Ultra-wideband terahertz metamaterial absorber based on Snowflake Koch Fractal dielectric loaded graphene

In this paper, an ultra-wideband terahertz metamaterial absorber is introduced based on a Snowflake Koch Fractal (SKF) dielectric loaded on a sheet of graphene. Instead of multilayered-graphene conventional structures, a single-layered non-structured graphene absorber is presented based on gradient width modulation and cavity method. The structure of the absorber is composed of four layers, which are upper SKF dielectric and metal film layer form two mirrors of an asymmetric Fabry-Perot cavity to confine terahertz electromagnetic (EM) waves. Full wave simulations demonstrate that the proposed structure is highly efficient whereas a 161% fractional bandwidth of over 0.9 absorbance is achieved under normal incident wave considering both TE and TM polarizations. The proposed structure is polarization insensitive yielding the same absorbance for both TE and TM polarizations. The absorbance and bandwidth of the structure is almost independent of altering the incident angle theta up to 60 degrees and 30 degrees for TM and TE polarizations, respectively. Avoiding graphene processing and simple shape geometry are the interesting advantages of this structure resulting in feasible fabrication. The proposed structure provides much greater absorbance bandwidth in comparison to previous works. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement