Thin electromagnetic absorber using frequency selective surfaces

Frequency selective surfaces (FSS) have been widely used for many years in antennas applications, like beams multiplexer, or filtering for microwave and optical signals. We present a new application for FSS. For the former applications, FSS are free standing or backed by a perfect dielectric. It can be also embedded into a dielectric medium or sandwiched between different dielectric media. In the new application, FSS are used as components of radar absorbing materials (RAM). Classical RAM are composed of several layers of dielectric or magnetic media. For example, the two most famous absorbing screens are the Dallenbach and the Salisbury screens. The first is a short circuited lossy dielectric (or magnetic) layer, while the second is composed of two layers. The Salisbury screen consists of a thin resistive film deposited on a perfect metal-backed dielectric layer. We show how a FSS can modify and improve the absorption performance of Dallenbach screens. The FSS is deposited on the outer surface of the Dallenbach screen in this new application. We show numerically that the absorption band can be either shifted or broadened by the presence of an FSS. We illustrate the numerical results with measurements. The theoretical aspects of the computation of the interaction between the electromagnetic field and the structure are discussed, and the properties of the new absorbing screen are examined.