Robots built by Dartmouth College researchers can march 200 in a row across an M&M and manipulate an object as small as a cell.

Just don't ask them to turn right.

Led by Bruce Donald, professor of computer science, Dartmouth researchers have built the world's smallest mobile robot, measuring 60 micrometers by 250 micrometers - as wide as a strand of hair and half the length of the period at the end of this sentence. It can move like a caterpillar over a grid of electrodes that provides not only power, but also instructions, allowing the robot to move freely over the grid.

"If you look at previous robots trying to do something similar, a lot of them had wires attached," Donald said. "At that scale, that would be like having an enormous steel beam attached to your car."

Donald worked with Christopher Levey, director of the Microengineering Laboratory at Dartmouth's Thayer School of Engineering, as well as Daniela Rus, a professor of computer science and electrical engineering at MIT, and graduate students Craig McGray and Igor Paprotny.

"What is the best at Dartmouth is this interdisciplinary interaction," Levey said. The robot is "not something that somebody from one isolated discipline could have come up with," he said.

Movies demonstrating the robot's abilities can be found on the Web at http:// http://www.cs.dartmouth.edu/reports/TR2005-553.CD/index.html. Donald said graduate students had "a great time" testing the robot's speed, turning radius and anything else they could think of. They drove it in circles - counterclockwise only because the robot has a steering arm on just one side - to see if it would get exhausted, but it never tired.

"This little robot has its own memory," said Levey, albeit a small memory, just enough to remember what it's supposed to be doing.

Levey pre-empted a question, asking himself, "Why not just put a computer chip on it? To do that, you would not have ended up with a robot as small as we did.

"The brilliant thing about what we did was to make all that functionality in one component," he said, citing the robot's unprecedented combination of size, mobility, communication and steering system.

"Making a robot that goes anywhere on a surface that is this small is incredibly exciting on its own," Levey said. "One thing that people think of right away is what would happen if you have swarms of these things? What would happen if they interact?"

The robots could form a micro-factory, building computer chips or other tiny objects that are challenging to assemble, said Levey. The robots have biomedical applications, as they are small enough to manipulate cells, Donald said. They also have the potential to create novel security systems, an appropriate application as the project was funded in part by the Department of Homeland Security through Dartmouth's Institute for Security Technology Studies.

Levey described a possible security application for the robots. "If you want to verify at a meeting that people, who are not known by sight to each other, are who they're supposed to be," each person could bring their own vial of these microbots and a code of instructions for them, Levey explained.

"The robots will assemble into something that's easily recognizable," Levey said. Because the robots are so small, it would be hard to reverse engineer the system, and each person could bring hundreds of microbots, adding complexity to a security technique that would already be difficult to tamper with.

"It's easy to know if there's an imposter," Levey said. "With this, you could imagine watching, under a microscope, every step of the way."

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