A Differential Excitation Eddy Current Probe Based on Novel Annular Fractal Curve for Defects Inspection

A flexible eddy current probe can detect the defects in components with a complex structure due to its bendability and adaptation to the surface of the tested specimen for nondestructive testing. However, the traditional, flexible eddy current probe with circular and rectangular coils may neglect small cracks along certain special orientations. In this paper, the authors introduce the theory of fractal geometry to guide the design of flexible probes. An annular fractal curve is first proposed, and its system of iterative functions and geometric characteristics are then studied. Following this, six flexible differential excitation-based eddy current probes are designed based on the annular fractal curve. Simulations and experiments are used to compare the performance of the probes to identify the optimum one for inspecting defects. The results show that the M6K3 probe delivers the best performance in terms of the identification of cracks with lengths shorter than half the length of the coil of the probe.