A funnel-shaped probe for sensitivity enhancement in pulse-modulation eddy current inspection of subsurface flaws in conductors

Abstract

The subsurface flaw has been taken as one of the most severe threats to integrity and safety of conductive structures, leading to structural failure and catastrophic accidents. The nonintrusive detection and evaluation of subsurface flaws via effective Non-destructive Evaluation (NDE) techniques are the pressing concern, which essentially relies on the high testing sensitivity to a subsurface flaw. Following the proposition of Pulse-modulation Eddy Current technique (PMEC) for high-sensitivity evaluation and imaging of subsurface defects in conductors with pancake-shaped probes, in this paper the funnel-shaped PMEC probe is proposed in a bid to further enhance the testing sensitivity to the subsurface flaw by geometrically extending the cross-section of the excitation coil from rectangle to parallelogram whilst keeping the inner and outer diameters of the bottom winding fixed. Closed-form expressions of field quantities and testing signals for the proposed probe are formulated, based on which the theoretical investigation of the probe and its comparison with the pancake-shaped probe is intensively conducted. In parallel, a series of experiments for evaluation and imaging of localised subsurface corrosion via PMEC are carried out together with intensive assessment regarding testing sensitivities of the funnel-shaped and pancake-shaped probes. Through theoretical simulations and experiments, it has been revealed that the proposed funnel-shaped probe is advantageous over the pre-designed pancake-shaped probe, giving higher sensitivity to hidden flaws in conductors. This is beneficial to detection, evaluation and imaging of subsurface defects in conductive structures.