Harald Reiss

Remote Sensing of the Thermal Diffusivity and the Absorption Coefficient at the Excitation Wavelength of Protective Coatings and Thin Film Materials

A front-face flash-monitoring method for remote sensing of the thermal diffusivity and of the absorption coefficient at the excitation wavelength of thin film materials is presented. Such a method relies on the surface transient temperature vs. time curve initiated by a short-duration heating pulse that is followed by time intervals during which the temperature response sensitively depends on absorption coefficient and thermal diffusivity. An analytical solution of the problem has been derived to solve the inverse heat transfer problem and, by comparison with a numerical experiment, to check the accuracy of the proposed algorithm for obtaining absorption coefficient at the excitation wavelength and thermal diffusivity. The accuracy of the proposed method is better than 0.1%.

Remote non-destructive monitoring of thermophysical properties using flash technique

The flash method for measuring thermophysical properties (TPP) has attracted wide-spread interest since it was introduced by Parker et al (1961). In an extension of this technique, we introduced a front-face flash-monitoring method (FFFMM) in which a radiative source delivering short heat pulses and an infrared detector to measure temperature excursion with time are positioned on the same side of an investigated object. In principle, front-face methods are more interesting than their rear-face alternatives because of the high signal-to-noise ratio. Moreover, front-face methods like the FFFMM are of vital importance in practice, e.g. when the rear side of the sample is inaccessible so that conventional transmission techniques cannot be applied. Time resolved thermograms allow depth profiling of the TPP of the sample using a dimensionless criterion of thermal homogeneity (DCTH), as described in our numerous reports. We showed that FFFMM can be applied virtually to thin films, coatings, layered materials, anisotropic materials and even to highly excited nuclear matter. Moreover, use of the DCTH gave us the possibility to exclude the influence of heat losses, of heat pulse duration, and of the depth of absorption of the applied heat pulse on the obtained TPP.