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Propagation of ultrasound in aqueous foams: bubble size dependence and resonance effects

“…In the intermediate range, there are results on very dilute bubbly liquids, 20,21 clouds of bubbles, [22][23][24] or 2D ras of bubbles. 25 On macroscopic 3D foams, it turns out that there are only some studies, [26][27][28][29][30][31][32][33][34] mostly evidencing that sound is strongly attenuated and basically propagates at a speed as low as 50 m s À1 (about 7 times slower than in air) inside a foam of submillimetric bubbles. If this order of magnitude can be captured by considering that foam has the compressibility of the gas, with the density of the liquid (following the classical model of Wood 36 ), the existing studies show that this picture is not sufficient.…”

Sound Velocity in Soap Foams

“…[16−19] Kann proposed a film mode to explain the effect of sound retardation in foams, who approximated foam to a periodic arrangement of "cubic" bubbles in two dimensions. [18,19] Compared with the experimental results, the theoretical prediction by Kann underestimates the size dependence of sound velocities. In fact, the configuration of foams is amorphous-like, and the periodic arrangement of bubbles inevitably deviates the realistic sound propagation in foams.…”