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The problem of attenuation and sound speed of bubbly media has remainedpartially unsolved. Comprehensive data regarding pressure-dependent changes ofthe attenuation and sound speed of a bubbly medium are not available. Ourtheoretical understanding of the problem is limited to linear or semi-lineartheoretical models, which are not accurate in the regime of large amplitudebubble oscillations. Here, by controlling the size of the lipid coated bubbles(mean diameter of ~5.4um), we report the first time observation andcharacterization of the simultaneous pressure dependence of sound speed andattenuation in bubbly water below, at and above MBs resonance (frequency rangebetween 1-3MHz). With increasing acoustic pressure (between 12.5-100kPa), thefrequency of the attenuation and sound speed peaks decreases while maximum andminimum amplitudes of the sound speed increase. We propose a nonlinear modelfor the estimation of the pressure dependent sound speed and attenuation withgood agreement with the experiments. The model calculations are validated bycomparing with the linear and semi-linear models predictions. One of the majorchallenges of the previously developed models is the significant overestimationof the attenuation at the bubble resonance at higher void fractions (e.g.0.005). We addressed this problem by incorporating bubble-bubble interactionsand comparing the results to experiments. Influence of the bubble-bubbleinteractions increases with increasing pressure. Within the examined exposureparameters, we numerically show that, even for low void fractions (e.g.5.1*10-6) with increasing pressure the sound speed may become 4 times higherthan the sound speed in the non-bubbly medium.

Probing the pressure dependence of sound speed and attenuation in bubbly  media: Experimental observations, a theoretical model and numerical  calculations