Numerical analysis of bandwidth of 2D cylindrical anisotropic EM cloaks

The frequency bandwidth of Split-Ring-Resonator-based and Transmission-Line-based 2D transformation electromagnetics cloaks is studied. Equivalent metamaterial of these cloaks is highly anisotropic with spatially varying relative permittivity and permeability tensors, entries of which are smaller than one. These structures support electromagnetic wave propagation with superluminal phase velocity, necessary for achieving the cloaking phenomenon. Due to basic dispersion constraints, relative permittivity and permeability smaller than one can be realized only within a limited frequency band, which inevitably causes a narrow bandwidth of any passive cloak. Full-wave simulations of a cylindrical anisotropic and inhomogeneous cloaking shell using nondispersive (non-Foster-element-based) and dispersive electromagnetic parameters (Drude dispersion) are performed and compared to results reported in literature available in public. All obtained results clearly show that all passive cloaks are inherently dispersive and narrowband while an active non-Foster cloak offers a much wider cloaking bandwidth.