ASA 124th Meeting New Orleans 1992 October

4aEA11. Measuring the acoustic reflectivity of panels at low frequencies and high oblique angles.

J. J. Dlubac

R. J. Deigan

Code 1945.1, Ship Acoust. Dept., David Taylor Res. Ctr., Bethesda, MD 20084-5000

Conventional short-pulse techniques for measuring the reflectivity of acoustic panels requires that the reflected and incident waves be separated in time so that their ratio can be established. This technique is limited to high frequencies and low oblique angles, since under these extremes the direct and reflected waves overlap. An interference method is investigated as a way of making reflectivity measurements at low frequencies and high oblique angles. The total field (incident and reflected) in the vicinity of the panel is measured relative to the incident field without the panel. The total field, which depends on frequency and angle of incidence as well as the panel material, is then examined and manipulated to extract information on the reflected wave. The technique is demonstrated with data reduced on steel plates of various thicknesses.