Patent ID: 8020447

Claim:
A self diagnostic method of an ultrasonic sensor, comprising: sending an ultrasonic wave from a first receiving device that is configured to be sendable and receivable; transmitting the ultrasonic wave through a vibration-reducing member; detecting the ultrasonic wave by a second receiving device; and determining whether the second receiving device is operated without malfunction based on a detection signal of the second receiving device, wherein: each of the receiving devices includes a detecting element and an acoustic matching part; each of the detecting elements has a first acoustic impedance and is configured to detect an ultrasonic wave that is sent from a sending device and that is reflected by an external object; each of the acoustic matching parts has a second acoustic impedance and has a receiving surface and an attaching surface; each of the receiving surfaces is exposed to an outside for detecting the ultrasonic wave reflected by the external object; each of the attaching surfaces opposes the receiving surface and is attached to the detecting element for transmitting the ultrasonic wave received by the receiving surface to the detecting element; the second acoustic impedance is larger than an acoustic impedance of air and is less than the first acoustic impedance; and the acoustic matching part of the first receiving device and the acoustic matching part of the second receiving device are arranged through the vibration-reducing member for reducing a transmission of a vibration between the acoustic matching parts.