Cloak of invisibility myth or reality research work. The invisibility cloak becomes reality
An amazing video has appeared on the Web in which a Chinese inventor demonstrates his creation - an invisibility cloak. Earlier we told why Muslims and Jews, the site reports.
The invisibility cloak sparked controversy on social media
The quantum cloak is made of a transparent material that can reflect light.
The video was watched by more than 20 million people, several thousand of which left their various comments. While some are shocked by such an invention, others are sure that all this is due to special effects.
So, an employee of Quantum Video is sure that the invisibility cloak does not exist, and for the filming of this video, ordinary green fabric was used, which was edited using a certain program. This is often used during the filming of action films and science fiction.
However, Chen Shikyu, deputy head of the Criminal Investigation Department, is pleased with this invention, noting that the invisibility cloak will help the army, since the soldier in it will not only not be seen by the enemy during the day, but also through a night vision device. The only thing that worries the official is what will happen if the invention falls into the hands of enemies.
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Scientists from several countries are close to creating such a material that makes a person or any other object invisible to others. However, in the current conditions, it is not enough to create a visual trick for the human eye. A real invisibility cloak must mask an object in dozens of different ways. And scientists-inventors are working on it.
At one time, the Japanese tried to solve the problem of creating an invisibility cloak, as they say, on the forehead. They created a special cloak with hundreds of mini video cameras on one side and hundreds of small screens on the other. When activated, the cameras capture the space behind the hidden object and transmit the image to the screens in front of it. As a result, an object covered with such a cloak is, as it were, covered with a television picture of the void. However, this path is a dead end. And the very idea of an invisibility cloak was replaced by the idea of a television illusion.
In parallel, scientists from a number of countries are looking for and creating materials with special properties that should work with light and take into account its nature. Scientists from Singapore presented their version of invisible technologies. At the TED conference in Los Angeles, they showed a transparent cube. Optical calcite crystals make it possible to refract rays in such a way that the object behind the cube becomes invisible. Singaporeans, however, are sure that calcite will most likely be used to improve the quality of transmission over fiber optics, as well as in the creation of new digital cameras.
The wave nature of light prompted scientists to create a material that these waves would be forced to flow around. It allows the waves to visually hide objects, creating the effect of invisibility. In this case, the rays should converge again behind the object, retaining their original direction. This requires the use of metamaterials with unusual properties. The first such materials appeared in 2006. Scientists at the University of Texas say they have created a version of this material, which they call "metascreen". This ultra-thin and flexible material is created from strands of copper and polycarbonate film.
However, Texas took a different approach. The waves do not flow around the material, the ultrathin film scatters and neutralizes ultrashort waves: the material itself is thinner than the wavelength. While such a cape makes relatively small objects invisible. During the experiments, scientists hid an 18-centimeter-high ceramic cylinder, which was wrapped in a "meta-screen". The object became invisible when viewed through a microwave scanner. It is microwave electromagnetic radiation with a wavelength from 1 mm (frequency 300 GHz) to 1 m (300 MHz) that is used in most radars.
However, by developing the model, Texas scientists will be able to shield the object from visible radiation, which is similar to microwaves and infrared waves. Most likely, this approach will become the main one in the creation of modern camouflage materials. The Massachusetts Institute of Technology is working on a similar material that affects the electromagnetic field. So far, only a computer model of special nanoparticles has been created.
It is assumed that the material created from them will not force the particles to flow around it, but will simply let the electrons pass through itself, as if the obstacle does not exist at all. And in this case "invisibility" is rather an additional property. With this technology, it is supposed to improve the materials used in thermoelectric devices, combining in them the qualities of high electrical conductivity with low thermal conductivity.
Also, these developments can be used to create switches in electronic environments. And by the way, the invisibility of an object to the naked human eye in modern conditions is worth little in itself. An object can be illuminated by waves of another type, calculated from the radiation of a mobile phone, etc. There are enough working technical devices of various types.
Therefore, it becomes relevant to create a material that can mask the carrier in dozens, if not hundreds of parameters. Something similar, but so far based on their own modest capabilities, is being created by designer Adam Harvey from New York. He is trying to use the growing concern in the United States about the use of drones for total surveillance of people. Last year, in a lawsuit filed by the Electronic Frontier Foundation (EFF), the US government acknowledged the existence of 64 operating drone bases in the country.
The ability to become invisible at will for centuries has been one of the top three greatest human desires, along with flying and the ability to see what is far away. Today, these are no longer stories from a fairy tale: we already have planes, orbital stations, television and the Internet. Scientists started creating a real invisibility cloak only a quarter of a century ago, but in such a short period of time they managed to find several technical solutions to this problem at once.In order to understand what “invisibility” is, you must first understand what “visibility” is. In a vacuum or in a transparent medium, light rays propagate in a straight line. However, if the beam meets an obstacle, it is transformed - reflected, refracted, absorbed. Once in the human eye, such a modified beam allows us to "see". The foregoing is true for opaque objects, but passing through thin glass, the light ray undergoes almost no changes and therefore the barrier is practically invisible.
Imagine a thin jet of water falling vertically downwards. Substitute a table tennis ball under the jet. Water, hitting the ball, will flow down on its surface, and from below it will again turn into the same thin stream. And looking at it, you might think that the jet did not meet any obstacle. So, to create an invisibility cloak, it is necessary to make sure that any beam that falls on the human body does not transform, but continues its path in the same direction, with the same brightness and spectral frequency, as if it had passed through thin glass. What technologies make it possible to turn theory into practice?
Metamaterial Quantum Stealth
The invisibility cloak should not change the properties of the item - it simply directs the light rays around and makes the outside observer see only what is behind. Today, substances with such properties already exist: these are metamaterials with a negative refractive angle, which makes light rays bend around an object and makes it invisible to the eye, night vision devices and thermal imagers, and also hides the shadow.
The pioneer in the field of creating such metamaterials was the physicist at Imperial College London, Sir John Pendry. In the mid-1990s, he suggested that achieving the desired refractive angle is possible not so much due to the chemical composition of the molecules, but due to their arrangement. The scientist proceeded from the well-known fact: waves can be reflected or refracted at the boundary of media, and inside the medium they can be absorbed or pass through it.
In 2006, professors at the University of Michigan Elena Semushkina and Xiang Zhang proposed the use of dielectrics: for example, uniaxial crystals, which are characterized by birefringence in all directions of incident light, except for one. Physicists from Birmingham joined the research, and soon they managed to create a material with silicon nitride crystals on a transparent nanoporous silicon oxide substrate. Having made nanometer-sized holes in the crystals, the scientists obtained a smooth optical mirror that can hide objects in the visible range.
A unique material called Quantum Stealth works without cameras, batteries, lamps and mirrors, weighs little and, according to developers from Hyperstealth, is inexpensive. However, it is not yet possible to buy a unique fabric, because it was originally intended for the Canadian, American and British army. The military and first responders began testing the Quantum Stealth in 2012. In April 2014, Hyperstealth announced the launch of a commercial version of its invisibility cloak, the Hyperstealth INVISIB, which should be available later this year.
Squid wardrobe
The ability of cuttlefish, squid and octopuses to become invisible in the water allowed scientists from the University of California and Duke University to create an "invisibility cloak" for the Marines. However, he will not make them literally invisible, but will allow him to ingeniously disguise himself against the background of the surrounding area, literally dissolving into the landscape.
The scientists used a protein from the skin of the longfin squid (Loligo pealeii) called reflectin, which can adjust to different wavelengths of light. They found that tissues had alternating layers of cells with high and low refractive index. By reducing and increasing the distance between the layers, the squid "reflects" light of different ranges and changes color.
To reproduce this ability, the scientists placed a layer of this protein on a graphene oxide and silicone dioxide film. By alternately treating the material with water vapor and an acid solution, they were able to cause the protein layer to expand and fall off, changing color. This is only the first stage of work, but there is no doubt that the appearance of a unique novelty is only a matter of time.
Shield of radio waves
Light rays and radio waves are of the same nature - they are electromagnetic oscillations. The difference is only in the wavelength. In visible light, it is measured in fractions of a millimeter, while radio waves can be several kilometers long. Some physical properties also depend on the wavelength. For example, light under normal conditions can only go around obstacles comparable in wavelength. Medium waves can bend around the human body, buildings and other objects. And long waves can even go around the globe.
However, a beam of light, combined with a radio wave, takes on some of its properties and also begins to go around obstacles. In history, there are many cases of aircraft collisions with radio transmitting towers. As a rule, the reason lies precisely in this effect: at a certain wavelength, the details of the tower lose their visual clarity. The pilots complained that the antennas were not visible, or had blurry contours.
To achieve a similar effect for a person, you need to accurately calculate the length of the radio wave depending on the size of the object. Empirically, a regularity was deduced, according to which light rays freely bend around the human body if it itself emits a stream of radio waves with a frequency of 1456 kilohertz (+ - 5%). Any competent radio amateur can become invisible with a 1.5 V power supply, an inductor, a capacitor, and terminals attached to the body.
The device was tested on many people with constant success, but it soon became clear that invisibility awakens not the best qualities in people. For example, Steve R. from Boston flew to Europe for free by sneaking into a British Airways plane unseen. One Mark A. couldn't think of anything better than stealing a portable DVD player from a store, and a week later he was arrested while trying to sell it. Superhero wisdom involuntarily comes to mind: "Great power - great responsibility" ...
A fairy tale often becomes a reality. Flying carpets, magic saucers that reflect a distant reality, walking boots and many other inventions have become quite an everyday reality. Now it's time for the invisibility hat. At least the American journal "Science" published an article that outlines the basic principles of operation of an almost ideal camouflage.
Problems of invisibility
The problem of optical secrecy of objects is being studied by scientists from the Department of Materials Science at the Lawrence National Laboratory at the University of Berkeley. Supervised by Mr. Xiang Zhang. The general idea is to make the light bend around an object. Similar developments have already been made in the past, but were not successful for the reason that previous attempts could deflect rays in a narrow angular range. It has not yet been possible to achieve complete optical permeability or its illusion. Distortion of the picture allows you to locate the object (that is, its visual detection). The lack of flexibility of masking surfaces was also a problem. All these shortcomings are devoid of ultra-thin material developed at Berkeley. The "cloak" invented at Lawrence National Laboratory is flexible, but still too expensive.
Operating principle
The role of storytellers in our time is played by filmmakers. In the movie Predator, the Alien (an antagonistic character) uses a cloaking device to stealthily approach his victims. The effect is far from perfect: the alien is given out by light distortions. It is not transparent (although it is not so easy to detect the enemy), in its place there is a certain haze. Reality surpassed the director's wildest dreams. The "cloak", invented at the Lawrence National Laboratory, makes the object truly invisible.
The principle of operation is that many microscopic mirrors automatically turn in the direction of the light source. The “table for the talking head” works in much the same way. The magician, surrounded by mirrors from below, remains invisible to the viewer, except for the part of the body that rises above them. In conditions of complexity of the relief and the shape of the hidden object, it is very difficult to achieve such an effect. But still possible.
Technical specifications
It is known that the "invisibility cloak" is coated with a layer of magnesium fluoride, on which is applied a pattern of tiny gold antenna bricks 30 nanometers thick. This is a very thin film, many times thinner than a hair. The total thickness including the substrate is 50 nanometers. The bricks come in six different sizes, ranging from 30 to 220 nanometers in length and 90 to 175 nm in width. Thanks to these microantennas, it is possible to rotate the mirror surfaces perpendicular to the direction of light and completely scatter it. In this case, both the frequency and the phase of the radiation are taken into account - they are rotated by 180 degrees relative to the initial parameter, which allows it to be fully compensated.
With the right setting of surfaces, polished gold planes can give any effect to the reflected light. It can represent the background of an object (such as a floor) or something completely different. If the invisibility cloak is big enough, it could theoretically cover just about anything. For example, the tank will look like a bicycle. Or it won't be visible at all.
Practical Perspectives
The studies were carried out in the light range with a wavelength of 730 nm (near infrared region of the spectrum). An almost perfect reflection was observed. This scientific achievement is impressive and suggests a new round of the arms race. However, it is too early to think about invisible tanks, missiles, aircraft and other types of deadly equipment. The fact is that the experiments were carried out with a certain object of a complex spatial configuration, with a size of 36 microns in the approximate diameter. If in inches, then this is about one thousandth. In millimeters ... in general, an ordinary grain of sand, only very small. It was she who was wrapped in a mysterious "invisibility cloak". Science is silent about how much it cost to make it optically transparent.
However, someday this invention may be of practical use. For example, cinema screens currently have to be perfectly flat, and in the case of the use of "smart microantenna crystals", this requirement will be unnecessary, and images can be projected onto any curved surfaces without distortion.
