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                            CAMBRIDGE, Massachusetts, November 30, 2001 (ENS) - A new semiconductor technology could allow efficient, affordable production of electricity from a variety of energy sources without a turbine or similar generator, says the research team responsible.  Many scientists have worked to convert heat to electricity without the moving parts of a generator. Among other advantages, such a device would be almost silent, vibration free, and low in maintenance costs.  But until now, the efficiency of such devices has been a problem. The amount of electricity they produce from a given amount of energy has been low.  The new device is two times more efficient than its closest commercial competitor.

                            "That such good results were obtained in the first generation of the new device technology … indicates that the general approach has great promise for improved performance in more mature implementations," write the researchers, associate professor Peter Hagelstein of Massachusetts Institute of Technology's Department of Electrical Engineering and Computer Science and Dr. Yan Kucherov of ENECO, Inc.

                            The new technology could turn waste heat from automobiles into electricity to augment or replace a vehicle's electrical and air conditioning systems. It could also boost the efficiency of stationary electric power plants.  The technology is based on thermionics, launched a century old ago with the basic vacuum tube, a device that consisted of two parallel conductive plates separated by a vacuum gap. In this high temperature tube, electrons boiled off one plate, traversed the gap and then were absorbed into a colder plate.  The conversion of heat to electricity "occurs as the electrons transport 'uphill' against an electric field in the gap region," said Hagelstein.

                            These early vacuum gap designs had high manufacturing costs and operating temperatures - above 1,000° Celsius (about 2,000° Fahrenheit) - which has limited the technology to nuclear powered converters in space probes, satellites and special military systems.  The new technology replaces the traditional vacuum gap with a multi-layer semiconductor structure. Hagelstein and Kucherov demonstrated two basic physical mechanisms that allow the technology to be implemented.

                            "Solid state thermal to electric energy conversion converts energy due to how electrons transport in the conductor, a process that generates no pollution," Hagelstein said. He noted, however, that some of the materials used in the present generation of devices are toxic, which will affect the eventual disposal of the devices.  The researchers presented their work at a poster session on Tuesday during the Materials Research Society's fall meeting in Boston.


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