JP2003037896A - Ultrasonic transducer using piezoelectric ceramics and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic transducer having the generating capability of short pulse-shaped ultrasonic waves capable of improving the distance resolution of various ultrasonic equipment. SOLUTION: This ultrasonic transducer is constituted of a piezoelectric ceramic board whose piezoelectric (e) constant is inclined and distributed in the thickness direction, and a ceramic board whose acoustic impedance is similar to that of the piezoelectric ceramic board. In this case, one face of the piezoelectric ceramic board is formed with an external electrode film, and the other face of the piezoelectric ceramic board is connected through an internal electrode film to the ceramic board whose acoustic impedance is similar to that of the piezoelectric ceramic board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic transducer using piezoelectric ceramics, and more particularly to an ultrasonic transducer using piezoelectric ceramics with high resolution and high sensitivity used in ultrasonic echo method. Furthermore, the present invention relates to an ultrasonic transducer using piezoelectric ceramics, which particularly improves distance resolution.

[0002]

2. Description of the Related Art For underwater ultrasonic equipment such as fish finder and sonar, ultrasonic non-destructive inspection equipment such as ultrasonic flaw detector and ultrasonic thickness gauge, and medical ultrasonic equipment such as ultrasonic diagnostic equipment, An ultrasonic echo method that inputs an electric signal to a sound wave transducer to generate ultrasonic waves, propagates the ultrasonic waves in an ultrasonic medium, and detects reflected waves from different portions of acoustic impedance existing in the medium is known. Widely used. Here, the acoustic impedance represents the ease of propagation of a sound wave in a medium, and has a unique value depending on the medium (substance). Reflection and transmission of sound waves occur at the boundary between media having different acoustic impedances. For example, if the acoustic impedance between the two media is about the same, the sound waves are well transmitted and the reflected waves are very small. On the contrary, if this difference is large, the transmitted wave is small and the reflected wave is very large.
The above-mentioned ultrasonic echo method utilizes this. With respect to the ultrasonic transducer used here, the shorter the time waveform of the generated ultrasonic waves, the more the distance resolution of the various ultrasonic devices described above is improved. Therefore, the time waveform of the ultrasonic waves is made as short as possible. Are being requested.

Conventionally, a typical structure of an ultrasonic transducer and a time waveform of an ultrasonic wave generated from the ultrasonic transducer are described in, for example, literature (29th EM Symposium Proceedings, May 18, 2000, Daisuke Yamazaki, Akira Yamada, Kira Nakamura, pp. 37-42). FIG. 9 is a diagram showing the structure of a conventional ultrasonic transducer,
A piezoelectric ceramic plate 7 having metal electrode films (electrodes) 6 formed on both sides and polarized in the thickness direction has a ceramic plate 8 of the same material not polarized on one side (hereinafter referred to as a ceramic plate that does not exhibit piezoelectricity) as an electrode. Adhesive (adhesive layer 1
0), and a packing material 9 made of a mixture of araldite and tungsten powder is formed behind it.

In FIG. 10, as a piezoelectric ceramic plate of the above transducer, a piezoelectric ceramic plate in which piezoelectric e constants are uniformly distributed in the thickness direction is used, and when a transducer is driven by a voltage pulse, the surface of the piezoelectric ceramic plate is exposed to the outside. The time waveform of the ultrasonic pulse radiated on the is shown. The emitted ultrasonic waves form a long pulse train instead of a single pulse, and the time waveform is long.

Further, in FIG. 11, as a piezoelectric ceramic plate,
Ultrasonic waves emitted from the surface of the tilted piezoelectric ceramic plate to the outside when a transducer using a piezoelectric ceramic plate (hereinafter referred to as a tilted piezoelectric ceramic plate) in which the piezoelectric e constants are distributed in the thickness direction is driven by a voltage pulse. The time waveform of the pulse is shown. Comparing this with FIG. 10 described above, the density of the ultrasonic pulse becomes low, but no change is observed in the width of the pulse train on the time axis, and the piezoelectric ceramic plate in which the piezoelectric e constant is uniformly distributed in the thickness direction. The time waveform is long, as is the case with the transducer described above.

[0006]

The problem of the above-mentioned prior art that the time waveform is long is that the piezoelectric ceramic plate that constitutes the transducer and the ceramic plate that does not exhibit piezoelectricity are joined together by using an adhesive agent, and piezoelectricity is exhibited. It occurs because the packing material is formed behind the ceramic plate.
That is, since the acoustic impedance of the ceramic plate and the adhesive is different, the ultrasonic waves generated by the piezoelectric ceramic plate are radiated to the outside while being repeatedly reflected at these boundaries (hereinafter referred to as multiple reflection). The waveform cannot be shortened. In the conventional configuration in which these constituent members are bonded together with an adhesive in this manner, it is basically difficult to solve this problem because the acoustic impedance of the adhesive and that of these ceramic plates are greatly different. Although it seems theoretically possible to solve the problem by making the thickness of the adhesive layer extremely thin, it is difficult to maintain a practical adhesive strength for the use of the ultrasonic transducer.

The present invention provides an ultrasonic transducer using a highly practical piezoelectric ceramic that eliminates the above acoustic discontinuity. For more information,
Since the ultrasonic transducer of the present invention does not generate a long pulse ultrasonic wave that is generated due to a reflected wave and is emitted to the outside, the ultrasonic pulse that is emitted to the outside can be shortened and the ultrasonic echo method can be performed. An ultrasonic transducer capable of improving the distance resolution of various ultrasonic devices used.

[0008]

SUMMARY OF THE INVENTION The present invention is an ultrasonic transducer mainly composed of a piezoelectric ceramic plate having piezoelectric e constants distributed in the thickness direction and a ceramic plate having an acoustic impedance similar to that of the piezoelectric ceramic plate. The external electrode film is formed on one surface of the piezoelectric ceramic plate, and the other surface is bonded to the ceramic plate whose acoustic impedance is similar to that of the piezoelectric ceramic plate through the internal electrode film. According to the present invention, in the invention, the piezoelectric ceramic plate is composed of two ceramic plates in which the piezoelectric e constants are gradiently distributed in the thickness direction. The plates have a laminated structure in which they are joined via an internal electrode film, and the piezoelectric e constant of these two ceramic plates is An ultrasonic transducer which is graded so that the largest at the side where are joined via a film in which the gist.

According to the present invention, in the above-mentioned invention, the ceramic plate whose acoustic impedance is similar to that of the piezoelectric ceramic plate has a porous end surface portion on the opposite side to the surface which is joined to the piezoelectric ceramic plate through the internal electrode film. Further, the present invention is based on an ultrasonic transducer that is a ceramic plate. Further, the present invention relates to a green sheet made of ceramic powder showing piezoelectricity, and a ceramic powder showing piezoelectricity coated with a metal paste on one surface. Green sheet, ceramic green sheet that does not show piezoelectricity, and ceramic paste green sheet that has a metal paste printed and applied on one side. With a piezoelectric e-constant gradient distribution in the thickness direction Ceramic plate and piezoelectric ceramic plate and the acoustic impedance is to the gist of the production method of the ultrasonic transducer whose main component a ceramic plate similar.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The ultrasonic transducer of the present invention will be specifically described below. (First Embodiment) FIG. 1 is a side sectional view showing a structure of an ultrasonic transducer using a piezoelectric ceramic according to a first embodiment of the present invention. In the figure, reference numeral 1 denotes a piezoelectric ceramic plate (gradient piezoelectric ceramic plate) in which piezoelectric e constants are distributed in the thickness direction as shown in the graph of FIG. Note that the slope distribution of the piezoelectric e constant may be right-downward, contrary to the graph in FIG. 2 is a ceramic plate having an acoustic impedance similar to 1. Further, 1 and 2 are joined without using an adhesive agent through a thin electrode film (internal electrode) 3 that does not reflect ultrasonic waves, so that the two are joined without mismatching in acoustic impedance. Reference numeral 4 is a metal electrode film (external electrode) formed on the surface of the inclined piezoelectric ceramic plate 1, and reference numeral 5 is an electrode lead and a terminal taken out therefrom. Further, 5'denotes electrode leads and terminals taken out from 3.

Here, it is preferable that the ceramic plate 2 has a porous structure at the end face portion opposite to the joint face with the internal electrode 3. Further, in the present invention, the ceramic plate 2
It is not necessary to attach a packing material to the side opposite to the surface to be joined to the internal electrode 3, but this may be used when manufacturing the transducer. The method for manufacturing a transducer of the present invention is, for example, used for manufacturing a multilayer ceramic capacitor, a ceramic green sheet and a ceramic green sheet obtained by printing and coating a metal paste on the green sheet are laminated and pressure-bonded. Can be baked. Ceramic powder production step, step of producing a green sheet from these ceramic powders, step of printing a metal paste on the surface of a desired green sheet, lamination and compression bonding of these green sheets to form a transducer having a predetermined structure And the step of sintering the obtained green sheet laminate, the step of forming external electrodes on the piezoelectric ceramic plate, the step of polarizing the piezoelectric ceramic plate, and the like. The inclined piezoelectric ceramic plate 1 is obtained by firing a laminate of a green sheet made of ceramic powder having a composition showing piezoelectricity and a green sheet made of ceramic powder having a composition not showing piezoelectricity. At this time, the components of the respective ceramics cause mutual diffusion at the boundary, so that the piezoelectric e constant whose composition changes continuously changes continuously in the thickness direction. The ceramic plate 2 having a similar acoustic impedance is, for example, a green sheet made of a ceramic powder having a composition showing piezoelectricity as described above, a green sheet made of a ceramic powder having a composition not showing piezoelectricity, or a composition similar to these. It is obtained by firing a laminate of green sheets made of ceramic powder. To make a part of the ceramic plate 2 porous, use a green sheet having a large number of through holes at arbitrary positions as a green sheet of a portion to be made porous of the green sheet forming the ceramic plate 2. good. Alternatively, a ceramic green sheet having resin beads mixed therein to form voids after firing may be used.

Next, a method of manufacturing the transducer having the structure of the first embodiment will be specifically described with reference to FIG. In the figure, 11 is a green sheet of ceramic powder that exhibits piezoelectricity, and 12 is a green sheet of ceramic powder that does not exhibit piezoelectricity. Further, a metal paste 15 is printed and applied on the same green sheet 13 as 12. At this time, if the electrode thickness after firing is too thick, ultrasonic waves will be reflected by this electrode surface, so printing is applied so that the ultrasonic waves are not reflected. 14 is a green sheet in which a large number of small through holes are provided in 12 green sheets. These green sheets are stacked and crimped as shown. And this laminated body is fired, and then
A transducer having the structure of the first form is obtained by printing and applying, for example, a metal paste to the end surface of the piezoelectric ceramic plate obtained by firing and firing to form an external electrode.

The external electrodes can be formed by various methods other than the above method. A sheet obtained by printing and coating a metal paste on a green sheet of ceramic powder having piezoelectricity is used at the same time as firing of the laminated body. It can also be formed by firing. In the transducer having the structure of the first embodiment thus obtained, a high DC voltage is applied between the electrode terminals 5 and 5'to polarize the piezoelectric ceramic plate. The direction of the polarization P may be the illustrated direction or the opposite direction. The ultrasonic wave is generated by applying a voltage pulse between the electrode terminals 5 and 5 '. At this time, ultrasonic waves are radiated bidirectionally from one surface of the ramp voltage ceramic plate with a large piezoelectric constant, but ultrasonic waves radiated toward the inside of the transducer pass through them without being reflected by the internal electrodes. Then, it is incident on a ceramic plate having a similar acoustic impedance and travels toward the opposite end face. This ultrasonic wave is not emitted from the front surface of the transducer because it is repeatedly diffused and attenuated by a large number of holes existing in the end face portion inside the ceramic plate, and then attenuates and disappears. As a result, by using this ultrasonic transducer, it is possible to obtain a short-pulse ultrasonic wave without multiple reflection of ultrasonic waves at both surfaces of the piezoelectric ceramic plate or at the boundary between the piezoelectric ceramic plate and a ceramic plate having a similar acoustic impedance. .

Example 1 An example of a prototype of the transducer according to the first embodiment and its ultrasonic characteristics will be described. The material showing piezoelectricity is 0.5 Pb (Ni _1/3 Nb _2/3 ) O ₃ .0.5.
Pb (Zr _0.7 Ti _0.3 ) O ₃ , 0.7Pb (Ni _1/3 Nb _2/3 ) O ₃ .0.3Pb for materials that do not show piezoelectricity
A ceramic powder having a composition of (Zr _0.7 Ti _0.3 ) O ₃ was used. To 100 parts by weight of these ceramic powders, 5 parts by weight of an acrylic resin and 20 parts by weight of an organic solvent mainly containing terpineol were measured and mixed to obtain a ceramic slurry, which was cast on a PET film and dried to obtain a ceramic green sheet. And For the metal paste for the internal electrode material, a platinum paste composed of platinum powder, a cellulosic resin, and an organic solvent mainly containing terpineol is used, and the electrode thickness after firing is 5 μm on a ceramic green sheet that does not exhibit piezoelectricity. It was applied by printing.
These green sheets were laminated and pressure-bonded as shown in FIG. 3, and then fired at a temperature of 1100 ° C. for 2 hours to obtain a fired body. This fired body has a thickness of l ₁ + l ₂ = 8 mm and a cross section of w
It was processed into dimensions of xw = 15 mm × 15 mm. Here, the thickness of the inclined piezoelectric ceramic plate is l ₁ = 1 mm, and the thickness of the ceramic plate that does not exhibit piezoelectricity is l ₂ = 7 mm.
The inner porous ceramic part occupies a thickness of about 2 mm.

Thereafter, as shown in FIG. 1, a silver paste made of an organic solvent containing silver powder, glass powder, a cellulosic resin and terpineol as a main component is applied to the surface of the inclined piezoelectric ceramic plate 1 as an external electrode 4. The temperature was kept at 650 ° C. for 10 minutes and then baked. A DC voltage of 2 kV was applied between the electrode lead terminals 5 and 5'for 10 minutes to polarize the tilted piezoelectric ceramic plate. Ultrasonic waves were generated by applying a spike-shaped voltage pulse of 20 V between the electrode lead terminals 5 and 5'and radiated into water. The ultrasonic waves radiated into the water were detected with a hydrophone.

The graph of FIG. 4 shows the measurement results of the time waveform of the ultrasonic waves radiated in water from this transducer. The vertical axis represents the output voltage of the hydrophone, which is a quantity proportional to the amplitude of ultrasonic waves. It is clear from comparison with FIGS. 10 and 11 that the ultrasonic wave has a short pulse. (Second Embodiment) FIG. 5 is a side sectional view showing the structure of an ultrasonic transducer using a piezoelectric ceramic plate according to a second embodiment of the present invention. Here, the ultrasonic transducer of the first embodiment is the same as the ultrasonic transducer except for the piezoelectric ceramic plate, so that the piezoelectric ceramic plate will be described in particular. In the figure, reference numerals 1 and 1'indicate a tilted piezoelectric ceramic plate, and both are bonded via an internal electrode 3'made of a thin metal electrode film. In 1 and 1 ', the slope of the piezoelectric e constant is symmetrically sloped with respect to the internal electrode 3', as shown in FIG. The directions of the polarization P are the same between 1 and 1 '.

The method of manufacturing the transducer of the second embodiment is similar to the method of manufacturing the transducer of the first embodiment, and a ceramic green sheet used for manufacturing a monolithic ceramic capacitor or the like and this green sheet. A ceramic green sheet printed with a metal paste is laminated and pressure-bonded to obtain a laminate.
This can be manufactured by firing and then providing an external electrode.

A specific manufacturing method will be described with reference to FIG. As described above, it is basically the same as the method for manufacturing the transducer of the first embodiment. Explaining only the different points, the piezoelectricity is obtained by printing and applying the metal paste 15 on the upper surface and the ceramic green sheet 16 having the piezoelectricity and the ceramic green sheet 12 having no piezoelectricity on the upper surface. No extra sandwiching on green sheet 13 and first on top of stack
That is, the layers and the second layer are interchanged. Other than that, there is no change in the manufacturing method of the transducer of the first embodiment.

In the transducer of the second embodiment, the common electrode lead and the terminal 5 are taken out from the internal electrode 3 and the external electrode 4, and the electrode lead terminal 5'is taken out from the internal electrode 3 '. A voltage pulse is applied between 5'to generate ultrasonic waves. In the second type transducer, ultrasonic waves are radiated from the interface between 1 and 1'in both directions. The ultrasonic wave that goes inside the transducer is the first
In the same manner as in the case of the transducer of the form (3), the light is scattered and attenuated and disappears inside the ceramic plate having a similar acoustic impedance. Ultrasonic waves traveling in the opposite direction are radiated outward from the surface of the transducer. At this time, some of the ultrasonic waves are reflected on the surface and travel to the inside, but after entering the ceramic plate with similar acoustic impedance from the beginning, the ultrasonic waves are directed to the inside. , Scattered, attenuated, and disappear. Therefore, also for the transducer of this form, the ultrasonic waves obtained in the same manner as the transducer of the first form are short pulses.

Another feature of the second form transducer is that it is more sensitive than the first form transducer. This matter is discussed in the Example 2 section below. Example 2 An example of a prototype of the transducer of the second embodiment and its ultrasonic characteristics will be described. This transducer was also manufactured by using the exact same method as that shown in Example 1, and the ultrasonic characteristics were measured.

The material exhibiting piezoelectricity is 0.5 P, respectively.
b (Ni_1/3 Nb_2/3 ) O₃・ 0.5Pb (Zr_0.7 T
i_0.3 ) O₃, 0.7Pb for materials that do not show piezoelectricity
(Ni _1/3 Nb_2/3 ) O₃・ 0.3Pb (Zr_0.7 Ti
_0.3 ) O₃A ceramic powder having the composition of was used.
Acrylic is added to 100 parts by weight of these ceramic powders.
Resin 5 parts by weight, terpineol-based organic solvent 20
Weigh and mix parts by weight to obtain a ceramic slurry.
After casting on PET film, dry and ceram
It was a green sheet. Metal paste for internal electrode material
Mainly platinum powder, cellulosic resin, terpineol
After firing using a platinum paste consisting of the organic solvent
Ceramics that do not show piezoelectricity so that the electrode thickness is 5 μm
It was applied by printing on a green sheet. These green
The sheets are laminated and pressure-bonded as shown in FIG.
Firing was performed at a temperature of ° C for 2 hours to obtain a fired body.

The dimensions of each part are as follows: the thickness of the tilted piezoelectric ceramic plate 1 is l ₁ = 0.5 mm, the thickness of the tilted piezoelectric ceramic plate l'is l ₁ '= 0.5 mm, and the thickness of the ceramic plate that does not exhibit piezoelectricity. Is l ₂ = 7 mm. The porous ceramic part occupies a thickness of about 2 mm. The cross section is w ×
It was processed into dimensions of w = 15 mm × 15 mm. Then, as shown in FIG. 5, a silver paste made of an organic solvent containing silver powder, glass powder, a cellulosic resin, and terpineol as a main component is applied to the surface of the inclined piezoelectric ceramic plate 1 as an external electrode 4, and the temperature is set to 650 ° C. It was held for 10 minutes and baked. 2 kV between the electrode lead terminals 5 and 5 '
Was applied for 10 minutes to polarize the tilted piezoelectric ceramic plate. Ultrasonic wave is 20V between electrode lead terminals 5 and 5 '
It was generated by applying a spike-shaped voltage pulse of, which was radiated into water. The ultrasonic waves radiated into the water were detected with a hydrophone.

FIG. 8 shows a time waveform of an ultrasonic wave radiated in water from this transducer. It is common that the pulse is shortened as compared with the waveform of the first embodiment, but it is clear that the amplitude of the ultrasonic pulse is about four times larger than that. Thus, it can be seen that the transducer of the second form has about four times the sensitivity of the transducer of the first form.

[0024]

As described above, the ultrasonic transducer using the piezoelectric ceramics of the present invention can shorten the generated ultrasonic pulse, and the distance of various ultrasonic devices utilizing the ultrasonic echo method. The resolution can be improved.

[Brief description of drawings]

FIG. 1 is a side sectional view of an ultrasonic transducer according to a first embodiment of the present invention.

FIG. 2 is a graph showing a change of a piezoelectric e constant of a tilted piezoelectric ceramic plate with respect to a thickness direction.

FIG. 3 is an explanatory diagram showing a method of manufacturing the ultrasonic transducer of the first embodiment using a green sheet.

FIG. 4 is a graph showing a time waveform of an ultrasonic wave emitted from the ultrasonic transducer according to the first embodiment.

FIG. 5 is a side sectional view of an ultrasonic transducer according to a second embodiment of the present invention.

FIG. 6 is a graph showing changes in the piezoelectric e constant of the tilted piezoelectric ceramic plate of the second embodiment with respect to the thickness direction.

FIG. 7 is an explanatory diagram showing a method of manufacturing the ultrasonic transducer of the second embodiment using a green sheet.

FIG. 8 is a graph showing a time waveform of an ultrasonic wave emitted from the ultrasonic transducer of the second embodiment.

FIG. 9 is a side sectional view showing an example of a structure of a conventional ultrasonic transducer.

10 is a graph showing a time waveform of ultrasonic waves emitted from the ultrasonic transducer having the structure of FIG. 9 using a piezoelectric ceramic plate having a uniform piezoelectric e constant.

FIG. 11 is a graph showing a time waveform of an ultrasonic wave emitted from the ultrasonic transducer having the structure of FIG. 9 using a piezoelectric ceramic plate in which the piezoelectric e constant is distributed in a gradient manner.

[Explanation of symbols]

l ₁ , l ₁ ′ Thickness of inclined piezoelectric ceramic plate after firing l ₂ Thickness of ceramic plate having acoustic impedance similar to that of inclined piezoelectric ceramic plate after firing w Width of ultrasonic transducer after firing p Direction of polarization 1 , 1'Inclined piezoelectric ceramic plate 2 Ceramic plate with acoustic impedance similar to that of inclined piezoelectric ceramic plate 3,3 'Internal electrode 4 External electrodes 5,5' Electrode lead terminal 6 Electrode 7 Piezoelectric ceramic plate 8 polarized in the thickness direction Ceramic plate 9 that does not show piezoelectricity 9 Packing material 10 Adhesive layer 11 Ceramic green sheet that shows piezoelectricity 12 Green sheet 13 that does not show piezoelectricity Ceramic green sheet that does not show piezoelectricity (printed with metal paste) 14 Ceramic green sheet with a large number of through holes that does not exhibit piezoelectricity 15 Mixed green sheet on the printed metallic paste 16 (printing the metal paste) ceramics showing a piezoelectric green sheet

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 41/187 H01L 41/08 S 41/22 41/18 101F H04R 31/00 330 41/22 Z F term (reference) 2G047 EA03 GB11 GB32 GB33 GB35 4C301 EE03 GB01 GB18 GB33 GB34 GB36 5D019 AA26 BB02 BB13 BB25 BB29 FF02 FF03

Claims (4)

[Claims] 1. An ultrasonic transducer comprising, as main components, a piezoelectric ceramic plate having piezoelectric e constants gradient-distributed in a thickness direction and a ceramic plate having an acoustic impedance similar to that of the piezoelectric ceramic plate. An ultrasonic transducer, wherein an external electrode film is formed on one surface, and the other surface is bonded to a ceramic plate having an acoustic impedance similar to that of a piezoelectric ceramic plate via an internal electrode film. 2. The piezoelectric ceramic plate is composed of two ceramic plates in which the piezoelectric e constants are distributed in a gradient in the thickness direction, and these two ceramic plates have a laminated structure in which they are joined via an internal electrode film. The ultrasonic transducer according to claim 1, wherein the piezoelectric e constants of these two ceramic plates are distributed so as to be maximized on the surface side where they are joined via the internal electrode film. 3. A ceramic plate having an acoustic impedance similar to that of the piezoelectric ceramic plate is a ceramic plate in which an end face portion on the opposite side of the surface joined to the piezoelectric ceramic plate through the internal electrode film is porous. The ultrasonic transducer according to 1 or 2. 4. A green sheet made of ceramic powder showing piezoelectricity, a green sheet made of ceramic powder showing piezoelectricity having a metal paste printed and applied on one side, a green sheet made of ceramic powder not showing piezoelectricity, and one side. A green sheet made of ceramic powder having no piezoelectricity, which is printed and coated with a metal paste, is appropriately stacked, pressure-bonded, fired, and then an external electrode is attached, and the piezoelectric e constant is inclined in the thickness direction. A method of manufacturing an ultrasonic transducer comprising a distributed piezoelectric ceramic plate and a ceramic plate having an acoustic impedance similar to that of the piezoelectric ceramic plate as main constituent elements.