Abstract
Microbubbles oscillate nonlinearly in the ultrasound field. By irradiating ultrasound, microbubbles reflect superharmonic or subharmonic signals. In particular, microbubbles coated by a protein, lipid, or polymer shell show a mechanical property different from that of micobubbles without shell. In this research, nonlinear oscillations of shell-coated microbubbls were compared with those of gas microubbles. We use the modified Rayleigh-Plesset equation introduced by P. Marmottant, et al. which describes the dynamics of microbubbless coated with lipid shell that has viscosity and elasticity. The dynamical behavior of insonified shell-coated microbubbles was investigated by numerical simulation. Our numerical results suggest the possibility that the oscillation center shifts to the side of bubble compression, and that the response of a shell-coated microbubble has both hardening and softening effects, because the surface tension changes with the bubble radius if the bubble shell exists. Moreover, these results are in qualitative agreement with experimental ones.
