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Many materials have anisotropic thermal conductivity, with diverseapplications such as transistors, thermoelectrics, and laser gain media. Yetmeasuring the thermal conductivity tensor of such materials remains achallenge, particularly for materials lacking in-plane symmetry (i.e.,transversely anisotropic materials). This paper demonstrates thermalconductivity tensor measurements for transversely anisotropic materials, byextending beam-offset frequency-domain thermoreflectance (BO-FDTR) methodswhich had previously been limited to transversely isotropic materials.Extensive sensitivity analysis is used to determine an appropriate range ofheating frequencies and beam offsets to extract various tensor elements. Thenew technique is demonstrated on a model transversely anisotropic material,x-cut quartz (<110> {\alpha}-SiO2), by combining beam offset measurements fromdifferent sample orientations to reconstruct the full in-plane thermalconductivity tensor. The technique is also validated by measurements on twotransversely isotropic materials, sapphire and highly oriented pyrolyticgraphite (HOPG). The anisotropic measurements demonstrated very goodself-consistency in correctly identifying isotropic directions when present,with residual anisotropy errors below 4% for sapphire and 2% for HOPG andquartz. Finally, a computational case study (simulated experiment) shows howthe arbitrary in-plane thermal conductivity tensor of a fictitious materialwith high in-plane anisotropy can in principle be obtained from only a singlesample orientation, rather than multiple orientations like the experiments onx-cut quartz.

Anisotropic thermal conductivity tensor measurements using beam-offset  frequency domain thermoreflectance (BO-FDTR) for materials lacking in-plane  symmetry