Research On Dynamic Characteristics And Low-frequency Energy-harvesting Mechanism Of Bistable Triboelectric Generator

With the rapid development of internet of things(Io T),sensor networks are progressively becoming tremendous in size.Given the extensive distribution and enormously high number of sensors,the task of powering these sensors is quite formidable,which restricts the development of Io T.Energy harvesting from ambient vibration is a potential solution to the energy supply problem of sensor networks.As an emerging energy harvesting device,the triboelectric generator(TEG)can harvest vibration energy effectively.However,the frequency band of ambient vibration is mainly concentrated in the low-frequency region.Therefore,how to innovatively design a TEG to effectively harvest energy from low-frequency vibration is still a challenge in the field of energy harvesting.This thesis focuses on developing novel bistable triboelectric generators(BTEGs)by introducing the negative-stiffness mechanism into the traditional TEG.Through the dynamic analysis of the BTEG,the mechanical characteristics of the BTEG are studied in depth.Moreover,the energy-harvesting principle and electrical performance of the BTEG are studied in details by using numerical simulations.Finally,a prototype of the BTEG is fabricated,the experimental studies on dynamic behavior and electrical performance of the BTEG are carried out,which validate the excellent performance of harvesting energy from low-frequency vibration by the BTEG.The BTEG provides a promising avenue to the tough issue on harvesting low-frequency vibration energy,which could be employed to power the sensor networks of the Io T.The main novelties and contributions of this thesis are listed as follows:(1)The friction effect on the dynamic behavior and electrical performance in a cantilever BTEG(CBTEG)with magnetic negative-stiffness mechanism is investigated.Based on the extended Hamilton’s principle,the Coulomb friction model and Macro-slip friction model,the motion equation of the CBTEG is derived.The static characteristics of the bistable structure and the dynamic responses of the CBTEG under different friction models are analyzed by numerical simulations,and the effects of positive pressure and friction coefficient on the performance of the CBTEG are discussed.In addition,the effects of parameters on the mechanical responses of the CBTEG are also dissected.The results show that the friction effect has a significant effect on the performance of the BTEG,and reducing the friction effect can effectively improve the performance of the BTEG.(2)To harvest low-frequency vibration energy efficiently,a bow-type TEG with a bistable feature is proposed.The dynamic model of the bow-type TEG is established based on extended Hamilton’s principle,which is numerically solved to obtain the dynamic responses.Subsequently,a prototype of the bow-type TEG is fabricated and tested to verify the design concept.Moreover,the dependencies of the energy-harvesting performance on the structural parameters are experimentally investigated,and the maximum average power is obtained.Finally,the bow-type TEG is employed to power a number of LEDs to display the word “HNU” and drive the low-power digital watch under low-frequency excitation.The results show that the bow-type TEG can efficiently harvest vibration energy at low frequencies.(3)To enhance the efficiency of harvesting energy from low-frequency intrawell oscillation,a novel sliding-impact BTEG(SIBTEG)is proposed.The equation of motion of the SIBTEG is derived using Hamilton’s principle and then numerically solved to obtain the dynamic responses.Subsequently,the output performance of the SIBTEG is evaluated by solving the electrical equation,which is unidirectional coupled to the equation of motion.In addition,the power growth rate of the SIBTEG is obtained,which indicates that the output power of the devised SIBTEG is improved by about 100% over the sliding BTEG when they experience intrawell oscillation.Finally,experiments on the prototype of the SIBTEG are conducted to verify this design concept.The results show that the impact mode can notably enhance energy harvesting from intrawell oscillation,and thus the SIBTEG enables high-efficiency energy harvesting whatever the oscillation pattern is.(4)To harvest low-frequency torsional vibration energy efficiently,a torsional bistable TEG(TBTEG)is proposed by using the S-shaped compliant beams.The stiffness expression of the S-shaped beams is derived using the energy method,and verified by the finite element analysis.Then,the mechanical and electrical responses of the TBTEG are obtained by solving the equation of motion and the unidirectional coupled electromechanical equation,respectively.The numerical simulations of the circuit model are also carried out to validate the theoretical predictions.Finally,the effects of system parameters of the TBTEG on both the dynamic responses and electrical outputs are investigated.The results show that the TBTEG can effectively harvest energy from low-frequency torsional vibration.(5)To harvest low-frequency human motion energy,a wearable bistable TEG(WBTEG)is proposed.The prototype of the WBTEG is fabricated and the experiments are conducted to test the output performance of the WBTEG.Subsequently,some experiments are carried out to investigate the output voltages under different excitation frequencies,the output power under varying load resistances and the durability of the WBTEG.In addition,the effect of the excitation amplitude on the output performance of the WBTEG is investigated in detail.Finally,The WBTEG is used to power the LED array and drive the temperature sensor under human motions.The results show that the WBTEG can harvest energy efficiently from the human motion and drive the low-power sensor,which can be used for self-power supply of wearable devices.