Ultrasonic sensor with piezoelectric elements and vibration isolator
View Patent ↗An ultrasonic sensor includes a transmitting device, receiving devices arranged in an array, and a circuit device. One receiving device is configured as a reference receiving device. The circuit device includes a reference signal generator and first and second synchronous detectors. The reference signal generator generates a reference signal by using a received signal of the reference receiving device. The first synchronous detector performs synchronous detection of a received signal of one of the receiving devices based on the reference signal to detect a distance to an object. The second synchronous detector performs synchronous detection of received signals of the receiving devices except the reference receiving device based on the reference signal to detect a direction of the object.
1. An ultrasonic sensor for detecting a first object, comprising:
a transmitting device for transmitting ultrasonic wave to the first object, the transmitting device including a first piezoelectric element for emitting the ultrasonic wave and a first acoustic matching member having a transmitting surface, the emitted ultrasonic wave propagated through the first acoustic matching member and being transmitted through the transmitting surface to the first object, the first piezoelectric element being configured as a multilayer piezoelectric element including a plurality of piezoelectric layers and a plurality of electrode layers interleaved with the plurality of piezoelectric layers;
a receiving device, arranged in an array with the transmitting device, for receiving the ultrasonic wave reflected from the first object, the receiving device including a second piezoelectric element for detecting the reflected ultrasonic wave and a second acoustic matching member having a receiving surface, the reflected ultrasonic wave being received through the receiving surface and propagated through the second acoustic matching member to the second piezoelectric element;
a housing having an inner space for accommodating the transmitting device and the receiving device, the housing having a bottom and an opening portion, the housing being mountable to a second object at the opening portion;
a vibration damper interposed between the opening portion of the housing and each of the first and second acoustic matching members to fix the first and second acoustic matching members to the housing, the vibration damper being interposed between the first and second acoustic matching members to reduce a propagation of the ultrasonic wave between the first and second acoustic matching members; and
a vibration isolator for partitioning the inner space of the housing and located between the transmitting device and the receiving device to reduce the propagation of the ultrasonic wave between the transmitting device and the receiving device.
2. The ultrasonic sensor according to claim 1 , further comprising:
a first absorber interposed between the bottom of the housing and each of the first and second piezoelectric elements and between an inner side wall of the housing and each of the first and second piezoelectric elements to protect the transmitting device and the receiving device from external force, wherein
the vibration isolator has a higher acoustic matching impedance than the first absorber.
3. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator is integrally formed with the housing.
4. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator has a first thickness on the first and second acoustic matching members side and a second thickness on the first and second piezoelectric elements side, and
the first thickness is less than the second thickness.
5. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator includes first and second members and a core member that are layered together such that the core member is sandwiched between the first and second members, and
each of the first and second members has a higher elastic modulus than the core member.
6. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator includes first and second members and a core member that are layered together such that the core member is sandwiched between the first and second members, and
each of the first and second members has a higher acoustic impedance than the core member.
7. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator includes first and second members that are joined together to provide a sealed space therebetween, and
the sealed space is filled with a material having a lower acoustic impedance than those of each of the first and second members.
8. The ultrasonic sensor according to claim 7 , wherein
the vibration isolator includes a honeycomb structural body placed in the sealed space to partition the sealed space into a plurality of spaces.
9. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator has a plurality of gas bubbles trapped therein.
10. The ultrasonic sensor according to claim 1 , further comprising:
a second absorber located on the first absorber to surround the first and second piezoelectric elements, wherein
the second absorber has a lower elastic modulus than the first absorber.
11. The ultrasonic sensor according to claim 10 , wherein
the first absorber includes a first portion located on the first piezoelectric element side and a second portion located on the second piezoelectric element side, and
the first portion of the first absorber has a higher elastic modulus than the second portion of the first absorber.
12. The ultrasonic sensor according to claim 11 , wherein
the first portion of the first absorber has a greater height, measured from the bottom of the housing, than the second portion of the first absorber.
13. The ultrasonic sensor according to claim 1 , wherein
the transmitting surface of the transmitting device and the receiving surface of the receiving device are covered with the vibration damper.
14. The ultrasonic sensor according to claim 1 , wherein
the transmitting device or the receiving device comprises a plurality of devices having different directivities.
15. The ultrasonic sensor according to claim 1 , wherein
the bottom of the housing has a through hole, and
the vibration isolator has a portion exposed outside the housing through the through hole.
16. The ultrasonic sensor according to claim 15 , wherein
the vibration isolator has a vibration inhibitor attached to the exposed portion of the vibration isolator to inhibit the exposed portion from vibrating.
17. The ultrasonic sensor according to claim 1 , further comprising:
a vibration damping circuit configured to apply to the vibration isolator a vibration having an opposite phase to a vibration of the vibration isolator to damp the vibration of the vibration isolator.
18. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator has an uneven side surface.
19. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator is supported by the housing at an edge portion, and
the vibration isolator is thinner at the edge portion than at a center portion.
20. The ultrasonic sensor according to claim 1 , wherein
the vibration isolator is reinforced with a reinforcing member placed on a side surface.
21. The ultrasonic sensor according to claim 20 , wherein
the reinforcing member has a honeycomb structure.
22. The ultrasonic sensor according to claim 1 , wherein
the vibration damper has a slit located between the first and second acoustic matching members.
23. The ultrasonic sensor according to claim 1 , wherein
the receiving device comprises a plurality of receiving devices, and
a distance from each receiving device to the transmitting device is the same, and
a distance from each receiving device to the vibration isolator is the same.
24. The ultrasonic sensor according to claim 1 , wherein
the receiving device comprises a plurality of receiving devices, and
the vibration isolator has a honeycomb structure to partition the inner space of the housing into a plurality of spaces,
the transmitting device is placed in a central one of the plurality of spaces,
each receiving device is placed in a corresponding space other than the central one, and
a distance from each receiving device to the transmitting device is the same.