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"Everything we're doing has been done on a macro scale. We are just
scaling it down," said Akinwande, a professor of electrical
engineering and computer science and member of MIT's Microsystems
Technology Laboratories (MTL).
Akinwande and MIT research scientist Luis Velasquez-Garcia plan to
present their work at the Micro Electro Mechanical Systems (MEMS) 2008
conference next week. In December, they presented at the International
Electronic Devices Meeting.
Scaling down gas detectors makes them much easier to use in a
real-world environment, where they could be dispersed in a building or
outdoor area. Making the devices small also reduces the amount of
power they consume and enhances their sensitivity to trace amounts of
gases, Akinwande said.
He is leading an international team that includes scientists from the
University of Cambridge, the University of Texas at Dallas, Clean
Earth Technology and Raytheon, as well as MIT.
Their detector uses gas chromatography and mass spectrometry (GC-MS)
to identify gas molecules by their telltale electronic signatures.
Current versions of portable GC-MS machines, which take about 15
minutes to produce results, are around 40,000 cubic centimeters, about
the size of a full paper grocery bag, and use 10,000 joules of energy.
The new, smaller version consumes about four joules and produces
results in about four seconds.
The device, which the researchers plan to have completed within two
years, could be used to help protect water supplies or for medical
diagnostics, as well as to detect hazardous gases in the air.
The analyzer works by breaking gas molecules into ionized fragments,
which can be detected by their specific charge (ratio of charge to
molecular weight).
Gas molecules are broken apart either by stripping electrons off the
molecules, or by bombarding them with electrons stripped from carbon
nanotubes. The fragments are then sent through a long, narrow electric
field. At the end of the field, the ions' charges are converted to
voltage and measured by an electrometer, yielding the molecules'
distinctive electronic signature.
Shrinking the device greatly reduces the energy needed to power it, in
part because much of the energy is dedicated to creating a vacuum in
the chamber where the electric field is located.
Another advantage of the small size is that smaller systems can be
precisely built using microfabrication. Also, batch-fabrication will
allow the detectors to be produced inexpensively.
The research, which started three years ago, is funded by the Defense
Advanced Research Projects Agency and the U.S. Army Soldier Systems
Center in Natick, Mass.
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