Dual-broadband and single ultrawideband absorbers from the terahertz to infrared regime

This paper presents the design and analysis of broadband metamaterial absorbers with single and dual absorption bands fromterahertz to infrared frequencies. The absorbers are made of a composite graphene/metallic structure.A metallic patch array is printed on a ground-plane-backed dielectric slab.Agraphene patch array is stacked on top of the metallic array, whereas a dielectric spacer separates the graphene and patch spacer from each other. The tunable property of the graphene surface conductivity at terahertz frequencies together with the complex permittivity of metal at the infrared regime are used to design broadband absorbers from the terahertz to infrared regime. The design is based on the combination and excitation of the plasmon polaritons of graphene and metallic patterned arrays at terahertz and infrared frequency bands, respectively. Two broad absorption bands occur from 4.56- 9.02 THz and 16.95-60.23 THz with the fractional bandwidths of 67% and 112%, respectively. Furthermore, by a proper design of the parameters, a single ultrawide absorption spectra from 6.6-58.13 THz can be achieved with a fractional bandwidth 160%. In order to validate the simulation results, a circuit model-based analysis is developed, where the patterned arrays are modeled as the surface admittances, and the dielectric spacers are modeled by transmission line stubs. The results obtained by the full-wave simulations in the high-frequency structure simulator are in good agreement with the circuit model results. The absorbers show great stability with respect to the incidence angle for both the transverse electric and transverse magnetic waves.