A group of researchers headed by Lu Lan from the Zhejiang University in China has created an invisibility cloak design using topology optimization within a time span of just 15 minutes. The wonder material was carved out of Teflon using a computer-controlled engraving machine.
Calling the fabrication process of a sample as ‘substantially simplified,’ the researchers said that the resulting “Teflon eyelid” invisibility cloak hides a cylindrical disc of metal the size of poker chip from microwaves. But crucially, its performance closely matches the prediction of the computer simulation.
When it comes to invisibility cloaks, one of the trickiest problems is how to make the things. The materials of choice are known as metamaterials which are created by assembling a repeating pattern of structures that interact with the light they are designed to cloak. This kind of detailed assembly means that making metamaterials is an expensive and time-consuming process. What’s more, the resulting invisibility cloaks are never perfect
The Chinese scientists’ approach is entirely different to the theoretical light-bending mathematics physicists have used until now. This current approach works by attempting to steer electromagnetic fields around an object in a way that hides it. The necessary material must be able to repeat this kind of light distortion in real life.
The new approach is to create a computer model of the cloak in the form of a conventional material with fixed light bending properties. The model simulates how this conventional material distorts light as it passes by. The computer then changes the shape and topology of the material to reduce this distortion.
By repeating this process many times, it is possible to find a topology that minimizes the distortion of light so that it remains more or less unchanged as it passes by. The result is an invisibility cloak; not a perfect one but one that can hold its own against many of those made of metamaterials.
This is significant because it brings invisibility cloaks into the realms of mass production. There is no reason why Teflon eyelids couldn’t be printed or molded en masse. The researchers now want to develop the technique to create cloaks that work over a range of frequencies and at a range of angles. If they can make them cheaply and easily for a cost measured in pennies, there’s no reason why invisibility cloaks won’t soon be everyday objects.