Smart Dust

Mighty motes for medicine, manufacturing, the military and more.

Picture being able to scatter hundreds of tiny sensors around a building to monitor temperature or humidity. Or deploying, like pixie dust, a network of minuscule, remote sensor chips to track enemy movements in a military operation.

"Smart dust" devices are tiny wireless microelectromechanical sensors (MEMS) that can detect everything from light to vibrations. Thanks to recent breakthroughs in silicon and fabrication techniques, these "motes" could eventually be the size of a grain of sand, though each would contain sensors, computing circuits, bidirectional wireless communications technology and a power supply. Motes would gather scads of data, run computations and communicate that information using two-way band radio between motes at distances approaching 1,000 feet.

Potential commercial applications are varied, ranging from catching manufacturing defects by sensing out-of-range vibrations in industrial equipment to tracking patient movements in a hospital room.

Design Impasse

Still, for all the promise, there are a number of technical obstacles to widespread commercial adoption. For instance, researchers are wrestling with design challenges in fusing MEMS and electronics onto a single chip, says Gary Fedder, associate professor of electrical and computer engineering and robotics at Carnegie Mellon University in Pittsburgh.

Fedder, a co-founder of Carnegie Mellon's MEMS Laboratory, has been trying to tackle these development issues through new fabrication and design techniques, but he acknowledges that the lab has quite a bit of work ahead of it.

"The paradigm has been to have a single engineer be the champion of these systems and fuse it all together to make a [single] chip. That requires a superhuman effort," says Fedder. The lab has been developing design tool technology to aid the engineers who may ultimately design these kinds of systems, he says.

What makes all this effort worthwhile is a growing feeling among researchers that these technologies may eventually have a huge impact on society. That also helps explain why the Defense Advanced Research Projects Agency began funding aspects of this work at the University of California, Berkeley, in 1998.

The goal for researchers is to get these chips down to 1mm on a side. Current motes are about 5mm, says Kristofer Pister, professor of electrical engineering at UC Berkeley, who's been working with smart dust since 1997.

Pister is on sabbatical from the university until early 2004 at Dust Inc., a Berkeley-based developer of peer-to-peer wireless sensor networks. Dust's charter is to give developers hardware and software interfaces "that are stable, reliable and low cost," he says.

The cost of motes has been dropping steadily. Prices range from $50 to $100 each today, and Pister anticipates that they will fall to $1 within five years.

He sees a plethora of potential commercial applications for smart dust, including serving as traffic sensors in congested urban areas and monitoring the power consumption of household appliances to determine whether they're operating at peak efficiency.

Pister and others are quick to point out that the size of these micromachines presents thorny power supply challenges. Ideally, researchers and commercial contractors want to be able to deploy wireless motes that aren't tethered to power sources, and many of the systems being tested or in use today rely on miniature battery power.

"You've got this limited pile of energy in your battery, and you need to distribute that out and make it last," says Mike Horton, CEO of Crossbow Technology Inc., a San Jose-based maker of MEMS technologies whose customers include a cosmetics company that uses wireless sensors to gauge humidity levels in its warehouses for moisture-sensitive products. "You can plug it into the wall, but that kind of defeats the purpose of these autonomous sensors."

Breakthroughs Expected

Researchers are attacking the problem in part by focusing on so-called low-power ad hoc routing protocols, which figure out how to get a message from one mote to another using the least amount of energy. Research on this kind of power has been emerging over the past two years at UC Berkeley, MIT and the University of California, Los Angeles.

"We haven't found a one-size-fits-all approach yet," Horton says. Still, he believes two near-term technical breakthroughs for these wireless sensors in the areas of power and size are poised to occur. The first involves paring the several semiconductors needed today to operate these motes down to a single semiconductor, a development Horton foresees occurring about two years from now.

On the power side, Horton points to research by UC Berkeley's Shad Roundy on fuel cells that can "scavenge" energy to make smart-dust devices run longer. This includes drawing off the ambient vibration energy generated by an industrial machine or gathering energy from low levels of light. These scavenger energy technologies might be five years off, Horton says.

While researchers and commercial developers are agog over the potential applications for smart dust, they're also careful to point out the design and power issues that still need to be resolved. Says Fedder, "There are a lot of people champing at the bit to commercialize this technology, but the technology still has to mature, and widespread use is still several years off."

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Multifunctional Mote

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