Absorption bandwidth enhancement technique using stacked unequal cross-shaped graphene absorber

Terahertz metamaterial absorbers (TMAs) are gaining considerable attention due to their unique characteristics. Graphene-based absorbers are a subclass of TMAs that exhibit tunable absorption characteristics for myriad applications. This paper proposes a TMA consisting of two layers of graphene in a cross-shaped structure where the absorption can be modified by altering the chemical potential of the graphene layers. A quarter-wave impedance transformer has been utilized to attain optimal absorption in the vicinity of the central frequency of this absorber. The normalized input admittance’s real and imaginary parts should be approximately tuned to 1 and 0 around the central frequency to achieve the ideal absorption rate. Also, the transmission line theory has been considered to verify the absorption level achieved around the central frequency. The conductivity of the graphene layer is changed by altering the levels of chemical potential; the Fermi levels for the upper and lower layers of the graphene cross-shaped THz absorber have been considered 1 eV and 0.3 eV, respectively, to achieve maximum absorption. Therefore, the bandwidth of this absorber reached 1.74 THz, around 7 THz as the central frequency. The proposed asymmetric stacked graphene structure provides broadband, polarization-insensitive, and electrically tunable absorption around 7 THz, making it highly suitable for applications such as THz imaging, sensing, and electromagnetic signature reduction technologies. Compared to prior designs, it offers improved bandwidth, tunability, and angular stability, making it a compact and practical solution for next-generation terahertz systems.