Ultrasonic sensor having vibrator mounted on substrate

Abstract

An ultrasonic sensor composed of a substrate and a piezoelectric vibrator mounted on the substrate is advantageously used as a sensor for detecting a distance to an object located in front of an automotive vehicle. Ultrasonic waves transmitted from the sensor are reflected by the object, and the reflected waves are received by the sensor. Based on the reflected waves, the distance from the vehicle to the object is calculated. To reduce rigidity and thereby to lower a resonant frequency of the substrate to a desirable level, grooves are formed in the substrate. A thickness of the substrate is not reduced to maintain its mechanical strength against an impact force. A resonant frequency which is desirable to realize a sufficiently high directivity and sensitivity is obtained in this manner without enlarging a size of the ultrasonic sensor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing an ultrasonic sensor according to the present invention, viewed from a first surface of a substrate on which a vibrator is mounted;

FIG. 1B is a cross-sectional view showing the ultrasonic sensor, taken along line 1B-1B shown in FIG. 1A;

FIG. 2A is a plan view showing a modified form of the ultrasonic sensor, viewed from a first surface of a substrate on which a vibrator is mounted;

FIG. 2B is a cross-sectional view showing the modified form of the ultrasonic sensor, taken along line IIB-IIB shown in FIG. 2A;

FIGS. 3A-3D show variously modified forms of the ultrasonic sensor shown in FIG. 1A;

FIGS. 4A-4B show variation 1 of the embodiment of the present invention, in which through-holes are formed in the substrate;

FIGS. 5A-5B show variation 2 of the embodiment of the present invention, in which cutout portions are formed along side surfaces of the substrate;

FIG. 6 shows variation 3 of the embodiment of the present invention, in which grooves formed in the substrate are filled with filler;

FIGS. 7A-7D show variation 4 of the embodiment of the present invention, in which grooves are formed on the second surface of the substrate; and

FIG. 8 is a cross-sectional view showing a conventional ultrasonic sensor mounted on a vehicle body member.

Claims

1. An ultrasonic sensor comprising: a substrate for transmitting and receiving ultrasonic waves; anda vibrator, mounted on the substrate, for converting electrical signals to the ultrasonic waves to be transmitted and for converting the ultrasonic waves received to electrical signals, wherein:the vibrator is mounted on a first surface of the substrate; andhollow spaces open to the second surface, opposite to the first surface, are formed in the substrate thereby to reduce rigidity of the substrate.

2. The ultrasonic sensor as in claim 1, wherein the hollow spaces are grooves formed on the second surface.

3. The ultrasonic sensor as in claim 2, wherein the grooves are formed in a lattice arrangement.

4. The ultrasonic sensor as in claim 1, wherein the hollow spaces are holes formed on the second surface.

5. The ultrasonic sensor as in claim 1, wherein cutout portions are formed along side surfaces, perpendicular to the second surface, of the substrate.

6. The ultrasonic sensor as in claim 1, wherein the hollow spaces are filled with filler having a rigidity lower than that of the substrate.

7. The ultrasonic sensor as in claim 1, wherein the vibrator is a piezoelectric element made of lead-zirconate-titanate.

8. The ultrasonic sensor as in claim 1, wherein the substrate is made of a resin material.

9. The ultrasonic sensor as in claim 1, wherein the substrate is made of a semiconductor material.

10. The ultrasonic sensor as in claim 1, wherein the substrate is made of glass.

11. An ultrasonic sensor comprising: a substrate for transmitting and receiving ultrasonic waves, the substrate having a first surface and a second surface opposite to the first surface; anda vibrator, mounted on the substrate, for converting electrical signals to the ultrasonic waves to be transmitted and for converting the ultrasonic waves received to electrical signals, wherein:grooves open to the first surface are formed in the substrate thereby to reduce rigidity of the substrate; andthe vibrator is mounted on the first surface of the substrate at a position where the grooves are not formed.