无线传感环境中的复合式能量转换方法及其器件

Reduction in size and power consumption of consumer electronics has opened up many new opportunities for low power wireless sensor networks. Sensor nodes are usually battery powered, so as sensor networks increase in number and size, replacement of depleted batteries becomes time consuming and wasteful. Additionally, the battery chemistries often involve toxic heavy metals, and present disposal issues, regardless of rechargeable technology. As a result, there is a clear need to explore novel alternatives to power sensor networks/nodes, as existing battery technology hinders the widespread deployment of these networks. By harvesting energy from their local environment, sensor networks can achieve much greater run-times, years not months, with potentially lower cost and weight. Energy harvesting is a newer approach and relies on technology to gather energy from the surrounding environment. It involves converting the ambient energy inherent in the sensor mode's environment into electrical energy. By doing so, a sensor node will have the opportunity to extend its life to a range determined by the failure of its own components. Traditionally, it has been believed that harvesting solar energy is sufficient because it has a high efficiency. Such a judgment was made based on a hypothesis that all of the operations are under one full sun illumination. However many sensor nodes are operated indoors and possibly in a hidden area with very dim light. In such a case, the power that can be harvested from available light drops probably by 2-3 orders of magnitude in comparison to full sun illumination. In this case, harvesting the energy contributed by other types of stimulation becomes viable. Herein, we propose a flexible hybrid architecture designed to harvest vibration and solar energies, either separately or simultaneously. The research content involves material, device architecture, and electric circuit. Firstly, we will investigate the growth of piezoelectric thin film which is the key material of the device. By using this film we will develop the hybrid energy harvesting device. Finally, we will explore a new interface circuit for hybrid energy harvesting, in which a charge pumping circuit is introduced into the traditional SSHI circuit.

无线传感器是无线传感环境中的基本单元，通常面临无人无源应用场景，并且数量庞大，因此如何实现持续可靠的能量供给是整个无线传感环境的关键问题。无线传感环境中弥散着多种能量，采集这些能量并转化为电能是解决上述问题的根本途径之一。近年来，寻找适当方法和设计新型器件实现这种能量转换的研究正在成为国际研究热点。这些研究中，器件一般采用单一能量转换方式实现能量转换。然而环境中的能量，密度较低，在时间和空间上的分布是变化的，单一能量转换方式可能难以向无线传感器提供足够的电能。本项目提出复合式能量转换方法，将两种能量转换方式原位复合，实现一个器件同时具备振动和光的能量转换能力。创新内容涉及三个方面：材料、器件结构和电路。首先从器件的关键材料入手，在柔性薄膜太阳能电池上开展柔性AlN压电薄膜的生长研究；在此基础上开展复合式能量转换器件的研制；最后在传统SSHI电路中融合电荷泵浦电路，实现一种高效的接口电路。

在无线传感环境中同时分布着各种形式的能量，若通过适当的方法把这些能量转换为电能，则可使无线传感器摆脱电池供电的束缚。然而环境中的能量往往在时间和空间上的分布是不确定的，在特定场所，单一的能量转换方法很可能难以提供足够的电能满足无线传感器能量消耗的需要。为此，本申请课题中提出一种复合式能量转换方法，将两种或两种以上能量转换方法集成于同一器件，实现为无线传感器供电。项目组始终根据研究计划来开展研究工作，较为圆满地完成了所拟定的各项研究任务。在项目开展的前期，完成了薄膜材料的制备及其性能调控等工作；在项目开展的中期，进行了能量转换器件的设计及其制作等工作；在项目开展的后期，进行了能量采集电路、能量转换器件以及无线传感器集成等工作。主要研究内容及其成果包括：1）在一个器件上集成了两种环境能量转换方法，实现了柔性薄膜太阳能电池技术和基于柔性压电薄膜的振动能量采集技术相融合；2）通过了多种手段（衬底表面处理和设备工作参数等）进行微结构调控，提高了AlN 压电薄膜的性能，在柔性太阳能电池上实现了高效的振动能量采集；3）通过计算分析，较好地理解了器件的构造参数与其机电耦合系数间的依存关系，在此基础上合理地设计了器件结构，获得了高能量转换效率；4）突破了常规SSHI 接口电路中阻抗不匹配以及整流二极管能量损耗的问题，提高了振动能量采集器的电能输出；5）使复合式能量转换器件能够高效地向无线传感器供电，部分实现了对普通电池的替代。项目组成员根据预定计划相应地承担了不同的工作任务，通过密切的交流和合作，获得了多项具有创新性的研究成果。在本领域权威学术期刊上了发表20余篇学术论文，超出原定目标；申请了发明专利22项目，其中7项已经获得授权，超出了原定目标；获得了中国通信学会、中国电子学会和江苏省通信学会等授予的多个奖项。