In this paper, a tunable absorber composed of graphene ring and quadrants, silicon dioxide layer and gold substrate is proposed. The absorption spectrum of the structure changes by variation of chemical potential of graphene. A perfect absorption peak is achieved for the chemical potential of 1eV, which is due to increasing the surface plasmons of graphene. Also, the effect of important geometric parameters on the absorption spectrum is investigated. It is shown that by changing the refractive index of the test medium, the proposed absorber has the high sensitivity of 2323 nm/RIU. According to the obtained results, the proposed absorber can be used in various applications.
