Date on Master's Thesis/Doctoral Dissertation

8-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Berfield, Thomas

Committee Member

Murphy, Kevin

Committee Member

Chen, Yanyu

Committee Member

McNamara, Shamus

Author's Keywords

Bistable energy harvesting; nonlinear dynamics; microelectromechanical systems (MEMS); smart materials; microfabrication

Abstract

Thanks to the rapid growth in demand for power in remote locations, scientists’ attention has been drawn to vibration energy harvesting as an alternative to batteries. Over the past ten years, the energy harvesting community has focused on bistable structures as a means of broadening the working frequency range and, by extension, the effective efficiency of vibration-based power scavenging systems. In the current study, a new method is implemented to statically and dynamically analyze a bistable buckled, multi-component coupled structure designed specifically for low-frequency vibration energy harvesting systems in both macro and MEMS-scale sizes. Furthermore, several micro-fabrication steps using advanced manufacturing technology methods were applied to design and fabricate a micro-scale version of the energy harvester at the University of Louisville Micro/Nano Technology Center. First, previously efforts performed on different aspects of vibration energy harvesting systems are reviewed to show the current challenges associated with such devices. The coupled structure proposed in this project is then introduced and its equations of motion are developed based on nonlinear Euler-Bernoulli beam theory. These governing equations are discretized and solved using a Galerkin method in two different approaches: with some known shape functions which only satisfies the geometrical boundary conditions; with the exact shape functions obtained from solving the linearized coupled structure as a one single system. An experimental setup is also used to verify the advantages of designed structure in capturing bistable motion at low-frequency range. To validate the modeling approaches, the obtained results are compared with the ones captured from both FEA model and the experimental setup, which shows the superiority of the proposed approach in which exact shape functions of the system are used as the basis in the discretization process. After the validation of the proposed approach, it is applied on a micro-scale version of the system in which structural, piezoelectric, and electrode layers are all considered as they exist in an actual device. Furthermore, a different bistable system, which was previously studied by other researchers in the area, is analyzed by this method to show the reliability of the proposed model. For all these cases, the amplitude-frequency response of the system and snap-through regime with the variation of various parameters, including exciting frequency, base vibration, and buckling loads are investigated based on the developed model. It is shown that bisatble motion and other nonlinear phenomena such as super-harmonic behavior in the system can be captured under certain circumstances, which can significantly impact major system functionalities such as output voltage response and is crucial for the performance of energy harvesting devices. As mentioned above, various micro-fabrication techniques were also used to design and fabricate a micro-scale version of the proposed system, which eventually led to the successful fabrication of a MEMS device as a result of experimental efforts performed to overcome the challenges and issues associated with the designed manufacturing process.

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