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  (Source: MGM)
So is a flying pyramid/saucer in the works for the CIA and USAF?

Want to make an object indistinguishable from the background?  Well you'll have to develop multiple cloaking technologies to cover common detection modes.
 
I. Activate the Cloaking Shroud
 
In the past we've written about optical cloaks, which thus far have been largely confined to the nanoscopic regime.  Optical cloaks make light bend around an opaque object such that the observer seemingly "see through" it.
 
Duke University has published a new study in Nature Materials that offers another kind of cloaking technology -- acoustic cloaking.  Acoustic cloaks are particularly handy in deep ocean water, where light does not travel far and where sound waves are the primary means of "seeing" one's surroundings.
 
The device is a hood of sorts that goes over the object you wish to cloak.  It consists of a pyramid, of sorts, with multiple stacked plastic shrouds.  Each shroud has holes in it allowing for the unique routing of sound waves around the object being disguised.

Duke acoustic cloak
Duke's accoustic cloak from schematic to fabrication [Image Source: Nature Materials/Duke]

Mounted to a flying plane or undersea craft, it might resemble a flying saucer or Ra's spaceship from Stargate (the feature film).
 
II. Building an Acoustic Cloak
 
Duke Electrical and Computer Engineering (ECE) Professor Steven Cummer describes in a university press release:

The particular trick we’re performing is hiding an object from sound waves.  By placing this cloak around an object, the sound waves behave like there is nothing more than a flat surface in their path.

The structure that we built might look really simple.  But I promise you that it’s a lot more difficult and interesting than it looks. We put a lot of energy into calculating how sound waves would interact with it. We didn’t come up with this overnight.

Professor Cummer was the senior author of the paper and led the effort.  Lucian Zigoneanu, Ph.D, a postdoctoral research in Professor Cummer's lab, and Bogdan-Ioan Popa, Ph.D, a research scientist with the lab, handled the experimental work and fine-grain design.

Duke cloak
Duke research scientist Bogdan-Ioan Popa checks out the acoustic cloak. [Image Source: Duke]

A video of the shroud in action is seen below:



To test the device, the team put a ping pong ball within the unique cloaking shroud and pinged it with sound waves.  



Duke cloak
The object is almost disguised when cloaked, as seen in this sound wave study.
[Image Source: Duke/Nature Materials]

Compared to alternatives, the pyramid showed no trace of the ping pong ball and made the cloaked object and cloaking construct almost invisible.
 
III. Tuning and Future Applications
 
The cloak still needs a bit of tuning.  
 
It does not yet completely disguised the object, even if viewed along a face.  The research team believes that with a bit more tweaking it can be made to provide a near-perfect cloak.

Duke cloak
Duke's cloak needs a bit more tuning. [Image Source: Duke/Nature Materials]

Obviously, cloaking military structures or stealth submarines would be a prime application of the technology, but it may also come in handy in designing materials for better concert halls.  Comments Professor Cummer:

We conducted our tests in the air, but sound waves behave similarly underwater, so one obvious potential use is sonar avoidance.  But there’s also the design of auditoriums or concert halls—any space where you need to control the acoustics. If you had to put a beam somewhere for structural reasons that was going to mess up the sound, perhaps you could fix the acoustics by cloaking it.

The U.S. military is clearly interesting in this novel cloaking technology; the successful project received funding from both the Office of Naval Research (ONR) (N00014-13-1-0631) and the Army Research Office (ARO) (W911NF-09-1-00539). 

Sources: Duke University, Nature Materials, Duke on YouTube



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RE: Not very...
By MrBlastman on 3/17/2014 4:33:11 PM , Rating: 2
lol

Yes, it'd be quite useful for cloaking mines and even underwater structures (or ambush basins).

You could truly make some nasty evil abodes using this stuff. >:)

I thought about it along a stretched axis, a la the pyramid "top" being the nose of the vessel but then, what worries me, is it'd mess up the refractory index for the length of the craft as it'd move from a pyramidal shape to a square one or a lengthened reverse pyramidal one. Of course, it could go "full pyramid" all the way from bow to stern (with stern being flat, square side)... you'd either end up with one tremendously huge craft to get plenty of useable space out of it or one small one with little space.

All the pictures point towards a compressed, layered pyramidal structure so I'm not sure if they can lengthen it and still have low friction with a smaller profile underwater.

So maybe we'll be stuck using it on stationary objects only?

Oh, and I figured I'd ask, how about an article on gravitational waves discovered from the Big Bang using the b-mode polarization study? :) :)


RE: Not very...
By Motoman on 3/17/2014 5:52:34 PM , Rating: 2
Yeah I'm wondering how crucial it is that the "pointy end" be oriented towards the source of the sonar. Their test seems to show the point being directly under the source of the sound.

If you're a sub, or whatever, in operation in the ocean, you're not going to know from what direction sonar is going to come at you. So...not sure this is practical. Not for that purpose, anyway.


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