JP2011077916A - Ultrasonic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transducer capable of improving temperature stability while preventing deterioration in reliability caused by an ambient temperature, and performing bending vibration at the bottom surface section. <P>SOLUTION: The ultrasonic transducer 1 is equipped with a piezoelectric body 2 and driving electrodes 3A and 3B. The piezoelectric body 2 is integrally formed with a cylindrical side wall section 2A and a bottom surface section 2B for closing at least one open end of the side wall section 2A. The driving electrodes 3A and 3B impress an electric field onto the piezoelectric body 2 to drive the piezoelectric body 2 in a mode where the side wall section 2A expands/contracts in the radial direction. According to the configuration, bending vibration is excited at the bottom face section 2B, since the bottom face section 2B is coupled physically to the side wall section 2A. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic transducer that transmits or receives ultrasonic waves by driving a piezoelectric body.

  As a conventional ultrasonic transducer, for example, a piezoelectric body is provided on the bottom surface of a bottomed cylindrical case, and the entire bottom surface of the case is bent and vibrated by driving the piezoelectric body (see, for example, Patent Document 1 and Patent Document 2). . By configuring the vibration plate portion with the plate-like case bottom surface and the piezoelectric body, the case bottom surface is indirectly bent by the spreading vibration of the piezoelectric body, thereby ensuring a large displacement of the case bottom surface.

JP 2001-326987 A Japanese Patent Laid-Open No. 2007-036301

  Generally, since the case bottom surface and the piezoelectric body are bonded with an adhesive, the difference in linear expansion coefficient between the case bottom surface and the piezoelectric body reduces the reliability, for example, the thermal stress acts to peel off the piezoelectric body. Moreover, since the adhesive used has temperature characteristics, the temperature range in which it operates with sufficient accuracy is narrowed. For example, when the ultrasonic transducer is left at a high temperature of 150 ° C. or higher for a long time, depending on the type of the adhesive, the adhesive is softened or carbonized, and the reliability is lowered.

  An object of the present invention is to provide an ultrasonic transducer capable of improving temperature stability while preventing a decrease in reliability due to environmental temperature.

The ultrasonic transducer according to the present invention includes a piezoelectric body and a drive electrode. The piezoelectric body is formed by integrally forming a cylindrical side wall portion and a bottom surface portion that closes at least one opening end of the side wall portion. The drive electrode applies an electric field to the piezoelectric body, and the piezoelectric body is driven in a mode in which the side wall portion of the piezoelectric body expands and contracts in the radial direction.
In this configuration, the side wall portion expands and contracts in the radial direction, so that bending vibration is excited on the bottom surface portion. The bending vibration is excited by being physically coupled to the vibration of the side wall portion, and has a larger displacement than a case where, for example, a plate-like piezoelectric element is vibrated by thickness longitudinal vibration or spread vibration. By adopting a structure in which the side wall portion and the bottom surface portion are integrated as a vibrating plate portion without adopting a structure in which the piezoelectric element and the bottom surface of the case are joined in this manner to form a vibrating plate portion, the linear expansion coefficient is reduced. Temperature stability can be improved while avoiding a decrease in reliability due to the environmental temperature of the ultrasonic transducer by avoiding the influence of differences and thermal deterioration of the adhesive.

It is preferable that the ultrasonic transducer of the present invention further includes a case and a buffer. The case accommodates the piezoelectric body by exposing the bottom surface portion from the inside of the case. The buffer is provided at a contact portion between the piezoelectric body and the case, and buffers vibration transmitted from the piezoelectric body to the case.
In this configuration, the buffer can prevent the piezoelectric body from being restrained by the case. Therefore, the expansion / contraction of the side wall portion and the displacement of the bottom surface portion can be prevented, and reverberation caused by the vibration of the piezoelectric body being transmitted to the case can be suppressed. Furthermore, since the piezoelectric body is protected by being accommodated in the case, the environment resistance of the ultrasonic transducer can be improved.

The bottom view shape of the bottom surface portion of the present invention is preferably a shape in which the aspect ratio of the short side passing through the center of the bottom surface portion is larger than 1 with respect to the long side passing through the center of the bottom surface portion.
In this configuration, the directivity of the ultrasonic waves is made anisotropic.

  According to the present invention, the bottom surface portion can be bent and vibrated by expanding and contracting the side wall portion in the radial direction. This bending vibration is excited because the bottom surface portion is physically coupled to the vibration of the side wall portion and is greatly displaced. Bending with a large displacement can be achieved by using a structure in which the side wall and bottom surface are integrated as a diaphragm without adopting a structure in which the piezoelectric element and the bottom of the case are joined to form a diaphragm. While utilizing the vibration, it is possible to avoid the influence of the difference in the linear expansion coefficient and the thermal deterioration of the adhesive, thereby preventing the reliability of the ultrasonic transducer from being lowered based on the environmental temperature and improving the temperature stability.

1 is a schematic diagram illustrating a configuration example of an ultrasonic transducer according to an embodiment of the present invention. It is a figure which illustrates the result of the finite element analysis of the ultrasonic transducer of FIG. It is a figure which illustrates the frequency characteristic of the ultrasonic transducer of FIG. It is a figure which illustrates the temperature characteristic of the ultrasonic transducer of FIG. It is a figure explaining the piezoelectric material polarization process of the ultrasonic transducer of FIG. It is a figure explaining the other structural example of the ultrasonic transducer which concerns on embodiment of this invention. It is a figure explaining the other structural example of the ultrasonic transducer which concerns on embodiment of this invention. It is a figure explaining the other structural example of the ultrasonic transducer which concerns on embodiment of this invention.

Hereinafter, an ultrasonic transducer according to an embodiment of the present invention will be described.
FIG. 1A is a schematic cross-sectional view of an ultrasonic transducer 1 according to this embodiment.
This ultrasonic transducer 1 is used for automobile back sonar, corner sonar, parking spot, etc., and is used as a transmitter for transmitting ultrasonic waves to a target or as a receiver for detecting a reflected wave from the target. Used for devices.

  The ultrasonic transducer 1 includes a piezoelectric body 2, driving electrodes 3A and 3B, a case 4, a buffer body 5, and terminal portions 6A and 6B. FIG. 1B is a bottom view of the piezoelectric body 2. The piezoelectric body 2 has a bottomed cylindrical shape and includes a side wall portion 2A and a bottom surface portion 2B. Side wall 2A is cylindrical. The bottom surface portion 2B is a flat plate shape perpendicular to the axial direction of the side wall portion 2A, and closes the top surface side opening end of the side wall portion 2A. The piezoelectric body 2 has the axial direction of the side wall 2A as the polarization direction. The drive electrode 3A is provided on the top surface of the bottom surface portion 2B, and the drive electrode 3B is provided on the bottom surface of the side wall portion 2A. The case 4 has a bottomed cylindrical shape that accommodates the piezoelectric body 2 in the opening, and the opening end on the bottom side is closed. The case 4 may have a structure in which a hole communicating with the opening of the piezoelectric body is provided on the bottom surface. In addition, a sound absorbing material may be provided in a space surrounded by the piezoelectric body 2 and the case 4. The buffer body 5 is an elastic body such as silicone rubber, and is provided between the case 4 and the side surface of the side wall portion 2 </ b> A and between the case 4 and the bottom surface of the side wall portion 2 </ b> A. The vibration of the piezoelectric body 2 is buffered by preventing direct contact with 4. The buffer body 5 may not be provided on the side surface of the side wall portion 2A, but only on the bottom surface of the side wall portion 2A. The terminal portion 6 </ b> A is connected to the driving electrode 3 </ b> A at the top surface side end portion, and the bottom surface side end portion projects from the bottom surface of the case 4. The terminal portion 6B is connected to the drive electrode 3B at the end on the top surface side, and the end portion on the bottom surface side protrudes from the bottom surface of the case 4. The terminal portions 6A and 6B are formed using a metal terminal plate, an insert mold or the like, and the piezoelectric body 2 to which the terminal portions 6A and 6B are connected is accommodated in the opening portion of the case 4, and the case 4 The terminal portions 6A and 6B are fitted into the provided holes.

  When this ultrasonic transducer 1 is used as a transmitter, an electric field is applied in the axial direction of the side wall portion 2A, which is the polarization direction, by applying a drive signal between the drive electrodes 3A and 3B. A spreading vibration occurs in which the portion 2A expands and contracts in the radial direction. Then, since the thickness in the axial direction of the bottom surface portion 2B is smaller than the thickness in the axial direction of the side wall portion 2A, bending vibration is excited in the bottom surface portion 2B and ultrasonic waves are transmitted. When used as a wave receiver, the piezoelectric body 2 receives an ultrasonic wave and vibrates to generate a received signal between the drive electrodes 3A and 3B.

  Since the piezoelectric body 2 is accommodated in the case 4, the ultrasonic transducer 1 has high environmental resistance. Further, since the buffer body 5 is provided between the piezoelectric body 2 and the case 4 to buffer the vibration, it is possible to avoid the case 4 from restraining the piezoelectric body 2. Further, reverberation in the case caused by the vibration of the piezoelectric body 2 being transmitted to the case 4 can be suppressed, and displacement of the bottom surface portion 2B can be prevented from being hindered.

FIG. 2 is a diagram illustrating the result of the finite element analysis of the ultrasonic transducer 1.
The side wall portion 2A and the bottom surface portion 2B have an integral structure. When the side wall portion 2A spreads and vibrates, the bottom surface portion 2B has a smaller thickness than the side wall portion 2A, and thus is easily deformed, and tensile stress is applied from the side wall portion 2A. As a result, bending vibration having a vibration node near the boundary between the side wall portion 2A and the bottom surface portion 2B is excited to the bottom surface portion 2B.

  Since this bending vibration is excited by physical coupling between the side wall portion 2A and the bottom surface portion B, for example, a plate-like piezoelectric element has a large vibration displacement due to thickness longitudinal vibration or spreading vibration, and the amplitude of the ultrasonic wave is increased. Can be big.

FIG. 3 is a diagram illustrating frequency characteristics in the ultrasonic transducer 1. The solid line in the figure indicates the impedance characteristic, and the broken line in the figure indicates the phase characteristic. The left vertical axis represents impedance | Z |, the right vertical axis represents phase θz, and the horizontal axis represents frequency.
The ultrasonic transducer 1 has resonance antiresonance frequencies in the vicinity of frequencies of about 55 kHz, 100 kHz, and 157 kHz. The frequency of about 55 kHz is the resonance frequency of bending vibration in the bottom surface portion 2B, and the frequency of about 157 kHz is the resonance frequency of spread vibration in the side wall portion 2A. The frequency of about 100 kHz is a spurious mode due to the above two vibrations. Due to such frequency characteristics, when the ultrasonic transducer 1 is driven with a drive signal having a frequency of 157 kHz, the side wall portion 2A spreads and vibrates, and bending vibration is excited on the bottom surface portion 2B at a frequency of about 55 kHz.

  FIG. 4 is a diagram for explaining temperature characteristics of an ultrasonic transducer that employs a structure in which a conventional piezoelectric element and a bottom surface of a case are joined to form a diaphragm, and the ultrasonic transducer of this embodiment. 4A is a graph showing the change rate of the resonance frequency based on 20 ° C., and FIG. 4B is a graph showing the change rate of the sensitivity based on 20 ° C. The solid line in the figure shows the temperature characteristic of the ultrasonic transducer of this embodiment, and the broken line in the figure shows the temperature characteristic of the conventional ultrasonic transducer.

  The conventional structure has a temperature characteristic in which the resonance frequency changes approximately in proportion to the temperature change due to the difference in the linear expansion coefficient of the material used between the piezoelectric element and the case bottom and the adhesive used between the piezoelectric element and the case bottom. However, in this embodiment, a single piezoelectric body is used, and the resonance frequency is constant even when there is a temperature change.

  In addition, the conventional structure is a structure in which different materials are joined by an adhesive, and when the environmental temperature exceeds the glass transition point, the adhesive is denatured and the sensitivity is greatly reduced. On the other hand, since the present embodiment uses a single piezoelectric body, it is not necessary to use an adhesive, and the sensitivity is substantially constant even when there is a temperature change.

  Therefore, in the ultrasonic transducer of this embodiment, temperature stability can be improved while preventing a decrease in reliability based on the environmental temperature.

FIG. 5 is a state diagram for explaining a piezoelectric body polarization method in the ultrasonic transducer 1.
The piezoelectric body 2 is produced by firing an unfired body of a piezoelectric ceramic material such as lead zirconate titanate, for example, and the fired body is polarized and used. At the time of polarization, there is a risk that polarization strain concentrates at the corners in the opening due to the application of an electric field and cracks occur. Therefore, in the present embodiment, electrodes are formed on all the planes that intersect the axial direction of the opening of the piezoelectric body 2, and voltages V1 and V2 that differ according to the dimensions in the axial direction are applied. Polarization is performed while controlling the electric field intensity to be within a predetermined range. After polarization, the electrode provided on the bottom of the opening is removed. Thereby, the danger that a crack will generate | occur | produce at the time of polarization can be suppressed.

  It is also possible to produce the piezoelectric body 2 by forming electrodes on both main surfaces of the plate-like piezoelectric body, and applying an electric field to polarize and then punching out the opening. Therefore, the ultrasonic transducer of the present invention is not limited to the polarization method described above, and any polarization method may be adopted. In addition, the electrode to be formed on the piezoelectric body can be manufactured by baking after applying the conductive paste, patterning using a resist, thin film forming method such as sputtering or vapor deposition, or plating method. Any electrode forming method may be employed.

  Next, another configuration example of the piezoelectric body will be described.

  FIG. 6 is a diagram illustrating a variation example of the cross-sectional shape of the piezoelectric body.

  FIG. 6A is a cross-sectional view of a piezoelectric body having a configuration in which the opening bottom surface is tapered. FIG. 6B is a cross-sectional view of a piezoelectric body having a configuration in which a protrusion is attached to the bottom surface of the opening. FIG. 6C is a cross-sectional view of a piezoelectric body having a configuration in which the bottom surface of the opening has a concave shape. FIG. 6D is a cross-sectional view of a piezoelectric body having a configuration in which the bottom surface of the opening is convex. FIG. 6E is a cross-sectional view of a piezoelectric body having a configuration in which the top surface of the bottom surface portion is convex. FIG. 6F is a cross-sectional view of a piezoelectric body having a concave bottom surface.

  The ultrasonic transducer of the present invention may be configured using the piezoelectric body as described above, and the directivity of the ultrasonic waves can be controlled by using these piezoelectric bodies.

FIG. 7 is a diagram illustrating a variation example of the drive electrode.
FIG. 7A shows an example in which drive electrodes are arranged on the bottom surface top surface and the side wall surface bottom. FIG. 7B shows an example in which drive electrodes are arranged on the bottom surface top surface, bottom surface bottom surface, and side wall surface bottom surfaces. FIG. 7C shows an example in which drive electrodes are arranged on the bottom surface top surface-side wall portion outer surface and the bottom surface bottom surface-side wall inner surface. Even when the electrodes are formed on the entire surface of the piezoelectric body as shown in FIG. 7C, the electrodes can be driven by selecting the electrodes for polarization and the electrodes for driving.

  In any of the examples, it is possible to excite the bending vibration on the bottom surface portion by ensuring a large spread vibration of the side wall portion.

FIG. 8 is a diagram for explaining a variation of the shape of the piezoelectric body viewed from the bottom.
FIG. 8A is a bottom view of a piezoelectric body whose bottom view shape is a square. FIG. 8B is a bottom view of the piezoelectric body whose bottom view shape is a rectangle. FIG. 8C is a bottom view of a piezoelectric body whose bottom view shape is elliptical.
In a bottom view shape such as a square or a circle, when the aspect ratio of the short side passing through the center of the bottom surface part is 1 with respect to the long side passing through the center of the bottom surface part, the directivity of the ultrasonic wave is equal It has a direction. On the other hand, in a bottom view shape such as a rectangle or an ellipse, if the aspect ratio of the short side passing through the center of the bottom surface part is greater than 1 with respect to the long side passing through the center of the bottom surface part, the direction of the ultrasonic wave Anisotropy can be given to sex.

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer 2, 12, 22, 32, 42, 52, 62, 72, 82, 92 ... Piezoelectric body 2A ... Side wall part 2B ... Bottom face part 3A, 3B ... Drive electrode 4 ... Case 5 ... Buffer 6A, 6B ... Terminal part

Claims (4)

A piezoelectric body integrally formed with a cylindrical side wall and a bottom surface that closes at least one open end of the side wall;
An ultrasonic transducer comprising: a drive electrode for applying an electric field to the piezoelectric body. The ultrasonic transducer according to claim 1, wherein the side wall portion of the piezoelectric body is driven in a mode in which the side wall portion expands and contracts in a radial direction. A case in which the bottom surface portion is exposed from inside the case and the piezoelectric body is accommodated;
The ultrasonic transducer according to claim 1, further comprising a buffer provided at a contact portion between the piezoelectric body and the case and buffering vibration transmitted from the piezoelectric body to the case.   The said bottom face part is bottom view shape, and the aspect ratio of the short side which passes along the center of a bottom face part is larger than 1 with respect to the long side which passes along the center of a bottom face part. Ultrasonic transducer.

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