Lock-in Thermography with Infrared Camera VarioCAM® HD research 800 (exact model not available in Australia)
New materials with precisely controlled optical and thermal transport characteristics can make a large contribution to resource-saving thermal management. Scientists of the University of Bayreuth are pursuing this vision. They use infrared thermography to quantitatively determine thermal conductivity in nano- and mesostructured polymer materials.
Thermal conduction and thermal radiation are essential transport mechanisms that play a key role in various applications, from the smallest microchips to complete buildings. Their control requires a sophisticated material design that reaches into the nanometre range. Prof. Markus Retsch and his team from the Chair for Physical Chemistry 1 of the University of Bayreuth are working on the development and characterisation of such innovative materials. Modern cooling and air conditioning systems still require an external energy supply. But the cooling technology of the future should work without additional energy. To achieve this, materials are needed that selectively radiate heat. This can take place, for example, in clear weather when radiation occurs into very cold outer space through the so-called “Sky Window” in the long-wave spectral range of 8 … 13 µm, in which the atmosphere is transparent. “This process is called passive cooling,” explains Prof. Retsch, “and requires materials that emit heat via thermal radiation within a selective spectral range. At the same time as little solar energy as possible should be absorbed from the sun, for instance by improving the reflection or scattering properties of the material.”
Thin Samples Actively Excited by a Laser
On the path to such passive cooling materials, understanding of the thermal conductivity process is important. To do this, Prof. Retsch’s group is working with free-standing samples of, for example, thin polymer foils, 3D-prints, and fibre mats with a film thickness of only a few hundred micrometres. These samples are investigated with the goal of determining their direction-dependent thermal diffusivity. With this value and including the specific heat capacity and density of the sample, the corresponding thermal conductivity is calculated.
As part of the analysis, the measurement objects are excited by an intensity-modulated laser. Depending on the characteristics of the sample, the heat flux extends differently into the material (see fig. 1). The scientists actively control the entire measurement through the thermography software IRBIS® 3. The infrared camera that they use, VarioCAM® HD research 800 from InfraTec, detects the emitted infrared radiation, whose intensity varies with the lock-in modulation frequency.