How does increasing the frequency of the alternating current in Eddy Current Testing affect the results?

Increasing the frequency of the alternating current in Eddy Current Testing reduces the depth of penetration of the eddy currents. This is a fundamental principle in electromagnetic theory related to how eddy currents interact with conductive materials.

As the frequency rises, the skin effect becomes more pronounced. The skin effect is a phenomenon where alternating current tends to flow near the surface of a conductor rather than uniformly throughout its entire cross-section. Higher frequency signals generate eddy currents that decay more rapidly with depth into the material. This means that higher frequencies are more sensitive to defects or changes occurring closer to the surface of the material.

For applications such as testing for surface defects or evaluating near-surface properties of materials, higher frequencies provide better resolution but limit the ability to assess issues deeper within the material. Thus, while they can offer enhanced sensitivity to surface features, they do not penetrate deeply, corroborating the reasoning behind the correct answer.