Dielectrophoretic levitation of spheres and shells

Abstract

Under certain conditions, the dielectrophoretic force can be used to levitate particles or bubbles in dielectric liquids. The strength of the dielectrophoretic force depends on the effective dipole moment which is directly related to the induced dipole field. The situation of a small dielectric sphere or shell with finite conductivity submerged in dielectric liquid also of finite conductivity is considered. Under certain conditions, a cutooff frequency exists which determines the limit above or below which levitation is no longer obtainable. To test the theory, spheres and shells of various materials are levitated in ac and dc electric fields using a cusped electric field. A fixed electrode structure is calibrated using a dielectric liquid with known properties and the quantitative results of numerous levitation experiments are favorably compared to the theoretical model. The frequency-dependent behavior of glass microballoons is found to be generally consistent with the predictions of the model. Results with dc electric fields are inconclusive due to electroconvection, electrostatic repulsion, and long charge relaxation time constants.