Eur. Phys. J. E (2013) 36: 113
https://doi.org/10.1140/epje/i2013-13113-1

Regular Article

Acoustic characterisation of liquid foams with an impedance tube

¹ Laboratoire MSC, Université Paris-Diderot, CNRS (UMR 7057), Paris, France
² Laboratoire de Physique des Solides, Université Paris-Sud - UMR 8502, Orsay, France
³ Université Pierre et Marie Curie, 4 place Jussieu, 75252, Paris Cedex 05, France

^* e-mail: valentin.leroy@univ-paris-diderot.fr

Received: 19 April 2013
Revised: 24 July 2013
Accepted: 10 September 2013
Published online: 15 October 2013

Abstract

Acoustic measurements provide convenient non-invasive means for the characterisation of materials. We show here for the first time how a commercial impedance tube can be used to provide accurate measurements of the velocity and attenuation of acoustic waves in liquid foams, as well as their effective “acoustic” density, over the 0.5-6kHz frequency range. We demonstrate this using two types of liquid foams: a commercial shaving foam and “home-made” foams with well-controlled physico-chemical and structural properties. The sound velocity in the latter foams is found to be independent of the bubble size distribution and is very well described by Wood’s law. This implies that the impedance technique may be a convenient way to measure in situ the density of liquid foams. Important questions remain concerning the acoustic attenuation, which is found to be influenced in a currently unpredictible manner by the physico-chemical composition and the bubble size distribution of the characterised foams. We confirm differences in sound velocities in the two types of foams (having the same structural properties) which suggests that the physico-chemical composition of liquid foams has a non-negligible effect on their acoustic properties.