‘Invisible’

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By Noah Shachtman
November 4, 2010

Don’t start picking out the pattern of your cloak, yet. But invisibility just became a whole lot more likely.

Tech journalists and military dreamers have talked about real-life invisibility cloaks for a while, and with good reason. With their specialized structures, so-called “metamaterials” can bend light around objects, making ‘em disappear.

But you haven’t seen the likes of Harry Potter or Frodo Baggins training at Fort Bragg (Fodo Braggins, maybe?), because the trick doesn’t work with visible light. Metamaterials warp things like infrared light or terahertz waves, neither of which we can see in the first place. In other words, we could still make out the “invisible” object with our own two eyes.

Or at least, that used to be the case. Physicists at the University of St. Andrews appear to have made a breakthrough, however. They’ve created a metamaterial that really does work in the “optical range,” the scientists note in the New Journal of Physics.

Not only did Andrea Di Falco and his research partners put together a metamaterial that could bend visible light. They built it in a way that could lead to larger-scale manufacturing — and real-world applications. Not just cloaks, but lenses made out of metamaterials that can zoom to the micron level, making it possible to spot germs, chemical agents and even DNA, using basically a pair of binoculars.

“It clearly isn’t an invisibility cloak yet — but it’s the right step toward that,” Ortwin Hess, a physicist at Imperial College London, tells the BBC. “A huge step forward in very many ways.”

Typically, metamaterials are built on top of rigid, brittle substrates like silicon. But that limits their size, and the wavelengths at which they work. Di Falco’s group instead made materials out of a superthin layer of flexible polymer, since “a ‘real’ cloaking device would have to be deformable and extend over a large area,” they write. If Di Falco and his partners can stack enough of these materials together — and show they can work while folded — we could be on our way to Hogwarts.

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‘Invisible’ Material Key to DARPA Dream Display

February 9, 2008

Reason # 573854961875 why I love blogs.
The other day, in a post about DARPA’s new projects for 2009, I mentioned that the agency wanted to work on transparent displays.

How would you make those? Simple… By "exploiting the optical plasmon phenomenology characteristics of nanoscale structures." (Contact DANGER ROOM HQ immediately in you can translate.)

Now, lo and behold, we’ve got a translation. And it makes all kinds of sense, believe it or not.

BW provides us with a relevant paper, and then explains:

Metamaterials can shape visible light and other wavelenths (sound, microwaves etc..). Metamaterials have tended to be metals with particular patterns. The wavelengths interact with the patterns and can be guided by them to make things invisible or to give wavelengths negative indexes of diffraction (enabling superlenses for better microscopes).

Metamaterials can also be made out of non-metals but to effect visible light would need to have nanoscale dimensions (nanoscale structures part).

Plasmons are what are interact[s] with the metamaterial to create the effect.

Plasmons :The quanta of waves produced by collective effects of large numbers of electrons in matter when the electrons are disturbed from equilibrium. Metals provide the best evidence of plasmons, because they have a high density of electrons free to move.

Got it. In fact, we’ve covered metamaterials a bunch of times here. They’re what’s behind the science of real-world invisibility cloaks, sonic dampeners, and maybe even levitation.

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Invisible Submarines?

November 6, 2007

Scientists are already making progress in developing real-world invisibility cloaks. Now, Navy-funded Duke University researchers are applying some of the same concepts to sound. One day, perhaps, it could make a sub invisible to sonar signals — and impossible to spot.

The key to both projects are metamaterials — composites than can be structured to let electromagnetic waves flow around them, rather than reflecting those waves back. Light waves, just outside the visible spectrum, have been bent. – can be turned into real-world invisibility cloaks. Duke University investigators are trying to finding out if "acoustic cloaking" is possible, too.

If so, you might be able to "’cloak’ a submarine so that sonar signals from another submarine flowed around it and didn’t bounce back," according to a Office of Naval Research newsletter. You could "make a submarine invisible (or inaudible)."

A submarine sends out a sonar "ping"—a burst of sound waves that travels through the water. If the sound waves encounter a solid mass, perhaps another submarine, some of the waves bounce back and return to the first submarine. Sonar receivers pick up this echo, which contains information about the location and distance of the object ahead. No echo, no sonar signature.

Maybe.

"In two dimensions, acoustic waves behave like electromagnetic waves" in a way that would "allow someone to build an acoustic cloaking device," theoretically. But it wouldn’t work three dimensions, "so presumably such a cloak would only hide a submarine from another submarine at the same depth, not one that was sending sonar upward or downward." Plus, the "surrounding fluid[s]…
must have different densities in different directions, such as a layer of oil floating on water, or bands of particles suspended in a liquid. This is not a typical property of your average ocean."

So it’s gonna be a while before we hear anything substantive about invisible subs.

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Invisibility Cloak Findings at Duke University