| Wireless Sensor and Actuator Networks,as the typical representative of the information network technologies,is continuously developing towards multidimensional directions such as wide area network distribution,extreme application environment and multi-functional network nodes.In information networks,using the novel energy technology to overcome the existing shortcomings such as limited energy,difficulty of maintenance,environmental pollution of the traditional battery technology has important strategic significance to the further development of the information technology.Piezoelectric vibration energy harvesting and conversion technology,as one of the novel energy technologies,is playing an important role in supplying the prolonged energy for microelectronic devices in the information network nodes due to its advantages of simple construction,high energy density,no electromagnetic interference,high stability,fatigue resistance,ease of miniaturization and integration,and so on.It is of great research value and challenging to develop the piezoelectric flow vibration energy harvester.Currently,the development of this technology is still at an initial stage.The further increasing performance,function expansion,integration and miniaturization development are limited due to its main restrictions such as less attention of the fluid environment,immature theoretical system,technical difficulty in fabricating process,and so on.In view of the limitations of current research work,this dissertation proposes a piezoelectric energy harvester based on wake vortex induced vibration for the liquid flow environment.Inspired by the multi-DOF multi-frequency harvesting technology,an improved broadband optimized architecture has been further proposed.Besides,miniaturization research has been developed on this new structure.The main research contents and achievements of this thesis include:1.This dissertation has proposed a theoretical model that is suitable for the piezoelectric energy harvester based on wake vortex induced vibration for liquid environment with low speed.In model building,the idea of modeling,the assumed conditions,the processes and the results of modeling are expounded.The three-filed coupling of the system and the internal mechanism of energy conversion are studied.After that,the model is validated.Through theoretical analysis,it is predicted that there exists an optimal distance scale factor of the system to enable its performance most optimization.Meanwhile,the specific influence rule of such factors as flow velocity,diameter of the bluff body and load impedance on the output performances of the system is revealed.Then,the structure design parameters of the device are optimized.2.This study has proposed a single beam shaped piezoelectric energy harvester based on wake vortex induced vibration for liquid environment with low speed.This device is based on vortex-induced resonance principle.In the system architecture,the separation type design scheme that the fixed end of the piezoelectric vibrator is placed in the downstream of the bluff body wakes while the free end is placed in the upstream is presented.The operating principle and motion process of the system are expounded.Beside,the multi-DOF multi-frequency harvesting technology has inspired us to propose an improved piezoelectric energy harvester with E-shaped beam multi-frequency architecture based on wake vortex induced vibration for the liquid environment with lower speed.Meanwhile,in order to explore the MEMS manufacturing process technology for miniaturizing the device,a micro piezoelectric vibration energy harvester with E-shaped beam architecture is proposed.3.This dissertation has studied the main manufacturing technologies for the piezoelectric vibrator and the piezoelectric energy harvester prototypes based on wake vortex induced vibration.In the process of fabricating the vibrator,this study has applied a sputtering technology which can prepare the electrode,a bonding technology which can obtain the bimorph,a grinding process which can reduce the thickness of the PZT functional layer and a cutting technology which can control the dimensions of the parts.In the process of fabricating the prototypes,this study has proposed an arrangement technology which can avoid the effects of gravity and fatigue,a waterproof technology which can achieve the function of insulation protection,a clamping technology which can provide reliable boundary constraints and a wire connecting technology which can transmit the unified electricity from the inside to the outside of the chamber.In the process of fabricating the micro device prototype,the complete MEMS technological process and manufacturing methods are proposed.The technological parameters,monitoring methods and controlling methods are discussed.4.The experimental systems are built to test the piezoelectric vibrators and prototypes.On the one hand,a circular flow experimental system that can simulate a real water flow environment is built.It not only has the function of rectifying which can solve the bubbles problem,but also has the function of adjusting the relative distance between the bluff body and the vibrator.The underwater output performance of the single beam shaped and E-shaped beam multi-frequency piezoelectric energy harvester based on wake vortex induced vibration is tested by this system.On the one hand,a vibration performance experimental system is built to test the vibration characteristics of the single beam shaped vibrator and the E-shaped vibrator and to test the vibration output performance of the micro device with E-shaped beam architecture.5.The underwater output performances of the single beam shaped piezoelectric energy harvester based on wake vortex induced vibration are studied.The key influence factors and action mechanism of these output performances are revealed.The output power of the prototype can be effectively increased by ascending flow velocity,optimize the placement position of the vibrator in the flow field and optimize the load impedance matching.Under the velocity condition of 0.75 m/s,the maximum power and efficiency of the prototype can be 0.37 m W and 3.6%,respectively.The prototype has much better performance than the same kind of energy harvester.Especially in the liquid application environments,the harvester proposed has superior characteristics such as simple structure,strong insulation and sealing ability,high output performances,compatibility with the enclosed pipe environment and ease of array arrangement.6.The underwater output performances of the piezoelectric energy harvester with E-shaped beam multi-frequency architecture based on wake vortex induced vibration and the vibration characteristics of the E-shaped beam vibrator are studied.The phenomenon that the relationship of vibrational states between the main beam and vice beams is decided by the main mode of the vibrator is found.The underlying mechanism that the multi-beams coupling vibration can expand the frequency band and improve the performance of the vibrator is also revealed.Compared with the traditional single beam shaped prototype,the maximum improvement of power,conversion efficiency and fluid velocity bandwidth in the same power of the prototype with the E-shaped beam multi-frequency architecture is 70%,326%and 60%,respectively.In the liquid flow environment with extreme low speed,the fabricated prototype has the advantages of high output performance,high space and energy utilization of the flow field,wide and adjustable band.Finally,the vibration output performances of the micro piezoelectric vibration energy harvester with E-shaped beam architecture are studied.The experimental results show that the first-order resonance frequency of this system is1129.7 Hz.Under the vibration excitation of 0.8g acceleration,the maximum open circuit voltage,load power and the corresponding power density of the prototype at resonance is 1.00 V,41.14?W and 10034.15?W/cm~3,respectively.The successful development of the micro device based on MEMS process proves the feasibility of the proposed manufacturing process scheme.It provides technical support for the miniaturization research of piezoelectric flow vibration energy harvester in the future. |
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