幾年前，已經(jīng)有許多的研究結(jié)果證實(shí)能夠從金屬材料中建構(gòu)出隱形斗篷──透過(guò)金屬與絕緣體的組成，可讓信號(hào)在物體之間進(jìn)行傳輸。然而，盡管其后仍持續(xù)投入開(kāi)發(fā)，但卻仍無(wú)法使這項(xiàng)研究走出實(shí)驗(yàn)室。如今，加拿大多倫多大學(xué)(University of Toronto)展示了一種采用與降噪頭戴式耳機(jī)相同原理的新開(kāi)發(fā)途徑，可望使隱形斗篷實(shí)現(xiàn)商用化。 “我們也曾試著用超穎材料來(lái)打造隱形斗篷，但較大的問(wèn)題是這種材料必須要夠厚才行，”多倫多大學(xué)教授George Eleftheriades表示，”所以，當(dāng)你想掩飾掉一個(gè)大型物體時(shí)，隱形斗篷就會(huì)變得非常巨大且十分笨重── 即使超穎材料是一個(gè)可讓物體傳輸?shù)睦硐敫拍?，但并不?shí)用?！?

多倫多大學(xué)教授George Eleftheriades(左)與博士候選人Michael Selvanayagam展示開(kāi)發(fā)隱形斗篷的新方法。
Source：University of TorontoFIzesmc

因此，Eleftheriades決定不再采用超穎材料，他在待隱形的物體周?chē)b上微型天線(xiàn)，并調(diào)整至可讓物體發(fā)生隱藏或偽裝的同一頻段。天線(xiàn)接著會(huì)發(fā)出一種信號(hào)來(lái)抵銷(xiāo)反射信號(hào)，從而有效地偽裝該物體。在實(shí)驗(yàn)中，研究人員們能以12磁偶極回路的天線(xiàn)數(shù)組有效地隱形金屬圓柱。透過(guò)改變控制電流施加于每一數(shù)組元 素的重量，金屬圓柱就能以向前或向后的方向有效地隱形。此外，透過(guò)調(diào)整各種配置的重量，他們還能夠展現(xiàn)物體如何偽裝成各種不同的尺寸大小或出現(xiàn)在不同的位 置，這是過(guò)去采用超穎材料從未被證實(shí)的新發(fā)現(xiàn)。 “透過(guò)天線(xiàn)，你不必在物體周?chē)淖儌鬏敓o(wú)線(xiàn)電波──天線(xiàn)可自動(dòng)偵測(cè)輸入信號(hào)并 反饋一個(gè)可用于抵消的信號(hào)，這有點(diǎn)像是降噪耳機(jī)的原理，”Eleftheriades解釋?zhuān)斑@是一種能夠付諸實(shí)際應(yīng)用的方式，對(duì)于電子工程師而言，也是一個(gè)完美的途徑，因?yàn)槲覀兡軌蛘想娮优c控制，使其得以讓物體隱形，我們能改變其散射截面，使其得以看起來(lái)更小或類(lèi)似不同材質(zhì)，或甚至改變其所在位置等 ──這些都可透過(guò)調(diào)整微型天線(xiàn)而實(shí)現(xiàn)?！? 該研究小組還包括博士候選人Michael Selvanayagam，他們聲稱(chēng)這種基于天線(xiàn)的隱形斗篷解決方案，由于采用的平面環(huán)形天線(xiàn)可印刷在像皮膚一樣薄的物體上，因而能讓物體看起來(lái)可擴(kuò)展到相當(dāng)大，也可以做得很薄。 未來(lái)，研究人員們打算進(jìn)一步試驗(yàn)采用天線(xiàn)數(shù)組偵測(cè)輸入信號(hào)的自適應(yīng)電子組件，然后再相應(yīng)地調(diào)整其重量。這種自適應(yīng)的方法也可以根據(jù)用戶(hù)或系統(tǒng)的需要而實(shí)時(shí)改變物體外形。 除了隱藏和偽裝軍事載具與偵測(cè)飛機(jī)以外，研究人員們希望該系統(tǒng)也能應(yīng)用在民用領(lǐng)域，如透過(guò)隱藏讓信號(hào)更自由地傳送，從而減少因蜂窩基站產(chǎn)生的干擾。從理論上來(lái)看，在納米天線(xiàn)技術(shù)日趨完善后，這種方法應(yīng)該也適用于可見(jiàn)光波段。 本文授權(quán)編譯自EE Times，版權(quán)所有，謝絕轉(zhuǎn)載 編譯：Susan Hong 參考英文原文：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.