Experimental demonstration of terahertz metamaterial absorbers with a   broad and flat high absorption band
  We present the design, numerical simulations and experimental measurements of THz metamaterial absorbers with a broad and flat absorption top both for transverse electric and transverse magnetic polarizations over a wide incidence angle range. The metamaterial absorber unit cell consists of two sets of structures resonating at different but close frequencies. The overall absorption spectrum is the superposition of individual components and becomes flat at the top over a significant bandwidth. The experimental results are in excellent agreement with numerical simulations. 
Li Huang, Dibakar Roy Chowdhury, Suchitra Ramani, Matthew T. Reiten,   Sheng-Nian Luo, Antoinette J. Taylor, and Hou-Tong Chen
physics.optics cond-mat.mtrl-sci