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."
Re:invisible != inaudible (Score:0, Informative)
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:Crap (Score:3, Informative)
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:Ideas.... (Score:5, Informative)
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:invisible != inaudible (Score:5, Informative)
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 (Score:5, Informative)
"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.
What if... (Score:3, Informative)
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.
Not necessarily (Score:3, Informative)
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.
Yes, but (Score:3, Informative)
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:invisible != inaudible (Score:3, Informative)