| The artificial metasurface(MS)is a planar form of three-dimensional electromagnetic metamaterial that has extraordinary electromagnetic wave manipulating abilities.MS can modulate key parameters such as amplitude,phase and polarization of electromagnetic waves.The reconfigurable MS is an electronically adjustable extension of the conventional MS,and the electromagnetic wave parameters can be dynamically adjusted by introducing active components.This laid the foundation for engineering application of artificial MSs.In recent years,artificial MS have been widely used in the study of special electromagnetic phenomena,such as generation of orbital angular momentum vortex waves,electromagnetic focused surfaces and metamaterial imaging system.Applications in these areas have demonstrated the abilities of MSs to modulate electromagnetic waves.The MS with reconfigurable characteristics can further realize wireless communication system based on vortex electromagnetic wave;electrically adjustable single-point and multi-point focused surface for wireless power transmission;and time-domain microwave imaging surface.The research on reconfigurable artificial MS is the current and future development trend,which provides the possibility of integration,platformization and digitization of metamaterials.The specific research content of this dissertation includes the following aspects:1.Reconfigurable MS element simulation method for lumped components loaded elements is studied.This dissertation proposes a multi-port cascaded method to simulate the lumped component loaded elements,which greatly improves the research and design efficiency of the reconfigurable unit.This method covers the design process of all reconfigurable units herein.At the same time,in order to improve the analysis efficiency of scattering problem of reconfigurable MS,the far-field radiation and near-field distribution of MS are studied.The angular spectrum plane wave approach is introduced to calculate the scattered fields.Comparing to the full-wave simulation software,the method is fast and accurate,which brings convenience to the design of the MSs.2.Diversity orbital angular momentum vortex wave generator based on reconfigurable artificial MS is studied.Continuous and discrete type of reconfigurable MS vortex beam generator are implemented in this dissertation.First,to simulate the continuous adjustable phase shift element of conventional MS,this dissertation proposes to realize the orbital angular momentum vortex wave generator using varactor tuned reconfigurable MS.A 16 × 16 reconfigurable MS operating at 5.0 GHz was designed,and four different vortex electromagnetic waves with different propagation directions and different modes were experimentally measured.In order to further simplify the design of the diversity vortex beam generator,a 1-bit reconfigurable MS vortex waves generator is proposed.The calculation process is given for the compensation phase calculation method of generating vortex waves using 1-bit quantization.A 12 × 12 1-bit digital MS was designed and experimentally measured vortex waves of different modes.These two schemes paved the way to build vortex-based communication systems.3.Digital electromagnetic focused surface research for wireless power transmitter is studied.Wireless power transmitter based on reconfigurable MSs,which is according to external demands,is a new method for wireless power transmission.It has further transmission distance and greater flexibility than conventional coupled wireless power transmission.From the analysis of both achievability and performance,2-bit scheme is a better trade-off for digital electromagnetic focused MSs.In this dissertation,a U-shaped two-arm asymmetric slitting unit is proposed,which uses two PIN diodes to achieve 90°,180° and 270° phase shifts.Based on this unit,a 12 × 12 2-bit electromagnetic focused surface is realized.The near-field energy focused effect was obtained and the power transfer flexibility was verified by antenna transmission simulations.This experiment enriches the application of digital MS,making them commercially viable.4.Time domain imaging surface is studied based on 1-bit reconfigurable MS.Metamaterial microwave imaging is a novel research field,which can realize microwave computing imaging by using the characteristics of flexible materials to tailor electromagnetic waves.In order to reduce the frequency requirements of existing metamaterials imaging system,this dissertation proposes to use a reflective 1-bit reconfigurable MS to form numerous stray beams in time domain to achieve imaging.A 1-bit reconfigurable unit operating at 35 GHz was designed and a 20 × 20 MS was designed based on this unit.Multiple sets of stray beams are experimentally measured for image reconstruction,and the ideal results are obtained.This experiment laid a solid foundation for the subsequent high-speed digital circuit controlled 1-bit MS imaging system.5.1-Bit wideband reconfigurable artificial MS and reconfigurable polarization converter is studied.The bandwidth of 1-bit reconfigurable MS is narrow thereby the study of this problem can greatly improve the practical application of 1-bit reconfigurable MS.In this dissertation,a design method of selecting center frequency is proposed.The experimental result showed that the-1 d B relative gain bandwidth is 8.4%.Existing polarization converter with reconfigurable characteristics can only achieve conversion of certain polarization.In this dissertation,the varactor diode is introduced into the truncated square patch,which realizes a variety of polarization conversions without changing the polarization of incident wave.Research on these issues has taken a step forward in the practical engineering application of reconfigurable MSs. |
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