A Method for Measuring the Thermal Diffusivity of Intermediate Thickness Surface Absorbing Samples and Obtaining the Ratio of Anisotropy by the Converging Wave Flash Method

The converging thermal wave, flash technique for measuring thermal diffusivity is suitable for use on samples that are sufficiently thick or thin in comparison to the annular heat source, to be described by a three-dimensional or two-dimensional approximation of the heat conduction equation, and sufficiently absorbing to ensure generation of a heat source at the surface. However, samples of intermediate thickness, which lie between these regimes, cannot be analyzed. In this article, heat diffusion in the samples of varying thicknesses is modeled, and a semi-analytic expression is used to describe the dimensionality of any thickness, allowing the converging wave method to be extended to intermediate thickness samples. Applying the analysis to anisotropic samples, a method is proposed to find the anisotropy ratio of the in-plane to perpendicular-to-plane diffusivity using the converging wave method.