Surface characterization by high-resolution nondestructive methods

The formal similarities and physical differences between eddy current and thermal wave techniques are discussed. For metals, the ratio of the thermal diffusion length to the electromagnetic skin depth varies from 0.12 to 0.002. Images of cementite plates in austenite were obtained by an eddy current and by a thermal wave microscope. The hybrid microscopical approach allows to identify the permeability of the cementite as main source of contrast.