ON THE RELATION BETWEEN SURFACE-WAVES ON A BUBBLE AND THE SUBHARMONICCOMBINATION-FREQUENCY EMISSION

The characterisation of bubbles using a two-frequency excitation techn ique is known to accurately detect and size certain bubble samples. Th is is done through the generation of a signal at omega(i) +/- w(p)/2 w hen the bubble is insonified by a fixed MHz imaging signal, omega(i), and a variable pumping frequency, omega(p), tuned to the bubble's reso nance. Recent work has suggested that the principal mechanism for the generation of the omega(i) +/- w(p)/2 signal is linked to the onset of surface waves on the bubble's surface. This paper strengthens this ar gument through the comparison of published experimentally measured thr esholds for the omega(i) +/- omega(p)/2 signal with recent theoretical models which predict the driving sound field pressure amplitudes requ ired for the onset of surface waves on a spherical surface.