The design and development of wearable, medical and other smart devices have rapidly grown in recent years. This can be attributed to their efficiency and vast applications in numerous areas. These devices enhance connectivity that enables effective collection, transfer, and presentation of data. However, they rely on batteries which is a big challenge to the adoption of the technology due to the burden of charging many devices considering the increase in the number of wearables per user.
Previously thermoelectric energy harvesting from the body heat has been identified as a promising solution for powering smart devices. Interestingly, it can be used to generate power at low temperatures irrespective of the body activity levels. This can support self-charging feature for the wearables. However, the low energy conversion efficiency and low voltage output have rendered most of the thermoelectric modules unsuitable for body energy harvesting. Alternatively, thermoelectric energy harvester design strategies have mainly focused on improving the material property thermoelectric figure of merit rather than optimization integration of the subcomponents. Some prior approaches at system level integration may not be readily applicable for general applications, as the usage of step-up converter will cause additional complication to the amount of power generation.
To this note, Santa Clara University researchers: Thomas Watson, Joshua Vincent and led by Dr. Hohyun Lee from the Department of Mechanical Engineering developed a new thermoelectric system design approach for small energy harvesting based on commercial products. The approach fundamentally incorporated a DC-DC voltage step-up converter and optimized the thermoelectric module geometry. The main objective was to maximize power production through the thermoelectric energy harvester by considering the impedance requirement of the DC-DC voltage step-up converter. The work is published in the journal, Applied Energy.
Briefly, the authors considered a design of thermoelectric module geometry and system integration to maximize power production under practical operation conditions. Next, a sensitivity analysis was conducted to account for the individual components’ performance and the varying environmental conditions. This was due to the inability of the module to change upon the system integration. Off-the-shelf components were utilized in the optimization of the design. This ensured that the system could be used by those who could not afford customized circuits, modules and materials.
The proposed design resulted in greater power production attributed to its ability to operate under non-ideal operation conditions. To verify this, an optimized thermoelectric energy harvesting system prototype was demonstrated using the off-the-shelf components. It exhibited the ability to generate 0.5mW at 5V and temperature gradient of 16K. From further analysis of the DC-DC voltage step-up converters and system configuration, the authors noted that the design approach could significantly enhance the system performance level. This framework will, therefore, provide further guidance for system integration and development of subcomponents and materials. Altogether, Santa Clara University study provided vital information that will advance the development of future energy harvesting systems for use in wearables and other smart devices.
Watson, T., Vincent, J., & Lee, H. (2019). Effect of DC-DC voltage step-up converter impedance on thermoelectric energy harvester system design strategy. Applied Energy, 239, 898-907.Go To Applied Energy