FSS-Enhanced Quasi-Optical Dielectric Measurement Method for Liquid Crystals in Sub-THz Band

In this letter, the dielectric characterization of nematic liquid crystals (LCs) materials using a complementary split-ring resonator (CSRR) frequency selective surface (FSS) at sub-THz is proposed. The CSRR FSS consists of two printed CSRRs separated by 130 μm thick layer of LCs. Because the metal pattern of the CSRR FSS covers most of the LC area, the director of the LC is well rearranged when an external electric field is applied. High-gain narrow beamwidth ultrathin transmitarrays (TAs) are used to foster a quasi-optical measurement setup instead of a dielectric lens, which is used for a conventional setup. Using TA endows the system with flexibility, such as in the size of the system, by changing the gain of the TA. To extract the dielectric constant and loss tangent of the LCs, it is necessary to shift the resonant frequency and vary the transmission loss. To obtain these data, a CSRR FSS with LCs was placed between two TAs. Finally, by comparing the measured and simulation results, the complex dielectric constants of the LCs were determined using the curve-fitting method.