The problem of suppressing the scattering from conductive objects is addressed in terms of contrast reduction. A unique compact closed-form solution for a surface impedance Zs(m, kr) is found in a straightforward manner and without any approximation as a function of the harmonic index m (scattering mode to suppress) and of the frequency regime kr (product of wavenumber k and radius r of the cloaked system) at any frequency regime. In the quasi-static limit, mantle cloaking is obtained as a particular case for kr << 1 and m = 0. In addition, beyond quasi-static regime, impedance coatings for a selected dominant harmonic wave can be build with their proper dispersive behaviour, resulting in improved reduction levels and harmonic filtering capability.
Labate, G., Podilchak, S., & Matekovits, L. (2017). Closed-form Harmonic Contrast Control with Surface Impedance Coatings for Conductive Objects. Applied Optics, 56(36), 10055-10059. https://doi.org/10.1364/AO.56.010055