A Dual-Tunable Ultra-Broadband Terahertz Absorber Based on Graphene and Strontium Titanate

An electrically and thermally dual-tunable broadband terahertz absorber based on graphene and strontium titanate is designed and analyzed. The results show that by lifting the Fermi energy of graphene, the absorption, particularly at higher frequencies, is significantly enhanced, resulting in a broader absorption bandwidth. By raising the temperature of strontium titanate, the center absorption frequency shifts to higher frequency and the bandwidth increases. At a Fermi energy of 1 eV and temperature of 400 K, the device exhibits an ultra-broad bandwidth of 3.36 THz and remarkable peak absorption exceeding 99%. Moreover, the absorber is insensitive to incident angles, maintaining a stable broad-bandwidth beyond 3.3 THz within a large incident angle of 55° and 50° for TE and TM polarizations, respectively. The physical mechanisms are elucidated by the impedance matching theory and electric field analyses. The structure shows great potential in tunable broadband terahertz absorbers and related applications.