Accurate Ultrasonic Ranging Using a Beat Signal

An ultrasonic ranging method using a beat was proposed to achieve higher accuracy and resolution. A single PZT transducer was used to send and receive ultrasound signals. When the emitted ultrasound reflected back to the transducer, the ultrasound frequency was switched from the first to the second frequency to generate a beat signal. The duration and phase of the beat signal corresponded to the distance to measure. Coarse measurement of the distance was obtained from the beat duration, while fine measurement was achieved through phase-sensitive detection of the beat phase. The duration measurement was accurate enough to resolve the ambiguity in the wavenumber in wavelength-based ranging. The phase measurement error was less than 0.1 mm, below one hundredth of the ultrasound wavelength.