Previous attempts to make much smaller fans failed largely because they were too noisy. One firm that persevered is Piezo Systems of Cambridge, Massachusetts, but its piezoelectric fans are larger and more power-hungry than the ones the Purdue team is developing. Piezoelectric fans were first developed in the 1970s, but finished up largely as novelty items.
The piezoelectric fans were able to suck heat out of nooks and crannies that other fans left untouched. In experiments for a laptop manufacturer, the team was able to lower the enclosure's interior temperature by 8☌. That compared with 300 milliwatts to do the same job using a conventional fan. In January, the Purdue researchers showed that the natural convection rate within a small enclosure could be doubled using a piezoelectric fan that consumed only two to three milliwatts of electricity. And because there is no electric motor inside, the fan produces no electromagnetic noise to interfere with the delicate electronics of the device it is cooling. Also, having no external friction to overcome, the device does not generate any heat itself. As the crystal vibrates, the Mylar blade flaps back and forth like a Japanese fan, albeit a good deal faster.īecause the piezoelectric fan is a solid-state device, it has few parts to wear out. Like the quartz crystal in a digital clock, an alternating voltage applied to the crystal in the fan causes it to expand and contract at a steady rate. The micro fans being developed at Purdue University, Indiana, use a Mylar blade attached to a ceramic with piezoelectric properties (ie, able to deform mechanically when an electric field is applied).