| Metasurface is a new two-dimensional artificial electromagnetic material that generates local electromagnetic resonance by designing unitary microstructures,thus achieving free modulation of physical quantities such as electromagnetic wave amplitude,phase,and polarization state in the subwavelength scale.Compared with conventional electromagnetic devices,the metasurface is flat and lightweight,with various modulation dimensions,and easy to integrate and coplanarize with carriers,providing a method of electromagnetic wave modulation applicable to the full wavelength band.Phase is one of the fundamental physical parameters of electromagnetic waves,and based on phase modulation,metasurfaces can achieve arbitrary wavefront modulation of electromagnetic waves,such as spin Hall effect,anomalous scattering,holographic imaging,and beam assignment.Most of the currently reported metasurface designs work on a single band,and multi-band metasurfaces based on shared aperture or spatial multiplexing reduce the overall device efficiency because of the reduced number of working meta-atom per band,and designing multi-band metasurfaces within a single cell structure remains a challenging topic.In addition,adding amplitude modulation to phase modulation,i.e.,achieving complex amplitude modulation,can improve image quality in imaging systems and modulate beam power in multi-beam antenna systems.Based on a single-layer dielectric substrate,this paper investigates the methods to achieve efficient radiation and complex amplitude independent modulation in the design of transmissive,reflective and full-space multiband metasurfaces,solves some of the key problems of metasurfaces in the research related to electromagnetic wavefront modulation,and conducts an in-depth study of electromagnetic devices with different functions.The main research contents and contributions are summarized as follows.In the study of transmissive half-space electromagnetic wave modulation: a highefficiency dual-band metasurface design method is proposed based on a single-layer dielectric substrate.Through the ingenious combination of magnetic resonator and electric resonator nested inside and outside,the 2? phase modulation of circularly polarized electromagnetic waves in X and Ku bands is achieved independently based on the geometric phase principle,and the dual-band focusing lens and dual-band OAM generator are further designed;the weak coupling property between electric and magnetic resonators is utilized,and the three-level amplitude modulation is added on top of the phase modulation to strengthen the metasurface for spatial The power distribution modulation capability is enhanced by adding three-stage amplitude modulation based on phase modulation.Compared with the conventional singlelayer metallic metasurface,the design significantly improves the transmission efficiency without increasing the processing complexity and cost,providing a new idea for the application of multi-band metasurfaces to realistic scenarios.In the study of reflective half-space electromagnetic wave modulation,two C-shape splitring resonators(CSRR)are used to achieve 2-bit phase modulation and continuous amplitude modulation of linearly polarized electromagnetic waves in two important frequency bands of5 G communication,18 GHz and 28 GHz,and to realize multi-focal lens and holographic imaging design.The innovative proposal of alternating two magnetic resonators and one electric resonator in an interleaved arrangement achieves a three-band circularly polarized metasurface with a compact 3:4:5 operating frequency ratio and continuous phase modulation and 1-bit amplitude modulation in each band,and then designs multi-functional metasurface devices,illustrating the functional versatility of multi-band metasurfaces.In the study of full-space electromagnetic wave modulation: To address the problem that both transmissive and reflective metasurfaces modulate only half space,a design method is proposed to realize full-space metasurfaces on a single-layer dielectric substrate to modulate transmissive half-space and reflective half-space electromagnetic waves at 10 GHz and 15 GHz,respectively,to achieve 2?-phase coverage as well as 3-level amplitude modulation.And based on the unit design multifunctional all-space super surface,four vortex beams are generated in the transmission half-space,and the models of the four vortex beams are l1 =-1,l2 = 0,l3 =-1,l4 = +1,which can improve the channel capacity by four times compared with the singlebeam OAM;while in the reflection half-space,with the emblem of East China Normal University "?(Hua)" as the target image,a metasurface hologram is achieved. |
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