Research engineers at Purdue University are developing very small fans for cooling laptop computers and other portable electronic devices. "Cell phones don't currently have fans, but as we increase their functions, we increase the heat generated and will have to have a way of removing that heat," says Suresh Garimella, professor of mechanical engineering at Purdue. He and colleague Arvind Raman designed the small piezoelectric fans that resemble classic hand-held Chinese fans. "We tried to imagine a cell phone with a rotary fan, but the picture we envisioned was something that would blow your hair in the air," explains Garimella. "The smallest fan we made so far is less than a half-inch square, but we believe we can make fans that measure 100 microns." In addition to their small size, the small fans use only 2 mW of electricity, compared to 300 mW used by conventional rotary fans in some laptop computers. Without motors that contain magnets, the new fans do not generate electromagnetic noise. The small fans also have no gears or bearings that produce friction and heat. Instead, the piezoelectric ceramic attached to the fan blades moves them back and forth with alternating current. Adjusting the frequency of the current helps optimize the fans for specific applications. "We are currently developing optimization techniques," says Garimella. "For example, we still need to determine the ratio of the thickness of the blade to other fan structures for particular applications." Other critical factors include where to attach the fan blade to the patch of piezoelectric material, the thickness of the blades, and their materials. "We think the blades could be made from Mylar, brass, or stainless steel," says Garimella. Mathematical models developed by the Purdue team provide design guidelines for specific applications such as computers, telephones, PDAs, and pharmaceutical mixing equipment. A research consortium whose members include Apple Computer, Nokia Research Center, General Electric, and Delphi Delco Electronics Systems funds the research. For more information, e-mail email@example.com or firstname.lastname@example.org. Also, visit http://widget.ecn.purdue.edu/~CTRC.