▎ 摘　　要

A dual-frequency broadband terahertz metamaterial absorber, composed of a periodically ellipse-shaped graphene array placed over a thin SiO2 layer and a lossy polyimide layer backed with a gold ground, is proposed in this article. The numerical simulation results reveal that the effective absorption band (absorption > 0.9) ranges from 0.3 THz to 0.75 THz and 1.57 THz to 1.87 THz, with a favorable independence of incident angle. Furthermore, replacing the gold ground with a frequency selective surface inserted with graphene, another absorbing peak appears between two broad absorbing bands and can be continuously tuned from 1 THz to 1.3 THz by controlling the chemical potential of graphene from 0 eV to 0.5 eV in the FSS. To improve the absorbance of the tunable absorbing peak, a backed cavity is added to the structure, which promotes the absorbance from 0.6 to more than 0.9 with unaffected tunability. These designs overcome limitations of traditional absorbers and have promising applications for filtering, detecting, and sensing. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement