Ultrasonic sensor is designed by ultrasonic characteristics.Ultrasonic is a kind of mechanical wave which vibration frequency is higher than the sound wave.  It has high frequency and short wavelength, especially the good direction, Which can transmit to the specified direction and location.Ultrasonic sensors can used in gas, Liquid and solid. Ultrasonic has the big ability to penetrate liquid and solid.Especially in the sunshine opaque solid, it can penetrate tens meters depth.
Ultrasonic sensors are widely used in car parking assistance, proximity alarms,Medical ultrasounds, and distance measurement.