A report discusses a research and development project that has made contributions to the art of metamaterials for directing electromagnetic radiation at frequencies of the order of several gigahertz. The next-generation metamaterials expected to emerge from this and related projects could enormously improve the performances of microwave radar and communication antennas.
The term "metamaterials" as used here denotes artificial material structures composed of metal, dielectric, and/or metal/dielectric-composite substructures that have feature sizes variously comparable to or smaller than the wavelengths of the electromagnetic radiation that they are intended to handle. Metamaterials that have periodic or quasiperiodic substructures can also be characterized as photonic crystals.
Natural materials and most artificial materials exhibit positive refraction: the real parts of their indices of refraction are positive. In contrast, metamaterials can be designed to exhibit negative refraction at certain wavelengths: At those wavelengths, the real parts of their indices of refraction are negative, and for optical waves propagating through them, optical power flows antiparallel to the wave vectors. A metamaterial that exhibits negative refraction is also denoted a left-handed metamaterial because mathematically, the antiparallelarity of the Poynting vector (the electromagnetic-power-density vector) and the wave vector is a consequence of the fact that the electric, magnetic, and Poynting vectors constitute a left-handed triple instead of a right-handed triple as in a vacuum or an ordinary material.
Heretofore, negative refraction has not been widely exploited as a means of directing electromagnetic radiation. The instant research and development effort has been directed toward understanding and exploiting negative refraction for directing microwave radiation. The advances made by this project include new metamaterial designs and the discovery of previously unknown negative-refraction phenomena.
This work was done by Sridar Srinivas of Northeastern University for the Air Force Research Laboratory. For further information, download the free white paper at www.defensetechbriefs.com under the Materials category. AFRL-0018
This Brief includes a Technical Support Package (TSP).
Metamaterials for Advanced Microwave Antennas
(reference AFRL-0018) is currently available for download from the TSP library.
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