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Acoustic "Superlens" Could Make Subs Invisible

kdawson posted more than 4 years ago | from the bending-it dept.

The Military 136

Al writes "Nicholas Fang and colleagues at the University of Illinois at Urbana-Champaign have created the first acoustic superlens, which could be used to create high-resolution ultrasound images, and perhaps ultimately make subs and ships invisible to sonar. Researchers have previously developed materials that bend light in ways that appear to violate the laws of physics, creating so-called optical superlenses. The acoustic superlens consists of an aluminum array of narrow-necked resonant cavities filed with water — the dimensions of the cavities are tuned to interact with ultrasound waves. When ultrasound waves move through the array, the cavities resonate and the sound is refocused."

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136 comments

With Jews You Lose (-1, Troll)

Anonymous Coward | more than 4 years ago | (#28137595)

Don't let the Jews create a refugee camp in your back yard.

They want your land and money.

With Jews you lose.

invisible != inaudible (5, Funny)

Anonymous Coward | more than 4 years ago | (#28137633)

Title should be "Acoustic superlens could make subs inaudible".

Re:invisible != inaudible (4, Insightful)

Arthur B. (806360) | more than 4 years ago | (#28137657)

No. They may still be audible, but ultrasound will appear to go through them as if they were water.

Re:invisible != inaudible (1, Funny)

Anonymous Coward | more than 4 years ago | (#28137665)

You must be fun at parties.

Re:invisible != inaudible (4, Funny)

cbiltcliffe (186293) | more than 4 years ago | (#28137699)

You must be fun at parties.

Of course not. That's why he's posting on /. instead of getting drunk and picking up chicks....

Re:invisible != inaudible (4, Funny)

Arthur B. (806360) | more than 4 years ago | (#28137751)

Oh yeah, you should come to the ultrasound imaging fridays, I'm the life of the party.

Re:invisible != inaudible (5, Funny)

Anonymous Coward | more than 4 years ago | (#28137979)

Yeah I can see it now.........
Capt. Bart Mancuso: All back full.
Lt. Cmdr. Thompson: Captain...
Capt. Bart Mancuso: I said, all back full!
Lt. Cmdr. Thompson: Back full, aye.
[the Dallas reverses, churning the water]
Seaman Jones: Captain, we're cavitating, he can hear us!
Capt. Bart Mancuso: No he can't we have that new super lense thingy that makes us inaudible!
Lt. Cmdr. Thompson: No Captain, you don't understand it doesn't make us inaudible to people only to sonar!!
Capt. Bar Mancuso: Oh Crap!

Re:invisible != inaudible (4, Informative)

LWATCDR (28044) | more than 4 years ago | (#28139207)

Which will not matter at all.
Search sonar uses low to medium frequencies not ultrasonic ones.
Also a large amount of the searching involves using passive sonar. Going active is kind of like using a spot light. Yea you can see but everybody can see you from an even greater distance.

This brings up an important point (4, Informative)

sean.peters (568334) | more than 4 years ago | (#28139323)

"Ultrasound" (generally understood as meaning sound of a frequency too high to hear... i.e. more than 20khz) is pretty well useless in submarine detection, as high frequency sound has a very, very short propagation range in water. If they get to the point where they can do this with some frequency range that can go more than a few meters without being attenuated, then color me interested. But I'm guessing that would require an apparatus so huge that you wouldn't be able to deploy it anyway - the resonant cavities have to have a size of the same order of magnitude (maybe 1/4 wavelength?) of the sound wavelength... and for frequencies with any hope of propagating far (you're typically talking from 60 Hz to a few Khz), the wavelengths are HUGE - around 25 meters for 60 Hz. Bear in mind that you apparently need an array of these cavities, so you're talking about a rather enormous system.

Note also (1)

sean.peters (568334) | more than 4 years ago | (#28139451)

I know, replying to myself is bad form, but... various navies also use anechoic coatings [wikipedia.org] that are conceptually similar to this. The difference is that they are tuned to absorb incoming active sonar pulses of a frequency that you think your enemy is likely to use. They also have an effect of muffling any sounds radiating from your own boat.

Re:This brings up an important point (5, Funny)

Alex Belits (437) | more than 4 years ago | (#28139567)

The trivial solution would be a cavity filled with water same shape and size as the submarine, at the same position as the submarine.

Re:This brings up an important point (1)

DerekLyons (302214) | more than 4 years ago | (#28139619)

While true that it's useless for submarine detection - torpedo ranging and homing sonars use higher frequencies. Making yourself less visible or invisible in these frequencies is a Big Win.

Yes, but... (1)

sean.peters (568334) | more than 4 years ago | (#28139659)

You don't need a metamaterial based apparatus like this to accomplish that - you just need an anechoic coating... which we already have.

Re:invisible != inaudible (1)

jonadab (583620) | more than 4 years ago | (#28139477)

> They may still be audible, but ultrasound will appear to go through them as if they were water.

Yeah, theoretically.

Thing is, "invisible to sonar" is not the same thing as "undetectable and untrackable". Ships would just have to start using more than traditional sonar. Given how *long* sonar has been in use essentially unchanged, I'm not sure this is really a big deal. An upgrade to the sonar room was probably overdue anyway.

Being invisible to traditional bounce-back-to-the-source sonar is one thing, but what happens if there are several sound emitters pinging at you from different angles and several listeners analyzing how each of those sound sources is deflected? Military ships don't usually travel alone these days, so networked multi-source multi-listener sonar grids ought to be very practical, if the sonar room equipment were designed to support it.

Also, besides sound, shouldn't they also be monitoring EM radiation (radio and infrared and such) at the very least?

Re:invisible != inaudible (0, Informative)

Anonymous Coward | more than 4 years ago | (#28138037)

Funny, it sounds like someone describing how human hearing works, although bat and fish hearing also make use of fluid filled canals, except we use bone and tissue. A stethoscope is how old? (a super lens of sort).

Relative to a powerful transmitter, a crystal radio, with a tuned antenna, sucks electricity out the air, and a Mr Tesla poked about a bit on this old theory. Gee thats how a magnetron may also work.

Physics have also gone out the window. Water is a excellent sound transmitter - ask any whale or dolphin. Subs already have a wind out loudspeaker on a rope making 'submarine' noises, and or noise canceling out of phase.

Nothing new here - move along.

Re:invisible != inaudible (1)

Anonymous Coward | more than 4 years ago | (#28138207)

That post was so full of fail it's hard to begin. Stethoscope? Sucking electricity? magnetron? You fail them all.

Re:invisible != inaudible (1)

pjt33 (739471) | more than 4 years ago | (#28138679)

In addition, the summary currently describes it as "an aluminum array of narrow-necked resonant cavities filed with water". Maybe someone has managed to create a cunning way of using water to smooth off rough surfaces, but I think it's more likely that the summary is missing a letter.

Re:invisible != inaudible (1)

ae1294 (1547521) | more than 4 years ago | (#28139493)

Article translation....

1974 VW van muffler converted for military use for only 700 trillion dollars.
(Military leaders say in between snorting lines of coke that "they really really needed this to stop the red menace uhhh I mean terrorists...")

News at 11.... am...

Invisicrash (5, Funny)

MadLad (1331393) | more than 4 years ago | (#28137643)

Thanks to this ground-breaking scientific research, submarines will be even better equipped to collide with each other [wikipedia.org].

Re:Invisicrash (1)

cbiltcliffe (186293) | more than 4 years ago | (#28137805)

Not really.

It just means that, as a sub commander, the only thing you can now be sure of is where something is, rather than where something isn't.

So, in order to avoid crashing into invisible, cloaked submarines, all a sub commander will have to do is crash into the seabed.

Ideas.... (4, Interesting)

cbiltcliffe (186293) | more than 4 years ago | (#28137669)

I haven't RTFA, big surprise, but just a thought...

If the cavities have to be tuned to match the sound, then what happens if somebody comes up with a sonar that uses variable pitch?

Or even just two separate sonar systems on a ship/sub/whatever, that use two different frequencies, with no matching harmonics.
If something shows up on one, and not the other, then somebody's trying to hide.

Re:Ideas.... (3, Interesting)

Amouth (879122) | more than 4 years ago | (#28137899)

i don't think this is nearly as focused as say a lens's ability to focus a nm of light.

i would think it would work on a wide range of frequencies (some better than others) but all should be better than nothing.

think of the sound proofing and dampening they use in recording studios.. sure it doesn't stop everything but it works well on a wide range.

now that said.. this is almost like the radar absorbsion on stealth planes.. - if you have 2 towers shooting back and forth and the plane goes inbetween you can track it based on the lack of reflection.

It might be possiable to do the same to a sub using this except it might be easier.. as sonar does pickup the reflections from the bottom and also veriations in water preasure (if the gain is high enough).. i would think that something like this would show up as a void in the response - and there for trackable.

Re:Ideas.... (1)

I'm not really here (1304615) | more than 4 years ago | (#28138109)

It sounded to me like this "bends" the sound around the object, and the sonar would simply reflect off the ocean floor below the sub, not leave a blank spot on the sonar, but I could be wrong.

Re:Ideas.... (0)

Anonymous Coward | more than 4 years ago | (#28138367)

Close, but still no cigar. Time-of-flight for sonar ping will be somewhat longer if it goes around object and that will show on the screen as a shadow over background, e.g. a depression in the ocean floor. Trained operator will be able to detect the object and even assess the distance to it if the size of the object is known.

Re:Ideas.... (1)

thelamecamel (561865) | more than 4 years ago | (#28138803)

Nup, time of flight will be exactly the same. If this is like the optics ones, then this cloak is designed so that sound is indeed bent around the object, and it's made out of a fancy resonant metamaterial that's cleverly designed so that sound travels faster through it than through the surrounding water.

Re:Ideas.... (3, Interesting)

cbiltcliffe (186293) | more than 4 years ago | (#28138115)

i would think it would work on a wide range of frequencies (some better than others) but all should be better than nothing.

True, but "ultrasound waves" essentially covers any sound from 20kHz up. There's no way it can work on that kind of a range effectively enough to hide something as big as a sub from someone who really wants to find it.

Comparing it to the soundproofing in recording studios doesn't really work, as audible sound only covers, at most, 20Hz to 20kHz. For most people, it's more like 35Hz to 18kHz. As well as that, studio sound baffling absorbs sound indiscriminately.

I get the impression from this that it's not absorbing it so much as redirecting it around the cloaked object. TFA (which I've read now) compares it to similar cloaks which have been worked on for visible light. These light cloaks redirect light around the object, so you see what's behind it. A sonar cloak would have to do the same thing to be effective, otherwise the viewing vessel would see:

seabedseabedseabed.........seabedseabed

Any gap in the seabed would indicate a cloaked sub between you and the bottom.

Re:Ideas.... (1)

Amouth (879122) | more than 4 years ago | (#28138589)

they refer to the cells as "array of narrow-necked resonant cavities"

while i agree that it more than likely will not "hide the sub" i have no dobut that at some point it can help in the hiding of the object.

if you can distort the reflection of the sonar you can alter the perception of your placement to the reciver. (unless they know how it has been distorted)

i see this as just making it harder to identify and pinpoint a sub. Another comment i say makes alot of sence too.. Via time in transit - if it has to wrap the sound around there will be a ever so slight delay - meaning you will see the shape of the sub as a depression in the image from the sea floor reflection,

Re:Ideas.... (1)

cbiltcliffe (186293) | more than 4 years ago | (#28138681)

Via time in transit - if it has to wrap the sound around there will be a ever so slight delay - meaning you will see the shape of the sub as a depression in the image from the sea floor reflection,

I can see this, although the time difference is going to be minuscule. I could see something like that being noticed with a fairly smooth seabed, and with the detecting ship riding on smooth water. But once you throw a few waves into the mix, and a moderately craggy sea bottom, I'd think the signal:noise ratio would be impossible to work with.

Of course, I could be wrong, as I have no idea how accurate sonar is. I'm just approaching this from a security guy's perspective, trying to figure out ways around the system, and I'm just giving my first impressions.....

Not necessarily (2, Informative)

sean.peters (568334) | more than 4 years ago | (#28139527)

You need to consider two cases: active sonar (in which the searching ship is attempting to ensonify the target ship with sonar pulses, and then detect returning echoes) and passive sonar (in which the searching ship is just listening for sound emanations from the target). In the first case, you typically wouldn't be able to identify the submarine from a gap in return from the seabed - most of the energy in a sonar pulse ends up being entrapped in one or more "sound channels" in the water column, and never makes it to the seabed (exceptions apply, for certain water depths, etc, but still, so much sound is lost all the time that you couldn't use this... you'd get false alarms continually). In the second case, there are no real independent sources of sound that could be blocked by a passing submarine that you could use to detect them (or we'd be doing this already). So realistically, this is probably not a viable means of detecting a submarine.

Re:Ideas.... (1)

thelamecamel (561865) | more than 4 years ago | (#28138909)

Actually it's the other way around - because this uses resonant cavities, it only works on a very small range of frequencies. But the 'super' thing about a superlens is that it can focus sound/light to a region smaller than any other kind of lens, 'beating the diffraction limit'.

Re:Ideas.... (1)

Amouth (879122) | more than 4 years ago | (#28139119)

but if you read they haven't beaten the diffraction limit yet, for light yes for sound no - this is just as close as they have gotten

Re:Ideas.... (5, Funny)

still cynical (17020) | more than 4 years ago | (#28138363)

You just have to modify the deflector array to rotate the shield harmonics. Problem solved, but you'll have to do it again every few episodes.

Re:Ideas.... (1)

thelamecamel (561865) | more than 4 years ago | (#28138665)

Yep, this particular design will work over a very narrow range of frequencies, because it uses resonant cavities, which are inherently narrowband. If they could build a design without the need for resonant effects, then in principle the acoustic cloak could work over a very large range of frequencies.

The idea behind the acoustic cloak is essentially the same as the optical cloaks that have already been demonstrated: 'squash' space around the object to open up a hole in the universe, as seen by light/sound sees. This uses the fact that light/sound travels faster in some materials than others - essentially a block of glass is a bit like a TARDIS, squashing space, in the sense that a ray of light circling the object from inside can 'travel further' (i.e. accumulate more phase) than a ray of light circling the object from the outside. The refractive index can be thought of as related to General Relativity's metric, i.e. a measure of how space has been 'squashed'.

So if you're clever you can warp space to create a no-go region for light, essentially choosing a point in space and opening it up to a circle. All parts of that circle have to be the same distance from each other, so light/sound has to be able to travel around that part of the circle instantly, i.e. for light the refractive index at the circle has got to be zero.

Getting a zero refractive index (or acoustic impedance - i'm not an acoustics person so i might have this wrong) is hard, and at the moment we can only do that using resonant materials (in optics, they're micro-ring resonators or fishnet structures - metamaterials). However, if you don't want to make the sub invisible, if you're happy to be able to just shrink it (or even distort it into the shape of a shark), then you don't need an impedance of zero, you just need a material in which sound travels faster than in water, the surrounding medium. The faster light travels in it, the smaller you can make your cloak.

Obviously this is an easier problem for sound than for light, since we usually want to cloak things surrounded by air, and there ain't too many natural media in which light travels faster than c.

Re:Ideas.... (4, Informative)

rickb928 (945187) | more than 4 years ago | (#28138687)

The same techniques that are used in radar will be used in sonar;

- Frequency agility will become the norm.

- The cavities will be tuned at first mechanically. It wasn't so long ago that radar was tuned with physical cavities. I haven't kept up on very high powered sets, but I suspect they do it all electronically now. Magnetrons are pretty much declassé.

- I would be surprised that pulse shaping and various AGC techniques are not already in use.

- Backscatter sonar will be developed. This is just an exercise in computing power, and we got that nailed.

- More useful than stealth or masking would be using superlenses for decoys. Nothing makes your sub commander's day like having 6 or 7 targets and KNOWING that only 1 or 2 are genuine. Torps are largely ineffective against decoys, and expose your position. In a robust countermeasures environment, whoever shoots first usually loses. They are dead from the bogey they didn't see, or prioritized wrong, shooting the decoy first. Whatever they shot at may or may not be real.

I wonder if we have many lone attack subs out there. Teamwork solves a lot of problems. Using another sub's pings is the simplest of tactics. Backscattering off of your teammate is somewhat more interesting. Using an array to listen to your teammate's pings and map the hole is even more fun.

Crap, I miss countermeasures. Wonder if the Air force is still hiring...

Re:Ideas.... (0)

Anonymous Coward | more than 4 years ago | (#28138695)

If the cavities have to be tuned to match the sound, then what happens if somebody comes up with a sonar that uses variable pitch?

You're describing Chirp [wikipedia.org]

Re:Ideas.... (1)

DerekLyons (302214) | more than 4 years ago | (#28138773)

Harder to do than it sounds (pardon the pun).
 
High power emitters (AFAIK/IIRC) pretty much work on only one frequency, which means (currently) that you have to carry two sets. Also, the transmitter arrays are pretty good sized, and there is only so much room available in a submarines nose or a ship's sonar dome. So while it's doable, there is going to be some pretty big impacts on design.
 
But, as posted elsewhere, passive sonar still works and is actually the preferred method for tracking.

Re:Ideas.... (1)

Maximum Prophet (716608) | more than 4 years ago | (#28138905)

Already been done. There are radar systems that essentially use a burst of microwave noise. Bats and dolphins use multiple frequencies. It's unlikely this system in it's present state would fool a dolphin.

Now, if you designed the system with electrically variable cavities, you'd be able to adjust it on the fly. The first few waves of a ping would bounce back, then you would disappear...

Re:Ideas.... (1)

tnk1 (899206) | more than 4 years ago | (#28139321)

Well most submarines these days use passive sonar, which means listening for sound, rather than pinging things with active sonar. If you ping something, you'll easily get a target solution on it, but you'll also be painting a big fat target on yourself. If you are lucky, the contact didn't know you were there and you take them by surprise and take them out. If you are unlucky, they either suspected you were around or they are fast enough that they could send a torp of their own right at you as soon as you turned on the glowing neon I'M OVER HERE sign on your boat.

Happily, passive sonar, especially on US boats, is more than enough to get a full solution and identification on the targets. A boat skipper who actually uses his active sonar in a fight is likely a very desperate one (or a very dumb one).

What that means is that having a variable pitch sonar really doesn't help much if the sound that is being listened for is that is being masked. You can listen any way you like, but if the majority of the sounds that identify the contact as a sub, let alone an enemy sub, are being masked out, you're screwed.

On the other hand, if this is only useful against active sonar, it is true that surface ships are so noisy that they usually just turn on their active sonar and leave it on. Being able to hide from a surface ship's active sonar would definitely be useful, and so a variable active sonar might be useful for them and their ASW helos with their dipping sonar and sonobouys.

What if... (2, Informative)

sean.peters (568334) | more than 4 years ago | (#28139385)

then what happens if somebody comes up with a sonar that uses variable pitch?

Someone's already come up with it - the AN/SQS-53. No link, as for obvious reasons the Navy is not keen on talking about the operating frequencies of its gear, but it's well known that it uses multiple frequencies around 3.5 KHz for active sonar, and it's got a passive sonar capability to detect between very low and rather high frequencies.

Crap (1)

grub (11606) | more than 4 years ago | (#28137679)


When I saw "subs invisible" I thought "Cool, I can get rid of those 2 huge black boxes hooked up to the receiver" but no...

Re:Crap (0)

cbiltcliffe (186293) | more than 4 years ago | (#28137745)

I'm assuming you're a guy......

So paint them pink, and put OMG PONIES!!1!!1 stickers all over them, then put up an SEP.

Re:Crap (1)

belthize (990217) | more than 4 years ago | (#28138073)

Pink subs attract nurses and sink trucks.

Re:Crap (0)

Anonymous Coward | more than 4 years ago | (#28138177)

So what's wrong with attracting nurses?

I'd highly recommend something that could attract [3wishes.com] nurses [odgirl.com] to my place....

Re:Crap (2, Informative)

cbiltcliffe (186293) | more than 4 years ago | (#28138197)

You don't know what an SEP [wikipedia.org] is, do you?

Read section 5.1.

Nobody'll see pink OMG PONIES!!1!!!1 subs in a guy's apartment.
Unless he's openly gay, or has a 5 year old daughter....

Re:Crap (1)

belthize (990217) | more than 4 years ago | (#28138415)

You've never seen this movie (http://en.wikipedia.org/wiki/Operation_Petticoat) have you.

Re:Crap (1)

cbiltcliffe (186293) | more than 4 years ago | (#28138585)

Nope, I haven't.

And I even Googled a bit to figure out what the heck you were talking about. But apparently not for the right stuff. Which isn't surprising, considering I haven't seen the movie....

Guess I should have Googled all terms together. Then, your /. comment is first (Damn! Google is fast!) and the movie review on answers.com is second.

detectible with rotating frequency or gamma burst (0)

Anonymous Coward | more than 4 years ago | (#28137685)

thank you star trek :)

Backwards refraction? (2, Funny)

Critical Facilities (850111) | more than 4 years ago | (#28137691)

Theorists have been working on materials that bend sound waves backward for several years.

So you mean, if this technology moves forward, and ends up getting incorporated into conventional home/portable audio systems, we may be able to settle once and for all whether or not Paul is dead?

Save the whales! (-1, Offtopic)

mariox19 (632969) | more than 4 years ago | (#28137723)

Isn't navy sonar already killing the whales? [discovermagazine.com]

I can't believe this is going to help things.

Re:Save the whales! (2, Insightful)

Anonymous Coward | more than 4 years ago | (#28137851)

Oh noes! Teh whales! You're right - the entire western Navy should just pack up and go home. I'm sure our enemies, being the reasonable and thoughtful people they seem to be, will follow suit.

Re:Save the whales! (1, Insightful)

Anonymous Coward | more than 4 years ago | (#28138075)

I think there's room for the GP on Obama's cabinet! Mr. Prez seems to like people who make knee-jerk decisions/comments without thought to their long-term ramifications.

Re:Save the whales! (1)

MadKeithV (102058) | more than 4 years ago | (#28138153)

No, you are missing the point. We will liberate the whales, and then equip them with lasers, so we won't need a Navy!

Re:Save the whales! (2, Funny)

Mindcontrolled (1388007) | more than 4 years ago | (#28138793)

Wrong again. We equip the whales with the lens-thingy, sonar gets bent around them, they won't get hurt, the environmentalists are happy. Then we equip them with lasers. Stealthed killer whales with friggin' lasers, dude. World domination, here I come. Muhahhahahahhaaaaa.....

Re:Save the whales! (0)

Anonymous Coward | more than 4 years ago | (#28138453)

Yeah, you're right - because we can't be guaranteed that everyone else won't also do the right thing means we should never undertake any actions to behave responsibly ourselves.

When did Americans' morals get so fucking twisted?

Re:Save the whales! (0)

Anonymous Coward | more than 4 years ago | (#28139061)

I share a similar view. There's so much of "do as I say, not as I do" coming from the mouths of political leaders.

The lack of solid logic is distressing, For example:
"Our enemies might be developing nuclear weapons." "Aye, then we must do so. We can't be at a disadvantage." has always sounded to me a lot like:

"Our enemies might be doing naughty things with farm animals." "Aye, then we must do so. We can't be at a disadvantage."

*grin*

Re:Save the whales! (1)

tech_fixer (1541657) | more than 4 years ago | (#28138167)

They should make the subs sound like whales... Imagine the face on sailors of Japanese whaling ships when they fish out a nuclear sub. Woot!

Redeeculous (4, Interesting)

Ancient_Hacker (751168) | more than 4 years ago | (#28137739)

The claim of "invisibility" sounds like exactly what one would write in a grant proposal to the Naval Research Lab.

Never mind it's very very unlikely.

Any practical cloaking device is almost certainly going to work in only one linear direction and at one temperature and frequency.
  And imperfectly at best.
        And probably be larger than what it's trying to cloak.

But sonar pulses are spread in frequency and can arrive from any direction, making such a cloaking device useless.

This just sounds like the perfect phrase to put in a grant proposal to get some Admiral to sign off on it.

Re:Redeeculous (1)

allawalla (1030240) | more than 4 years ago | (#28138175)

That's right... all forward progress needs to be stopped. All the creative people need to put on their headphones that squash intelligent thought. In fact, we should probably do it to everyone straight from the womb, just to make sure no free thinkers get by... You never know what might actually work until you try. It sounds like they have made some progress on something that even in one-dimension was thought to be impossible for a long time. Good for them!

Re:Redeeculous (1)

gardyloo (512791) | more than 4 years ago | (#28138429)

It sounds like they have made some progress on something that even in one-dimension was thought to be impossible for a long time.

Focusing in one dimension? You might want to rephrase that.

Re:Redeeculous (1)

WindBourne (631190) | more than 4 years ago | (#28138441)

This just sounds like the perfect phrase to put in a grant proposal to get some Admiral to sign off on it.
Admirals are not the ones signing off on this. It would be gates and congress or DARPA. In both cases, Gates controls them WRT DOD budget. And IMHO, with the exception of the ABL, I think that he is doing a damn good job.

Invisible to *active* sonar, maybe. (5, Insightful)

pushing-robot (1037830) | more than 4 years ago | (#28137779)

Passive sonar, on the other hand, still works fine.

After all, the thing's got to have a tailpipe.

Re:Invisible to *active* sonar, maybe. (0)

Anonymous Coward | more than 4 years ago | (#28138117)

See Hunt for Red October.

"One ping only!"

Re:Invisible to *active* sonar, maybe. (3, Interesting)

DerekLyons (302214) | more than 4 years ago | (#28138279)

Even so, reducing or eliminating the vessels visibility to active sonar is still a pretty big deal - active sonar is sometimes used for range confirmation prior to firing, and damn near all torpedoes use active sonar for ranging and homing.
 
(Former submariner.)

Yes, but (2, Informative)

sean.peters (568334) | more than 4 years ago | (#28139601)

At frequencies actually usable for submarine detection, this apparatus would have to be freakin' enormous - the cavities would need to be on the order of the same size as the wavelength... so you're talking meters in diameter. And you apparently need an array of them. I don't think that's something you can drag around on your submarine.

Not to get into a credentials war, but (former surface ship ASW evaluator) (have a masters degree in anti-submarine warfare from the Naval Postgrad School)

Re:Yes, but (1)

DerekLyons (302214) | more than 4 years ago | (#28139995)

I hadn't thought about the freqs for submarine detection - but torpedo sonars use pretty short freqs, so it may be useful there.

Re:Invisible to *active* sonar, maybe. (1)

thelamecamel (561865) | more than 4 years ago | (#28138707)

Not so sure. Sound reflects at an abrupt change of medium/impedance. If these acoustic cloaks are like the optical cloaks, then the innermost part of the cloaking device has an impedance of zero, which reflects all sound. So it could get noisy inside the cloak if there's no damping...

noise cancelation? (1)

circletimessquare (444983) | more than 4 years ago | (#28138713)

its just waves. if they can create antiwaves in noise canceling headphones on the fly, surely they can create antiwaves in water near the "tailpipe", especially since the noise source is probably relatively unchanging and well characterized

Re:noise cancelation? (0)

Anonymous Coward | more than 4 years ago | (#28139389)

But... wouldn't the waves and anti-waves annihilate each other, releasing incredible amounts of energy which would then form a mini black hole that destroys the Earth?

These people must be stopped!

Tailpipe? (0)

Anonymous Coward | more than 4 years ago | (#28138891)

Submarines use electric motors. Non-atomic subs use diesel generators when they are near the surface. They only use the generators when they aren't worried about being detected by sonar. The loudest noise they make is the swishing of their propellers through the water. A diesel-electric sub is nearly inaudible. The Soviet subs on the other hand; everybody in the Atlantic knew the moment those subs left port.

A wily submariner is already an expert at being invisible by hiding below abrupt changes in the water's density (caused by temperature or salt concentration).

BTW. The reason we use mostly passive sonar is that if you are pinging, everybody knows exactly where you are.

HoHum (5, Funny)

senorpoco (1396603) | more than 4 years ago | (#28138061)

Another day, anther Slashdot cloaking device story.

Re:HoHum (1, Funny)

Anonymous Coward | more than 4 years ago | (#28139615)

Another day, anther Slashdot cloaking device story.

I see what you did there.

Invisibility works both ways. (4, Interesting)

gr8_phk (621180) | more than 4 years ago | (#28138091)

It's the ostrich philosophy - if you can't see it, it can't see you. If all incoming waves (light or sound) are diverted around the object, then it can't "see" anything. If it absorbs some, then it will appear dark against it's background. Granted, it doesn't take much light to feed a camera, but how do you make an exception for a little bit of it?

Re:Invisibility works both ways. (2, Interesting)

thelamecamel (561865) | more than 4 years ago | (#28138753)

You could intentionally let a little bit of light/sound in and out at your favourite frequency. Or you could choose not to be entirely invisible, designing the cloaking device to warp your submarine into, say, the shape of a shark. All the sound that would have hit the shark will be spread across your submarine's surface (or if you design the cloak REALLY cleverly it could be focussed on your receiver). So with this kind of cloak, the enemy COULD see your submarine and receiver, but it would just be disguised like a shark. Since they can see you, you can see them. And you know your cloak's design, so you can use clever computer stuff to unwarp the pictures you get of the outside world.

Re:Invisibility works both ways. (1)

ColdWetDog (752185) | more than 4 years ago | (#28139513)

the enemy COULD see your submarine and receiver, but it would just be disguised like a shark

"Captain - we're picking up a contact on active sonar - doesn't look like a sub"

"OK, what does it look like then?"

"Uh, Captain, not sure, it's about the same size as a sub but it looks like.... looks like ... no that can't be right"

"Come on sonar, spit it out"

"Well sir, it looks like a giant shark"

"Somebody go relieve sonar please".

Might work....

Re:Invisibility works both ways. (1)

thelamecamel (561865) | more than 4 years ago | (#28139927)

Oops, I neglected to mention the 'shrink' part. It's a lot easier to shrink (and warp) a submarine than make it disappear entirely. Proper cloaks have a singularity on the inner surface of the cloak, as the entire inner surface has to seem like a single point. If you build the outer part of the cloaking device properly, but just give up when you get to a certain radius, then your cloaking device more or less makes the cloaked region appear much smaller than it really is, e.g. turning your submarine-sized object into a shark-sized object. Tweak the cloak a bit and you can shape the visible object like a shark.

This kind of cloak should even be possible to build without resonant structures, since it doesn't need the presence of a medium in which the speed of sound is infinite (the singularity), it just needs a medium in which the speed of sound is greater than in water.

Violate the laws of physics? (4, Insightful)

Yvan256 (722131) | more than 4 years ago | (#28138103)

Researchers have previously developed materials that bend light in ways that appear to violate the laws of physics.

If they have developed materials that bend light in ways that appear to violate the laws of physics, then it means the laws of physics need to be redefined. That's what science is. Formulas made from observations. New observations may modify your existing understanding of how things work.

And if you can't accept that, you shouldn't call yourself a scientist.

Re:Violate the laws of physics? (0)

Anonymous Coward | more than 4 years ago | (#28138691)

True, but mute, since it doesn't actually violate any physical laws, it only "appears" to.

Re:Violate the laws of physics? (2, Insightful)

MozeeToby (1163751) | more than 4 years ago | (#28139019)

The key word here is 'appear'. Meta-materials (which is what this is, just on a large scale) appear to violate the laws of physics but if you look more closely they don't. The point is that if you showed it to a college undergrad with decent physics knowledge they would say it violates the laws of physics, that doesn't mean the college kid is right.

Re:Violate the laws of physics? (0)

Anonymous Coward | more than 4 years ago | (#28139331)

>New observations may modify your existing understanding of how things work.

That was probably implied by the statement. That's why they used "appear to", don't you think? There's no need to be so pompous, everyone here understands what the statement means.

Just a little problem (1)

Aceticon (140883) | more than 4 years ago | (#28138121)

Their acoustic meta-material uses resonant cavities. The problem with it is that resonance works perfectly for a specific frequency and not at all for different frequencies.

A sonar cloak made of this material would be the equivalent of an invisibility cloak for people that are only capable of seing in a very narrow spectrum of Red: worthless if your enemy can "see" in more than one frequency.

Kidney stones (2, Interesting)

dvoecks (1000574) | more than 4 years ago | (#28138333)

My first thought (aside from "invisible" submarines) is what this could do for kidney stones... Somebody with more knowledge on the subject may want to check my reasoning (the best part of /.), but I would think that better-focused ultrasound could really cut down on "collateral damage" from breaking up kidney stones, possibly allowing the technique to be used more effectively on a wider variety of cases.

Re:Kidney stones (1)

Maximum Prophet (716608) | more than 4 years ago | (#28139285)

There's already better techniques for breaking up kidney stones. One sends a small signal out and looks for a bounce from the stones. Once it sees the stones, and has measured their resonances, it sends a larger pulse along multiple paths to destroy the stone. I don't know if the new system is available out of the lab yet though.

Subs are already hidden from us... (1)

owlstead (636356) | more than 4 years ago | (#28138461)

They've already managed to vanish the subs from the original article it seems. Must be the refracted light and sound that completely goes around it. Or have they dived? I think I saw a periscope!

Maybe they are just hiding from the sharks.

I misread the title... (-1, Redundant)

Anonymous Coward | more than 4 years ago | (#28138501)

Disappointed after reading this that my home theater subwoofer is still going to be visible; I thought I would be able to sneak a much larger one past my wife... :)

Tro7L (-1, Flamebait)

Anonymous Coward | more than 4 years ago | (#28138521)

the facts a8d And executes a

Am I the only one (0, Redundant)

Theoboley (1226542) | more than 4 years ago | (#28138811)

who thought this was about Speakers for car stereos?

Thank god its friday... my thought process is shot.

Oh and I didn't bother to RTFS

How does this help thwart passive listeners? (1)

tjstork (137384) | more than 4 years ago | (#28138861)

It's pretty rare that submarines are identified through active pinging, because, once you ping, everyone knows where you are. Instead you try and listen for other people, and that means machinery and cavitation. I could see using this technology to dampen expected sounds from internal machinery, but that would only work so long as the machinery actually makes predictable sound and one has to wonder if this technology would actually be better at damping than other technology. In any case, its certainly not going to hide that propeller!

Re:How does this help thwart passive listeners? (0)

Anonymous Coward | more than 4 years ago | (#28139143)

Technology for low-noise propellers has been in use and development for decades. If you are going sub-vs-sub then active sonar isn't likely to be used. If you are a sub trying to hide from what that some helo just dumped in the water then active sonar is much more of a concern.

Now, one more thing... (2, Interesting)

MrWin2kMan (918702) | more than 4 years ago | (#28139461)

Sounds great! Now, can we make sure we don't have any spies in the Navy or the Military Industrial Complex who will sell the technology to the Israelis, the Iranians, the North Koreans, the Chinese, the Russians or anyone connected to Toshiba?

Not really needed (4, Interesting)

whitroth (9367) | more than 4 years ago | (#28139739)

I have it on good authority - I know someone who, in the early eighties, was in the "Hunt for Red October" command (COMOCEANSYSLANT) - who tells me that all a sub needs to do is drop below a cold current in the ocean, and they're invisible.

What's more important is silence on the sub - she also told me about them finding a Soviet sub because of a noisy coffeepot (for real).

                      mark

Can I use this to shield my house from boom cars? (1)

digsbo (1292334) | more than 4 years ago | (#28139837)

If I could do something to make loud subwoofers on the street inaudible from my house, I'd pay probably $15K to install it on my property. Should operate on the same principle, though I imagine the wavelength could be a problem due to the targeted frequency band.
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