Vibration Energy Harvesting Using Piezoelectric Materials

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dc.contributor.advisor Yang, Y en Tang, Lihua en 2018-10-08T03:04:31Z en 2012-07-02 en
dc.identifier.uri en
dc.description.abstract Harvesting environmental energy around a system provides a promising solution to implement self-powered electronic devices, which currently rely on batteries as power supply. Vibration energy is a ubiquitous energy source in the environment which can be converted into electricity via different transduction mechanisms. Due to their high power density and ease of application, piezoelectric materials have been enthusiastically pursued for vibration-to-electricity transduction. The work in this thesis focuses on developing advanced modeling methods for piezoelectric energy harvesting systems and improving their efficiency from both sophisticated interface circuit and advanced mechanical configuration perspectives. Piezoelectric energy harvesting can be achieved by directly bonding piezoelectric elements, or by installing harvesters as add-on systems (usually cantilever configurations with bonded piezoelectric elements) on a vibrating host structure. The former scheme is first investigated in this thesis. A prototype of vibration energy harvesting system using flexible and durable piezoelectric element, macro-fiber composite (MFC), is fabricated and tested. The bonded MFC elements are relatively tiny and the energy harvesting process barely affects the dynamics of the host structure. Thus, based on uncoupled assumption, finite element and circuit simulation models are established to predict the open circuit voltage and system performance of charging storage capacitor. The simulation models are then validated by experiment. Based on the validated models, the effects of various MFC parameters are discussed through parametric study. An optimal MFC configuration is thus proposed. When piezoelectric energy harvesting is pursued with harvesters installed on a host structure as add-on systems, most of the reported literature either simplified the structure or employed a simple resistor as electric load. This thesis presents a novel generic equivalent circuit modeling method for piezoelectric energy harvesters. The established equivalent circuit model (ECM) is more accurate than that based on uncoupled assumption. Equivalent circuit parameters of multiple modes of a harvester are identified by theoretical analysis for simple structures and finite element analysis for complicated structures. The identified parameters are then applied in system-level circuit simulation to evaluate the system performance. Numerical examples and experimental work are presented to validate the proposed method and to show its accuracy in accounting for the backward electromechanical coupling effect and its capability of handling complicated structures and sophisticated energy harvesting interface circuits. To improve the efficiency of piezoelectric energy harvesting, one of the sophisticated interface circuits, namely, synchronized charge extraction technique (SCE), is pursued. The analytical solution is derived in this thesis for a system employing SCE technique, which is more accurate than those based on uncoupled and in-phase assumptions reported in the literature. With this solution, the applicability of the SCE technique is discussed. Circuit simulation is also conducted with the aforementioned ECM of piezoelectric harvesters to validate the analytical outcomes. Both analytical and simulation results show that the SCE technique cannot improve or even reduces the power output at resonance if the electromechanical coupling of a piezoelectric harvester is not negligible. The SCE technique is capable of significantly boosting the efficiency only for the harvester vibrating at off-resonance or with weak coupling. Another aspect for efficiency improvement of piezoelectric energy harvesters involves increasing their bandwidth and functionality in practical scenarios. A novel multiple-DOF piezoelectric energy harvesting system is developed aiming at addressing the above issue. The 2DOF model is first analyzed and its two configurations are characterized. Based on the characterization, the 2DOF model is then generalized to an n-DOF system and its generic analytical solution is provided. With such n-DOF model for parametric study, a harvester can be designed to have close and effective multiple peaks, or to have one peak with significantly enhanced magnitude, with only slight increase of system weight. The ECM of the proposed n-DOF harvester is also developed in order to evaluate the system performance when sophisticated interface circuits are attached. This thesis also presents a comprehensive experimental work to investigate the use of magnets for improving the functionality of piezoelectric energy harvesters under various practical vibration scenarios. First, nonlinear configurations by magnets are exploited. Both monostable and bistable configurations are investigated under sinusoidal and random vibrations with various excitation levels. The optimal nonlinear configuration is determined to be near the monostable-to-bistable transition region. Near this region, both monostable and bistable nonlinear configurations can significantly outperform the linear harvester. Second, for ultra-low-frequency vibrations, a frequency up-conversion mechanism using magnets is proposed. Parametric study shows that the repulsive configuration of magnets is preferable, which is efficient and insensitive to excitation conditions when the magnets are placed sufficiently close. en
dc.publisher Nanyang Technological University en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.title Vibration Energy Harvesting Using Piezoelectric Materials en
dc.type Thesis en Structures and Mechanics en Nanyang Technological University en Doctoral en PhD en
dc.rights.holder Copyright: The author en en
dc.rights.accessrights en
pubs.elements-id 713070 en
dc.relation.isnodouble 721974 * Engineering en Mechanical Engineering en
pubs.record-created-at-source-date 2017-11-15 en

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