Polarizable Particles and their Two-Dimensional Arrays: Advances in Small Antenna and Metasurface Technologies
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Metamaterials are subwavelength-structured materials designed to exhibit tailored electromagnetic properties. Metamaterials have allowed extreme control over constituent material parameters (i.e. permittivity, permeability, and chirality), which has enabled a myriad of counterintuitive physical phenomena. However, metamaterials typically suffer from high losses, difficulties in fabrication, and are bulky. This has led to the development of metasurfaces, which are the two-dimensional equivalent of metamaterials. Metasurfaces can impart abrupt discontinuities on electromagnetic wavefronts, allowing electromagnetic fields to be tailored across subwavelength length scales. At microwave frequencies, novel lenses, antennas, and radomes can be realized with metasurfaces. At optical frequencies, metasurfaces can find application in sensors, displays, and microparticle manipulation. In contrast, more conventional optics such as dielectric lenses and spatial light modulators are bulky, which limits their integration into nanophotonic systems.
The building blocks of metasurfaces are subwavelength textured, polarizable particles. Near resonance, these particles support strong currents, which makes them excellent antennas. Therefore, methods to both analyze and fabricate small antennas are developed first. These small antennas are important for a number of emerging technologies resulting from the rapid expansion of the mobile electronics industry. Next, two-dimensional arrays of polarizable particles (i.e. metasurfaces) are considered, which provide extreme polarization and wavefront control. It is shown that adding a magnetic response in addition to an electric response can significantly improve the efficiency of previously reported metasurfaces, which only exhibited electric responses. Further, adding magneto-electric coupling enables arbitrary control of a wavefront (i.e. control of the transmitted and reflected phase as well as the transmitted/reflected amplitude). Methods to systematically design and fabricate high performance metasurfaces are proposed. In addition, the experimental verification at frequencies ranging from microwaves to optics highlights the versatility of the proposed design processes.