1 February 2002
Heat is on for mini fans
West Lafayette, Ind.Quiet mini fans that wiggle back and forth can help cool future laptop computers and other portable electronic gear.
The devices will remove heat by waving a small blade in alternate directions, said research engineers at Purdue University. On top of that, they will consume only about 1/150 the electricity of conventional fans and have no gears or bearings, which produce friction and heat.
Because the fans work without motors that contain magnets, they do not produce electromagnetic "noise" that can interfere with electronic signals in computer circuits, said Suresh Garimella, an associate professor of mechanical engineering at Purdue.
As future computer chips become smaller and smaller, engineers will have to cram more circuitry into a smaller area, producing additional heat. Because excess heat reduces the performance of computer chips and ultimately destroys the delicate circuits, it will be important to develop new cooling technologies, Garimella said.
"Even if it's just a bit overheated, its performance and reliability go down," Garimella said. "Another reason for cooling is to improve performance as you go to smaller and smaller devices."
The cramped interiors of laptop computers and cell phones contain empty spaces too small to house conventional fans but large enough to accommodate the new fans, some of which have blades about an inch long. Placing the fans in these previously empty spaces can dramatically reduce the interior temperatures of laptop computers.
The fans will not replace conventional fans. Instead, they can enhance the cooling now provided by conventional fans and passive design features, such as heat-dissipating fins.
In experiments on laptop computers, the Purdue researchers reduced the interior temperatures by as much as 8°C, Garimella said.
The fans, which could be in use commercially in about two years, run on 2 milliwatts of electricity, or 0.0002 watt, compared with 300 milliwatts for conventional fans, the researchers said.
The fans move back and forth by a "piezoelectric" ceramic material attached to the blade. As electricity hits the ceramic, it expands, causing the blade to move in one direction. Then, electricity applied in the alternate direction causes the ceramic material to contract and move the blade in the opposite direction. The alternating current causes the fan to move back and forth continuously.
The piezoelectric fans fit into a wide range of sizes. The Purdue engineers will develop fans small enough to fit on a computer chip; their blades will be only about 100 microns long, which is roughly the width of a human hair, Garimella said.
Such fans might be used to cool future chips that produce more heat than their conventional counterparts. The concentrated circuits in a semiconductor computer chip generate more heat per square centimeter of chip area than an area of equal size on the sun's surface, he said.