Acoustic "Superlens" Could Make Subs Invisible

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."

Comments

invisible != inaudible

[Anonymous Coward]

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

Re:invisible != inaudible

[Arthur B.]

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

Re:invisible != inaudible

[cbiltcliffe]

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

[Arthur B.]

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

Re:invisible != inaudible

[Anonymous Coward]

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

[LWATCDR]

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.

Invisicrash

[MadLad]

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

Ideas....

[cbiltcliffe]

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....

[still cynical]

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....

[rickb928]

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...

Redeeculous

[Ancient_Hacker]

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.

Invisible to *active* sonar, maybe.

[pushing-robot]

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

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

HoHum

[senorpoco]

Another day, anther Slashdot cloaking device story.

Invisibility works both ways.

[gr8_phk]

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?

Violate the laws of physics?

[Yvan256]

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.

Just One Problem

[JoelMartinez]

They will still have to de-cloak to fire their torpedoes ...

This brings up an important point

[sean.peters]

"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.

Re:This brings up an important point

[Alex Belits]

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

Not really needed

[whitroth]

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