An optically transparent dual-band frequency selective surface for polarization independent RF shielding

This article reports on a compact dual band, Frequency Selective Surface (FSS) based spatial filter for Wi-Fi and WLAN shielding applications on a transparent glass surface with optical transparency of 70%. The unit cell comprises an outer square loop resonator with a disconnected and concentric annular ring resonator. To introduce frequency tuning and compactness T shape stubs are strategically loaded on these resonators and it is ensured that the mutual coupling remains minimal. The outer square resonator suppresses the 2.4 GHz band, and the inner circular ring resonator stops the 5.4 GHz band. The unit element is four-fold symmetric thus it offers complete polarization independence. A detailed parametric and electromagnetic field analysis has been conducted to elucidate the significance of different sections of the unit element. An equivalent lumped circuit model is also derived for the proposed unit element to better explain the underlying working mechanism. A finite prototype of 15 x 11 elements is fabricated on a soda lime float glass by using ordinary adhesive copper foils with a standard chemical etching process. Polarization independence and angular stability up to 45 degrees are measured and compared with the simulated responses. The FSS shield offers frequency suppression up to 45 dB and 43 dB for 2.4 GHz and 5.4 GHz bands respectively. With high optical transparency, the design allows maximum light through it and causes no extra burden on energy consumption for indoor applications. The compact dual band design and the possibility of direct application on host surfaces like glass windows and doors make this design an excellent candidate for data security and privacy applications in secure installations with an esthetically pleasing outlook.