基于三维磁场测量的脉冲涡流检测探头的设计

Design of a Novel Pulsed Eddy Current Testing Probe Based on 3D Magnetic Field Measurement

为了获取更多的特征信息以提高脉冲涡流检测技术对缺陷的检测能力,设计一种新型的脉冲涡流检测探头,该探头包含一个矩形激励线圈和三个用于测量三维磁场分量的感应线圈。利用有限元法建立三维瞬态涡流问题的计算模型,研究当矩形线圈切向放置在平板导体上方时,其尺寸变化对导体内部感应涡流流动模式的影响,在线圈的长、宽和高之比为1:0.625:0.625情况下涡流分布具有如下特征:在线圈正下方的导体区域内,感应涡流同向平行流动且其密度近似相等,这种近似均匀的场分布对缺陷的尺寸和形状变化极为敏感,且十分有利于实现三维场分量的独立测量,因此脉冲涡流检测技术中传统的单维测量方式可扩充为三维检测,有效地增加可用的信息量,试验和数值结果均表明在有缺陷存在时,三维方向上的响应信号可直观地反映缺陷参数的变化,两者结果吻合,证明了新型探头的有效性和实用性。

To improve detectability of pulsed eddy current testing （PECT） for surface/subsurface defects by obtaining more information, a novel PEC probe, which consists of a rectangular driver coil and three orthorhombic pickup coils for sensing three-dimensional magnetic field components, is designed. A calculation model for three-dimensional transient eddy-current problem is built by using finite element method （FEM）. When a rectangular coil is tangentially placed above the conducting plate, the effect of change of coil dimension on the flow pattern of induced eddy-current inside the plate is investigated. When the ratio of coil length, width and height is 1：0.625：0.625, eddy-current distribution has characteristics as follows： the induced eddy-current flows uniformly toward the same direction and its density is approximately equal in the plate region beneath the coil. Such approximately uniform field distribution is highly sensitive to the shape and dimension of a defect, and it is quite helpful to the realization of independent measurement of three-dimensional magnetic field components. As a result, the traditional one-dimensional measurement mode in the pulsed eddy current technology can be extended to three-dimensional testing, thus effectively increasing useful information. The numerical and experimental results show that defect dimensions can be evaluated quantitatively by analyzing three-dimensional transient signals. Both are in good agreements. Consequently, the high performance of the novel PEC probe is validated.