Date of Award

Summer 8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Hamzeh Bardaweel

Abstract

Continuous advancements in electronics manufacturing have resulted in the widespread use of low-power sensors, necessitating the development of energy harvesters capable of generating electric power from abundant and free energy sources such as ambient vibrations. A rising interest in energy harvesting technology inspires the work discussed herein using magnetic interactions to target nonlinear energy harvesting, which is compatible with ambient vibration energy sources with a broad frequency spectrum and particularly rich in low frequencies. This research aimed to look into a magnetic-levitation-based vibration energy harvester that could be tuned from a mono-stable to a bi-stable configuration. An oscillating magnet is levitated between two stationary top and bottom magnets in a mono-stable arrangement. A bi-stable configuration is achieved by fixing a cluster of peripheral solid magnets around the harvester housing. Magnetic forces in magnetic-levitation-based harvesters have traditionally been represented by polynomial functions integrated into the equation of motion. Analytical models for the interaction of magnets were developed and integrated into the equation of motion in this study. The analytical model of magnetic force delivers more accurate results for the bi-stable configuration than those produced using polynomial functions, according to the findings from this study. The results demonstrated that adjusting the geometric ratios of the peripheral magnets in the bi-stable configuration can produce a variety of load-deflection properties. The bi-stable design exhibits inter-well, chaotic, and intra-well motion at varying accelerations during dynamic operation. The bi-stable architecture benefits from thinner peripheral magnets, especially at lower acceleration values. Lower energy barriers, improved frequency responses, and nearly zero stiffness at equilibrium position are all advantages of thinner peripheral magnets. The harvester moved towards mono-stability when thinner peripheral magnets were utilized, showing that mono-stability is the preferred mode for vibration energy harvesting under harmonic excitation. We also propose an experimental and theoretical platform for developing design platform and performing analysis on mono-stable magnetic springs used in vibration energy harvesting devices. The results reveal a high level of agreement between the model and the experiment. For linear and nonlinear stiffness coefficients, approximate analytical expressions are found. The findings indicate that the linear and nonlinear stiffness coefficients are linked. The stationary ring magnet's outer diameter can be utilized to modify the energy harvesting system's nonlinearity to provide linear, hardening nonlinear, or softening nonlinear responses. Designers can use this work to understand the behavior of magnetic spring-based harvesting systems and assess their performance concerning design factors. Other energy systems that use magnetic springs, such as energy sinks, could benefit from this research.

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