Assessment of Artificial Anisotropic Materials for Transverse Thermoelectric Generators

By alternately stacking layers of two materials that differ in their Seebeck coefficient and electrical and thermal conductivity, a composite material with artificial anisotropy of thermal and electrical transport properties is formed. Due to the transverse Seebeck effect, a thermoelectric (TE) voltage is generated perpendicular to a temperature gradient Delta T, that is applied at a certain angle phi with respect to the stacked layers (0 degrees < phi < 90 degrees). The TE properties of layered artificial anisotropic materials are described analytically using existing concepts and extending the available definitions to develop a consistent image of anisotropic media for TE energy generation. Based on these analytical descriptions, the TE performance of ceramic oxide-metal composites and transverse TE generators (TTEG) made of them are numerically calculated and presented in contour plots. These so-called micro- and macro-Babin plots map the influence of internal geometric parameters, i.e., the layer thickness ratio nu t$\left(\nu\right)_{\text{t}}$ and the angle phi of the applied temperature gradient with respect to the stacked layers. Based on these diagrams, the optimal TTEG geometry can be narrowed down in a simple and fast way. In addition, the diagrams are used for a material screening to evaluate the suitability of different oxide ceramics for use in a TTEG.