Eddy-current techniques are applied in non-destructive testing of surface and sub-surface layers (detection of metal discontinuities), structure analysis, estimation of coat thickness, dimensions, chemistry, and heat treatment quality. Eddy current testing is based on the analysis of the interaction between external and eddy-current electromagnetic fields that are induced in test objects. Eddy currents are electric current loops which are excited in a conductor while changing the magnetic field that permeates it. The distinctive feature of eddy current inspection is that it can be performed without any contact between a flaw detector and a test object. The interaction is normally achieved at a short distance which is, nevertheless, sufficient for moving the probe relative to the object. This enables the procurement of excellent measurements even when test objects are moving at a high rate of speed.