基于共面边缘场电容成像原理的无损检测技术研究

It is proposed to provide further investigations into a novel Non-Destructive Evaluation (NDE) technique known as coplanar fringing field capacitive imaging (Referred to as Capacitive Imaging). The capacitive imaging technique uses a pair of metal electrodes, placed close to the surface of the testing material. Interaction of the electric field distribution from the electrodes with the testing material leads to changes in signal when the electrical properties of the sample themselves change, leading to the possibility of imaging. Due to its capacitive nature, the capacitive imaging technique requires single side non-contact access to the testing material and little sample surface preparation. In addition, it provides a very clear and simple defect indication. Previous feasibility studies have demonstrated promising results on a wide range of material types, from insulators (e.g. glass fibre composite structures) to conductors (e.g. corrosion under insulations). Whilst the new NDE technique has the exciting advantages mentioned above, it is not ready for implementation in industry because currently we can only confirm the presence of a defect but cannot further characterise it. This project aims to bridge the gap between the feasibility studies and industrial applications by presenting an in-depth investigation into the properties of this technique. This include: studying the factors that affect imaging performance, determining the reliability in the inspection of real components, obtaining and characterising the probe measurement sensitivity distributions, optimising probe design parameters, and developing image reconstruction methods. This project will greatly improve the testing performance of the capacitive imaging approach, and this approach will through time become a focus for applied research, thereby providing solutions for some very real and difficult problems in industry.

前期工作中，我们提出一种以共面电容极板间的边缘场为检测工具的新型无损检测技术-共面边缘场电容成像技术，并实验验证了该技术在非金属复合材料、混凝土及包覆层下金属表面等多种材料中缺陷检测的可行性。但目前尚未从深层次上对该技术的原理与方法进行全面研究，检测结果也未经处理直接呈现，导致现阶段该技术对缺陷定量识别能力不足。针对这一问题本项目拟从建立可靠的有限元模型、获取并分析探头检测灵敏度分布、系统考察共面电容成像系统的成像性能、探索总结探头优化设计原则、开发缺陷形状反演算法及提取缺陷量化信息等方面，深入剖析共面电容成像的机理与规律，同时结合对标准试块和实际工件进行的检测实验及对检测结果的后处理，最终初步建立共面电容成像技术研究体系。本项目对共面边缘场电容成像技术的研究将丰富无损检测学科内容，同时有助于提升该技术检测性能，使其在石化、航天、建筑、能源等多个领域满足工程实际检测需要。

无损检测技术是保证产品质量和设备安全运行的一门共性技术，已成为各工程领域不可缺少的关键技术之一。近年来，工业界和科学界为满足新型材料和复杂结构的检测需求，提出新的无损检测理念和思路，以克服传统无损检测技术在特定情况下的局限性。本项目所关注的共面边缘场电容成像技术即在这种背景下，为解决传统无损检测手段缺陷检测难题而提出。.本项目从深层次上探讨了将共面边缘场电容成像技术作为一种新型无损检测手段涉及到的理论和方法。首先对共面电容成像检测原理和准静态电磁场理论进行了研究，并以此为依据构建了有限元模型，进而推导出一个从有限元模型中获取共面电容成像探头灵敏度的数学方式，快速精确的获取检测灵敏度的三维分布，并把检测对象和环境也引入到模型中，考察了实际测量状态下探头灵敏度的分布。以检测灵敏度为工具，建立了衡量共面电容成像系统检测性能的评价体系，提出完整的电容成像探头设计原则及系统优化方案，获取了合理的缺陷形状反演算法，从而提高电容成像技术的精确度、可靠性。同时通过检测试验明确了被测对象、检测环境、探头设计参数等对电容成像系统检测性能的影响，并实现了金属表面缺陷的定量识别及形状可视化反演。本项目的研究成果表明，该技术可以检测绝缘材料表面及内部的缺陷，同时它也对靠近的导体表面有非常敏感的感应能力，可透过较厚的绝缘层对导体表面的缺陷进行检测。.本项目的研究成果有助于推动电磁无损检测理论和技术发展，通过检测准确、形象地提供被测对象中缺陷信息，将有效地保证结构安全性评估的精度，从而有效延长设备使用寿命，最大限度地发挥潜能，提高机械装备的本质安全水平，具有良好的学术价值和经济应用前景。