Metamaterials in electromagnetics

This article takes a look at metamaterials in electromagnetics from a general point of view. The terminology of complex electromagnetic materials is discussed critically. A unique definition for metamaterials does not exist, but certain salient points can be distinguished in the ongoing discussion within the research community and in various formal suggestions for this definition in the literature. Also several different classes of special materials are identified as candidates for metamaterials and their particular characteristics are discussed. Finally it is pointed out that the boundary between “ordinary” materials and metamaterials is difficult to draw because also many everyday natural materials are dielectric mixtures which may display very surprising and non-linear macroscopic response functions.