A scanning laser Doppler vibrometer acoustic array

Experiments confirm that a laser Doppler vibrometer can be used to detect acoustic particle velocity on a fluid-loaded acoustically compliant, optically reflective surface. In these experiments, which were completed at the Acoustic Test Facility of the Naval Undersea Warfare Center, Scotchgard (TM) reflective tape was affixed to the interior surface of a standard acoustic window. The polyurethane array window had a thickness of 0.9525 cm (0.375 in.) and a material density of 1000 kg/m(3). The surface velocity measured, using a commercial scanning laser vibrometer system (SLVS), was beamformed conventionally and flawlessly detected and localized acoustic signals. However, the laser Doppler vibrometer used in the experiments had relatively poor acoustic sensitivity, presumably due to high electronic noise in the photodetector, speckle noise, standoff distance, and drifting laser focus. An improved laser Doppler vibrometer, the simplified Michelson interferometer laser vibrometer sensor (SMIV), is described in brief. The SMIV achieves sensitivity of 61 dB/mu Pa in a 1-Hz band at 11.2 kHz, which represents a 39-dB acoustic sensitivity improvement. (c) 2006 Acoustical Society of America.