1978 Volume 16 Issue 1 Pages 27-32
For the purpose of blood-flow measurement within small sampling area, the pulsed Doppler system and M-sequence modulation Doppler system have been used. In the pulsed Doppler system, it is difficult to generate and process transmitted and received signals and to maintain a sufficient average power in the transmitted signals. On the other hand, in the M-sequence modulation system, unnecessary Doppler signals are not eliminated completely because of the auto-correlation property of the M-sequence. The unnecessary signals, therefore, cause decline in the sensitivity for detecting Doppler signals from a desired sampling area.
In this paper, new cross-correlation sequences are presented whose cross-correlation values are zero, except that one sequence with the width tc of clock pulse and the period N is shifted by kNtc and kNtc+tc/2 (k=0, ±1, ±2 ……) with respect to the other with the width tc/2 of clock pulse and the petiod 2 N. Moreover, a new ultrasonic Doppler system using these sequences is described. With this proposed modulating method, unnecessary reflected signals can be eliminated completely.
