Which test frequency would lead to the largest depth of penetration for eddy currents?

The depth of penetration in eddy current testing is significantly influenced by the frequency of the alternating current used in the testing process. Lower frequencies result in deeper penetration because the eddy currents generated are less affected by the skin effect, which causes the currents to concentrate near the surface of conductive materials at higher frequencies.

In this context, a frequency of 100 Hz would allow for the eddy currents to penetrate much deeper into the material compared to higher frequencies such as 10 kHz, 1 MHz, and 10 MHz. As frequency increases, the skin effect becomes more pronounced, limiting the effective depth of penetration. Therefore, the lower frequency of 100 Hz is particularly advantageous when seeking to assess the characteristics of materials at greater depths, making it the correct choice for achieving the largest depth of penetration.