Viscosity in the compression phrase is appreciably different than in the rarefraction phase. Forces on the suspended particles are not enough to return them to initial position. FDA recently approved a commercial device for that purpose. Improved and more rapid bone repair is reported with daily ultrasound treatments. Appearance of bubbles or cavities represent rupture of a liquid medium.
Rupture is the breaking of molecular bonds as a result of stress, fatique of the medium.
Increase in temperature of the medium can reduce rupture threshold. The collapse of the bubbles may create sonochemicals formed by free radicals and their products, and sonoluminescence , the production of light. A class of cavitation in which a violent collapse of the bubble does not occur. In noninertial cavitation motion of bubbles can cause acoustic streaming, heat production, and radiation forces on surrounding particles. Bubbles are stabilized and grow by rectified diffusion or coalescence, and exert forces on each other.