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Make your own invisibility cloak with a 3D printer

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May 12, 2013

Yaroslav Urzhumov with the 3D-printed invisibility cloak developed at Duke University

Yaroslav Urzhumov with the 3D-printed invisibility cloak developed at Duke University

Image Gallery (5 images)

Invisibility cloaks have been around in various forms since 2006, when the first cloak based on optical metamaterials was demonstrated. The design of cloaking devices has come a long way in the past seven years, as illustrated by a simple, yet highly effective, radar cloak developed by Duke University Professor Yaroslav Urzhumov, that can be made using a hobby-level 3D printer.

As envisioned by Harry Potter and DARPA, invisibility cloaks are an important new direction for camouflage technology. In contrast to conventional stealth technology, which concentrates on reducing the detection signature (radar cross section, heat signatures, optical detection, etc.) of an object, invisibility cloaks work by making it seem as if radar and light flows around the cloaked object. When successfully accomplished, neither the cloaked object nor the cloak will be detected.

How a cloak works can be illustrated by an analogy offered by Duke University Professor David Smith. Imagine a fabric in which the threads are optical fibers. As seen on the left of the image below, light will travel freely from one edge to the opposite edge of a piece of this fabric. If an opaque object is placed so that it blocks some of the light, it is equivalent to cutting a hole in the optical fiber fabric, as seen in the top right-hand image.

The invisibility cloak can be thought of as is a piece of optical fiber cloth where the th...

In the invisibility cloak at the bottom of the above image, the optical fibers are not cut, but rather bend around the object, with the result that light continues to pass through the fabric without any visible sign that the object exists. Differences in the travel distance for light passing through the various fibers is being ignored, as the resulting phase changes can also be compensated.

Cloaking technology is a happy offspring of the new science of optical metamaterials, in which artificially structured materials display a range of optical properties that cannot be attained using ordinary glasses and crystals. The newest Duke microwave cloak that looks like a disc with oddly-shaped holes dotted throughout is made from only two materials – ABS plastic and air. Because the cloak consists of a single piece of plastic, “essentially anyone who can spend a couple thousand dollars on a non-industry grade 3-D printer can literally make a plastic cloak overnight,” said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke University.

The new 3D-printed cloak is designed to make objects invisible to 10 GHz microwaves, which are about 3 cm (1.2 in) in wavelength. Whereas prior cloaks were made of lossy materials which prevented cloaking an object larger than a few wavelengths in size, Urzhumov's cloak is made of ABS plastic, which has very little loss at 10 GHz. In addition, ABS has an index of refraction of 1.56, meaning that similar cloaks that hide their contents from visible light can in principle be made from optical glass and plastics having micron-scale structure rather than centimeter-scale structure.

Electric fields inside the new Duke University invisibility cloak (Photo: Duke University)

The cloak is about 3 cm thick, and cloaks a region nearly 14 cm (5.5 in) in diameter. The cloak itself is a plastic/air composite formed into an annulus about 3 cm thick that surrounds the cloaked region. The object and cloak are illuminated with radially directed microwaves. The left side of the above image shows the electric fields inside and around the cloak, while the right side shows the electric fields flowing around a solid piece of polyethylene carbonate polymer (PEC). Microwaves are approaching from the left: Deep blue indicates no electric field, dark red is the largest field.

Total scattered microwaves as a function of frequency for bulk plastic, the theoretical cl...

Whereas the electric field fills the PEC, which also casts a definite shadow, essentially none of the incoming microwaves penetrate the cloak, which accomplishes this task with only minimal disturbance of the flow of microwaves. The level of invisibility can be indicated by the total proportion of microwaves scattered by the cloak in all directions. As seen in the figure above, the microwave scattering of the cloak in its working frequency (around 9.9 GHz) is about one-fifth of the amount scattered by a solid disk of ABS plastic of the same overall dimensions.

While the cloak currently only works with microwaves, the researchers believe it will be possible in the not-too-distant future to develop the technology further to work for higher wavelengths, including visible light.

"We believe this approach is a way towards optical cloaking, including visible and infrared," Urzhumov said. "And nanotechnology is available to make these cloaks from transparent polymers or glass. The properties of transparent polymers and glasses are not that different from what we have in our polymer at microwave frequencies.”

The science and technology of metamaterial-based cloaking devices is advancing in leaps and bounds. Devices such as Prof. Urzhumov's new cloak should hasten the day when such devices become integrated into consumer products.

Source: Duke University

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson
11 Comments

So, I'd have to spend a couple thousand dollars on a 3D printer that's only good for hobby stuff, who knows how much on ABS printer media, whatever the copyright fees are for the cloaking device's pattern and enough electricity to run the printer all night long. All of this to produce a chunk of plastic that will only block microwaves? Well, I suppose if I could wear it on my head I could get rid of all of my tinfoil hats, but I'm afraid it might render my cell phone useless.

Dan Parker
13th May, 2013 @ 10:35 am PDT

Maybe something like this could beat police radar. Not that I ever exceed the posted limit, mind you. Just curious.

Bruce H. Anderson
13th May, 2013 @ 12:08 pm PDT

Gee, an invisible bomb sitting right out in the open. If you think we've got security problems now just wait 'till this stuff gets developed further... I dread to think.

JAT
13th May, 2013 @ 01:19 pm PDT

No, you'd have to spend $500 on a 3D printer that's only good for hobby stuff, as that's all a ready built solidoodle costs. Unless you wanted to go to the trouble of making something like a reprap from parts, which would be far cheaper. The part he's holding would be $5 of plastic at most, but if you wanted to buy top quality ready extruded filament that might run you up to $50 if you didn't shop around at all. And the electricity to run a 3D printer overnight is about the same as an old 100W light bulb. You could buy the design off the guys who did the research, but I suspect they'd let you print it for personal use if you just asked. The pattern is right there in the picture. You can copy it in an hour on free 3D CAD software.

It's expensive if you don't want a microwave invisibility cloak, and if you can't think of anything else to do with a 3D printer. Of course, so far I've seen people print vacuum pumps, prosthetics, clothing, sculptures, toys, gifts, homewares, and more. Any price is expensive if you don't want the item. I still think this is an amazing bit of physics you could do yourself.

314159
13th May, 2013 @ 03:02 pm PDT

I've seen a lot of cool stuff here, but I don't get how this thing is a cloak.

Gargamoth
13th May, 2013 @ 04:26 pm PDT

for cop radar use the miltech paint, which because of the pigment size does the job of not reflecting. been around a while...good while.

Walt Stawicki
13th May, 2013 @ 07:16 pm PDT

Notice that it's only invisible at precisely that frequency.

It will be very hard (if not mathematically impossible) to make something that cloaks effectively from DC to light. Even harder to make something that cloaks multi-aspect. Multi-aspect means that both monostatic and bistatic radars (or other illuminative sensors) would find the object invisible.

The other thing, unless it is very cleverly powered, a sort of co-operative jammer if you will, it will always appear as a "hole" which is slightly absorptive of energy. So when the thing diffracts or blocks a known signal source, the source will distort or attenuate. If it's optical, it will likely also not work well with polarized light, or polarized sensors.

And even if it was possible, the thing still may make:

- A far-infrared thermal signature (if it's alive or powered by anything)

- Noise (possibly lots of noise)

- Reflections from ultrasound

- Micro Seismic signals when it moves on the ground (that's how the Area 51 police know you're coming)

- Compression waves when it moves through the air (that's how cockroaches know you're coming, they don't see you)

- Ionization when it moves through the air quickly

Also, if the thing has any tactical significance, it will probably communicate, emitting RF. A directional antenna and spec-an could find it.

So I'm not excited yet. Probably soon.

sleat
13th May, 2013 @ 08:23 pm PDT

I agree with 314159.

Arahant
13th May, 2013 @ 11:19 pm PDT

I could use this stuff on my cars and motorcycle to protect me from unwanted speeding tickets!

Jim Pelkey
14th May, 2013 @ 12:04 pm PDT

My first (and only) thought about this is, could you make a container that would allow you to microwave your food and have only part of the food get hot while the other part stayed cold?

So.. maybe you could make a frozen, prepackaged hot fudge sundae that you could microwave and out comes a dessert with hot fudge and still frozen ice cream...

Aric Caley
15th May, 2013 @ 07:54 pm PDT

How 'bout we just wait for the Klingons or Romulans to show up, then we jump them, steal their cloaking device, and run off a few thousand copies with our replicator. Sounds like a better use for the damn thing than just brewing hot Earl Grey tea all the time.

OuldBill
18th May, 2013 @ 08:26 am PDT
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