What is the skin effect in the context of Eddy current testing?

The skin effect is defined as the phenomenon where alternating current (AC) tends to travel along the surface of a conductor rather than penetrating its entire cross-section. This effect occurs because, as the frequency of the AC increases, the current density decreases exponentially with depth from the surface of the conductor.

In the context of Eddy current testing, this aspect is particularly significant because it affects how well the method can detect flaws within the material. Since eddy currents are induced on the surface, the ability to effectively evaluate the material’s integrity is closely linked to the skin depth, which is the measure of how far the current can penetrate into the conductive material.

Understanding the skin effect is crucial for interpreting results in Eddy current testing, as it defines the sensitivity of the method concerning surface and near-surface defects. Higher frequencies result in shallower penetration, which can be beneficial for detecting surface-breaking cracks but may limit the technique's ability to identify deeper flaws. This intricate relationship highlights the importance of frequency selection in Eddy current testing procedures.