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Title: A novel design in harvesting energy from operating machines by converting their generated waste energies to electricity
Other Titles: Cong yun xing ji qi zhong ti qu fei qi neng liang er zhuan hua cheng you yong de dian li zhi zhan xin she ji
Authors: Lam, Cheuk Yi (林卓怡)
Department: Department of Manufacturing Engineering and Engineering Management
Degree: Master of Philosophy
Issue Date: 2008
Publisher: City University of Hong Kong
Subjects: Energy conversion.
Electric current converters.
Notes: xiv, 127 leaves : col. ill. 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2008.
Includes bibliographical references (leaves 125-127)
CityU Call Number: TK2896 .L36 2008
Type: thesis
Abstract: Wireless devices have been widely adopted in machine health monitoring because they can acquire data from machines that are operating and can be installed in hazardous environments. However, the major deficiency of wireless sensors is the need to replace batteries frequently. Moreover, it may be unsafe to change the batteries manually if the wireless devices are located in a hazardous environment. To overcome such deficiency, a novel alternative is to recharge the batteries by harvesting wasted energies generated from the ambient environment. This study investigates the feasibility of implementation of an energy harvester to convert wasted energies generated from operating machines to electricity. In this research, three fundamental findings are observed. First, piezoelectric material, QP20N, is found to be a promising energy harvesting material to convert vibration to electricity. Second, the amount of power transfer can be optimized by matching the impedance of the piezoelectric material to that of the load. In addition, minimization of the internal impedance of the material can significantly increase its output power. Third, making the piezoelectric material vibrate at its resonance frequency will produce maximum electricity output. The most promising design of a piezoelectricbased energy harvester can be realized. Based on the findings, a novel piezoelectric energy harvester was implemented using two designs: “frequency converter” and “inductor circuit”. In order to maximize the electricity output from the energy harvester, two criteria should be fulfilled. First, the harvester should be tuned by the “frequency converter” so that its resonance frequency could be located within the dominant vibration frequency range of the operating machine. Second, the internal impedance of the piezoelectric material could be minimized by the “inductor circuit”. Maximum power transfer occurs when the impedance of the load matches that of the piezoelectric material. Experimental results show that the inductor circuit can increase the harvested power by at most 43% at the first mode of vibration of QP20N. Moreover, the power generated from QP20N by using a frequency converter can be 83 times much more than that from QP20N alone. The harvested energy can therefore partially supply electricity to power a low-power wireless device.
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