What does the "skin effect" refer to in Eddy Current Testing?

The term "skin effect" in the context of Eddy Current Testing specifically refers to the phenomenon where alternating current (AC) tends to flow near the surface of a conductor rather than penetrating deeply into the material. This behavior is due to the electromagnetic fields generated by the alternating current, which induce opposing currents—in turn, limiting the current's penetration into the bulk of the conductor.

As the frequency of the AC increases, the skin effect becomes more pronounced, meaning that the effective cross-sectional area through which the current flows decreases. Consequently, the current density is higher at the surface compared to the interior, which is a critical concept in Eddy Current Testing. This tendency of current to be concentrated at the surface influences the interpretation of the test results, particularly when assessing defects, material properties, and other characteristics of the conductive material being tested.

In this context, while the other options might relate to relevant principles within electrical engineering or testing methods, they do not specifically define the skin effect as it is understood within the framework of Eddy Current Testing. Understanding the skin effect is crucial for improving defect detection and material characterization during testing.