【作者】 李楠；

【导师】 郭宝龙；

【作者基本信息】 西安电子科技大学 ， 电路与系统， 2010， 博士

【摘要】 虽然电容传感器是很早的技术之一,但是由于用于测量电容的外部电路以及电容传感器在工艺制作方面的不足,直到近年来关于电容传感器技术的应用才得到了突飞猛进的发展。从电脑、手机等电器设备的屏幕触摸功能的广泛应用,到电容断层层析成像ECT (Electrical Capacitance Tomography,)技术的出现,都证明了电容传感器技术尤其是相邻电容传感器技术在精密测试领域的有着广阔的应用前景。相邻电容传感器的设计成为电容传感器技术研究的热门课题。因此,研究相邻电容传感器的结构设计并结合具体系统工程中的应用给出更好的参数优化规则,具有重要的理论意义和实际应用价值。本文主要围绕相邻电容传感器在设计中出现的参数平衡问题,针对不同系统工程应用中的特殊要求,以软件仿真与实际测试数据为依据,对其工作原理及若干相邻电容传感器设计中的关键参数调试、参数确定、应用系统和新型工业应用ECT技术等进行了系统的深入研究。本文的主要工作及贡献如下:1.给出了电容边缘效应在特定电容传感器模型下的数学描述,证明了影响边缘电容的传感器设计参数。此外,针对目前应用较为广泛的多种传感器技术,深入探讨了传感器技术发展的背景、分类;研究了经典传感器技术——光电传感器,压电传感器技术,相邻电容传感器技术的典型应用以及基本测量原理,系统实现方案、传感器技术的优缺点;补充了三类流行传感器技术,并对此三类传感器技术进行了基础分析;结合已出现的多种传感器技术及其在系统工程中应用,对其进行了操作原理的总结与主流应用归类。2.建立了相邻电容传感器的性能综合评价标准体系,填补了以往在设计相邻电容传感器时没有执行或优化标准的空白。将相邻电容传感器性能分为穿透深度,信号强度,测量灵敏度与图像重组分辨率等。通过有限元法(Finite Element Method,FEM)对传感器总体设计参数,包括相邻电容传感器极板几何尺寸、材料选择、极板数量、间距以及屏蔽层等,与传感器测量性能之间的关系进行了定量分析,以验证设计参数对测量性能影响的结论,并对如何进行参数间的平衡优化给出了定量化实验结果。3.设计了三种用于工业电容断层层析成像系统的ECT电容传感器结构,包括矩形、正八边形与传统圆形ECT传感器,并以圆形ECT传感器为例,给出了传感器设计参数总体优化规则,对今后ECT传感器设计起到了指导作用。通过仿真与实际测量实验,推断电容传感器空间结构对于电容测量结果的影响。利用有限元法(FEM),对传感器进行了3D建模,数值分析与仿真,针对屏蔽保护极板对ECT传感器测量结果的影响进行了深入讨论与分析,利用已优化的ECT电容传感器结合成熟的成像算法对实验结果进行图像重组,效果理想。4.设计了一种针对未知液体安全特性检测的基于电容传感器技术的系统,弥补了在安全检测方面,对液体等非导电,非金属物质的检测空白。围绕其中的关键技术进行了深入系统的研究;明确了利用相邻电容传感器技术实现该系统工程的可行性与重要意义;设计了带状4极板平面板电容传感器与柱型8极板电容传感器两种多极板相邻电容传感器结构,并进行了详细的分析与讨论,总结了各传感器结构的优缺点;针对柱型8极板电容传感器进行了大量软件仿真与实际测量实验;提出了将快速图像重组技术应用于液体特性检测中的理论。通过大量的成像实验,验证了设计的柱型8极板电容传感器在保证分辨率的情况下能够大量的降低系统成本,并且可以应用于未知液体特性检测系统。5.设计了一种基于相邻电容传感器的车辆雨雾检测控制系统,并提出了一种传感器优化设计方案。该系统能够根据车辆挡风玻璃上的雨雾量自动控制雨刷工作速度;对相邻电容传感器作为雨雾探测单元进行了可行性分析与系统结构分析,针对专门用于雨雾探测的相邻电容传感器提出了优化设计,并对最终设计的传感器进行了性能测试与结果分析;由于利用电容边缘效应测量的相邻电容传感器采集到的信号非常微弱,为了提高系统灵敏度,设计了相应的集成数据采集,数据转换与系统控制单元的PCB电路;提出了系统的软件算法设计,并最终对系统实验结果出现的误差进行了分析。更多还原

【Abstract】 Amongst all types of electrical devices, the capacitor is definitely the oldest. However, the real application of the capacitive sensing technique is developed rapidly until recently. All of these applications, from the technique of touch screen on computers and cellphones to the new technology - electrical capacitance tomography (ECT), have proven that the capacitive sensing technique especially the proximity capacitive sensing technique is potential and powerful. As an important part of sensing technique, the design of sensor which directly decides the measured results of the system is always attractive and fascinating. To find out the rules of capacitive sensor design, plenty of research works are needed to be realized and improved. It is also believed that the optimization of design parameters is important and necessary.The thesis focuses on the problems of tradeoff among parameters in procession of capacitive sensor design. By using simulation software, such as COMSOL and Matlab, and practical test platform (ECT test system), the relations between design parameters and the performance of the designed sensor are presented and the detailed design parameters are listed at the end of the paper. The main research works in the dissertation are as follows:1. A mathematical modeling of capacitive fringe effect under the special conditions is presented based on the operation principle of capacitive sensor. It indicates the exact parameters of sensor design which will affect the sensor performance. For many types of sensing techniques, which have been developed and applied in various field, the background and the categories of them are introduced. Three typical sensing techniques, such as optical, piezoelectric and proximity capacitive sensing techniques are discussed. The working principles, merits and shortcomings of these techniques are analyzed. In addition, other three sensing techniques are introduced as the supplements. By investigating and reading a large number of the references, the basic working principle and application field are summarized and classified.2. The evaluation standards of capacitive sensor performance were established. Firstly, the performances of designed proximity capacitive sensor were concluded into several parts including penetration depth, signal strength, sensitivity of the measurements and reconstruction imaging resolution. Then, by using Finite Element Method (FEM), the relations between general parameters, which include geometry and size of the sensor electrodes, sensor materials, number of the sensor electrodes, gaps between the electrodes and the outer earthed screen, etc.. At the last, the sensor measurement performances are quantitative analyzed.3. Three types of ECT sensor, including square-shaped, octagon-shaped and traditional circular-shaped ECT sensor structures are designed for application of industrial tomography system., and the general parameter optimization standards are concluded and presented. By numerical experiments, the influence of different sensor structures on capacitive sensor measurement is concluded. By using finite element method (FEM),3D modeling of designed capacitive sensors are built. The influences of earthed outer screen, axial driven guards, axial earthed end guards and radial earthed guards on sensor performance is discussed and analyzed. The reconstruction imaging test by using optimized sensor with proper imaging algorithms indicates satisfied results.4. An unknown liquid properties detection system based on multi-electrode of capacitive sensor is presented. Two types of sensor structures including plannar-electrode sensor and traditional cylindrical sensor are designed and compared. The disadvantages and merits of each type of sensor are listed. For an 8-electrode cylindrical capacitive sensor, a large number of simulations and practical test have been completed. An algorithm for system image reconstruction is presented. The image reconstruction results indicate that the 8-electrode cylindrical capacitive sensor is feasible to be used in liquid properties detection, and the same time, it clearly decreases the cost of the system.5. Based on the measurement features of the proximity capacitive sensor, an automatic car wiper control system is presented. Moreover, a new capacitive sensor structure is assumed. The system can adjust the operation speed of car wiper automatically according to the amount of the liquid on the windshield. Three types of capacitive sensor are designed, and 4-leaves-shape sensor is selected to be a data acquisition unit of the system. Sensor design parameters are optimized, and the sensor performance is simulated and practically tested. Since the signal of the sensor derived is very weak, the circuit for signal detection is designed. The software algorithms are developed at the last, and the system errors are analyzed.更多还原