Scattering design : absorption enhancement and frequency selective metasurfaces

Abstract

In this work, we develop frameworks to study and design the scattering properties in two kinds of systems. For the first problem, we find approximate angle/ frequency-averaged limits on absorption enhancement due to multiple scattering from arrays of "metaparticles", applicable to general wave-scattering problems and motivated here by ocean-buoy energy extraction. We show that general limits, including the well known Yablonovitch result in solar cells, arise from reciprocity conditions. The use of reciprocity in the radiative transfer equation (similar to a stochastic regime neglecting coherent effects) justify the use of a diffusion model as an upper estimation for the enhancement. This allows us to write an analytical formula for the maximum angle/frequency-averaged enhancement. We use this result to propose and quantify approaches to increase performance through careful particle design and/or using external reflectors. For the second problem, we develop a design method for multi-grid frequency selective metasurfaces based on temporal coupled mode theory (CMT). In particular, we design an elliptic passband filter with a center frequency of 10 GHz, bandwidth of 10% and relatively good angle dependence.