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'Ionic wind' could help keep devices from overheating

Excessive heat plaguing consumer electronics stems from electrons racing through microchips that make the gadgets operate, and how might one solve this problem?

Pump in a few more electrons.

Purdue University researchers report a prototype that improves cooling by up to 250 percent through creation of an "ionic wind."

Microchip heat builds in part because the little buggers are so tiny that air molecules nearest their surface get stuck and don't move, the so-called no-slip effect.

To solve this, Purdue's team, led by Suresh Garimella, a mechanical engineering professor, designed a tiny anode and cathode arrangement with a 10-millimeter gap through which electrons pass right above a computer chip.

As the negatively charged electrons collide with air molecules, they create positively charged ions that rush toward negatively charged electrodes, creating a tiny wind to carry off heat.

The research, supported by Intel Corp., could be commercially developed within a few years, the engineers estimate, if it can be made cheaply and is rugged enough.

"We've been trying to make this work for about a year," said Garimella, "and now we've shown that it works quite well."

The device was created at Purdue's Birck Nanotechnology Center, and is an example of how things operating at the smallest levels might be counterintuitive. Another example was described last month by Chicago researchers who find that the thinner a layer is made, the stronger it might become.

Working with nanoparticles of gold separated by organic molecules, University of Chicago researchers found a way to make the material just 50 atoms in thickness.

"It drapes over a substrate just like putting a tablecloth on a tabletop," said Heinrich Jaeger, a U. of C. physics professor. "So we said, 'What if the table had a hole in it?'"

They thought the stuff would just fall through the hole, but it didn't, so the scientists brought in an atomic-force microscope and started poking the material, like trying to push a screwdriver through a hole covered by a tablecloth.

They couldn't do it, their ultrathin material was as strong as plexiglass.

Applying heat didn't even melt it as expected, Jaeger said.

"Rather than melting like butter, it stays together as you heat it, and then it finally rips," he said. "It fails in ways that are unexpected. This was very surprising."

Nanotechnology, which builds materials as a mason would construct a house, brick by brick, can imbue materials with unusual characteristics.

Most research has focused on the changed electrical conduction or optical properties, Jaeger said, but mechanical properties are also subject to change at the nano level.

"It's an amazing little marvel," said Jaeger. "This is not a very fragile layer, but rather a robust, resilient membrane."

3-D CELL IMAGES: In another development along the frontier of really small stuff, researchers at the Massachusetts Institute of Technology report they can make three-dimensional images of living cells much as a radiologist might do with a human using X-ray CT machines.

The MIT technique involves making many two-dimensional shots of the cell from different angles, using light. It also measures how much the light's speed is delayed as it travels through the cell.

A computer uses this information to create 3-D images, similar to what a CT scanner does.

"Accomplishing this has been my dream and a goal of our laboratory for several years," said Michael Feld, director of MIT's spectroscopy lab.

Most techniques for viewing cells involve fixing them with chemicals, freezing them or otherwise incapacitating them. The MIT technique doesn't do that, so presumably it will give scientists a better look at cells in their natural state.


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