Polarization-Insensitive Triband FSS for RF Shielding at Normal and Higher Temperatures by Retrofitting on Ordinary Glass Windows

Abstract

A comprehensive novel framework for retrofitting frequency-selective surface (FSS) shields to any glass surface using low-cost copper foils has been proposed in this work. The realization technique is demonstrated through a novel triband FSS shield. Global System for Mobile Communication (GSM)-1800, Wi-Fi 2.5 GHz, and wireless local area network (WLAN) 5.6 GHz spectrum, with–10 dB bandwidth of 680, 190, and 1300 MHz, respectively, are suppressed by the shield. The unit cell is made up of a combination of square and circular concentric loops with some alterations. The design is entirely polarization-insensitive and has a steady frequency response for oblique angles up to 60°. The unit element is highly miniaturized for triband operation measuring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> /9 at 1.8 GHz frequency. An equivalent circuit model (ECM) is also derived to better elaborate the working mechanism of the shield. The pattern is chemically etched on low-cost copper adhesive foil and affixed to ordinary glass as a sticker. The design retains the visual transparency of 72% allowing enough light to enter through windows while rejecting the intended frequencies by at least 28 dB or more in all three bands. The design exhibits a very high shielding efficiency of above 98% for all three bands. Experimental demonstration for single-layer glass, sandwiched glass, as well as air-filled double-glazed glass is carried out. The thermal stability of the proposed design is measured and found intact up to the ambient temperature of 50 °C.