Assessment of Operational Progress of NASA Langley Developed Windshield and Microphone for Infrasound

Report No. ARL-TR-6417
Authors: W.C. Kirkpatrick Alberts, II, Stephen M. Tenney, and John M. Noble
Date/Pages: April 2013; 20 pages
Abstract: A recent National Aeronautics and Space Administration (NASA) effort to create a compact alternative to porous hose windscreens for infrasound applications resulted in the creation of spherical, closed-cell polyurethane foam windshields. Some researchers suggest that closed-cell foam windshields, at infrasound frequencies, sound should pass through the material of the foam to reach the enclosed microphone. This report details an U.S. Army Research Laboratory attempt to independently observe the experimental results reported in the literature and to evaluate compact, non-porous, spherical windshields for use in Department of Defense infrasound applications. Transfer functions between an instrument grade microphone and an infrasound microphone covered by eight different densities and thicknesses of spherical closed-cell foam windshields demonstrate at least a 30 dB decrease in sound level at the interior microphone across all of the frequencies studied regardless of foam density or thickness.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2013