Design of a continuous-wave Doppler ultrasonic flowmeter for perivascular application

Abstract

The paper details the design of the signal processing system of an ultrasonic Doppler flowmeter intended for perivascular application. The system is designed to work in conjunction with a transducer system described in an earlier paper, in a range of vessels varying from 5 mm to 12 mm. The system incorporates conventional quadrature processing for directional discrimination and uses phaselocked loop technology to extract signals corresponding to the instantaneous mean frequency (velocity equivalent). The use of a PLL also permits the extraction of a quasi-spectral analysis signal. The baseline stability of the Doppler system is enhanced by the use of an auto-zeroing system which enables the system to resolve Doppler shifts down to 20Hz. Testing of the complete transducer/signal processor system in a hydraulic rig demonstrates the ability of the flowmeter to accurately measure both steady and pulsatile flow.