A Laptop Cooled with Ionic Wind

http://www.technologyreview.com/computing/22668/?nlid=2037
Anyone who uses a laptop will be familiar with the whir that the fan makes as it kicks in when the processor's temperature reaches around 100 °F. As laptops and other electronics have gotten smaller and thinner, researchers have begun searching for alternative cooling methods, which add less bulk and are quieter.

• One novel idea is to cool a system by using ions to push air molecules across a hot microprocessor, thereby creating a cooling breeze. So-called ionic-cooling systems have been demonstrated in research labs before, but now Tessera, an international chip-packaging company based in San Jose, CA, has demonstrated an ionic-cooling system integrated into a working laptop.

• Researchers from Tessera and the University of Washington presented details of the ionic-cooling system at the IEEE Semi-Therm Symposium in March. The system can extract roughly 30 percent more heat from a laptop than a conventional fan can, and lab tests show that it could potentially consume only half as much power, the company says.

• The ionic-cooler is based on work originally done in 2006 by Alexander Mamishev, a professor of electrical engineering at the University of Washington, and his colleagues. Last year, Tessera licensed the technology, and the company has since modified it to fit into a laptop. In addition to removing heat more efficiently than a fan, "it has silent operation--no moving parts," Mamishev says. "This is a big milestone."

• Tessera's ionic cooler sits near a vent inside the laptop. Heat pipes, which transfer heat using the evaporation and condensation of a fluid, draw heat away from the computer's processing units and toward the ionic-cooling system.
• Inside the ionic-cooling device are two electrodes: one that ionizes air molecules such as nitrogen, and another that acts as a receiver for those molecules. When a voltage is applied between the two electrodes, the ions flow from the emitter electrode to the collector. As they move, their momentum pushes neutral air molecules across a hot spot, cooling it down.

• One of the main challenges of integrating an ionic-cooling system into a laptop was designing a sufficiently compact voltage converter capable of converting the laptop battery's 12 volts DC into the approximately 3,000 volts required to operate the cooler. Using a power supply from a cold cathode fluorescent lamp, engineers at the company were able to construct a supply that is only three centimeters square.

• Tessera isn't the only company looking at ionic breeze as a means to cool consumer electronics. Researchers at Garimella's own lab at Purdue have demonstrated a similar technology, which is being developed commercially by an early-stage Silicon Valley startup called Ventiva.

• Neither technology is quite ready for the next generation of laptops, though. A major challenge will be ensuring the reliability of the electrodes. Laptops are built to operate for at least 30,000 hours, and in early tests of the ionic-cooling system, certain electrode materials corroded too quickly. Without giving specifics, due to pending patents, Honer says that engineers at the company have identified better materials and are focusing on optimizing their lifetime.

• Another hurdle for the technology is the accumulation of dust. Honer says that his engineers are trying to make sure that the ionic cooler is "as insensitive to dust as a fan." He adds that one way to protect the cooler from potentially damaging particles is to use a prefilter.