Acoustical properties of liquid foams (INVITED)

Abstract eng:
Sound velocity and attenuation measurements in well-characterized liquid foams were performed over a wide frequency range (1-600 kHz). The study was limited to the long wavelength case: even for the highest frequencies explored, the wavelength was larger than the typical size of the micro-structure of the foams. Typical results are shown, for a foam with a liquid volume fraction of 10%. A strongly dispersive behavior was found, with three regimes of propagation: at low frequencies, the effective velocity was 33 m/s, as predicted by Wood’s law; at high frequencies, the velocity was of the order of 220 m/s; in the intermediate regime, velocity and attenuation varied strongly with frequency, presenting the typical features of a low frequency resonance. A new model is proposed, based on the coupled displacements of films, liquid channels and gas in the foam.

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