Dielectrophoretic levitation of spheres and shells

The effective dipole moment was calculated for small solid spheres and shells of insulating and conducting dielectric material. Steady state dc and ac solutions were obtained. The step response to a suddenly applied dc electric field was also determined. The steady state ac case was characterized by a cutoff frequency which determined whether levitation was possible for certain types of particles. Spheres and shells of various materials were levitated in ac and dc electric fields using a cusped electric field. A fixed electrode structure was calibrated by use of a dielectric liquid with known properties, and the quantitative results of numerous levitation experiments were favorably compared to the theoretical model. The frequency dependent behavior of glass microballoons was found to be generally consistent with the predictions of the model. Results with dc electric fields were inconclusive due to electroconvection, electrostatic repulsion, and long charge relaxation time constants.