Stimulated InfraRed Thermograhy (SIRT)
The stimulated Infrared thermography system has been developed byt the LRMH and the University of Reims Champagne Ardenne. This instrumentation aims at seeking the state of conservation of different artworks, especially mural painting. It consists on a bried light excitation of the surface in order to loot at the heat diffusion to detect defects of the material.
First, the analyzed sample is excited with a flux of photons that produce an increase of the temperature of the area. The variation of temperature leads to a variation of the infrared radition that is visualized the area. The variation of temperature leads to a variation of the infrared radiation that is visualied through an infrared thermography camera. The photo-thermal signal depends on parameters governing these physical phenomena: thermal conductiviy, thermal emissivityn thermal diffusivity, temprature, specific heat and density. In addition, theses parameters can be correlated with the following characteristics of the objecy: 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.
For the mapping, the hotter colors reveal warmer spots, which are linked to the presence of an active interface between materials or layers with different properties, for example a void beneath the surface or an interface between two different mortars.
All relative technical data can be inserted here. It 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 lamps (Halogen I.R. Ceramic 500W). This excitation source is modulated, in a pulse way, by means of electronics and of a computing of monitoring. The detection system is constitued of an infrared camera of thermography working in a synchronous way with detection system (20 °x 15° /0,3 m Field of view, 1,1 mRad Spatial resolution, 50 mK at 30°C Thermal sensivity, 7,5 to 13 µm Spectal range). FInally, an analysis module completes the system. The measurement can be done in the range of temperatre -40 °C to 120 °C, with 2 °C or 2% of accuracy.