随着电力网络和设备的广泛使用，如变电站、输电线、电力设备、大型建筑和房屋居室等，其安全性、稳定性和节能性对现代社会的生产和生活都极其重要。无线传感器网络技术的兴起，为电力网络和设备的实时、长期监控提供了有力的解决方案；能够集成电/磁场测量器件的传感器节点也极大地吸引了研究人员的注意。在该传感器节点的研究中，电/磁场测量器件普遍面临着高灵敏度、小尺寸、低功耗等方面的挑战。本研究提出了基于静态偏置的交流弱电/磁场测量方法，从理论和实验上证明该方法在电场和磁场测量中均能大幅提高器件的灵敏度；此外还有集成度高，功耗低等特点。对应的器件主要包含两部分：其一是易被极化，且能增强电磁场耦合的压电悬臂梁，如能敏感静电场的压电片，或安装有铁磁质量块以耦合磁场的压电悬臂梁；另一个是能提供强偏置静态场的元件。该方法利用电磁力与场强成平方关系而实现电磁力放大的技术；当有强偏置场存在的时候，场敏感元件所受的电磁力为偏置场强度与外加交流场强度的乘积。本文分析了驻极体的静态电场和永磁体的静态磁场，分别建立了偏置技术的电场和磁场器件解析模型，并进一步总结为一致的电磁力规律；还利用了有限元分析工具对磁场模型进行了仿真。在此基础上，又分别制作了基于静态偏置原理的电场和磁场传感器原型，并测试了相应的器件特性，包括偏置效果的验证、偏置条件对器件灵敏度的影响、频率响应和输出性能等。本文还利用MEMS技术设计并加工了基于该原理的电场传感器件。使用PTFE驻极体做静电偏置，并利用PVDF压电悬臂梁读出信号的电场传感器，在驻极体表面平均电势-770V和PTFE到PVDF间距为1.6mm条件下，测试所得的灵敏度高达0.84mV/(kV/m)。采用AlN做压电层的MEMS电场器件灵敏度进一步提升到15.8mV/(kV/m)，实验显示其分辨率达到20V/m。而偏置优化的另一磁场传感器件，在45匝线圈电流幅值10mA的交流测试磁场中，输出电压高达0.66V。实验还表明，所设计的三个电磁场器件在50Hz工频附近均工作良好。该实验结果、理论分析和仿真测试，三者十分吻合；充分证明了静态偏置方法的有效性，并为该类器件的设计和电磁场的测量提供重要参考。
The security, stability and energy efficiency are of great importance, as ‘Smart Grid’ and electric equipment are used everywhere including transformer substations, high voltage power lines, large building and smart home etc. With the emerging of Wireless Sensors Network technology, the electromagnetic field sensor nodes with the ability of being integrated into the WSN, provide a promising solution for the long-term, real-time monitoring of the Smart Grid. However, the development of these qualified sensors is facing many challenges, such as requirements of high sensitivity, small size, low power-consumption and so on.This thesis has proposed a static electric/magnetic bias based method for weak AC field detection. Theoretically and experimentally, the method is efficient in both electric and magnetic field measurement. What’s more, it’s proved to have a high sensitivity, high integration and consume low power. The two main components of the method are an easy-polarized piezoelectric cantilever under electric/magnetic field and the object that can generate strong electric field or magnetic field bias. As known, the electromagnetic force is proportional to the square of the magnitude of field. When the biased device is placed in the AC field, the AC force applied to the cantilever is determined by the product of the bias field and the external AC field. The corresponding theoretical models and equations in electric/magnetic field are built after giving the field distribution of electret bias and permanent magnet bias. Furthermore, the electromagnetic force is summarized to a centralized discipline due to the relationship between electric field and magnetic field, which agrees well with the following Finite Element Analysis simulation.Based on the static bias method, two middle-size prototypes for electric field and magnetic field are built and tested, including the verification of the bias, the influence of different bias conditions, the frequency response and the output performances. The electric field sensor with PTFE electret bias and PVDF piezoelectric cantilever to readout the signal is simple in structure and low in power-consumption because there is no requirement of high voltage sources. In addition, a MEMS electric field sensor with AlN piezoelectric layer is designed and fabricated. As the experiment results show, the tested highest sensitivity of the PTFE-PVDF electric field sensor achieves 0.84mV/(kV/m) with -770V average surface potential of electret and 1.6mm gap between PTFE and PVDF; while the sensitivity is improved to 15.8mV/(kV/m) and the resolution reaches 20V/m in the MEMS device. The output voltage of another bias optimized magnetic field sensor achieves 0.66V under the AC magnetic field generated by a 45-turn coil with 10mA current. Both the devices work well near the power line frequency. Finally, the theory, simulation and experiments are in good agreement with each other, confirming the method is effective in electromagnetic field measurement and providing an important reference for the design and application of this kind of devices.
