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This paper presents the capacitive transduction technique involved with liquid crystal (LC) based sensors in partially disordered systems. These sensors have the potential applications in chemical and biological systems. The theory for tracking the average molecular deformation (state of alignment) and degree of ordering of anisotropic and partially disordered LC film via capacitive sensing is investigated. This system is modeled using the Q-tensor approach in modeling uniaxial LC material. The proposed sensor design is an interdigitated electrodes structure. Transverse and fringing capacitances as function of the molecular deformation are calculated. It is verified that three capacitance measurements are required to track the average molecular orientation and the degree of disorder in the LC film. The sensitivity for the sensor at different alignments and ordering degree is also studied. Toward practical sensor, neuro-fuzzy system is modeled to simulate the capacitive transduction and to monitor the LC profile. Sensors are fabricated and tested. Both the experimental and calculated capacitances are presented and compared.
Date of Publication: Sept. 2008