Impedance matching and acoustic absorption in granular layers of silica aerogels

Experimental results on the acoustic properties of silica aerogel granules of sizes 80 mum and 3.5 mm ale presented. An acoustic absorber made of a tw o-layer granular aerogel structure, an impedance matching layer and an abso rbing one, has been designed. The reflection coefficient, the attenuation, and the sound velocity of the granular aerogels have been measured as a fun ction of frequency (between 20 and 2500 Hz) and compared with those of a gl ass wool sample. It has been found that the acoustic transmission losses in the aerogel absorber are at least 10 dB higher than in the glass wool samp le of the same thickness (4 cm) for the frequency range 300 1700 Hz. (C) 20 01 Elsevier Science B.V. All rights reserved.