EVALUATION OF THE 2-FIBER LASER-DOPPLER ANEMOMETER FOR IN-VIVO BLOOD-FLOW MEASUREMENTS - EXPERIMENTAL AND FLOW SIMULATION RESULTS

A two-fiber laser Doppler anemometer was built and tested with the fib er probe placed parallel to the flow. Nine combinations of fiber diame ters and fiber separations were tested, and the dominant and maximum s hift frequencies were plotted as a function of the unperturbed (or fre estream) flow velocity. For both the forward (toward the fiber tip) an d reverse (away from the fiber tip) flow directions, the graph of the flow velocity against the maximum shift frequency shows better lineari ty and approaches closer to the theoretical line than the graph of the flow velocity against the dominant shift frequency. For the forward f low, the Doppler frequency is close to that predicted and linear above 20 cm/s, but for the reverse flow the slope is only one-quarter of th at predicted. Analysis of the data showed that the region of flow pert urbation decreases towards the fiber tips in the forward flow, whereas it extends away from the fiber tips in the reverse flow. In its prese nt form, the two-fiber system cannot then be used for accurate blood v elocity measurements, since linear calibration between the forward and reverse flow velocities cannot be achieved.