Holographic visualization of secondary ultrasonic waves radiated from micro-bubbles

When the micro-bubble oscillates under the ultrasonic wave, the bubble radiates secondary waves around it. This wave generates secondary Bjerknes force between the neighboring bubbles and the force assists inherent bubble movements such as bubble aggregation inside the ultrasonic wave field. In this paper, a novel technique to characterize the secondary ultrasonic wave from the bubbles is proposed. This method is based on the observation of fringe like pattern produced around the bubble of interest. This pattern is produced by micro bubbles which are trapped inside the interference wave field of incident wave and the secondary wave. The experiments are carried out by an ultrasonic wave contrast agent "Levovist" (SCHERING A.G. Germany). The fringe like patterns are observed for relative large aggregated bubbles.