Journal
SUSTAINABLE COMPUTING-INFORMATICS & SYSTEMS
Volume 11, Issue -, Pages 38-49Publisher
ELSEVIER
DOI: 10.1016/j.suscom.2016.05.003
Keywords
Wearable devices; Autonomous systems; Zero-power; Indoor energy harvesting; Human harvesting; Power management
Funding
- Transient Computing Systems, a SNF project [200021_157048]
- ETH Zurich Grant funding
- Swiss National Science Foundation (SNF) [200021_157048] Funding Source: Swiss National Science Foundation (SNF)
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Wearable technology is gaining popularity, with people wearing everything smart from clothing to glasses and watches. Present-day wearables are typically battery-powered, and their limited lifetime has become the critical issue. Most devices need recharging every few days or even hours, falling short of the expectations for a truly satisfactory user experience. This paper presents the design, implementation and in-field evaluation of InfiniTime, a novel sensor-rich smart bracelet powered by energy harvesting. It is designed to achieve self-sustainability using solar cells with only modest indoor light levels and thermoelectric generators (TEG's) with small temperature gradients from the body heat. The wearable device is equipped with an ultra-low power camera and a microphone, in addition to accelerometer and temperature sensors commonly used in commercial devices. Experimental characterization of the fully operational prototype demonstrates a wide range of energy optimization techniques used to achieve self-sustainability with harvested energy only. Our experiments in real-world scenarios show an average of up to 550 mu W for photovoltaic in indoor and 98 mu W for TEG with only 3 degrees temperature gradient and up to 250 mu W for 5 degrees gradient. Simulations using energy intake measurements from solar and TEG modules confirm that InfiniTime achieves self-sustainability with indoor lighting levels and body heat for several realistic applications featuring data acquisition from the on-board camera and multiple sensors, as well as visualization and wireless connectivity. The highly optimized low-power architecture of the presented prototype features image acquisitions at 1.15 frames per second, powered only from the energy harvesters. (C) 2016 Elsevier Inc. All rights reserved.
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