磁芯位置对涡电流探头阻抗变化影响的解析分析

Analytical Analysis of the Influence of Ferrite Core Position on Impedance Change of Eddy Current Probe

本文提出了一种置于两层导体上方的Ⅱ磁芯线圈阻抗解析计算模型。采用解域截取特征函数展开方法进行了求解,最终获得了Ⅱ磁芯线圈阻抗的闭合形式表达式。利用Mathematica软件,在线圈受到频率从100 Hz到100 kHz变化的交变电流激励情况下,计算了Ⅱ磁芯线圈阻抗。获得了线圈置于两层导体上方及置于空气中两种情况下线圈阻抗的变化。为分析磁芯位置对线圈阻抗变化测量灵敏度的影响,在线圈各项参数保持不变情况下,将Ⅱ磁芯线圈阻抗变化计算结果分别与Ⅰ磁芯线圈和空气磁芯线圈阻抗变化进行了比较。结果表明,磁芯形状及磁芯与线圈的相对位置不同,对改变线圈阻抗测量灵敏度的作用也不同。将解析计算结果与Maxwell有限元软件仿真结果进行了比较,二者吻合很好,证明了所提出解析计算模型的正确性。

An analytical model of anⅡ-cored coil located above a two-layer conductive material has been presented.The final closed-form expression for the coil impedance was derived using the truncated region eigenfunction expansion(TREE)method,the coil impedances were calculated in Mathematica under AC excitation with a frequency from 100 Hz to 100 kHz.When the probe was placed over a two-layer conductor and with the conductor removed,the changes in normalized resistance and reactance were obtained.In order to investigate the influence of the core position on the sensitivity of the coil impedance measurement,under the same coil parameters,the impedance change results of theⅡ-cored coil were compared with theⅠ-cored coil and the air-cored coil.The results show that the ferrite cores have different effects on the sensitivity of coil impedance measurement,depending on the shape of the core and its position relative to the coil.The analytical calculation results were compared with the results obtained by finite element method,the results agreed very good,which verified the correctness of the proposed analytical model.