Characterization of secondary ultrasonic waves radiated by two oscillating bubbles

Purpose A bubble oscillating under an ultrasonic wave produces an interference sound field with the incident ultrasonic wave, forming fringe patterns of trapped microbubbles. We discuss secondary ultrasonic waves radiated by two oscillating bubbles in the incident ultrasonic wave in terms of both theory and experimental conditions.Methods Two oscillating bubbles produce an inherent secondary wave field that varies with the distance between the two bubbles and the phases of these waves. Here we discuss the Bjerknes force derived for two bubbles and microbubble trapping around the bubbles. The experiments were carried out using microbubbles produced with an ultrasonic contrast agent (Levovist).Results and conclusions The microbubble-trapping pattern observed around the bubbles in the experiment closely agrees with the numerical simulation.