What is an ultrasonic sensor?

An ultrasonic sensor is a sensor that converts an ultrasonic signal into other energy signals, usually electrical signals. Ultrasound is a mechanical wave with a vibration frequency above 20kHz. It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directionality, and can become a ray and propagate directionally. Ultrasound has a great ability to penetrate liquids and solids, especially in solids that are opaque by sunlight. Ultrasonic waves hitting impurities or interfaces will produce significant reflections to form reflected echoes, and Doppler effects can occur when encountering moving objects. Ultrasonic sensors are widely used in industry, defense, biomedicine and other aspects.
Commonly used ultrasonic sensors consist of piezoelectric wafers that can both emit and receive ultrasonic waves. Low-power ultrasonic probes are mostly used for probing. It has many different structures, which can be divided into straight probe (longitudinal wave), oblique probe (shear wave), surface wave probe (surface wave), Lamb wave probe (Lamb wave), dual probe (one probe transmitting, one probe receiving), etc.