Microwave chiral materials

A chiral material is one that has a distinct left- or right-handedness about its structure, arising from handed molecules or from handed scattering particles such as helices. The electromagnetic consequence of this is that left-handed circularly polarised waves travel with a different velocity and absorption from right-handed waves. Chirality is thus a generalisation of the more familiar phenomenon of optical activity. Initial theoretical explorations of possible applications have often used arbitrary chiral parameters. It is necessary to establish whether the chirality can be made large enough in practice, and that no undesirable side-effects are introduced with the chirality. The helices commonly used as chiral elements affect the permittivity and the permeability of the composite, as well as its chirality. Thus the chirality cannot in practice be varied independently. We have therefore constructed a theory to predict the constitutive parameters of the composite in terms of the basic properties of the host medium and the chiral scatterers. These can be varied independently, and the chirality obtained should then be realizable. We have also performed experimental measurements to validate the theory