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Spinning Ideas

If the delicate manipulation of DNA and photons seems a likely match for tiny machines, consider the research going on at the gas turbine laboratory at MIT. This is home to engineers expert on the multi-ton turbines and jet engines that have powered industry for decades. But these days it is also home to one of the most promising new twists in tiny machines-power MEMS. What if you could use the energy from tiny combustion chambers to drive microturbines and microgenerators? Or if you could build rocket engines the size of a coat button?

A group of several dozen MIT scientists are trying to do just that. One project involves building a microjet that runs on hydrogen and that could be used to power a 15-centimeter-long airplane. “The whole idea was somewhere between silly and fantastic when we started about 10 years ago,” says Alan Epstein, director of the Institute’s gas turbine lab and one of the originators of the power MEMS effort. “But we ran the numbers. They said this could work.” Since then, Epstein and his collaborators at MIT and elsewhere have chipped away at many of the necessary parts-little fuel injectors, combustion chambers and silicon microturbines that look something like high-tech pinwheels. Says Epstein: “This is not vaporware.”

The microjets could end up becoming part of a fleet of surveillance air vehicles several inches long that military planners would like to see in their bag of intelligence tricks. But the implications of power MEMS go far beyond that-it could solve a fundamental challenge facing engineers as they try to build smaller and smaller devices (see table “MEMS Mania”). How do you power them? Conventional batteries have not kept pace with the miniaturization trend. “The most important economic possibility is to use these little engines like batteries,” suggests Epstein.

Just as power companies use massive gas turbines to drive electrical generators, Epstein says microturbine gas engines could become an alternative to batteries for supplying portable power. In a package of a few cubic centimeters, he says, a microturbine fueled by a tiny aluminum tank of hydrocarbon fuel could supply 20 or 30 times the energy of a conventional battery. Laptop computers could start feeling more like pads of paper and cell phones could last weeks without needing to be rejuiced. Such a MEMS power source is still at least several years off. But, says Epstein, “we’re convinced it can work.”

Battery manufacturers like Duracell may not need to look over their shoulders-at least not yet. But the progress of Epstein’s microturbines from theoretical musings a decade ago to prototypes today shows that once-arcane MEMS projects could end up transforming even a multibillion-dollar business like batteries. And the ambition of Epstein and his colleagues at MIT to use tiny spinning turbines to power the next machine revolution shows just how strong an impact MEMS has already made on the engineering mindscape.

How fast the revolution of tiny silicon machines will take to change the technology that we all use and rely on is still anyone’s guess. But if George Lucas could make a squat little robot into a worldwide movie star, he-and thousands of scientists-just may be able to help do the same for microscopic machines. Only this time, it’s not science fiction.

MEMS Mania

Company Goal Status Analog Devices Micromachined accelerometers and actuators Commercial products BF Goodrich Aerospace sensors Research Caliper Technologies (1995 startup: Mountain View, CA) Lab-on-a-chip for microscopic fluid handling Commercial products Cepheid (1996 startup; Sunnyvale, CA) Micro-chips for processing of DNA samples Commercial products Goodyear Tire Intelligent tires that sense pressure Prototypes Hewlett-Packard High-capacity data storage Research Honeywell Polymer actuators capable of affecting macroscale objects Research IBM Terabit data storage devices Research Lucent Technologies Components for optical communications Prototypes Rockwell Radio frequency switches for communication systems Research Seagate Technology Optical-based data storage devices Prototypes Texas Instruments Digital projection systems Commercial TRW Digital propulsion for micro-satellites Research Xerox PARC Microscopic controls for macroscopic systems Research Silicon Light Machine (1994 startup; Sunnyvale, CA) High-resolution displays Product development Leading MEMS projects by industrial groups in the United States. Source: Company reports and Defense Advanced Research Projects Agency (DARPA).

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