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Knife and guns appear visible through the t-ray technology becoz its sharp edges scatter the radiation. And yet, unlike X-rays, T-ray screeners could be used routinely on people, because the radiation is harmless. But some terahertz imagers have another ability, one not even claimed by the comic-book specs: not only can they see hidden objects, but they can tell what those objects are made of. Many explosives, including all the plastic explosives popular with terrorist groups, reflect and transmit a characteristic combination of terahertz waves that make them distinguishable from other materials, even those that might seem identical to the eye and hand. They have “standoff capability,” meaning they can see a few meters away, a very desirable feature in the security business.In just two or three years, versions that can see at a distance of tens of meters should be available, which would be a great safety boon to security personnel. There are lots of uses outside of the security arena f...