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

Abstract

A recent paper [Guo et al., J. Appl. Phys. 121, 095101 (2017)] intends to demonstrate that from the photothermal radiometry signal obtained on a coated opaque sample in 1D transfer, one should be able to identify separately the following three parameters of the coating: thermal diffusivity, thermal conductivity, and thickness. In this comment, it is shown that, in the considered experiment arrangement, these three parameters are correlated, the identifiability criterion is in error, and the thickness inferred therefrom is not trustable.