A new damping mechanism in strongly collapsing bubbles

A gas‐filled bubble in a liquid undergoes cycles of growth, rapid collapse, and damped rebounds in response to a driving pressure. These nonlinear oscillations can be simulated using the Rayleigh‐Plesset equation (RPE), which was developed 50 years ago and is the foundation for almost all theoretical analyses of nonlinear bubble dynamics. A major deficiency of the RPE is that for strongly driven bubbles, such as sonoluminescing bubbles, it produces large‐amplitude rebounds that often last until the next acoustic cycle of the periodic driving pressure. This is in contrast to the data, which show rapidly damped rebounds. Every derivation of the RPE assumes that the compressibility of the liquid gives rise to the damping. It is shown here that appreciable damping also comes from the most compressible part of the system, which is the gas; specifically, the damping arises from the inhomogeneous pressure field within a rapidly collapsing or expanding bubble. This simple physical reasoning generates a new modification of the RPE that better reproduces the extreme damping that is observed experimentally; a result that cannot be obtained with any other version of the RPE. Our results affect theoretical predictions of the limits of stability of sonoluminescing bubbles as well as theoretical predictions of the magnitude of acoustic emissions from collapsing bubbles.