摘要
无线网络传感器技术已经成为全球未来十大技术之一,无线网络传感器的能量供应是该项技术研究的核心问题之一。但是由于无线网络传感器的体积非常小,而且传统供能方式存在无法长期有效供能等诸多不足,影响到无线传感器网络的使用。因此如何为无线网络传感器长期有效方便的提供能量就变得十分重要。
本文采用“能量采集”的方法,用理论研究与仿真实验相结合的方式展开研究。以压电材料作为能量转换元件,设计了一种振动能量采收系统,将环境中的振动能量转换为电能,为无线网络传感器提供能源。
1.研究了压电振子的压电发电机理与振动发电理论,分析了压电材料的性能参数,选用压电材料PZT作为采收振动能的功能元件,依据环境中振动源频率较低、加速度形式存在的特性,研究采用惯性自由振动式悬臂梁结构的压电振子,利用其d31压电发电模式,在外界激励下做上下弯曲振动,来采收振动能量。
2.对压电振子发电时的振动特性与发电输出特性进行了理论分析,研究了压电振子的振动与频率特性、电压输出与输出功率特性等,为振动发电模型的建立提供了理论基础。3.对压电悬臂梁结构的特性进行仿真试验研究。建立了压电振子的机电耦合模型,利用有限元分析方法,采用ANSYS有限元分析软件,通过静态、模态、谐响应与压电耦合电路仿真分析,得到了结构参数与质量块对其固有频率、电压与功率输出的影响关系,最高转换效率与最强发电能力时的最大输出电压与功率,以及串联双晶片压电振子相比单晶片的输出特性。为建立最佳的机电耦合模型提供了依据,并得到了适合采收环境低频振动能的压电悬臂梁结构。
4.设计了采收环境频率在64Hz左右的振动能的压电悬臂梁结构尺寸,在2m/s2加速度的激励下,输出功率最大可达到86微瓦,并可输出5V的电压。该结构所产生的电能能够满足网络传感器供能的需要。并设计了两种能量存储电路:电容储能电路和充电电池储能电路,对电能进行储存并为无线网络传感器供能。
基于以上研究,该振动能量采收系统能实现无线网络传感器的供能,具有长期有效、连续供能、节能环保等许多优点。对悬臂梁压电振子的结构设计具有指导意义,为振动能量采收系统的设计提供理论与设计依据。
Wireless network sensor technology has become one of the top ten global technology in the future, and the energy supply of which has been one of the core issues. Because the network sensor is small, and the traditional energy supply device has disadvantages of not supplying termly, etc. As influences the apply of wireless network sensor technology.
In this paper, the method of "energy harvesting" is used , which studied in theory combined with simulation analysis. Piezoelectric materials is selected as the conversion components, a piezoelectric vibration energy harvesting system is designed, through which environmental vibration energy is converted to electrical energy for wireless networks.
1.The piezoelectric power generation mechanism of the piezoelectric vibrator and the theories converting vibration energy to electrical energy are studied, the properties of piezoelectric material parameters are discussed, and the piezoelectric material PZT is chosen as the component harvesting vibration energy. For low frequency vibration in the form of acceleration in environment, piezoelectric cantilever vibrating freely under inertia is selected to harvest vibration energy in model d31, which inspired by the outside acceleration.
2.And characteristics of output voltage and natural frequency of the vibrator is studied. Characteristics of bending, natural frequency, output voltage and power of the piezoelectric cantilever are analyzed. As provides a theoretical basis for establishing model.
3.Characteristics of the piezoelectric cantilever are studied with simulation analysis. The electromechanical coupling model of piezoelectric vibrator is established, using finite element analysis and software ANSYS, through the static, modal, harmonic response and the piezoelectric coupling circuit simulation analysis, the influence of the vibrator’s size on those characteristics, the largest output voltage and power when the highest conversion efficiency and the best power generation capacity, as well as the output of the piezoelectric bimorph chip in series are abttained. As provides a basis for the establishment of the best electromechanical coupling model, and the suitable structure is gained.
4.The size of the piezoelectric cantilever is designed for harvesting vibration, the frequency of which is at 64Hz.Under the incentive of acceleration at 2m/s2, the maximum output power is about 86μw, and output voltage about 5V. It can meet the sensor network’s needs. Two kinds of energy storage circuit is designed: capacitor circuit and rechargeable battery circuit, through which electrical energy is supplied for wireless sensor networks.
Based on the above studies, the vibration energy harvesting system can realize the energy supply for the wireless network ,it can provide long-term, effective ,continuous energy supply, and has advantages of energy saving and environmental protection ,etc. It has the significance guiding the structural design of piezoelectric cantilever, and provides theory basis for designing vibration energy harvesting system.
引文
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