Constant-Q acoustic attenuation in silica aerogels

Abstract

The reverberation technique was applied to measure the acoustic absorption of silica aerogels. This technique uses the decay of a diffuse sound field within an irregularly shaped specimen. The measured attenuation increased linearly with frequency between 10 and 200 kHz. The influence of acoustic losses due to the surrounding medium (air, vacuum) and the exciting and detecting transducers was eliminated. The inverse quality factor, Q −1, was found to be (0.5–3.0) × 10 −3, in approximate agreement with earlier measurements at higher frequencies. The temperature dependence of Q −1, measured between 250 and 330 K, is comparable with that found by Raman scattering and acoustic attenuation measurements in fused silica. The linear frequency dependence in aerogels deviates from the quadratic behaviour governing the acoustic attenuation in vitreous silica.