Completely spin-decoupled geometric phase of a metasurface

Metasurfaces have provided an unprecedented degree of freedom(DOF)in the manipulation of electromagnetic waves.A geometric phase can be readily obtained by rotating the meta-atoms of a metasurface.Nevertheless,such geometric phases are usually spin-coupled,with the same magnitude but opposite signs for left-and right-handed circularly polarized(LCP and RCP)waves.To achieve independent control of LCP and RCP waves,it is crucial to obtain spin-decoupled geometric phases.In this paper,we propose to obtain completely spin-decoupled geometric phases by engineering the surface current paths on meta-atoms.Based on the rotational Doppler effect,the rotation manner is first analyzed,and it is found that the generation of a geometric phase lies in the rotation of the surface current paths on meta-atoms.Since the induced surface current paths under the LCP and RCP waves always start oppositely and are mirror-symmetrical with each other,it is natural that the geometric phases have the same magnitude and opposite signs when the meta-atoms are rotated.To obtain spin-decoupled geometric phases,the induced surface current under one spin should be rotated by one angle while the current under the other spin is rotated by a different angles.In this way,LCP and RCP waves can acquire different geometric phase changes.Proof-of-principle prototypes were designed,fabricated,and measured.Both the simulation and experiment results verify spin-decoupled geometric phases.This work provides a robust means to obtain a spindependent geometric phase and can be readily extended to higher frequency bands such as the terahertz,IR,and optical regimes.

Remotely mind-controlled metasurface via brainwaves

The power of controlling objects with mind has captivated a popular fascination to human beings.One possible path is to employ brain signal collecting technologies together with emerging programmable metasurfaces(PM),whose functions or operating modes can be switched or customized via on-site programming or pre-defined software.Nevertheless,most of existing PMs are wire-connected to users,manually-controlled and not real-time.Here,we propose the concept of remotely mind-controlled metasurface(RMCM)via brainwaves.Rather than DC voltage from power supply or AC voltages from signal generators,the metasurface is controlled by brainwaves collected in real time and transmitted wirelessly from the user.As an example,we demonstrated a RMCM whose scattering pattern can be altered dynamically according to the user’s brain waves via Bluetooth.The attention intensity information is extracted as the control signal and a mapping between attention intensity and scattering pattern of the metasurface is established.With such a framework,we experimentally demonstrated and verified a prototype of such metasurface system which can be remotely controlled by the user to modify its scattering pattern.This work paves a new way to intelligent metasurfaces and may find applications in health monitoring,5G/6G communications,smart sensors,etc.