Normally, a difference of several tens of degrees is required in order to generate enough power, but the difference between the body's surface temperature and that of its environment is only a few degrees. This produces about 250 millivolts, while electronic devices require at least one or two volts. As part of their research, Spies and his team 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.
Matthias Ueltzen, an application engineer at Freiburg, Germany-based Micropelt, a developer and manufacturer of thermoelectrics, said, while the "idea of generating some electric power from the heat of the body is a great idea," there are certain difficulties, which lie in the low temperature differences between the skin and the outside air.
"Only a very small part of the thermal heat flow can be converted into electrical power, and for that reason, the technology may only work for applications that don't require a lot of energy," said Ueltzen.
Source: TOI, 20/8/2007
