As frequency increases, resonant size of the bubbles decreases. Vibration amplitude of neighboring liquid particles is maximized at resonant size. Two bubbles attract if they are equal in size or if both are smaller than resonant size. If one bubble is larger than resonant size and one smaller, the bubbles repel at large distances but attract at small distances. Net movement forces propel bubbles along the direction of propagation, maximum velocity of movement when bubbles are resonant size.
Large bubbles collect at pressure minima in standing wave conditions.
Bubbles smaller than resonant size collect at pressure maxima in standing wave conditions. Very active region. Particles near the bubbles are attracted to area of bubbles and may attach to bubbles. Microstreaming around bubbles is complex and may cause significant shearing action in the area between and around bubbles. Lung tissue - Ultrasound induced lung hemorrhage has been demonstrated under experimental conditions in several species.