Biomedical monitoring systems worn by a patient, monitors for machinery or industrial installations in remote or inaccessible situations are just two such applications. Monitoring warm exhaust gases in the flues of a chemical plant, or air quality in the ducts of a heating and ventilation system are two more applications.

According to MIT researchers power for sensors in such applications could be provided 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 MIT devices are able to harness differences of just one or two degrees, producing about 100 microwatts but nevertheless usable amounts of electric power.

Harvesting ambient vibration energy through piezoelectric means can potentially supply 10 to100's of microWatts of available power. Existing piezoelectric harvesters are limited by their interface circuits.

MIT researchers developed a control circuit that optimizes the match between the energy output from the thermoelectric material that generates power from temperature differences and a storage capacitor.

They designed a bias-flip rectifier circuit that can improve by greater than 4X the power extraction capability from piezoelectric harvesters over conventional full-bridge rectifiers and voltage doublers. The experimental chip was all implemented in a 0.35 micron CMOS process.

Yogesh Ramadass, MIT 2009 PhD graduate, said that because power consumption of various electronic sensors, processors and communications devices has been greatly reduced, such devices can be powered by wearable energy harvesting thermoelectric systems.

MIT researchers developed a control circuit that optimizes the match between the energy output from the thermoelectric material that generates power from temperature differences and 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 would almost always be different from the surrounding air.

"There's work to be done on miniaturizing the whole system," Ramadass said. Combining and simplifying the electronics and improving airflow over the heat sink are two avenues being pursued.

MIT professor Anantha Chandrakasan, ISSCC 2010 general chairman, and alumnus Yogesh Ramadass PhD '09 presented their findings at ISSCC.