Toward an end-to-end design procedure for electromagnetic Huygens' metasurfaces
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Date
2023-04-21
Authors
Kelly, Max
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Abstract
This thesis presents a systematic end-to-end design procedure for electromagnetic metasurfaces. Metasurfaces are electrically thin (and often planar) transformers for electromagnetic fields. A designer aims to construct a metasurface such that it transforms a known incident field into a new desired one. Given the input and desired output, the designer computes the required surface properties along the metasurface. These surface properties are implemented using a grid of subwavelength scattering elements, known as unit-cells or meta-atoms. Computing the necessary surface properties of a metasurface given the desired transformation is known as macroscopic metasurface design. This thesis uses previously developed methods to accomplish the macroscopic design step. The focus of this thesis is therefore on microscopic design. Microscopic design entails computing the physical structure of the unit-cells, so that the required surface property profile along the metasurface is fulfilled. There are several issues that arise during the unit-cell design process. For Huygens' metasurfaces considered in this thesis, the unit-cell is a layered structure, with each layer implemented using a metallic trace. If each trace is selected without consideration for the rest of the structure, near-field coupling effects between the different layers significantly degrade the performance. Additionally, each unit-cell is designed and simulated under periodic conditions, which are not met in the final metasurface design. In this work, an evolving microscopic design strategy is developed to select the unit-cells for several different metasurfaces. An optimization procedure is adapted to tune the unit-cells in a manner that accounts for the mutual coupling effects. Two metasurfaces are designed that synthesize a desired far-field power pattern under both transverse electric (TE) and transverse magnetic (TM) assumptions. A third metasurface is designed for the purpose of plane wave refraction. Lastly, a fourth metasurface is designed which uses auxiliary surface waves to redistribute the incident power over the metasurface. This thesis therefore presents an end-to-end design process that provides a physically realizable metasurface structure, given the desired function of the metasurface. The results are verified both using full-wave simulation and in a laboratory setting.
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Electromagnetic metasurfaces