Metamaterial covers over a small aperture
  Recently, it has been experimentally shown by several other researchers in the physics community that a properly designed periodic corrugation of a metallic opaque screen may significantly enhance the power transmission through a sub-wavelength hole in the optical frequency band. Oliner, Jackson and their co-workers explained and justified this phenomenon as the result of the excitation of the leaky waves supported by the corrugated screen. Here we suggest another setup, in which metamaterial layers with special parameters may be utilized as covers over a single sub-wavelength aperture in a perfectly electric conducting (PEC) flat screen in order to increase the wave transmission through this aperture, and we provide a detailed analytical explanation for this aperture setup that may lead to similar, more pronounced effects when the metamaterial layers are used in the entrance and the exit face of the hole in the flat PEC screen with no corrugation. Some physical insights into the function of these covers and some numerical results confirming this theory are presented and discussed. We also discuss the sensitivity of the transmission enhancement to the geometrical and electromagnetic parameters of this structure. 
Andrea Alu, Filiberto Bilotti, Nader Engheta, and Lucio Vegni