Electronic Design

Tiny Sensor Detects Dangerous Gases Quickly And Efficiently

Under the leadership of Akintunde Ibitayo Akinwande, professor of electrical engineering and computer science at the Massachusetts Institute of Technology (MIT), a team of engineers is developing a very small gas sensor that they predict will be able to detect very tiny amounts of hazardous gases faster than currently available gas sensors. It also will be able to detect toxic industrial chemicals and chemical-warfare agents.

In addition to being significantly faster than existing technologies, the sensor is quite compact, a feature that seems to be in constant demand. Employing standard gas chromatography and mass spectrometry techniques, the researchers have created prototypes small enough to fit within a standard-size computer mouse (see the figure). The team is now shooting for a sensor about the size of a matchbox.

“Everything we’re doing has been done on a macro scale. We are just scaling it down,” says Akinwande. “Scaling down gas detectors makes them much easier to use in real-world environments, where they could be dispersed in a building or outdoors. Making the devices small also reduces the amount of power they consume and enhances their sensitivity to trace amounts of gases.”

THE SENSOR AND ANALYZER
The sensor relies on standard gas chromatography and mass spectrometry strategies to identify gas molecules by detecting their unique electronic signatures. Another component working in conjunction with the sensor, an analyzer, breaks the gas molecules down into ionized fragments.

Detectable via their specific charges, which are defined as the ratio of the charge to molecular weight, these gas molecules are dismantled either by directly stripping electrons off the molecules or via bombardment with electrons stripped from carbon nanotubes.

Finally, the molecular fragments are channeled through a long and narrow electrical field. Passing the ions through this charge field converts their charges to voltage, which is measurable with an electrometer and indicative of the molecules’ distinctive electronic signatures.

COMPARISONS
According to the research team, existing portable gas chromatography and mass spectrometry instruments are pretty large and fairly slow in generating data. They measure approximately 40,000 cubic centimeters, about the size of a common paper shopping bag, and can take around 15 minutes to yield results. In terms of efficiency, they consume about 10,000 joules.

MIT’s sensor/analyzer is significantly smaller and delivers data in approximately 4 seconds. The research team has shown that reducing the sensor’s size translates into a dramatic reduction in the amount of power needed to drive it—just 4 joules in operation—because most of the energy that’s consumed is used to create a vacuum in the long chamber where the electric field resides.

The researchers point out yet another advantage of the smaller size. By shrinking these systems, future manufacturers and OEMs can take advantage of micro-fabrication techniques. Of great importance, employing batch-fabrication will allow for fairly inexpensive production of the detectors.

ON THE HORIZON
Initial research on the sensor began three years ago with the help of funding from the Defense Advanced Research Projects Agency and the U.S. Army Soldier Systems Center in Natick, Mass. The international research team, which includes scientists from the University of Cambridge, the University of Texas at Dallas, Clean Earth Technology, and Raytheon, as well as MIT, plan to complete the project within the next two years.

Back in January, professor Akinwande and MIT research scientist Luis Velasquez-Garcia presented their sensor/analyzer system at the 2008 Micro Electro Mechanical Systems (MEMS) conference in Tucson, Ariz. Future applications for their sensor system include water supply protection, medical diagnostics, and the detection of hazardous airborne gases in industrial and security environments.

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