Complex dynamics of charged bubble oscillators in a fluid under acoustic forcing

Theoretical studies of an electrically charged gas bubble in a fluid, undergoing forced radial oscillations due to an acoustic pressure wave, reveal distinct dynamical behaviour in different regimes. These have long been of interest, be it in the context of cavitation damage or in studies of sonoluminescence. The presence of electrical charge greatly influences the dynamical properties of the oscillating bubble, which shows a very nonlinear dependence on the control parameters affecting it. Parameters include charge, the driving frequency of the acoustic wave, the pressure amplitude, etc., and bifurcation plots for the bubble radius plotted against these show distinct regimes ranging from regular periodicity to nonlinear oscillations that also go into chaotic oscillations. An expansion-compression ratio which we introduce immediately allows us to pinpoint the pressure range between the upper transient and Blake thresholds in which the oscillating bubble is in an unstable regime. We have also shown how there are thresholds for the charge and the pressure. The dynamics of the bubble is crucially dependent on its radius, with nano- and micrometer scale behaviour showing distinct differences, and we present some of our recent results. We also present some of our recent results for viscosity effects on bubble oscillations, very relevant for non-Newtonian and complex fluids.