Patent ID: 8166824

Claim:
An ultrasonic sensor for detecting an object, comprising: a transmitting device for transmitting an ultrasonic wave to the object, the transmitting device including a first piezoelectric element configured to emit the ultrasonic wave, the transmitting device further including a first acoustic matching member through which the emitted ultrasonic wave propagates to an outside; a receiving device for receiving the ultrasonic wave reflected from the object, the receiving device including a second piezoelectric element configured to detect the reflected ultrasonic wave, the receiving device further including a second acoustic matching member through which the reflected ultrasonic wave propagates to the second piezoelectric element; a circuit device for applying a first voltage of a first frequency to the first piezoelectric element to cause the first piezoelectric element to emit the ultrasonic wave of the first frequency, the circuit device including a resonance frequency detection section configured to detect a resonance frequency of one of the first or second acoustic matching members, wherein the circuit device adjusts the first frequency of the first voltage to the detected resonance frequency.