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

• Author / Creator

  Lueke, Jonathan S.

• 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.

• Subjects / Keywords

  • Packaging
  • MEMS Characterization
  • Frequency Optimization
  • Microfabrication
  • MEMS
  • Piezoelectric Energy Harvesting

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3T972

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.