Controlling asymmetric reflection of metasurfaces with loss

Optical theorem, being the manifestation of the energy conservation law, relates the total scattering cross-section of a structure with its scattering in the forward direction. However, there are no fundamental restrictions on other  directions. Strong asymmetric reflection and backscattering can be achieved in structures with magneto-electric coupling, taking place between constitutive elements. Here scattering properties of single meta-particles, based on  near-field coupled electric and magnetic dipoles, and their arrays are analyzed. It is shown that dissipation is the key mechanism, responsible for the asymmetric backscattering behavior. While far-field scattering can serve as a sufficient loss mechanism in the case of single structures, ohmic dissipation should be added in the case of periodic arrays (metasurfaces). In this case, the practical realization is based on split-ring resonators, loaded with resistance, and wires, both printed on a PC board.