Cloaking devices -- it's not just 'Star Trek' anymore
During the 175th Meeting of the Acoustical Society of America, being held May 7-11, 2018, in Minneapolis, Minnesota, [Amanda D.] Hanford will describe the physics behind an underwater acoustic shield designed in her lab.
Hanford and her team set out to engineer a metamaterial that can allow the sound waves to bend around the object as if it were not there. Metamaterials commonly exhibit extraordinary properties not found in nature, like negative density. To work, the unit cell -- the smallest component of the metamaterial -- must be smaller than the acoustic wavelength in the study.
[...] To date, most acoustic metamaterials have been designed to deflect sound waves in air. Hanford decided to take this work one step further and accept the scientific challenge of trying the same feat underwater. Acoustic cloaking underwater is more complicated because water is denser and less compressible than air. These factors limit engineering options.
(Score: -1, Spam) by Anonymous Coward on Thursday May 10 2018, @11:51PM (2 children)
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(Score: 2) by bob_super on Friday May 11 2018, @01:16AM (1 child)
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I guess that protecting messages from being completely obliterated is a good thing overall, so maybe the Spam mod math should ignore the -1 floor ?
(Score: 1, Troll) by realDonaldTrump on Friday May 11 2018, @06:17AM
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(Score: 3, Interesting) by Snotnose on Friday May 11 2018, @12:00AM (7 children)
If something dark goes overhead in the night sky I see a shadow where the object blocks the stars. Will something with this cloak show a similar shadow?
Every time a Christian defends Trump an angel loses it's lunch.
(Score: 3, Informative) by bob_super on Friday May 11 2018, @01:01AM (5 children)
For a directional sonar, it would show as an area or infinite depth (equivalent to seeing a black object). The problem is that in most places underwater, the surrounding area is also beyond detection range, and therefore infinite depth (unlike stars).
(Score: 2) by Immerman on Friday May 11 2018, @01:27AM (2 children)
That's complete absorption though - not invisibility. I believe most "invisible" meta-materials cause the wavelengths affected to bend around the target, so that you can still "see" things behind it - i.e. a meta-material invisible to visual light would NOT blot out the stars, though there might be some distortion. Nobody refers to vanta-black and other ultra-black coatings as "invisibility paint" - because it's not invisible, just near-fully absorbent.
(Score: 2) by bob_super on Friday May 11 2018, @01:39AM (1 child)
Bending around so it's not reflected, I can fathom.
Bending around with such precision and so little interference that it is emitted from the back exactly as if the object wasn't there, and back for the return path if reflected (or emitted in the case of stars), without noticeable distortion ? Sci-Fi.
Even with perfect material, somehow interference-free bending (esp hard in the sonar range), the mechanical constraints on the object would be amazing and applicability unrealistic.
(Score: 3, Insightful) by mhajicek on Friday May 11 2018, @04:20AM
There would be distortion, like the sonar equivalent of predator camo. It may be possible for advanced processing to pick up the outline.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 2) by RS3 on Friday May 11 2018, @01:33AM (1 child)
Reflecting sonar is already defeated by anti-reflective coatings they use on mil subs. However, with passive sonar, sensor arrays and processing detect the sonar shadow / disturbance in the background acoustic noise caused by an object in the water. The idea here is to minimize that disturbance.
(Score: 2, Interesting) by Ethanol-fueled on Friday May 11 2018, @05:31AM
I dunno, an effective spectrum of 7-12 KHz might bamboozle Zimbabwean subs, but won't fool the Chink subs or anything else constructed in the past 40 years.
(Score: 2) by RS3 on Friday May 11 2018, @01:25AM
Light travels in a relatively straight line through space and atmosphere. If the night sky object absorbs light (is opaque), you observe a loss of starlight- a dark shadow. If that object is clear, you might not see it, but you might notice some kind of disturbance, especially around the edges.
Sound waves are not like light- they spread out and wrap around objects. Yes, they will be disturbed, but casual listening might not detect it. But with sensor arrays and processing one can get a pretty good idea of the size and shape of the object.
The Penn State research attempts to get the sound waves to reconnect coherently- very little net disturbance or distortion- so the object is pretty much invisible even to advanced sensing systems.
(Score: 2, Informative) by Anonymous Coward on Friday May 11 2018, @12:03AM (2 children)
The government can and will step in and prevent disclosure of technology which would confer an advantage to an enemy.
Because this has not happened, it can be inferred the government is a few steps ahead of this technology.
(Score: 3, Interesting) by JNCF on Friday May 11 2018, @12:52AM (1 child)
I'm also paranoid about governments suppressing technology, but I'm not under the impression that they can suppress all of the technology they want to all of the time. If this was funded by DARPA or a similar agency and still public knowledge, I would agree with your assessment. This is how I feel about the optical cloaking tech DARPA has admitted to. [theguardian.com] But when something comes from academia, it's possible that they're actually breaking ground. It's also possible that the government has had something like this for a while, but no perfect counter-measures for it, and didn't succeed in keeping academia from investigating the same avenues.
(Score: 1) by Ethanol-fueled on Friday May 11 2018, @05:34AM
Anything called "Applied Physics Laboratory" has some government funding or otherwise has government tentacles in it.
This one, [jhuapl.edu] for example, doesn't even try to hide it.
(Score: -1, Offtopic) by Anonymous Coward on Friday May 11 2018, @01:03AM
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(Score: 5, Informative) by requerdanos on Friday May 11 2018, @01:13AM
That kind of goes beyond oversimplification into legendary nonsense.
First, you can't just cook up a batch of random metamaterials and have it exhibit magical properties because it "commonly" does so. There is quite a bit of science and also some engineering involved.
Second, the "Negative Density [issp.ac.ru] [PDF Warning]" is not a property of any metamaterial (or indeed, any material), such that the more you add, the less you have.
Rather, a single (uncommon) metamaterial, used as a shield in a very particular way, causes what it's covering to appear, to measurements taken under certain very specific circumstances, to have less mass than it does. (The "dual-resonator metamaterial exhibits its negative effective mass density over a" certain frequency spectrum, according to the source linked above, which is admittedly still pretty cool.)
(Score: 4, Interesting) by legont on Friday May 11 2018, @03:31PM (3 children)
In 2005 military drill a single Sweden diesel submarine was able to sink an entire US aircraft group after sneaking under the sonars https://www.popularmechanics.com/military/navy-ships/a19784775/gotland-class-sub-ronald-reagan-war-games/ [popularmechanics.com]
The US supposedly improved the detection, but Russians supposedly designed even better subs.
The sub, mind you, costs about the same as one navy fighter plane. This discovery will make aircraft carriers obsolete and hopefully save us all some serious money.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by JNCF on Friday May 11 2018, @04:55PM (2 children)
I doubt that. If long range detection can't keep up, there are other counter-measures they could pursue. A hemisphere of submersible drones doesn't seem unreasonable. Aircraft carriers are too important for global dominance -- consider the godawful amounts of money we already throw at them, and ask yourself if the cost of a pile of drones would deter us from building more. I suspect that they will eventually become seasteads of a sort, much like the European towns whose central layouts look suspiciously like Roman military forts. With nuclear reactors on board, all they'll really need is local food production.
(Score: 2) by legont on Friday May 11 2018, @07:18PM (1 child)
At sea, the bigger the boat the faster it can go and speed is important. So, no, underwater drones will not do.
"Wealth is the relentless enemy of understanding" - John Kenneth Galbraith.
(Score: 2) by JNCF on Friday May 11 2018, @07:25PM
Slow carriers are better than no carriers, but they'll probably come up with something much more clever than my spitball solution.