Characterising nematic liquid crystals using a circular patch resonator

ABSTRACTReconfigurable microwave material is a promising candidate for designing and manufacturing tunable microwave components. Nematic liquid crystals (NLC) are such materials since their permittivity can be tuned by an external electric field. However, many NLC mixtures were not properly characterised at higher frequency bands due to requiring a complex measurement setup. In this work, a novel method using circular patch resonator (CPR) is developed to measure the dielectric constant and loss tangent of NLCs at microwave frequencies. In addition to using the cavity model for the preliminary design and analysing the fringing effect for a better accuracy, full-wave simulations are employed to confirm the final design and aid the characteristic analysis. Three prototypes were fabricated and measured to reduce uncertainty from manufacturing defects. To avoid the possible damage when higher voltage is required for a large range tuning, a coupling mechanism is proposed between the microstrip line and coplanar waveguides (CPWs) to replace connection through vias. A high accuracy with an uncertainty of 0.02 for relative permittivity estimate has been demonstrated with experiment verification, approximate 80% improvement than other typical methods. The simple design and PCB-based manufacturing techniques can be widely employed to characterise the properties of newly-developed LC mixtures.KEYWORDS: Cavity modeldielectric measurementsfull-wave analysismillimetre-wave devicesnematic liquid crystal Supplementary materialSupplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2023.2200741.AcknowledgmentsThe authors would like to thank Miss Huijuan Xing for her help in fabrication of the prototypes in this study.Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingThis work was supported in part by the Basic Science Research Program of Nantong City [JC2020142], in part by the NSFC under Grants [62174091 and 62201294], in part by Post-Doc International Exchange Programme [YJ20210098].