An Eddy Current Probe With Minimum Background Magnetic Field for the Detection of Deeply Buried Defects

Detecting deeply buried subsurface defect is a challenging task for eddy current testing (ECT). This study introduces a novel ECT probe designed for the detection of deeply buried defects in conductive materials. The key innovation of this probe lies in the utilization of two identical rectangular coils coupled with a high-sensitivity Hall sensor. The configuration of the coils generates maximum magnitude of eddy current while minimizing the background magnetic field perpendicular to the specimen surface, ideally achieving zero magnetic field in the center region of probe. This design allows the probe to effectively leverage magnetic sensors with high spatial resolution and sensitivity, enabling the detection of weak magnetic field disturbances caused by subsurface defects. To optimize the probe parameters, as well as maximizing the distribution of eddy currents in the plate, a theoretical model based on the second-order vector potential (SOVP) formalism was derived. Moreover, FEM simulations and experiments were conducted to evaluate the detection capabilities of the optimized probe. The experimental results demonstrate that the ECT probe is capable of reliably detecting subsurface defects, when a defect with the size of $20\times 1\times 1$ mm3 locates 9 mm below the surface of a 10-mm-thick stainless-steel specimen.