Lock-in Thermography is an active infrared thermography technology which is based on thermal wave processing. It is especially used for the nondestructive evaluation of subsurface defects of composite materials and compound structure component

and has been widely applied on aerospace

aircraft structure

machine

and electronics fields. The principle of Lock in thermography for non destructive test and evaluation and defect depth measurement are deeply researched

and the honeycomb structure materials and welding bearing are detected by Lock in thermography for NDT. The finite difference method is used to compute the temperature history on the surface of sample under the law of sine modulated heat flux

and the Lock in method is applied to obtain the amplitude and phase differences between defect region and non defect one

the result is similar to the experiment. The thermal-electronic equivalence modeling is developed between the fundamental laws of heat and electricity

the simulation of Lock in thermography is researched used in this modeling

the relation between phase difference of both incident and reflected thermal waves and defect depth is reached

and the computation results is close to the experiment. The Lock in thermography is applied on the modeling defect of honeycomb structure sample and welding bearing for non destructive test and evaluation. The defect size and position can be soon and exactly detected by Lock in thermography

and it has more advantages for curve surface of structure.