Design of broadband superstrate FSS for terahertz imaging and testing applications

Recent advancement in bioengineering and terahertz (THz) technology has stimulated interest in studying the interaction between THz radiation and biological agents, molecules and tissues. The THz imaging and testing system in clinical settings usually needs a samples holder to hold the freshly excised ex-vivo maligned specimen for diagnosis purposes. The conventional specimen holder being used in clinical trials has inherited material losses that eventually deteriorate the transmission of THz signal through the sample under test. In this article, a nearly perfect transparent superstrate frequency selective surface (FSS) operating at THz frequency is proposed for the improved THz imaging and testing applications. The designed superstrate FSS structure shows a typical attenuation of less than 1 dB for the frequency range 300−760 GHz. This superstrate FSS structure is numerically tested with the computational electromagnetic solver, the CST STUDIO SUITE, based on finite integration technique (FIT) and later the obtained results are verified using another solver, the Ansoft HFSS, based on the finite element method (FEM). The out of band rejection for the proposed design is found to be better than −25 dB for normal illumination. It is found that the designed superstrate FSS is polarization insensitive and works as a perfect transparent window for oblique incidence over a limited bandwidth. The detailed study of the proposed superstrate FSS structure demonstrates that the proposed structure is a viable choice and may replace the conventional sample holders for better transmission of THz waves through the test medium.