| Over the last decade, vibration-based energy harvesting has provided a technology push on the feasibility of self-powered portable small electronic devices and wireless sensor nodes. Vibration energy harvesters in general transduce energy by damping out the environmentally induced relative emotion through either a cantilever beam or an equivalent suspension mechanism with one of the transduction mechanisms, like, piezoelectric, electrostatic, electromagnetic or magnetostrictive. Two major challenges face the present harvesters in literature, one, they suffer from the unavoidable mechanical damping due to internal friction present in the systems, second, they cannot operate efficiently in the low frequency range (< 10 Hz), when most of the ambient vibrational energy is in this low frequency broadband range. Passive and friction free diamagnetically stabilized magnet levitation mechanisms which can work efficiently as a vibration energy harvester in the low frequency range are discussed in this work.;First, a mono-stable vertical diamagnetic levitation (VDL) based vibration energy harvester (VEH) is discussed. The harvester consists of a lifting magnet (LM), a floating magnet (FM) and two diamagnetic plates (DPs). The LM balances out the weight of the FM and stability is brought about by the repulsive effect of the DPs, made of pyrolytic graphite. Two thick cylindrical coils, placed in grooves which are engraved in the DPs, are used to convert the mechanical energy into electrical energy. Experimental frequency response of the system is validated by the theoretical analysis which showed that the VEH works in a low frequency range but sufficient levitation gap was not achieved and the frequency response characteristic of the system was effectively linear. To overcome these challenges, the influence of the geometry of the FM, the LM, and the DP were parametrically studied to assess their effects on the levitation gap, size of the system and the natural frequency. For efficient vibration energy harvesting using the VDL system, ways to mitigate eddy current damping and a coil geometry for transduction were critically discussed. With the optimized parameters, an experimental system was realized which showed a hardening type nonlinearity and an improved efficiency from the initial study.;Even after the optimization study, several challenges still hindered the VDL system from being an efficient system. The main challenges faced were the strict stability conditions and the limitations of the maximum amplitude of the FM, which was inherently limited by the distance between the DPs which in turn was coupled back with the stabilization condition. To overcome these challenges, an alternative configuration called as a horizontal diamagnetic levitation (HDL) system was investigated.;In the HDL configuration, two magnets, alias LMs, are arranged co-axially at a distance such that in between them a third smaller magnet, alias FM, is passively levitated at a laterally offset equilibrium position. The levitation is stabilized in the horizontal direction by two DPs placed on each side of the FM. This HDL configuration mitigates the limitation on the amplitude of the FM imposed in the VDL configuration. The parameters of the HDL system were characterized to understand the key factors that affect the static levitation, stability, frequency response and the power density of the HDL energy harvester. As a result of the analysis an efficient low resonant frequency vibration energy harvester was experimentally validated.;Finally, a bi-stable system based on HDL is proposed to take advantage of the broad frequency bandwidth response inherent in a bi-stable system. From initial conceptual design which involves multiple lifting magnets to a final robust frequency tunable design involving multiple lifting magnets and repelling magnets are discussed. Experimental and theoretical results of this low frequency wideband vibration energy harvester are presented. |
