Your Body Could Be The Power Source For Your Wearables

The Scientists Harvesting Energy from Humans to Power Our Wearables

An MIT lab has produced a device the size of a stamp that harvests energy from bending movements. Commercialising it could be a breakthrough for wearables

Ucilia Wang | February 4, 2016

Inside a lab at the Massachusetts Institute of Technology (MIT), Sangtae Kim has been tinkering with a paper-thin device the size of a stamp. Kim is interested in harvesting energy from humans (though not the kind that turns people into batteries in the movie, The Matrix). He wants to harness motions, such as walking and running, to power sensors and wearable gadgets.
“It provides a new way of harvesting human energy,” Kim says of his prototype device, which he described recently in an article co-authored with his adviser, Prof Ju Li and other researchers.

This diagram illustrates the principle behind the proposed energy-harvesting system. Two metal electrodes made of lithium-alloyed silicon form a sandwich around a layer of electrolyte, a polymer that ions (charged atoms) can move across. When the sandwich is bent, unequal stresses cause lithium ions to migrate across the electrolyte, producing a compensating electron current that can be harnessed by an external circuit. When the bending is relaxed, the process reverses. The process can be repeated thousands of times with little change. (The amount of bending is greatly exaggerated in the diagram for clarity.) Source: http://news.mit.edu/2016/harnessing-energy-bending-motions-0106

<more at http://www.theguardian.com/sustainable-business/2016/feb/04/harvesting-energy-humans-walking-charge-wearables-bending-mit; related links: http://www.theguardian.com/sustainable-business/2015/apr/01/the-fat-burning-and-energy-producing-gyms (The fat-burning and energy-producing gyms. Whilst the energy producing gym won’t immediately solve the energy crisis, it does at least require its members to physically engage with the issue. April 1, 2015) and http://www.nature.com/ncomms/2016/160106/ncomms10146/full/ncomms10146.html (Electrochemically driven mechanical energy harvesting. Sangtae Kim, Soon Ju Choi, Kejie Zhao, Hui Yang, Giorgia Gobbi, Sulin Zhang and Ju Li. Nature Communications 7, Article number: 10146 doi:10.1038/ncomms10146. [Abstract: Efficient mechanical energy harvesters enable various wearable devices and auxiliary energy supply. Here we report a novel class of mechanical energy harvesters via stress–voltage coupling in electrochemically alloyed electrodes. The device consists of two identical Li-alloyed Si as electrodes, separated by electrolyte-soaked polymer membranes. Bending-induced asymmetric stresses generate chemical potential difference, driving lithium ion flux from the compressed to the tensed electrode to generate electrical current. Removing the bending reverses ion flux and electrical current. Our thermodynamic analysis reveals that the ideal energy-harvesting efficiency of this device is dictated by the Poisson’s ratio of the electrodes. For the thin-film-based energy harvester used in this study, the device has achieved a generating capacity of 15%. The device demonstrates a practical use of stress-composition–voltage coupling in electrochemically active alloys to harvest low-grade mechanical energies from various low-frequency motions, such as everyday human activities.])>