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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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A Circuit to Boost Battery Life

Digital low-dropout voltage regulators will save time, money, and power

11 min read
Image of a battery held sideways by pliers on each side.
Edmon de Haro

YOU'VE PROBABLY PLAYED hundreds, maybe thousands, of videos on your smartphone. But have you ever thought about what happens when you press “play”?

The instant you touch that little triangle, many things happen at once. In microseconds, idle compute cores on your phone's processor spring to life. As they do so, their voltages and clock frequencies shoot up to ensure that the video decompresses and displays without delay. Meanwhile, other cores, running tasks in the background, throttle down. Charge surges into the active cores' millions of transistors and slows to a trickle in the newly idled ones.

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