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.

We have used a microfabricated device to measure the thermal contact resistance between a 152-nm-diameter carbon nanofiber and the measurement device, and found that heat conduction models based on Fourier’s law can underestimate the thermal contact resistance at the nanoscale constriction if a large reduction in the effective thermal conductivity of the constriction is not taken into account. With the thermal contact resistance reduced by the deposition of a platinum layer on the contact, we observed that the thermal conductivity of the carbon nanofiber grown by using a plasma enhanced chemical vapor deposition method is comparable to that of graphite fibers grown by pyrolysis of natural gas prior to high-temperature heat treatment.