[Editors] MIT: Engine on a chip promises to best the battery

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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Engine on a chip promises to best the battery
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For Immediate Release
TUESDAY, SEP. 19, 2006
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

IMAGES AVAILABLE

CAMBRIDGE, Mass. --MIT researchers are putting a 
tiny gas-turbine engine inside a silicon chip 
about the size of a quarter. The resulting device 
could run 10 times longer than a battery of the 
same weight can, powering laptops, cell phones, 
radios and other electronic devices.

It could also dramatically lighten the load for 
people who can't connect to a power grid, 
including soldiers who now must carry many pounds 
of batteries for a three-day mission -- all at a 
reasonable price.

The researchers say that in the long term, 
mass-production could bring the per-unit cost of 
power from microengines close to that for power 
from today's large gas-turbine power plants.

Making things tiny is all the rage. The field -- 
called microelectromechanical systems, or MEMS -- 
grew out of the computer industry's stunning 
success in developing and using micro 
technologies. "Forty years ago, a computer filled 
up a whole building," said Professor Alan Epstein 
of the Department of Aeronautics and 
Astronautics. "Now we all have microcomputers on 
our desks and inside our thermostats and our 
watches."

While others are making miniature devices ranging 
from biological sensors to chemical processors, 
Epstein and a team of 20 faculty, staff and 
students are looking to make power -- personal 
power. "Big gas-turbine engines can power a city, 
but a little one could 'power' a person," said 
Epstein, whose colleagues are spread among MIT's 
Gas Turbine Laboratory, Microsystems Technology 
Laboratories, and Laboratory for Electromagnetic 
and Electronic Systems.

How can one make a tiny fuel-burning engine? An 
engine needs a compressor, a combustion chamber, 
a spinning turbine and so on. Making 
millimeter-scale versions of those components 
from welded and riveted pieces of metal isn't 
feasible. So, like computer-chip makers, the MIT 
researchers turned to etched silicon wafers.

Their microengine is made of six silicon wafers, 
piled up like pancakes and bonded together. Each 
wafer is a single crystal with its atoms 
perfectly aligned, so it is extremely strong. To 
achieve the necessary components, the wafers are 
individually prepared using an advanced etching 
process to eat away selected material. When the 
wafers are piled up, the surfaces and the spaces 
in between produce the needed features and 
functions.

Making microengines one at a time would be 
prohibitively expensive, so the researchers again 
followed the lead of computer-chip makers. They 
make 60 to 100 components on a large wafer that 
they then (very carefully) cut apart into single 
units.

The MIT team has now used this process to make 
all the components needed for their engine, and 
each part works. Inside a tiny combustion 
chamber, fuel and air quickly mix and burn at the 
melting point of steel. Turbine blades, made of 
low-defect, high-strength microfabricated 
materials, spin at 20,000 revolutions per second 
-- 100 times faster than those in jet engines. A 
mini-generator produces 10 watts of power. A 
little compressor raises the pressure of air in 
preparation for combustion. And cooling (always a 
challenge in hot microdevices) appears manageable 
by sending the compression air around the outside 
of the combustor.

"So all the parts workŠ. We're now trying to get 
them all to work on the same day on the same lab 
bench," Epstein said. Ultimately, of course, hot 
gases from the combustion chamber need to turn 
the turbine blades, which must then power the 
generator, and so on. "That turns out to be a 
hard thing to do," he said. Their goal is to have 
it done by the end of this year.

Predicting how quickly they can move ahead is 
itself a bit of a challenge. If the bonding 
process is done well, each microengine is a 
monolithic piece of silicon, atomically perfect 
and inseparable. As a result, even a tiny mistake 
in a single component will necessitate starting 
from scratch. And if one component needs changing 
-- say, the compressor should be a micron smaller 
-- the microfabrication team will have to rethink 
the entire design process.

For all the difficulties, Epstein said the 
project is "an astonishing amount of fun" -- and 
MIT is the ideal place for it. "Within 300 feet 
of my office, I could find the world's experts on 
each of the technologies needed to make the 
complete system," he said.

In addition, the project provides an excellent 
opportunity for teaching. "No matter what your 
specialty is -- combustion or bearings or 
microfabrication -- it's equally hard," he said. 
"As an educational tool, it's enormously useful 
because the students realize that their success 
is dependent upon other people's success. They 
can't make their part easier by making somebody 
else's part harder, because then as a team we 
don't succeed."

This research was funded by the U.S. Army Research Laboratory.

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Written by Nancy Stauffer, MIT Laboratory for Energy and the Environment