In the context of multifunctional materials, this dissertation presents the utilization ofcarbon nanotube fibers (CNTF) and vanadium dioxide (VO2) in an effort to improve energy harvesting and micromechanical systems research areas, respectively. First, a characteriza- tion study of the electrode interface in polypropylene ferroelectret nanogenerators, focusing on a comparison between carbon nanotube fiber electrodes with traditional metallic thin film electrodes is introduced. The study also included the effects of acetone treatment on CNTF- based electrodes and PPFE. Results showed a higher VOC values for the thin film metal electrodes regardless of the applied pressure. Factors such as conductivity and thickness of the electrodes were considered. Although the analysis points out these are the dominant factors on the VOC for metallic electrodes, volume and roughness of the CNTF-based elec- trodes might play additional roles in the open-circuit voltage outputs. On the other hand, the difference in ISC values between metal and CNTF-based electrodes were not as signifi- cant. Ultimately, a study on generation and leakage of induced charge in the electrodes was done. It was found, in contrast to dipole relaxation, that current leakage through parasitic elements is a faster process for discharge. Moreover, this work presents -for the first time- a tunable V O2 comb drive resonator. A theoretical model was proposed to incorporate V O2 phase transition material on comb drive resonators. A change in the Young’s modulus of the material was first considered. The- oretically, an active tuning capability of 5% was feasible when the material was deposited over the beams. On the other hand, VO2 deposition on the shuttle showed a 1.5% tuning capability when the thermal expansion coefficient of the material changed between the mon- oclinic and rutile phases. To better predict the resonant frequencies and electrical output of the resonators, an FEM model was also proposed. From the results, it was determined an increase on the number of combs would allow a larger displacement current. From the afore- mentioned analysis, deposition of VO2 over the beams or shuttle would result in a shifting of resonance frequencies to lower values. To validate the theory, comb drive resonators were fabricated and electrically characterized. It was shown the VO2 deposited over the shuttle resulted in a ∼2% active tuning. Finally, in the attempt to improve the effects of VO2 as an active tuning method, a second generation of comb drive resonators was fabricated. By utilizing static beam theory, the mode shape equation describing the beam’s shape is derived. Combined with the Rayleigh’s method of energy conservation, the presented work extends on the vibration analysis of comb drive resonator beams towards the derivation of an analytical equation able to estimate residual stress from measured lateral resonances. In addition, for a heating cycle, it was found the VO2 can increase the lateral frequencies up to 10% when transitioning from monoclinic to rutile. More importantly, a clear hysteretic behavior was measured on a heating-cooling cycle, demonstrating the feasibility of the comb drive resonator’s design to incorporate active tuning due to VO2 phase transition material
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