Duke University Creates “Perfect” Microwave Cloak


Perfect invisibility cloak built by Duke University graduate engineering students. Credit: Duke University

Scientists have been able to successfully cloak an object, rendering a centimeter-scale cylinder invisible to microwaves. Many different invisibility cloaks have been demonstrated, but all of those reflect some of the incidental light, making the illusion incomplete. This is the first to cloak an object perfectly.

The scientists published their findings in the journal Nature Materials. This illusion does have drawbacks. It only works from one direction, and would be difficult to achieve with visible light. The initial invisibility cloaking papers from 2006 sparked a flurry of activity to move the work on to different wavelengths.


Simulations of the fabricated cloak design. Credit: Figure by Nathan Landy & David R. Smith

No effort has been able to achieve a perfect cloak, as was described by the original theory. The structures needed to pull that off are difficult to manufacture, and each attempt has resulted in an approximation to the theoretical idea that results in reflections.

The scientists at Duke University took a different approach. They tried to rework the edge of a microwave cloak so that they line up, ensuring that the light passes around with no reflections.

A diamond-shaped cloak, with properties carefully matched at its corners, was used to shuttle light perfectly around a cylinder 7.5 cm in diameter and 1 cm tall.

While the illusion is perfect, it only works in one direction. It would also be difficult to replicate this at optical wavelengths. However, microwaves have many applications, primarily in telecommunications and radar, and improved versions of cloaking could vastly improve microwave performance.

Reference: “A full-parameter unidirectional metamaterial cloak for microwaves” by Nathan Landy and David R. Smith, 11 November 2012, Nature Materials.
DOI: 10.1038/nmat3476

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