MTL Annual Research Report 2011

There exists great interest in the utilization of the human body as a possible power supply for running such electronics as medical monitoring devices and sensors. This project details the effective utilization of a new type of form-fitting, wearable, wristband thermoelectric heat sink, Figure 1, which relies on 2D heat-spreading for dissipating heat from the cold side of the TEG for the purposes of energy harvesting. The performance of the TEG/heat sink systems is limited by (1) the small working temperature differential between the body and ambient temperature; (2) the desire to use natural air convection cooling on the cold-side of the generator; and (3) the requirement for thin, light-weight systems that are comfortable for long-term use. The 2D heat-spreading wristbands produce 285 μW from a Bi₂Te₃ TEG module (256 thermocouples, each is 2 mm in thickness and 1 mm² in area). The large available surface area of the wristband as well as the highly thermally conductive nature of copper ensures effective cooling of the cold side and allows heat to spread and dissipate throughout the wristband, thereby enhancing the effective heat transfer coefficient. A 75-minute field test was conducted that measured the voltage output from the TEG as well as the temperature difference across the module when worn on the upper forearm. In addition, the output of the TEG was connected to a commercially available DC-DC converter, which boosted the voltage to a steady 4.15 V, shown in Figure 2, allowing for coupling with external applications such as EKG chips and pulse oximeters.