| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 97 === Wireless sensor networks become increasingly important in modern life for structural health monitoring or related applications. In these applications, due to their overall population and possible covered area, the replacement of batteries becomes a difficult and unrealistic task. As a result, an energy harvester to convert environment waste energy into electricity becomes important. In this dissertation, a piezoelectric energy harvester is proposed and fabricated to convert environmental vibrations into electricity. Unlike previous MEMS-based piezoelectric energy harvesters, which suffer matching between environmental low frequency vibration and the high system natural frequency, this work proposes a novel beating design using polymer piezoelectric materials. That is, by exerting impact force via beating, it is possible to excite system natural frequency by low frequency environmental vibration. This thesis contains details in designing piezoelectric harvester systems with flexible PVDF elements, exploring their vibration characteristics, and energy accumulating strategies by using a capacitor with a full-bridged rectifiers or a boost conversion. The overall efficiency of the proposed design is estimated as 28.9%. In comparison with the traditional design using a cantilever beam operated under steady state vibration, which only results in an overall efficiency of 4.1%, the efficiency is significantly improved and the proposed design could potentially revolutionize the future design approach for piezoelectric energy harvesters. In summary, this preliminary study shows that it is a feasible scheme for the application of piezoelectric materials in harvesting electricity from environmental vibrations. Although this work is still in its initial phase, the results and conclusions of this work are still invaluable for guiding the development of high efficient piezoelectric harvesters in the future.
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