Efforts to capture energy from the human body usually focus on harnessing the kinetic energy of the body’s movement. However the human body is also generating energy in the form of heat that could also be used to run low power electronic devices. New energy-scavenging systems under development at MIT could generate electricity just from differences in temperature between the body (or other warm object) and the surrounding air.
The idea of harnessing heat energy from the body isn’t new, but the unique aspect of the new devices is their ability to harness differences of just one or two degrees, producing tiny (about 100 microwatts) but nevertheless useful amounts of electricity. While it won’t be enough to recharge your mobile phone, it should be enough to power low power devices, such as biomedical monitoring systems or sensors in remote and inaccessible locations.
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The researchers, MIT Prof. Anantha Chandrakasan and alumnus Yogesh Ramadass PhD ’09, point out 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 feasible to power such devices from very low-power energy harvesting systems such as their wearable thermoelectric system.
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.
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 37 degree C (98.6-degree F) summer day, would almost always be different from the surrounding air). It could also 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.
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.
The MIT researchers presented their findings at the International Solid State Circuits Conference (ISSCC) held recently in San Francisco.