A three-dimensional negative refractive index medium operated at multiple-angle incidences

We present a negative refractive index medium (NRIM) operating at multiple-angle incidences by expanding a conventional planar metamaterial to a three-dimensional (3D) structure. The proposed 3D NRIM is comprised of semi-spherical metal shells and planar plamonic wires, thus giving rise to negative magnetic permeability and negative electric permittivity, respectively. Our results show that reflectance (transmittance) peaks slightly which locate the region of negative refraction index are insensitive to the incident angles from 0 degrees to 45 degrees and the polarization of the excitation wave at a certain range of frequencies. Such pseudo-isotropic NRIM may be exploited for superlens and antenna applications.