基于暂态磁场梯度信号的脉冲涡流无损检测和定量评估技术

摘要

Pulsed Eddy Current Testing(PECT) is an effective Electromagnetic Nondestructive Evaluation (ENDE) technique for quantitative evaluation regarding the integrity of multi-layer conductors. Conventional PECT utilizes induction coils and solid-state magnetic field sensors which give the transient signals of net magnetic field for defect detection, classification and characterization. In this paper, we introduce Gradient Magnetic Field Measurement(GMFM), which has been intensively used in Magnetic Resonance Imaging(MRI), to PECT in an effort to improve the PECT sensitivity to multi layer conductors. The closed-form expressions of GMFM-based PECT signals have been formulated via the Extended Truncated Region Eigenfunction Expression (ETREE} modeling. Through theoretical and experimental investigation, it is found that the proposed GMFM-based PECT is significantly advantageous over traditional PECT in terms of high detection-and-evaluation sensitivity to subsurface material degradation of multi-layer conductors.%脉冲涡流检测技术是目前对多层金属结构实施有效检测和定量评估的无损检测方法之一。传统脉冲涡流检测技术基于电磁感应原理，采用感应线圈或磁场传感器采集暂态磁场信号，以实现对多层金属结构内部缺陷的定位、识别以及量化评估。文章提出一种新型脉冲涡流检测技术，该技术主要基于已在核磁共振成像（MRI）领域得到应用的磁场梯度测量技术，将磁场梯度信号测量与脉冲涡流检测相结合，以实现对多层金属结构脉冲涡流检测灵敏度的提高。基于ETREE解析法，建立了所提方法的理论模型，推导了脉冲涡流检测磁场梯度信号理论表达式。通过仿真和试验，证明了该方法在多层金属结构亚表面材质劣化检测中的优势。