Acoustic "Superlens" Could Make Subs Invisible 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."
Ideas.... (Score:5, Interesting)
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.
Redeeculous (Score:5, Interesting)
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:Ideas.... (Score:4, Interesting)
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.
Invisibility works both ways. (Score:5, Interesting)
Re:Ideas.... (Score:4, Interesting)
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:Invisible to *active* sonar, maybe. (Score:4, Interesting)
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.)
Kidney stones (Score:2, Interesting)
Re:Invisibility works both ways. (Score:3, Interesting)
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.
Now, one more thing... (Score:2, Interesting)
Not really needed (Score:5, Interesting)
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
Re:Not really needed (Score:3, Interesting)
Using underwater thermoclines helps because pressure pulses (sonar) moving through thermoclines distort. Think refraction of light between air and water. It doesn't hide you, though: it just misrepresents your position. That's why subs since WWII have had bathythermographs [wikipedia.org], so they can map thermoclines to their advantage. If they know where the cold and hot areas are and people above them don't, they can use them.
But it's only useful to keep you from getting hit by another sub's torpedo or a depth charge. It isn't useful if what you want is to be undetected, because you're still reflecting noise.
This resonant thing tries to make you undetected.
I may be wrong because I'm not a submarine dude, just a dude who reads a lot, but that's my understanding.