Designing thermoelectric generators for self-powered wearable electronics

Body wearable sensors and electronics for health and environment monitoring are becoming increasingly popular as their functionality increases. Thermoelectric generators (TEGs) are of interest to make these wearables self-powered by making them rely entirely on the heat harvested from the human body. The challenge with using thermoelectrics on the human body is the large thermal resistances experienced at the skin/TEG and TEG/ambient interfaces. These parasitics can be potentially so large that they can dominate the device performance. Therefore, it is critical to have accurate models to predict the device performance considering material properties, module design and parasitics. In this paper, we present a computationally efficient, quasi three-dimensional TEG model and use this model to explore the design criteria for current state-of-the-art rigid TEG modules as well as prospective flexible modules for body wearable applications. We show the impact of the properties of the thermoelectric material, module design and dimensions, heat spreaders, filler material, heat sink and skin contact resistance on device performance. We also identify the significance of material thermal conductivity over the Seebeck coefficient and electrical resistivity in improving the output power for wearable applications. For flexible TEGs, we identify the thermal conductivity of the filler material as one of the critical parameters that need to be taken into consideration for optimal performance. Finally, the model was used to design a custom TEG with improved material properties and device design. The measurements indicate a nearly 3x improvement in power output over a commercial TEG with similar area as successfully predicted by the calculations.