Frequency shift, laser Doppler anemometry

Laser Doppler anemometry A velocity measurement device using the principle of Doppler shifted frequency of laser Hght by particles moving with the fluid. 

Modified Laser-Doppler Anemometry is another alternative method to monitor liquid wicking in a 2D fabric plane based on the Doppler principle. When a laser beam is passed through a flowing liquid, light is scattered by the particles suspended in the liquid. The scattered light is subject to a frequency shift and contains information about the velocity of the particles, which can then be examined by electro-optical techniques. This measurement, therefore, requires the flow medium to be partly transparent and containing particles, that scatter light used this method, to obtain the local velocity of liquid flow in a nonwoven fabric. 

In many technical problems in hydrodynamics or aerodynamics, the velocity profile v(r,t) of a flowing medium in pipes or around solid bodies is of great importance. Doppler anemometry (Sect. 7.12) is a heterodyne laser spectroscopy technique where these velocity profiles are determined from the measured Doppler shifts of the scattered light [1503-1505]. The beam of a HeNe or Ar laser with wave vector A l passes through a volume element dV of the flowing medium. The frequency co of light scattered in the direction ks by particles with velocity v (Fig. 10.34) is Doppler-shifted to... 

Phase Doppler anemometry or phase Doppler analysis was proposed two decades ago, based on the then well-established flow measurement technology-laser Doppler velocimetry [110]. PDA is widely used in sizing spherical and homogeneous particles, such as liquid sprays, aerosols, air bubbles in liquid, or other spherical particles. When single particles move through the intersection of at least two focused laser beams, they scatter light from each beam with different individual Doppler frequency shifts. Multiple detectors are placed at... 

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