JP2878302B2 - Piezoelectric vibrator and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a piezoelectric vibrator that transmits and receives ultrasonic waves, and more particularly to a piezoelectric vibrator that generates ultrasonic waves having a plurality of resonance frequencies and a method of manufacturing the same.

[Prior art]

Ultrasonic waves are harmless to the human body and can detect foreign substances by non-destruction, and are therefore used in a wide range of fields such as medical treatment and fishing. When an ultrasonic wave is propagated in a living body or in the sea, a reflected wave is not generated if the propagator is homogeneous, but if a portion having a different acoustic impedance is present in the propagator, a reflected wave is generated in that portion. By measuring the magnitude of the reflected wave and the time until reception, the position and properties of the foreign matter can be observed. For example, in the medical field, it is applied to inspection of tumors, observation of fetuses or hearts, and in the field of fishery, it is applied to exploration of fish schools, marine topography, obstacles, and the like. The frequency of the ultrasonic wave differs depending on the object to be observed. Ultrasonic waves having a high frequency can observe fine foreign matters because of their high resolution. On the other hand, the propagation distance is short because the propagation loss is large. On the other hand, in the case of an ultrasonic wave having a low frequency, it is more difficult to observe a fine foreign substance than in the former case, but the propagation distance of the ultrasonic wave becomes longer. These ultrasonic waves are, for example, barium titanate BaTiO ₃ ,
Lead titanate PbTiO ₃ , lead zirconate titanate Pb (Zr, Ti) O
₃ Generated by applying voltage to a piezoelectric vibrator made of ferroelectric ceramics such as (PZT). The resonance frequency is controlled by determining the shape and size of the piezoelectric vibrator according to the application of the ultrasonic wave. However, it is difficult to generate ultrasonic waves having arbitrary plural frequencies from one piezoelectric vibrator whose dimensions are determined. Conventionally, in order to generate ultrasonic waves of a plurality of frequencies, for example, radial vibration and thickness vibration are applied as vibration modes of the piezoelectric vibrator, or a plurality of piezoelectric vibrators having different resonance frequencies are arranged. I have. In the medical and fishery fields, lead zirconate titanate is frequently used as a piezoelectric vibrator material. This is lead zirconate PbZr
It is a binary system of O ₃ and lead titanate PbTiO ₃ , and the characteristics are diversified by changing the composition ratio. However, it is difficult to provide a plurality of arbitrary frequencies to one piezoelectric vibrator 1 having a fixed shape and dimensions. In general, the probe must use different resonance frequencies due to different vibration modes of the piezoelectric vibrator, or different resonance frequencies depending on the sum or difference of the resonance frequencies. Further, it is necessary to use different resonance frequencies from a plurality of elements obtained by arranging a plurality of elements having different frequency constants, which are products of the resonance frequency and the thickness of the piezoelectric vibrator, in a matrix or ring.

However, when different resonance frequencies of one piezoelectric vibrator are used, interference occurs at a target frequency depending on the diameter and thickness of the piezoelectric vibrator, that is, the shape and size of the piezoelectric vibrator. In some cases, it is difficult to set the frequency. Further, when a plurality of piezoelectric vibrator materials having different frequency constants are arranged, there is a problem that the shape of the probe becomes complicated and large. Each of the individual vibrators also needs to be electrically coupled, which inevitably complicates the manufacturing process and structure. SUMMARY OF THE INVENTION The present invention has been made to eliminate the above-described problem. By providing a plurality of resonance frequencies to one piezoelectric vibrator, the number of components of the vibrator can be reduced, the cost can be reduced, and the size can be reduced. It is an object of the present invention to obtain a piezoelectric vibrator.

[Means for Solving the Problems]

In order to solve the above problems, the present inventors have repeated research on a porous piezoelectric vibrator. As a result, the ratio of the porosity per unit volume, that is, the voltage characteristics of the porous piezoelectric vibrators having different porosity, are as shown in the porosity and frequency constant characteristic diagram of FIG. It has been found that the frequency constant, which is the product of the resonance frequency and the thickness of the piezoelectric vibrator, is different due to the change in. Therefore, if regions having different porosity are provided in one piezoelectric vibrator, different resonance frequencies can be obtained. For a porous piezoelectric vibrator having multiple regions, most of the piezoelectric vibrator may be made of a normal ferroelectric, and some regions may be formed in a porous structure. A mixture of powder (vaporizable powder) that evaporates at a low temperature depending on the firing temperature of the ferroelectric substance is integrally formed, fired, and further subjected to a polarization treatment. However, if the difference in the coefficient of thermal expansion is large at the boundary between different materials during firing, the sintered body may be broken by thermal stress. The thermal expansion coefficient of piezoelectric vibrators having different porosity was measured. As a result, the temperature and expansion coefficient of dense lead zirconate titanate and lead zirconate titanate having porosity of 35% are shown in FIG. Have the following characteristics. In the same figure, A is a dense lead zirconate titanate, and B is a porosity.
Shows the properties of lead zirconate titanate with 35%. According to this characteristic, the difference in the coefficient of thermal expansion between the two was small at a temperature of 500 ° C. or higher, which is the solid-phase reaction region. This relationship holds even in a region having a porosity of less than 35%. However, if the porosity exceeds 35%, the difference in the coefficient of thermal expansion at 500 ° C. or more increases. For this reason, it was found that when the dense lead zirconate titanate and the lead zirconate titanate having a porosity of 35% or more were integrally fired, breakage easily occurred. As a result, by providing a porous structure in some regions or a porous structure having a different porosity in some regions of a piezoelectric vibrator that has been made porous, the resonance frequency differs in each region. Can be provided. It was confirmed that when the porosity was less than 35%, a stable sintered body having high mechanical strength was obtained. The present invention based on the above knowledge will be described below with reference to the drawings corresponding to the embodiments. The piezoelectric vibrator 1 of the first invention of the present invention (see FIG. 1)
The inner pillar portion made of the dense ferroelectric material 3 and the outer cylindrical portion made of the porous ferroelectric material 2 are integrated and fired, and the dense ferroelectric material and the porous ferroelectric material are arranged in parallel. It is characterized in that a polarization process is performed in the direction. The piezoelectric vibrator 8 of the second invention of the present invention (see FIG. 2)
Plurality of ferroelectrics 2 having different porosity and made porous
And 9 are made into an inner pillar portion and the other is made into a cylindrical portion, and are integrally fired, and are subjected to a polarization treatment in a direction in which a plurality of ferroelectrics are arranged in parallel. A piezoelectric vibrator according to a third invention of the present invention is characterized in that the porosity of the porous ferroelectric material according to the first invention or the second invention is in a range up to 35%. A piezoelectric vibrator according to a fourth invention of the present invention is characterized in that the ferroelectric substance of the first invention, the second invention or the third invention is a substance selected from lead zirconate titanate, barium titanate and lead titanate. Features. The method for manufacturing a piezoelectric vibrator according to the fifth invention of the present invention is a method for manufacturing a piezoelectric vibrator 1 (see FIG. 1) in which a ferroelectric substance 2 and a dense ferroelectric substance 3 are adjacent to each other. Partition 6
The raw material powder of the ferroelectric and the powder that evaporates at a temperature lower than the temperature at which the ferroelectric is fired are mixed and placed in one side 2a of the mold 4 (see FIG. 3) having The ferroelectric material alone is put into the other side 3a of the mold 4 and the partition 6 is put into the mold 4
And molded. It is heated to vaporize the powder and bake the ferroelectric. Then, a polarization process is performed. The method for manufacturing a piezoelectric vibrator according to the sixth invention of the present invention is a method for manufacturing the piezoelectric vibrator 8 (see FIG. 2) of the ferroelectrics 2 and 9 adjacent to each other and made porous with different porosity. A ferroelectric raw material powder and a powder that is vaporized at a temperature lower than the temperature at which the ferroelectric is fired are mixed and molded into one side 2a of a mold 4 having a partition 6 (see FIG. 3). Then, a ferroelectric raw material powder and a vaporizable powder are mixed in a ratio different from that described above in the other side 3a in the mold 4 and the mold is formed. The partition 6 is removed from the mold and molded. It is heated to vaporize the powder and bake the ferroelectric. Then, a polarization process is performed.

【Example】

Hereinafter, embodiments of the present invention will be described in detail. FIG. 1 shows an embodiment of the piezoelectric vibrator of the present invention,
(A) is a plan view and (b) is a longitudinal sectional view. The sintered body 1 shown in FIG. 1 has an inner pillar portion 2 made of a dense sintered body of lead zirconate titanate and an outer pillar made of a sintered body of lead zirconate titanate having a porous structure with a porosity of 35%. It is formed in a cylindrical shape from the cylindrical portion 3. When the fired body 1 is formed, a forming die 4 including an outer cylinder 5 and a boundary cylinder 6 serving as a partition shown in FIG. 3 is used. Only lead zirconate titanate is put into the inside 2a of the boundary cylinder 6. A mixture of lead zirconate titanate and 10% by weight of methacrylic powder is placed in the intermediate portion 3a between the outer cylinder 2 and the boundary cylinder 6. Then, the boundary cylinder 6 is removed and pressurized to obtain a molded body.
The molded body is held while being heated at 500 ° C. for 2 hours in an electric furnace. Then, the methacrylic powder evaporates from the molded body. By firing it at 1200 ° C for 2 hours,
A dense sintered body of lead zirconate titanate was obtained in the inner column portion 2 and a sintered body 1 of lead zirconate titanate having a porous structure with a porosity of 35% was obtained in the outer cylindrical portion 3. As a result of examining the boundary between the inner column portion 2 and the outer cylindrical portion 3 of the sintered body 1, both portions were found to have a good joint. Further, the cylindrical sintered body 1 was polished to a thickness of 1 mm, and then subjected to polarization treatment in the thickness direction by a known method to obtain a piezoelectric vibrator. As a result of examining the resonance frequency of the piezoelectric vibrator, the resonance frequency of the dense lead zirconate titanate portion 2 was 1840 KH.
z. The resonance frequency of the portion 3 of porous zirconate titanate having a porosity of 35% was 940 KHz. In the above embodiment, lead zirconate titanate was used as the ferroelectric, but barium titanate BaTiO ₃ , lead titanate PbTi
Similarly, different resonance frequencies can be obtained with O _{3 and the} like. Also, methacrylic powder is used as a material for forming pores, but synthetic resin such as crosslinked polystyrene powder, carbon powder, and inorganic powder which evaporate at a temperature lower than the firing temperature of ferroelectrics, and pores are similarly used. Can be formed. Further, in the above-described embodiment, the configuration of dense lead zirconate titanate and porous zirconate titanate was shown, but a fired body obtained by combining a plurality of porous materials having different porosity was used. In addition, a single piezoelectric vibrator that oscillates a plurality of arbitrary resonance frequencies can be obtained. Further, in the configuration of the above embodiment, the resonance frequency obtained by one piezoelectric vibrator is two frequencies, but the number of resonance frequencies can be further increased by increasing the number of regions having different porosity.

【The invention's effect】

As described above, in the piezoelectric vibrator of the present invention, a plurality of regions in one have different resonance frequencies, so that the number of components of the vibrator is reduced, the cost is reduced, and the size is reduced. And high performance can be achieved. The structure of the ultrasonic transducer using the piezoelectric vibrator can be simplified, and it can be applied to a wide range such as medical use, fishery use and the like. Further, according to the manufacturing method of the present invention, a piezoelectric vibrator having the above characteristics can be efficiently manufactured.

[Brief description of the drawings]

FIG. 1 is a plan view and a longitudinal sectional view of an embodiment of a piezoelectric vibrator to which the present invention is applied. FIG.
FIG. 4 is a plan view and a longitudinal sectional view of an embodiment of a molding die, FIG. 4 is a characteristic diagram of frequency constant and porosity, and FIG. 5 is a characteristic diagram of temperature and linear expansion coefficient. 1, 8 ... piezoelectric vibrator, 2, 9 ... porous ferroelectric,
3 ... dense ferroelectric, 4 ... molding die, 5 ... mold outer cylinder,
6 ... partition

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 41/08 H01L 41/24 H04R 17/00

Claims (6)

(57) [Claims] 1. A piezoelectric vibrator characterized in that an inner column portion made of a dense ferroelectric and an outer cylindrical portion made of a porous ferroelectric are integrally fired and polarized. . 2. The method according to claim 1, wherein one of a plurality of porous ferroelectric materials having different porosity is formed into an inner pillar portion, and the other is formed into a cylindrical portion, which is integrally fired and subjected to a polarization treatment. Piezoelectric vibrator. 3. The porosity of the porous ferroelectric material is 35%.
The piezoelectric vibrator according to claim 1, wherein the piezoelectric vibrator is in the range described above. 4. The method according to claim 1, wherein said ferroelectric substance is a substance selected from the group consisting of lead zirconate titanate, barium titanate, and lead titanate. Piezoelectric vibrator. 5. A ferroelectric raw material powder and a powder that is vaporized at a temperature lower than the temperature at which the ferroelectric is fired are mixed and placed in one of the molds having a partition. On the other hand, only the ferroelectric material is put into the mold, the partition is removed from the mold, and after molding, the powder is heated to evaporate, the ferroelectric material is baked, and a polarization process is performed. A method of manufacturing a piezoelectric vibrator in which a ferroelectric that has been converted and a dense ferroelectric are adjacent to each other. 6. A ferroelectric raw material powder and a powder which is vaporized at a temperature lower than the temperature at which the ferroelectric is fired are mixed and placed in one of the molds having a partition. On the other hand, after mixing the raw material powder and the powder at a ratio different from the above and molding, removing the partition from the mold and molding,
A method for producing a ferroelectric piezoelectric vibrator having adjacently different porosity and being porous, comprising heating to vaporize the powder, firing the ferroelectric, and performing polarization treatment. .