A feasible and accurate technique for determining the time-of-flight in ultrasonic distance measurements

This paper presents a digital signal processing technique with an efficient algorithm for ultrasonic distance measurement in the air with high accuracy. The time difference -in terms of samples- between the beginning of a transmitted pulse and the peak value of the response is used to determine the Time-of-Flight (TOF). The peak value of the filtered response is determined using the magnitude of a special complex signal using Hilbert transform and an appropriate parabolic interpolation. The method effectively eliminates the noise and disturbance in the received signal and makes the TOF independent of the received signal strength. Experimental results show accuracy better than 1 mm at a distance of about 1 m.