隐形斗篷可望通过微型天线实现

几年前，已经有许多的研究结果证实能够从金属材料中建构出隐形斗篷──透过金属与绝缘体的组成，可让信号在物体之间进行传输。然而，尽管其后仍持续投入开发，但却仍无法使这项研究走出实验室。如今，加拿大多伦多大学(University of Toronto)展示了一种采用与降噪头戴式耳机相同原理的新开发途径，可望使隐形斗篷实现商用化。 “我们也曾试着用超颖材料来打造隐形斗篷，但较大的问题是这种材料必须要够厚才行，”多伦多大学教授George Eleftheriades表示，”所以，当你想掩饰掉一个大型物体时，隐形斗篷就会变得非常巨大且十分笨重── 即使超颖材料是一个可让物体传输的理想概念，但并不实用。”

多伦多大学教授George Eleftheriades(左)与博士候选人Michael Selvanayagam展示开发隐形斗篷的新方法。
Source：University of TorontoIHSesmc

因此，Eleftheriades决定不再采用超颖材料，他在待隐形的物体周围装上微型天线，并调整至可让物体发生隐藏或伪装的同一频段。天线接着会发出一种信号来抵销反射信号，从而有效地伪装该物体。在实验中，研究人员们能以12磁偶极回路的天线数组有效地隐形金属圆柱。透过改变控制电流施加于每一数组元 素的重量，金属圆柱就能以向前或向后的方向有效地隐形。此外，透过调整各种配置的重量，他们还能够展现物体如何伪装成各种不同的尺寸大小或出现在不同的位 置，这是过去采用超颖材料从未被证实的新发现。 “透过天线，你不必在物体周围改变传输无线电波──天线可自动侦测输入信号并 反馈一个可用于抵消的信号，这有点像是降噪耳机的原理，”Eleftheriades解释，“这是一种能够付诸实际应用的方式，对于电子工程师而言，也是一个完美的途径，因为我们能够整合电子与控制，使其得以让物体隐形，我们能改变其散射截面，使其得以看起来更小或类似不同材质，或甚至改变其所在位置等 ──这些都可透过调整微型天线而实现。” 该研究小组还包括博士候选人Michael Selvanayagam，他们声称这种基于天线的隐形斗篷解决方案，由于采用的平面环形天线可印刷在像皮肤一样薄的物体上，因而能让物体看起来可扩展到相当大，也可以做得很薄。 未来，研究人员们打算进一步试验采用天线数组侦测输入信号的自适应电子组件，然后再相应地调整其重量。这种自适应的方法也可以根据用户或系统的需要而实时改变物体外形。 除了隐藏和伪装军事载具与侦测飞机以外，研究人员们希望该系统也能应用在民用领域，如透过隐藏让信号更自由地传送，从而减少因蜂窝基站产生的干扰。从理论上来看，在纳米天线技术日趋完善后，这种方法应该也适用于可见光波段。 本文授权编译自EE Times，版权所有，谢绝转载 编译：Susan Hong 参考英文原文：Invisibility Cloak Comes to Life，by R. Colin Johnson

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{pagination} Invisibility Cloak Comes to Life R. Colin Johnson PORTLAND, Ore. -- A few years ago, a flurry of research results demonstrated that invisibility cloaks could be constructed from meta-materials -- assemblies of metals and insulators that channel signals around objects. However, despite continued development efforts none have made it out of the laboratory yet. Now an approach to invisibility cloaks that uses the same principle as noise-canceling headphones has been demonstrated at the University of Toronto, for which the researchers claim commercialization is more feasible. "We tried to build invisibility cloaks using metamaterials, but the big problem was that they have to be very thick," professor George Eleftheriades told us. "So when you want to cloak a big object the invisibility cloak becomes very large and bulky -- metamaterials are just not very practical, even though its a very elegant concept to channel waves around an object." Professor George Eleftheriades (left) and doctoral candidate Michael Selvanayagam showing their new approach to invisibility cloaking. (Credit: Marit Mitchell) SOURCE: University of Toronto Instead of using metamaterials, Eleftheriades's approach surrounds the object to be cloaked with tiny antennas tuned to the frequency band in which the cloaking is to occur, such as radar. The antennas then send out a signal that cancels out the reflected signal -- effectively cloaking the object. In experiments, the researchers effectively cloaked an aluminum cylinder with an array of 12 magnetic-dipole loop antennas. By changing the weights controlling the current applied to each element of the array, the cylinder was effectively cloaked in the forward and backward directions. And by adjusting the weights in various configurations, they were able to demonstrate how the object could be disguised to be a different size or in a different location, feats that were never demonstrated by meta-material cloaks that merely channel signals around objects. "With antennas, you don't have to channel waves around the object -- the antennas just adaptively sense the incoming signal and feedback a signal that cancels it, sort of like noise-canceling headphones," Eleftheriades told us. "This is the way to do it practically, and for electrical engineers this is a perfect way because we can hook up electronics and control them to make the object invisible, we change its scattering cross-section to make it look smaller or of a different material or even displaced in space -- all by adjusting the weights on these tiny antennas." The research team, which included doctoral candidate Michael Selvanayagam, also claimed that its antenna-based solution to invisibility cloaks is scalable to large objects and can be made very thin -- by using flat loop antennas that could be printed on the object like a skin. For the future, the researchers are experimenting with adaptive electronics that first uses the antenna array to sense the incoming signal, then adjusts its weights accordingly. This adaptive approach could also allow an objects profile to be changed in real time at the user's or system's discretion. Besides hiding and disguising military vehicles and surveillance aircraft, the researchers hope their system can also be used in civilian applications, such as reducing interference caused by cellular base stations by cloaking them to allow signals to more freely pass nearby. Theoretically, the approach should also work at visible wavelengths, once the necessary nanoscale antenna technologies are perfected.