Useful cloaking device is one step closer to reality
1/3/2007 3:00:05 PM, by Matt Ford
Last October saw a major breakthrough in an area of research that, until very recently, was squarely in the realm of science fiction—cloaking technology. An article published in Science by a team of researchers at Duke University discussed how they had created a device that was able to cloak simple objects from microwave radiation. While this was a stunning announcement, it wasn't what many Trekkies would think of off the top of their head. The Duke team used metamaterials—synthetic materials whose physical structure interacts with electromagnetic (EM) waves in ways that natural materials do not—to essentially guide microwave radiation at a given frequency around a cavity that held the object. If one looked at it, they would still clearly see the entire setup as microwaves have a much longer wavelength than visible light. Another shortcoming was that while the cloak kept the material invisible from outside viewing, it did nothing to keep EM radiation originating from inside the cavity from getting out. This means that anything emitting EM radiation—heat from a person's body, RF signals from a cell phone/radio, or even a simple flashlight—would be instantly detectable. Now, some new mathematics suggests a way one can get around this issue.
The mathematics behind this new cloaking were actually first published in 2003 by a team of mathematicians working on electrical impedance tomography (EIT), a medical imaging technique that uses electrical voltages to generate images of structures inside the human body and can be used to look for tumors. While doing this work, Professors Greenleaf, Lassas, and Uhlmann showed that if they allowed the electrical conductivity function (which can be determined from EIT measurements) to be a tensor function—that is, allowing the function to have a directionality to it—it would be mathematically possible to have structures with differing conductivities (e.g., a tumor and normal tissue) be indistinguishable or invisible to EIT measurements. However, they concluded that this was highly improbable to occur on the surface of a tumor, and did not give it much thought beyond it being a mathematical curiosity.
Fast forward to the summer of 2006. A research collaboration between Duke University, Imperial College, and St. Andrew's University published a paper where this mathematical curiosity appeared anew. Their Science article discussed the mathematics behind a device that could be used to cloak an object to a specific frequency of EM waves. Drawing on their previous experience with the mathematics behind this phenomenon, the team of Greenleaf, Kurylev, Lassas, and Uhlmann looked at how they could improve on the theories published over the summer. In order to do this, they had to answer the question of "What is happening within the cloaked region?" When the Duke team published that they had actually built a working cloaking device, the mathematicians felt it was even more important to understand the details of how this phenomenon worked.
In order to gain an in-depth understanding, the team of mathematicians had to solve a set of equations: the Helmholtz equation, which dictates how light propagates, and Maxwell's equations, which govern how electric and magnetic fields interact. The solutions to the Helmholtz equation were well-behaved, but trouble arose when the team tried to solve Maxwell's equations for the cloaking device. If the device was passive, such as the simple objects used in the experimental study, everything would work out fine; however, when the devices emitted EM radiation the predicted behavior of the device would be wonky. They found that the EM fields would become infinite at the border of the cloak, destroying the invisibility. They also found the curious effect that someone inside the cloak—as it was built—would see a perfect mirror no matter what direction they looked. The mathematicians were able to find a way around this problem. They suggest that by adding in a second layer of conductive material that this problem (the infinite fields) could be solved.
With this new mathematics derived—which can be read on arXiv for free for the mathematically inclined—the theory exists for a device to be built that can cloak an actively emitting object at all wavelengths of electromagnetic radiation. However, that is theory—the reality is very different. In reality a device may be able to cloak something at a very narrow band of wavelengths; e.g., if it could be cloaked to green light, it would still be visible in all other colors. This is often the case with theory-leading experimental work, but here Prof. Greenleaf (Math) and Prof. Smith (Experiment) have gotten together to collaborate on real world improvements that can be applied to the already existing device, or future revisions of it using the new theory that has been derived. Collaborations across disciplines such as this show how pure science or mathematics that may not have an obvious application at first can be turned into real world (or out of this world) applications that have the potential to change the world as we know it.
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I read about that a few months ago. Its some really crazy stuff. Itd be so cool having technology like that redily available.
The ability to smoke anywhere without being seen! lol
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When they took the 4th Amendment away I was quiet because I didnt deal drugs//When they took the 6th Amendment away I was quiet because Id never been arrested//When they took the 2nd Amendment away I was quiet because I didnt own a gun//Now they took the 1st Amendment and all I can do is be quiet...
Marijuana
01-04-2007, 12:37 PM
Cloaking Device Development 
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