Research On Far-field And Near-field Manipulation Mechanism Based On Metasurface

As a novel type of electromagnetic material,metasurfaces have been introduced into the microwave,millimeter wave and terahertz wave region from optical regions recently.Due to its advantages of low-volume,low-profile and excellent ability in manipulating wavefront,metasurfaces have been further developed.Metasurfaces are planar arrays composed of artificially designed subwavelength sized units.This subwavelength sized artificial unit can be regarded as the functional element of metasurfaces,which can manipulate the basic characteristics of electromagnetic waves(such as polarization,amplitude,phase,etc.);The artificial sequencing of metasurface is to arrange the functional elements in an orderly manner,which can manipulate the interference and coupling effects between functional elements;Through the cooperation of functional elements and artificial sequencing,the metasurface can realize high-performance and multi-functional far-field and nearfield manipulation of electromagnetic waves.Devices for far-filed and near-field manipulation are very important microwave devices,which are widely used in wireless communication,wireless power transfer and information storage.The research of microwave far-field and near-field manipulataion devices based on metasurface has made some progress,but there are also many challenges.In this dissertation,the construction of metasurface functional elements,artificial sequencing optimization and the cooperative correlation mechanism between functional elements and artificial sequencing are systematically studied,and functional devices design method aiming at high-performance and multi-functional regulation mechanism are proposed.A series of metasurfaces are designed for farfield beam and near-field energy distribution manipulation,laying foundation for engineering application of metasurfaces based devices for far-field and near-field manipulation.Firstly,methods for far-field beam and near-field energy distribution manipulation of metasurface are systematically analyzed.Firstly,based on Floquet theory,a modulation method for diffraction harmonics of periodic metasurface is proposed.Then,based on the computer-generated hologram algorithm of the optical region,the Green’s function is used to replace the Fraunhofer diffraction propagation formula in the classical holographic algorithm,and the weight factor is introduced into the formula.A near-field holographic algorithm which can flexibly and efficiently manipulate the near-field energy distribution is proposed,laying theoretical foundation for the application of metasurface in microwave near-field wireless communication and wireless energy transferSecondly,a circularly polarized retroreflector based on the modified geometric phase theory and polarization synthesis theory is proposed,providing efficient methods to manipulate the oblique incident circularly polarized wave.Based on the harmonic modulation theory,the artificial sequencing of the dual channel retroreflector is optimized,and the metasurface retroreflector with helicity-preserving characteristics based on the modified geometric phase theory,and the metasurface retroreflector with helicity-switching characteristics based on the polarization synthesis theory are realized respectively.The high-efficiency retroreflection under each polarization and channel is verified by experiments.Then,the artificial sequencing of the metasurface is optimized by using the weight factor in the microwave region holographic algorithm.Based on Huygens’ principle,a Huygens’ metasurface functional elements with perfect transmission efficiency and 360° phase full coverage is designed.The experiment shows that by optimizing the coding artificial sequencing of the metasurface,the high-quality multifocal holographic imaging and the modulation of energy distribution between different focal points are realized in the transmission near field.By embedding active devices,a reconfigurable metasurface functional element with reflection phase covering nearly 360° is designed.The experiment shows that the dynamic and aberration-free near-field manipulation can be realized by dynamically optimizing the artificial sequencing of the metasurface through the external control circuit,expanding function of the metasurface.Finally,by comprehensively optimizing the geometric phase and propagation phase,the expansion methods of metasurface channel capacity is studied to obtain functional elements with multi-channel multiplexing characteristics.By combining geometric phase and propagation phase,a functional element which can simultaneously manipulate the co-polarized and cross-polarized components in the transmission field is constructed.Experiments show that such method can realize the function of dual-channel near-field polarization based multifocal convergence in the transmitted field.In addition,using the method of polarization and frequency multiplexing,a functional element which can independently manipulate electromagnetic waves with different frequencies and different polarizations is constructed.The metasurface constructed by functional elements realizes six-channel high-quality holographic imaging,which provides a feasible scheme for multichannel and high-capacity near-field holographic manipulation.To sum up,aiming at the problems existing in the practical application of farfield and near-field manipulation devices based on metasurface,a series of research and experimental testing from the construction of functional elements,the optimization of artificial sequencing to the synergy mechanism between functional elements and artificial sequencing by closely combining theoretical research,model optimization,simulation design and experimental verification are carried out in this dissertation,providing a solid theoretical basis and application guidance for the potential application of far-field and near-field manipulation devices based on metasurface.