Robo-Nose: Hi-Tech Bomb Sniffer Smells Like a Dog

Stefan Lovgren
for National Geographic News

October 1, 2003

A terrorist enters a busy airport carrying hidden explosives. But he doesn't get far. Micro-sensors embedded in the airport's ventilation system immediately detect the explosive vapor in the air, alerting security.

This could be the future in the battle against terrorism—and it may be closer than you think, thanks to new explosives detection technology. Researchers from the University of Nevada in Reno and Oak Ridge Laboratory in Oak Ridge, Tennessee, have developed a miniature cantilever that can sense TNT vapor and distinguish it from non-explosive vapors.

Conventional sensors—like the detection machines used in airports—are expensive and bulky. Until now, dogs have been the most effective explosives detectors. But canine detection has practical limitations; dogs can only be in one place at a time.

On the other hand, the new explosive-vapor sensors—or miniature mechanical noses, if you will—have a detection capability that may surpass that of dogs. Perhaps more importantly, the devices could be used on a large scale—in airports, office buildings, even restaurants.

"These self-sensing micro-cantilevers are 10,000 times smaller than current explosives detection technology, consume 10,000 times less power than other micro-cantilever technologies, and when mass fabricated could reach a price point 100 times lower than what is on the market today," said Jesse Adams, an assistant professor of mechanical engineering at the University of Nevada in Reno, who developed the sensors.

The research is described in tomorrow's issue of Nature.

Setting Off Explosions

Here's how it works. The micro-cantilever has two integrated elements, both smaller than an ant's eye. One is a combined sensor and actuator to both sense and create reference motion, and the other is an integrated heating element that can raise the temperature of the cantilever by hundreds of degrees Celsius in less than a second.

When the device catches tiny particles of an explosive from the air, an integrated heater on the micro-cantilever triggers miniscule quantities of explosive material on the surface of the device.

"We're detecting the presence of the explosive on the micro-sensor by actually causing a small explosion on the sensor," said Adams.

While the sensors are able to detect a miniscule amount of explosive vapor, they can distinguish it from non-explosive vapors.

The idea of using micro-cantilever sensors to detect explosives is not new. But previous technology has struggled to integrate a sensor and an actuator. Sensing still usually requires external optics, like lasers and photodiodes. There were also difficulties with high power consumption, and figuring how to use many cantilevers at a time.

The new devices, however, are "self-sensing," consume very little power, and many micro-cantilevers can be used simultaneously.

Mechanical Sniffer Dogs

The capture of explosive particles requires special air handling.

"Explosives have very low vapor pressures, and don't give off a lot of molecules at room temperature," said Adams. "So what you need to do is shake up a few particles, heat them up, get a hold of a couple of particles, and run their vapor by the sensors."

An air conditioning system used at the front entrance of a building could help dislodge the particles and drive them towards an array of distributed sensors.

"The technology could be used anywhere you want to know if there's someone moving around with explosives, like in countries where there are constant acts of terrorism," said Adams.

He says the sensors could be mass-produced and, therefore, cost-effective. In the future, they could replace dogs as the primary detectors of explosives. "Dogs can not be strapped to packages, ventilation systems or airport walls," he said. "Dogs are complex animals that require training. They need naps, they need to eat, and they can only be at one place at one time. You can't train a dog and then multiply it by a million and have copies communicating with each other over a building network. You can do this with silicon and signal processing technology."

Expanding the Technology

The technology is still at a very early stage. But the sensors have already been able to detect the deflagration, or small explosion, of as little as 70 picograms of TNT. (A picogram equals one trillionth of a gram.)

This limit of detection is the same as that of an improved version of something called ion-mobility mass-spectrometry technology that is now used in airports. According to his calculations, Adams should be able to further increase the sensitivity of his micro-sensors by a thousand times.

So far, the new technology only works on TNT, but the sensors could also be modified to detect other explosive molecules. Perhaps a device could be developed to locate landmines.

"The technology holds great promise," said Adams. "This could be a powerful explosives detection technology and on the market in three to five years."