Formal derivation of an inversion formula for the approximation of interface defects by means of active thermography

Thermal properties of a two-layered composite conductor are modified in case the interface is damaged. The present paper deals with nondestructive evaluation of perturbations of interface thermal conductance due to the presence of defects. The specimen is heated by means of a lamp system or a laser while its surface temperature is measured with an infrared camera in the typical framework of Active Thermography. Defects affecting the interface are evaluated using an inversion formula obtained by means of Laplace transformation and suitable symmetries of parabolic differential operators (reciprocity). Results of numerical inversion from simulated data are encouraging