What are ultrasonic sensors?

Ultrasonic sensor is based on some of the characteristics of ultrasonic manufacturing, used to complete the transmission and reception of ultrasound, the internal transducer wafer by the voltage excitation and vibration to produce ultrasound, ultrasound frequency, short wavelength, good directionality, can be linear propagation, on the liquid or solid has a good penetration effect, for example, some of the opaque objects, ultrasound can penetrate dozens of meters, but also when it encounters impurities and other objects will occur reflection phenomenon, thus generating an echo. Encountering impurities and other objects will occur when the reflection phenomenon, thus generating an echo.