# Frequency Selective Surfaces: A Review
## 6 Conclusions  
This review provides a useful perspective of rapidly growing directions in the modern electromagnetism: the study of an important periodic structure, named as Frequency Selective Surfaces, types, and functionalities. With recent emergent trends in communication, until now, diverse research works on FSS structures have been presented. This includes traditional single layer FSS, advanced multilayer FSS, antenna filter antenna FSS, three-dimensional FSS, convoluted/meandered FSS, fractal-based FSS, microwave absorbing FSS, active FSS, and many other types. This range consists of simple single screen 2D FSS, with low mass, cost, and volume that can be applicable in myriads of applications, to highly complex and advanced 3D active FSS whose superior performance can be compensated for their fabrication complexity. Extensive information in the form of tables is provided, when comparing different design techniques employed, array element structures, frequency ranges, bandwidths, and polarisability.  
This review can be interesting and helpful to a broad circle of microwave researchers and FSS design community, to make a comparison and set off new methodology for development. Important to mention that various promising and practical application can be facilitated by FSS design in the range of different frequency bands from microwave, millimeter wave, terahertz, to optical regimes. Table 11 summarizes the current major achievements by FSSs engineering in different applications. Thus far, as more research is carried out in FSS architecture, modern or new implementation, and fabrication procedures are being adopted, many of the foreseen challenges will be resolved in the near future. This will make the novel FSSs more viable alternatives to traditional low performing FSSs approaches. It is expected that this review will assist to ascertain closer linkages among theoretical background, structure parameters, and performance features in cutting edge designs of FSSs.  
**Author Contributions:** [PERSON] conducted the literature retrieval and information, concluded the categorization for FSSs, summarized the core design and applications involved, proposed the paper structure and wrote the manuscript; [PERSON] helped to reorganize and finalize the article, and [PERSON] decided the topic and proposed challenges and open issues.  
**Funding:** This work was supported in part by the National Natural Science Foundation of China (Grant No. 61774014) and the Fundamental Research Funds for the Central Universities (Grant No. FRF-BD-18-016A).  
**Conflicts of Interest:** The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**FSS Ref.** & **Application** & **FSS Ref.** & **Application** \\ \hline
[162; 168; 194] & MMs FSS & [117; 119; 154; 195] & FSS for mobile communication \\ \hline
[10; 196; 197] & MM/MSs Lens & [50; 162; 177] & X band \\ \hline
[191; 192; 193] & Textile FSS & [74; 198] & C band \\ \hline
[188; 190; 191; 192; 193] & Optical FSS/MSs & [11] & 5G EMI reduction \\ \hline
[186] & Near Infrared & [168] & RCS reduction \\ \hline
[184; 185] & Infrared & [61; 88; 155] & Secure wireless network \\ \hline
[187] & Multi spectral filter/Mirrors/Anti-reflecting coating & [25; 123; 199; 200; 201] & RF interference and harmonic suppression \\ \hline
[170; 171; 172; 173; 174; 175; 176; 177; 178; 179; 179; 170; 171; 172] & Wearable FSS & [11; 91; 151; 172] & EMI shielding \\ \hline
[139; 140; 145; 150] & FSS absorber & [202] & Radio Astronomy \\ \hline
[28; 126] & Sensors & [8] & Dichroic sub-reflector \\ \hline
[9, 116; 178] & RFID & [159; 160] & Terahertz band \\ \hline
[77; 118; 124; 169; 174] & FSS antenna & [75; 103; 121; 139; 164] & Stealth radome \\ \hline
[154] & Electrically reconfigurable mechanisms & [122] & Wireless charging of portable devices \\ \hline \hline \end{tabular}
\end{table}
Table 11: Practical applications of FSSs.