Optically Transparent Smart Electromagnetic Skin for Energy-Free 5G Signal Redirection in Smart Cities

This study introduces a novel, optically transparent, and passive smart electromagnetic skin (EMS) designed for millimeter-wave 5G signal redirection to enhance coverage in dense urban environments of smart cities. The proposed EMS targets 5G frequency bands n258 (24.25–27.5 GHz) and n257 (26.5–29.5 GHz), utilizing transparent indium tin oxide (ITO) conductive films with a sheet resistance of 2.5 Ω/sq, deposited on soda-lime glass substrates. The structure comprises a 40 × 40 array of subwavelength ITO unit cells, each capable of providing a full 0°–360° reflection phase shift. The array features periodicities of 0.42λ at 26 GHz and 0.45λ at 28 GHz, with total dimensions of 200 mm × 200 mm × 2.1 mm. A case study demonstrates the EMS's ability to redirect incident 5G signals, establishing a virtual lineof-sight (VLoS) link between a hypothetical base station (BS) located 10 meters away at a 15° incidence angle and mobile users (MUs) positioned at a 37° reflection angle. Both simulation and experimental results confirm stable and efficient signal redirection across the 24–30 GHz band, maintaining a consistent reflection angle of 37° ± 3°. Furthermore, the EMS achieves a measured optical transparency of 73.7% in the visible spectrum (380–760 nm), allowing near-invisible integration onto urban surfaces such as windows without requiring any external power source.