A Theoretical Model for Wearable Thermoelectric Generators Considering the Effect of Human Skin

Wearable thermoelectric generators (w-TEGs) are attracting interest due to their ability to self-power miniaturized electronic devices by converting human body heat into electricity. However, the harvested power density utilizing w-TEGs is in the range of microwatts to milliwatts per square centimeter, which is not sufficient for powering wearable sensors and electronics. In this paper, a theoretical model for w-TEGs considering the human skin effect is developed based on one-dimensional heat transfer analysis. Human skin is geometrically modeled as a multilayer structure consisting of fat, dermis and epidermis, and metabolic heat generation and blood perfusion in skin tissues are taken into account. The influence of load resistance, skin effect, thermal contact resistance at the skin/w-TEG interface, fill factor, thermal conductivity of fill material and heat convection of the spreader on the performance of w-TEG are investigated. Numerical results show that the effect of metabolic heat generation can be negligible, but the heat transfer by blood perfusion in dermis should be considered for the power analysis of w-TEG. The simplified solutions with high accuracy which are more convenient for engineering application of w-TEGs are obtained through rigorous mathematical analysis. The closed-form optimal expressions of load resistance, fill factor and leg height corresponding to maximum power output are provided, and these results can be used to explore the design criteria of w-TEGs. The proposed model considering the effect of human skin is extremely helpful in the actual design of w-TEG devices.