Tunable UWB Metasurface Absorber for Smart City Compatible IoT Applications

Abstract

This work presents an ultra-wideband tunable graphene-based metasurface absorber for the terahertz (THz) gap region of the electromagnetic (EM) spectrum. The proposed absorber provides an absorption bandwidth (BW) of 7.8 THz (fractional BW = 195%) with absorptivity A(f) $\ge$ 90%, i.e., from 0.1 to 7.9 THz. The impedance matching between free space and the absorber’s surface has been achieved by engraving different shapes of slots on the top graphene layer. The working principle behind the UWB absorption mechanism has also been studied with the help of parametric studies and field plots. The thickness of the metasurface is only 2 $\upmu$m, i.e., $\lambda _g$/958.3, where $\lambda _g$ has been computed at 0.1 THz, thus, maintaining the ultra-thin nature required for the metasurface design in the THz regime. The absorber’s periodicity is also quite less, i.e., 6 $\upmu$m ($\lambda _g$/319.43), which is sufficient to achieve an effective homogeneity condition. The four-fold symmetry in the design makes the structure polarization insensitive to the incoming plane wave. The metasurface also works well for a wide incidence angle ($\theta$) under both transverse electric (TE) and transverse magnetic (TM) polarizations. The A(f) $\ge$ 80% has been achieved for $\theta$ up to 45$^\circ$. In addition, the absorber provides full-width at half-maxima (FWHM) BW in the complete frequency range, i.e., from 0.1 to 7.9 THz. Hence, the proposed metasurface absorber is found suitable for suppressing/absorbing unwanted electromagnetic radiation in a close indoor environment for smart city-enabled Internet of Things (IoT) applications.