Graphite based metal-free and polarization-insensitive multiband THz absorber with wide incident angle

Abstract

In this paper, a novel non-metallic graphite-based tri-layered absorber is proposed to achieve multi-band absorption with perfect resonant peaks using a graphite disk resonator. The basic unit cell for the proposed metal-free absorber comprises a simple tri-layered structure with a graphite disk at the top, which acts as a resonator, followed by a dielectric substrate in the middle, and a graphite sheet at the bottom. Here, the dielectric substrate and the graphite sheet collectively behave as a cavity oscillator, responsible for generating the multi-band absorption. Further, a graphite disk at the top, owing to its high absorption coefficient and refractive indices in the lower THz range, is responsible here for achieving the near-perfect absorption for all the resonant peaks. Hence, the complete structure behaves as a resonant cavity oscillator, producing a standing wave pattern at multiple resonant frequencies. This results in four discrete absorption peaks with narrow bandwidth profiles and high absorption rates in the frequency range of 1–6 THz, with near-unity absorption peaks at 1.665 THz, 2.89 THz, 4 THz, and 5.23 THz. The optimized parameters, like the thickness of the dielectric substrate, confirm the applicability of this multiband metal-free absorber for a wide frequency range. The response of this proposed absorber is validated numerically using the standing wave mechanism by considering its equivalence to a Metal–Insulator–Metal (MIM) waveguide model. The results are further verified using the resonant mode analysis method. It is worth mentioning that the proposed absorber is operative for a wide incident angle of 75°and is non-susceptible to polarization as well.