Polarization Insensitive and Transparent Frequency Selective Surface for Dual Band GSM Shielding

This article proposes a single-layer, dual-band, optically transparent frequency-selective surface (FSS) for GSM shielding. The design evolves from a fractal cross dipole to achieve dual-band response, polarization insensitivity, and wide angle of incidence stability with a miniaturized size. A two-axis symmetric structure helps to provide a stable frequency response for incident waves with different polarization angles up to 60 degrees. Capacitive loading further reduces the unit size and extends the maximum stable incident angle. The working mechanism of the design has been explained through an equivalent lumped element circuit model (ECM), which provides a generic approach to retune or optimize the design for another frequency band. Both the full-wave EM and circuit simulations are in good agreement. A prototype has been realized by screen printing a custom silver nanowire (Ag NW)-based transparent ink on a flexible polymer substrate. A decent reflection performance has been achieved from 0.71 to 1.25 GHz and from 1.73 to 2.16 GHz in measurements, which are consistent with the simulations. Optical measurements reveal a transparency of 81.6%. Printed FSS is completely flexible, and the performance does not deteriorate after bent or rolled up conditions. Field testing on a glass box demonstrates decent shielding from the incoming GSM signals. The highly transparent and flexible nature of the FSS structure makes it suitable for mounting on glass windows of cars or home environments for EM shielding purposes.