A Reconfigurable Multifunctional Metasurface for Full-Space Control of Electromagnetic Waves

Metasurfaces have attracted much attention in recent years due to their powerful abilities in manipulating electromagnetic (EM) waves. However, most of the previously reported metasurfaces are incapable of real-time control of full-space EM waves, including transmission, reflection, and absorption at the same time. In this paper, a reconfigurable multifunctional metasurface is proposed that demonstrates real-time control of transmission, absorption, and reflection of EM waves, which can be continuously controlled from total transmission to total reflection, and to perfect absorption. In the case of total reflection, the reflected waves can be further manipulated in a programmable way by changing the digital coding sequences via bias voltages. Meanwhile, the metasurface can independently control vertical and horizontal polarized waves in broadband. The reconfigurable functionalities of the metasurface are validated by experiments, which agree very well with numerical simulations. In addition, a potential application of the reconfigurable multifunctional metasurface in a stealth radome is proposed and demonstrated.     

Radiation-Type Metasurfaces for Advanced Electromagnetic Manipulation

Manipulating the phase, polarization, and energy distribution of electromagnetic (EM) waves has facilitated numerous applications. Nowadays, metasurface provides an innovational scenario to carry out more promising and advanced control of EM waves. However, it is a great challenge to manipulate polarization, phase, and energy distribution simultaneously with a low profile. Herein, a class of single-layer radiation-type metasurfaces to achieve advanced EM manipulation is proposed. Desired EM functions can be achieved based on the geometric phase and resonant phase. Such metasurfaces enable the capability to manipulate arbitrary phases and linear polarization states simultaneously. Moreover, arbitrary energy distributions can be controlled. As examples of potential applications, three advanced EM functional devices are presented: a novel multiple-input multiple-output antenna with efficient crosstalk suppression and information encryption, an energy-controllable router, and a metasurface holographic imaging based on power transmission algorithm, respectively. The proposed strategy may open up an alternative way of controlling EM waves with advanced performance and minimalist complexity. Moreover, it may lead to advances in information encoding and cryptography.     

Coherent Control of Wave Beams Via Unidirectional Evanescent Modes Excitation

Conventional coherent absorption occurs only when two incident beams exhibit mirror symmetry with respect to the absorbing surface, i.e., the two beams have the same incident angles, phases, and amplitudes. This study proposes a more general metasurface paradigm for coherent perfect absorption with impinging waves from arbitrary asymmetric directions. By exploiting excitation of unidirectional evanescent waves, the output can be fixed at one reflection direction for any amplitude and phase of the control wave. It shows theoretically and confirm experimentally that the relative amplitude of the reflected wave can be tuned continuously from zero to unity by changing the phase difference between the two beams, i.e., switching from coherent perfect absorption to full reflection. It hopes that this study will open up promising possibilities for wave manipulation via evanescent waves engineering with applications in optical switches, optical computing, one-side sensing, photovoltaics, and radar cross-section control.     

Programmable Acoustic Metasurfaces

Metasurfaces open up unprecedented potential for wave engineering using subwavelength sheets. However, a severe limitation of current acoustic metasurfaces is their poor reconfigurability to achieve distinct functions on demand. Here a programmable acoustic metasurface that contains an array of tunable subwavelength unit cells to break the limitation and realize versatile two‐dimensional wave manipulation functions is reported. Each unit cell of the metasurface is composed of a straight channel and five shunted Helmholtz resonators, whose effective mass can be tuned by a robust fluidic system. The phase and amplitude of acoustic waves transmitting through each unit cell can be modulated dynamically and continuously. Based on such mechanism, the metasurface is able to achieve versatile wave manipulation functions, by engineering the phase and amplitude of transmission waves in the subwavelength scale. Through acoustic field scanning experiments, multiple wave manipulation functions, including steering acoustic waves, engineering acoustic beams, and switching on/off acoustic energy flow by using one design of metasurface are visually demonstrated. This work extends the metasurface research and holds great potential for a wide range of applications including acoustic imaging, communication, levitation, and tweezers.     

太赫兹波前调制超表面器件研究进展

超表面是一种由人工微结构组成的超薄平面器件,能够实现对电磁波振幅、相位以及偏振态的调控,具有体积小、重量轻、集成度高、可灵活操控电磁波等优势,在电磁波谱、波前调制中发挥着巨大的作用。综述了近年来基于超表面的太赫兹波前调制器件的研究进展。总结了基于Pancharatnam-Berry相位、基于局域表面等离子体共振(LSPR)、基于Mie共振的三种超表面单元结构对电磁波的振幅、相位调控机理,并讨论了实现高效率超表面的方法。之后,介绍了用于设计波前调制超表面器件的纯相位调制方法和复振幅调制方法。综述了在太赫兹波段典型的超表面波前调制器,包括单一功能、复合功能以及可调谐功能的超表面波前调制器件。在早期的研究工作中,设计的超表面可实现波束偏转、波束聚焦、全息成像、以及涡旋光束、自聚焦光束、洛伦兹光束等特殊光束产生等功能。为提高太赫兹器件的利用率,波分复用、偏振复用等功能复用的太赫兹超表面器件被提出。随着对太赫兹波前动态调控需求的增长, 一些主动的太赫兹超表面器件被提出并在实验上被验证。共有两种主动的超表面器件。其中一种主动超表面是通过将超表面结构与半导体材料或相变材料结合形成的,另一种是通过光泵浦硅片形成的全光器件。全光超表面在不用重新加工的前提下能够被重复使用。通过调整投影在硅片上的超表面图像即可动态操控太赫兹波前。全光超表面具有动态控制波束扫描和波束聚焦的能力,将来可应用于太赫兹通信、太赫兹雷达等领域。最后,对太赫兹波前调制超表面器件的发展趋势与应用前景进行了展望。     

基于异常反射型超表面的天线反射面设计

在实际应用中有许多场合需要对电磁波的传播进行人工调控, 传统的光学器件或者人工电磁介质都是采用三维结构, 但传统的三维结构介质很难与其他器件或设备进行集成.利用相位非连续人工电磁表面则可以在传播路径的介质分界面上引入相位突变, 进而实现人工调控电磁波.文章在此基础上在微波波段利用构造分界面相位梯度提出了一种异常反射型超表面的设计, 用作天线反射面可将圆极化波高效地转化为交叉极化波, 为微波段的电磁波人工调控提供了新的手段.根据广义反射定律及斜入射时相位突变修正设计的天线反射面, 在X波段可以实现对入射电磁波的人工调控, 并通过仿真分析验证了该设计方法的准确性, 为人工电磁表面作为天线反射面提供了一种设计思路.     

基于超表面的智能电磁感知:理论、系统与实验

电磁感知是现代社会迫切需要的非接触式探测技术，而实现实时数据处理、低成本、低能耗的智能电磁感知系统一直是微波探测领域的长期追求目标. 为了实现这一目标，文中将能够任意调控电磁波前的可编程超表面与具有强大信息处理能力的深度学习技术相结合，实现了智能电磁感知系统；并分别从理论、系统设计与实验三个角度深入研究了深度学习驱动的智能电磁感知方法. 文中首先利用“k空间”法分析了基于可编程超表面的电磁感知系统的理论分辨率和影响因素；然后介绍了一款32×24的1比特可编程超表面的系统设计，并实验验证了其动态调控电磁波前的良好性能；在此基础上将深度学习技术引入感知系统中，建立了自适应处理高维感知数据的成像卷积神经网络，实现了高保真度的人体姿态成像. 本文的研究成果可用于指导智能电磁感知系统的设计与分析，并且为未来人工智能时代的电磁感知系统开辟了一条新的途径.     

一种用于宽带RCS减缩的电磁超表面

本文提出了一种用于宽带雷达散射截面减缩的电磁超表面。该电磁超表面一面印制有周期性的金属贴片,另一面为金属面。由于每个金属贴片均会影响反射电磁波的相位,不规则尺寸排列的金属贴片会引起不规则反射相位的反射波,反射能量将在空间分散,这样对比金属平板实现了在 9.5GHz~13.5GHz 频率范围内 2~10dB 的 RCS 减缩。     

动态调控电磁隐身表面

电磁隐身表面在雷达通信与隐身领域具有重要的意义. 本文首先从带内透波/带外反射和带内透波/带外吸波隐身表面、带内透波/吸波和电磁感知隐身超表面四部分介绍了电磁隐身表面的研究进展,并提出了一种动态调控电磁隐身超表面,利用PIN二极管实现通带可开关带外吸收的超表面. 当PIN二极管断开时,在11.34 GHz处出现窄带透明窗口,在带外4.8~11.0 GHz和13.5~16.0 GHz的吸波性能均在?10 dB左右;当PIN二极管导通时,吸波频段的吸波性能基本无变化,但关闭了11.34 GHz处的窄带透明窗,从而实现了通带可开关的吸透一体化超表面,在现代军事雷达中有重要应用前景.     

RCS reduction and gain enhancement of SRR inspired circularly polarized slot antenna using metasurface

In this work, a novel Circularly Polarized (CP) slot antenna is proposed for low RCS and high gain applications. The proposed antenna is designed in two phases. Initially, a metasurface is designed, which is composed of two similar artificial magnetic conductor (AMC) unit cells arranged orthogonally in chessboard-like configuration for broadband RCS reduction. Then, the CP slot antenna is designed by placing dual SRR on the backside of the slot for impedance matching and to achieve circular polarization. Detailed analysis is conducted to investigate the performance of metasurface loaded CP slot antenna. The proposed antenna shows 10 dB RCS reduction over the bandwidth of 41.3% at boresight direction compared to CP slot antenna. The maximum in-band and out-of-band RCS reduction achieved is 24 dB and 20 dB, respectively. The maximum gain of the antenna is also increased by 2.7 dB as a result of parasitic radiation of the metasurface and an improvement in overall performance of the antenna is observed by the employment of metasurface. Measured results of the fabricated prototype are in good agreement with the simulated results.     

基于相位梯度表面的缝隙阵列天线宽带RCS减缩

提出了一种基于耶路撒冷十字单元的相位梯度表面, 并将该表面加载到缝隙阵列天线表面.通过利用该表面将空间波(propagating wave, PW)转化为表面波(surface wave, SW)及奇异反射特性, 天线可以在很宽的频带内实现显著的雷达散射截面(radar cross section reduction, RCS)减缩.与参考天线相比, 设计天线在TE和TM两种极化波垂直和斜入射状态下均在6~18 GHz频带范围内实现了单站RCS减缩, 并且在9.5 GHz处的最大减缩量达到20 dB.与传统的天线RCS减缩技术相比, 该方法可以在保证天线原本辐射性能的基础上同时实现天线带内和带外的RCS减缩.     

具有超宽带RCS减缩特性的天线设计

该文设计了两种人工磁导体(AMC)单元,在8～20 GHz的超宽频带内,两种AMC结构能够实现180°±37° 的反射相位差,将这两种单元组成棋盘结构时,能够实现入射电磁波的散射场相消,从而在超宽的频带内实现棋盘表面法向雷达散射截面(RCS)的显著减缩。同时,利用超表面天线的概念,设计馈电网络,将设计的AMC结构用做天线,仿真发现在9.08～10.30 GHz的范围内,天线的S₁₁小于–10 dB,可以实现天线的有效辐射。实测结果和仿真吻合较好,因此该文的棋盘结构可以实现具有RCS减缩特性的天线设计。

     

基于可编程超表面的Wi-Fi信号调控

可编程超表面是由可调谐的单元在二维平面上组成的平面阵列,具有任意、动态操控电磁波波前的能力,是微波领域前沿研究方向之一.尽管目前基于可编程超表面的电磁调控研究已取得丰硕进展,但是现有技术都需要采用专用发射源主动馈电超表面,这不仅增加了实际系统的复杂性和成本,而且在一定程度上限制了这些技术在现实环境中的应用.因此,该文提...     

Exact solutions of electromagnetic fields in both near and farzones radiated by thin circular-loop antennas: a general representation

This paper presents an alternative vector analysis of the electromagnetic (EM) fields radiated from thin circular-loop antennas of arbitrary radius a. This method, which employs the dyadic Green's function in the derivation of the EM radiated fields, makes the analysis more general, compact, and straightforward than those two methods published recently by Werner (1996) and Overfelt (1996). Both near and far zones are considered so that the EM radiated fields are expressed in terms of the vector-wave eigenfunctions. Not only the exact solution of the EM fields in the near and far zones outside the region (where r>a) is derived by the use of the spherical Hankel function of the first kind, but also the closed-series form of the EM fields radiated in the near zone inside the region 0⩽r   

Digital Nonlinear Metasurface with Customizable Nonreciprocity

Recently, investigation of metasurface has been extended to nonreciprocity through breaking time‐reversal symmetry. Among a number of magnetless strategies, nonlinearity is an important nonreciprocal principle amenable to the metasurface. As passive analog‐based devices, most of the existing nonlinear nonreciprocal metasurfaces are inherently characterized by the relatively unchangeable performance, sharp frequency response, and hysteresis loops. Here, an analog–digital–analog mechanism is proposed to realize the nonlinear nonreciprocity, which provides a digitally reconfigurable solution for a family of nonreciprocal performance within a shared hardware architecture. This concept is validated by a metasurface prototype with the integration of a digital module at microwave frequencies. Based on the proposed mechanism, the properties can be customized as demanded, ranging from a normal reciprocal response to a variety of nonreciprocal functions, including electromagnetic (EM) diode and EM unidirectional limiting functions, which have been experimentally demonstrated with direction reversibility and threshold tunability. The proposed metasurface is also underpinned by the nonhysteretic performance and wide operating bandwidth, thereby potentially making it an inexpensive and stable candidate for advanced manipulations of EM waves.     

Transmission‐Reflection‐Integrated Multifunctional Coding Metasurface for Full‐Space Controls of Electromagnetic Waves

Digital coding metasurfaces are aimed at simplifying the design and optimization procedures, and manipulating electromagnetic waves in digital manner. In this paper, a multilayered anisotropic coding metasurface is designed to realize multiple independent functionalities by changing the polarization and direction of incident waves. As a proof of concept, the beam deflection, diffuse scattering, and vortex beam generation are realized by using only a single transmission‐reflection‐integrated (TRI) coding metasurface. This design can achieve three different functionalities and simultaneous controls of transmitted and reflected wavefronts on a shared aperture with the TRI coding scheme. Both numerical and measured results verify the excellent performance of the multifunctional digital coding metasurface, which provides a simple way to extend the functionality of high‐efficiency metadevices.     

一种基于机械旋转的可重构超表面电磁开关设计

为了提高微波无线能量传输的效率以及灵活性,提出并设计实现了一款基于机械控制的可重构超表面电磁开关。该设计基于Pancharatnam-Berry(P-B)相位原理,是一种可机械旋转、具有波束控制能力的反射型超表面,可以直接应用于无线传输系统中。仿真与优化设计表明,对于垂直入射的右旋圆极化平面波,超表面能够实现同极化聚焦或散射两种可重构功能。将该超表面放在无线传输系统中的发射端可以形成反射面天线,从而对微波无线功率传输系统实现电磁开关的功能。实验结果表明,在设计的5.8 GHz 附近,发射天线位于超表面焦点处时,通过调节超表面实现聚焦功能,可以使天线增益提高2.7 dBi;在无线传输系统中,可以通过超表面的引入实现电磁开关的功能。     

基于3D打印技术的任意曲面共形超表面隐身衣

超表面因其具有强大的电磁操控能力以及损耗小、剖面低和易加工等优势,在电磁工程领域受到了研究人员的广泛关注.然而,由于受加工技术的限制,目前所报道的超表面地毯隐身衣大多由二维平面结构拼接而成,研制能与任意目标曲面共形的地毯隐身衣仍然是一个挑战.为此,本文基于超表面和3D打印技术设计并验证了一款具有任意曲面的共形超表面隐身...     

相位不连续超材料表面的研究进展

近年来,超材料表面性能研究得到快速发展,在电磁波亚波长操纵等领域展现了独特的应用前景。超材料表面通常由许多周期性排列的金属结构单元组成,如果合适地设计结构单元的几何构型,就能够按照意愿得到拥有特定光学性质的材料。对近期利用相位不连续超材料表面对电磁波进行操控的研究进展进行了综述,包括:利用相位不连续表面控制电磁波出射方向;利用相位不连续表面结构合成圆偏振光;相位不连续应用于隐身;太赫兹波段相位不连续结构的应用;最后对该研究领域的发展进行了展望。     

Boundary waves along an impedance plane with a linearly varying impedance

A formal and asymptotic solution has been obtained for boundary waves which are supported by an infinite plane impedance boundary with a linearly varying impedance. The asymptotic solution (with respect to large distance from the origin) has three terms which are recognized as an incident, a reflected boundary wave, and a radiated wave. It is found that an increasing rate of change of the boundary impedance corresponds to more tightly bound boundary waves, to a power reflection coefficient approaching unity, and to a radiation efficiency approaching zero.