In this research, a three-dimensional (3D) graphene intrinsically chiral metastructure in terahertz (THz) region was proposed and analyzed. The unit cell consists of bi-layer cross-shaped graphene ribbons in which the back layer is rotated compared to the front layer. Parameter retrieval method and Kramers-Kronig relations are used for theoretical analysis and derivation of the right-handed and left-handed electromagnetic effective refractive indices of the proposed structure. Based on our analysis, the proposed meta-structure has a tunable and controllable chiral response due to the tunability of graphene and circular dichroism (CD) was reached to 0.2. In order to evaluate the performance of the THz device in biosensor application, its characteristics in chiral biomolecule (collagen) sensing was analyzed. With an optimum design, our simulations show that the refractive index sensitivity value can be obtained as high as 0.96 THz per refractive index unit (THz/RIU) for the CD spectra. Proposed graphene chiral metastructure is promising enabler for controllable polarization-sensitive devices and systems such as tunable polarization filters, rotators, polarizers, biosensors, phase shifters, operating in the THz region.
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