JPH0865795A - Ultrasonic sensor - Google Patents

Abstract

PURPOSE: To increase output sound pressure. CONSTITUTION: For this ultrasonic sensor, a piezoelectric element is fixed to an acoustic matching layer 15 composed of resin in which glass balloon is mixed. Heating means 20, 22 and 23 for heating the acoustic matching layer 15 are provided. Also, fiber oriented so as to convert force in a direction along the radiation surface of the acoustic matching layer 15 to the force in the direction vertical to the radiation surface is provided in the acoustic matching layer 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor, and more particularly to an ultrasonic sensor for transmitting or receiving ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, there is an ultrasonic sensor for detecting an object and measuring a distance by using ultrasonic waves. For example, Japanese Patent Application Laid-Open No. 5-244692 discloses an ultrasonic sensor including a piezoelectric element, a vibrating case, a resonator, a base and a vibration isolator, and driving the vibrating case by the piezoelectric element to transmit ultrasonic waves. ing. The object of this publication is to obtain a stable output by forming a groove in the outer peripheral edge portion of the piezoelectric element and absorbing excess adhesive material when the piezoelectric element is bonded to the vibration case by the groove.

[0003]

Although the conventional ultrasonic sensor can obtain a stable output sound pressure, there is no disclosure about further enhancement of the output sound pressure for use in a vehicle.

In the case of an on-vehicle ultrasonic sensor for measuring the ground speed and vehicle height of a vehicle, when the road surface is wet asphalt or the like, the reflection of ultrasonic waves by the road surface becomes small, so that the output sound pressure must be increased. However, the conventional ultrasonic sensor has a problem that the output sound pressure is still insufficient.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ultrasonic sensor for increasing the output sound pressure by heating an acoustic matching layer or the like.

[0006]

According to a first aspect of the present invention, in an ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin mixed with glass balloon, a heating means for heating the acoustic matching layer is provided. Set up.

According to a second aspect of the present invention, there is provided an ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin,
Fibers are provided in the acoustic matching layer that are oriented to convert forces along the emitting surface of the acoustic matching layer into forces perpendicular to the emitting surface.

According to a third aspect of the present invention, in an ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer and the acoustic matching layer is supported by a body portion, the acoustic matching layer has a minute gap with respect to the body portion. Supported.

According to a fourth aspect of the present invention, in an ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin mixed with a glass balloon, the glass balloon has a high density on the radiation surface of the acoustic matching layer. Distribute.

[0010]

According to the first aspect of the present invention, by heating the acoustic matching layer, the output sound pressure can be increased with the elastic modulus of the acoustic matching layer being in an optimum state.

According to the second aspect of the present invention, since the fibers provided in the acoustic matching layer convert the force in the direction along the radiation surface due to the driving of the piezoelectric element to the direction perpendicular to the radiation surface,
The output sound pressure increases by the amount converted.

According to the third aspect of the present invention, since the acoustic matching layer has a minute gap with respect to the body portion, the vibration of the acoustic matching layer is not limited by the body portion and can freely vibrate to increase the output sound pressure. To do.

In the invention according to claim 4, since the glass balloons are distributed at a high density on the radiation surface of the acoustic matching layer, the acoustic impedance of the acoustic matching layer becomes gradually smaller toward the radiation surface and becomes smaller than that of air. Is improved, the output sound pressure for reducing the loss is increased, and the water-repellent effect of the radiation surface is increased by the water-repellent treatment of the glass balloon.

[0014]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, the ultrasonic sensor is generally composed of a base 10, a support 11, a piezoelectric element 14, and an acoustic matching layer 15. One end of the support 11 is fixed to the base portion 10, and the acoustic matching layer 15 is fixed to the other end of the support 11. The piezoelectric element 14 is fixed to the driving surface (lower surface) 15a of the acoustic matching layer 15.

The acoustic matching layer 15 is formed by mixing an epoxy resin with a hollow glass balloon having a diameter of several tens of microns to form a disk shape. This is because if you use only resin, the weight will be heavy and the acoustic impedance will be large compared to air, so you can not match the acoustic impedance with air, so mix the glass balloon to reduce the weight and match the acoustic impedance with air. Is taking.

A heater 20 is provided on the outer periphery of the acoustic matching layer 15.
Is provided. This heater 20 is a heater control circuit 2
By the on / off control of No. 2, when the power is turned on, power is supplied from the heater power supply 23 to heat the acoustic matching layer 15.

The piezoelectric element 14 is made of, for example, a PZT (lead zirconate titanate) type piezoelectric ceramic and is formed in a disk shape. Terminals 14 provided on both sides of the piezoelectric element 14
A signal having a predetermined frequency is supplied from the signal source 24 to a and 14b. The piezoelectric element 14 expands and contracts mainly in the radial direction (arrow X direction) and vibrates by the application of the signal. The acoustic matching layer 15 vibrates due to the vibration of the piezoelectric element 14, and ultrasonic waves are emitted from the radiation surface (upper surface) 15b of the acoustic matching layer 15.

The piezoelectric element 14 and the acoustic matching layer 15 are respectively provided with temperature sensors 25 and 26, and the temperature detected by each of the temperature sensors 25 and 26 is the heater control circuit 22.
Is supplied to

Here, the acoustic matching layer 15 is mixed with a glass balloon in order to reduce the acoustic impedance as described above. For this reason, the acoustic matching layer 15 has a larger elastic modulus, that is, is harder than when it is formed of a resin alone. A signal is supplied from the signal source 24 to the piezoelectric element to heat the heater 2.
When the acoustic matching layer 15 is heated by energizing to 0, the temperature of the acoustic matching layer 15 rises as shown by the solid line I in FIG. 2, and the sound pressure output from the ultrasonic sensor is also shown by the solid line II in FIG. , The temperature of the acoustic matching layer 15 peaks in the range from Tb to Ta, and the temperature is Tb (for example, 40 ° C.) or lower, and Ta
It becomes smaller above (for example, 60 ° C.).

The temperature / elastic modulus characteristic of the acoustic matching layer 15 is as shown by the solid line in FIG. Assuming that the elastic modulus of the acoustic matching layer 15 near 0 ° C. is A, the elastic modulus at the temperature Tb is approximately 0.9 A and the elastic modulus at the temperature Ta is approximately 0.7 A.

In the heater control circuit 22, the heater power supply 23 is turned on when the temperature detected by the temperature sensor 26 is Tb or lower,
When the detected temperature is equal to or higher than Ta, the heater power supply 23 is controlled to be turned off. Further, when the temperature of the piezoelectric element 14 rises, the resonance frequency shifts. Therefore, in the heater control circuit 22, the temperature Tc at which the resonance frequency of the piezoelectric element 14 deviates by 1 KHz or more is compared with the detection temperature of the temperature sensor 25, and when the detection temperature becomes Tc or more, the heater power supply 23 is forcibly turned off. The deviation of the resonance frequency is suppressed.

As a result, in contrast to the frequency / sound pressure characteristic of the conventional ultrasonic sensor shown by the solid line III in FIG. 4, the frequency / sound pressure characteristic of the above embodiment is improved as shown by the solid line IV.

By the way, the piezoelectric element 14 vibrates mainly in the radial direction (the direction of arrow X in FIG. 1), whereby the acoustic matching layer 1
5 causes bending stress, the acoustic matching layer 15 vibrates in the vertical direction (direction of arrow Y) and emits ultrasonic waves, and the output sound pressure is proportional to the vertical amplitude of the acoustic matching layer 15.

Therefore, in order to efficiently convert the radial vibration of the piezoelectric element 14 into the vertical vibration of the acoustic matching layer 15, the acoustic matching layer 15 has a non-stretchable fiber 30 as shown in FIGS. 5 (A) and 5 (B). Are embedded to give the acoustic matching layer 15 anisotropy. As the non-stretchable fiber 30, glass fiber such as SiC is used, and the non-stretchable fiber 30 is used as the non-stretchable fiber 30 as shown in the two-dimensional view of FIG. 5A and the three-dimensional view of FIG. 5B.
Are concentrated in the center of the circle, spread in the peripheral direction at the radiation surface 15b, and oriented in a conical shape. At the time of manufacture, the non-stretchable fibers 30 are arranged in a conical shape as described above and placed in a mold, and an epoxy resin mixed with a glass balloon is poured into the mold to be formed. The perspective view is shown in FIG.

The acoustic matching layer 1 is generated by the vibration of the piezoelectric element 14.
When 5 vibrates in the radial direction and a vector a is added to the non-stretchable fiber 30 as shown in FIG. 5A, the vector a is decomposed into a component b in the longitudinal direction of the fiber 30 and a component c in the direction orthogonal thereto. Since the fiber 30 is non-stretchable, the component c remains, and the acoustic matching layer 15 vibrates vertically due to the component c.

As a result, the amplitude of the vertical vibration of the acoustic matching layer 15 is increased, and the output sound pressure is increased.

Further, as shown in FIG. 1, when the acoustic matching layer 15 is fixed to the support 11, the vibration of the acoustic matching layer 15 is limited and the amplitude becomes small. Therefore, as shown in FIG. 7, a body portion is formed by the support body 16 and the frame body 17 instead of the support body 10. One end of the support 16 is fixed to the base 10. Next, the acoustic matching layer 15 to which the piezoelectric element 14 is fixed is placed on the support 16, and the annular frame 17 is fixed to the other end of the support 16. The frame body 17 has a collar portion 17a,
As a result, the peripheral portion of the acoustic matching layer 15 has a structure in which it is sandwiched between the support 16 and the frame 17.
The height from 6 to the flange portion 17a is set to be several tens to several hundreds of microns larger than the height of the acoustic matching layer 15, and the inner diameter of the frame body 17 is set to several tens to several hundreds microns from the outer diameter of the acoustic matching layer 15. It is said to be large.

Therefore, the vibration of the acoustic matching layer 15 is not restricted and the output sound pressure increases.

When an ultrasonic sensor is used for vehicle mounting such as vehicle height measurement and ground speed measurement, if oil, mist, water or the like adheres to the acoustic matching layer 15, the ultrasonic wave is reflected or diffused, resulting in output sound pressure and sensitivity. Is reduced. For this reason, the water-repellent treatment of the acoustic matching layer 15 is indispensable for in-vehicle use. The water repellent treatment is, for example, fluoroalkylsilane 0.1 + tetraethoxylane 0.1.
After immersing the solution of No. 9, heating to about 300 ° C. is performed. However, as shown in FIG. 8, the acoustic matching layer 15 is formed by uniformly mixing the glass balloon 35 with the epoxy resin 36. Since the epoxy resin is used as the base material, the acoustic matching layer 15 is deformed by heat treatment. Therefore, the water repellent treatment cannot be performed.

Therefore, in this embodiment, first, the glass balloon 35 is subjected to a water repellent treatment. Since the material of the glass balloon is glass, water repellent treatment is possible. After that, the glass balloons 35 are mixed with the epoxy resin 36, and the glass balloons 35 are non-uniformly distributed by centrifugation or the like so that the glass balloons 35 have a high density on the radiation surface 15b and a low density on the driving surface 15a as shown in FIG. Solidify.

As a result, the radiation surface 1 of the acoustic matching layer 15 is
Since the water-repellent glass balloons 35 are present at a high density on 5b, the water-repellent effect of the radiation surface 15b of the acoustic matching layer 15 becomes large, and the output sound pressure and sensitivity due to the adhesion of oil, mist, water, etc. It can prevent the deterioration. By the way, even when the glass balloon 35 is not subjected to the water repellent treatment, the glass balloon density of the acoustic matching layer 15 is changed from the driving surface 15a to the radiation surface 1.
By inclining the acoustic matching layer 15 to have a high density toward 5b, the acoustic impedance of the acoustic matching layer 15 gradually decreases toward the radiating surface, the matching with air is improved, and the output sound pressure for reducing loss is reduced. Will increase.

[0032]

As described above, according to the first aspect of the present invention, by heating the acoustic matching layer, the elastic modulus of the acoustic matching layer can be optimized and the output sound pressure can be increased. According to the invention described in claim 2, the force provided in the acoustic matching layer in the direction along the radiation surface due to the driving of the piezoelectric element is converted into the direction perpendicular to the radiation surface. Only the output sound pressure increases.

Further, according to the third aspect of the invention, since the acoustic matching layer has a minute gap with respect to the body portion, the vibration of the acoustic matching layer is not limited by the body portion,
It vibrates freely and the output sound pressure increases.

According to the invention described in claim 4, since the glass balloons are distributed at a high density on the radiation surface of the acoustic matching layer, the acoustic impedance of the acoustic matching layer gradually decreases toward the radiation surface. It improves the consistency with the air, increases the output sound pressure to reduce the loss, and the water repellent treatment of the glass balloon increases the water repellent effect of the radiation surface, which is extremely useful in practice. is there.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a sound level of an acoustic matching layer and an output sound pressure.

FIG. 3 is a diagram showing temperature / elastic modulus characteristics of an acoustic matching layer.

FIG. 4 is a diagram showing frequency / sound pressure characteristics of an acoustic matching layer.

FIG. 5 is a diagram for explaining the structure of an acoustic matching layer.

FIG. 6 is a diagram for explaining the structure of an acoustic matching layer.

FIG. 7 is a configuration diagram of an embodiment of the present invention.

FIG. 8 is a diagram for explaining the structure of an acoustic matching layer.

FIG. 9 is a diagram for explaining the structure of an acoustic matching layer.

[Explanation of symbols]

 10 Base Part 11 Support 14 Piezoelectric Element 15 Acoustic Matching Layer 15b Radiating Surface 20 Heater 22 Heater Control Circuit 23 Heater Power Supply 24 Signal Source 25, 26 Temperature Sensor 30 Non-Expandable Fiber 35 Glass Balloon 36 Resin

Claims (4)

[Claims] 1. An ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin mixed with glass balloons, wherein heating means for heating the acoustic matching layer is provided. 2. An ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin, and fibers oriented so as to convert a force along a radiation surface of the acoustic matching layer into a force in a direction perpendicular to the radiation surface. An ultrasonic sensor, wherein: is provided on the acoustic matching layer. 3. An ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer and the acoustic matching layer is supported by a body portion, wherein the acoustic matching layer is supported with a minute gap with respect to the body portion. Ultrasonic sensor. 4. In an ultrasonic sensor in which a piezoelectric element is fixed to an acoustic matching layer made of resin mixed with glass balloons, water-repellent treated glass balloons are distributed so as to have a high density on the radiation surface of the acoustic matching layer. An ultrasonic sensor characterized in that.