Figure 6.

Variation of subharmonic response (a) with excitation pressure for a free bubble of $R_0^0=2\mu \mathrm{m}$ at different excitation frequencies and zero ambient over-pressure, (b) with ambient over-pressure for a free bubble of $R_0^0=2\mu \mathrm{m}$ at different excitation frequencies and P_A = 0.3 MPa, and (c) with ambient over-pressure for free bubbles of radius $R_0^0=1,2,3,4$, and $5\mu \mathrm{m}$ at excitation frequencies such that $f=1.8f_0^0$.