Elektrooptische und dielektrische Eigenschaften von flüssigkristallinen Nanokompositen

• Applicants: Professor Dr. Wolfgang Haase; Professor Dr.-Ing. Rolf Jakoby
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2010 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 168245587

• Final Report Year: 2014

Final Report Abstract

During this project, investigations on doping with different materials have been carried out to improve the dielectric properties of LCs. Three different measurement setups are designed and built at IMP to characterize the LCs for this project. These are cavity perturbation, capacitance and coaxial line methods as listed in WP4. The resonant cavity perturbation method is used for high precision measurements, i.e. such that provide high accuracy both in permittivity and loss. The resonators are temperature controllable. With respect to this project, the cavity perturbation method allows electrode free measurement. Therefore, problems like electrophoresis can be avoided and the dielectric material properties can be studied in principle. In order to investigate the FLC, where thin layer of LCs has to be guaranteed and electric biasing has to be applied, capacitance method is developed. The coaxial line method achieves a true broadband evaluation of the dielectric behavior of the LC mixtures with temperature dependency. However, due to the requirement of a relatively large amount of LCs of at least 60 mL for coaxial line setup and no obvious enhancements can be concluded from the cavity resonator and capacitance methods, coaxial line setup is decided not to be used in this project. Cavity resonator and capacitance methods are used to characterize the LCs in this project. The scattering parameters of both the undoped and doped LCs are measured. Permittivities and loss tangent are extracted, respectively. Consequently, LCs tunability and efficiency are derived and compared. After the measurements, the characterized samples are kept by IMP. It has been observed that the LC nanocomposites saturated after a few days, long term stability as mentioned in WP6 could therefore not be studied. Based on the current measured results, LC nanocomposites exhibited no enhanced performances by doping with nanocomposites in terms of dielectric properties at microwave frequencies. As a result, demonstrators as mentioned in WP8 with LC varactors, which has been already designed and fabricated in IMP, were decided not to build up once again for the provided LCs from IPC because of the lack of enhanced LC nanocomposites.

Publications

• Electronic Beam Steering and Polarization Agile Planar Antennas in Liquid Crystal Technology. Springer, 2013
  O.H.Karabey
  
• ”Temperature Controlled Artificial Coaxial Line for Microwave Characterization of Liquid Crystal,” in German Mircorwave Conference (GeMiC), 2014
  W. Hu, O.H. Karabey, A. Prasetiadi, M. Jost and R. Jakoby