Nearly Ideal Transparency with Artificially Designed Meta-Atoms.

The ideal electromagnetic transparency refers to the ability of an object to remain scatteringless to any incoming waves, resulting in vacuum invisibility. However, natural solid substances can hardly be transparent in free space as they are responsive to external polarizations. Completely eliminating the polarization effect of an obstacle under arbitrary field illumination is a long-standing scientific challenge. Here, it is shown that a subwavelength meta-atom can be nearly ideally transparent in the vacuum. The overall vacuum-like property of the meta-atom is achieved through judiciously designing its internal polarization and magnetization. Remarkably, any large-scale objects made by stacking the meta-atoms inherit the vacuum-like property and are scatteringless in free space. By both the simulations and experiments, the meta-atom's peculiar property is reasonably verified. The proposed meta-atoms are excellent candidates for a wide range of applications, such as perfect radar radomes, scatteringless walls, filtering devices, and self-stealth materials.