Research on Self-Differential Uniform Eddy Current Probes for Measuring Electrical Conductivity and Magnetic Permeability of Moving Objects

Abstract

The research materials present definitions of known eddy current probe designs, which possess inherent properties of self-differential and self-nulling, intended for measuring the electrical conductivity and magnetic permeability of planar, moving test objects at a specified speed. Among these, the most promising modification in terms of output signal level was identified. Among the candidate designs, variants with rectangular excitation coils were considered, oriented both parallel and perpendicular (i.e., tangential) to the object’s surface. These configurations provide a nearly uniform distribution of eddy currents in the measurement zone. In all analyzed probe designs, the pick-up coils were oriented orthogonally relative to the excitation coil. Both rectangular and cylindrical variations were considered. Magnetodynamic models for a whole range of designs were developed, and software was created to calculate the probes’ output signals. The software was validated with acceptable accuracy by comparing its results with original signal characteristic data published by other researchers. To select the design, data sets for non-magnetic metals and weakly magnetic alloys were used, enabling numerical experiments to determine the probes’ output signals while varying the electrophysical properties of different materials. Experiments were conducted for both static measurement objects represented as two-layer structures and moving objects consisting of two layers of materials with different electrophysical properties. As a result, a tangential design with an orthogonal cylindrical pick-up coil was selected, as it provided the best signal performance.