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Improving Absorber

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Scientists have long been seeking ways to cloak items and render them invisible for the purposes of stealth and surveillance.

Using concepts from transformation optics, in which metamaterials are designed to produce specific optical properties, scientists from Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE), led by Prof Luo Yu and Imperial College London led by Prof Sir John Pendry have proposed a theoretical flat absorber that could better absorb light to cloak objects and hide them from view.

The scientists showed that it is theoretically possible, through a series of transformations, to compact a three-dimensional structure into a two-dimensional surface without losing any of the former’s properties.

Light waves that hit the two-dimensional surface are directed to singular points with sharp edges that confine the waves’ energy and convert it into heat. This reduces the amplitude of reflected light waves, making the surfaceless visible to observers. Furthermore, the surface will remain dark even when illuminated with white light.

The scientists proposed using a compacted layer of doped graphene as a flat absorber. In simulated experiments, the absorber had an absorption level of about 50 percent with a bandwidth of more than 10 terahertz, even in the presence of losses.

“The compacted, hidden dimension has a dramatic effect on the electromagnetic properties of the system: transmission through a single sheet of graphene structured according to our prescription shows a strong broadband absorption of terahertz radiation, as opposed to the isolated absorption peaks of a conventional grating,” said the scientists.

They added that while they had made a few assumptions in their simulations that will not hold up in some real life circumstances, these should not have a significant impact on the realised absorber’s performance.





By Professor Luo Yu

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Published on 29 June 2018​
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