Electric energy from human-body heat-difference with air: MIT innovation

MIT Professor Anantha Chandrakasan and alumnus Yogesh Ramadass PhD '09 have developed energy scavengers, which produce electric energy from difference in temperature from body and air. This technology can eliminate battery used in electronic devices that need to work for long periods of time, either in biomedical monitoring systems worn by a patient or in monitors for machinery or industrial installations in remote or inaccessible situations.

These devices can harness differences of just one or two degrees to produce about 100 microwatts of electrical power. The findings were presented at the recently held International Solid State Circuits Conference (ISSCC) in San Francisco.

Ramadass says that as a result of research over the last decade, the power consumption of various electronic sensors, processors and communications devices has been greatly reduced, making it possible to power such devices from very low-power energy harvesting systems such as this wearable thermoelectric system.
Now most of the highly integrated semiconductor devices for portable applications are designed to work from such low energy sources.

Such a system, for example, could enable 24-hour-a-day monitoring of heart rate, blood sugar or other biomedical data, through a simple device worn on an arm or a leg and powered just by the body's temperature (which, except on a 98.6-degree F summer day, would almost always be different from the surrounding air). Or it could be used to monitor the warm exhaust gases in the flues of a chemical plant, or air quality in the ducts of a heating and ventilation system.

How they did it: The key to the new technology is a control circuit that optimizes the match between the energy output from the thermoelectric material (which generates power from temperature differences) and the storage system connected to it, in this case a storage capacitor.

Next steps: The present experimental versions of the device require a metal heat-sink worn on an arm or leg, exposed to the ambient air. "There's work to be done on miniaturizing the whole system," Ramadass says. This might be accomplished by combining and simplifying the electronics and by improving airflow over the heat sink.

To know more here is the pdf link
http://mtlweb.mit.edu/researchgroups/icsystems/pubs/journals/2010_ramadass_jssc_jan.pdf