Ultrasonic wave is a kind of mechanical wave with higher vibration frequency than acoustic wave, which is generated by vibration of transducer wafer under voltage excitation. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity, and can be used as directional propagation of light. Ultrasonic waves have great penetration ability to liquids and solids, especially in solids with opaque sunlight, which can penetrate to a depth of tens of meters. Ultrasonic waves will have obvious reflection when they touch impurities or interfaces, and will be reflected as echoes when they touch moving objects, which can produce Doppler effect. Sensors based on ultrasonic characteristics are called "ultrasonic sensors" and are widely used in industry, national defense, biomedicine and other fields.

Disadvantages:

Because the Curie point of piezoelectric materials is generally high, it is especially used for diagnostic ultrasonic probes.

Ultrasonic sensor has low power, so its working temperature is relatively low, and it can work for a long time without failure. The temperature of medical ultrasonic probe is relatively high, which requires separate refrigeration equipment.

Sensitivity mainly depends on the wafer itself. Large electromechanical coupling coefficient and high sensitivity; On the contrary, the sensitivity is low.