US Patent 8020447 Ultrasonic sensor and self diagnostic method of the same

In an ultrasonic sensor, a first receiving device is configured to be sendable and receivable an ultrasonic wave. The ultrasonic wave sent from the first receiving device is transmitted through a vibration-reducing member disposed between the first receiving device and a second receiving device, and the second receiving device detects the ultrasonic wave. The ultrasonic sensor self diagnoses whether the second receiving device is operated without malfunction based on a detection signal of the second receiving device.