Compensation of Parametric-Effect-Induced Error in Airborne Ultrasound Doppler Velocimetry

A non-contact vibration measuring technique based on ultrasonic Doppler effect is studied. Two effects induce phase modulation on the received ultrasound signal, which are Doppler effect and nonlinear parametric effect. With the increasing of vibrating frequency, the phase variation due to parametric effect is getting greater and greater. In this paper, by measuring the acoustic pressure generated by the low frequency vibration, the parametric effect is taken into account for estimating the vibrating velocity. The results show that it is better than the method of only taking account of the Doppler effect especially as the vibrating frequency increases. For example, for a vibrating body of diameter 10 cm at frequency of 1.5 kHz, the error of velocity measurement with parametric-effect-compensation is getting less than one half of that without compensation.