On acoustic cavitation of slightly subcritical bubbles

The classical Blake threshold indicates the onset of quasistatic evolution leading to cavitation for gas bubbles in liquids. When the mean pressure in the liquid is reduced to a value below the vapor pressure, the Blake analy sis identifies a critical radius which separates quasistatically stable bub bles from those which would cavitate. In this work, we analyze the cavitati on threshold for radially symmetric bubbles whose radii are slightly less t han the Blake critical radius, in the presence of time-periodic acoustic pr essure fields. A distinguished limit equation is derived that predicts the threshold for cavitation for a wide range of liquid viscosities and forcing frequencies. This equation also yields frequency-amplitude response curves . Moreover, for tired liquid viscosity, our study identifies the frequency that yields the minimal forcing amplitude sufficient to initiate cavitation . Numerical simulations of the full Rayleigh-Plesset equation confirm the a ccuracy of these predictions. Finally, the implications of these findings f or acoustic pressure fields that consist of two frequencies will be discuss ed, (C) 1999 American Institute of Physics. [S1070-6631(99)00302-5].