A Nano Fan for Nano Gadgets

Louise Knapp  

The Piezofans

The trend toward smaller gadgets and the demand for more and more functions means electronic gadgets may look really cool, but they may also be too hot to handle.

Cramming an increasing amount of circuitry into smaller and smaller spaces makes electronic portables hotter and hotter.

Desktops and laptops already have cooling fans in them, but smaller devices make lots of heat, too.

"People have been able to get away with not needing a fan in cell phones or Palm Pilots, but we have pretty much reached the limit of what we can do with these handhelds," said Suresh Garimella, associate professor of mechanical engineering at Purdue University.

To address the problem, Garimella and colleagues have developed a miniature fan that requires very little power and can be made to fit into some really small places.

The fan consists of blades made of stainless steel, brass or even Mylar. Attached to the blades is the magic ingredient -- a patch of piezoelectric ceramic material.

Piezoelectric material deforms in the presence of a voltage field. The shape and size of the material determines the way it bends.

Positive and negative electrical voltage affect the material differently. As a positive voltage is applied, the ceramic can expand, causing the blade to move in one direction.

A negative electrical voltage can cause the ceramic material to contract and move the blade back in the opposite direction.

"As the piezoelectric material expands and contracts, it pushes the shim over to one side and then the other," Garimella said. "The shim stock oscillates from side to side much like a traditional Chinese paper fan."

The fan's speed can be adjusted by changing the frequency of the current. The fan can be adjusted to run at the speed necessary to cool its gadget.

Piezoelectric material is not a new discovery -- there have been piezoelectric fans available as novelty items since the 1970s -- but the Purdue team was the first to adapt its use for tiny fans in electronic gadgets.

The Piezofan, as it's called, has several advantages over a regular fan -- one being that it only consumes 1/150 of the electricity of a regular fan.

This, coupled with the fact that the Piezofan has no gears or bearings, means that the heat it generates is negligible.

"There'd be no point if it consumed a lot of power, because then it would get hot," Garimella said.

Another advantage is that the fan runs almost silently.

Because the Piezofan works without motors that contain magnets, it does not produce electromagnetic noise that can interfere with electronic signals in the computer circuits. Nor does it irritate the user with an incessant buzzing.

Another plus is that the Piezofan can be made in many sizes.

The Purdue team will eventually develop fans small enough to fit on a computer chip, with blades only 100 microns long -- roughly the width of a human hair.

Designing the Piezofan is not, however, a total breeze.

One problem the team dealt with was finding the right glue to attach the piezoelectric patch to the blade. The glue needs to be robust and reliable to meet the needs of the gadgets it's employed to cool.

The Piezofan's reliability on this front has yet to be tested.

Another complication is that each gadget will need a fan that meets its own specific requirements.

Each electronic gadget will have different needs in terms of how far the fan's blade moves, how much airflow it produces and how that flow produces circulation patterns.

An improperly designed fan could make matters worse by recirculating hot air back onto electronic components.

The Purdue team developed some relatively simple mathematical formulas to give engineers guidelines for building gadgets -- these will need to be precise to suit each gadget's requirements.

Another critical factor is where to attach the fan in the gadget.

"If you move the fan around in a cell phone, say, it gives very different results, and it's not very intuitive as to where it would work the best, so it is down to trial and error," Garimella said.

Despite these problems, the Purdue team is confident the Piezofans will be in use within the next couple of years -- not as a replacement for conventional fans, but rather to enhance the cooling techniques currently in use.

Many people in the electronics industry are interested in the concept.

"It's a neat technology because of the low noise performance it offers," said Girish Upadhya, senior thermal scientist at Apple.

"One fan for all the cooling needs is now no longer working in a laptop, so we need several fans. But we also need to cut down on the noise, and so the piezoelectric fan would be the answer," Upadhya said.

D.H.R. Sarma, engineering group manager at Delphi Delco Electronic Systems, part of Delphi Automotive Systems, agrees about the fan's usefulness.

"Thermal management separates the men from the boys," Sarma said. "People who can figure out the right way to manage heat will be more successful in this business."

"We saw a match between our needs and this technology. Cars have a limited space and this offers compact cooling," Sarma added.