Unity absorbance layers - optimal design criteria

TL;DR

This paper derives the conditions for achieving perfect absorption in thin planar layers, revealing that a double-layer grid can be optimized for zero transmission and reflection, especially at large wavelengths.

Contribution

It provides necessary and sufficient conditions for unity absorbance in thin layers, including explicit criteria at large wavelengths and design insights for ultra-thin absorbers.

Findings

Zero transmission and reflection require the second sheet to be a perfect conductor.

Operational frequency tuning is possible by adjusting grid impedance.

Explicit conditions are derived for large wavelength limits.

Abstract

We present the necessary and sufficient conditions for the unity absorbance of thin planar layers. With a simple structure comprising a double-layer grid, it is shown that zero transmission and reflection is feasible only if the second sheet is a perfectly conducting wall. The operational frequencies can be varied by tuning the grid impedance. Explicit conditions are given at the large wavelength limit; these underline the fundamental of ultra-thin perfect antennae and absorbers.