In this paper, we proposed and designed a plasmonic filter based on a suspended graphene sheet using ring resonator to operate in terahertz range of frequencies. The effective index method is applied to simulate and analyze the structure in two-dimension modeling. We evaluated the transmission coefficient and tunability behavior of the proposed structure via applying finite element method. It is found that the characteristic of the structure can be adjusted through two techniques; (1) controlling the resonant frequencies by fine-tuning the Fermi level of the graphene and (2) tuning the resonant wavelengths by changing the ring resonator dimensions and shape (making a gap in the ring). Also the simulated results show that the terahertz wave transmission ratio can be adjusted from 33.64 to 97.17% by changing the chemical potential of the suspended graphene sheet. These properties are very suitable for adjustable multi-resonance applications such as wavelength based electro-optical switching in terahertz range of operation.
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