The interest in the millimeter-wave band has been renewed recently, driven by the need for short-range high-speed data communications equipment. There is demand for compact and low-cost components, that are mass producible and have low power consumption. It is desirable for these systems to be reconfigurable in order to ensure continuity in data transmission. Nematic Liquid Crystal (LC) materials possess a birefringence that extends into the microwave range. Low voltages can be used to control this birefringence, making these materials an attractive modulation medium in such systems.
Very few LC mixtures have been characterized at milli-meter wave frequencies. The conventional optical methods are very often impractical due to the need for large cell thicknesses, which lead to oversimplification resulting in inaccurate characterisation.
We take a comprehensive approach in modeling both the liquid crystal orientation and the microwave fields, using a Finite Element Method (FEM) approach. The spatial distribution of the permittivity tensor resulting from the minimization of the free energy of the liquid crystal is used to calculate the microwave fields. Characterization is then made possible through the comparison of modeling results and experimental results for simple waveguiding structures. With these modeling tools we are not only able to characterize the liquid crystal better, but they can also be used to design more complicated liquid crystal based components such as filters and couplers.
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