Thermal depth profile reconstruction by neural network recognition of the photothermal frequency spectrum

A new neural network method for reconstructing the depth profile of thermally inhomogeneous materials from a photothermal spectrum is described in detail. The possibilities and limits of this kind of photothermal depth profiling are evaluated. The influence of the network architecture and several profile and signal parameters on the reconstruction quality is discussed. Statistical predictions are given for the accuracy of the reconstructed profiles for different levels of Gaussian noise in the signal and at different depths.

[1]  H. G. Walther,et al.  Theory of microstructural depth profiling by photothermal measurements , 1995 .

[2]  Jan Thoen,et al.  Thermal waves in materials with linearly inhomogeneous thermal conductivity , 1994 .

[3]  Jan Thoen,et al.  Quantitative photoacoustic depth profilometry of magnetic field‐induced thermal diffusivity inhomogeneity in the liquid crystal octylcyanobiphenyl , 1991 .

[4]  Jan Thoen,et al.  Thermal waves in materials with inhomogeneous thermal conductivity: An analytical approach , 1996 .

[5]  A. Rosencwaig,et al.  Thermal‐wave depth profiling: Theory , 1982 .

[6]  George Cybenko,et al.  Approximation by superpositions of a sigmoidal function , 1992, Math. Control. Signals Syst..

[7]  C. Glorieux,et al.  Photoacoustic depth profiling of the thermal conductivity of an inhomogeneously aligned liquid crystal at a free surface , 1995 .

[8]  Anders Krogh,et al.  Introduction to the theory of neural computation , 1994, The advanced book program.

[9]  Kurt Hornik,et al.  Multilayer feedforward networks are universal approximators , 1989, Neural Networks.

[10]  Gert Goch,et al.  Experimental results of photothermal microstructural depth profiling , 1995 .

[11]  C. Glorieux,et al.  Photoacoustic investigation of the thermal properties of layered materials: Calculation of the forward signal and numerical inversion procedure , 1993 .

[12]  Jan Thoen,et al.  Photoacoustic frequency‐domain depth profiling of continuously inhomogeneous condensed phases: Theory and simulations for the inverse problem , 1991 .

[13]  P. R. Bevington,et al.  Data Reduction and Error Analysis for the Physical Sciences , 1969 .

[14]  V. Gusev,et al.  Thermal-wave depth profiling of inhomogeneous solids , 1989 .

[15]  Allen Gersho,et al.  Theory of the photoacoustic effect with solids , 1975 .

[16]  K. Cole,et al.  Solutions of the heat conduction equation in multilayers for photothermal deflection experiments , 1992 .

[17]  A. Miklós,et al.  Photothermoelastic transfer matrix , 1994 .

[18]  H. J. Vidberg,et al.  Inverse determination of the thermal-conductivity profile in steel from the thermal-wave surface data , 1986 .