Resonance effects for different states of a circulating bubble

The influence of an RF field superimposed on the DC bias on the tangential drive requirement of a moving bubble was measured. The bubble was maintained in continuous circular motion in a rotating gradient apparatus. With appropriate amplitude and frequency of RF field, the drive field required to move the bubble could be reduced. A minimum in the drive field occurred at an RF frequency of about 20 MHz. The measurements were performed for bubbles with and without Bloch lines. There was no discernible difference in drive field requirement between S=1 and S=0 bubbles. A harmonic oscillator model for the radial motion combined with the standard model for coercive pressure was used to calculate the expected velocity versus tangential drive relation. The principal features of the experimental results were borne out in the calculations