Abstract
Metasurfaces have made significant progress in recent years, offering complete control of electromagnetic waves in amplitude, phase, polarization and wavevector with subwavelength thickness. However, single functionality and imbalances between various properties like working bandwidth, efficiency and fabrication complexity still limit their practical applications.This thesis is focused on addressing these limitations and advancing the design of functional mm-wave metasurfaces. In Chapter 1, the advantages of metasurfaces over other electromagnetic wave devices are discussed, highlighting their unique capabilities. Chapter 2 summarizes the design principles of metasurfaces, including phase manipulation methods and spatial phase profiles.
Chapter 3 presents an optical transparent reflective metasurface for broadband mono- and bi-static Radar Cross Section reduction with robust angular performance. This design utilizes two single layer unit cells which have high reflection amplitudes and π phase difference across a broad bandwidth. The spatial phase distribution is optimized using particle swarm optimization. Compared to conventional chessboard metasurfaces, the optimized metasurface shows improved mono- and bi-static RCS reductions.
Chapter 4 demonstrates a dual-polarized achromatic Huygens’ metalens with a large numerical aperture and a broad bandwidth. A dual-polarized three metallic unit cell is firstly proposed to realize a broad phase coverage and a large group delay with multiple resonances. Then an achromatic metalens is designed, showing large NA focusing with high efficiency. Finally, a more broadband unit cell is developed and used to construct a broadband and high aperture efficiency transmitarray.
In Chapter 5, we propose a metalens focusing stable under a wide angular incidence range [-45°, 45°]. This design combines Huygens’ unit cells with resonances and mildly-resonant unit cells to achieve a 2π phase coverage with robust angular performance. The phase profile is optimized with even-order polynomials. Simulation results demonstrate stable focusing performance under oblique incidences. Furthermore, the wide-angle metalens is verified with a multibeam transmitarray.
Chapter 6 proposes a full-space metalens with four controllable channels in the mm-wave region. The design combines the geometric phase and propagation phase with an ultra-thin PCB layer and a 3D printed dielectric post, which enables the decoupling of orthogonal-circular-polarization output channels in each half space. Two full-space metalens designs are simulated and measured, demonstrating flexible focusing control and multiple OAM beam generations.
Chapter 7 summarizes the outcomes of this thesis and discusses future research directions based the current designed multifunctional metasurfaces.
| Date of Award | 23 Sept 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Man Hon Alex WONG (Supervisor) |
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