Free-space characterization of conductor-backed absorbing materials using an aperture screen

Absorbing materials are often adhered to conducting surfaces for the purpose of controlling the electromagnetic field scattered by objects. Many of these materials have both electric and magnetic properties, and these properties may degrade with time, thereby decreasing the effectiveness of the coatings. Because of this, it is important to accurately assess the condition of the coatings by interrogating them with an electromagnetic wave and analyzing the interaction of the wave with the coating materials. Ideally, the permeability and permittivity of the coatings would be measured and compared to baseline values. Since these measurements must be done in the field, the materials cannot be removed from the underlying conducting surfaces.