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The Sound Cloak


Euclidean

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Seeing and hearing are two senses that operate similarly, in that both require waves as sensory input. With sight, light waves enter our eyes, which bend the light toward the retina, which in turn convert the light into electrical impulses that carry information to our brain. With hearing, sound waves cause vibrations in the hairs of our cochlea, an inner part the ear, and the vibrations translate into electrical impulses that go to the brain.

Knowing this, scientists have sought for years to cloak objects from our seeing and our hearing by making light and sound waves pass around the objects. While this seems like the most obvious solution, it requires the design and development of complex (and sometimes expensive) synthetic materials.

At the Polytechnic Institute in Spain, though, researchers took a different approach. Rather than using some complicated mechanism to make the waves pass around the object, why not change the way the object scatters the waves. Thus, they designed a cage-like structure, which they wrapped around a plastic sphere. The purpose of the strange-looking apparatus was to essentially cancel out the sound waves scattered by the plastic sphere. The waves that scattered from the sphere would, in effect, cancel out with the sound waves emitted by the cage-like structure, so no sound would escape the cage. While the research is admittedly quite preliminary, it opens a door to a whole new angle of cloaking research. Who knows? A decade from now, the US Navy (which, unsurprisingly, helped to fund this research) might be sporting submarines invisible to sonar detectors.

You can read more about this fascinating research here:

http://www.sciencenews.org/view/generic/id/349255/description/Sound_cloaks_enter_the_third_dimension

One thing that stood out to me a lot when I first read the article was that the researchers used a computer simulation that predicted that the sound waves from the sphere and cage-like structure would cancel out. One day, I would love to build simulation programs that can help scientists to do studies like this one. Computer modeling affords us a lot of time saved from frustrating trial and error, and it affords us safety, since we don't have to experiment with something firsthand all the time and we can model the experiment instead. In essence, computer modelling can't replace experimentation, but it can certainly guide our experiments by helping us avoid unnecessary complications. This study is just one of many examples of the advantages of computer modeling.

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Great tie-in too.  Physics is strongly associated with modeling.  We build models of what we know and think we understand, test them, refine them, test again, refine, ...

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