The periodicity between the aggregated microbubbles by secondary radiation force

Secondary radiation force originates from the pressure gradients in the re-radiated ultrasonic field of pulsating bodies. The expansion and contraction of microbubbles generates a force due to the relative acceleration between the fluid and pulsating body, which can attract or repel other microbubbles. This mutual interaction between the pulsating bubbles can causes the formation of stable bubble clusters. This aggregation pattern of the bubbles is also referred as a “bubble grape”. In this study, stable microbubble clusters with periodicity were observed in an acoustically and optically transparent tube. Different theories and models were given to explain the periodic aggregation pattern in a microbubble cloud due to the secondary radiation force.