Abstract
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.
Highlights
One of the most frequently used methods of interpreting the results obtained in eddy current testing uses theoretical analysis to predict the changes of the probe impedance components [1,2,3,4,5]
What is commonly used in the process of interpreting the changes in the coil impedance are mathematical models which make
The technique of replacing the mathematical model of an air-cored coil with an ideal filamentary coil was developed for the needs of eddy current conductometry [15, 16]
Summary
One of the most frequently used methods of interpreting the results obtained in eddy current testing uses theoretical analysis to predict the changes of the probe impedance components [1,2,3,4,5]. The probe may be an alternating current fed coil, the impedance of which changes because of the probe fields interaction defects in the tested material. The technique of replacing the mathematical model of an air-cored coil with an ideal filamentary coil was developed for the needs of eddy current conductometry [15, 16]. Following this method, each cylindrical air-cored coil can be assigned such a particular pair of parameters r0, h0, that the change in the impedance of both coils is the same.
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