In eddy current inspection, which material properties determine the amount of induced current?

• A. Conductivity only
• B. Permeability only
• C. Conductivity, mass, and permeability
• D. Thickness only

Answer: (C)

Eddy currents are driven by a changing magnetic field, so how large those currents become depends on how easily charges can move in the material and how the material responds to the magnetic field. The ease of charge movement is set by conductivity: higher conductivity means a stronger induced current for the same changing field. The way the material channels and distribution of that current is affected by permeability: a higher permeability alters how the magnetic field penetrates and focuses the flux, changing the current path and skin depth. The total amount of current that can flow in the region also depends on how much conductive material is present, which relates to the material’s mass (and thus the available cross-sectional area for current paths). So, conductivity, permeability, and the amount of material present together determine the amount of induced current in eddy current inspection.