Greater security with EM coil

A research scientist applies the EM coil to the Russian AT-400 weapons component storage container to verify that the container's contents are as declared and have not been modified. The information is generated in less than one minute by a coil impedance measurement, monitored on the screen display shown at left. Click here for a high resolution photograph.

When are a handshake and a promise not sufficient? When we're talking about bilaterally reducing nuclear weapons. An electromagnetic coil system developed at Pacific Northwest National Laboratory adds truth serum to treaty verification by narrowing the uncertainty for what's inside a sealed container.

The device noninvasively supplies information about the physical properties of metallic items stored inside sealed containers without revealing design parameters that may be sensitive. "The EM coil does not reveal specific attributes of the metal, but rather a measurement response consistent with a particular metal, say aluminum, of a certain size and shape," said PNNL's Ronald Hockey, who is the principal investigator for the EM coil project. "In a treaty verification setting, the EM coil could be combined with other basic measurements to provide just enough information to determine whether the contents of a container are consistent with the declared contents without revealing detailed design information."

The converse, and sometimes more useful application of the EM coil, is providing evidence that a particular item is not present in a sealed container. For example, it may be necessary to distinguish between radioactive elements being stored in either their metallic or oxide state, both having the same nuclear properties. The EM coil can distinguish between these two states because it is particularly sensitive to the metallic state and virtually insensitive to the oxidized form of the same element.

Traditionally, investigators have used nuclear sensors to identify radioactive material based on the properties of its nuclear structure. The EM coil responds to the electronic properties of materials, rather than their nuclear structure. With the additional information the EM coil offers, it becomes easier to discern between two materials with the same nuclear signature but different electronic signatures.

The EM coil consists of a wire that's coiled around a cylindrical form. The device, which surrounds the container, generates a low-frequency magnetic field, which interacts with the contents of the sealed container. This interaction changes the coil's electrical impedance, producing a measurement commensurate with the geometry and type of metal inside the container.

The EM coil technology requires only seconds to evaluate a single container, making it suitable for a high-speed inspection environment, where hundreds of items must be inspected daily.

In addition to treaty verification, the EM coil concept offers a solution to many other inspection-related problems. It can be used for different applications by modifying the sensor to meet specific objectives. For example, its high-speed measurement capability makes it a candidate for automatically sorting containers according to their potential threat, flagging potentially dangerous situations for further investigation.