Classification of the mechanisms of wave energy dissipation in the nonlinear oscillations of coated and uncoated bubbles

Abstract

Acoustic waves are dissipated when they pass through bubbly media. Dissipation by bubbles takes place through thermal damping (Td), radiation damping (Rd) and damping due to the friction of the liquid (Ld) and friction of the coating (Cd). Knowledge of the contributions of the Td, Rd, Ld and Cd during nonlinear bubble oscillations will help in optimizing bubble and ultrasound exposure parameters for the relevant applications by maximizing a desirable parameter. In this work we investigate the mechanisms of dissipation in bubble oscillations and their contribution to the total damping (Wtotal) in various nonlinear regimes. By using bifurcation analysis, we have classified nonlinear dynamics of bubbles that are sonicated with their 3rd superharmonic (SuH) and 2nd SuH resonance frequency (fr), pressure dependent resonance frequency (PDfr), fr, subharmonic (SH) resonance (fsh=2fr), pressure dependent SH resonance (PDfsh) and 1/3 order SH resonance. The corresponding Td, Rd, Ld, Cd, Wtotal, scattering to dissipation ratio (STDR), maximum wall velocity and maximum back-scattered pressure from non-destructive oscillations of bubbles were calculated and analyzed using the bifurcation diagrams. We classified different regimes of dissipation and provided parameter regions in which a particular parameter of interest (e.g. Rd) can be enhanced. Afterwards enhanced bubble activity is linked to some relevant applications in ultrasound. This paper represents the first comprehensive analysis of the nonlinear oscillations regimes and the corresponding damping mechanisms.