Excitation thresholds for subharmonic response of ultrasound contrast microbubbles

Abstract

The excitation threshold for subharmonic generation plays an important role in accurate prediction of various subharmonic scattering related observations. The classical understanding suggests that minimum subharmonic threshold occurs near twice the resonance frequency. We numerically show that for a number of models-Newtonian (Chatterjee and Sarkar 2003) and viscoelastic (Sarkar et al 2005) interfacial rheological models, and a model due to de Jong et al (1994)-of encapsulation as well as for free bubbles, the minimum subharmonic threshold is obtained near twice the resonance frequency. However, for other models-linear viscoelastic model (Church 1995, Hoff et al 200), model due to Marmottant et al (2005) and strain-softening interfacial rheological model (Paul et al 2010), the minimum threshold does not always occur at twice the resonance frequency. They have minimum threshold near resonance frequency depending on encapsulation parameters such as elasticity and viscosity. © 2011 Acoustical Society of America.