%0 Journal Article
%T In Search of Early Time: An Original Approach in the Thermographic Identification of Thermophysical Properties and Defects
%A Daniel L. Balageas
%J Advances in Optical Technologies
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/314906
%X Active thermography gives the possibility to characterize thermophysical properties and defects in complex structures presenting heterogeneities. The produced thermal fields can be rapidly 3D. On the other hand, due to the size of modern thermographic images, pixel-wise data processing based on 1D models is the only reasonable approach for a rapid image processing. The only way to conciliate these two constraints when dealing with time-resolved experiments lies in the earlier possible detection/characterization. This approach is illustrated by several different applications and compared to more classical methods, demonstrating that simplicity of models and calculations is compatible with efficient and accurate identifications. 1. Introduction The evolution of thermophysical properties metrology and nondestructive evaluation (NDE) is characterized by the increased use of refined inverse techniques [1] requiring the establishment of models taking into account many parameters, although among these parameters often only one parameter is of interest for the experimenter. This complexity is particularly important when the analyzed thermal fields are 3D, a situation characteristic of the experiments realized with thermographic systems producing sequences of large thermal images of complex structures presenting important heterogeneities in their thermal properties, internal geometries, and boundary conditions. This approach leads to time-consuming calculations that may be prohibitive for thermographic data processing. Furthermore, it happens that in many situations the reality remains more complex than the sophisticated model used. How to conciliate the existence 3D thermal situations involving numerous parameters and the necessity to have rapid calculations compatible with the very high number of information to process in a thermographic image sequence? A solution lies in the use of 1D thermal models for pixel-wise data processing and the choice of a limited early time domain (for time-resolved techniques) or high frequency domain (for modulated techniques) for which the measured temperatures are essentially depending on the sole parameter to be identified and weakly affected by the 3D heat transfer. To achieve that, the proposed approach consists in performing the identification at the earlier possible time (or at the higher possible frequency) after the thermal stimulation. Here, we will mainly consider time-resolved techniques and early time detection (emerging signal). The present work wants to show the following.(i)A detailed procedure can be defined for
%U http://www.hindawi.com/journals/aot/2013/314906/