High power output from body heat harvesting based on flexible thermoelectric system with low thermal contact resistance

This paper reports body heat harvesting and refrigeration effects based on a flexible thermoelectric (TE) system made of rigid inorganic bulk materials. The TE device itself is integrated with small segments that consist of Bakelite holders containing the inorganic bulk TE elements. These holders are connected by wires passing through holes at each side of the holders. Owing to its structural design, the wearable TE system shows enough flexibility to be used on curved or nonflat surfaces such as human skin. Powered by a portable battery, it performs refrigeration on human skin and is embedded in an arm band. It refrigerates human skin at approximately 4.4 K, which is cold enough for humans, based on a theoretical analysis. A wearable TE system was also attached to human skin for power generation. It produces 138.67 μW of power with an 8.8 mV voltage output. Considering the size of the system, 55 mm by 45 mm, it records a 5.6 μW cm^-2 power density based on body heat harvesting. From the theoretical analysis based on human thermoregulatory modeling, the refrigeration and power generation performance can be further enhanced by reducing the thermal contact resistance. The TE system shows potential for use as a body heat harvester or human body refrigerator.