Oldfart,

While he is correct, I believe that is not pertinent to the applications at hand in this case.

Take, for example, the use of this technology to conceal aircraft from radar.

Any radar has a particular signature, the frequencies it transmits, and the signal strength at those frequencies. The metamaterial cloak will be effective if it conceals the aircraft from the radar, making the aircraft invisible to the tool used to detect it at distance. It need be invisible in the optical end of the spectrum only if the radar used visible light for target detection, currently impractical for multi-mile sensing.

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Eudaimonia