Abstract: A system for positioning and sizing microbubbles in a liquid such as water. first source of acoustic energy produces a first acoustic signal in the liquid, and a second source of acoustic energy produces a second acoustic signal in the liquid. The first and second sources of acoustic energy are positioned and aligned so they produce a standing wave field in the liquid. The standing wave field creates forces which position microbubbles at the antinodes or nodes of the standing wave field. By selecting a frequency for the acoustic signal and a frequency for the second acoustic signal which are slightly different, the standing wave field can cause the positioned microbubbles to move towards or away from a surface region in contact with the liquid.