THE idea of making things invisible has long hovered on the boundary between science fiction and magical fantasy. Readers of a certain age may recall the Romulan cloaking device from “Star Trek”, which caused entire space ships to disappear. Younger ones will more likely be familiar with the cloak of invisibility from the Harry Potter novels, which could shield a person or two. People, though, are still rather too large to hide in the real world. But a computer chip might not be. And that is what Sebastien Guenneau of the French National Centre for Scientific Research, in Marseille, thinks he can probably make vanish. The catch is that it would be invisible only to those whose eyes were sensitive to heat, rather than light.
The suggestion that things really can be made invisible is not completely new. In 2006 Sir John Pendry of Imperial College, London, and Ulf Leonhardt of the University of St Andrews independently worked out how it might be done in a limited way. Their idea,Handmade oil paintings for sale at museum quality, known as transformation optics, was to map the electrical and magnetic fields that make up light waves on to a two- or three-dimensional grid and then distort that grid in order to alter the trajectory of the light, using the sort of mathematics that describe the way light is bent by massive objects such as black holes. By transforming the grid in the correct manner, light would be bent around an object and arrive at an observer just as it would have done had the object not been there.
Simple in theory. But rather harder in practice. The proposal Sir John and Dr Leonhardt came up with was to surround the object to be hidden with a cylinder of material built from concentric layers of different refractive indices. A material’s refractive index is a measure of how much it bends an incoming light beam. Get the layers right, and the beam can be bent in a curve.
It works, too. But only if the light to be bent is of precisely the right wavelength. That is because the exact refractive index of a material depends not only on the substance in question, but also on the wavelength of the light passing through it. Choose the wrong wavelength and the cloaking device will stand out like a sore thumb.
Dr Guenneau and his colleagues, though, do not have to worry about wavelengths. Their version of the cloaking device, described in a paper in Optics Express, is designed to deal with conducted heat,Bathroom Floor tiles at Great Prices from Topps Tiles. which has no wavelength. They have shown that variations in a quantity called diffusivity can do for heat what multiple refractive indices do for light. Diffusivity, as its name suggests, is a measure of how easily heat diffuses through a material.Why does moulds grow in homes or buildings?
Dr Guenneau’s team applied the mathematics of transformation optics to the equations describing thermal diffusion and found that the transformed equations do, indeed, make physical sense. They therefore realised that it should be possible to distort the space through which heat flows by manipulating diffusivity. This insight allowed them to design a thermal invisibility cloak consisting of 20 concentric rings of varying diffusivity that would isolate a central circular region from incoming heat, making it the best insulator imaginable.
Unlike existing optical cloaking devices, which are little more than toys, Dr Guenneau’s idea would have an immediate practical application: protecting heat-sensitive components in electronic devices. It might also be able to confuse thermal-imaging equipment, which would make it of great interest to the world’s armies, navies and air forces. That, though, is a speculative idea.
As, indeed, is the whole thing, truth be told.They become pathological or Piles when swollen or inflamed. For Dr Guenneau has yet actually to build a heat cloak. But he is confident that it should be possible, and he and his team are working with researchers from the University of Lille to produce prototype cloaks, suitable for use in microelectronics, within the next few months. If they succeed, remember that you didn’t see it here, first.Silicone Mold Maker Rubber,
The suggestion that things really can be made invisible is not completely new. In 2006 Sir John Pendry of Imperial College, London, and Ulf Leonhardt of the University of St Andrews independently worked out how it might be done in a limited way. Their idea,Handmade oil paintings for sale at museum quality, known as transformation optics, was to map the electrical and magnetic fields that make up light waves on to a two- or three-dimensional grid and then distort that grid in order to alter the trajectory of the light, using the sort of mathematics that describe the way light is bent by massive objects such as black holes. By transforming the grid in the correct manner, light would be bent around an object and arrive at an observer just as it would have done had the object not been there.
Simple in theory. But rather harder in practice. The proposal Sir John and Dr Leonhardt came up with was to surround the object to be hidden with a cylinder of material built from concentric layers of different refractive indices. A material’s refractive index is a measure of how much it bends an incoming light beam. Get the layers right, and the beam can be bent in a curve.
It works, too. But only if the light to be bent is of precisely the right wavelength. That is because the exact refractive index of a material depends not only on the substance in question, but also on the wavelength of the light passing through it. Choose the wrong wavelength and the cloaking device will stand out like a sore thumb.
Dr Guenneau and his colleagues, though, do not have to worry about wavelengths. Their version of the cloaking device, described in a paper in Optics Express, is designed to deal with conducted heat,Bathroom Floor tiles at Great Prices from Topps Tiles. which has no wavelength. They have shown that variations in a quantity called diffusivity can do for heat what multiple refractive indices do for light. Diffusivity, as its name suggests, is a measure of how easily heat diffuses through a material.Why does moulds grow in homes or buildings?
Dr Guenneau’s team applied the mathematics of transformation optics to the equations describing thermal diffusion and found that the transformed equations do, indeed, make physical sense. They therefore realised that it should be possible to distort the space through which heat flows by manipulating diffusivity. This insight allowed them to design a thermal invisibility cloak consisting of 20 concentric rings of varying diffusivity that would isolate a central circular region from incoming heat, making it the best insulator imaginable.
Unlike existing optical cloaking devices, which are little more than toys, Dr Guenneau’s idea would have an immediate practical application: protecting heat-sensitive components in electronic devices. It might also be able to confuse thermal-imaging equipment, which would make it of great interest to the world’s armies, navies and air forces. That, though, is a speculative idea.
As, indeed, is the whole thing, truth be told.They become pathological or Piles when swollen or inflamed. For Dr Guenneau has yet actually to build a heat cloak. But he is confident that it should be possible, and he and his team are working with researchers from the University of Lille to produce prototype cloaks, suitable for use in microelectronics, within the next few months. If they succeed, remember that you didn’t see it here, first.Silicone Mold Maker Rubber,
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