Topological Non-Trivial Möbius Unknot Metamaterials with Robust Electromagnetic Properties

Metamaterials can precisely control the propagation characteristics of electromagnetic waves to realize novel physical properties. The electromagnetic response of a metamaterial, however, is strictly dependent on the incident angle, as well as the polarization mode, which greatly limits the application of the metamaterial. To realize angular stability and polarization insensitivity in metamaterials has become the key challenge in the roadmap of metamaterial development. Here, the concept of the classical geometric phase shift is proposed to be used in metamaterial design to improve angular stability and polarization insensitivity. A non-trivial geometric Möbius unknot structure has been used as the basic unit, in which a robust resonance mode, called a topological resonance, is induced, with the angular stability reaching up to −180° to 180° at both vertical and horizontal polarization. Even twisting or bending the Möbius unknot will not affect the topological resonance behavior. This approach opens a new pathway toward novel metamaterial design.