*The frequency of vibration is higher than that of sound waves.
*With high characteristic frequency, short wavelength, small diffraction phenomenon, especially good directivity, and is the directional propagation of radiation.
*Ultrasonic ranging usually uses TOF (time of flight) mode. 
*The distance between sensor and obstacle S=vt/ 2. 
*Can detect transparent or colored objects, metal or non-metal objects, solid, liquid, and powdery substances.