Nonreciprocal-Beam Metasurfaces Based on Asymmetric Frequency-Phase Transitions in Time-Modulated Meta-Atoms

We present a full-duplex nonreciprocal-beam-steering transmissive phase-gradient metasurface realized by leveraging the unique characteristics of the frequency-phase transition in twin time-modulated meta-atoms. Such a metasurface can provide directive and diverse radiation beams, and steerable beams by simply changing the modulation phase. The proposed twin meta-atoms inherently suppress undesired time harmonics, yielding a high conversion efficiency.