Ultrasonic frequency modulated continuous wave for range estimation

As an alternative implementation of the pulse-compression (PuC) technique, the frequency modulated continuous wave (FMCW) approach is here presented as a method to perform time-of-flight (ToF) measurements by relaxing both hardware and software resources with respect to the standard PuC procedure based on the application of the matched filter. Precisely, by using linear chirps as excitations and by replacing the cross-correlation step between input and output signals with a mixing of the two waveforms, it is possible to retrieve the envelope Env[h](t) of the system impulse response by performing frequency analysis of the mixed signal. It will be shown that by exploiting this procedure, it is possible to attain a high precision in the measurement of ToF values also by using sampling intervals larger than the achievable temporal resolution. As a consequence, also the computational resources can be significantly reduced with respect to those requested by the standard cross-correlation approaches. Both numerical and experimental analyses are reported to illustrate this method and also some processing techniques are introduced and compared to further improve the ToF resolution.