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Waste Heat to Electricity Breakthrough

Northwestern University boosts material’s ability to transform heat into current by refining it on three size scales

3 min read
photo of light bulb giving off flame
Photo: iStockphoto

19 September 2012—When utilities burn fossil fuels to produce electricity, roughly two-thirds of the energy in the feedstock is lost as waste heat. As far back as the preparation for the first moon landing, researchers have been working to efficiently convert waste heat into electrical energy. But so far, the conversion efficiency of thermoelectric materials has been way too low to yield a commercially viable device. This week, however, researchers at Northwestern University, in Evanston, Ill., report in Nature that they have smashed through the old efficiency record, and they claim that further improvement to efficiencies previously thought impossible are within reach.

Materials scientists have long known that in order to improve the performance of a thermoelectric material, they must inhibit its thermal conductivity. For decades they were able to reach but not surpass the long-standing figure of 1 ZT. (ZT, the figure of merit for thermoelectric energy conversion, refers in this case to the amount of electricity generated for a given amount of thermal energy applied.) They did so by replacing certain atoms in the thermoelectric materials’ crystal lattice. This doping created enough atomic-scale disorder to disrupt the movement of phonons, the waves that carry thermal energy.

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The Transistor at 75

The past, present, and future of the modern world’s most important invention

2 min read
A photo of a birthday cake with 75 written on it.
Lisa Sheehan

Seventy-five years is a long time. It’s so long that most of us don’t remember a time before the transistor, and long enough for many engineers to have devoted entire careers to its use and development. In honor of this most important of technological achievements, this issue’s package of articles explores the transistor’s historical journey and potential future.

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