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 phaseinverted (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 40 kHz (wavelength λ ∼ = 9 mm). The sharp envelope generated by the AMPI signal determined a zero-crossing time without any uncertainty. As a result, an accuracy better than 0.02 mm was achieved in the range of 0.1 − 0.5 m.

Robust High-Accuracy Ultrasonic Range Measurement System

“…This technique uses a frequency change detector to estimate the Time of Flight and refine the estimate by adding the phase shift measured by a digital phase meter. Amplitude change and phase inversion detection and phase shift using Amplitude Modulation and Phase Modulation Envelope Square Wave form (APESW) was proposed in [17], [18], [19]. This technique is quite similar to that proposed in [16] except that an amplitude and phase change detector is used for Time of Flight estimation instead of a frequency change detector.…”

“…Many ultrasonic range measurement methods have been proposed in the literature [12][13][14][15][16][17][18][19]. Time of Flight (TOF) and phase shift methods are used in most ultrasonic range measurement systems.…”

Active damping of ultrasonic receiving sensors through engineered pressure waves

“…There is an inherent delay between the application of the drive signal and the time at which the vibration response of the transmitting transducer reaches a maximum amplitude, attributable to the inertia of the transducer's vibrating components. By modulating the amplitude and duration of the damping pulse to account for this change in signal amplitude over time, a greater reduction of the transmitter's response time can be achieved in comparison to the technique of implementing a pulse phaseshifted by 180 • [8,9]. This is an example of an active damping strategy.…”