Frequency Error of Doppler Beat Signals due to Extended Scattering Particles

The dependence of the frequency error of Doppler beat signals on the size of scattering particles is theoretically investigated by assuming the probing area to be finite, i.e. by assuming beat signals to have a burst form. The effect of the particle size on output beat signals can not be ignored when the laser Doppler flowmeter is applied to measure the flow velocity in a microscopic area of the order of several microns in one dimension. The present analysis reveals that the frequency error occurs in some cases as the frequency deviation of more than 6% from the ideal Doppler beat frequency due to point-like scattering particles.