Investigation and Optimisation of Kinetic Energy Harvesters with Nonlinear Electromechanical Coupling Mechanisms

This thesis applies various nonlinear analysis techniques to reconstruct the qualitative and quantitative characteristics of Kinetic Energy Harvesters (KEHs) and proposes methods to optimize them. Having the optimization of electromagnetic and electrostatic harvesters achieved, a concept of the near-limit KEH is introduced specifically on realistic patterns of motion. Chapter 2 gives a general review of the KEH field with regard to types of energy harvesting devices, the amount of power they can generate and their compatibility with different sensors. Chapter 3 contains a detailed description of modeling approaches for KEHs with various transduction mechanisms. It provides comprehensive information on how to model various interaction forces acting on the proof-mass of an KEH, particularly, dissipative forces and piece-wise stopper interactions. Finally, various techniques to model the dynamics of the system, such as numerical solutions of the motion equations, harmonic balance method and multiple scales method are shown in this chapter. Chapter 4 shows a successful application of the methods described in Chap. 3 to meso-scale KEHs with the electromagnetic transduction mechanism. A fast and reliable method of equivalent coils is used to solve for the magnetic field developed in such a system. Chapter 5 is focused on the problem of frequency up-conversion in KEHs with electrostatic transduction. Employing the technique shown in Chap. 3 on experimental resonance curves, we reproduce the waveforms of the mechanical motion of the proof-mass. By analyzing them in terms of higher harmonic, we discover the reason behind high-power generation at low frequencies in systems with up-conversion. The Concept of kinetic energy harvesting that is forced to move following the optimal trajectory for a given excitation is shown in Chapter 6. The main feature of the near-limit control of KEH is prediction of the next maximum-minimum pair in the external acceleration, and the corresponding control. The acceleration patterns of various human motion waveforms are measured and used as the possible external excitation to test Near-Limit Kinetic Energy Harvester (NLKEH). In addition, techniques to predict the next extremum in generic acceleration pattern are investigated. Finally, Chapter 7 summarizes the thesis and presents main conclusions.