Numerical analysis of a lumped-element-based planar anisotropic cloak

A transformation electromagnetics (TO) cloak requires highly anisotropic metamaterial, permittivity and/or permeability of which may have values very close to zero (ENZ and/or MNZ metamaterials). Published experimental studies of SRR-based structure clearly proved the existence of cloaking phenomenon. Recently, there have been several attempts to design fully anisotropic cloak using transmission-line-based metamaterials. Here, we show that the bandwidth in both realizations (a volumetric SRR-based cloak or planar TL-based cloak) is constrained by the basic physics and not by applied technology. Briefly, one must use some kind of resonant circuit in order to synthesize either ENZ or MNZ behavior. The detailed circuit simulations showed that is indeed possible to construct a 2D TM_z fully anisotropic cloak based on the uniaxial properties of the permeability tensor in cylindrical coordinates. The equivalent permeability and permittivity can be achieved by transmission lines loaded with lumped elements. Such a cloak can have a bandwidth broader than the SRR-based cloak but it is again fundamentally constrained by the bandwidths of used resonant LC circuits.