FIG. 1.
Simulation illustrating the acoustic radiation force from the same vortex beam on 3-mm (a-d) and 4-mm (e-h) diameter solid glass spheres located near the acoustic beam axis. The acoustic wave propagates from left to right in the z direction, and with the color pattern displays the distribution of the instantaneous pressure. The location of the center of the sphere is indicated by xs in mm. The arrow indicates the direction and magnitude of the acoustic radiation force, which comprises x and y components. Depending on the sphere’s radial location, the resulting acoustic force either restores the sphere toward the center of the beam as in (b & f) or pushes the sphere out of the beam as in (d & h).