The propagation of ultrasound through a bubbly medium is a challenging task because of a) multiple scattering the occurs in a bubble cluster and b) the nonlinear dynamics of the microbubble interaction with the ultrasound and their effect on the effective attenuation and sound speed of the medium. Most studies treat simple systems (one or few bubbles) and apply linear models describing the oscillations of the microbubbles. This approach will generate inaccurate results, especially for exposure of higher-pressure excitations.

We have developed an efficient technique for investigating the dynamics of large microbubble clusters considering multiple scattering from all the bubbles in the cluster. We validated our method using numerical simulations and comparison with established techniques. Moreover, we have numerically simulated the attenuation and sound speed of a bubbly medium taking into account the nonlinear microbubble oscillations of the interacting microbubbles. An efficient method to investigate the nonlinear bubble-bubble interaction and multiple scattering was developed, and numerical investigations simulating a cluster of 130 randomly distributed interacting were done. We have performed controlled experiments in nonlinear regimes with ultrasound measurements acquired at multiple acoustic pressures and frequencies by sonicating a size controlled population of lipid-coated micro-bubbles. Model predictions are in good agreement with experimental results.