Use of frequency-selective surfaces (FSSs) is proposed to shield rooms against electromagnetic fields in order to achieve secure indoor communications and reduce human exposure to external fields. The secure room is designed using two-layer FSSs with an FR4 substrate to cover 10–12 GHz frequency band. Different elements in each layer and shift in the position of elements are the reasons for more than 3 GHz bandwidths in X band. The performance of the structure is also stable versus the misaligned position of layers. An equivalent circuit model is proposed for the structure and results show −20 dB isolation between inside and outside of the room in the desired frequency band. Bio tissue is located inside the cubic structure with FSS walls and the results of the specific absorption rate are demonstrated and compared in two rooms with FSS cover on concrete walls and a room with concrete walls. The 17 × 17 cm2 two-layer FSS is fabricated for the measurement and the results are presented. The designed FSS can be used in the construction of wave-isolated room for any application.

The possibility to characterize infinite and periodic frequency-selective surfaces (FSS) filters that have two orthogonal axes of symmetry inside a waveguide is reported. Thus, preliminary measurements can rapidly be obtained at low cost with few elementary cells instead of using a large FSS panel in free space. This is possible because of the equivalence that exists between the electromagnetic fields of two symmetric and oblique plane waves incident on and reflected from an infinite periodic surface and the incident/reflected fields that exist inside a single-mode rectangular waveguide containing a finite number of elementary cells. Comparisons of the measurements with some full-wave simulations for FSS belonging to the first three groups as they were defined by Munk confirm the good agreement between them. This is an interesting and simple assessment tool concerning the fabrication quality of FSS. The extension of this technique to non-symmetric FSS patterns is also discussed and supported by experimental and simulation results. The limitations of the technique are finally discussed.

A recently developed material based on carbon nanotubes is used here for the realization of single- and double-layered frequency-selective surfaces (FSSs) with relevant absorbing properties. The peculiar characteristics of carbon nanotubes are exploited to devise high-loss resonant ring structures periodically arranged to build the FSS. By introducing two layers of rings, an absorber with stable characteristics over a wide frequency band and over a wide range for the incident wave angle is achieved.