Surprising acoustic propagation in foams: from liquid to solid

Abstract

Liquid and solid foams present surprising acoustic properties. A liquid foam is a complex gas-liquid system with a low liquid fraction (<30%). Its rigidity is due to a liquid skeleton, containing the most important part of the liquid and linked by thin liquid films. The bubble size distribution is strongly polydisperse. Over the past years we investigated, in a large frequency range, how a liquid foam behaves when insonified. We showed that liquid foams act as natural and 3D isotropic acoustic metamaterials. Moreover, this work confirmed that liquid foams have important soundproofing properties. First, I will show you how an acoustic wave propagates and dissipates when it travels through a collection of thin liquid films loaded by the surrounding air and a massive liquid skeleton. More recently, we investigated the case of solid foams elaborated by solidification of liquids foams and where the entire liquid skeleton (even films) has been preserved. In this second part, I will show you that the presence of very thin membranes is far from being a handicap to blocking sound.