Measurement of thermal diffusivities through processing of infrared images

Abstract

The measurement of the thermal diffusivity of a thin layer in the direction of its plane is usually a difficult operation. The standard "flash technique" is very appropriate for diffusivity measurement in the direction of the thickness of the sample but adaptations of this method to in-plane measurements remain very sensitive to the position and form of heat excitation and temperature sensors. The new procedure proposed here consists of applying any geometrically nonuniform heat impulse on the front face of the sample and recording the entire transient temperature image on the rear face thanks to an infrared camera. The influence of axial diffusion can be avoided for periods much longer than the axial diffusion characteristic time. Integral transforms on the radial space variables (Fourier transform) are very suitable for treating the temperature field and to estimate radial diffusivity. The main advantage of this method is to avoid any experimental precaution (no knowledge of the geometrical form of the excitation -replacement of the sensor positioning by an image calibration). Furthermore, the considerable number of data produced by the camera is processed using a statistical approach. The validation of the method is made on a homogeneous sample by comparison between the in-plane direction measurements (obtained with the present procedure) and the thickness direction measurements (obtained by the classical flash technique). © 1995 American Institute of Physics.