PASSIVE INFRARED DETECTION OF SUBSURFACE DELAMINATIONS IN THIN ELASTIC MEDIA.

Phase-sensitive IR detection techniques have been used to study ultrasonically excited thermal wave propagation as a function of frequency in a single Mylar polyester film layer. Good data correlation was obtained. Several artificially induced delaminations in a 4-layer-thick Mylar film sample have been resolved with a scanning IR detection system, with results consistent with the temperature and spatial limitations of the IR detection system. Thus experimental verification has been obtained of the feasibility of using ultrasonics to thermally excite a thin elastic medium containing delaminations and to spatially resolve these delaminations with an appropriate IR detection system. The spatial and spectral response of an IR thermal-wave detection system must be matched appropriately to the detection requirements. In principle, such a system, comprised of off-the-shelf optical components, should be capable of spatially resolving microstructures whose dimensions are on the order of 100 mu m, at near ambient surface temperatures.