In eddy current testing, what happens to the impedance as the frequency increases?

In eddy current testing, as the frequency of the alternating current applied to the coil increases, the impedance of the coil tends to increase as well. This occurs due to the relationship between frequency and the skin effect, which is the tendency of alternating current to flow near the surface of conductors at higher frequencies. As the frequency increases, the effective resistance of the material also increases because eddy currents are generated more intensely, which causes more opposition to the flow of current.

This increased impedance at higher frequencies can result in a variety of responses in the eddy current testing system, including changes in the output signal that are used for evaluating material properties or detecting flaws. Therefore, understanding this relationship between frequency and impedance is crucial for effectively interpreting eddy current testing results and optimizing inspection parameters.