Engineering nanostructures allow one to achieve some unconventional and practically useful electromagnetic properties (for example, negative refraction index, near-zero values of permittivity and permeability, and so on). Such novel “metamaterials” can have many applications, e.g. superlenses, cloaks, field concentrators, optical nanocircuits, improved or novel antennas, microwave devices,... But on the other hand, unconventional electromagnetic response poses enormous challenges in characterization of these materials.
Electromagnetic properties of ”conventional materials” like glass or silver are characterized by the constitutive material parameters: permittivity, permeability, conductivity. This simple description is possible because the size of molecules and the distances between molecules are very small as compared with the wavelength of light or microwave radiation. The electromagnetic wave “sees” the averaged response of a huge ensemble of molecules, and the fine features of the field distribution near a single molecule are irrelevant for device design.
The situation is dramatically more difficult for nanostructured materials for optical applications. Indeed, the typical inhomogeneity scale is in the order of tens (or even hundreds) of nanometers, which is commensurate with the wavelength of light (about 400-800 nanometers). Thus, modeling material response to light as an average polarization of a large number of identical and identically excited nanoparticles (as is done for conventional materials) in most cases is not adequate to describe the material properties.
One can experimentally characterize a nanostructure using conventional techniques (like ellipsometry or S-parameter retrieval) and arrive at some value of “effective permittivity”, for example. But in most cases it appears that the obtained quantities are applicable to description of only this particular sample excited by this particular incident electromagnetic wave. Unfortunately, this means that this value cannot be used in device design tools (for example, for designing a lens).
Approaches to proper characterization of complex nanostructures are now actively developed in many laboratories. With this project we try to help researchers and engineers dealing with electromagnetic characterization of such composites.
As a starting point in learning the state of the currently employed approaches to characterization of nanostructured metamaterials we suggest the brochure Nanostructured Metamaterials, recently published by the European Commission. Some introductory tutorial slides can be downloaded here. The experimental techniques used to probe metamaterial properties are conventional optical techniques – the difficulties are rather in interpreting the measurement results. On this web site you can find a description of relevant equipment and a database of facilities available in Europe.
At this stage our recommendation is to use a pragmatic approach to characterization and limit the interpretation of the measured data to experimental validation of the desired phenomena (e.g., sought phase delay across the sample or refraction law).
NEW: A step-by-step road map for experimental characterization of metamaterials has been posted on this page. Please give your feedback via the guestbook!
More advanced information on state-of-the-art in characterization of nanostructured metamaterials can be found at this website on the pages For Beginners and For Specialists.
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The project finished its activities on March 31, 2011, and the content of this site is not anymore regularly updated.