Ultrasonic Ranging using Frequency Selective Attenuation

Positioning can be calculated from measurement of the distances between multiple reference points and moving sensors. A new technique to measure the distance between emitter and receiver by using ultrasonic signals in air is proposed, without the use of the time of flight measurement based on expensive time synchronization between emitter and receiver. The attenuation level that the ultrasonic signal suffers at different frequencies provides information on the emitter-receiver distance. A mathematical relationship between emitter and receiver distance and the attenuation level experienced along the traveled path by two ultrasonic signals is provided. The actual level of attenuation in the air for the employed frequencies is measured online during the ranging operations. The simulations show the effectiveness of the technique under feasible operational conditions. In particular, an error of less than ±2.5 cm is reached along two significant paths of the vertical section of a typical office room.