode area is formed into a pattern shape that follows a cosine squared curve, and a high resistance is connected to the vibration damping electrode to drive it by a supplied power source. Therefore, various effects listed below can be obtained.

■ The directional characteristics of the emitted ultrasonic waves become sharper, making it possible to suppress side lobes occurring in the ultrasonic radiation pattern to approximately zero.

(2) If a silk screen printing method or the like is used as the electrode formation method, it is possible to extremely easily form an electrode pattern with a complicated shape without increasing the manufacturing cost.

■ The creepage distance between the excitation electrode and damping electrode is approximately 1/2 that of the conventional one.
This makes it possible to improve the utilization efficiency of the piezoelectric vibrator.

■ Since the resistor ensures a cycle in which the charge is discharged, the deterioration of the electrical/ultrasonic conversion efficiency due to charge accumulation is reduced.

■ The voltage value applied between the excitation electrode and the damping electrode is 172
Therefore, the possibility of cracks occurring in the piezoelectric vibrator itself due to electrostrictive action is eliminated.

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

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the directivity 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. 3a is shown in Fig. 2. FIG. 3 is a cosine squared amplitude characteristic curve diagram, FIG. 4 is a perspective explanatory diagram of a piezoelectric vibrator according to the prior art, and FIG. 5 is an electric circuit connection diagram according to FIG. 4. 6 is a perspective explanatory diagram of a rectangular parallelepiped piezoelectric vibrator including an electric circuit drive unit according to the present invention, FIG. 7 is an electric circuit connection diagram according to FIG. 6, and FIG. 8 is a rectangular parallelepiped piezoelectric vibrator according to the present invention. FIG. 7 is a perspective explanatory view showing another embodiment of the child. 20... Piezoelectric vibrator 22... Front part 24.
...Back part 26.28...Excitation electrode 30
a, 30b, 32a, 32b - Vibration damping electrode E3... AC power supply M... Main rope S... Side lobe U,... Ultrasonic radiation surface 3e5a FIG, 3 Piezoelectric expansion Y! a Yamakata Riki 1 River-

Claims (2)

[Claims] (1) In a rectangular parallelepiped-shaped piezoelectric vibrator that generates ultrasonic waves, opposing electrode surfaces are arranged in a shape that is substantially congruent with each other and that is vertically and horizontally symmetrical with respect to an axis orthogonal to the center of each surface. The electrode shape is formed to include one excitation electrode and a pair of damping electrodes, and the area of the excitation electrode per unit length in the longitudinal direction of each surface is gradually narrowed from the center toward both ends. At the same time, the area of the damping electrode per unit length in the longitudinal direction is formed so that it gradually becomes narrower from both ends toward the center, and furthermore, the area of the damping electrode on one side and this damping electrode is The electrode is electrically connected to a damping electrode on the other electrode surface side facing the electrode, and a resistor is connected to the two damping electrodes, and the resistor is connected to a drive voltage source connected to the excitation electrode. A piezoelectric vibrator characterized by: (2) In the piezoelectric vibrator according to claim 1, the area narrowing shape of the excitation electrode and the damping electrode is a shape that follows a non-linear function so that the middle side lobe of the directional characteristic of the sound wave becomes small. A piezoelectric vibrator composed of