Two-Focused Optical Measurement Method of Flow velocity with Low-Coherent Laser Source

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(1) The theoretical analysis of scattering media signals has been performed. According to this theory ;The flow velocity can be calibrated by using of the half peak value in the spectral width which is obtained by Fourier processing the interference output signals.This half peak value of spectral width is calculated without any relation to number density of scattering media.(2) By using the biological tissues(intralipid 1O%) as scattering media, the reproducible results can be obtained.(3) The interference output includes not only the fluctuation of scattering amplitude but noise signals. By subtracting noise signals from output signals, the useful fluctuation of scattering amplitude can be selected.(4) As the measurement point becomes deeper along a depth in a flow passage, the Fourier spectra of scattering amplitude gets smaller under the influence of the multiple scattering. Using intralipid 1O% as scattering media this tendency is the same.(5) The existence of wall can be recognized by the results of signal processing.(6) Near the wall surface, the positional resolution is about 40 mu m.(7) The spectral width measured at the chosen depths in the flow passage corresponds to flow velocity.(8) From the theory and simulation, it was clarified that the spectral signals are biasd toward higher region of spectral distribution by the velocity components differences of scattering particles passing through the measurement volume and by the time coherence function.(9) The effect of velocity gradient in measurement volume was analyzed quantitavely by using simulation and experemental results.