Space-Time Metallic Metasurface for Frequency Conversion and Beamforming

Abstract

This paper details a class of metal-based space-time metasurfaces for application in wireless com- munications scenarios. Concretely, we describe space-time metasurfaces that periodically alternate their properties in time between three spatial states: “air,” “conductor,” and “grating.” We analyze the physics of these metastructures via a computationally efficient analytical technique based on the use of Floquet-Bloch series, integral equations, and circuit models. By doing so, we reveal features of these spatiotemporal metasurfaces: scattering parameters, field profiles, diffraction angles, and the nature of the space-time harmonics. The results, corroborated with a self-implemented numerical finite-difference time-domain approach, show the potential application of these space-time metasurfaces as beamformers acting in reflection, in transmission or both. The amplitude and direction of the diffracted orders can be electroni- cally controlled with the parameters of the metasurface. Moreover, the intrinsic ability of time-modulated diffractive metasurfaces to mix and multiply frequencies is tested. We show how two different modulations can lead to the same diffraction angle but with different mixed output frequencies.