A computationally efficient TLM thermal model in the beam displacement modulation regime

The beam displacement modulation (BDM) method is increasingly being used for examination of the uniformity or detection of non-uniformities in relatively large objects such as high power thyristor structures. The main feature of this method is that during the experiment the examined object is moving in relation to the source of excitation and in relation to the device which measures the disturbance of temperature field. Such method is fast, but its modeling is complicated. The complexity of this method lies in a fact that the source of excitation, e.g., optical radiation, moves over the surface of the object—also in a model. Used by the authors, well known and often used TLM thermal model is time consuming by the fact of possible multidimensional description of the real object. However this model enables the easy way to optimize the spectrum of excitation signal due to maximization of the temperature contrast of the observed physical properties of the object. Such possibility is particularly important in BDM regime as well as in using one device to examination objects with different thermal properties. To reduce the time of calculations in case of two- and three-dimensional models, the authors propose a novel method of replacing the moving excitation source over the surface of the object by a uniform excitation source that excite the entire object's surface at once. This method gives the same results as in the case of modeling the real (moving) source of excitation. Such approach in the case of usage 3D cylindrical model presented in the paper significantly speeds up the calculations.