What happens to the distribution of eddy currents when a nonmagnetic rod is placed inside an eddy current test coil?

When a nonmagnetic rod is placed inside an eddy current test coil, the presence of the rod significantly affects the distribution of the eddy currents generated. As alternating current flows through the coil, it creates a time-varying magnetic field. This magnetic field induces eddy currents in any conductive material nearby, like the rod.

The nature of the induced eddy currents is such that they are strongest at the surface of the rod. As these currents flow through the conductive material, they face decreasing resistance due to the geometry and the skin effect. The skin effect phenomenon indicates that, at high frequencies, the current tends to flow near the surface of the conductor, resulting in the concentration of eddy currents at the outer layer. Therefore, as you move towards the center of the rod, the strength of these eddy currents diminishes, reaching zero at the center.

This characteristic distribution is crucial for assessing the material’s properties, especially in detecting flaws or changes in conductivity. Thus, the correct understanding of how the distribution behaves when a conductive material is introduced to an oscillating magnetic field underlines the effectiveness of the eddy current testing technique in non-destructive evaluations.