Engineers create tiny fans to cool future electronics

Research engineers at Purdue University are developing tiny, quiet fans that move back and forth to help cool future laptop computers and other portable electronic gear.

The devices remove heat by waving a small blade in alternate directions. They are said to consume only about 1/150th as much electricity as conventional fans, and they have no gears or bearings, which produce friction and heat.

Because the new 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 increasingly compact, more circuitry will be crammed into a smaller area, producing additional heat. Because excess heat reduces the performance of computer chips and can ultimately destroy the delicate circuits, it will be important to develop new cooling technologies, Garimella said.

The cramped interiors of laptop computers and cell phones contain empty spaces that are 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 has been shown to dramatically reduce the interior temperatures of laptop computers.

The innovative fans will not replace conventional fans. Instead, they will be used to 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 eight degrees Celsius, Garimella said.

The fans, which could be in use commercially in about two years, run on two milliwatts of electricity, or 2 1/1,000ths of a watt, compared to 300 milliwatts for conventional fans, the researchers said.

The fans are moved back and forth by a piezoelectric ceramic material that is attached to the blade. As electricity is applied to the ceramic, it expands, causing the blade to move in one direction. Then, electricity is applied in the alternate direction, causing the ceramic material to contract and moving the blade back in the opposite direction. The alternating current causes the fan to move back and forth continuously.

The operating efficiency of a fan can be optimised by adjusting the frequency of alternating current until it is just right for that particular fan.

The piezoelectric fans can be made in a wide range of sizes. The Purdue engineers will be developing fans small enough to fit on a computer chip: their blades will be only about 100 microns long.

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 can generate more heat per square centimetre of chip area than an area of equal size on the surface of the sun.

The fans are made by attaching a tiny ‘patch’ of piezoelectric ceramic to a metal or Mylar blade. Two factors affecting the performance of the fans are how much the ceramic patch overlaps the blade and how thick the patch is compared to the blade’s thickness.

Another critical factor is precisely where to attach the blade to the patch as an improperly designed fan could recirculate hot air back onto electronic components.

The Purdue researchers have developed mathematical techniques that take these factors into consideration when designing fans for specific purposes.

‘What we bring to the table is a knowledge of the modelling of these fans,’ Garimella said. ‘How to analyse the design, to figure out how large a patch should be for how long a blade, how thick the patch should be and what happens if you modify all these quantities.’