JP4415445B2 - Ultrasonic transducer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer used as an element of an electronic component such as an ultrasonic sensor.
[0002]
[Prior art]
Conventionally, for example, as disclosed in Japanese Utility Model Laid-Open No. 3-59798, there is an ultrasonic transducer formed by fixing a conical funnel-shaped resonator in the vicinity of a node of a piezoelectric vibrator. This piezoelectric vibrator is formed by bonding a piezoelectric plate and a metal plate with an adhesive. As the piezoelectric body, for example, piezoelectric ceramics are used, as the metal, for example, 42 alloy is used, and as the adhesive, for example, an epoxy adhesive is used.
[0003]
[Problems to be solved by the invention]
However, the linear expansion coefficient of 42 alloy is generally larger than that of piezoelectric ceramics. Further, the linear expansion coefficient of an adhesive mainly composed of a synthetic resin is generally larger than that of a metal such as 42 alloy or a piezoelectric body such as piezoelectric ceramic. For this reason, the conventional piezoelectric vibrator made by laminating these materials tends to stretch greatly in one direction on one side of the piezoelectric ceramic, so that when the temperature changes, the stress that tends to warp in one direction in the thickness direction is reduced. As a result, the change in the resonance frequency when the temperature changes is likely to increase. If the resonance frequency change due to the temperature of the piezoelectric vibrator is large, there is a disadvantage that the temperature-sensitivity change characteristic and the temperature-sound pressure change characteristic of an ultrasonic transducer using the piezoelectric vibrator deteriorate.
[0004]
Therefore, the main object of the present invention is to provide an ultrasonic transducer having good temperature-sensitivity characteristics and temperature-sound pressure change characteristics.
[0005]
[Means for Solving the Problems]
Ultrasonic transducer according to the present invention, an ultrasonic transducer comprising a piezoelectric transducer formed by bonding a piezoelectric element and a metal with an adhesive, and a funnel-shaped resonator is secured to the piezoelectric transducer, the adhesive The agent has a larger linear expansion coefficient than that of the piezoelectric body, and the metal has a smaller linear expansion coefficient than that of the piezoelectric body. The ultrasonic transducer can be used as an element of an electronic component.
In the ultrasonic transducer according to the present invention, an adhesive having a linear expansion coefficient larger than that of the piezoelectric body is formed by integrally bonding the piezoelectric body and a metal having a smaller linear expansion coefficient than the piezoelectric body, thereby changing the temperature. The elongation of the adhesive due to is suppressed by the metal, and as a result, the stress that tends to warp the piezoelectric body is reduced. As a result, the amount of frequency change due to the temperature of the ultrasonic transducer is reduced, and the temperature-sensitivity characteristics and temperature-sound pressure change characteristics are improved.
[0006]
The above object, other objects, features, and advantages of the present invention will become more apparent from the following detailed description of the embodiments of the present invention with reference to the drawings.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The ultrasonic transducer according to the present invention can be used as an element of an electronic component such as an ultrasonic sensor for detecting an obstacle or a medical echo device. Examples used for the ultrasonic sensor will be described below. .
[0008]
FIG. 1 is a cross-sectional view showing an embodiment of an ultrasonic sensor using an ultrasonic transducer according to the present invention.
The ultrasonic sensor 10 includes a base member 12. Base member 12 is formed of an insulating material such as synthetic resin. An ultrasonic transducer 16 is fixed on the base member 12 via a buffer material 14 for preventing the vibration of the piezoelectric vibrating body from being disturbed as much as possible. As the buffer material 14, for example, a silicone resin is used.
[0009]
The ultrasonic transducer 16 includes a piezoelectric vibrator 24. The piezoelectric vibrating body 24 is formed by bonding a piezoelectric plate 18 and a metal plate 20 with an adhesive 22. The piezoelectric plate 18 is made of, for example, piezoelectric ceramics. The metal plate 20 is formed of a metal having a linear expansion coefficient smaller than that of the piezoelectric plate 18. As such a metal, for example, Invar is selected. As the adhesive 22, a general synthetic resin adhesive can be used, and for example, an epoxy adhesive can be used. Further, a conical funnel-shaped resonator (horn) 26 is fixed to the metal plate 20 in the vicinity of the node of the piezoelectric vibrating body 24.
[0010]
Input / output terminals 28 a and 28 b are attached to the base member 12. One input / output terminal 28a is electrically connected to the metal plate 20 via a lead wire, and the other input / output terminal 28b is connected to the piezoelectric plate 18 via a lead wire. Further, a cover member 30 for protecting the ultrasonic transducer 16 is attached on the base member 12.
[0011]
FIG. 2 is a graph showing the relationship between the temperature of the piezoelectric vibrating body and the amount of change in resonance frequency. In FIG. 2, the example of the present application means that our ceramics having a linear expansion coefficient of 2.0 ppm / ° C. is processed into a plate shape having a size of 5.6 × 5.6 × 0.2 mm, and the ceramic plate is linearly expanded The piezoelectric vibrator 24 is bonded to a disc-shaped invar having a linear expansion coefficient of 1.2 ppm / ° C., a diameter of 8.4 mm, and a thickness of 0.3 mm with an epoxy adhesive of 60 ppm / ° C.
The ceramic alone is obtained by processing our ceramics having a linear expansion coefficient of 2.0 ppm / ° C. into a plate shape having a size of 5.6 × 5.6 × 0.2 mm.
Furthermore, in the conventional example, our ceramics having a linear expansion coefficient of 2.0 ppm / ° C. are processed into a plate shape having a size of 5.6 × 5.6 × 0.2 mm, and the ceramic plate is subjected to a linear expansion coefficient of 60 ppm / ° C. The piezoelectric vibration member is bonded to a disk-shaped 42 alloy having a linear expansion coefficient of 4.0 to 4.7 ppm / ° C., a diameter of 8.4 mm, and a thickness of 0.3 mm.
[0012]
As is clear from FIG. 2, the change amount of the resonance frequency of the ceramic alone at 110 ° C. is −1%, but the change amount of the resonance frequency of the conventional piezoelectric vibrator using 42 alloy as the metal plate is −2%. It shows a large value of%. This is because the linear expansion coefficient (4.0 to 4.7 ppm / ° C.) of 42 alloy is larger than the linear expansion coefficient (2.0 ppm / ° C.) of the piezoelectric ceramic plate. This is considered to be due to the fact that it has a linear expansion coefficient (60 ppm / ° C.) that is one digit larger than 42 alloys.
On the other hand, the resonance frequency change amount at 110 ° C. of the piezoelectric vibrating body 24 of the embodiment of the present application is −1.5%, and the resonance frequency change amount is reduced as compared with the piezoelectric vibrating body of the conventional example. This is because in the piezoelectric vibrating body 24 of the present embodiment, the elongation of the epoxy adhesive at the time of temperature change is suppressed by the invar having a smaller linear expansion coefficient than that of the piezoelectric ceramic, and as a result, the stress that tries to warp the piezoelectric ceramic is reduced. It is thought that it is because.
[0013]
FIG. 3 is a graph showing the relationship between the temperature of the ultrasonic sensor and the sensitivity change. In FIG. 3, the embodiment of the present application is the ultrasonic sensor 10 including the ultrasonic transducer 16 using the piezoelectric vibrator 24 of the above-described embodiment of the present invention used for measuring the data of FIG. 2. On the other hand, the conventional example is an ultrasonic sensor using the above-described conventional piezoelectric vibrator used for measuring the data of FIG. As is apparent from FIG. 3, the sensitivity change of the ultrasonic sensor 10 of the present embodiment is improved by 2 dB at 110 ° C., for example, as compared with the conventional ultrasonic sensor.
[0014]
FIG. 4 is a graph showing the relationship between the temperature of the ultrasonic sensor and the change in sound pressure. In FIG. 4, the examples of the present application and the comparative example are the same as those used for measuring the data of FIG. As is apparent from FIG. 4, the ultrasonic sensor 10 of this embodiment has an improvement in sound pressure change of 2 dB at 110 ° C., for example, compared to the conventional ultrasonic sensor.
[0015]
【The invention's effect】
According to the present invention, since the resonance frequency change of the piezoelectric vibrating body due to temperature change is reduced, an ultrasonic transducer having good temperature-sensitivity characteristics and temperature-sound pressure change characteristics, and an electronic component such as an ultrasonic sensor equipped with the ultrasonic transducer Can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an ultrasonic sensor using an ultrasonic transducer according to the present invention.
FIG. 2 is a graph showing the relationship between the temperature of a piezoelectric vibrating body and the amount of change in resonance frequency.
FIG. 3 is a graph showing the relationship between temperature and sensitivity change of an ultrasonic sensor.
FIG. 4 is a graph showing the relationship between the temperature of an ultrasonic sensor and sound pressure change.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Ultrasonic sensor 12 Base member 14 Buffer material 16 Ultrasonic transducer 18 Piezoelectric board 20 Metal plate 22 Adhesive 24 Piezoelectric vibrator 26 Resonator 28a, 28b Input / output terminal 30 Cover member

Claims (2)

An ultrasonic transducer including a piezoelectric vibrator formed by bonding a piezoelectric body and a metal with an adhesive, and a funnel-shaped resonator fixed to the piezoelectric vibrator,
The ultrasonic transducer, wherein the adhesive has a larger linear expansion coefficient than the piezoelectric body, and the metal has a smaller linear expansion coefficient than the piezoelectric body. An electronic component comprising the ultrasonic transducer according to claim 1.

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