Body Heat Eliminates Need for Batteries

Engineers at the Fraunhofer Institute for Integrated Circuits IIS have developed a novel voltage converter that can handle input voltages as low as 20 millivolts. This means that tiny amounts of energy extracted from the environment can be used to power small electrical loads.

Imagine an MP3 player that never needs to be recharged from a wall outlet, or a jogger having their heart and respiratory rates simply displayed on a wristwatch with no need for batteries. This is not a pipedream, but a snapshot of the current state of Fraunhofer research. The electricity required by these devices can be generated from human body heat, for example.

Utilizing a 2 °C temperature gradient, which is the equivalent of the difference between the temperature of human skin and room temperature, for instance, a 2 cm by 2 cm thermoelectric generator used in connection with the new voltage converter IC can produce up to 4 mW. Other energy sources that are adequate for use with this new IC are dimly lit solar cells as well as fuel cells. If the energy thus produced is collected over a lengthy period and stored in a battery, it becomes possible to power larger loads such as MP3 players or PDAs.

The IC, which measures only 1.5 mm by 1.5 mm, can, for instance, supply 3.3 volts to commercial electronic components such as sensors, wireless transceivers and displays. Its efficiency varies between 30 and 80 percent, depending on the load and input voltage. This is the first solution worldwide that operates on supply voltages as low as 20 millivolts. Such small and hence low-cost voltage converters are very useful in a variety of application areas, for instance in medical and automotive engineering, facility management, automation and logistics.

Background information: The voltage converter is a result of an ongoing Fraunhofer project on thermoelectric nanocomposites. The project is aimed at developing thermoelectric generators specially geared to distributed power generation for self-powered sensor/actuator networks. For this purpose, various approaches to creating highly efficient polycrystalline thermoelectric materials and components are being pursued, and highly integrated electronic circuits are being created that are essential for use in a thermoelectric generator.