Acoustic levitation by Oseen drag

Acoustic levitation of spherical particle samples was demonstrated using the steady force exerted by a harmonically distorted acoustic wave. The force arises due to a nonlinear dependence of the fluid drag on the velocity of flow around the sphere. The experimentally determined acoustic intensity required for levitation against gravity was found to be proportional to the particle radius and the particle density in agreement with theory. Levitation was demonstrated for samples with particle diameters ranging from 5 μm to 8 mm and in a variety of gases and at several gas pressures.