Human body heat for powering wearable devices: From thermal energy to application. (1st January 2017)

• Record Type: Journal Article
• Authors: Thielen, Moritz; Sigrist, Lukas; Magno, Michele; Hierold, Christofer; Benini, Luca
• Is Part Of: Energy conversion and management. Volume 131(2017)
• Page Start: 44
• Page End: 54
• Publication Date: 2017-01-01
• Subjects: Energy harvesting -- TEG -- Wearable -- DC-DC conversion; Direct energy conversion -- Periodicals; Energy storage -- Periodicals; Energy transfer -- Periodicals; Énergie -- Conversion directe -- Périodiques; Direct energy conversion; Periodicals; 621.3105
• DOI: 10.1016/j.enconman.2016.11.005
• Languages: English
• ISSNs: 0196-8904

Abstract

Highlights: A complete system optimization for wearable thermal harvesting from body heat to the application is proposed. State-of-the-art thermal harvesters and DC-DC converters are compared and classified. Extensive simulation and experiments are carried out to characterize the harvesting performance. A case study demonstrates the feasibility to supply a multi-sensor wearables only from body heat. Abstract: Energy harvesting is the key technology to enable self-sustained wearable devices for the Internet of Things and medical applications. Among various types of harvesting sources such as light, vibration and radio frequency, thermoelectric generators (TEG) are a promising option due to their independence of light conditions or the activity of the wearer. This work investigates scavenging of human body heat and the optimization of the power conversion efficiency from body core to the application. We focus on the critical interaction between thermal harvester and power conditioning circuitry and compare two approaches: (1) a high output voltage, low thermal resistance μTEG combined with a high efficiency actively controlled single inductor DC-DC converter, and (2) a high thermal resistance, low electric resistance mTEG in combination with a low-input voltage coupled inductors based DC-DC converter. The mTEG approach delivers up to 65% higher output power per area in a lab setup and 1–15% in a real-world experiment on the human body depending on physical activity and environmental conditions. Using off-the-shelf and low-cost components, we achieve an average power of 260 μW (μTEG) to 280 μW (mTEG) and power densities of 13 μW cm −2 (μTEG) to 14 μW cm −2 (mTEG) for systems worn on the human wrist. With the small and lightweight harvesters optimized for wearability, 16% (mTEG) to 24% (μTEG) of the theoretical maximum efficiency is achieved in a worst-case scenario. This efficiency highly depends on the application specific conditions and requires careful system design. The harvesters can power wearables in different use cases, for example a multi-sensor bracelet that measures activity, acquires images and displays results.