Optically-Transparent EM Skins for Outdoor-to-Indoor mm-Wave Wireless Communications

TL;DR

This work addresses the outdoor-to-indoor mmWave propagation challenge by introducing optically-transparent opportunistic EMS (OTO-EMS) that retrofit existing glass windows with a two-layer copper-mesh meta-atom on insulating glass. A semi-analytic field model based on Love's equivalence and surface-current homogenization guides a two-step SbD design: (i) constructing a low-visibility, high-transparency meta-atom with a five-descriptor parameter set to maximize phase coverage and transmission, and (ii) synthesizing the EMS layout to realize desired non-Snell refraction with focus toward a target receiver. Numerical results show the meta-atom can deliver >80% local optical transmittance with substantial mmWave phase control, and EMS layouts can achieve anomalous beam steering with acceptable scan losses, outperforming plain IG windows in transmitted power while maintaining optical clarity. Full-wave validations using HFSS corroborate the semi-analytic predictions, indicating that patterned IG windows can practically enable high-data-rate O2I links with minimal visual impact, paving the way for experimental prototyping and real-world deployment.

Abstract

Optically-transparent opportunistic electromagnetic skins (OTO-EMSs) are proposed to enable outdoor-to-indoor (O2I) millimiter-wave (mmW) wireless communications with existing windows/glass-panels. More in detail, static passive EMSs consisting of optically-transparent conducting patterned layers attached to standard glass-panels are designed. Towards this end, both the phase coverage and the optical transparency of a meshed copper-based meta-atom printed on a non-dedicated insulated glass substrate are optimized. Successively, the feasibility of OTO-EMSs able to support mmW high-efficiency O2I transmissions along non-Snell refraction directions is numerically demonstrated.

Figures (16)

• Figure 1: Sketch of (a) the O2I scenario at hand and (b) the OTO-EMS architecture.
• Figure 2: OTO Meta-Atom Design - Picture of (a) the parametric representation of the unit cell and (b) the corresponding HFSS 3D model.
• Figure 3: Flowchart of the customized SbD approach for the computation of $\mathcal{D}^{opt}$.
• Figure 4: OTO Meta-Atom Design ($f_{0}=26$ [GHz]) - Plot of (a) the magnitude and the phase of $T_{TE}\left(\underline{d}\right)$ and (b) the behaviour of the meta-atom transparency $\mathcal{T}_{atom}^{OTO}$ versus $d^{\left(1\right)}$.
• Figure 5: OTO-EMS Layout Synthesis ($f_{0}=26$ [GHz], $P=Q=30$) - Plot of (a)(b) the OTO-EMS layouts and (c)(d) the corresponding optical transparency index when (a)(c) $\theta^{rx}=180$ [deg] and (b)(d) $\theta^{rx}=160$ [deg].