Portable electronics are only as good as their batteries and, let's face it, batteries aren't very good. Especially when compared with, say, gasoline, which packs 1oo times a battery's energy into an equivalent space. That's why a large group of mechanical engineers (centered at the Massachusetts Institute of Technology, but with participants at other universities and companies) are hard at work in an effort to replace batteries with a tiny engine that runs on fuel. Imagine a battery-free life! When the fuel runs out in your laptop, you just fill'er up and go.

The engine—about the size of a dime and slightly thicker— starts with a combustion chamber that ignites hydrogen and shoots hot gas past a spinning turbine. Its tiny components (bearings, chambers, and turbine) are etched with great precision onto silicon wafers in the same manner that computer components are imprinted onto integrated circuits. The prototype consists of five stacked wafers. And since these wafers could be manufactured in much the same way as computer chips, they could probably be produced quite cheaply.

But the devil in all this exquisite detail is efficiency. Miniscule engine components don't always behave like their scaled-up counterparts. Molecular attraction between the parts can boggle up the works, according to Columbia University professor Luc Frecheete, one of the engine's designers. Excess heat from the combustion chamber is also a problem, often leaking to other components of the engine.

The scientists' goal is to create an engine that will operate at 10 percent efficiency — that is, 10 times better than batteries operate. Frechette predicts that a complete system, with all components in place and working, will be assembled in the next couple of years, but commercial models aren't likely until at least the end of the decade.