Heat-powered Devices Could Eliminate Need for Batteries 

It can be inconvenient to replace batteries 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. But, new technology being developed by MIT researchers could make such replacements unnecessary.

New energy-scavenging systems being developed by MIT Professor Anantha Chandrakasan and alumnus Yogesh Ramadass could provide power for such sensors just from differences in temperature between the body (or other warm object) and the surrounding air, eliminating or reducing the need for a battery.

The unique aspect of the new MIT-developed devices is their ability to harness differences of just one or two degrees, producing tiny (about 100 microwatts) but nevertheless usable amounts of electric power. The findings were presented at the 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.

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.

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. 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.