by Cade Metz
Think of it as pixie dust for practical situations. In 1994, Kris Pister, a professor of electrical engineering at the University of California, Berkeley, set out to build a network of tiny sensors capable of detecting the slightest changes in light, vibration, and air acceleration. Each so-called mote would communicate via wireless radio. Each would run on solar power. And each would fit inside a single cubic centimeter.
Supported by DARPA, the research organization run by the Department of Defense, Pister and his team didn’t quite reach this lofty goal, but they came tantalizingly close. They built a working wireless sensor measuring less than 5 cubic centimeters—about the size of a grain of rice. "Each mote was totally autonomous," says Pister. "It could do bidirectional communication, and it could transmit as far as 100 meters." He called his tiny sensors "smart dust."
Sprinkled in the right places, smart dust could have magical effects. Equipped to monitor vital signs as well as movement, it could alert doctors and nurses to changes in a patient’s condition. Equipped to read water and chemical levels, it could alert farmers to problems with growing crops. It could even improve a building’s heat and air-conditioning systems, keeping an eye on temperatures and airflow.
Sensor technology is already used in many of the same situations. But in theory, smart dust is less obtrusive and far cheaper than today’s wired devices. "At the moment, the cost of each sensor inside an air-conditioning system is in the $500 to $1,000 range, and most of that is related to all the wiring and the labor needed to put it into place," says Pister. "With smart dust, you can install more sensors, have a more efficient ventilation system, and do it at a much lower cost."
A form of the technology has already reached the marketplace. Currently on leave from Berkeley, Pister is also the CTO and cofounder of Dust Networks, a company that recently produced a smart-dust prototype suitable for manufacturing plants as well as heating and air-conditioning systems. And a second company, Crossbow Technologies, is selling industrial and agricultural smart dust based on TinyOS, the miniature operating system.
"TinyOS is Linux for very small devices, an open-source OS that’s now used by over 500 different organizations," says Crossbow CEO Mike Horton. "It includes a scheduler, a database, a wireless radio stack, mesh networking software, power management, even encryption technology so you don’t have to worry about security."
The only hitch is that today’s commercially viable sensors aren’t quite as dustlike as they could be. Dust Networks’ sensors are each about the size of matchbook, and Crossbow’s are no smaller than a quarter. "They’re more like dust bunnies," says Pister. With solar technology still too expensive for everyday use, the size of these devices is limited by the size of their batteries. Pister’s dust sensors can each run for up to five years on a pair of double-A batteries. Crossbow’s quarter-sized mote is built around a single-cell coin battery.
Within the next few years, these sensors will be whittled down to the size of an aspirin. But even now you can put them almost anywhere. "Outdoors, all you have to do is protect them from wind, rain, sleet, and snow," says Horton. "And in an ordinary indoor environment, you pretty much have free reign." Need a sprinkle?