Wideband and multi-frequency infrared cloaking of spherical objects by using the graphene-based metasurface

The ultrathin graphene metasurface is proposed as a mantle cloak to achieve wideband tunable scattering reduction around the spherical (three-dimensional) objects. The cloaking shell over the metallic or dielectric sphere is structured by a periodic array of graphene nanodisks that operate at infrared frequencies. By using the polarizability of the graphene nanodisks and equivalent conductivity method, the metasurface reactance is obtained. To achieve the cloaking shell for both dielectric and conducting spheres, the metasurface reactance as a function of nanodisks dimensions, graphene's Fermi energy, and permittivity of the surrounding areas can be tuned from the inductive to capacitive situation. Inhomogeneous metasurfaces including graphene nanodisks with different radii provide wideband invisibility due to extra resonances. We could significantly increase the 3-dB bandwidth more than the homogenous case by simpler realistic designs compared to the multi-layer structures. The analytical results are confirmed with full-wave numerical simulations.