Invisible devices with natural materials designed by evolutionary optimization

It is a longstanding dream to put on a cloak and escape from sight. Transformation optics (TO) and artificial metamaterials turn this circumstance into reality, but the requirements for inhomogeneous and anisotropic materials make it almost impossible in practical realization. Furthermore, invisibility can only be constructed at a narrow frequency regime in previous studies and depends critically on the inescapable material losses. Here, the authors propose the multifrequency isotropic invisible devices and natural hyperbolic invisible devices using realistic materials, such as microwave materials and van der Waals (vdW) materials. The inherent material losses are taken into account in the optimization process, bringing the concept of invisibility closer to realistic conditions. To verify the stability of the proposed method, full-wave numerical simulations and analytical calculations are performed, and both obtained excellent invisibility performance. Due to the combined advantages of the simple two-layer core-shell configuration and natural materials, our work provides a promising platform for fabricating invisible devices at low cost and paves the way for new implementations of intelligent photonics beyond the limitations of TO.