Design and Experimental Investigation of Thermoelectric Generators for Wearable Applications

A critical challenge in using thermoelectric generators (TEGs) for charging the portable or wearable electronics has been their limited outputs, as available temperature differential on human body (∆T_ext) is typically less than 10 K. Furthermore, the thermal resistance (R_th) at the TEG–air interface often overwhelms R_th of TEG itself, which makes the temperature differential within the TEG merely a small fraction of ∆T_ext. Here, the designs of TEG systems for wearable applications based both on theory and systematic experiments are studied. First, this study fabricates the TEGs having different fill factors (equivalently, varied internal R_th of the TEGs) and finds an optimum fill factor that is determined by both thermal matching condition and the electrical contact resistance. Next, to investigate the effects of heat sink and external air flow, this study combines plate fin heat sinks with the TEGs and evaluates their performance under three different convection conditions: natural convection, and convection with either parallel or impinging flow. Lastly the effect of R_th at the skin–TEG interface is studied. Although the TEG system produces an output power of 126 µW cm⁻² (∆T_ext = 7 K) on a smooth heat source (Cu heater), it generates reduced power of 20 µW cm⁻² (∆T_ext = 6 K) on wrist (uneven heat source).