Design And Optimization Of A Broadband Vibration Energy Harvester Based On Multi-modal Vibration

With the development of microelectronics technology,computer technology and communication technology,some low-power new microelectronic devices and systems have been developed rapidly and widely used.At present,most of these microelectronic devices and systems are still powered by traditional chemical batteries.However,in some harsh application environments such as high and low temperature environment,or the application environment that human is difficult to close to,the traditional chemical battery power has the problem of supply failure,charging difficulties or replacement problems and other issues,limiting the application of some microelectronic devices and systems.Therefore,there is an urgent need to find a long-term power supply technology.Energy harvesting technology can convert energy in the environment into electrical energy and provide long-term power supply for the load to solve the problem of short charging thime of traditional battery power.However,the study shows that only when the frequency of external vibration source is consistent with the natural frequency of the energy harvester,the device will have a relatively large energy output.But the frequency of vibration source in the environment is usually not fixed,in order to improve the practicability of energy harvester.It is an urgent need to expand the working bandwidth of energy harvester.In this paper,a three cantilever – single mass vibration energy harvester was proposed based on multi-mode band expansion for the problem that the working bandwidth of the vibration energy harvester was too narrow.The equivalent "KMC" model of the three cantilever – single mass vibration energy harvester was studied to analyze the relationship between the natural frequency and the structural parameters.In addition,the finite element model of the harvester was established and the finite element simulation was carried out to prove that the energy harvester have good collection performance in the first two resonant modes,and the working frequency is twice as large as that of the common cantilever beam,and the working bandwidth was broadened effectively.The coverage of the piezoelectric material was optimized,and the open-circuit output voltages of the structure in the first-order and second-order modes were both increased to 10 V,which were 70 times and 82 times before optimization respectively.The effects of three different piezoelectric materials on the output power were studied and it was found that PZT-5H had better output performance compared with PZT-4 and PZT-5A.After optimization,the first two order resonant frequencys are 53.7Hz and 63.7Hz,respectively.They are so close that it is easy to match working frequency of energy harvester and vibration frequency of the vibration source to improve the energy conversion rate.Apply 0.98m/s2 acceleration and 15k? load impedanceto the device,the first and second order open-circuit voltages of the structure were both 10 V,and the first and second order output powers were 0.91 mW and 0.41 mW,respectively.