January 16, 2009
There has been a large amount of interest generated by recent work on invisibility cloaking. While the concept of invisibility has many corollaries in popular fiction which inspire the imagination, from the Harry Potter stories to Predator, researchers are taking only the first steps- both theoretical and experimental- towards these sci-fi goals. The general approach being used, which combines transformation optics with metamaterials operating in the microwave region of the electromagnetic spectrum, has developed significantly from the first publication by Schurig et al (Duke University) which focused on a cylindrical structure composed of 10 concentric resonant metamaterial rings. While this first structure succeeded in wrapping electromagnetic waves around a concealed region it suffered from high loss and narrow operational bandwidth. The most current work from Duke University, led by Ruopeng Liu, realizes a much more sophisticated metamaterial structure which is used to cloak an object resting on a ground plane. By limiting the cloaked region to the half-space above a ground plane, and using a quasi-conformal mapping technique, Liu et al have successfully increased the operational bandwidth of the cloak to cover the entire x-band and have simultaneously reduced the loss from the metamaterial dramatically. This new type of cloak is composed of thousands of uniquely shaped unit cells, as opposed to 10 for the original cloak, requiring an entirely new automated rapid design process. While all of this might seem mundane in comparison with the Romulan starship cloak from Star Trek, the advances in metamaterial design which enabled Liu et al to build the first broadband ground plane cloak will certainly lead to the development of a wide array of useful optical devices by Duke University in the near future.
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