Space-time-coding digital metasurfaces

Abstract

The recently proposed digital coding metasurfaces make it possible to control electromagnetic (EM) waves in real time, and allow the implementation of many different functionalities in a programmable way. However, current configurations are only space-encoded, and do not exploit the temporal dimension. Here, we propose a general theory of space-time modulated digital coding metasurfaces to obtain simultaneous manipulations of EM waves in both space and frequency domains, i.e., to control the propagation direction and harmonic power distribution simultaneously. As proof-of-principle application examples, we consider harmonic beam steering, beam shaping, and scattering-signature control. For validation, we realize a prototype controlled by a field-programmable gate array, which implements the harmonic beam steering via an optimized space-time coding sequence. Numerical and experimental results, in good agreement, demonstrate good performance of the proposed approach, with potential applications to diverse fields such as wireless communications, cognitive radars, adaptive beamforming, holographic imaging.

Tunable, reconfigurable, and programmable metamaterials

“…The space‐time metasurfaces have the advantages to be more flexible in beam forming and controlling, benefiting from the electronically controlled parameter‐time. Zhang et al designed a space‐time‐coding metamaterial using the time modulation of the reflection coefficient which can operated both spatial and spectral characteristics of the EM waves . The desired harmonic scattered‐power distribution in frequency domain can be acquired by switching the coding sequences on the space‐time‐coding metamaterial cyclically.…”

“…Reproduced with permission from Ref. . © 2018, Springer Nature [Color figure can be viewed at wileyonlinelibrary.com]…”

“…The controls of all harmonics are determined by the temporal modulations of incident waves on the programmable metamaterials. Based on these theories about space‐time programmable metamaterials, a binary frequency‐shift keying (BFSK) communication system is explored by Zhao et al In this communication system, the mixing processes are not needed, which show the advantages of simplicity and efficiency. Figure A shows the schematic of the designed BPSK system which uses a programmable metamaterial to replace the analogue‐digital converter, and RF network.…”

“…The programmable metamaterials are composed of particles in which the pin‐diodes are loaded. By controlling the bias voltages, these diodes show distinct circuit parameters at “ON” and “OFF,” corresponding to the digital codes “0” and “1.” The programmable metamaterials essentially work as the wave‐based information system with programmable coding sequences . When the bias voltages are connected to a field‐programmable gate array (FPGA), the wave based information process on physical levels of metamaterials can be realized in real time.…”

A Tunable Metasurface with Switchable Functionalities: From Perfect Transparency to Perfect Absorption

“…Metasurfaces, ultrathin metamaterials composed by planar meta‐atoms with tailored EM properties, have exhibited strong abilities to control EM waves, with perfect transmission and absorption of EM waves both realized. With active elements integrated, one can further construct tunable metasurfaces with dynamically controlled functionalities including tunable absorbers and filters. However, most tunable metadevices realized so far are based on reflection geometry which are relatively easy to design, since only two channels exist in such systems for EM waves to radiate or dissipate (i.e., the reflection port and absorption) .…”