One of the Department of Homeland Security’s 12 academic centers of excellence is seeking to adapt millimeter wave technology currently used at airport screening stations to detect suicide bombers at standoff distances.
Person-borne improvised explosive devices, which are shaped from a variety of metals and concealed under clothing, are difficult to detect. Airport-style scanners and pat-downs are of limited value, given that a detonation could still claim many victims.
DHS’ Science and Technology Directorate wants to stop suicide bombers before they reach their intended target.
“For the suicide bomber problem we need a high performance radar system that can send out very specific types of signals a half a football field away and identify specific features under clothing,” Carey Rappaport, professor of electrical and computer engineering at Northeastern University, said in a statement. Northeastern is the location of the ALERT Center, an acronym that stands for Awareness and Localization of Explosives Related Threats. This center of excellence focuses on the detection, mitigation and response to explosives-related threats.
The center ultimately selected a millimeter wave based system as the best available technology, said Rappaport. Millimeter waves are a subset of the microwave band, which in turn is part of the larger radio wave band. These waves operate within a frequency range of 30 to 300 GHz. Unlike X-rays, millimeter-waves are non-ionizing and universally considered non-carcinogenic. They don’t have the bad reputation of the backscatter detectors that the Transportation Security Administration recently pulled from airports.
Once an exotic technology only used by the military, millimeter wave hardware is now coming down in price, Rappaport said. HXI, a supplier of millimeter-wave products, components and sub-systems, is providing radar modules for the project.
To increase the field of view and pick out fine-depth features, the millimeter wave radar sensor needed to be multi-static. Such systems contain multiple radar components located in separate locations with a shared area of coverage. The spatial diversity allows for different aspects of a target to be viewed simultaneously, and the data to be fused together to generate an image with high resolution, Rappaport said.
However, the concept of multiple radars in different, far apart locations creates challenging triangulation issues when attempting to focus on a single individual within a crowd, he said.
Instead, the multi-static system would involve multiple radars mounted with as much distance as possible, but still designed to fit on a single vehicle roughly the size of a delivery truck. With several meters of separation between antennas, the system could effectively distinguish features on pedestrians at a range of 50 meters, Rappaport said.
With a phased array, the system will be able to focus on a specific small-scene area of one person or a crowd of people, Rappaport said. Like the airport scanners, it can detect objects that don’t meet the smooth contours and characteristics of skin such as metallic objects, or those that meet other characteristics of person-borne IEDs.
“By adjusting how much signal goes to each antenna, you can electronically steer a beam back and forth,” said Rappaport. “In doing so, you can bounce between an individual, the person next to him and maybe three or four people off to the side.” Photo Credit: Thinkstock