實現隱身一直是人類身自古以來的夢想：從《西游記》中孫大圣的隱身術到《哈利波特》中哈利的隱身斗篷，這一夢想受到全世界人們的廣泛關注。隱身在狹義上僅僅指用眼睛看不見，更廣義的隱身則不僅僅局限于眼睛，而是泛指使用某一探測手段（如雷達、聲吶）無法探測到，就稱之為在這種探測手段下隱身。實現隱身在軍事上有重要的應用，比如隱身飛機、隱身艦艇等可以悄無聲息的接近目標，因此隱身技術成為各國在軍事領域的研究焦點。隨著科學技術的發展，各類隱身衣在許多不同物理場中成功實現，并且持續成為不同領域的研究熱點。隱身衣的原理是什么？都有哪些不同的隱身衣？它們是怎樣被實現的？如果有朝一日可以穿上隱身衣，你打算給親朋好友一個怎樣的驚喜（驚嚇）呢？假如你對這些問題感興趣，這篇文章就是為你精心準備的 。

　　Realizing invisibility has always been a dream of humanity since ancient times: from Sun Dasheng's invisibility technique in Journey to the West to Harry's invisibility cloak in Harry Potter, this dream has received widespread attention from people around the world. In a narrow sense, invisibility refers only to the inability to see with the eyes, while in a broader sense, invisibility is not limited to the eyes, but generally refers to the inability to detect using a certain detection method (such as radar or sonar), which is called invisibility under this detection method. The implementation of stealth technology has important military applications, such as stealth aircraft, stealth ships, etc., which can approach targets silently. Therefore, stealth technology has become a research focus in the military field of various countries. With the development of science and technology, various types of invisibility cloaks have been successfully implemented in many different physical fields and continue to become a research hotspot in different fields. What is the principle of invisibility cloak? What are the different invisibility cloaks available? How are they implemented? If one day you could wear a invisibility cloak, what kind of surprise (shock) would you give to your family and friends? If you are interested in these issues, this article has been carefully prepared for you.

　　隱身衣的工作原理

　　The working principle of invisibility cloak

　　欲要實現隱身，讓我們先了解一下為什么我們可以看見。一種比較普遍的情況是：物體反射或散射的光線進入我們的眼睛，從而可以看見物體

　　To achieve invisibility, let's first understand why we can see. A common situation is that the light reflected or scattered by an object enters our eyes, allowing us to see the object

　　知道了這個原理，不禁讓人生出一個大膽的想法：如果一件衣服可以把光線完全吸收而不反射或散射任何光線，是不是就可以隱身了呢？眾所周知，黑色可以很好地吸收光線，穿一件超級黑色的斗篷覆蓋全身

　　Knowing this principle, one cannot help but have a bold idea: if a piece of clothing can completely absorb light without reflecting or scattering any light, can it become invisible? As is well known, black can absorb light very well, wearing a super black cloak to cover the whole body

　　計隱身斗篷的基本原理是使光線的傳播不受物體影響。

　　The basic principle of the invisibility cloak is to prevent the propagation of light from being affected by objects.

　　原理雖然簡單，實現卻是難題：因為絕大多數物體都是不透明的，光線無法穿透它們繼續傳播。怎樣讓光線不受物體影響呢？目前的基本思路是設計一層特殊結構的材料包裹物體，而這層特殊材料可以讓光線繞過物體并沿著原來的傳播路徑繼續傳播

　　Although the principle is simple, implementation is a challenge: because the vast majority of objects are opaque, light cannot penetrate them and continue to propagate. How to prevent light from being affected by objects? The current basic idea is to design a layer of special structured material to wrap around an object, which can allow light to bypass the object and continue to propagate along its original path

　　如何讓光線繞過物體？普遍的做法是先從理論上計算所需的折射率，然后尋找具有這種折射率的材料從實驗上實現。一種重要的理論計算方式是2006年倫敦帝國學院的John Pentry教授及其合作者提出的變換光學理論。其關鍵在于利用坐標變換的方式將一個體積為零的點變換成一個體積非零的區域，并將物體隱藏在這個特殊區域中。由于體積為零的點對光線傳播不會產生任何影響，它變換出來的特殊區域也會有類似的性質，從而實現光線繞過物體的效果，具體折射率參數可以從坐標變換中求出

　　How to make light pass around objects? The common practice is to first calculate the required refractive index theoretically, and then find materials with this refractive index to experimentally implement. An important theoretical calculation method is the transformation optics theory proposed by Professor John Pentry and his collaborators at Imperial College London in 2006. The key is to use coordinate transformation to transform a point with zero volume into a region with non-zero volume, and hide the object in this special region. Due to the fact that a point with zero volume has no effect on the propagation of light rays, the special area it transforms will also have similar properties, thus achieving the effect of light rays bypassing objects. The specific refractive index parameters can be obtained from coordinate transformation

　　所以隱身衣的本質就是，制造一個光線會繞過的區域并把物體隱藏其中，從而實現隱身。這種方式已經可以在實驗中實現，比如用幾個透鏡制造出一個光線會完全繞過的區域，當把物體放入這個區域時外界完全無法探測到

　　So the essence of invisibility cloak is to create an area where light will pass through and hide objects, thereby achieving invisibility. This method can already be implemented in experiments, such as using several lenses to create an area where light will completely bypass, and when an object is placed in this area, the outside world cannot detect it at all

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