Dual-band Polarization- and Incident-angle Independent Air-like Metamaterials

An air-like material requires itself to neither reflect nor refract electromagnetic (EM) waves in free space, regardless of the polarization and the incident angle. Such a medium is thus omnidirectionally invisible with arbitrary shape, having great application prospects in fields of radar radomes and EM windows. Recently, air-like meta-atoms without any restriction to the incident waves have been proposed, with quite limited operating bandwidth. In this paper, we present a dual-band air-like metamaterial without the polarization- and incident-angle constraints. It is achieved by introducing dual Lorentz resonances along both the tangential and the normal directions. By precisely engineering the dispersion of the unit cell, a planar metamaterial with both the unity relative permittivity and the unity relative permeability along three orthogonal directions is realized. Full-wave simulations demonstrate that the designed metamaterial slabs are nearly scatteringless at both C and X bands, regardless of the incident angle for both TE and TM waves. The proposed approach provides a universal way to realize multi-band air-like materials, which may contribute to the development of multi-band wireless communication systems.