DESIGN OF METALLIC METAMATERIAL STRUCTURES AT HIGH FREQUENCIES

We discuss the design of metamaterials made up of metallic structures that can have negative material parameters such as the dielectic permittivity (∊), the magnetic permeability (μ) and the refractive index (n), with a view to optimize their performance at high frequencies. We also discuss the behavior of metamaterials in the optical frequency regime where homogenization procedures become questionable. A medium consisting of an array of split ring resonators (SRRs) can have negative phase velocity (suggesting a negative index of refraction) for specific directions of incidence at optical frequencies. However, owing to the fact that the size of the SRR is comparable to the wavelength of the incident radiation, the electric fields interact strongly with even symmetric SRRs at these frequencies. The negative phase velocity is found to arise from plasmonic excitations of the SRR and we cannot describe this effect by means of the usual paradigm of negative permittivity and negative permeability. The focusing of light by arrays of SRRs (both ordered and disordered) in the manner of the Veselago lens is presented. The results show that the focusing properties and the negative phase velocity arise primarily from excitations of localized resonances and not from Bragg scattering.