Weather resistant low-e coatings on polycarbonate substrates transparent to 5G signals

Abstract

Low emissivity (low-e) windows contain a semi-transparent multilayer coating that consists of ultra-thin metallic and dielectric layers (nano-scale) which block the infrared (IR) radiation from the Sun. However, there are two major drawbacks in the technology: firstly, the lack of environmental stability due to the metallic content in the low-e coating. Secondly, the metallic layers attenuate modern-day telecommunications such as Fifth Generation (5G) signals. As there is an ever-increasing demand to reduce energy consumption plus having reliable interior-to-exterior signal coverage, a smarter design for low-e windows is required. In this study, low-e coatings, with the structure TiO₂/NiCr/Ag/NiCr/TiO₂, were deposited on polycarbonate (PC) substrates by magnetron sputtering. To improve environmental stability, a transparent siloxane resin was applied on top. To enhance the 5G signal transmittance, the Frequency Selective Surface (FSS) technique was applied, and hexagonal patterns were laser ablated from the Ag layers. The samples were characterised using spectrophotometry, signal attenuation measurements, salt spray tests, and both accelerated and outdoor weathering. This work demonstrates that the FSS patterning improves the low-e coating transmittance to 5G signals, and the top protective coating contributes to extend the lifetime of the coatings as demonstrated by aggressive durability tests.