Ultrasonic sensors are sensors that convert ultrasonic signals into other energy signals (usually electrical).Ultrasonic wave is a mechanical wave whose vibration frequency is higher than 20kHz.It has the characteristics of high frequency, short wavelength, small diffraction phenomenon, especially good directivity, and directional propagation as a ray.Ultrasonic waves are very penetrating to liquid and solid, especially in the opaque solid of sunlight.Ultrasonic contact with impurities or boundary surface will produce significant reflection to form reflection echo, touching the moving object can produce Doppler effect.Ultrasonic sensors are widely used in industry, national defense, biomedical and other fields.