FDTD Analysis of Sub-Wavelength Focusing Phenomena in Plasmonic Meta-Screens

The Finite-Difference Time-Domain (FDTD) method is used to study the frequency dependence of the transmission through a plasmonic screen with slots of sizes and spacing that were chosen using the spatially shifted beam approach to achieve subwavelength focusing. It is shown that the electric field beamwidth at the focal plane exhibits a resonance-like behavior in the vicinity of the frequency for which the meta-screen was designed to work. At this frequency range, the power flow path is shown to exhibit circulation around the slotted screen. Results are also compared with those given in [1] for a similar device working at a lower frequency range where the metallic screen behaves as a perfect electric conductor.