Chinese researchers have succeeded in using a highly novel approach to craft a Teflon-based invisibility cloak in just 15 minutes. The process, called topology optimization, uses computer software to algorithmically and automatically design a material with specific qualities -- such as an invisibility cloak. The design, once desired qualities have been achieved, is then produced using a 3D printer or similar computer-controlled manufacturing device.
To create a the cloak, Lu Lan and fellow researchers at Zhejiang University in China started off with a computer model of a solid object surrounded by some kind of material. The model simulates how the material bends and distorts electromagnetic radiation (light, microwaves, etc.) around the object. Using some kind of algorithm (possibly genetic), the software then slowly alters the shape and design of the material to achieve a certain end goal. In this case, as the end goal is invisibility, the computer model is trying to create a material that can surround an object while causing as little distortion as possible.The Teflon invisibility cloak (left). A and B are the electromagnetic signature without the cloak; C and D are with.
Historically, invisibility cloaks have generally been fashioned out of metamaterials -- man-made materials that have weird and wacky properties not found in nature. Metamaterials can have a negative refractive index, allowing for materials that can bend light around an object without distortion. The problem is, it's hard and time-consuming (and thus expensive) to create a cloak out of metamaterials -- which is why researchers are looking at alternative solutions, such as simple mirrors or Teflon.
Teflon, also known by its generic name of polytetrafluoroethylene (PTFE), is popularly used as a non-stick coating on frying pans and other objects, but as far as the Chinese researchers are concerned it's just a rugged polymer that can easily be engraved to the specifications dictated by the topology optimization. Once the computer model has finished its optimization, the computed topology is sent to a Jingdiao CNC engraving machine (pictured right), which fashions the Teflon into the exact shape and patterning required.
According to Technology Review(Opens in a new window), this is the first time that topological optimization -- which is a fairly mature area of computer science and applied physics -- has been made manifest in the physical realm. It took just 15 minutes for the CNC machine to create the cloak out of Teflon, too.
The finished cloak, which resembles an eyelid, successfully cloaks a metal disc that's roughly the size of a poker chip from microwaves. According to the researchers, it should be possible to build a cloak that works with visible light, too, though (for some reason) they haven't done it yet. A lot more work will need to be done to create materials that can cloak a broad range of frequencies from a wide range of angles, but in general the concept is sound. The possibility of a real-world, Harry Potteresque invisibility cloak creeps slowly forward.arXiv:1308.6049(Opens in a new window) - "Experimentally demonstrated an unidirectional electromagnetic cloak designed by topology optimization"