Aug. 17, 2007 — It used to be that human-generated electricity meant riding a stationary bicycle, or some such thing, to power a generator. But couch potatoes take note: simply sitting around could one day generate enough electricity to power electronic devices.

Scientists have developed new circuits that are able to harness electricity from body heat that would otherwise be wasted to the air. The advance could lead to battery-less cell phones and medical monitors that draw energy from their users.

"The idea behind it is that you can replace the batteries or at least you can enlarge the operation times of batteries," said Peter Spies, electrical engineer and group manager at Fraunhofer Institute for Integrated Circuits in Erlangen, Germany.

Spies and his team improved upon semiconductors called thermoelectric generators that produce electrical energy in the face of temperature differences.

Normally, a difference of several tens of degrees would be required in order to generate enough power, but the differences between the body's surface temperature and that of its environment are only a few degrees. That produces about 250 millivolts, while electronic devices require at least one or two volts.

Spies and his team devised a solution. They incorporated a component into the circuit called a charge pump. The pump temporarily stores the incoming millivolts until they reach 1.8 volts. At that threshold, an internal transistor turns on and delivers the higher voltage to a component that can transfer the electricity to a device.