▎ 摘　　要

In this paper, an ultra-wideband terahertz absorber is designed utilizing a graphene-based metasurface. The absorber is composed of three layers including the graphene metasurface, Topas-cyclic olefin copolymer dielectric substrate, and a gold ground layer. The particle swarm optimization algorithm and interpolate quasi-Newton optimization are utilized to find an optimized structure with the widest bandwidth. Full-wave simulations verify achieving absorbance of more than 90% in an extremely wide frequency band within the range ofl THz to 3.5 THz (fractional bandwidth = 111%) under illumination of a normal incident wave. The proposed structure is polarization insensitive up to a polarization angle of 75 degrees, while the performance of the absorber (absorbance level and bandwidth) is al most fixed for incident angles theta up to 60 degrees. Moreover, the switching capability of the structure from reflection (>92%) to absorption (>90%) is investigated. The equivalent circuit model is extracted for the designed absorber, and the corresponding result is compared to that of the full-wave simulation, which confirms the validity of the extracted circuit. (C) 2020 Optical Society of America