The proximity sensor is designed to measure the distance from the sensor face to a target. The level sensor is the same as a proximity sensor except with the surface of a fluid or bulk solid as the target.

The blanking distance is the minimum sensing range in an ultrasound proximity sensor. Blanking distance is a function of the ring down time of the transducer as the transducer must ring down before it can receive the sound reflected from the tissue.

To calculate the echo position, a constant sound speed of 1538.5 m/sec is assumed. Tissue penetration is frequency depended, if the frequency increases, the imaging depth decreases. The range resolution defines the depth. Ultrasound propagating in tissue is attenuated due to scattering and absorption. The attenuation is proportional to depth and frequency and is typically in the range from 0.5 to 1 dB/(MHz cm).

See also Attenuation Coefficient, Proximity Sensor, and Echo Ranging.