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A New Spin on Recovering Heat For Power

Using heat to manipulate magnetic fields on the micro scale may provide a way to capture waste power | Photo: Matthieu Yiptong/Flickr/Creative Commons License

The notion of capturing waste heat from our technology and using it to generate electrical power isn't new: factories use it fairly often in a process called "cogeneration." But a team of scientists at UCLA has come up with a new spin on the practice, using a branch of applied physics that didn't even exist 40 years ago.

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Traditionally, waste heat is used to run turbines that generate electrical power. This week, researchers at the UCLA Henry Samueli School of Engineering and Applied Science announced that they'd found a potential way to turn much smaller amounts of waste heat into electrical energy using spin transport electronics, a branch of physical engineering born in the 1980s and usually called "spintronics" for short. The team's lead authors are postdoctoral researcher Wanjun Jiang and graduate student Pramey Upadhyaya; their principal investigator is Kang Wang.

We rely on electrons' charge to power our society, but electrons have other properties besides their charge. One of those properties is spin, and the relatively new science of spintronics concerns the behavior and properties of electrons that derive from that spin.

Magnets and potentially magnetic materials derive their properties from the way the electrons in them move -- both in orbit around the atomic nuclei, and in the direction of their spin. (Imagine the earth both rotating every day -- "spin" -- and orbiting the sun once a year.) In most materials, electrons' spin averages out; in magnetic materials such as iron or nickel, the structure of the molecules allows their electrons' spin to align so that a majority of them are spinning in the same direction. This creates a magnetic field within the material.

Outside forces can alter the spin of the electrons in a matrix of magnetic material. If that force propagates across the magnetic material, that disturbance is called a "spin wave." Spin waves can provoke changes in the magnetic makeup of the material they pass through, making a whole section of the substance's magnetic field switch directions -- the region's magnetic "north pole" will wander.

The boundaries between sections of different magnetic field orientation in such a matrix are called "domain walls."

That's a long explanatory preamble, but we needed to give those ReWire readers without physics expertise the basics to explain this new study out of UCLA.

According to this recent (paywalled) article in Physical Review Letters, a team from the Samueli School found a way to use heat -- such as might be generated in a laptop or hard-working smartphone -- to set up a spin wave that then moves a domain wall in magnetic material. Moving this domain wall means changes in the material's magnetic field, and a changing magnetic field should, in theory, be able to generate conventional electrical power. After all, that's how generators work: they move a magnetic field around a bunch of wires, and that gets current flowing.

As always with interesting new tech that we here at ReWire comprehend only well enough to call NSFW Insane Clown Posse lyrics to mind, there are details to be worked out before this research finds its way into your tablet computer. But as the UCLA press release puts it,

If housed within the central processing unit of a computer or other electrical device, a domain wall would serve as a sort of turbine, capturing the heat from the traveling spin wave and converting it into energy, just as a turbine harnesses the power of water and converts it into electrical energy that can be used to redirect the water or serve another purpose. The captured energy can then be used to help power the electrical device.

In other words, this could provide a way to make our technology significantly more efficient by taking some of the heat our machines create and sending that energy back into their batteries.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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