This paper investigates the use of large Reconfigurable Intelligent Surfaces (RISs), also known as “Smart Skins,” to improve outdoor-to-indoor millimeter-wave (mmWave) propagation, taking advantage of ventilation holes commonly found – or easily implemented – in European buildings. By using a transmissive, focusing RIS, the signal can be concentrated and routed through the opening, enhancing signal penetration into the indoor space even in modern, highly insulated buildings that particularly hinder signal penetration. Using Ray Tracing simulations, we compare scenarios with and without RIS at 29 GHz, demonstrating significant indoor signal coverage improvements in the first case. The study highlights the use of RIS – or Smart-Skins – as a cost-effective solution to address the challenges of mmWave propagation in modern building designs.

This paper presents the design and characterization of a unit cell for dual-polarized liquid crystal (LC)-based reconfigurable intelligent surfaces (RIS), as well as an efficient, full-wave simulation methodology for the far-field beam-steering capabilities of large-scale LC-RIS. Within this framework, the unit cell relies on defected delay lines with a 4.6 μm thin LC layer aperture coupled to a patch antenna. This delay line architecture aims towards simultaneous optimization of loss, bandwidth and response time. Full-wave simulations of the unit cell in a periodic environment show an operating frequency between 26.5 and 29.5 GHz with wide angle radiation. Measurements of the unit cell in a 3 $\times$ 3 rectangular grid exhibit wideband impedance matching and overall good agreement with simulations. Furthermore, a simulation methodology is introduced that evaluates large-scale LC-RIS far-field beam-steering capabilities without requiring full-wave simulations of the entire structure, but just few unit cells. Within this scope, the LC-RIS achieves a maximum efficiency of 20.8% with a beam-steering range from −48° to +48°, despite the use of a lossy glass substrate and gold as a conductor. It exhibits a minimum bandwidth of 8.2% for an efficiency of at least 10% across all analyzed steering angles in E-Plane and H-Plane.

This work presents a passive intelligent surface designed at 2.45 GHz that has the capability of transmitting and reflecting electromagnetic waves that are incident upon it. The proposed surface does not require any circuitry or power source to function. Therefore, it makes a cost-effective and simple intelligent surface. It is a simple metallic structure that has embedded waveguide slots on its surface, allowing the waves to couple for transmission. A prototype of the proposed surface is designed using an aluminum foil and analyzed for both transmission and reflection of the wave. Further, the designed surface is investigated for tuning the directionality of the radiated field from the antenna. For this purpose, a coplanar patch antenna is first designed and then combined with the surface to tune the directionality of the radiated field of this antenna. The outcome of the measured performance validates that the proposed surface has the potential capability of field reconfiguration in wireless communication for Wi-Fi, WLAN, and Bluetooth applications.