Metamaterial Devices for Wavefront Manipulation from Microwave to Optical Frequencies

This thesis presents highly efficient metamaterial devices for wavefront manipulation from microwave to optical frequencies. In this framework, compact and efficient quarter-wave and half-wave plates for long-wave infrared applications are designed based on elliptical antenna array sheets. Half-wave plate unit cells are used in conjunction with the Pancharatnam-Berry (PB) phase principle for efficient refraction, focusing and polarization discrimination. To avoid high losses introduced by metal in the near-infrared regime, an all-dielectric metalens is proposed. The metalenses comprises an array of tapered nano-holes etched into the indium phosphide (InP) substrate. This tapering of the nano-holes acts as a graded-index matching layer, resulting in metalenses with near-unity transmission from 0.9 μm to 1.7 μm. Furthermore, the hole array concept is adapted to designing a grade-index (GRIN) lens at millimeter-wave frequencies. GRIN matching layers are proposed to match the GRIN lens. The optimal permittivity in the GRIN matching layers is calculated through the transfer-matrix method. The resulting matched GRIN lens has very high radiation efficiency. In this thesis, anti-reflection or impedance matching with anisotropic metamaterials is also investigated. With specific material tensors, an anisotropic matching layer can be used to match an arbitrary substrate to free space at an arbitrary incident angle. Realistic metamaterial structures are proposed at microwaves to achieve the required material parameter tensors and perfect matching is demonstrated for either TE or TM polarization at a near grazing angle of 88 degrees. To match TE and TM polarizations simultaneously, a magneto-electric uniaxial matching layer (MEUML) is proposed and matching is demonstrated at 45 degrees. The MEUML is applied to a sandwich radome design at X-band and the resulting radome has an exceptional angular performance. Lastly, a single-layer metamaterial radome is designed at 34.3 GHz. Two coupled metasurfaces are patterned on a regular dielectric substrate to transform it into a homogenized metamaterial slab. By tuning the metasurfaces and their coupling, the metamaterial slab exhibits equal effective permittivity and permeability. The resulting structure is impedance matched to free space. The single-layer metamaterial radome is polarization-insensitive, low loss, broadband, and easy to fabricate, making it attractive for many millimeter-wave applications.Ph.D