A multifrequency AM-based ultrasonic system for accuracy distance measurement

With conventional time-of-flight sonar ranging systems, it is difficult to obtain a high ranging accuracy due to the finite bandwidth of the transducer used and the serious acoustic attenuation in the air for the high acoustic frequencies. In this paper a multifrequency amplitude modulation (AM)-based sonar system is exploited to obtain information about the high-resolution distance measurement for robotic ranging applications. The target distance is obtained by measuring the linear phase shift of the reflected acoustic waves with respect to the reference signal. In order to analyze the ranging error two theoretical formulations are presented for characterization of the noisy phase measurement. The error effects on the phase measurement of the distorted input waveform due to the acoustic cross coupling are detailed, leading to the development of a multitransmitter sensing configuration. Since multifrequency is used, the nature of the target surface may bring about a certain ranging ambiguity to the system. The error effect of the rough surface is also analyzed at the end of the paper