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A MEMS-based Fixed-Fixed Folded Spring Piezoelectric Energy Harvester Open Access


Other title
Piezoelectric Energy Harvesting
Frequency Optimization
MEMS Characterization
Type of item
Degree grantor
University of Alberta
Author or creator
Lueke, Jonathan S.
Supervisor and department
Moussa, Walied (Mechanical Engineering)
Examining committee member and department
Yavuz, Mustafa (University of Waterloo, Mechanical and Mechatronics Engineering)
Toogood, Roger (Mechanical Engineering)
Carey, Jason (Mechanical Engineering)
Tang, Tian (Mechanical Engineering)
Department of Mechanical Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Energy harvesting is an important developing field in Microelectromechanical Systems (MEMS) research. In this thesis, a fixed-fixed folded spring-based harvester is presented as an alternative mechanical element for beam-based piezoelectric harvesters to reduce its natural frequency for low frequency applications (30-300 Hz). The research focused on decreasing the natural frequency of the harvester through mechanical stiffness reduction, which leads to an increase in output power. Two classes of folded spring-based energy harvesters were produced in order to characterize the frequency response of the folded spring harvesters - single folded spring harvesters and harvesters consisting of arrays of folded springs and proof masses. The critical parameters of the folded spring harvester were identified: the length of the individual beam elements and the thickness of the folded spring. Through the manipulation of these parameters, it was found that the fixed-fixed folded spring geometry allowed for a large increase of beam length, reducing the natural frequency of the structure without generating significant length-enhanced residual stress stiffening. Additionally, the folded spring structure increased the quasi-linear stiffness range of the harvester, allowing for the correct match of load resistance without potential drift and losses due to non-linear spring stiffening. To experimentally test the energy harvesters, a microfabrication process flow was developed to produce the piezoelectric harvesters with the chosen materials and cross section. This process flow, combined with the folded spring methodology, resulted in several publications and a US Patent Application (Serial No. 14/032,018). Packaging and testing methodologies were developed in order to allow the harvesters to be tested under a base excitation. The frequency reduction methodology applied to the harvester allowed for wide frequency range of input vibration to be captured by the harvesters, ranging from 45 to 3667 Hz. The maximum power harvested by a single harvester was 690.50 nW at 226.25 Hz, with a PZT layer thickness of 0.24 μm. The natural frequency reduction methodology presented in this thesis can be applied to any MEMS-based energy harvesting scheme that requires high amplitude, low frequency, out of plane displacement to maximize the energy harvested.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
J. Lueke and W. A. Moussa, "MEMS-Based Power Generation Techniques for Implantable Biosensing Applications," Sensors, vol. 11, pp. 1433-1460, 2011.M. Rezaei, J. Lueke, D. Raboud, and W. Moussa, "Challenges in fabrication and testing of piezoelectric MEMS with a particular focus on energy harvesters," Microsystem Technologies, pp. 1-25, 2013.

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