Nonuniform permeability distribution in ferromagnetic materials creates noise in eddy current testing (ECT). To overcome this problem, ferromagnetic materials are magnetized and inspected in the magnetic saturation state to reduce noise. In this study, I targeted a spring steel material that is not easily magnetized and developed an ECT system with an encircling coil probe that was able to detect microcracks. Clear signals for 70 μm deep microcracks were obtained with a signal-to-noise ratio of 3.5 by magnetizing a test object using the optimal exciting current.
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