Shaving foam: A complex system for acoustic wave propagation

While liquid foams have applications in an increasing number of industrial areas (food, cosmetic or petroleum industry), it remains difficult to non-invasively probe their structure and/or composition. Since the propagation of acoustic waves is very sensitive to parameters such that the liquid fraction, the bubble size distribution, or even the nature of the liquid phase, acoustic spectroscopy could be a very powerful tool to determine the structure and/or composition of liquid foams. In this context, we present an investigation of the acoustic properties of a useful and common foam, often considered as a model system: shaving foam. Phase velocity and attenuation of acoustic waves in a commercial shaving foam (Gillette) were measured over a broad frequency range (0.5 to 600 kHz), using four different experimental setups: an impedance tube (0.5-6 kHz), an acousto-optic setup based on Diffusive Wave Spectroscopy (0.4-10 kHz), and two transmission setups with narrow-band (40 kHz) and broad-band (60-600 kHz) transducers. We present the results and discuss the advantages and shortcomings of each setup in terms of a potential spectroscopy technique.