Tunable terahertz broadband absorber based on elliptical graphene ribbon metamaterials

By utilizing graphene patterns consisting of an ellipse and four quarter-ellipse rings, the tunable propagation properties of elliptical graphene ribbon broadband metamaterial absorbers (EGBMAs) have been investigated in the terahertz (THz) region, including the effects of structural parameters, graphene Fermi levels, incident angles, and polarization angles. On the condition that the Fermi level is 1.0 eV, the proposed EGBMA achieves a relative bandwidth reaching more than 78% and an absorption of more than 90% in the frequency range of 0.82-1.87 THz. By optimizing the geometric parameters of the absorbers and adjusting the Fermi level of graphene, near-perfect absorption (>99%) can be achieved in the frequency range of 1.04-1.13 THz. In addition, by replacing the metal substrate with a thin layer of InSb, the absorption curves can be tuned by varying the temperature in the range of 250-600 K, while the resonant curves are roughly identical to those with gold as the substrate if the temperature increases are larger than 400 K. The proposed broadband absorber can be utilized to develop novel tunable functional devices, to the best of our knowledge, such as absorbers, detectors, and sensors.