Metamaterials in Relation to Microwaves

Metamaterials are defined as artificial materials composed of periodic structural units to obtain their unusual properties that are not usually found in nature. Of particular interest in the microwave range are materials that interact with the electromagnetic field, as if they would have negative permittivity and/or magnetic permeability. In ordinary materials, negative permittivity or magnetic permeability is possible in the frequency range of antiresonances of polarization or magnetization. The paper examines the possibility to classify metamaterials by the negative values of their susceptibilities, since just these parameters characterize the antiphase response of substance to the applied electromagnetic field. Therefore, there are certain grounds for expanding the usual concept of metamaterials in relation to their use in microwaves.