Analytical and experimental comparisons between the frequency-modulated–frequency-shift measurement and the pulsed-wave–time-shift measurement Doppler systems

Abstract

In previous publications, a new echo-ranging Doppler system based on transmission of repetitive coherent frequency-modulated (FM) sinusoids in two different implementations was presented. One of these implementations, the frequency-modulated–frequency-shift measurement (FM–fsm) Doppler system is, in this paper, compared with its pulsed-wave counterpart, the pulsed-wave–time-shift measurement (PW–tsm) Doppler system. When using transmitted PW and FM signals with a Gaussian envelope, the parallelism between the two systems can be stated explicitly and comparison can be made between the main performance indices for the two Doppler systems. The performance of the FM and PW Doppler systems is evaluated by means of numerical simulation and measurements of actual flow profiles. The results indicate that the two Doppler systems have very similar levels of performance.

Coded Excitation in TCD Ultrasound Systems to Improve Axial Resolution

“…Wilhjelm and Pedersen (1993a, 1993b, 1996 proposed a method for velocity estimation with a Doppler system transmitting linear FM signals. This had the disadvantage that it required separate transmit and receive transducers because the periods of transmit and receive overlapped, and also had a range resolution of the same order as conventional systems.…”