Dipole antennas enclosed in double negative (DNG) and single-negative (SNG) nested spheres: efficient electrically small antennas

Metamaterials are engineered media whose electromagnetic responses are different from those of their constituent components. They are often generated by incorporating in a periodic manner various types of artificially fabricated, extrinsic inhomogeneities in some background substrate. The dimensions of these inhomogeneities are usually much smaller than the operating wavelength, e.g., ~lambda/10, which leads to effective media. Metamaterials that mimic known material responses or that qualitatively have new response functions that do not occur in nature have been realized. There are several classifications of metamaterials. We choose to name them based on their fundamental properties, i.e., by the signs of their permittivity and permeability. The double positive (DPS) metamaterials have both the permittivity and permeability positive, i.e., epsi > 0, mu > 0. The epsilon-negative (ENG) metamaterials have the permittivity less than zero, i.e., epsi < 0, mu > 0. The mu-negative (MNG) metamaterials have the permeability less than zero, i.e., epsi > 0, mu < 0. The double negative (DNG) metamaterials have both the permittivity and permeability negative, i.e., epsi < 0, mu < 0. There have been a variety of antenna applications conceived and realized with these various types of metamaterials that provide significant improvements in their performance. We consider here an electrically small dipole antenna enclosed in a set of nested DPS, DNG, and ENG shells