Session: P2B

oscillation of newly coming bubble is between -90 to 90 degrees. Under this condition, the radius of the aggregated bubbles is determined by the ultrasonic wave frequency and the relative phase. Based on the model, numerical analysis is carried out. The Bjerknes force over (x,y) plane is evaluated for two or more bubbles cases. The stability of a couple of aggregated bubbles is also discussed. The experiments are done for the bubbles which are produced by an ultrasonic contrast agent “Levovist” (Schering, A.G. Germany) and the bubbles with relative hard PVC shell. The frequency of the ultrasonic wave is from 2.5MHz to 7.5MHz. The sound pressure is up to 200 kPa. The aggregated bubble size and the micro bubble trapping pattern around the center bubble are well in agreement with the numerical estimation. As an application of the bubble aggregation by ultrasonic waves, characterization of secondary ultrasonic wave radiation from the aggregated bubble is proposed. This method estimates the relative phase of secondary ultrasonic waves by measuring the bubble aggregation pattern. This gives useful information in considering the bubble motion due to the interactive force between the neighboring bubbles.