This article presents an innovative technique for detecting flaws in conductive materials by using an ideal filamentary coil. To characterize such a coil accurately and explicitly, it is sufficient to be in possession of merely two parameters: the radius of the circle within which all the turns are located and the distance of the coil from the tested surface. The mathematical model derived using the truncated region eigenfunction expansion method enables the calculation of the changes in the components of the filamentary coil impedance that are the result of positioning the coil close to the conductive material with a hole. Because of this, the air-cored coil model can be replaced with a much simpler filamentary coil model. This solution makes it is possible to detect various types of holes (internal, surface, subsurface or through) occurring in both multilayer magnetic and non-magnetic materials. The derived results were verified by means of measurements and numerical calculations based on the finite element method. Very good agreement was observed in both cases. The paper contains the source code implemented in Matlab, which is used to for calculations.

本文介绍了一种使用理想灯丝线圈检测导电材料缺陷的创新技术。为了准确而明确地表征这样的线圈，仅拥有两个参数就足够了：所有匝所在的圆的半径以及线圈与被测表面的距离。使用截断区域本征函数展开方法导出的数学模型能够计算丝状线圈阻抗分量的变化，这些变化是将线圈靠近带有孔的导电材料定位的结果。因此，空芯线圈模型可以替换为更简单的灯丝线圈模型。该解决方案可以检测各种类型的孔洞（内部、表面、次表面或通过）发生在多层磁性和非磁性材料中。基于有限元方法的测量和数值计算对推导出的结果进行了验证。在两种情况下都观察到非常好的一致性。论文包含在Matlab中实现的源代码，用于计算。