Simultaneous measurement of thermal conductivity and diffusivity of microscale films using lock-in thermography

The optimal design of thermal management materials depends on comprehensive thermal property data to improve the accuracy of predictive models. However, the accurate and rapid characterization in these materials remains a significant challenge. To address this challenge, a lock-in thermography (LIT) technique is developed to characterize the thermophysical properties of thin films. A modulated laser beam with adjustable power was focused onto the sample surface to induce periodic heating, while the sample was placed in a vacuum chamber to minimize convective heat loss. The resulting temperature distribution on the back surface was captured by an infrared camera and processed using a lock-in module to extract the mapping of the phase lag and the amplitude. The anisotropic thermal diffusivity of the sample film was determined from the spatial distribution of the phase lag using a sub-region fitting method. The anisotropic thermal conductivity and volumetric heat capacity were calculated by analyzing the linear relationship between the amplitude and the laser power. The laser transmission loss rate was calibrated using a standard SUS304 stainless-steel film, and the maximum relative uncertainty of the method was found to be less than 4.9 %. The method was applied to isotropic aluminum films and anisotropic paper films, demonstrating the effectiveness and applicability of this point-source-based LIT approach for characterizing a wide range of materials in thermal science.