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Abstract: The experimental studies of the dielectric response in liquid crystal at different temperatures have been done by using a microwave cavity spectrometer. The Microwave Cavity Spectrometer has been used to measure and compare the relative shift, width and amplitude of the resonance profile for the sample loaded in the cavity operated in TM010 mode at two different frequencies 20.900GHz and 29.867GHz. The comparative study of dielectric loss, and relaxation time of above liquid crystal at different frequencies has also been done at different temperatures. The method is used for its inherent accuracy and requirement of minute quantity of sample. Importance of nematic liquid crystal for infiltrating photonic crystal fibers for modification of their properties is indicated. [Copyright &y& Elsevier]

• Dielectric response of Pentyl Cyano Biphenyl (PCB) nematic liquid crystals was done for two frequencies 9.0 GHz and 20.9 GHz. • Microwave cavity spectrometer is used to measure the width of the resonance profile and shift of the resonance frequency. • The theory of perturbation is used for computation of Activation energy and Relaxation time. • The thermo-dynamical parameters calculated for a suitable temperature range. • This method is well known in scientific community for its requirement of small quantity of sample and inherent accuracy. A comparable study of the dielectric response of PentylCyano Biphenyl (PCB) nematic liquid crystals over the temperature range 297–316°K is reported for two frequencies i.e. 9.0 GHz and 20.9 GHz. The loaded resonant microwave cavity operated in TM 010 mode at two different frequencies mentioned above. The theory of perturbation is used to analyze the data. The computation of Activation energy and Relaxation time was done. Calculation for the thermo-dynamical parameters such as ΔG, ΔH and ΔS was done for a suitable temperature range. It has been observed that the change in temperature and the change in frequency both effects the properties such as relaxation time, activation energy, entropy and enthalpy. This method is well known in scientific community for its requirement of small quantity of sample and inherent accuracy. The possible applications are reversible optical memories, beam steering antenna, and fabricating frequency agile components. [ABSTRACT FROM AUTHOR]