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From science fiction to fact: 3D printed metamaterial bends light to make objects disappear
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By Kira | 3Ders

In the realm of science fiction and fantasy, the power to disappear has long been coveted. The Invisible Woman, Frodo Baggins, Harry Potter and even Batman have relied on either superpowers or invisibility cloaks to fool their enemies. Now, scientists are developing 3D printed technology that brings this fantastical idea one step closer to reality. In fact, according to lead researcher Hao Xin, invisibility cloaks for military airplanes and even people will exist within our lifetime.

Xin is a professor of electrical and computer engineering at the University of Arizona who has been working with the production of metamaterials—synthetic materials engineered to have properties that do not exist in nature, such as the ability to bend electromagnetic, acoustic and other types of waves. Along with his co-researchers, Xin has found a way to 3D print metamaterials from metals, plastics and other substances that exhibit a property known as ‘negative refraction,’ meaning they can actually bend a wave backwards.

The metamaterials in question resemble porous bowling balls and tiny copper wire circuit boards. When they are assembled in precise geometrical patterns, the result is negative refraction: an unnatural bending of the surrounding energy waves, a.k.a, the illusion of invisibility.

One example provided by the University of Arizona is to imagine a straw leaning inside a glass of water. With a normal refractive index (i.e, the property that dictates how light passes through a medium), the straw will appear slightly bent beneath the surface of the water. Now, if the water had a negative refractive index, the straw would actually appear to be bending back on itself and eventually disappearing. In future scenarios, this same technique could be applied to people wearing invisibility cloaks (materials with artificially designed refraction properties) to bend the light around them and at least partially disappear.

This practice of bending light has been around for years, however the downside to the current technique is that a small percentage of light is inevitably still reflected, meaning that the object is never completely invisible. In fact, current designs often draw even more attention to the object due to the strange way they look. “One of the biggest problems with metamaterials is that they produce energy loss. The waves decay as they pass through the artificial material,” said Professor Xin.

In order to solve this problem, the research team has found a way to incorporate battery powered tunnel diodes, a type of semiconductor device, and micronanofabrication technologies into his design. “We have designed a metamaterial that retains negative refraction but does not diminish energy.” In fact, the 3D printed device not only prevented energy loss, it caused energy gain, with the microwave intensifying in strength as it passed through the material. "Many people did not think it was possible to achieve energy gain along with negative refraction," said Xin.

The article was published in the online journal Nature Communications. Titled “Microwave Gain Medium with Negative Refractive Index,” the research was funded by the Air Force Office of Scientific Research (AFOSR), as there are obvious military advantages to invisibility devices. Imagine fighting against an attacker, be it a jet plane or actual person, that you simply cannot see. If the technique is good enough for Batman, you better believe the US Department of Defense is interested in making it a reality.

However, Xin’s work has applications outside of military use as well. His studies in microwave frequencies can be used for optical, acoustic and other types of radiation, allowing engineers to improve microscopes so that they can see the tiniest, most precise details such as individual proteins and viruses. Other metamaterials are being studied to produce higher-performance microwave circuits, energy-efficient and earthquake-resistant buildings, solar power converters, and many other highly advanced technologies.

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Posted on July 18, 2014
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By Hannah Rose Mendoza | 3D Print