Estimating ultrasonic time-of-flight through quadrature demodulation

A new digital signal-processing (DSP) method for ultrasonic time-of-flight (TOF) estimation is presented hereinafter. The method applies a traditional quadrature-demodulation scheme to the acquired ultrasonic signal in order to suitably extract the envelope of the main echo and locate its onset (i.e., the starting time of the echo). It is also possible to assure reduced bias and uncertainty in critical TOF measurements, such as those involving low signal-to-noise ratio (SNR) as well as severe distortion of echo shape. A number of numerical tests are conducted on simulated signals with the aim of highlighting the good performance of the method when operating in critical conditions; to reduce the computational burden without losing significance in the analysis, a statistical experimental design-based technique is enlisted. Results attained in TOF-based distance measurements finally assess the method's reliability and efficacy even in the presence of actual ultrasonic signals.