US Patent 9662680 Ultrasonic transducer

An ultrasonic transducer is provided that includes an ultrasonic wave generator having piezoelectric vibrators, and cases having ultrasonic wave emission holes and accommodating the ultrasonic wave generator. Acoustic paths in which air serves as a medium are formed by the ultrasonic wave generator and the and extend from the piezoelectric vibrators to the ultrasonic wave emission holes. Resonance of air is generated in the acoustic paths by ultrasonic waves generated by the piezoelectric vibrators in which the ultrasonic wave emission holes are open ends of the resonance. The piezoelectric vibrators are driven at a driving frequency at which the temperature-sound pressure characteristic for the resonance of air and the temperature-amplitude characteristic at the driving frequency of the piezoelectric vibrators have opposite tendencies.