AFRL-Demonstrated Metamaterials Technology Transforms Antenna Radiation Pattern Published Oct. 22, 2008 By Beverley Thompson Sensors Directorate WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL researchers demonstrated the capacity of electromagnetic metamaterials to tailor antenna radiation patterns. Metamaterials have inherent properties not present in naturally occurring materials. This distinction usually stems from the way in which a given metamaterial's constituents are structured. The researchers designed and fabricated a block of "post and split-ring resonator" metamaterial that, with its microwave frequency of nearly 13.8 GHz, has a refractive index that is close to zero. Refractive index is a measure of how a particular material bends and/or reflects electromagnetic radiation (including microwaves or light waves) impinging upon it. For "normal" materials, such as glass, this index is greater than 1; for air, it is almost exactly 1. Near-zero index materials (NZIM) do not exist in nature; radiation emitted from these manufactured materials into the surrounding air must exit in a direction essentially perpendicular to the NZIM. The AFRL research team exploited this NZIM characteristic to transform properties of the well-known dipole antenna (which is similar to the stick-type antenna on many automobiles). The demonstrations showed that while the microwave radiation emitted from a dipole antenna into free space has no directionality, the radiation emitted from a dipole placed inside the NZIM radiates strongly in the direction perpendicular to the plane of the metamaterial. This phenomenon is the opposite of what happens with optical fibers--which, with refractive indices greater than 1, trap and can "guide" light. This unusual result indicates how further research on metamaterials-based antenna combinations may lead to surprising and useful radio frequency components.