All-Dielectric Air-Like Transparent Meta-Atoms

A perfect transparent object in free space should neither reflect nor refract under electromagnetic waves coming from arbitrary directions, regardless of shape and size. Therefore, metamaterials with air-like constitutive relations are required. The usual way of metamaterial design is to edit the composition of metallic rods and wires. Nevertheless, dielectrics are much more stable and less lossy than metals, which can be an alternative candidate to make metamaterials. In this paper, we propose a 3D all-dielectric example to render a nearly perfect transparent metaatom, which is composed of high-permittivity dielectric rather than metals. Detailed analysis shows that the macroscopic constitutive parameters of the object are identical to air by the dipole moment neutralization in its interior. Consequently, the designed structure behaves as the basic building block of a transparent object with arbitrary shape and size, which can be made by a simple stacking procedure. The effectiveness is validated through theoretical analysis and full-wave simulations. Due to the metal-free feature of our design, the proposed strategy is scalable to higher frequencies, i.e., terahertz and optical range. Thus, we envision that this approach can inspire some new applications, such as functional antenna radomes, ideal optical windows, and invisible obstacles.