What type of current typically offers the shallowest penetration in materials when magnetizing?

The choice of alternating current (AC) is recognized for its characteristics that affect magnetic fields and their interaction with materials. AC generates a magnetic field that changes direction continuously, which leads to a current that is not steady, resulting in a magnified effect on the surface and near-surface areas of a material. This fluctuation causes the magnetic particles used in testing to concentrate more closely along surface discontinuities and only slightly deeper.

This shallow penetration is due to the skin effect, where AC tends to confine the current to the surface of the conductor. As a result, defects or discontinuities that are located at or very near the surface can be highlighted effectively, making AC particularly suited for detecting surface flaws. In contrast, other types of currents, such as half-wave direct current, pulsed direct current, or direct current across a coil, create more stable and deeper electric fields, allowing the magnetic field to penetrate further than what is typical with AC.

Understanding this property of alternating current is essential in magnetic particle testing, as it guides inspectors in selecting the right magnetizing method based on the type of flaw they are trying to detect.