Air-coupled ultrasonic time-of-flight measurement system using amplitude-modulated and phase inverted driving signal for accurate distance measurements

Abstract

This paper proposes an amplitude-modulated and phase-inverted (AMPI) ultrasonic driving signal for accurate distance measurements. Undesirable part of the ultrasonic wave was canceled using the phase-inverted wave and its active canceling effect was enhanced by the amplitude-modulation, so that a unique ultrasonic waveform having a sharp envelope could be generated even with a narrow-band transducer of frequency 40kHz (wavelength λ ≅ 9mm). The sharp envelope generated by the AMPI signal determined a zero-crossing time without any uncertainty. As a result, an accuracy better than 0.02mm was achieved in the range of 0.1 - 0.5m.