Abstract
The thesis titled "Towards Sustainable Environment: Novel Designs in Vibration Energy Harvesting Technology: Modelling and Experiment," by presenting a novel method in enhancing the power harvested in electromagnetic vibration energy harvester through different mechanical and electrical circuit design. The research focuses on the integration of analytical modelling techniques and experimental validation to optimize the performances of different electromagnetic vibration energy harvester designs. Various considerations to enhance the overall energy conversion efficiency by leveraging the specific inherent characteristics of various proposed designs through material/transducer selection, geometric configurations, and energy conversion mechanisms are explored. Generally, the work emphasizes and aims to contribute to the development of sustainable energy harvesting technologies with the potential to address environmental challenges and promote a greener future. Preliminary analysis and simulation by designing and simulating different transducer coil-magnet geometries indicate that 10.00% increase in magnet size with flux converging material, resulted in 18.55% improvement in flux and harvested power while a new approach of predicting the electromagnetic damping ratio equation to an accuracy of 99.21% was presented.Firstly, an approach to maximize the power output on a 2DOF harvester design by using different coils connection was presented. Analysis shows that by selecting the appropriate connection mode can enable achieving impedance matching between different sensors/micro devices since the coils could be connected either in individual, series, and parallel modes to match varying load requirements. This approach allows for continuous power to onsite and remote sensors. In addition, while the analytical formulations of the 2DOF designs achieved over 99.20 % fit with the experiment, the designs likewise maximized the harvested power/power densities by over 400 % relative to worse case scenarios of conventional SDOF designs in literatures.
Secondly, an improved damping-stress equation for predicting the linear and nonlinear damping ratio for any fatigue stress level (σ_f ) is presented. The nonlinear stress (σ_nL ) formulation is based on the Osborne Goodman’s approach shows that nonlinear behavior onsets in the cantilever beam in the interval 0.64σ_f<σ_nL<0.8σ_f. Below this interval, the stress is purely linear and it is modelled based on the Lazan hysteresis models while σ_nL>0.8σ_f initiate a pure nonlinear characteristic in the system. A general comparison of the linear critical stress-damping profiles for material mechanical properties ranging from plastic to non-plastic shows that plastic material attained a larger damping at equivalent stress. The implication of the above is that while the non-plastic material maintains the linear response profile at larger critical stress, the plastic material onset material/geometric nonlinearity due to larger response associated with it damping. Further studies on the energy harvesting capabilities shows that high-performance thermoplastic polymer are desirable for improved power densities while compromising the bandwidth while using a more rigid steel cantilever configuration compromised the power densities while increasing the bandwidth at equivalent excitations. Fitting the linear and nonlinear analytical equations resulted to an accuracy of 95.00 % with the experimental data thus showing that these methods undertaken for the linear and nonlinear performances provide good approximation for engineering design when the stress-damping relation deviates from linear into nonlinear domain.
Lastly, a novel design which attains a near resonant simultaneous harvester-isolation capabilities through levered configurations was undertaken. The levered design used either a vertical and/or a horizontal guiderail to respectively constrain the responses in desired DOF and to dispel the buckling energy in the spring. Two different designs namely with and without the guiderails are compared. Different from conventional isolators which isolation onsets after √2 of the resonant frequency ratio, this design characteristically activate double banded isolation about resonance at resonance frequency ratio ∓0.099. The lower and upper bands of the isolation onset occurred on the left- and right- hand sides of the lever while simultaneously harvesting power for efficient and autonomous sensor operations. The shifting of the point of isolation to lower near resonant frequency band considerably reduce the risk of resonant amplification without compromising the stiffness matrix of the design. The analytical solution of the system attained approximately 93.52 % fit with the experimental across all levels of excitations. While the Coulomb damping introduced from the guiderails was found to enhance the bandwidth and degree of isolation. Results showed that using larger energy harvesting coil is beneficial for improved harvestable power while improving the isolation by about 2.90 %. Lastly, while the Coulomb damping from guiderail was also identified beneficial for simultaneous harvester-isolation at optimum resistance at lower spring stiffness, standalone vibration energy harvesting and standalone vibration isolation are enhanced at zero Coulomb force (no guiderails) at larger stiffness and maximum Coulomb force respectively.
| Date of Award | Nov 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Chung Ket Thein (Supervisor) & Dunant Halim (Supervisor) |