Near-perfect ultrabroadband metal-free ultrathin THz absorber

An ultrathin metal-free terahertz (THz) absorber is implemented and numerically analyzed. The absorber struc-ture with a rectangular graphite resonator is designed to operate with the fundamental magnetic resonance in the lower-and higher-order magnetic resonance in the upper band. Carving the slots in the graphite resonator converts the magnetic resonance into the electric resonance at the upper frequency and merges the resonance spectra. The proposed absorber provides near-perfect flat broadband absorption of more than 99% in the 7.28-11.21 THz frequency range. Further, the absorber provides absorption of more than 90% and 80% in the 6.26-13.05 and 5.69-14.25 THz frequency range, respectively. The absorber structure utilizes a graphite-based resonator and backreflecting plane and provides the polarization insensitive response with the allowed incidence angle of more than 20 degrees with the absorption more than 99%. The absorber response is validated through a transmission line method-based equivalent electrical circuit. Moreover, the reliability of the implemented absorber for its use in electromagnetic shields and stealth applications is calculated in terms of shielding effectiveness, which remains high in range of 50 to 250 dB.(c) 2022 Optica Publishing Group