The dashed lines represent the refracted path of radiation entering a conventional material with a positive index of refraction. Electromagnetic radiation refracts or bends at a negative angle when entering and leaving a slab of material with a negative index of refraction as indicated by the solid lines. The negative refraction angles enable radiation to converge to a focal point.
Long description of figure 1.
Left-handed metamaterials (LHMs), also known as negative-index materials, are a new media engineered to provide an effective negative index of refraction over a selected frequency range. This characteristic enables LHMs to exhibit physical properties never before observed. In particular, a negative index of refraction causes electromagnetic radiation to refract or bend at a negative angle when entering and leaving an LHM as shown in this schematic. This enables radiation to be focused with a flat LHM lens. With a flat lens, unlike a conventional curved lens, the focal length can be varied simply by adjusting the distance between the lens and the electromagnetic wave source. Researchers at the NASA Glenn Research Center developed computational models for LHMs with commercial three-dimensional electromagnetic simulation codes (ref. 1), constructed an LHM flat lens, and used it to experimentally demonstrate reversed refraction and multifocal flat lens focusing of microwave radiation (ref. 2).
Part of the left-handed metamaterial array configuration, which was constructed of copper split-ring resonators and wires mounted on interlocking sheets of fiberglass circuit board. The total array consists of 3 by 20 by 20 unit cells with overall dimensions of 10 by 100 by 100 mm.
Long description of figure 2.
The LHM configuration used in this experiment is a periodic array of metallic rings and wires based on work by researchers at the University of California at San Diego (refs. 3 and 4). The photograph shows part of the flat lens array of LHM cells that Glenn researchers constructed. For the focusing experiment, the metamaterial slab was placed inside a parallel-plate waveguide. On the source side, microwaves were emitted from a dipole antenna and directed into the metamaterial array.On the other side of the array, a computer-controlled detecting probe measured the power distribution in the x-y plane.
Measured power beyond the metamaterial array with a microwave source located distances of 30 mm (top), 50 mm (center), and 70 mm (bottom) in front of the array. The corresponding focal points are indicated by the maxima in power and are positioned at 87.5 mm (top), 60 mm (center), and 40 mm (bottom) beyond the metamaterial array. As the source was moved farther from the array, the focal point occurred closer to the array.
The graphs show the measured power beyond the metamaterial array. These results indicate the effects of negative refraction and demonstrate the feasibility of a multifocal left-handed metamaterial flat lens. Because of the high attenuation with the ring and wire geometry, approaches that could be more promising for practical applications are being investigated. A low-loss flat lens could enable objects positioned at different distances from the lens to be recorded by simply moving a recorder toward or away from the lens. If such a lens can be developed with ultrahigh resolution, it could have tremendous impact on a wide range of applications including wireless communications, integrated circuit manufacturing, biomedical imaging, detection of low levels of biological and chemical elements, and molecular viewing and manipulation.
Find out more about this research:
Glenn’s Communications Division:
http://ctd.grc.nasa.gov
Glenn’s Independent Research & Development Fund:
http://www.grc.nasa.gov/WWW/5000/IRD/
Glenn contact:
Dr. Jeffrey D. Wilson, 216-433-3513, Jeffrey.D.Wilson@nasa.gov
Analex Corporation contact:
Christine T. Chevalier, 216-433-6082, Christine.T.Chevalier@nasa.gov
Authors:
Dr. Jeffrey D. Wilson, Zachary D. Schwartz, and Christine T. Chevalier
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Last updated: October 16, 2006
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