Electrical currents (eddy currents) are generated in a conductive material by a changing magnetic field.

There are factors which contribute to the strength of eddy currents such as:

  • frequency
  • applied voltage
  • permeability;
  • and lift-off.

Relevant indications are noted by the inspector when the flow of eddy currents is interrupted by a defect. These electrical currents are also affected by the electrical and magnetic permeability of a material, which allows this method to be used to sort some materials based on these properties.