Invisibility cloaking is already a reality, but don’t expect it works just like in Harry Potter.
The idea of invisibility has fascinated people for millennia and has been an inspiration or ingredient of myths, novels and films, from the Greek legend of Perseus versus Medusa to H.G. Well’s Invisible Man and J.K. Rowling’s Harry Potter.
For the past decade or so, extremely promising advances have been reported. Using either metamaterials – artificial materials with properties typically not found in nature – or natural materials, scientists have devised all sorts of invisibility cloaks. All of these work, yet all of them are flawed in one way or the other. They render an object invisible only from one angle or only for a particular set of frequencies like microwaves and so on. In order to make a perfect invisibility cloak, one needs extremely advanced manufacturing methods. Scientists at University of Cambridge have devised a breakthrough technique that will allow us to build materials previously unavailable, including those that could be used to build invisibility cloaks – the genuine kind.
Cambridge University researchers used laser light as “needles” to sew nanoparticles into materials that can be used to make invisibility cloaks.
The study, reported overnight in the journal Nature Communications, is part of the quest to develop metamaterials that
contain nanoparticles smaller than light waves.
The theory is that objects made of these artificial materials can reverse the arrangement of light that bounces off them, making them look like something else or rendering them invisible.
“We have controlled the dimensions in a way that hasn’t been possible before,” said co-author Ventislav Valev, a Bulgarian-born physicist and science-fiction buff.
Light really only does one of two things when it hits an object — it can be reflected or absorbed. When you look at a surface, the color you’re seeing is the light that is reflected off its surface. To make something “invisible” all you really need to do is wrap it in something that makes light behave in a different way (as if that’s an easy thing to do). There are a variety of promising nanoparticles that may be able to refract light in unusual directions, making them essentially invisible, but assembling those into a metamaterial has been virtually impossible until now.
Metamaterials might be the way to develop cloaking technology, but it has potential in a wide variety of more practical (and less sexy) uses. For example, some metamaterials could absorb certain very narrow wavelengths of the electromagnetic spectrum while reflecting others, making them ideal for use in sensors and scientific equipment.
Laser Thread whatever you’re going to use a metamaterial for, you first have to build one, and the nanoscale construction method developed by the University of Cambridge team has the potential to make that possible. The lasers being used are unfocused and produce billions of tiny needles of light that line up gold nanoparticles in long strings. The strings can then be stacked on top of each other to make larger pieces, eventually leading to a macroscopic scrap of the desired metamaterial. [Read: The wonderful world of wonder materials.]
It’s not as easy as flipping on the laser and watching the nanoparticles string themselves together, though. The particles have to be electrically connected to join up into a proper metamaterial strand. To get everything lined up, the team used spacer molecules called cucurbiturils (CBs). These hydrocarbons form a scaffold that keeps the particles just the right distance apart so that ripples of electrons can flow along the surface of the chain (this is called a plasmon). The plasmons concentrate laser energy on the particles and reinforce billions of nanoparticle connections simultaneously.
This is only the first step towards building metamaterials that not too long ago would have been deemed impossible. Before invisibility cloaks can become a reality, scientists must work out how to make the right materials at a microscopic scale. The scientists say light holds promise as a way of triggering the assembly of nanomaterials because of its speed and “highly tunable interaction with matter”.
Sewing an invisibility cloak with lasers
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