Pretty soon movies like the Hunt for Red October will confuse the hell out of the children of the world. Gone will be the days of playing cat and mouse in the depths of the ocean, carefully struggling to avoid the sonic ping of the enemy’s sonar because apparently, it is now possible to bend sound waves to your will.
Shu Zhang, Chunguang Xia and Nicholas Fang of the Beckman Institute of Advanced Science and Technology at the University of Illinois have demonstrated the ability to use an acoustic cloak to hide objects behind a disc-shaped shield 55 mm in diameter. Though it looks like a flat donut, it certainly isn’t made out of yeasty, chewy goodness.
(Side note: This is the end of where I’m going to try to sound like I know what I’m talking about. This is some crazy shit way above anything I have much of a clue about, but I’ll try to fill in the gaps where I can.)
The cloaking device is made out of a substance called metamaterial. This term covers a large class of materials carefully engineered in the laboratory for very specific structural properties. And it is this structure – not necessarily the substance it is made out of – that helps create the desired effect. The device makes use of nano-sized structural designs and the integration of serial inductors (passive electrical components lined up so their magnetic fields interact) and shunt capacitors (tiny electrical storage units that improves the power of a circuit) in order to control sound waves.
As seen in the picture to the right, the cloak consists of 16 concentric rings of these specialized acoustic circuits. Each ring causes the sound waves to vary their speed in a slightly different way. The interior rings cause the waves to speed up while the exterior ones make them slow down.
Now, keep in mind that in order for something to speed up, it requires more energy. So the sound waves really don’t want to go through the interior rings. Instead, they deflect into the outer rings via a complex system of channels inside of the circuits. The specially structured acoustic circuit disc actually bends the sound waves to wrap them around the outer layers of the cloak.
The cloak hides pretty much any object that fits within its field of influence for ultrasound waves from 40 to 80 KHz.
But they’re certainly not done there.
Theoretically, similar cloaks could be made to bend pretty much any range of acoustic waves. Actually, if you want to talk theory, this whole idea originated with the intentions of bending light waves in order to create an honest-to-God Klingon cloaking device.
In 2006, Duke engineers led a team that effectively cloaked objects from microwave beams, considered the first step to creating a cloaking device for the visible world. And just two years ago, David Smith from Duke Engineering created a series of algorithms developed to guide the design and fabrication of new metamaterials. He was quoted as saying, “The difference between the original device and the latest model is like night and day. The new device can cloak a much wider spectrum of waves—nearly limitless—and will scale far more easily to infrared and visible light. The approach we used should help us expand and improve our abilities to cloak different types of waves.”
Romulans, eat your hearts out.
You too, Harry Potter.