Fundamental investigations of double-negative (DNG) metamaterials including applications for antenna systems

Abstract

The postulated characteristics of double-negative (DNG) materials--i.e., materials with simultaneously negative permittivity and negative permeability (ε < 0, μ < 0)--and recent attempts to realize those characteristics with synthetic metamaterials are briefly reviewed. Investigations into the causality of signal propagation in a DNG medium are then presented. Previous research in this topic is examined, and it is verified that a DNG medium must be dispersive in order to be causal. An accurate time-domain description of propagation in a DNG medium is shown to be elusive due to the presence of dispersion, though approximate solutions and recommendations for future analytical research are provided. The results of numerical investigations into this topic are then discussed, and the anticipated combination of causal signal transmission and a negative phase shift are observed in the numerical data. Potential applications of DNG metamaterials to antenna systems are then presented. A DNG shell is observed to reduce the intrinsic reactance sensed by an infinitesimal electric dipole, thereby increasing the dipole's radiated power. Analytical expressions for the fields in the dipole--DNG shell system are derived, and numerical results for a variety of DNG shell configurations are discussed. The presence of a DNG shell is shown to increase the dipole's radiated power by orders of magnitude in some cases. A circuit model of the dipole--DNG shell system is additionally presented and used to interpret the system's physical behavior. The scattering properties of nested metamaterial shells are then analyzed. Various layering combinations of DNG, double-positive (DPS) and single-negative (SNG) shells are observed to produce resonant scattering of an incident, fundamental radial transverse-magnetic (TMᵣ) wave. Reciprocity between the metamaterial configurations that exhibit TMᵣ scattering resonances and those shown to maximize the power radiated by the infinitesimal electric dipole is demonstrated. Several additional metamaterial configurations are shown to produce both resonant TMᵣ scattering and resonant dipole radiation. A resonant configuration with one epsilon-negative (ENG) shell is especially appealing due to its manufacturability. The effects of a DNG layer on the creeping waves scattered by a small metal sphere are also discussed as a minor yet curious offshoot to the scattering analyses.