Extending the 3 Omega Method to Measure Thermal Conductivity Anisotropy in Three Dimensions

A simplified method of measuring three-dimensional thermal conductivity anisotropy has been developed around the popular 3ω method. This approach utilizes a pair of surface mounted test elements as both heating and sensing probes. 3ω has historically been used to measure thermal conductivity in homogeneous, low conductivity substrates and thin surface films. The present technique employs a combination of broad band frequency measurements and directionally oriented test elements to extract property information that was previously inaccessible. Data reduction is dramatically improved through the use of a full accuracy analytical solution that replaces the heavily approximated original 3ω solution. Anisotropic degrees of freedom are optimized using an efficient gradient based algorithm that can be coded using any number of commercially available software packages. Test element design guidelines are presented to help insure that optimal experimental conditions exist during material testing. Comparative experimental results are presented for an aligned graphite fiber / epoxy composite.