Measurements of anisotropic complex permittivity of liquid crystals at microwave frequencies

Recent interest in application of liquid crystals for tuning of microwave frequency range devices generated a need for better microwave characterization of these anisotropic and DC electric and magnetic fields sensitive materials. We report on measurements of the complex permittivity tensor of two liquid crystals and on determination of their DC electric field bias dependence. Measurements were carried out using a novel microwave cylindrical dielectric resonator technique which utilizes TE011 and TM011 modes. Liquid crystals are inserted into the inner hole in the dielectric resonator. Results of measurements have shown significant anisotropy in crystals dielectric properties and also allow estimates of tunability and tuning speed. The measurements showed some promises for liquid crystals to be used for tuning, but more characterization and technological work is needed.