Date of Award

Summer 8-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

First Advisor

Hamzeh Bardaweel

Abstract

In recent years, vibration based energy harvesting techniques showed a promising alternative to power wireless sensor networks (WSN). Billions of low power sensors are currently used widely in wireless sensor networks (WSN) and the Internet of Things environment (IoT). These sensors are currently powered by a traditional power source, i.e. a disposable battery. Vibrations are an abundant source of kinetic energy that can serve as the power source for these sensor nodes. This approach eliminates the necessity for frequent battery replacement due to their short-life span and hazardous disposal process. The adverse and irreversible effect from the disposal of these batteries have an alarming impact on the environment.

In order to limit the severity of this impact, the vibration energy harvesting alternative is proposed as a solution. Vibration energy harvesting provides on site power sources for these small sensors by utilizing kinetic vibrations from its surroundings. This was the drive for much of the research done in vibration based energy harvesting. Most of the work that has been done so far focused on linear resonators with limited operational bandwidth. This limitation opposes a challenge, considering that vibrations exist on a wide frequency spectrum. This challenge was met by the invention of levitation based magnetic energy harvester. In a traditional magnetic levitation design, two stationary magnets are fixated in an orientation to repel a center magnet to allow it to float in between.

This mechanism shows considerable lever in terms of power generation and operational bandwidth over linear counterparts. The traditional design shows superior performance over linear generators. Nonetheless, it remains deficient in power output as well as operational bandwidth. This work introduces an Enhanced Energy Harvester (EEH) design over the traditional design (TEH) based on dual mass moving magnets. The proposed design shows significant increase in power output and a wider frequency response bandwidth. The presented EEH design consists of a levitated magnet, an FR4 spring-guided magnet, and coils. Prototypes of the EEH have been fabricated and characterized experimentally. Nonlinear dynamical models of the EEH are developed and validated against experimental data.

The results show excellent agreement between model simulations and experimental data. The figure of merits shows that the presented EEH design significantly outperforms the commonly studied magnetic spring based vibration energy harvesters. The EEH generates 1.97 mW/cm3 g 2 at 0.4 g[m/s2] which is approximately 400% the amount of power generated by the traditional magnetic spring based harvester, i.e. 0.5 [mW/cm3 g 2 ]. At lower acceleration, i.e. 0.1 g[m/s2], the enhanced harvester exhibits 4000% increase in power density compared to the traditional harvester. This makes the presented enhanced harvester design exceptionally suitable for applications where low acceleration oscillations are abundant, including harvesting vibrations from highway bridges and human body motion. Additionally, the half-power frequency bandwidth of the EEH is 90% wider than the bandwidth of its rival traditional magnetic spring based energy harvester.

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