Doctor of Philosophy
Faculty of Engineering and Information Sciences
Yildirim, Tanju, Enhanced broadband vibration based energy harvesting coupling geometric nonlinearity and parametric excitation, Doctor of Philosophy thesis, Faculty of Engineering and Information Sciences, University of Wollongong, 2017. https://ro.uow.edu.au/theses1/46
In this work, theoretical, numerical, and experimental investigations for vibration based energy harvesters (VBEH) have been conducted. To improve the current limitations of VBEHs, a combination of parametric excitation, geometric nonlinearity arising from centreline extensibility (mid-plane stretching), geometric imperfection, mechanical stoppers and an array configuration have all been explored as suitable mechanisms for increasing the broadband behaviour of a VBEH. This work mainly focused on the increased broadband behaviour of a doubly-clamped beam resonator with a magnetic tip mass and electromagnetic induction as the transduction mechanism; however, cantilever beam setups were also used in some cases when combining this work with existing methods in the literature.
A comparison of a transversely and parametrically system was conducted first to assess the benefits of parametric excitation; a model identification procedure was proposed and it was found, sustained oscillations could be achieved and this led to a greater nonlinear broadband behaviour. Using parametric excitation, the effects of electrical damping, load resistance, initial axial displacement, geometric imperfection have been investigated; it was found that by slightly adjusting geometry, the fundamental and parametric resonance were combined and using imperfections an initial softening followed by strong hardening behaviour was observed.
Furthermore, the end of this thesis explores using parametric excitation and geometric nonlinearity with conventional methods in the literature, such as, mechanical stoppers and an array configuration; it was found that parametric resonance offered an increased bandwidth and power harvested for the VBEH devices fabricated.
Parametric excitation, geometric nonlinearity and other nonlinear mechanisms have a significant effect on the qualitative and quantitative change in the frequency bandwidth of a VBEH device. This behaviour can be used to further enhance the bandwidth, power, efficiency, and performance of VBEH technology.