Evaluation of the performance of two acquisition and signal processing systems for measuring acoustic particle velocities in air by means of laser Doppler velocimetry

A laser Doppler velocimetry bench adapted for measuring acoustic particle velocities is used to measure sinusoidal structural velocities in order to assess the performance of two signal processing techniques, one available commercially and the other being developed in our laboratory. Considering a sinusoidal excitation signal of the vibrating structure, both techniques use frequency demodulation approaches in order to extract the instantaneous frequency of the Doppler signal which is scattered by the vibrating object and use synchronous analysis in order to estimate the amplitude and the phase of the velocities estimated by means of the frequency demodulation. The performance and limitations of the processing tools are evaluated by means of a comparison of the estimated velocities with reference values given by a laser vibrometer. Both systems show close and satisfactory performance up to 2 kHz for rms velocities higher than 1 mm s−1.