Quadrupole modelling of dual lock-in method for the simultaneous measurements of thermal diffusivity and thermal effusivity

The simultaneous measurement of thermal diffusivity and thermal effusivity based on the temperature wave analysis (TWA) is proposed by introducing the dual lock-in temperature sensor with a photo-thermal ac heat source. The thermal effect from each component in the multilayered experimental system is simulated by the quadrupole modeling adopted to the pure periodic heating of the temperature wave. The frequency dependency of the thermal effect from the thermal contact resistance and capacitance in the sensor were analyzed and minimized by taking the optimal frequency range of the temperature wave. The proposed method is applied to examine the nematic-isotropic phase transition of the liquid crystal 4'-(pentyloxy)-4-biphenyl carbonitrile (5OCB). The results were compared with the previous results measured with a single sensor and the advantage of the dual lock-in temperature sensor was demonstrated. (C) 2020 Elsevier Ltd. All rights reserved.