Ultrasonic position and velocity measurements for a moving object by the simultaneous transmission of preferred-pair M-sequences

Abstract

A method of ultrasonic position and velocity measurements for a moving object by M-sequence pulse compression has been proposed. In the proposed method, the Doppler velocity is estimated from the peak in the autocorrelation function of the received signal, which includes cyclic M-sequences reflected from the object. Then, the received signal is correlated with the reference M-sequence expanded or compressed in accordance with the estimated Doppler velocity. The position is determined from the acoustic image formed from cross-correlation functions obtained in different propagation paths of ultrasound. In this paper, the simultaneous transmission of preferred-pair M-sequences is studied to improve the spatial resolution of the image while keeping the original frame rate of the proposed method. Experiments using the moving pole, two loudspeakers and three microphones are conducted to evaluate the estimated Doppler velocities and determined positions. In most situations, Doppler velocities can be accurately estimated when two different Doppler components are included in the received signal. In some situations, however, accurate Doppler velocities inevitably cannot be estimated due to the peak overlapping in the autocorrelation function. The accuracy of determined positions may degrade when the signal-to-noise ratio of the received signal is insufficient or Doppler velocities are not accurately estimated.