Recently, we have presented an idea for using metamaterial layers to enhance the transmission through a sub-wavelength aperture in an opaque screen. Our work was inspired and motivated by the experiments performed in the past few years by several groups worldwide, in which they demonstrated a significant enhancement of optical transmission through a single sub-wavelength hole in a metallic screen when the aperture is surrounded by properly designed periodic corrugations. Oliner, Jackson and their co-workers have elegantly explained this effect in terms of the leaky-wave theory, revealing how this phenomenon may be enhanced by a judicious choice of corrugation periods. Two important features were shown to be essential in their theory: (1) the screen material must have a negative permittivity at the operating frequency, thus allowing presence of the surface plasmons on the screen; (2) the corrugation should have a certain periodicity to excite the leaky waves. Here we present a review of our recent theoretical results, which rely on a different setup: a homogeneous metamaterial slab is placed over a perfectly conducting flat screen with a small hole. In some recent works, we have shown theoretically how a proper choice of material parameters for the metamaterial cover may lead to an analogous enhancement of transmission through the hole. In this problem, the screen may be perfectly conducting, and unlike the cases studied by others, no corrugation or periodicity on this screen is needed here. The leaky wave at the surface of the metamaterial cover provides similar effects both in collecting power from an incident plane wave and directing it into the hole and in increasing the wave transmission in the broadside direction on the other side of the screen. In this chapter, an overview of this idea is given, and the interested reader is referred to the references with detailed information.
Alù, A., Bilotti, F., Engheta, N., Vegni, L. (2005). A review on the potential use of metamaterial layers for increasing the transmission through a single sub-wavelength aperture in a flat opaque screen. In Periodic Structures (pp.271-291). pavia : Maurizio Bozzi and Luca Perregrini.