Wavefront control of microwaves with a conductive mesostructure: theory

摘要

The initial theory for a novel type of wavefront controller for microwaves is described. This controller is based on the principle that the effective refractive index of a structure is a square root product between the permittivity and permeability of a material, n = (εμ)~(1/2). With high conductivity metals, such as silver, light acquires an effective mass so that, the longitudinal mode has a finite frequency known as the plasma frequency, ω_p. Below that frequency the dielectric function is negative, allowing no modes in the bulk of the metal. This is responsible for the amazing and unique properties of structured metals. One may, by extension of scale, design a metallic structure whose effective ε is negative, for wavelengths longer than the structure's unit cell. Such structures have been suggested recently by Pendry et al. The symmetry of Maxwell's equations implies that magnetic structures can be engineered from non-magnetic materials, so that an effective μ is produced down to negative values. An example of such a structure is investigated here in detail. I also discuss how the electric and magnetic structures are combined to produced a controllable refractive index over the unit cell, implying that we can construct wavefront controllers from conductive mesostructures.