The Dependence of Ultrasound Doppler Bandwidth on Beam Geometry

Abstract

.4bstrmt-The output spectrum of ultrasound Doppler flowmeters contains information about flow parameters such as degree of turbulence, flow velocity gradient, and direction. This information can be extracted if the effects of the sound beam geometry on the Doppler spectrum can be understood and controlled. Equations for calculating the Doppler output signal bandwidth caused by constant velocity flow through the waist of focused transducers and through the intermediate and far field of unfocused transducers are derived and experimentally verified in this paper. The results presented show how to minimize the bandwidth caused by beam geometry and thus maximize the accuracy of flow parameter estimation. It is also shown that the angle between flow and beam can be estimated from the Doppler bandwidth if the velocity gradient in the range cell is small enough and if flow is laminar.