Position and velocity measurement for moving objects by pulse compression using M-sequence-coded ultrasound

Abstract

The pulse-echo method is one of the typical methods for ultrasonic distance measurement. Pulse compression using an M-sequence can improve the SNR of the echo reflected from an object and distance resolution in the pulse-echo method by the cross correlation between the received signal and the reference signal which correspond to the transmitted M-sequence-coded signal. In the case of a moving object, however, the echo is modulated due to the Doppler effect. The Doppler-shifted M-sequence-coded signal cannot be correlated with the original reference signal. Therefore, Doppler velocity estimation by autocorrelation of cyclic M-sequence-coded signal and cross correlations with Doppler-shifted reference signals which correspond to estimated Doppler velocities has been proposed. In this paper, measurement of position and velocity of the static and moving objects by the proposed method using the loud speaker and the microphone array are described. First, the Doppler velocity of the moving object is estimated in each array element. Second, received signals are correlated with the original reference signal for the static object. Then, received signals are correlated with Doppler-shifted reference signals for the moving object. Finally, positions of both objects are determined from the B-mode image formed by the synthetic aperture focusing technique.