Photothermal infrared thermography applied to the identification of thin layer thermophysical properties

Abstract: The aim of the present work is the thermal non-destructive characterisation of layers at the surface of metals. The sample is sinusoidally heated by means of an argon ion laser and a focal plane array infrared camera (CEDIP IRC 320-4 LW) is used to measure the temperature variations at the surface of the layer. A numerical lock-in procedure allows the detection of very weak temperature variations at the surface of the sample, down to a few mK when working from the acquisition of hundreds of images, yielding amplitude and absolute phase maps for modulation frequencies ranging from 0.1 Hz to 1000 Hz. An inverse procedure uses the Gauss-Newton parameter estimation method, in order to identify the thermal conductivity and the optical absorption coefficient of the layer. Confidence intervals on the parameters can also be estimated by the inverse procedure. More particular attention is devoted to the study of the sensitivity coefficients, as functions of the frequency range and of the radial range along the profiles, in order to optimise the identification procedure

Thermoelastic analysis under harmonic excitation: Comparison between optical and electronic heat sources

The thermal behaviour of a sample submitted to a sinusoidal optical irradiation or a sinusoidal electronic irradiation is modelled in axisymmetrical two- dimensional geometry. This modelling mixes an integral transform and a one-dimensional thermal harmonic response. It shows the spherical thermal behaviour of the harmonic heat diffusion. The same solving method is applied to the Navier-Stokes equation using one-dimensional acoustic harmonic responses. The latter solution leads to the calculation of the displacement field. Finally, the two heat sources are compared from thermal and thermoelastic points of view

Real time analysis of erythrocyte sedimentation by photothermal methods

Whole blood is an inhomogeneous, thermally fragile liquid suspension. It was shown that photothermal radiometry yields meaningful results, but required irradiation level might disturb the sedimentation process. Despite the necessity for direct contact, photopyroelectric method is more sensitive and also easier and cheaper to implement for routine measurements. All the experimental results are in a good agreement with developed theoretical models

Analysis of stress influence on thermal diffusivity by photothermal infrared thermography

Abstract An infrared thermography equipment is used to measure the temperature rise at the surface of a steel bar, simultaneously submitted to the irradiation of a modulated laser beam and to a static uniaxial mechanical stress. The camera measures the radial temperature profiles across the laser beam, in order to point out the influence of stresses on the local thermal properties. Since this influence remains rather weak, a careful identification of the properties is to be undertaken