Figure 7.

Variation of the subharmonic threshold of a Sonazoid microbubble with normalized excitation frequency (a) as predicted by the viscoelastic EEM. Inset: The variation of the effective surface tension with instantaneous radius for the same contrast agent. (b) Effects of radius variation on viscoelastic EEM. (c) Non-negative [γ=0 if γ(R)<0] viscoelastic EEM. (d) Effects of radius variation on the non-negative [γ=0 if γ(R)<0] viscoelastic EEM. For the non-negative cases (c) and (d), $f_0^n$ is defined in the text.