A Model Based Design of Low-Frequency Electromagnetic Systems for Metal Tube Inspection

Measurement systems for low-frequency electromagnetic inspection of metal tubes require one or more exciter/pick-up coil pairs for measurement of inner diameter, wall thickness and electromagnetic properties (electrical conductivity and magnetic permeability) of tube material. When designing such systems, it is essential to model how the changes in coil separation and excitation waveform will affect the sensitivities to the tube properties. Furthermore, a model, if employable in inverse procedures, would also enable model-based measurement of the tube properties. In this paper, we present relatively simple, but exact analytical model of magnetic field distribution of an exciter coil within the tube. We compare predictions of the model and previously published results of finite element analysis and experiments. This comparison validates the model for design purposes and confirms its applicability for model-based measurement