On the relation between surface waves on a bubble and the subharmonic combination-frequency emission

Abstract

The characterisation of bubbles using a two-frequency excitation technique is known to accurately detect and size certain bubble samples. This is done through the generation of a signal at Wi ± Wp/2 when the bubble is insonified by a fixed MHz imaging signal Wi and a variable pumping frequency, Wp , tuned to the bubble's resonance. Recent work has suggested that the principal mechanism for the generation of the Wi ± Wp /2 signal is linked to the onset of surface waves on the bubble's surface This paper strengthens this argument through the comparison of published experimentally measured thresholds for the Wi ±Wp /2 signal with recent theoretical models which predict the driving sound field pressure amplitudes required for the onset of surface waves on a spherical surface