Covert Scattering Control in Metamaterials with Non-Locally Encoded Hidden Symmetry

Area of Science:

• Metamaterials and wave physics
• Applied physics
• Information security

Background:

• Symmetries are crucial for wave scattering control but pose reverse-engineering risks in metamaterials.
• Obvious symmetries in metamaterial designs can be a significant vulnerability.
• Existing methods lack robust methods for hiding these fundamental symmetries.

Purpose of the Study:

• To demonstrate covert symmetry-based scattering control in cable-network metamaterials.
• To achieve physical-layer security in wired communications using hidden symmetries.
• To explore novel tuning mechanisms for complex scattering metamaterials.

Main Methods:

• Theoretical and experimental investigation of symmetry in reduced vs. canonical bases.
• Utilizing internal secondary meta-atoms to mediate non-local interactions and hide primary meta-atom symmetries.
• Demonstrating hidden parity (P) symmetry and hidden PT-symmetry preserving/breaking tuning mechanisms.
• Approximation of negligible absorption for tuning metamaterials.

Main Results:

• Successfully demonstrated covert symmetry-based scattering control in a cable-network metamaterial.
• Achieved physical-layer security in wired communications using domain-wise hidden P-symmetry as a shared secret.
• Reported the first tuning of a complex scattering metamaterial to feature exceptional points (EPs) of PT-symmetric reflectionless states and quasi-bound states in the continuum.
• Reproduced results in metamaterials with non-reciprocal interactions, including the first observation of reflectionless EPs in a non-reciprocal system.

Conclusions:

• A hidden symmetry in the reduced basis of primary meta-atoms, coupled with specific non-local interaction topology, can conceal symmetry from the canonical basis.
• Covert symmetry offers a viable strategy for physical-layer security in wired communication systems.
• This work presents novel methods for tuning complex scattering metamaterials, leading to reflectionless exceptional points and quasi-bound states in the continuum.