Waltzing microbots are all the rage at Duke University.

Researchers there today said they made microrobots shaped something like a spatula but with dimensions measuring just microns, or millionths of a meter pirouette to the music of a Strauss waltz on a dance floor just 1 millimeter across. In another sequence, the devices pivot in a precise fashion whenever their boom-like steering arms are drawn down to the surface by an electric charge. This response resembles the way dirt bikers turn by extending a boot heel, researchers said. The researchers said they have also been able to get five of the devices to group-maneuver in cooperation under the same control system.

Known as microelectromechanical system (MEMS) microrobots, the devices are of suitable scale for Lilliputian tasks such as moving around the interiors of laboratories-on-a-chip.

They are almost 100 times smaller than any previous robotic designs of their kind and weigh even less, researchers noted. "Initially, we wanted to build something like a car that could drive around at the microscopic scale," said Bruce Donald, a Duke professor of computer science and biochemistry. "Now what we've been able to do is create the first microscopic traffic jam."

Propelling themselves across such surfaces in an inchworm-like fashion impelled by a "scratch-drive" motion actuator, the microrobots advance in steps only 10 to 20 billionths of a meter each, but repeated as often as 20,000 times a second. The microrobots can be so small because they are not encumbered by leash-like tethers attached to an external control system. Built with microchip fabrication techniques, they are each designed to respond differently to the same single "global control signal" as voltages charge and discharge on their working parts.

In their new reports, the team shows that five of the microrobots can be made to advance, turn and circle together in pre-planned ways when each is built with slightly different dimensions and stiffness, researchers said.

Following a choreography mapped out with the aid of mathematics, the microdevices ultimately assemble into group micro-huddles that could set the stage for something more elaborate.

Donald said it took him and various colleagues from 1997 to 2002 to create a microrobot that can operate without a tether, three more years to make the devices steer under global control, and another three to independently maneuver more than one at a time.