Acoustic cloak hides underwater objects from sonar

Acoustic cloak hides underwater objects from sonar

Summary: Researchers have used metamaterials to create a new acoustic cloak, a technology that renders underwater objects invisible to sonar and other ultrasound waves.

TOPICS: CXO, Hardware

You've probably heard of invisibility cloaks that can hide tiny objects, even those visible to the naked eye. Now, researchers have used the same types of metamaterials to create an acoustic cloak, a technology that renders underwater objects invisible to sonar and other ultrasound waves.  A metamaterial is a class of artificial materials that have enhanced properties as a result of their structure.

Credit: L. Brian Stauffer

Credit: L. Brian Stauffer

“We are not talking about science fiction. We are talking about controlling sound waves by bending and twisting them in a designer space,” said Nicholas Fang, a mechanical science and engineering professor at the University of Illinois at Urbana-Champaign and leader of the project.

“This is certainly not some trick Harry Potter is playing with,” he said in a university release.

Fang and his team of researchers designed a two-dimensional cylindrical cloak made of 16 concentric rings of acoustic circuits structured to guide sound waves. Each ring has a different index of refraction, meaning that sound waves vary their speed from the outer rings to the inner ones. The speed is slower at the outer rings so that's where sound waves propagate since greater energy is required for them to move to the inner rings. The specially structured acoustic circuits bend the sound waves to wrap them around the outer layers of the cloak.

“Basically what you are looking at is an array of cavities that are connected by channels. The sound is going to propagate inside those channels, and the cavities are designed to slow the waves down,” Fang said. “As you go further inside the rings, sound waves gain faster and faster speed.”

Tests revealed that the acoustic cloak can effectively bend the ultrasound waves around the hidden object. The researchers submerged a steel cylinder in a tank with an ultrasound source on one side and a sensor array on the other, then placed the cylinder inside the cloak and watched it disappear from their sonar. They also tested other various objects and found the same results.

“The structure of what you’re trying to hide doesn’t matter,” Fang said. “The effect is similar. After we placed the cloaked structure around the object we wanted to hide, the scattering or shadow effect was greatly reduced.”

It is also capable of hiding an object from a broad range of sound waves from 40 to 80 KHz and potentially tens of megahertz with modifications.

Applications for the acoustic cloak include military stealth, soundproofing, and healthcare. For instance, ultrasound and other acoustic imaging techniques used in medical practice produce images that are often marred by things in the body that can cause interference. A metamaterial bandage or shield could effectively hide a troublesome area so the scanner could focus on the region of interest.

While materials that can wrap sound around an object rather than reflecting or absorbing it have been theoretically possible for a few years, this is the first time it has been demonstrated.

The research describing the working cloak prototype appears in a paper for the journal Physical Review Letters.

Topics: CXO, Hardware

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  • issue is..

    how does this evvect the aero/hydrodynamics of the device? Will it slow the device down? is this material placed around the device like your finger through a loop, or is the device wrapped in the material? Either way it seems that those cavities would cause drag. Still awesome though and definately useful
    • RE: Acoustic cloak hides underwater objects from sonar

      @KBot I was thinking the same thing. Maybe not useful on a submarine in it's present form. Not only would those cavities cause drag, but likely turbulence as well, which might be seen by sonar. It sounds like it only works if there is little to no current to deal with. Maybe if they could fill in the channels with something transparent to the sound waves then you could make it slip through the water.
    • RE: Acoustic cloak hides underwater objects from sonar

      Good luck everyone :3 <a href="">imitation Watches</a>
  • Real World Problem

    The drag could also limit the ability to hide a submarine that was moving. More drag means more turbulence, and more turbulence means more noise. Most detection today is done by listening for the noise a submarine generates, not by actively sending out sonar signals to be bounced back by it. The reason is that if you are sending out active signals, you have given away your presence before you have detected the other submarine.
    • RE: Acoustic cloak hides underwater objects from sonar

      @RichN_z But mine warfare could be changed dramatically!
  • Think more about hiding stationary objects

    This would be a great concern for detecting sea mines.
  • RE: Acoustic cloak hides underwater objects from sonar

    Whew! Thank god I found this blog, this was exactly what I have been looking for. Whatever it is.
    • RE: Acoustic cloak hides underwater objects from sonar

      @james347 It's emerging tech! :)
  • RE: Acoustic cloak hides underwater objects from sonar

    It's a little early to discuss fluid dynamics. They're interested in the cloaking principle, not applications yet. Just because it doesn't look like a good skin in its experimental form doesn't mean the principle couldn't be applied, ultimately. With some creativity, maybe you could imagine the cavities at such a small scale that water wouldn't significantly drag, or the cavities filled with a substance that smooths out the surface but allows sound waves to pass about the same as through water itself. Voila!
    • RE: Acoustic cloak hides underwater objects from sonar

      oh i'm not bashine it, these were just a few concerns i got from looking drirectly at the prototype. believe me acoustic cloaking could come in really handy in multiple applications, not just on moving vehicles.
  • RE: Acoustic cloak hides underwater objects from sonar

    That "mysterious contrail" off of the U.S. West Coast a couple of months ago - there has been some speculation that if was a small missle fired from a hidden Red Chinese sub that had (somehow) evaded the sonar net that is SUPPOSED to protect our coastlines from just such a "stealthy approach".
    • Nonsense

      If you notice the ridges around the side (where the sonar would be dampened by entering the chambers) you'll also notice that it only works in a ZERO current environment- meaning the sub would have be kill engines and float into US sea space under the power of the ocean's currents and its own momentum... meaning that, even if they were lucky enough not to hit something on their way in, they wouldn't have been able to get out of US sea space as turning around or moving against the current would create enough turbulence to be picked up by sensors, not even considering the fact that the design of the 'cloak' only works from a certain angle, unless they built the sub inside a giant sphere, which would just be silly.
      It's completely useless in its current form for mobile purposes.
  • RE: Acoustic cloak hides underwater objects from sonar

    Maybe the Chinese, with their abundance of "rare earths" might be ahead of us with this technology.
    • RE: Acoustic cloak hides underwater objects from sonar

      @JTF243@... their abundance just means mass production is economical for them, but everybody has access to the materials for research, development and some mass production.
  • RE: Acoustic cloak hides underwater objects from sonar

    Useless? you fix the fluid dynamics by sheathing it in a material that is acoustically transparent. This allows a smooth profile as far as moving through water. (just like you cover the wave guide/trap structures used in radar evading aircraft in a material that is transparent to radar, but lets you maintain airflow)