Inverse analysis for the measurement of thermal properties of hard coatings

Comment on “Photothermal radiometry parametric identifiability theory for reliable and unique nondestructive coating thickness and thermophysical measurements” [J. Appl. Phys. 121, 095101 (2017)]

“…A significant number of papers have already addressed the problem of identifiability regarding the parameters of a coating in the course of a photothermal measurement, with periodic excitation [2][3][4][5] , pulsed excitation [6][7][8][9][10][11][12] or both 13 . Of benefit are also some works on the thermal characterization of a given layer in a multilayer stacking [14][15][16] .…”

“…Applying the quadrupole formalism would have highlighted this feature much easier (see Ref. 17, 18 and applications 2,[5][6][7][8][9][10][11][13][14][15][16] ). As a matter of fact, when deprived from internal sources, the layer contribution is fully represented by the quadrupole 17,18 :…”

“…This is exactly what is encountered with the combination of parameters { 2 L , 2  , 2  } because they are fully correlated. The conditions of identifiability of 2 Q and 2 P (or related parameters) were analysed in many instances [2][3][4][5][6][7][8][9][10][11][12][13] (in particular, 2…”