【作者】 刘伟；

【导师】 程强；

【作者基本信息】 东南大学 ， 电子与信息（专业学位）， 2024， 博士

【摘要】 超表面是由亚波长单元按周期或非周期排列形成的人工电磁结构,近年来凭借其强大的电磁调控能力在国内外引发了研究热潮,催生出多种新的物理现象和工程应用。2014年,数字编码超表面和可编程超表面的概念首次被提出,实现了超表面技术与信息技术的有效结合,极大简化了超表面的设计过程,并为超表面在雷达系统、无线通信以及电磁成像等领域的发展和应用提供了新的思路。近年来,时域编码超表面以及时空编码超表面被进一步提出,实现了同时在时间和空间两个维度上对电磁波的操控,显著扩展了其研究方向和应用范围。随着研究的深入,能够在多个维度上调控电磁波的超表面逐渐成为一种发展趋势。本论文系统研究了超表面在调控电磁波极化、相位、频率、幅度和波矢方面的能力,实现了多维度的电磁波调控。论文主要研究内容和创新点概括如下:1.提出了两种具有不同极化转换功能的超表面。第一种是具有极化不敏感性的交叉极化转换超表面,能够将任意极化方向入射波的极化方向偏转90°。首先,推导出该超表面传输特性的琼斯矩阵,并将该矩阵分解成两个子矩阵。其次,设计两种基片集成波导(SIW)以满足两个子矩阵的传输特性,并将这两种SIW以相互交错的排列方式进行排列组合,实现了极化不敏感的交叉极化转换特性。在9.5～10.9 GHz频率范围内,该超表面的转换效率达到-0.2 dB以上。第二种是线/圆极化调控的极化转换超表面,能够对线极化波激励实现任意极化转换,对圆极化波激励实现交叉极化转换并调控其传输相位。借鉴第一种超表面设计思路,设计了两种不同极化转换功能的SIW,通过相互交错排列方式实现了上述功能。在9.7～10.3 GHz频率范围内,该超表面的转换效率达到-0.3 dB以上。实验与仿真结果的一致性验证了所提方法的可行性。2.提出了两种具有宽带极化可重构功能的超表面,第一种能够在整个X波段内,通过控制外部偏置电压,实现线/圆极化波的共极化和交叉极化反射状态切换。在7.4～12GHz频率范围内,该超表面的转换效率达到-1 dB以上。第二种是宽带极化-相位可重构超表面。在线/圆极化波激励下可以实现极化不敏感的共极化1比特相位调控以及交叉极化转换的1比特相位调控。此外,利用不同的空间极化编码方案,实现波束指向和极化方向的独立调控。在7～11.1 GHz频率范围内,转换效率为-1.7 dB以上且极化隔离度在20 dB以上。3.提出了一种独立调控极化和相位的方法。为了验证该方法,设计了一个由两种不同传输/反射特性的子结构单元上下堆叠组成的超表面,其反射特性的琼斯矩阵是两种子结构传输/反射特性琼斯矩阵的乘积。结合时空编码理论,进一步提出了时空极化编码超表面的概念以及一般性理论。相比于时空编码超表面,时空极化编码超表面增加了对极化方向进行任意调控的功能。为了展示其对电磁波多维度调控能力,设计了几个示例实现了在基波以及非线性谐波上对极化方向、相位和波束指向的灵活调控。理论计算、仿真和实测结果的一致性验证了该方法的可行性。4.提出了基于时空极化编码超表面的反射波幅相独立调控方法。具体来说,在时空极化编码超表面上堆叠一个单极化传输结构,该结构仅允许共极化波的传输,并完全吸收交叉极化波。这种设计使得反射波的幅度和相位可以通过两个正交方向上的电压来调控。此外,利用时空编码方案,在基波和非线性谐波上实现了对波束指向和能量的独立调控。理论计算、仿真和实测结果的一致性验证了该方法的可行性。更多还原

【Abstract】 Metasurfaces are artificially electromagnetic(EM)structures composed of sub-wavelength units arranged in periodical or non-periodical patterns.Due to the powerful EM control capabilities,metasurfaces have recently sparked a research boom among domestic and foreign scholars,giving rise to numerous new physical phenomena and engineering applications.In 2014,the concepts of digital coding metasurfaces and programmable metasurfaces were first put forward,effectively integrating metasurfaces technology with information technology.This greatly simplified the design process of metasurfaces and laid the foundations for their development and application in radar systems,wireless communication,and EM imaging.Recently,time-domain digital-coding metasurfaces and space-time-coding(STC)metasurfaces have been proposed,enabling simultaneous manipulation of EM waves in both time and space dimensions,significantly extending their research directions and application.As the investigation moved forward,metasurfaces capable of controlling EM waves in multiple dimensions have gradually become a development trend.This dissertation systematically investigates the manipulation of polarization,phase,frequency,amplitude,and wavevector of EM waves based on metasurfaces,achieving multidimensional manipulation of EM waves.The main contents and innovations of the dissertation are summarized as follows:1.Two types of metasurfaces with distinct polarization conversion functions are proposed.The first is a polarization-insensitive cross-polarization conversion(PICPC)metasurface,which can rotate the polarization direction by 90°for incident waves with the arbitrary polarization direction.Initially,the Jones matrix describing the transmission characteristics of this metasurface was derived and decomposed into two sub-matrices.Subsequently,two types of substrate integrated waveguides(SIWs)were designed to meet the transmission characteristics of the two sub-matrices and were arranged in a cross manner to achieve the polarization-insensitive cross-polarization conversion features.The conversion efficiency of the metasurface is above-0.2 dB in the frequency range of 9.5-10.9 GHz.The second is a linear polarization(LP)/circular polarization(CP)manipulation metasurface,which is capable of arbitrary rotation of polarization direction for LP wave excitation and crosspolarized conversion with phase modulation for CP wave excitation.Learning from the design approach of the first metasurface,two types of SIWs with different polarization conversion functions are designed and arranged in a cross manner to achieve the above functions.The consistency between experimental and simulated results validates the feasibility of the proposed methods.2.Two types of metasurfaces with broadband polarization-reconfigurable capabilities are proposed.The first type can switch between co-and cross-polarized reflection states for LP/CP waves across the entire X-band by controlling the external bias voltage.The conversion efficiency of the metasurface is above-1 dB within the 7.4-12 GHz frequency range.The second type is a broadband polarization-phase reconfigurable metasurface,which can achieve polarization-insensitive co-polarized 1-bit phase manipulation and 1-bit phase manipulation of cross-polarized conversion under the excitations of LP/CP waves.Moreover,independent manipulation of beam direction and polarization direction can be achieved using different space-polarization-coding schemes.Within the 7-11.1 GHz frequency range,the conversion efficiency was above-1.7 dB,and the polarization isolation was more than 20 dB.3.A method for independent manipulation of polarization and phase is proposed.To verify this method,a metasurface composed of two substructure units with different transmission/reflection characteristics was designed to be stacked vertically.The Jones matrix of the metasurface’s reflection characteristics is the product of the Jones matrices of the two substructures’ transmission/reflection characteristics.Integrating this with STC theory,the concept and general theory of space-time-polarization-coding(STPC)metasurface is further proposed,adding the functionality of arbitrarily controlling polarization direction compared to STC metasurfaces.Several examples are designed to demonstrate its capability in the multidimensional manipulation of EM waves,including the control over polarization direction,phase,and beam steering for fundamental wave and nonlinear harmonics.The consistency of theoretical calculations,simulations,and experimental results confirms the feasibility of the proposed methods.4.A method for independent manipulation of reflection amplitude and phase based on the STPC metasurface is proposed.Specifically,a single-polarization transmission structure was stacked on the STPC metasurface,which allows only co-polarized wave transmission and completely absorbs cross-polarized wave.This design enables the manipulation of the reflected amplitude and phase through voltages in two orthogonal directions.Furthermore,utilizing the STC scheme,independent manipulation of beam deflection and energy for both fundamental and harmonic waves has been achieved.The consistency of theoretical calculations,simulations,and experimental measurements validates the feasibility of our proposed approach.更多还原