Individually addressable, interdigitated electrode arrays energized either by ac or by traveling-waves can create electric field shields. Some arrays were coated with thin dielectric layers to improve stability. In conductive aqueous solutions (up to 7 S/m) and at frequencies between 1 kHz and 200 MHz, microscopic particles and living cells showing negative dielectrophoresis are repelled from the electrode plane. Calculations were carried out to estimate the forces acting on particles and the heat production (losses) for various electrode geometries and properties of the insulating layer. We show, both experimentally and theoretically, that surfaces can be protected from cells adhesion and deposition of most artificial particles with effective diameters above 100 nm for many days. Additionally, the presented structures can be used as efficient microparticle filters.