| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 100 === The present thesis proposes a model based on the idea of equivalent impedance to study piezoelectric energy harvesting. First, several nonlinear interface circuits, including the standard and parallel-/series-SSHI (Synchronized Switch Harvesting on Inductor) electronics, are replaced by several equivalent load impedances. Next, using the concept of impedance matching, the optimal power and the conditions to achieve it are derived. It is shown that the optimal condition refers to the case that electrically induced damping ratio is equal to the mechanical damping ratio. In addition, there always exists an optimal load such that the optimal condition is achieved for an SSHI system with weakly coupled electromechanical coupling.
The model of equivalent load impedance is applied to the case of multiple piezoelectric oscillators connected in parallel and attached to distinct interface circuits. As the present commercial finite element softwares are unable to simulate the electrical response of power generators connected to nonlinear interface circuits, our proposed approach successfully resolves such a numerical difficulty. In addition, the parametric study provides a way for analyzing the system response under various imperfect conditions. To see it, we consider a model problem consisting of three oscillators with different system parameters. For a system with strong electromechanical coupling, it is remarkably found that the drop in power is not significant for the standard system operated at the large optimal load. However, there is a significant drop in harvested power for the medium and weak electromechanical coupling systems. However, the parallel-SSHI system exhibits a significant improvement in bandwidth for the case of medium electromechanical coupling and boots harvested power significantly for the case of weak electromechanical coupling.
Finally, we present a modification such that harvested power obtained originally from a 3D finite element simulation is approximated by quadratic interpolation of results obtained by 2D plane-stress and plane-strain simulations. It shows satisfactory results.
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