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.     

A novel finite-element method for nonreciprocal magneto-photonic crystal waveguides

A new formulation of the finite-element method to analyze nonreciprocal waveguides in magneto-photonic crystals (MPCs) is proposed. Accurate solutions of light propagations for two different directions are obtained by the asymmetrical input condition. As numerical examples, the performance of a waveguide-type optical isolator in MPCs designed by the eigenmode analyses is confirmed by using this method. Subsequently, an effective way to enhance the nonreciprocity of the optical isolator is shown.     

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.     

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...     

Magnetically programmable bistable laser diode with ferromagneticlayer

A new design of bistable laser diode, which consists of a gain section, absorption section, and nonreciprocal section, is proposed. The nonreciprocal section is made of a semiconductor optical amplifier covered by a ferromagnetic layer. The nonreciprocity of magneto-optical effect significantly modifies a photon density distribution in the laser cavity and enlarges a width of hysteresis loop of bistable laser diode. The bistability can be switched on or off by reversing magnetization of the ferromagnetic layer     

Metasurface Patch for Wireless Power Transfer in Implantable Devices

Wireless power transfer (WPT) systems enable the long-term operation and miniaturization of implantable devices by eliminating the need for battery replacement and wired power supplies. Although wireless power transfer systems for implantable devices are extensively studied, their practical application is still challenging owing to the constraints and requirements of the human body, such as reflection loss owing to differences in the tissue dielectric properties, mm-sized devices, and electromagnetic (EM) wave attenuation of the tissue. Here, a phase-gradient metasurface patch is presented to achieve 5.8 GHz EM power focusing at a focal point of depth 10 mm in the tissue via EM wavefront modulation at the skin–air interface. The proposed metasurface patch is fabricated by arranging subwavelength-thickness (<λ/10) unit cell structures composed of four metallic layers separated by dielectric substrates that exhibit high-Q resonance properties and a sufficient phase modulation range with enhanced transmission. By applying the fabricated metasurface patch to a wireless power transfer system for implantable devices, it is experimentally confirmed that the transmission coefficient (S₂₁) is improved by 6.37 dB compared with that of a wireless power transfer system without the metasurface patch. Furthermore, it is confirmed that the transmission coefficient can be maintained for an incident angle variation up to 30° from the transmitter to the metasurface patch, resulting in a stable power delivery of the proposed wireless power transfer system.     

Full‐State Synthesis of Electromagnetic Fields using High Efficiency Phase‐Only Metasurfaces

A metasurface is a thin array of subwavelength elements with designable scattering responses, and metasurface holography is a powerful tool for imaging and field control. The existing metasurface holograms are classified into two types: one is based on phase‐only metasurfaces (including the recently presented vectorial metasurface holography), which has high power efficiency but cannot control the phases of generated fields; while the other is based on phase‐amplitude‐modulated metasurfaces, which can control both field amplitudes and phases in the region of interest (ROI) but has very low efficiency. Here, for the first time, it is proposed to synthesize the field amplitudes and phases in ROI simultaneously and independently by using high‐efficiency phase‐only metasurfaces. All points in ROI may have independent values of field amplitudes and phases, and the requirements for X and Y components may be different in achieving spatially varied polarization states. To this end, an efficient design method based on equivalent electromagnetic model and gradient‐based nonlinear optimization is proposed. Full‐wave simulations and experimental results demonstrate that the phase‐only metasurface designed by the method has 10 times higher efficiency than the phase‐amplitude‐modulated metasurface. This work opens a way to realize more complicated and high‐efficiency metasurface holography.     

Analysis of asymmetrical multilayer ferrite-loaded finlines by theextended spectral domain approach

The spectral domain approach is extended to analyze the nonreciprocal propagation characteristics of asymmetrical multilayer finlines containing magnetized ferrites. This extended method offers several advantages. It can be applied to nonuniform cross-section geometries, uses only one set of basis functions, and the dyadic Green's function is efficiently derived by a recursive algorithm. Fast convergence is obtained and the accuracy of the method is verified by comparison with available computed and measured data. In comparison with symmetrical structures, the additional design degree of freedom of the asymmetry can be used to obtain wider bandwidth and higher nonreciprocity. Of the various structures considered, a four-layer dual ferrite (DF) structure is seen to be the best choice for realization of nonreciprocal phase shifters with widest bandwidth     

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。     

Integrated Control of Radiations and In-Band Co-Polarized Reflections by a Single Programmable Metasurface

Integrated control of radiated and reflected electromagnetic (EM) waves is of great importance in information science and engineering, which are mostly achieved by elaborately integrating metasurfaces and antennas. However, most of the radiation-reflection-integrated designs remain difficulties to modulate the radiated waves directly without cascading additional radio-frequency (RF) modules. More importantly, the completely independent control of radiated waves and in-band co-polarized reflected waves has rarely been achieved. Herein, direct, dynamic and integrated control of radiated waves and in-band co-polarized reflected waves is realized merely by a single programmable metasurface. The radiation-reflection-integrated programmable metasurface (RRIPM) can dynamically choose to radiate EM waves only or reflect incident EM waves only, and even dynamically modulate the radiation phases and reflection phases, thus realizing arbitrary radiation functions and in-band co-polarized reflection functions without crosstalk. To illustrate the capabilities of RRIPM, an ultra-compact and broadband RRIPM prototype is designed and fabricated, and this is used for the radiation and reflection of multiple beams with arbitrary energy distributions, low-gain-fluctuation reflection-beam scanning, and low-side-lobe-level broadside radiation.     

Nonreciprocal attenuation of magnetoelastic Rayleigh waves on bulk-YIG samples

Experimental results on nonreciprocal attenuation of magnetoelastic Rayleigh waves are reported for two bulk-YIG samples. In both cases, the nonreciprocity is found to be weak. In particular, the bulk-YIG version of the Lewis-Patterson YIG-film configuration (which exhibited a maximum nonreciprocity of about 20 dBs) is found to be essentially reciprocal.     

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。     

A Design Method of Hybrid Analog/Asymmetrical‐FIR Pulse‐Shaping Filters with an Eye‐Opening Control Option against Receiver Timing Jitter

This paper presents a method of designing hybrid analog/asymmetrical square‐root (SR) FIR filters. In addition to the conventional frequency domain constraints, the proposed method considers time‐domain constraints as well, including the inter‐symbol interference (ISI) and the opening of the eye pattern at the receiver output. This paper also reviews a systematic way to find the discrete‐time equivalence of analog parts in a band‐limited digital communication system. Thus, a phase equalizer can be easily realized to compensate for the nonlinear phase responses of the analog components. With the hybrid analog/SR FIR filter co‐design, examples show that using the proposed method can result in a more robust ISI performance in the presence of the receiver clock jitter.     

Asymmetric fiber-optic coupler for LAN applications

This paper presents experimental results of an asymmetric, effectively nonreciprocal fiber-optic coupler fabricated from unequal core diameters multimode fibers. It is shown that the nonreciprocity is due to modal dependent coupling.     

Plasmonic Metasurfaces for Simultaneous Thermal Infrared Invisibility and Holographic Illusion

In 1860s, Gustav Kirchhoff proposed his famous law of thermal radiation, setting a fundamental contradiction between the infrared reflection and thermal radiation. Here, for the first time an ultrathin plasmonic metasurface is proposed to simultaneously produce ultralow specular reflection and infrared emission across a broad spectrum and wide incident angle range by combining the low emission nature of metal and the photonic spin–orbit interaction in spatially inhomogeneous structures. As a proof‐of‐concept, a phase gradient metasurface composed of sub‐wavelength metal gratings is designed and experimentally characterized in the infrared atmosphere window of 8–14 µm, demonstrating an ultralow specular reflectivity and infrared emissivity below 0.1. Furthermore, it is demonstrated that infrared illusion could be generated by the metasurface, enabling not only invisibility for thermal and laser detection, but also multifunctionalities for potential applications. This technology is also scalable across a wide range of electromagnetic spectrum and provides a feasible alternative for surface coating.     

Isotropic Holographic Metasurfaces for Dual‐Functional Radiations without Mutual Interferences

The dual‐functional and/or multifunctional devices have huge fascinations and prospects to conveniently integrate complex systems with low costs. However, most of such devices are based on anisotropic media or anisotropic structures. Here, a new method is proposed to design planar dual‐functional devices using an isotropic holographic metasurface, in which two different functions are written on the same holographic interference pattern with no mutual coupling. When the metasurface is excited by two orthogonally ported sources, the corresponding dual functions can be controlled by the object waves, which are not affected by each other due to suppression of mutual interference. The proposed metasurface is composed of subwavelength‐scale isotropic metallic patches on a grounded dielectric. In this specific design, double‐beam and double‐polarization radiate devices are realized independently by the orthogonal excitations. Based on the theoretical analysis, scanning radiate beams that are only controlled by frequency with different performances under orthogonal polarizations are demonstrated. To the best of our knowledge, this is the first time for actualizing dual‐functional devices using isotropic textures. Full‐wave simulations and experimental results in the microwave frequencies are presented to validate the proposed theory and confirm the corresponding physical phenomena.     

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.     

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.     

Electromagnetic study of a ferrite coplanar isolator suitable for integration

The transmission coefficient of a nonreciprocal coplanar waveguide (CPW) using ferrite rods is studied. A new approximate method is proposed to evaluate the propagation constant of such a perturbed waveguide, which is based on the use of numerical data referring to the nonperturbed waveguide. We have estimated the value of the nonreciprocity effect and settled the condition of the validity of our theory. Some experimental data of a CPW with ferrite inclusions are also presented.     

Expectation–maximization‐based joint data detection and channel estimation for a cellular multi‐carrier code division multiple access network using single‐hop relaying

This paper is concerned with channel estimation and data detection for a cellular multi‐carrier code division multiple access network using single‐hop relaying in the presence of frequency selective fading channels. The proposed expectation–maximization (EM) algorithm was used to jointly estimate both the coefficients of the channel between a relay and a base station and the data. EM algorithm is particularly suited to multi‐carrier code division multiple access systems because they have multi‐carrier signal format. The considered network uses single‐hop relaying technique to provide a higher quality transmission to the users with low quality channels. The base station (managing mechanism) gives them an opportunity to send their messages via the users with high quality channels in a time sharing mode. The performance of the proposed EM algorithm, with and without hopping and with cooperative communication technique, was analyzed by a computer simulation, and the results are presented. Copyright © 2011 John Wiley & Sons, Ltd.