Analytical Method of Probe Footprint Based on Equivalent Model of Pulsed Eddy Current Field

In the pulsed eddy current testing for the local wall-thinning corrosion of ferromagnetic components, it is significative to accurately calculate the effective coverage area of the probe for analyzing the spatial resolution of corrosion detection. Based on the analytical expressions of the pulsed eddy current field of ferromagnetic plate, an equivalent model is established to analyze the probe footprint, by taking the eddy current ring in the conductor as the excitation source, and by replacing the conductor region with non-conductive and magnetic conductive medium. First, the boundary value problem of the equivalent model is solved analytically, and the contribution function of the eddy current loop is proposed to calculate the voltage signal in the detection coil induced by a single eddy current loop in the conductor. Then, the voltage induced by the eddy current field in the equivalent model is derived by integrating the contribution function in the whole conductor region, and the equivalent model is verified by comparing with the existing analytical results. Finally, combined with the thickness detection results of a steel plate with rectangular groove defects, the analysis method for the footprint of the probe is proposed using the contribution function. Considering not only the distribution of eddy current field induced by the excitation coil but also the influence of the shape and position of the detection coil, the analytical method for the probe footprint proposed in this article can provide more detailed and accurate guidance for the probe design in the eddy current testing.