Programmable Metamaterials for Software-Defined Electromagnetic Control: Circuits, Systems, and Architectures

Abstract

Metamaterials and their two-dimensional analogues, metasurfaces, have recently attracted enormous attention because of their powerful control over electromagnetic (EM) waves from microwave to visible range. Moreover, by introducing explicit control of its sub-wavelength unit cells, a metamaterial can become programmable. Programmable metamaterials may not only host multiple EM functionalities that can be chosen or combined through simple software directives, but also be provided with means to adapt to the environment or communicate with other metamaterials, thereby enabling a myriad of applications in sensing, imaging, or communications. The realization of such a software-driven cyber-physical vision comes, however, at the cost of significant hardware requirements. In this paper, recent progress in the field of programmable metasurfaces is reviewed, cutting across layers from the application down to the device and technology levels. The main aim is to present the current status, main benefits, and key challenges of this thriving research area with a tutorial spirit and from a hardware perspective.

Scalability Analysis of Programmable Metasurfaces for Beam Steering

“…For instance, beam steering requires exerting specific amplitude and phase profiles to the impinging wave [30], [36]- [39]. Programmability in MSs is achieved via the inclusion of tunable elements within the MS structure and the addition of means of control over such tunable elements [39]- [44]. These aspects have led to the recent proposal of MSs that could be indeed encoded, this is, where the polarizationphase-direction of the reflected beam can be controlled by (re)programming each single cell unit choosing among a finite set of states [45].…”

“…At the software level, the encoding process can be tackled by modeling the EM functionalities via a set of well-defined software primitives [50]. The promises of the SDM/RIS paradigm, however, come at the expense of a non-trivial complexity in the MS. On the one hand, the performance of a SDM depends on the size of the unit cells, the number of unit cell states, or the size of the whole MS. On the other hand, there are costs and energy overheads associated with the fabrication and operation of SDMs that also scale with the aforementioned factors [44]. Hence, in order build SDMs capable of satisfying a set of applicationspecific requirements with the minimum cost, it becomes necessary to quantify the main scaling trends and tradeoffs of the underlying MS.…”

A Prospective Look: Key Enabling Technologies, Applications and Open Research Topics in 6G Networks

“…To facilitate simultaneous functionalities within an uninterrupted connectivity, AI tools are envisioned to be indispensable in programmable metasurfaces as they enable the identification of the best operation policy based on data driven techniques [143], [144]. Leveraging AI is particularly attractive in heterogeneous wireless applications, with diverse networks, and QoS user requirements, as it can potentially provide an efficient and dynamic means to adapt network parameters, such as coding rate, route selection, frequency band, and symbol modulation.…”

An Outlook on the Interplay of Artificial Intelligence and Software-Defined Metasurfaces: An Overview of Opportunities and Limitations

“…The metasurface architecture, comprising meta-atoms as its building block, is a sophisticated metallic or dielectric small scattering particle that is periodically repeated over a certain area to create a planar (also called a tile) [2], [4]. Owing to their artificially engineered structures, metasurfaces enable unprecedented capabilities in interacting with the impinging EM waves, such as wave focusing, absorption, imaging, scattering, polarization, to name a few [2], [4].…”