| Recently,metasurfaces have attracted enormous interest in physics and engineering communities owing to their powerful abilities of controlling electromagnetic(EM)waves.By introducing a series of the artificially designed meta-particles on the two-dimensional surface,the metasurface is able to control the magnitude and phase of the EM waves over the wavelength scale and thus realize full-control of reflection and refraction from the microwave to optical regions.A series of electromagnetic scattering control devices based on metasurfaces can realize free modulation of electromagnetic scattering characteristics and many interesting functions,such as electromagnetic absorption,beam focusing,polarization conversion,beam deflecting and diffusion,vortex beam generation and holography.One of the most important advantages of the metasurface device over the traditional electromagnetic scattering control device is the design freedom of the sub-wavelength structure,which makes it possible to integrate multiple electromagnetic scattering control functions into one metasurface device.This paper starts with the design and integration of subwavelength structure,aiming at the application problems that are difficult to be solved by several traditional devices,and explores the design methods of multifunctional electromagnetic scattering control devices.The main contents of this dissertation include:1.A multi-functional metasurface device is designed to achieve high-efficiency in-band transmission and out-band radar cross-section(RCS)reduction.The FSS layer allows the metasurface to achieve high-efficiency transmission at about 3.9GHz,while maintaining the total reflection characteristics required by the top-level phase modulation structure.Through the special distribution of 0 and ? reflection phase units,the backscatter energy in the 8-16 GHz can be reduced.Compared with simple RCS reduction device proposed before,our multi-functional metasurface can combine the characteristics of wave transmission and low RCS,which is suitable for stealth radome.The simulation and experimental results of the cylinder model verify the applicability of the device to the curved surface application environment.In addition,the numerical simulation shows that the special electromagnetic control functions such as polarization conversion can be further integrated in the passband by changing the metal structure of FSS layer without affecting the RCS reduction performance.This concept can pave the way for the development of stealth detection technology and has important potential applications in the field of radome.2.A broad-band low scattering metasurface is proposed by combining two kinds of EM scattering control functions.By using geometric phase element and RFSS film,the metasurface is constructed,beam scattering and electromagnetic absorption are introduced in different frequency bands to achieve wide-band RCS reduction.Through the study of far-field scattering pattern,electric field distribution and power loss density,the detailed physical mechanism is analyzed.The RCS Reduction in the 13-21.5GHz band is mainly due to the beam scattering realized by the phase modulation of geometric phase units,while the RFSS film plays a leading role in RCS Reduction in the 21.5-31.5GHz band by absorbing the incident electromagnetic wave.Simulation and experimental results show that the backscattering energy of our metasurface can be effectively reduced by 10 dB from 13-31.5GHz,which has good angular stability and polarization stability.This method can be applied to similar beam scattering metasurfaces to reduce the RCS bandwidth by introducing RFSS.Compared with the traditional single RCS Reduction Mechanism,the application of the two electromagnetic scattering control functions provides more freedom for the realization of ultra wideband or multi band RCS reduction devices,and has potential application prospects in some specific fields.3.A method of realizing different OAM mode vortex beams by using a single-layer metasurface is proposed.The meta-atoms,which combines the resonant phase modulation structure and the geometric phase modulation structure,is used to construct the vortex metasurface device.When the linearly polarized wave is incident on the metasurface,the resonant phase element with spiral phase distribution can realize the vortex beam with topological charge + 1 at 5.2GHz.When the left-handed circularly polarized wave is set as the incidence from 10.5GHz to 12 GHz,the geometric phase element helps the metasurface generates a deflected vortex beam with a topological charge of + 2.Simulation and experimental results show that the proposed single-layer metasurface has good performance in the above two frequency bands.Because all the metal subwavelength structures are printed on the single-layer dielectric substrate,it is a convenient and effective design method when it requires small thickness and low cost. |
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