▎ 摘　　要

In this paper, tunable and efficient absorbers are proposed based on graphene-metal nano structures. The designed structures are consisted of multi layers of graphene (ring- and plate-shaped) and gold (5*5 cells) on the background of silica. By introducing different ring-shaped graphene layers (one, two or three), the near unity absorption coefficient can be achieved. The effects of different parameters like the distance, radius and chemical potential (h(1), R-in1, E-fR1, h(2), R-in2, E-fR2, h(3), R-in3, E-fR3) on the absorption spectrum (wavelength and value) are also considered. The best resonant peak (near unity) is obtained for the structure with three ring-shaped graphene layers. The final proposed structure (with three rings) can be utilized as an effective sensor for detecting materials with different refractive indices (from 1. to 1.5) with sensitivity of 100 (nm/RIU). The designed structure can be applied as a strong absorber or sensitive sensor in nano-optical systems.