Invisible cloak berkeley8/29/2023 ![]() ![]() "It is the first bulk material that can be described as having optical magnetism, so both the electrical and magnetic fields in a light wave move backward in the material." "Natural materials do not respond to the magnetic field of light, but the metamaterial we created here does," said Valentine. In the case of the "fishnet" material described in Nature, the strongly interacting nanocircuits allow the light to pass through the material and expend less energy moving through the metal layers. Valentine also noted that both materials achieve negative refraction while minimizing the amount of energy that is absorbed or "lost" as light passes through them. Stacking the alternating layers together creates a series of circuits that respond together in opposition to that of the magnetic field from the incoming light. Jason Valentine, UC Berkeley graduate student and co-lead author of the Nature paper, explained that each pair of conducting and non-conducting layers forms a circuit, or current loop. At wavelengths as short as 1500 nanometers, the near-infrared light range, researchers measured a negative index of refraction. In the Nature paper, the UC Berkeley researchers stacked together alternating layers of silver and non-conducting magnesium fluoride, and cut nanoscale-sized fishnet patterns into the layers to create a bulk optical metamaterial. Not surprisingly, there has been more success in manipulating wavelengths in the longer microwave band, which can measure 1 millimeter up to 30 centimeters long. (A human hair is about 100,000 nanometers in diameter.)įor a metamaterial to achieve negative refraction, its structural array must be smaller than the electromagnetic wavelength being used. Infrared light wavelengths are longer, measuring from about 750 nanometers to 1 millimeter. Humans view the world through the narrow band of electromagnetic radiation known as visible light, with wavelengths ranging from 400 nanometers (violet and purple light), to 700 nanometers (deep red light). Zhang is also a faculty scientist in the Material Sciences Division at the Lawrence Berkeley National Laboratory. "Both bring us a major step closer to the development of practical applications for metamaterials." "What we have done is take two very different approaches to the challenge of creating bulk metamaterials that can exhibit negative refraction in optical frequencies," said Xiang Zhang, professor at UC Berkeley's Nanoscale Science and Engineering Center, funded by the National Science Foundation (NSF), and head of the research teams that developed the two new metamaterials. Thicker, 3-D metamaterials with negative refraction have only been reported at longer microwave wavelengths. Other research teams have previously developed metamaterials that function at optical frequencies, but those 2-D materials have been limited to a single monolayer of artificial atoms whose light-bending properties cannot be defined. ![]() Or, to give another example, a fish swimming underwater would instead appear to be moving in the air above the water's surface. If water exhibited negative refraction, the submerged portion of the pole would instead appear to jut out from the water's surface. In a classic illustration of how refraction works, the submerged part of a pole inserted into water will appear as if it is bent up towards the water's surface. In contrast, all materials found in nature have a positive refractive index, a measure of how much electromagnetic waves are bent when moving from one medium to another. ![]() The common thread in such metamaterials is negative refraction. For optical microscopes to discern individual, living viruses or DNA molecules, the resolution of the microscope must be smaller than the wavelength of light. In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock. 15 issue of Science.Īpplications for a metamaterial entail altering how light normally behaves. 13 advanced online issue of Nature, and in the Aug. Two breakthroughs in the development of metamaterials - composite materials with extraordinary capabilities to bend electromagnetic waves - are reported separately this week in the Aug. ![]()
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