Metamaterials are to materials science what quantum theory is to physics. Metamaterials seem to do magical things and hold much promise, but you have to throw out half of what you thought you knew about reality just to understand them.
John Hunt, a graduate student in Duke University working with metamaterials, defines them as artificial materials that perform in ways not found in nature. Hunt and his colleagues are creating metamaterials that don’t seem to play by the laws of physics, and one result could be hallways that undress you with their myriad metamaterial “eyes.”
Every material has a set of properties: how it conducts electricity, refracts light, etcetera. But metamaterial scientists are changing those properties, sometimes in amazing ways. (Here’s a deeper explanation.)
For example, in 2006, Duke University researchers used metamaterials to create a so-called invisibility cloak. They were able to make an object almost invisible in microwave light, which is used in radar to detect things like aircraft.
Today, Hunt and his colleagues at Duke’s Center of Metamaterials and Integrated Plasmonics say they can create sheets of thin metamaterials capable of searching people with microwaves, radically simplifying how airport personnel search for prohibited items. Hunt is the lead author of an article on this innovation in the Jan. 18 issue of Science.
Is this a touch less glamorous than an invisibility cloak? Maybe, but the proposed sensor would be no less exotic. While it would use microwaves, which are an invisible segment of light, the sensor has no lens, nor does it include any moving parts.
In fact, the sensor is a thin layer of copper etched with very small squares, each “tuned” to a different microwave frequency. Laminated, the metamaterial-based sensor would be one-sixteenth of an inch deep, and it would be deployed in sheets of almost any size, covering halls, buildings, vehicles—you name it.
This would be a major security advance as microwaves, at levels far lower than those used in microwave ovens, can pass effortlessly through clothing.
Security personnel around the United States already use a type of microwave, in a process called millimeter imaging, to find objects hidden under clothes.
The problem is that these systems require a person to stand still in a booth while a motorized microwave transceiver moves in front of them. Any movement by a person causes the image to blur, like a camera used in a dark room without a flash.
From a physical-health standpoint, these systems are considered safe. They don’t create the kind of radiation that causes cancer, for instance, according to Hunt.
The technology demonstrated by Duke researchers does away with a single scanning detector, and even manages to lose the booth. Every inch of their metamaterial sensor would send microwaves that would read the reflections continuously, soundlessly, invisibly and without a touch. Images would be sent from the sensor to a computer to be analyzed by an operator.
There’s no getting around the fact that anyone using this technology would be recording video of naked people walking around, but, that’s another matter altogether.
Interestingly, Duke’s earlier innovation, the cloaking device, could conceivably be a challenge for this newer development.
In that experiment, a beam of invisible microwaves was pointed at solid column wrapped in a metamaterials film. The film prevents most of the light from reflecting. Instead, it channels it so that it slides around both sides of the column, rejoins at the back side, and continues on almost as if nothing had interrupted it.
You can think of how eight lanes of traffic, all headed the same direction, will flow around an errant construction barrel between lanes four and five (minus the swearing and rubbernecking).
The metamaterials not only reflect exceedingly little of the microwaves, they also leave only a small microwave shadow behind the column. That makes the object largely invisible to that frequency of light, an intriguing trick for those trying to hide bombers and tanks from microwave radars.
The fate of the invisibility cloak is uncertain, but the metamaterial security device is already being shopped around.
Hunt said that it would be cheaper to use than millimeter imaging in airports because it’s simpler, has no moving parts and is more compact. He declined to say how much less expensive, as there are discussions underway about commercializing it.
“I can say that in some applications, the savings would be a factor of 10 over current technology,” Hunt said.
Hunt said that these thin panels could be wrapped around cars to warn of potential collisions, even in the presence of dust and snow, when conventional systems are more likely to fail. They could be put on the bottom of aircraft, too, to see through weather, netting, tents and the like.
“There are more fanciful ideas, too,” Hunt said. “You could put it over a soldier’s body armor, for example. But we’re not targeting that right now.”