Tiny fans that flap

Recognising the importance of developing new cooling technologies, a group of Purdue University engineers have developed tiny, piezoelectric fans.

As computer chips shrink and gadgets get smaller, temperature control is becoming more of an issue. You can hardly put a big, noisy fan in a fancy new laptop, but excess heat reduces the performance of computer chips and can even destroy the delicate circuits.

Recognising the importance of developing new cooling technologies, a group of Purdue University engineers have developed tiny, piezoelectric fans.

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

According to Suresh Garimella, who heads up the project, the devices consume only about 1/150th as much electricity as conventional fans, and have no gears or bearings to produce friction and heat.

An absence of motors means that the fans don’t produce electromagnetic ‘noise’ that can interfere with electronic signals in computer circuits, adds Garimella.

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, claims Garimella, reduced the interior temperatures of laptops by as much as 8°C.

The device runs on 2 milliwatts of electricity, compared to 300 milliwatts for conventional fans. However, despite being less power hungry than conventional fans, the new devices are expected to enhance, rather than supplant, the cooling provided by conventional fans and features like heat fins.

Garimella believes that the fan could be commercially available in about two years. The Purdue team is now looking at developing fans that are small enough to fit on a computer chip.

With blades only 100µ long it’s thought that such fans might be used to cool future chips that produce more heat than their conventional counterparts. Indeed, the concentrated circuits in a semiconductor computer chip can generate more heat per cm2 of chip area than an area of equal size on the sun’s surface, adds Garimella.Whilst Piezoelectric fans aren’t particularly new (they were originally developed during the 1970s) the old versions were noisy. The Purdue group says that its fans are almost inaudible.

Made by attaching a tiny ‘patch’ of piezoelectric ceramic to a metal or Mylar blade, the fan’s performance is affected by 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.

These factors dictate characteristics such as how far the blade moves, how much airflow it produces and how that flow produces complicated circulation patterns. An improperly designed fan could actually make matters worse by recirculating hot air back onto electronic components.

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

The research is funded through Purdue’s Compact High-Performance Cooling Technologies Research Consortium, led by Garimella, which is now becoming a National Science Foundation Industry/University Cooperative Research Centre. The centre is being formed to help industry develop miniature cooling technologies for a wide range of applications, from electronics and computers to telecommunications and advanced aircraft.