Development of electromagnetic vibration energy harvesters as powering solution for IoT based applications
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Date
2022-09-20
Authors
Paul, Kankana
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Publisher
University College Cork
Published Version
Abstract
The drive towards building pervasive intelligence encompassing urban as well as rural environments has paved the way for the Internet of Things (IoT), which has reshaped our regular lifestyle alleviating the dependence on wired communication systems since its inception. The inexorable advancement in low to ultra-low power electronics have steered the rapid growth of the IoT platform expanding into several application fields. With the ongoing implementation of 5G (Fifth generation) and the emergence of 6G (Sixth generation) wireless technology on the horizon, the explosive growth of IoT connected devices reinforces the requirement of a robust and reliable power solution for the deployed wireless communication platforms. Utilizing distributed clean energy sources, especially the ubiquitous mechanical energy available in environment through dedicated transducers in the form of vibration energy harvesters (VEHs) to power the IoT-based wireless sensor platforms is a sought after alternatives to batteries in the forthcoming IoT applications.
The potential of the resonant/linear VEHs have been limited owing to the narrow operable frequency bandwidth as well as due to the lack of intelligent device designs that aids to yield large electrical power from the provided mechanical energy. In this thesis, a concertina shaped linear VEH spring architecture has been exploited to instigate large amplitudes of oscillation, which aids to yield a high power density (455.6μW/cm3g2) at resonance from a relatively small device footprint. From the application perspective, this concertina-VEH has been utilized to power the electronics interface and enhance the performance of a NFC (Near Field Communication) based wireless sensor platform which offers the benefits of low power consumption and on call data acquisition through this short range NFC based communication protocol. Such a robust autonomous wireless sensing platform offers the potential to be used in a large number of IoT based applications.
Despite of the large deliverable power obtained from the resonant VEH, the energy extraction drops dramatically as the excitation frequency deviates from the resonance condition, which is inevitable owing to the random nature of vibrations. A novel broadband VEH with tapered spring geometry has been developed as a part of this thesis to address this issue. Nonlinear restoring forces arising from the stretched springs enables the VEH to generate large power over a considerably wide bandwidth (45Hz of hysteresis width that is the difference of the jump down and jump up frequency with 1g excitation amplitude) of operable frequencies. Suitable power management strategies have been proposed to enhance the energy extraction capabilities. The nonlinear VEH has been successfully used to harness mechanical energy from the broadband vibrations of a car; the extracted energy is fed to a wireless sensor platform that reports on ambient temperature and humidity. This self-powered sensing system opens up the scope for exploiting this technology for monitoring food and medicinal quality during transportation while the VEH extracts mechanical energy from the transporting vehicle and perpetually powers the wireless sensor node.
Multiple nonlinearities arising from the stretching of the VEH spring as well as from the interaction of repulsive magnets have been introduced into the energy harvester, which gives rise to coexisting multiple energy branches. Not all of these energy states are achieved through the typical excitation frequency routine, some of these energy states are rather hidden. Experimentally a route to achieve these hidden energy branches have been explored in this work. Suitable frequency routines have been designed to achieve and sustain these higher energy states. A useful graphical representation has been introduced in the form of ‘eye diagrams’ that essentially estimates the transaction of energy from mechanical to electrical domain, and provides deep insight of the dynamical features of each energy branches, based on time resolved measurements of acceleration and voltage. A mathematical model has been developed to investigate the intricate complexities of the nonlinear system, which supports the experimental findings.
One of the major impediments in miniaturizing high-efficiency macroscale VEHs into MEMS (Micro-Electro-Mechanical-System) scale is the lack of matured technology for the CMOS (Complementary-Metal-Oxide-Semiconductor) compatible integration of magnets and the adverse effect of scaling on the permanent hard magnets. A part of the presented work investigates the effect of patterning continuous thin films of magnets into micromagnet array. With detailed analytical framework and exhaustive finite element analysis, the shape, size and distribution of these micromagnets have been optimized to maximize the stray magnetic field emanating from each edge of these magnets. Novel MEMS device topologies comprising of linear/nonlinear MEMS springs, micromagnet arrays and copper microcoil have been proposed which systematically maximizes the electromagnetic interaction between the micromagnets and the integrated coil that in turn translates into large deliverable power.
In addition to the developed device prototypes and demonstrations, this thesis further provides a firm roadmap that highlights the potential routes for enhancing the energy harvesting capabilities through highly integrated MEMS scale VEHs as well as for improving system level integration to establish these VEHs as a reliable and sustainable alternative of batteries in IoT applications.
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Keywords
MEMS , Internet of Things , Energy harvesting , Electromagnetic
Citation
Paul, K. 2022. Development of electromagnetic vibration energy harvesters as powering solution for IoT based applications. PhD Thesis, University College Cork.