Nonlinear Modeling of Interactions between Ultrasound Propagation and Cavitation Bubbles

The mechanism of interaction between ultrasound waves and cavitation bubbles in therapeutic ultrasound applications is responsible for several therapeutic effects as well as for undesired side-effects. To further develop therapeutic applications it is essential to improve the understanding of these interactions. In this paper a numerical model is presented to simulate nonlinear ultrasound propagation in the presence of cavitation bubbles. The model is based on a two-phase continuum approach for the bubbly liquid. Simulation results for the propagation of shock waves in water with different gas contents demonstrate that the first positive pressure part of a shock wave is not affected. But with increasing gas content the tensile part gets shorter and is followed by augmented pressure oscillations even for the propagation of a single pulse. Numerical investigations are validated by measurements in water with different gas contents. Calculations as well as experiments demonstrate that the activity of cavitation bubbles induced by the shock wave itself causes significant changes in the decaying part of the pressure signal.