| Recently, the rapid advancement of the low power consumption microelectronics and wireless sensor make passive power supply particular topical. Traditional battery has the disvantage of finite lifespan, high mantance cost and enviroment pollution. The technology and method of scavenging energy from the ambient environment as power source(such as vibration, heat, light, wind) and transfering it to electrical energy have generated much interest. In particular, piezoelectric vibration energy generators have a wide range of application and become an effective solution for powering the microelectonics continuously because of the advantages of high energy densities, requring no external voltage source and simple structure. This study mainly aims at the piezoelectric cantilever and makes investigation on impact-excited piezoelectric energy harvester from human motion through modelling, FEM simulation and experimental verification.The dissertation proposes an impact-excited piezoelectric energy harvester which utilize low frequency human motion drive the high resonant freqeucny piezoelectric cantilever through impact based on current research. Its creative design and principle are described detailedly. The effect of the implusive force,implusive contact surface and impact interveal are analyzed. The revised design for improving power density is presented based on previous research.The electromechanical coupling model of the piezoelectric vibration energy harvesting system is established and verified by finit element simulation. The effects of stimulation, mechanical damping ratio and external resistance for the output power are analyzed. Moreover, the effect of the piezoelectric coupling coefficience and mechanica damping ratio for the optimal resistance are also analyzed. The impact-excited model of the piezoelectric energy harvester is developed and verified by numerical simulation. The effect of the impulse force on energy conversion performance is analyzed and the maximum output power and optimal load are also investigated. According to the previous modeling analysis and based on non-resnonant and equal open circuit voltage conditions, the output performance on the vibration and impact circumstances are compared. The effect of the impact-exctied frequency up-conversion strategy on improving output power is revealed.An harvester prototype is fabricated and experimental platform is establised. Firstly, the output power of the piezoelectric cantilever is tested under vibration condition; Then the imapct-excited piezoelectric energy harvsting performance based on the human motion are investigated, the dissipated electric energy across multiple resistances over a range of walking speeds are measured. Experimental results reveal that the average output voltage increases correspondingly with a faster walking speed, the maximum power occur at the optimal resistance. Modeling and dynamic analysis of the implusive contact surface are performed. The influence of the asysmetric circle contact surface on the conversion performance are discussed. The theoretical conclusion are verified by experimental results.The ratio of the impact time interval and vibration period is presented and the effect of which is analyzed. The dynamic modeling of the cylinder and piezoelectric cantilever are established and analyzed based on the structure design and vibro-impact theorem. Subsequently, the limited expression of the overlap distance and the optimal theoretical value of impact interval are obtained. Numerical simulation are performed to compare the theoretical analysis.The influence of the impact interval on the energy conversion performance is evaluated. Several harvester prototypes are designed and manufactured, which can provde different impact interval. Moreover, the theoretical analyses are verified through comparision experiments.The dissertation investigates the method of improving power density based on previous research. The harvesters with revised structure are fabricated based on above-mentioned dynamic and motion analysis. The theoretical values of the revised harvesters are evaluated. According to the AC current generated by the PZT beam, a complete energy storage circuit with capacitor is designed and fabricated as PCB module which should provide steady DC current. The performance of the proposed harvesters and previous harvester are verfied and compared through experiment. Morever, the error between the theory and experiment is discussed.The proposed piezoelectric impact-excited energy harvester from human motion can accumulate enough energy during normal gait and power portable micro sensor or biological sensor, which may achieve autonomous sensor system. The research achievements provide practical value on energy harvesting field and makes foundation for further theoretical research. |
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