| With the development of wireless sensor technology and MEMS technology,the miniaturization and integration of energy supply are required.The current way of energy supply is mainly chemical battery,which has the inconvenience of regular maintenance and environmental pollution,so it is particularly important to seek a new way of energy supply.In nature,vibration is widely distributed and contains huge energy.Vibration energy harvester can replace traditional chemical battery to solve the energy supply problem of low power portable electronic equipment and wireless sensor.Piezoelectric energy harvesting technology has been paid more and more attention because of its simple structure and easy integration due to its force-electric coupling characteristic of mechanical energy and electric energy conversion.As a simple,reliable and easy to implement system,bistable structure is widely used in the design of wide-band piezoelectric vibration energy harvester.Therefore,the research on the structure optimization and dynamic performance of bistable energy harvester has very high practical significance for the development of self-powered micro electronic devices.In this paper,two bistable piezoelectric energy harvester are proposed based on the dynamic magnetic coupling and the abrupt change characteristics of the buckling beam.The dynamic response of the piezoelectric energy harvester under low wind speed or low frequency vibration excitation is studied by numerical simulation and experiment,and the influence of different system parameters on the output voltage of the piezoelectric energy harvester is analyzed.The galloping energy harvester based on dynamic magnetic coupling reduces the cut wind speed and improves the energy harvesting efficiency at low wind speed.Compared with linear stiffness system,the cantilever bistable piezoelectric energy harvester with adjustable prestress greatly widens the response frequency band under sweep excitation.The galloping voltage response is also greatly improved with the addition of square blunt body.The main work is as follows :（1）A dynamic magnetically coupled galloping energy harvester is proposed.Firstly,the multi-field coupling vibration control equations of the magnetically coupled galloping energy harvesting system are established based on the energy method.Secondly,the voltage outputs of dynamic magnetic coupling galloping energy harvesting system（DM-GEH）and fixed magnetic coupling galloping energy harvesting system（FM-GEH）at low wind speed are compared and analyzed by numerical simulation.The entry wind speed of DM-GEH system is advanced by 81.82%,and the energy harvesting efficiency is improved by 124.22% in the wind speed range of 1m/s-5m/s.Finally,the parameters of spring support stiffness were optimized to improve energy harvesting efficiency at low wind speed.The results show that changing the fixed magnet support mode to elastic support will reduce the vibration frequency and the entry wind speed of the system.Compared with the spring stiffness of1000N/m,the entry wind speed of the system with the spring stiffness of 500N/m is reduced by 54.55%,and the energy harvesting efficiency is increased by 15.35%（2）A cantilever bistable piezoelectric energy harvester with adjustable prestress is proposed and its piecewise restoring force curve is measured experimentally.The effects of displacement compression,excitation direction pair and resistance on output voltage under fixed frequency excitation,sweep frequency excitation and random excitation are studied experimentally.The results show that the displacement compression of the cantilever bistable piezoelectric energy harvester has the optimal value.In the sweep frequency experiment with1 g acceleration,the frequency band range of the system voltage large response（voltage amplitude >30V）with the displacement compression of 0.2mm（Δy=0.2mm）increases by740% and 1330% respectively compared with the forward sweep frequency and reverse sweep frequency when Δy=0mm.When Δy=0.25 mm,the forward and reverse sweep frequency increases by 40% and 72%,respectively.The optimal excitation direction changes with the excitation frequency,and the optimal load resistance appears in the direction of 40°and 50° respectively at 7.5Hz and 9Hz excitation frequencies.The optimal load resistance of the system at 1g acceleration and 7Hz excitation frequency is 140kΩ,and the corresponding output power is 0.68 m W.In the random excitation experiment,the voltage and strain responses of the system under two kinds of prestress are studied with the excitation intensity and direction.The results show that when Δy =0.2mm and Δy =0.25 mm,the voltage and strain responses of the system increase with the increase of excitation intensity.The optimal excitation direction is also affected by the prestress.The maximum voltage response of the system appears in the direction of 40° Angle with Δy=0.2mm displacement compression.When Δy=0.25 mm displacement compression,the maximum voltage response of the system appears in the direction of 60° Angle.（3）A bistable galloping energy harvesting system was constructed by adding a blunt head to the cantilever beam of the adjustable prestressed cantilever piezoelectric energy harvester.By using x Flow finite element software,the change of lift force of blunt body under different attack angles is simulated,and the lift curve of blunt body is fitted.The voltage and strain response curves of the system under different wind speeds were measured through wind tunnel experiments,and the vibration frequencies and optimal load resistance were compared under different wind speeds.The influence of axial compression on system voltage response and optimal load resistance is investigated.An experimental application platform based on the energy harvesting system was built to verify its power supply capability for micro electronic devices.The results show that compared with the voltage response of linear galloping system when Δy=0mm,the arm piezoelectric bistable energy harvester has a critical threshold when Δy>0.When the wind speed is lower than the critical threshold,the effect of the linear system is relatively superior.When the wind speed is higher than the critical value,the response of the bistable energy harvester is greater.For the bistable system,the critical threshold for the occurrence of jump is related to and the response amplitude is related to the amount of prestress compression.When Δy=0.3mm,the critical threshold for the occurrence of jump is larger,and the voltage response at each wind speed is smaller than that at Δy=0.2mm. |
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