Broadband graphene-metal hybrid polarization-insensitive FSS with a wide tuning range at terahertz frequency

In this paper, a broadband graphene-metal hybrid frequency-selective surface (FSS) is designed and numerically investigated for tunable band-pass-filtering applications in the terahertz range. The unit cell of the proposed FSS comprises a gold nanostructure and a distinctive graphene pattern. These layers are separated by a thin silicon dioxide (SiO₂) layer and are uniformly applied on both sides of a thick foam block. The results demonstrate that the proposed FSS exhibits broadband transmission in the range of 7.71-9.89 THz. This corresponds to a fractional bandwidth of 24.77%. The originality of the proposed work, to our knowledge, lies in the incorporation of the dual-patterned graphene layers in the design, enabling the proposed FSS to provide an extended tunable filtering response. The design facilitates the preservation of continuity in the graphene pattern, promoting an efficient way of electrical biasing of the device. Simulations reveal that it can achieve a tunable transmission band from 6.67 to 10.20 THz (∼41.85%), with an adequate out-of-band attenuation when the graphene's chemical potential is adjusted between 0 and 1.5 eV. The design is analyzed in a detailed manner with the aid of various simulated results, which have been subsequently validated by an in-house equivalent circuit model approach. The proposed FSS is polarization independent and exhibits angular stability under oblique incidence up to 40° for both transverse electric and transverse magnetic wave polarizations. Owing to these unique features, it has huge potential to be employed in EM shielding, 6G communication systems, and cognitive radio-based futuristic devices.