Metamaterials composed of nano-woven invisibility cloak nanoparticles can turn the light around and bypass obstacles. How can people wrapped in metamaterials see outside without being seen? American materials scientists discover metamaterials, and Chinese physicists study anti-stealth materials, so that invisibility is no longer out of reach. Metamaterial stealth trick Fraghi Shalayev created an invisibility cloak. He knows neither magic nor magic. As an expert in materials science at Purdue University in Indiana, he knows the secret of light reflected by materials: "What if the light reflected by something doesn't reach your eyes at all?" Just like you turned your back on it "But we all know how to face things-as long as there is a mirror to help the light reflect to our eyes." However, even in the face of invisibility cloak, I still can't see it. Not only that, you will see what should be blocked by it. Because as long as no light is reflected from it to your eyes, you can't see it. "The so-called' metamaterial' is a kind of synthetic composite material with extraordinary material functions beyond the ordinary nature inherent in nature. They do not exist in nature, but are completely developed by scientists in the laboratory. Therefore, scientists try their best to endow them with extraordinary physical properties that natural substances do not have, and finally break through the limitations of some natural laws. In fact, there are indeed substances in nature that make light reflect abnormally. For example, natural opal, because of its incomplete photonic band gap structure, has strong reflectivity and emits different colors and brilliance to different angles. This photonic band gap structure also exists in butterfly wings, peacock feathers and sea rat hair, and it is they that make the originally colorless creatures show sparkling colors due to the structure's luminescence. Stealth and anti-stealth stealth materials were not discovered until Shalayev produced metamaterials by artificial atoms, relay atoms and other engineering methods. This kind of metamaterial has tiny particles arranged neatly in three-dimensional space, and their size reaches the nanometer level. Under the observation of scanning probe microscope, it presents an ordered microstructure: "When the size of microstructure is equivalent to the wavelength of light wave, it can show some optical and electromagnetic specificity. And my material structure is smaller than the wavelength of light waves. "In fact, ordinary materials look smooth anyway. For microscopic particles, just like raindrops hitting the rough walnut shell as big as the Bird's Nest Stadium, they always reflect from all angles. Only by making the structure smaller than photons, it is possible to make a streamlined body that allows light to pass through pebbles like a torrent. This is how Shalayev finished his invisibility cloak. Later, he relied on a row of tiny needles to radiate outward from the center of the spokes like a circular comb, reducing the refraction and distortion of light to almost zero, bending the light around the invisibility cloak and making people invisible. From June 5438 to October 2008 10, Shalayev revealed the secret of invisibility cloak to the world in the American magazine Science, and announced to people: "Only metamaterials can weave invisibility cloak. "However, when he was full of ambition, he seemed to ignore the fact that when the invisibility cloak covered him tightly, he also became a mouse sewn in a cloth bag. Others can't see him, and he can't see anything. Unless he digs two holes to expose his eyes, two big blinking eyes hanging in the air are enough to surprise the audience. Now, we must design a pair of matching sunglasses to make the invisibility cloak completely invisible. If people can't see the inside of sunglasses, it's like stealth technology; Then, it can be called anti-stealth technology, so that people wearing sunglasses can see the outside clearly. In fact, Shalayev's unsolved anti-stealth technology has long been concerned by other scientists. From June 5, 2007 to 10, Dr. Chen of Shanghai Jiaotong University published his research structure of anti-stealth technology in the American Journal of Applied Physics. He and his colleagues designed a material whose optical properties perfectly match the invisibility cloak: "In technical terms, it is an anisotropic negative refractive index material, and its impedance matches the positive refractive index of the invisibility cloak. "In fact, its principle is a bit like installing a silencer on a pistol: the peaks of sound waves with the same frequency are used to fill the valleys of sound, and finally the vibration of the air is completely offset. In fact, as long as Shalayev sticks such anti-invisibility material on the invisibility cloak, some light can penetrate according to the specified path, thus partially offsetting the effect of the invisibility cloak. The anti-stealth technology studied by Chen and his colleagues destroyed the stealth performance in the invisibility cloak and initially solved the communication problem inside and outside the invisibility cloak. In fact, Chen Ye is doing research on stealth technology, but not for making clothes. In his idea, we can use stealth technology to design a hidden door: putting the material made of stealth technology in the middle of the door can make the door look like the surrounding wall; The people inside the door can observe every move of people outside through anti-stealth technology. This technology may be developed in the military field, so it is no wonder that the former US military attache to China quoted this example on the website of US Defense News, exclaiming that China will pose a great threat to the stealth weapons of the United States in the future.