22 October 1999

An underwater bomb detector

by Kate Melville

A new portable chemical sensor system about the size of a soccer ball promises a new way of detecting and identifying even the smallest traces of explosives under water.

Developed by scientists at the US Department of Energy, the system consists of separate components that take a sample of liquid drawn from water surrounding submerged objects containing explosives. Molecules of interest are extracted and de-absorbed into an Ion Mobility Spectrometer (IMS), that identifies the explosive based on its chemical signatures.

Ron Woodfin, project manager said that ,"This system will fill a unique niche. Unlike the commonly used anomaly detectors, such as metal detectors or ground-penetrating radar, the IMS analyzes the material's actual molecular makeup to identify the explosive type. Its best role is not as a search device, but as a classifier or identifier."

Woodfin's team miniaturized the IMS, reducing it from a 30-pound device to a five-pound unit that fits in a person's hand. The complete sensor system - including IMS, concentrator, computer, display and batteries, will weigh no more than 20 pounds and be about the size of a soccer ball.

Experiments were conducted at the US Navy facility at San Clemente Island, in the waters near Panama City and in Halifax, Nova Scotia.

The system relies on several factors: 1 All ammunitions or unexploded ordnance emit molecules of explosive chemicals

2 That a certain type of polymer fiber (polydimethysiloxane/divinylbenzene copolymer) attracts specific types of explosive molecules in cool temperatures.

3 Molecules lose their attraction to the fiber when it is heated slightly, causing them to rapidly de-absorb.

To date the system can only work outside water, but the team are developing a new waterproof packaging so that it will function under water. The currently way of seeking out explosives on the ground and in water is by using anomaly detectors that identify objects not expected in the environment. But, the IMS system exploits a different principle as it looks for actual explosive materials, thereby eliminating the number of false alarms. Either it's an explosive or it's not.

At this stage the project is a prototype only, however the developers are confident that the prototype can quickly be scaled up to full scale development.