A full-parameter unidirectional metamaterial cloak for microwaves

Abstract

Invisibility is a notion that has long captivated the popular imagination. However, in 2006, invisibility became a practical matter for the scientific community as well, with the suggestion that artificially structured metamaterials could enable a new electromagnetic design paradigm, now termed transformation optics1. Since the advent of transformation optics and subsequent initial demonstration of the microwave cloak2, the field has grown rapidly. However, the complexity of the transformation optics material prescription has continually forced researchers to make simplifying approximations to achieve even a subset of the desired functionality3,4,5,6,7,8,9,10,11,12,13,14. These approximations place profound limitations on the performance of transformation optics devices in general11, and cloaks especially15,16. Here, we design and experimentally characterize a two-dimensional, unidirectional cloak that makes no approximations to the underlying transformation optics formulation, yet is capable of reducing the scattering of an object ten wavelengths in size. We demonstrate that this approximation-free design regains the performance characteristics promised by transformation optics.

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Figure 1: Simulations of the fabricated cloak design.
Figure 2: Photographs of the fabricated cloak.
Figure 3: Metamaterial-unit-cell design.
Figure 4: Measured electric field data for free space, the cloak and a copper cylinder at the optimum cloaking frequency of 10.2 GHz.

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Acknowledgements

This work was financially supported by the Office of Naval Research through contract No. N00167-11-P-0292, administered by the Naval Surface Warfare Center. Partial support for this project also came from a Multidisciplinary University Research Initiative, sponsored by the US Army Research Office (Grant No. W911NF-09-1-0539). We also acknowledge insightful discussions with D. Rule, K. Boulais, L. Hale and R. Stark.

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N.L. and D.R.S. jointly conceived of the full-parameter implementation of the carpet cloak. N.L. conceived of the use of corrugations as anisotropic, permeable media. N.L. designed, fabricated and measured the cloak. The manuscript was prepared by N.L. under the supervision of D.R.S.

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Correspondence to Nathan Landy.

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The authors declare no competing financial interests.

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Landy, N., Smith, D. A full-parameter unidirectional metamaterial cloak for microwaves. Nature Mater 12, 25–28 (2013). https://doi.org/10.1038/nmat3476

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