Transducer characterization by laser Doppler vibrometry

Description/Abstract

A laser Doppler vibrometer (LDV) can be set up such that its laser beam passes through the glass wall of a water tank to be incident upon the radiating surface of an immersed ultrasonic transducer. Scanning the laser beam across a transducer in this way has the potential to be a fast, noninvasive method for source characterization and, in turn, field prediction. Such measurements are, however, significantly complicated by the acousto-optic interaction—that is, the effect on the measurements of the acoustic field through which the laser beam passes. To increase understanding of the resultant acousto-optic artifact, a detailed simulation of the LDV measurement of a circular, plane-piston transducer emitting a tone-burst has been created. The use of a transient field is important for simulation and experiment, such that measurements can be made over a time window which ends before any acoustic signal reaches the water tank boundaries. The simulation results show a significant acousto-optic artifact contribution to the surface velocity data, but also that for some applications useful field predictions may be made in spite of this. To complement the simulations, experimental measurements have been made using a commercial LDV (Polytec PSV-400) on a 500 kHz circular transducer