PULSE-FREQUENCY THERMOWAVE METHOD OF DETECTING DEEPLY BURIED DEFECTS

The article deals with a method of thermographic detection of deeply B uried microdefects in opaque solid specimens based on the synchronous recording of pulsed thermal emission of the specimen and harmonically modulated by a double-spectrum ''sandwich'' photoreceiver in the IR ra nge. Relations are presented for determining the depth of occurrence a nd the dimensions of microdefects from the independently measured phas e shift of the thermal wave relative to the modulated laser radiation on the first channel with Delta lambda(1) = 3-5 mu m, as are relations of the rate of change of the photosignal from the thermal pulse to th e magnitude of the photosignal measured on the second channel with Del ta lambda(2) = 8-14 mu m. The method makes it possible to detect elong ated microdefects with minimal dimensions delta' greater than or simil ar to (0.1-0.2)h at depths of up to h approximate to 500-700 mu m.