Switchable and optically transparent ultrawide stopband frequency selective surface for electromagnetic shielding

In view of the fact that high-frequency electromagnetic waves mainly enter buildings through windows and glass doors, switchable optically-transparent shielding with broad stopband is increasingly needed. Herein, a novel design for a switchable and optically transparent frequency selective surface (FSS) with ultrawide-stopband is presented in this study. The structure consists of a polymethyl methacrylate (PMMA) layer sandwiched between polydimethylsiloxane (PDMS) layers which contain liquid metal microchannels arranged in an orthogonal Omega-shaped configuration. The mobility of the liquid metal can switch the FSS response from an all-pass to an ultrawide bandstop behavior. The proposed FSS achieves a rejection bandwidth of 18.1 GHz, covering P, L, S, C, X and Ku bands, while maintaining a transparency of 81% and high angular stability up to 80 degrees, regardless of polarization. Furthermore, the mechanism behind the ultrawide stopband and high angular stability is explored through an analysis of reflection and absorption for both TE polarization and TM polarization. Experimental validation under both normal and oblique incidence demonstrates the ultrawide-stopband performance of the fabricated FSS.