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Invisibility Cloaking Still Isn't Much to Look At

Unless you're the size of a few human cells, you're too big to hide under science's current version of an invisibility cloak. That may change, but not for many years.

by Ryan Faith
Sep 23 2015, 10:15pm

Photo via BAE

"Berkeley Lab Researchers Create Ultrathin Invisibility Cloak."

So reads a news release from the US Department of Energy's venerated lab at the University of California, Berkeley. The cloak is too small for even the tiniest of boy wizards — it can cover no more than a few human cells — but it's a neat accomplishment. It is not, however, a sign that practical invisibility cloaks are close to being a reality.

There are basically two real-world approaches to camouflage: crypsis and mimesis. (Motion dazzle is a third approach — think of the stripes on a zebra — but no one can really prove it works.) Crypsis involves blending into the background and disappearing, like a ninja. Mimesis, on the other hand, involves disguising an object to look like something else, like one of those Mission: Impossible masks.

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In warfare, there are a fair number of legal restrictions to mimesis. For instance, you can't paint your tank white with a big red cross on it and pretend it's an ambulance that just so happens to have a gigantic gun. Other forms of mimesis are much better known, like the various countermeasures — chaff and flares — used by aircraft to distract hostile missiles.

Chaff is made from little strips of metallic or metal-coated stuff that reflects radar waves being used to target an aircraft. Flares are basically like road flares; they burn at high temperatures, producing infrared (IR) signals that heat-seeking missiles are supposed to lock on to. Both chaff and flares represent a specific type of mimesis, but are distinct from each other in one particular way: Chaff is passive — it emits no signal of its own — while flares actively emit an IR signal.

A great example of both mimesis and active camouflage is a system developed by BAE called ADAPTIV, which plasters a vehicle with tiny IR emitters that put out signals making the vehicle, like a tank, appear on enemy IR sensors to be something harmless, like an ambulance. They can also make the vehicle appear to be whatever is behind it, like a field.

Unfortunately, active camouflage like this runs into all kinds of problems. For starters, it's not very good at camouflaging something against sensors operating at other wavelengths. The ADAPTIV system, for example, is great against IR sensors. It is not great against radar — or against plain ol' soldier-mounted eyeballs.

Active camouflage systems also often have a problem with multiple viewers. Say, for example, that you want to blend into a wall. So you stand facing a wall while an image of the wall is projected onto your back. From across the street, you're all but undetectable. But to someone walking down the sidewalk next to you, you look like an idiot with a picture of a wall on his back. To be a perfect active system, you'd need to present the guy across the street with one image and the guy on the sidewalk with a different image. Since there are an infinite number of different perspectives, a perfect active system would need to be able to project an infinite number of different images. Which would be, in technical terms, an utter pain in the ass.

Most crypsis camouflage is therefore passive. Stealth, for instance, absorbs and deflects incoming radar waves so very little signal makes it back to the antenna. In other words, a stealthy aircraft looks like nothing much at all to a radar, which means it blends very nicely into the nothing that radars usually see when they're staring off into the sky.

This brings us back to ninjas. Ninjas in stealth mode basically use passive camouflage to blend into the background. But a fair amount of ninja stealth is the result of not just black clothing, but also all the skulking around in shadows ninjas do, which gives them have a background that blends nicely with their black clothing.

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If, however, you've ever seen a ninja in line at Starbucks for a pumpkin spice latte, you know that a change in background can eliminate the stealth. Thus, passive crypsis comes with usage limitations.

In theory, one could wear something with tunable camouflage that changes colors depending on the background, but aside perhaps from some clever lizards and cephalopods, nobody knows how to do that particularly well. And so we come to the holy grail of camouflage: workable, practical invisibility. It would solve all of these problems. It was just never possible.

Until, that is, the development of metamaterials. They are, like the name implies, materials made of other materials. Which isn't a very useful definition on its face. In a nutshell, naturally occurring materials have physical properties that are based, in very large measure, on the physical arrangement of their various atoms and molecules. Man-made metamaterials have physical properties that aren't found in nature, and that affect how the metamaterials do things like interact with light.

And it turns out that metamaterials can be used to flow light around an object, rendering it effectively invisible.

Of course, for now, if you're comparatively big — let's say bigger than a few human cells — you're too big to be rendered invisible using current technology. That kind of limits the practical applications of the stuff. So if you're looking to take over the world with invisible tanks, you've got two options, both of which are very technically challenging: make microscopic tanks, or make bigger invisibility cloaks.

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Making something that is so tiny it's already invisible to the naked eye become invisible may not sound like much, but researchers are in the very early stages of the proof-of-concept phase. And there aren't any physical laws or insurmountable engineering challenges that would absolutely prevent scaling up the technology. Some of the more optimistic researchers even say that this stuff could be ready for demonstration on a large scale by the end of the decade.

Then again, there aren't any laws of physics or insurmountable engineering challenges that prevent humanity from sending people to Mars, but careful observers will note that humanity has yet to do so.

Follow Ryan Faith on Twitter: @Operation_Ryan

Photo via BAE