APS News

New Device Tells Bombs from Harmless Trash

Cleaning up a region after a bloody conflict can often take years or decades. One of the biggest long-term challenges to make an area safe are unexploded bombs, landmines and munitions. These often get buried and stay hidden for years until unearthed by a plow or other means.

“There are tens of millions of acres that have been polluted with bombs that haven’t been exploded,” said Eugene Lavely of BAE systems.

He is part of a team developing a device to find these hidden dangers. Team members presented their results at the March Meeting. The device uses what they call time domain electromagnetic (TDEM) induction methods to find dangerous buried munitions, and importantly, to differentiate them from benign buried garbage.

“Detection is not the biggest problem. The main problem is discrimination,” Lavely said. “It becomes economically unfeasible to dig up every detection.”

Lavely’s device is essentially made up of 25 coils on a square platform that can be pushed across the ground. The apparatus looks a bit like a giant lawnmower about the size of a ping-pong table. Electric pulses are sent through the coils, which generate magnetic fields. These magnetic fields induce a slight current in any buried piece of metal the device rolls over. The buried object likewise emits its own signature magnetic field which can be picked up by detector coils. It’s the same principle that a beach comber’s metal detector uses.

“Think of these as fancy metal detectors on the beach,” Lavely said.

The TDEM takes the detection one step farther. Using the multiple coils, the device measures not just the presence of another magnetic field, but also the shape of one as it decays. This is key to identifying whether a buried object might be a dangerous unexploded bomb, or a harmless piece of trash. By analyzing the way the field decays, the device can characterize the buried object’s conductivity, shape and size, all important characteristics for identification. The operator of the device can compare the signature of the field picked up by the device to the signatures of known munitions, and make a determination as to what might lie under the surface.

Lavely said that even improvised explosive devices, or IEDs, the scourge of forces in Iraq and Afghanistan, can be picked up by the device.

“IEDs have very well established forms,” Lavely said, adding that the downside is that one needs to be close to an object in order to detect it.

Lavely’s team has already done tests on dummy mortar rounds with much success. They have also tried the device out on a hollow sphere, but he says that they still need more refinement to better identify if a metal object is hollow, another key characteristic of unexploded bombs.

The device also needs further work to reduce its size. The 25 coils are spread over a wide base, making it impractical for forests and other constricted environments.


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