Reconfigurable Metasurface Research Articles

Erratum

VIEWEarly View 171 ERRATUMOpen Access Erratum This article corrects the following: On-demand field shaping for enhanced magnetic resonance imaging using an ultrathin reconfigurable metasurface Hanwei Wang, Hsuan-Kai Huang, Yun-Sheng Chen, Yang Zhao, Volume 2Issue 3View First Published online: February 21, 2021 First published: 18 September 2021 https://doi.org/10.1002/VIW.171AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat In Chen and colleagues[1], the following errors were published in paragraphs 2 and 4 on page 2. Paragraph 2 Another approach to enhance SNR is to increase the oscillating B0 field emitted and/or received by the receiving coil. The corrected sentence is below: Another approach to enhance SNR is to increase the oscillating B1 field emitted and/or received by the receiving coil. Paragraph 4 In MRI, the RF coil generates an oscillating magnetic field B0 to excite the proton-spin, and the decay is captured by the receiving coil. The corrected sentence is below: In MRI, the RF coil generates an oscillating magnetic field B1 to excite the proton-spin, and the decay is captured by the receiving coil. The publisher regrets this error. REFERENCE 1H. Wang, H.-K. Huang, Y.-S. Chen, Y. Zhao, VIEW 2021, 2, 20200099. Wiley Online LibraryGoogle Scholar Early ViewOnline Version of Record before inclusion in an issue171 ReferencesRelatedInformation

Photoionic Driven Movement of Metallic Ions as a Nonvolatile Reconfiguration Mechanism in Amorphous Chalcogenide Metasurfaces

AbstractChalcogenide glasses have been widely adopted as a material platform for achieving reconfigurable metamaterials and metasurfaces, primarily through exploiting nonvolatile phase transitions inherent to these semiconductors. In such devices, the atomic lattice of the nanostructured medium reversibly changes between amorphous and crystalline phases, invoked through an energy‐intensive melt/quench process that can reduce device endurance due to chemical and geometrical drift. Metal‐doped amorphous chalcogenide semiconductors (MdACs) exhibit a directional photoinduced movement of their constituent metal‐ions when exposed to light with a photon energy equivalent or higher than the bandgap of the host chalcogenide glass. This “photoionic” movement results in nonvolatile changes of refractive index and conductivity at the nanoscale enabling a nonvolatile, nonbinary dynamic modulation of light removing the need for a phase transition. It is shown here that this photoionic movement in silver‐doped amorphous germanium selenide metasurfaces enables reversible optical switching. Understanding and integrating the photoionic mechanism within various optoelectronic device platforms presents significant potential for realizing a range of nonvolatile optically reconfigurable nanophotonic devices for emerging display, data storage, and signal processing applications.

Angular-Adaptive Reconfigurable Spin-Locked Metasurface Retroreflector.

Metasurface retroreflectors, which scatter the incident electromagnetic wave back to incoming direction, have received significant attention due to their compelling advantages of low profile and light weight compared with conventional bulky retroreflection devices. However, the current metasurface retroreflectors still have limitations in wide‐angle and omnidirectional operations. This work proposes a high‐efficiency, wide‐angle, reconfigurable, and omnidirectional retroreflector composed of spin‐locked phase gradient metasurface with a thickness of only 5.2 mm or 0.07 operating wavelength. The reflection phase of constituent meta‐atoms can be controlled dynamically and continuously by altering their orientation states through individually addressing each mechanically rotational meta‐atom, whereas the reflection handedness is kept the same as incidence. Therefore, adaptive and arbitrary momentum can be imparted to the incident wave, providing high‐efficiency retroreflection over a wide continuous range from −47° to 47°. Moreover, such high‐performance retroreflection is extended to omnidirectional level, enabling great degrees of freedom that are unavailable by previous researches. As a proof of concept, a retroreflective metasurface is fabricated and experimentally demonstrated at microwave frequencies. The proposed thin thickness, high efficiency, and reconfigurable metasurface retroreflector can be extended to other frequencies that may offer an untapped platform toward reconfigurable spin‐based retroreflection devices for electromagnetic signal processing.

Ultra-Wideband Reconfigurable X-Band and Ku-Band Metasurface Beam-Steerable Reflector for Satellite Communications

A continuously reconfigurable metasurface reflector based on unit cell mushroom geometry that was integrated with a varactor diode is presented in this paper. The unit cell of the metasurface was designed and optimized to operate in the X-band and Ku-band, improving satellite communication’s quality of service. The losses mechanisms of continuous control over the unit cell phase reflection in beam steering resolution are considered and the analysis results are presented. The unit cell design parameters were analyzed with an emphasis on losses and dynamic reflection phase range. The unit cell magnitude and phase reflection are shown in the wide frequency bandwidth and showed a good agreement between all the measurements and the simulations. This metasurface enabled a high dynamic range in the unit cell resonant frequency range from 7.8 to 15 GHz. In addition, the reflection phase and absorption calibration are demonstrated for multiple operating frequencies, namely, 11 GHz, 12 GHz, and 13.5 GHz. Furthermore, design trade-offs and manufacturing limitations were considered. Finally, a beam-steering simulation using the designed metasurface is shown and discussed.

Fiber‐Integrated Phase Change Metasurfaces with Switchable Group Delay Dispersion

AbstractDemonstration of a fiber‐integrated non‐volatile reconfigurable metasurface providing high‐contrast group delay dispersion switching functionality is reported, which may be engineered to operate at wavelengths across the near‐infrared (telecoms) band. Light‐induced amorphous‐crystalline phase switching in a chalcogenide (germanium antimony telluride) metasurface, only a fraction of a wavelength thick, fabricated on the end‐facet of a single‐mode optical fiber, enables intensity and phase modulation of the guided wave at metasurface designated bands. Such devices present a range of opportunities in fiberized remotely programmable phase/intensity multiplexing and dynamic dispersion compensation for emerging telecommunications and data storage/processing applications, including in photonic neural network and neuromorphic computing architectures.

Versatile metasurface platform for electromagnetic wave tailoring

The emergence of metasurfaces provides a novel strategy to tailor the electromagnetic response of electromagnetic waves in a controlled manner by judicious design of the constitutive meta-atom. However, passive metasurfaces tend to perform a specific or limited number of functionalities and suffer from narrow-frequency-band operation. Reported reconfigurable metasurfaces can generally be controlled only in a 1D configuration or use p-i-n diodes to show binary phase states. Here, a 2D reconfigurable reflective metasurface with individually addressable meta-atoms enabling a continuous phase control is proposed in the microwave regime. The response of the meta-atom is flexibly controlled by changing the bias voltage applied to the embedded varactor diode through an elaborated power supply system. By assigning appropriate phase profiles to the metasurface through voltage modulation, complex beam generation, including Bessel beams, vortex beams, and Airy beams, is fulfilled to demonstrate the accurate phase-control capability of the reconfigurable metasurface. Both simulations and measurements are performed as a proof of concept and show good agreement. The proposed design paves the way toward the achievement of real-time and programmable multifunctional meta-devices, with enormous potential for microwave applications such as wireless communication, electromagnetic imaging, and smart antennas.

Neural networks enabled forward and inverse design of reconfigurable metasurfaces.

Nanophotonics has joined the application areas of deep neural networks (DNNs) in recent years. Various network architectures and learning approaches have been employed to design and simulate nanophotonic structures and devices. Design and simulation of reconfigurable metasurfaces is another promising application area for neural network enabled nanophotonic design. The tunable optical response of these metasurfaces rely on the phase transitions of phase-change materials, which correspond to significant changes in their dielectric permittivity. Consequently, simulation and design of these metasurfaces requires the ability to model a diverse span of optical properties. In this work, to realize forward and inverse design of reconfigurable metasurfaces, we construct forward and inverse networks to model a wide range of optical characteristics covering from lossless dielectric to lossy plasmonic materials. As proof-of-concept demonstrations, we design a Ge2Sb2Te5 (GST) tunable resonator and a VO2 tunable absorber using our forward and inverse networks, respectively.

Single-RF MIMO: From Spatial Modulation to Metasurface-Based Modulation

In multiple-input multiple-output (MIMO) systems, multiple radio frequency (RF) chains are usually required to simultaneously transmit multiple data streams. As a special MIMO technology, spatial modulation (SM) activates one transmit antenna by requiring one RF chain and exploits the index of the active antenna for information transfer at each time slot. Recently, reconfigurable metasurfaces have emerged as a promising technology that is able to reconfigure the wireless propagation environment by altering the amplitude and/or phase of the incident signal. In this article, we aim for the implementation of single-RF MIMO by shifting the focus from SM to metasurface-based modulation. Specifically, the principles of SM and metasurfaces are first presented. After reviewing the evolution of SM, we elaborate on the idea of metasurface-aided single-RF MIMO and discuss some implementations for it in line with notable variants of SM. A comparison between antenna-based and meta-surface-based modulation is made to highlight the advantages of using metasurfaces. We finally investigate the research challenges and opportunities in the context of metasurface-based modulation.

A Deep-learning Approach for Modeling Phase-change Metasurface in the Mid-infrared

Reconfigurable metasurface constitutes an important block for future adaptive and smart nanophotonic applications. In this work we introduce a new modeling approach for the fast design of tunable and reconfigurable metasurface structures using convolutional deep learning network. The metasurface structure is modeled as a multilayer image tensor to model the material properties as image maps. The dimensionality mismatch problem is avoided by using the operating wavelength as an input to the network, so the model is used as single-point solver. As a case study, we model the response of a reconfigurable absorber employing phase transition of vanadium dioxide in the mid-infrared. The results show that our model provides accurate prediction of the metasurface response using small training dataset.

Bianisotropic origami metasurfaces for mechanically controlled asymmetric radiation

Bianisotropic metasurfaces have been attracting increasing attention due to their strong capability for magneto–electric coupling manipulation on electromagnetic fields. Bianisotropic effect is physically determined by the symmetries of structure and switching among various bianisotropic states is thus difficult by varying material properties. Here, we propose a reconfigurable bianisotropic metasurface by arranging meta-atoms in a Miura-ori lattice. The bianisotropic properties are dynamically controlled via the deformation of the Miura-ori pattern, i.e., zero bianisotropy at the unfolded state and enhanced bianisotropy in folded geometries. It is also demonstrated that asymmetric radiation performance can be flexibly controlled by changing only the folded angle of deformation. Our work provides an alternative pathway toward dynamically control over the bianisotropy of metasurfaces, which may provide potential applications for smart directional radiation and scattering.

Active switching control of field-localized waveguide using time-modulated non-reciprocal reconfigurable metasurface

Active metamaterials with embedded control allow reconfiguring of the physical properties needed for wave propagation control. This flexibility provides useful features important for various waveguiding applications. Previous approaches to active metamaterials could change the material properties; however, their overall physical properties remained static. Time-modulated metamaterials, which can change physical properties dynamically, have recently attracted great interest. In this work, we present a time-varying, non-reciprocal, reconfigurable metasurface, which achieves active switching control of the field-localized waveguide. An experimental demonstration of the non-reciprocal metasurface is presented using two examples of sub-wavelength waveguides operating at 13 MHz and 13.5 MHz. The dynamic reconfiguring capability provides a wide range of versatile, practical applications, overcoming static passive metamaterials’ limitations. Because the waveguide’s location and shape can be controlled readily, the proposed method can be used for a broad range of applications that require dynamic wave propagation control.

Linear optical switch metasurface composed of cross-shaped nano-block and [formula omitted] film

The all-dielectric metasurface composed of nanostructured materials with a large dielectric constant is the latest research trend of metasurfaces, which overcomes the ohmic loss of metal metasurfaces at optical frequencies. However, once the metasurface is manufactured, its function is usually fixed, which has certain limitations for system integration and practical applications. Therefore, the all-dielectric metasurfaces that can be dynamically reconfigured and controlled have attracted more attention. Here, we present a design based on an optical switch metasurface consisting of a Ge2Sb2Te5 (GST-225) film with phase transition properties. Changing the crystalline state of GST-225, the maximum transmittance difference of meta-atoms is 0.7. Then, we demonstrate the deflective optical switch based on the dynamic control of the metasurface. By numerical simulation results, the proposed metasurface can modulate 1550 nm linearly polarized light, the average transmission efficiency difference can be up to 50.4%. Besides, a two-dimensional meta-lens based on the designed meta-atoms with sensitive switching performance is presented. We believe that the design and application in this work are significant for the design of reconfigurable and efficient metasurface light modulators.

Reconfigurable time-frequency division multiplexing metasurface: giving a helping hand to high signal-to-noise ratio and high data holographic imaging.

A holographic imaging system based on reconfigurable time-frequency division multiplexing metasurface (RTFDMM) has been designed, in an attempt to address the problems of insufficient flexibility, low signal-to-noise ratio (SNR), and low data of traditional metasurface imaging devices. The modified Gerchberg-Saxton (MGS) algorithm in the front end of this system has been proposed to calculate the phase distribution required by the diffraction metasurface at the back end. The 1-bit low loss reconfigurable metasurface has been desiged in X-band. To obtain the best imaging results, the appropriate ranges of imazging distance, pixel size and resolution ratio are given by adjusting the phase distribution of metasurface. Based on the MGS algorithm and the 1-bit metasurface, the high-quality imaging system has been successfully established through the time-frequency division multiplexing (TFDM) technology. The high SNR imaging can be generated with the expansion of the time domain, while the high data imaging can be yielded with the quantization of the frequency domain. The proof-of-concept has demonstrated that the high data, high SNR, and high flexibility of the RTFDMM are critical technologies for the advancement of detection imaging equipment. Therefore, there are great possibilities for RTFDMM holographic imaging system to be applied in the intelligent detection platform in the future.

Electrically Reconfigurable Microwave Metasurfaces With Active Lumped Elements: A Mini Review

Metasurfaces, a kind of two-dimensional artificially engineered surfaces consist of subwavelength unit cells, have recently attracted tremendous attention, owing to their exotic abilities for tailoring electromagnetic responses. With active lump elements incorporated into the design of metasurfaces, dynamic reconfigurabilities enabled by external stimuli could be realized, offering opportunities for the dynamic manipulation of electromagnetic waves. In this mini review, we present a brief review on the recent progress of electrically reconfigurable metasurfaces at microwave frequencies. A brief discussion will also be given with our outlook on future development direction and possible challenges in this interesting field.

Nonvolatile Optically Reconfigurable Radiative Metasurface with Visible Tunability for Anticounterfeiting.

Control of thermal emission underpins fundamental science, as it is related to both heat and infrared electromagnetic wave transport. However, realizing nonvolatile reconfigurable thermal emission is challenging due to the inherent complexity or limitation in conventional radiative materials or structures. Here, we experimentally demonstrate a nonvolatile optically reconfigurable mid-infrared coding radiative metasurface. By applying laser pulses, infrared emissive patterns are directly encoded into an ultrathin (∼25 nm) Ge2Sb2Te5 layer integrated into a planar optical cavity with the optically crystallized Ge2Sb2Te5 spots, and the peak spectral emissivity is repeatedly switched between low (∼0.1) and high (∼0.7) values. In addition, the visible scattering patterns are independently modulated with submicron-sized bumps generated by high-power laser pulses. An anticounterfeiting label is demonstrated with spatially different infrared emission and visible light scattering information encoded. This approach constitutes a new route toward thermal emission control and has broad applications in encryption, camouflage, and so on.

Frontispiece: On‐demand field shaping for enhanced magnetic resonance imaging using an ultrathin reconfigurable metasurface (View 3/2021)

In article number 20200099, Hanwei Wang and co-workers have proposed a theoritical design of an ultrathin reconfigurable metasurface to enhance the signal-to-noise ratio of magnetic resonance imaging. The enhancement can target a specific region in the imaging plane with any desired shapes while minimumly disrupt the spin-excitation to maintain a high imaging quality. In this cover, the spins pointing up illustrate the uniform excitation of protons of an imaging object. The different shapes of the component forming the metasurface create a strong coupling with the protons in a specific region, where the signals are selectively enhanced. The selected enhancement region in this cover is designed to form the shapes of “U” and “I” representing the University of Illinois.

Switching plasmonic resonance in multi-gap infrared metasurface absorber using vanadium dioxide patches

Reconfigurable metasurface absorbers enable collecting or emitting radiation within selected frequency bands. It is thus necessary to decipher such behavior for many applications, including plasmonic energy harvesting, radiative cooling and thermal emitters. In this article, we propose a compact reconfigurable vanadium dioxide (VO2)-based metasurface absorber/emitter to demonstrate switching between dual and single-band absorption modes in the mid-infrared regime. The unit cell of the design employs a four-split gold circular ring resonator with gaps filled with VO2 patches. The phase-transition property of VO2 between semiconductor and metallic states is used to control the mode of operation of the metasurface absorber. When VO2 is in the semiconductor state, a dual-band absorption at 6 μm and 10.6 μm is obtained. When it attains a metallic state, the metasurface exhibits a single-band absorption at 8.25 μm. To achieve the maximum absorption efficiency in both single and dual-band modes, adaptive wind-driven optimization was employed as a global optimization technique. The proposed absorber provides polarization-independent behavior for both Transverse Electric and Transverse Magnetic polarizations. Moreover, the proposed design shows above 80% absorptance for incidence angle up to 45° for the dual-band mode, and up to 35° for the single-band mode. When operating the absorber as a tunable emitter, a switching of 79% in emissivity is achieved at 8.25 μm. These favorable findings may facilitate the development of important devices for temperature regulation, smart windows, and thermal imaging.

Guided-Wave-Excited Binary Huygens’ Metasurfaces for Dynamic Radiated-Beam Shaping with Independent Gain and Scan-Angle Control

This paper presents a reconfigurable metasurface that is able to dynamically and independently control the gain and propagation direction of the radiated field, with reduced biasing complexity and power consumption at a low profile. Moreover, the proposed metasurface is guided-wave fed thus leading to a compact tunable leaky-waveguide structure. Heretofore, reported reconfigurable metasurfaces have mainly demonstrated dynamic tailoring of free-space waves by redistributing their reflection or transmission phase profiles at a fixed amplitude. In contrast, we demonstrate dynamic transformation of a guided wave into an aperture field with controlled amplitude such that the gain and scan angle of the corresponding radiated field are dynamically and independently controlled. In particular, the aperture field is digitally synthesized by the proposed tunable Huygens' metasurface whose local transmission coefficient is able to be dynamically tuned as two digital bits of $\ensuremath{-}|{T}_{o}|$ and $+|{T}_{o}|$, where ${T}_{o}$ represents a user-defined constant. This digital synthesis and the deliberate utilization of a nonbianisotropic type Huygens' metasurface simplify biasing requirements, and make the proposed design more feasible. Through simulations and experiments, we show dynamic steering of a beam from $\ensuremath{-}{40}^{\ensuremath{\circ}}$ to $+{40}^{\ensuremath{\circ}}$, and two broadside radiations with different radiation gains at a fixed operating frequency of 5 GHz.

Liquid-Crystal-Elastomer-Actuated Reconfigurable Microscale Kirigami Metastructures.

Programmable actuation of metastructures with predesigned geometrical configurations has recently drawn significant attention in many applications, such as smart structures, medical devices, soft robotics, prosthetics, and wearable devices. Despite remarkable progress in this field, achieving wireless miniaturized reconfigurable metastructures remains a challenge due to the difficult nature of the fabrication and actuation processes at the micrometer scale. Herein, micro-scale thermo-responsive reconfigurable metasurfaces using stimuli-responsive liquid crystal elastomers (LCEs) is fabricated as an artificial muscle for reconfiguring the 2D microscale kirigami structures. Such structures are fabricated via two-photon polymerization with sub-micrometer precision. Through rationally designed experiments guided by simulations, the optimal formulation of the LCE artificial muscle is explored and the relationship between shape transformation behaviors and geometrical parameters of the kirigami structures is build. As a proof of concept demonstration, the constructs for temperature-dependent switching and information encryption is applied. Such reconfigurable kirigami metastructures have significant potential for boosting the fundamental small-scale metastructure research and the design and fabrication ofwireless functional devices, wearables, and soft robots at the microscale as well.

Tunable quantum two-photon interference with reconfigurable metasurfaces using phase-change materials.

The ability of phase-change materials to reversibly and rapidly switch between two stable phases has driven their use in a number of applications such as data storage and optical modulators. Incorporating such materials into metasurfaces enables new approaches to the control of optical fields. In this article we present the design of novel switchable metasurfaces that enable the control of the nonclassical two-photon quantum interference. These structures require no static power consumption, operate at room temperature, and have high switching speed. For the first adaptive metasurface presented in this article, tunable nonclassical two-photon interference from -97.7% (anti-coalescence) to 75.48% (coalescence) is predicted. For the second adaptive geometry, the quantum interference switches from -59.42% (anti-coalescence) to 86.09% (coalescence) upon a thermally driven crystallographic phase transition. The development of compact and rapidly controllable quantum devices is opening up promising paths to brand-new quantum applications as well as the possibility of improving free space quantum logic gates, linear-optics bell experiments, and quantum phase estimation systems.