A recently proposed novel technique for thermal non-destructive characterization based on digitized frequency modulated thermal waves is described. Defect detection in metallic, composite and semiconductor samples are presented as applications of digitized frequency modulated thermal wave imaging (DFMTWI). High peak power heat source requirement in pulsed thermography, and limited depth resolution of lock-in thermography due to fixed modulating frequency of sources, are over come by the proposed new technique by use of appropriately modulated excitation signal, limited both in time duration and frequency bandwidth.