Method for separation of acoustic levitation and rotation modes leading to arbitrary axes of rotation

Abstract

A method for separating acoustic levitation and rotation of small objects has been developed and tested experimentally. Sample rotation in an acoustical resonance chamber requires a phase difference between two equal frequency (degenerate) modes. Therefore, this method uses one set of nondegenerate modes for levitation and higher order sets of degenerate modes for rotation. This separation of modes may be accomplished by appropriate choices of chamber dimension ratios producing up to three sets of degenerate orthogonal higher order modes. By appropriate excitation of these sets of modes, arbitrary axes of rotation may be achieved. This technique for one rotation axis was verified experimentally using a rectangular chamber. Spherical samples were stably levitated without rotation using the three orthogonal fundamental modes, and rotated about the z axis by generating a phase difference between the degenerate third and fifth harmonics of the x and y directions, respectively. A video tape of these levitation experiments will be presented. [Work supported by NASA.]