An ultra-wideband absorber with an absorption rate of near unit is studied and numerically simulated in the terahertz frequency band. The proposed absorber is a stacked compact structure consisting of a double-layer patterned graphene embedded between two separated dielectric. Under normal incidence, the absorption rate exceeds 99% at 2.31–3.92 THz. The absorption bandwidth can reach 2.54 THz for absorptions greater than 90% (1.91–4.45 THz), and the relative bandwidth achieves 80%. Furthermore, the absorber is tunable, with absorption ranging from 14% to almost 99.9% by altering the Fermi energy of graphene from 0 to 1 eV. The phenomenon of ultra-wideband absorption is analyzed in relation to impedance matching and field distribution. Moreover, the absorber has high polarization-independence and can operate across a broad range of incidence angles. This tunable ultra-wideband absorber has promising functions in modulation, stealth, switching, and imaging technologies.
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