【作者】 田丰；

【导师】 吕文中；

【作者基本信息】 华中科技大学 ， 微电子与固体电子学， 2019， 硕士

【摘要】 压电俘能器能够直接将周围环境中存在的振动能量转换为电能,是目前能源领域研究的热点。压电悬臂梁作为压电俘能器中最为常见的结构形式,具有相对较低的谐振频率以及较高的机电转换效率。值得注意的是,只有当其工作在谐振频率附近时,才能产生较高的发电性能。然而,我们生活周围大多数振动的频率分布在次声频段,同时振动的形式是多元的,其大小、方向具有波动性。因此,绝大部分振动环境难以为压电悬臂梁提供一个稳定的谐振条件,从而导致了压电悬臂梁的能量收集效率大大降低。本文对压电悬臂梁的能量收集特性进行了研究和分析,指出了其在低频振动下应用的局限性。结合碰撞升频转换的方法,提出了一种基于摆球碰撞式压电俘能器的设计方法,并对其进行了有限元分析和实验验证,为如何有效在低频振动环境下进行能量收集提供一个新的研究思路。通过有限元分析和实验验证的方法,对压电悬臂梁的材料属性以及结构参数进行了分析;研究了单压电片悬臂梁、并联双压电片悬臂梁以及串联双压电悬臂梁三种不同连接形式下输出电压、输出功率、最优负载以及内阻抗之间的关系。通过分析指出谐振模式下压电悬臂梁的工作带宽窄,当外界振动频率偏离谐振频率时,输出功率迅速下降。通过有限元仿真对碰撞力作用下压电悬臂梁的输出特性进行了分析。结果指出压电片长度越短,厚度越薄,机械结构阻尼比越小,自由衰减产生的开路电压幅值越大,衰减振动持续时间越长。在压电悬臂梁结构的基础上,提出一种单摆球碰撞式压电俘能器,利用有限元软件对摆球和压电悬臂梁的碰撞过程进行了模拟仿真。根据有限元的仿真分析和实际测试结果,该装置能有效地将外界低频振动转换为摆球与悬臂梁的高频碰撞,从而使得压电悬臂梁上产生较高的电压输出。当外界振动频率为2Hz、幅值为2.5mm时,摆球和悬臂梁之间的碰撞频率达到了10Hz,碰撞作用引起压电悬臂梁产生的输出电压峰值可达30.2V和26.1V。当将两压电悬臂梁并联之后,在最优负载130kΩ下的平均输出功率为10.53μW。通过仿真分析和实验测试指出,外界振动频率在1Hz到8Hz之间时均能引起摆球和悬臂梁的碰撞。结合实际的应用场景(如波浪环境或人体运动环境),针对这种抖动振动形式,在单摆球压电俘能器的基础上,提出一种双摆球压电俘能结构。相比于单摆球结构,双摆球结构下每次碰撞能够与两个压电悬臂梁同时发生作用。该结构不仅增加了压电俘能器的输出功率,提高能量收集密度,同时还能够有效降低压电俘能器的匹配负载。在频率为2Hz、幅值为10°的摆动激励下,外接负载为47kΩ,测得双摆球压电俘能器的平均输出功率达到了43μW。最后,对经过整流滤波电路后的输出电信号进行了测试与分析,在470μF滤波电容下测得电容两端稳定直流输出电压为5.07V,足以满足微机电系统供能需求。更多还原

【Abstract】 Piezoelectric energy harvester can directly convert the ambient vibration energy into electricity to supply low-power electronic devices,has become a research focus in energy technologies.As one of the most common structural,piezoelectric cantilever beams are being widely studied with relatively low resonant frequencies and high conversion efficiencies.However,the piezoelectric cantilever beams can produce high energy density only near the resonant frequencies.In natural environment,most of the vibration are in infrasound frequencies(such as wave fluctuation,human motion and so on),at the same time,its magnitude and direction are fluctuant.Therefore,the random nature of ambient vibration makes it difficult for piezoelectric cantilever beams to work at resonant frequencies,which results in a very low generation performance.This article mainly aims at the piezoelectric cantilever beams and make investigation on pendulum ball impactexcited piezoelectric energy harvester in low frequency vibration through finite element analysis and experimental verification.The influence of material properties and structural parameters on the output characteristics of piezoelectric cantilevers have been analyzed by finite element method and verified by experiments.In addition,the relationships among output voltage,output power,optimal load and internal impedance of single piezoelectric cantilevers,parallel bipiezoelectric cantilevers and series bi-piezoelectric cantilevers have been discussed.Through the analysis,when the excitation frequency slightly shifts away the resonance frequency of the harvester,the power generation is drastically reduced,which results in a narrow operating frequency bandwith of piezoeletric cantilever beam.The output power characteristics of piezoelectric cantilever beam under impact force are demonstrated by finite element simulation analysis.Based on the cantilever beam structure,a single pendulum ball impact-excited piezoelectric energy harvesting device has been designed.According to the finite element simulation analysis and actual testing results,it is confirmed that the device can effectively convert the vibration energy of the low-frequency environment into the high-frequency collision between the pendulum and the cantilevers,so as to generate a high output voltage and power.When the ambient frequency of vibration is 2Hz,the collision frequency between the pendulum and the cantilevers reaches 10 Hz.The peak output voltage generated by the collision of two piezoelectric cantilevers are respectively 30.2V and 26.1V.Under the parallel connection of two piezoelectric cantilevers,a maximum average power of 10.53μW can be achieve across a 130kΩ external load resistance.The impact between the pendulum ball and the cantilevers can be caused by the external vibration frequency range from 1Hz to 8Hz.According to the practical application,such as collecting vibration energy from wave fluctuation or human motion,a bi-pendulum ball impact-excited piezoelectric energy harvester has been proposed.Compared with the single pendulum ball structure,the bipendulum ball structure can interact with two cantilever beams in one collision.By this structure,not only the output power of the piezoelectric energy absorbing device is increased,but also the optimal load of the piezoelectric energy absorbing device can be effectively reduced.A maximum average power of 43μW can be achieve across a 47kΩ external load resistance and 2Hz jitter vibration.By using a bridge rectifier circuit,the AC can be converted into DC output with an open-circuit voltage of 5.07 V,which is sufficient for the MEMS power requirements.更多还原