The Design Of Non-beam Type Bistable Energy Harvesting System

Energy harvesting technology is the key technology to solve the limitation of energy supply in the Internet of things.With the depletion of traditional fossil fuels,more and more attention have been paid to collecting the energy dissipated in the environment.Vibrational energy exists widely in nature and collecting vibration energy is not restricted by weather,occasion and so on.The vibration energy harvesters have been developed from the initial resonant energy harvesting devices to the nonlinear energy harvesting devices that are represented by bistable energy harvesters.Common nonlinear vibration energy harvesters are mainly beam-type energy harvesting devices that include cantilever beams or buckled beams.As the classical structure of the vibration energy harvesting device,the configuration of beam structure is simple and the working principle of beam structure is complete.However,the beam structure has some obvious shortages in the vibration energy harvesting device.For example,the stress concentration occurring near the fixed positions of the beam structure limits the effective working area of the piezoelectric elements leading to reducing the energy harvesting efficiency of the energy harvester.The structure of the beam-type vibration energy harvesting device is not compact,beam-type energy harvester is in general used as an independent unit,which leads the beam-type energy harvester is difficult to integrate with other components effectively.The practicality of beam-type energy harvesters are limited significantly.This dissertation aiming at improving the practicability and applicability of nonlinear energy harvesting device,puts forward the novel design of the non-beam type bistable energy harvester and designs two different non-beam type bistable energy harvesters which have different working principles.The dynamic responses and the performance of these two non-beam type bistable energy harvesters considering various structural parameters are investigated through the establishment of their theoretical model,the contrast of the finite element simulations and the verification experiments.The main work and research contents of this dissertation include three aspects:(1)According to the different working principles,the bistable energy harvesting devices are sorted and classified.The structures of the nonlinear energy harvesting devices are summarized.It can be found that the configurations of the nonlinear energy harvesters are mainly based on the beam structures.Through the analysis of the beam structure,it can be found some shortages of beam structure in the energy harvesting device---stress concentration reduces the energy harvesting efficiency and the structure is not compact leads to limiting the practicability of the energy harvesting device.Comparing the vibration mode and stress distribution of the bellows structure with that of the beam structure in the energy harvesting device,demonstrates the advantages of the bellows structures in energy harvesting device---the stress distribution of the bellows structure is periodic and the bellows structure has the potential to be used as an elastic unit in other vibration devices.Two different non-beam type bistable energy harvesting devices that have different working principles,are designed by using bellows structure.They are non-beam type bistable magnetic repulsion harvester and non-beam type bistable magnetic attraction harvester,respectively.(2)The theoretical model of the proposed non-beam type bistable magnetic repulsion harvester is established.The potential energy function of the proposed non-beam type bistable magnetic repulsion harvester is analyzed and the relationship between the dynamic behaviors of the proposed magnetic repulsion harvester and the structural parameters of the model is derived by static bifurcation analysis.The equations of motion are derived for the proposed magnetic repulsion harvester.According to the equations of motion,the parameters that affect the bistable characteristics of the proposed magnetic repulsion harvester,including the horizontal spacing between the magnets,the excitation amplitude and the excitation frequency,are confirmed.The influence of each parameter on the dynamic behaviors and the energy harvesting efficiency of the proposed magnetic repulsion harvester are obtained by the finite element simulations,the constant frequency experiments and the scanning frequency experiments.(3)The theoretical model of the proposed non-beam type bistable magnetic attraction harvester is derived by using the magnetic dipole model.The relationship between the parameters that affect the dynamic behaviors of the proposed magnetic attraction harvester and the bistable characteristics of the proposed magnetic attraction harvester are obtained by analyzing the potential energy function and the dynamic equilibrium positions of the proposed magnetic attraction harvester.The equations of motion of the proposed magnetic attraction harvester are derived.According to the equations of motion,there are four parameters effecting the bistability of the proposed magnetic attraction harvester,which are the horizontal spacing between the magnets,the vertical spacing between the magnets,the amplitude of excitation and the excitation frequency.In order to demonstrate that the bistable characteristics of the proposed non-beam type bistable energy harvester contribute to broadening the working bandwidth and enhancing the performance of the energy harvester,the finite element simulations compare the displacement-velocity-time trajectories of the proposed harvester with bistable characteristics to that of the proposed device with linear characteristics under low frequency excitation,the scanning frequency experiments compare the dynamic responses,the output voltage,the effective working bandwidth and the output power of the proposed harvester with different parameters.