| Summary: | The quest of novel materials and structures to design an efficient absorber for realizing wave trapping and absorption at terahertz (THz) frequencies is an open topic. But the design of a thin, wideband, and tunable THz absorber is still an arduous job. Hence, in this paper, a hybrid THz metamaterial absorber integrated with a cascaded graphene frequency selective surface (FSS), with ultra-high absorbance over a wide frequency range is designed using an analytical equivalent circuit model. Such an approach provides a feasible way to optimize the device by interrelating the effective electromagnetic and circuit parameters with the unit cell dimensions of FSS. A systematic study and critical analysis over a wide range of device parameters including graphene chemical potential and FSS design variables is demonstrated. A peak dip in reflection coefficient of -30.27 dB is observed at 2.94 THz for an optimal device with a chemical potential (μ<sub>c</sub>) of 0.38 eV (μ<sub>c1</sub>), and 0.25 eV (μ<sub>c2</sub>) in the range of 0.1-4.0 THz. The cascaded FSS configuration results in the unique anti-reflection-based absorption phenomena, which is responsible for the achievement of -10 dB absorption bandwidth of 2.34 THz (0.85-3.19 THz). In addition, the frequency-dependent effective permittivity, permeability, and impedance is extracted using reflection data, in order to understand the device physics. Such ultra-thin and broadband absorbing device architecture may confer potential application perspectives in THz sensing, imaging, and detection.
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