Will We Ever Achieve Invisibility?

The universe is a world of infinite possibilities. Well, at least theoretically. Theoretical physics predicts anything from parallel universes to time travel. But, as we came to find out, neither of these two concepts are really so easy to prove. Invisibility cloaks are not different. Although physicists clearly showed that optical cloaks could be built, so far they have been capable only to create cloaks working in the microwave spectrum. And even those are not three dimensional!

So, engineers at Duke University, the institution which the 2D microwave cloak originated from, decided to leave the electromagnetic waves aside for a second and try something different. Like sound for example. Similar to the invisibility cloak, they started to create a model of the 2D sound cloak, in order to prove that this concept is even physically possible.

Not surprisingly, it seems that the Duke University engineers demonstrated that, theoretically, it would be possible to create a region in space which would be acoustically disconnected from its surrounding environment. Quite a useful application taking into consideration today's sound pollution and the fact that military submarines use sonar to make detections of the enemy submarines.

It seems that sound cloaks are mostly using the same principle as the invisibility cloaks, meaning that metamaterials are involved. As in the case of electromagnetic invisibility, the sound waves interact with the complex structure of the metamaterial in order to eliminate sound reflection towards the source, thus rendering it invisible to the acoustic detectors.

However, Steven Cummer, working on the invisibility of sound cloak mathematical models, soon found himself in a dilemma. How to make a 2D matematerial invisible structure behave like a 3D one? He showed that, by making the whole structure invisible, both 2D and 3D optical and sound cloaks could, in theory, work.

Not only that, but the principle used in the creation of acoustic cloaks could in fact be used to bend sound and concentrate it into a specific direction or object.