The system used comprises an excitation device, a detection device, and electronic and computing instrumentation for monitoring. In order to obtain homogeneous energy deposition, the excitation source is a couple of halogen lamp (500 W). This excitation source can be modulated, in a pulse way. The detection system is constituted of an infrared camera of thermography (20°x 15°/0.3 m Field of view, 1.1 mRad spatial resolution, 50 mK at 30°C Thermal sensitivity, 7.5 to 13 μm Spectral range). Finally, an analysis module completes the system. The measurement can be done in the range of temperature -40 °C to 120 °C, with 2°c or 2% of accuracy.
The photo-thermal signal depends on parameters governing these physical phenomena: thermal conductivity, thermal emissivity, thermal diffusivity, temperature, specific heat, and density. In addition, theses parameters can be correlated with the following characteristics of the object: aspects of the surface, presence of delamination, presence of cracks, internal structure of the material, progress of a physical and chemical transformation, drying and sedimentation, etc…The sub-surface defects appear after some time depending on their respective depths. Such defects cause air pockets in otherwise uniform material, resulting in different distributions of the heat inside the materials. Different defects in material exhibit different thermal reponses to the same excitation.