In academic careers as in others, circumstances can land you in what are popularly called “minefields.” But Timothy Swager’s role as an MIT professor of chemistry has put him in the middle of a real minefield.
Well, almost real. Involved in an effort to create a new mine-detecting system, Swager last year went explosive-hunting in a specially created field at the request of his program’s overseer, Regina Dugan of the Defense Advanced Research Projects Agency (DARPA). “She wanted us to get a taste of what it’s really like,” says Swager.
This wasn’t a standard minefield. The mines are deactivated. And the field itself occupies a super-secure patch of a Missouri Army base. Still, the experience stayed with Swager.
After you get a signal on your metal detector, he explains, “you get low–basically down on your stomach–because the pressure points that set a mine off are oriented vertically, so you want to come at it from the side. It makes you appreciate just how laborious the work is.”
Finding mines faster
Though Swager’s well-being wasn’t at risk, millions of people around the world do face real danger from mines. The Kosovo conflict put the situation in the spotlight; returned Kosovars are still losing limbs and even their lives to mines laid before or during the war. But Kosovo is just the tip of the iceberg.
“It’s been estimated there are 120 million live mines in minefields around the world,” says Swager, “but that’s an old estimate; I suspect that number is higher after Kosovo.”
The hidden explosives are in war zones new and old. Cambodia, for example, is still mine-ridden years after hostilities in that country died down.
Since virtually all mines contain metal, de-mining crews can root them out with metal detectors, but it’s brutally time-consuming work. One basic problem: many of today’s mines contain little metal. “You can set your detector to detect very small amounts,” notes the faculty member, “but you may get hundreds and even thousands of false positives before you find a mine.”
Swager aims to improve that situation. He’s working under a DARPA effort called the Unexploded Ordnance Detection Program, or, more informally, the Dog’s Nose Program (so named because trained dogs bring highly sensitive smelling skills to anti-mine work.) His goal is a technology that can sniff out TNT molecules in the air over buried mines.
Tiny amounts of TNT
The key to the system is a chemosensor. The concept isn’t new: systems based on materials that can identify small amounts of a target compound include the glucose sensors used by diabetics. But Swager’s system must be able to pick out almost unimaginably small quantities of TNT.
In the optimal environment of a closed system, the saturation vapor pressure of TNT is 10 molecules per billion molecules of gas. Minefields, though, are anything but closed. “You start with problems like local air movements,” he notes. “And these environments tend to be very cluttered chemically.”
To get a quick yes-or-no signal, therefore, Swager’s system must reliably pick up TNT quantities measured in the 10-15 gram range. His solution is based on creating long chains of custom-tailored polymers–sophisticated cousins of the polymers we use in everyday life, like plastics.
TNT binds to these polymers. Importantly, though, it only takes one such coming-together to cut the flow of energy along an entire chain. “It’s something like a strand of Christmas tree lights,” he explains. “When one bulb goes, the whole strand shuts down.” This effect, in turn–though not the only key to the system–would help users identify minuscule amounts of TNT.
A “star producer”
The faculty member didn’t start with the goal of creating anti-mine technologies. A Montana native, Swager pursued his interest in matters chemical along an educational path that included Montana State, grad school at Caltech and a two-year “postdoc” at MIT under former provost Mark Wrighton, now president of St. Louis-based Washington University.
Swager’s early work involved basic explorations. “That tends to be what people in this profession do,” he notes. After he developed the principles of his “chemical sniffer,” though, he started seeking ways to apply it, and a DARPA request for proposals two years ago gave him an answer.
Swager’s approach has made an impression. “Tim’s one of our star producers,” says DARPA’s Dugan. “Several sensor developers have already incorporated his amplification polymers into their systems.”
Swager himself works with an Oklahoma-based firm called Nomadic, Inc., that’s now developing and testing a prototype using his polymers. If the tests work out, the system could be in the field within a year or two.But as Swager’s quick to note, this is just one of several innovative anti-mine technologies in development.
Still, the faculty member says the key isn’t whose system works best, but rather their cumulative impact on a seemingly insoluble dilemma. “There’s a good chance that we may be on our way to solving the land-mine problem,” he notes. “That’s something really exciting to think about.”