Casimir-Polder Repulsive Interaction

The Casimir effect is attractive in most vacuum-separated metallic or dielectric geometries. Two electrically neutral spatially separated systems interacting via Casimir force will have access to the stable separation state only when the force transitions from repulsive at small separations to attractive at large separations. Such issues are important in the future development of micro- and nano-electromechanical systems (MEMS and NEMS). We investigate here the Casimir-Polder free energy corresponding to interactions of a magnetically and electrically polarizable micro-particle with a magneto-dielectric sheet. Our theoretical study shows that such an interaction is tunable in strength and sign.The latter, particularly, is true provided we go beyond the natural materials and look for the meta-materials fabricated at scales between the micron and the nanometer. We assume that the particle and the sheet have access to non-tivial values of the polarizability ratio and the electromagnetic impedance, respectively. The crossover between attractive and repulsive behavior is found to depend on these quantities.