Design and Fabrication of a Novel Vibration Energy Harvester for Rail Applications

This thesis investigates vibrational resonance (VR) phenomena and their application to nonlinear vibration energy harvesting (VEH) and acoustic energy harvesting (AEH) systems. The work is motivated by the need to enhance the efficiency of energy harvesters and to develop advanced vibration control strategies through the exploitation of inherent nonlinearities. First, VR is examined in a nonlinear oscillator subjected to weak low-frequency (LF) and strong high-frequency (HF) excitations. Analytical and numerical analyses reveal that the modulation of system parameters, particularly stiffness nonlinearity and HF forcing, can be used to control resonance states. The introduction of negative stiffness elements within a double-well potential regime provides a mechanism for resonance tuning, suppression of unwanted oscillations, and improved vibration isolation. Building on this, the study extends to a Duffing-type electromagnetic VEH, where nonlinear stiffness is shown to play a crucial role in optimizing energy harvesting. The average harvested power, used as the performance metric, is maximised through careful adjustment of system parameters, demonstrating that nonlinear vibratory mechanisms can significantly enhance energy extraction. Furthermore, the dynamics of air particles in a Helmholtz resonator (HR) subjected to amplitude-modulated acoustic excitation are investigated. The interplay between LF and HF components is shown to induce VR, with system behaviour strongly dependent on excitation frequency and resonator geometry. Regimes of optimal performance are identified, enabling the design of broadband acoustic resonators with enhanced sensitivity. Finally, an experimental AEH device is developed, consisting of a HR coupled with a piezoelectric film. The system demonstrates nonlinear behaviours such as hysteresis, while xxiii amplifying sound pressure inside the cavity and substantially improving energy conversion. At resonance, the device achieved a maximum voltage output of 84.2 mV under a 95 dB sound pressure level, corresponding to fourfold enhancement compared to a configuration without the resonator. Overall, this thesis establishes the theoretical, numerical, and experimental foundations for exploiting VR and nonlinear dynamics in the design of efficient VEH and AEH systems. The findings advance the development of sustainable energy solutions for powering low-power devices and contribute to the broader understanding of nonlinear resonance phenomena.