A high-performance broadband terahertz absorber based on multilayer graphene squares

The efficient electromagnetic absorber is highly demanded in device applications. A big challenge is to design the absorber of very thin thickness and broad bandwidth, which is even more difficult at terahertz regime. In this article, we propose and numerically (finite element method, FEM) demonstrate a high-performance broadband absorber with near-perfect absorption over terahertz band based on multilayer graphene squares. The absorber consists of four graphene layers in which the width of the square is gradually increased, and a bottom gold layer separated by a dielectric spacer. The proposed structure can achieve above 90% wave absorption for the frequencies from 1.45 THz to 4.35 THz, with a bandwidth of 2.9 THz and the bandwidth fraction of 100%. Because of symmetry of the structure, this terahertz absorber is polarization insensitive and can work at a large angle range of oblique incidence, for instance absorptance can be maintained nearly unchanged up to 40° for transverse electric polarization and up to 45° for transverse magnetic polarization. Except for the layer stacking, our design is very easy to be realized in experiment, since only the simple square shape and a uniform 0.4 eV Fermi level are used in our design, which may play an important role in future terahertz device applications. (paper)