Reconfigurable Metasurface Research Articles

Reconfigurable absorptive and polarization conversion metasurface consistent for wide angles of incidence

In this paper, a single-layer reconfigurable reflective metasurface is presented. The proposed metasurface operates at 5.4 GHz and can achieve either absorption or cross-polarization conversion corresponding at two different diode biasing states. The reflective metasurface acts as an absorber for an incident wave when the diodes are forward-biased. Similarly, it changes the polarization state of the reflected wave for a linearly polarized incident wave when the diodes are reverse-biased. The proposed structure maintains the aforementioned performance characteristics for oblique incidence, up to 60° compared to the perpendicular incidence. The proposed metasurface can achieve linear to linear polarization conversion with polarization conversion ratio (PCR) > 95% and absorption, with absorption ratio (AR) > 80% in the same frequency band just by reconfiguring the state of the PIN diodes.

Reconfigurable chiral metasurface based on vanadium dioxide: Modulation of phase and intensity for high-quality hologram and near-field imaging

Circular dichroism (CD) has gained significant recognition in the field of artificial materials. However, there is still a need for a flexible approach to modulate CD, which would enable spin-selective multidimensional manipulation of terahertz (THz) waves. In recent years, reconfigurable metasurfaces have emerged as a prominent area of research in the field of micro/nanophotonic. This study proposes a novel reconfigurable chiral metasurface utilizing the phase transition properties of vanadium dioxide (VO2), capable of modulating CD. This metasurface not only realizes the modulation of the Pancharatnam-Berry (PB) phase in two states of VO2 but also enables the modulation of CD at the dual THz band. Based on the principle of the PB phase to control the phase of the meta-atom, the 3-bit coded metasurface arrays were proposed to achieve high-quality THz holographic imaging. Furthermore, the near-field imaging effect is realized by utilizing the differentiation property of the absorption intensity of chiral CD meta-atom. This multifunctional device, with its simple structure, exhibits tremendous potential for applications in THz holographic imaging, THz circular polarized wave detection, and image encryption.

Chameleon-like intelligent camouflage metasurface

Humans have been long dreaming of obtaining the ability of changing electromagnetic (EM) attributes intelligently according to the environment so as to camouflage just as chameleons do. Thanks to the unprecedented high degree of freedom in manipulating EM waves, metasurfaces can mimic EM characteristics of various environments vividly and have pushed a giant step towards this long-desired dream. Nevertheless, for most metasurfaces, the EM characteristics are fixed and thus cannot be altered according to changing environments, which hinders their applications in intelligent scenarios such as moving target camouflage. With the aim to achieve intelligent camouflage, in this work we propose a chameleon-like framework for intelligent camouflage based on EM metasurface, which integrates transfer-learning-empowered perceptron into a reconfigurable metasurface. As a demonstrative example, a chameleon-like intelligent camouflage metasurface (CLICM) system with robust extendibility was developed and measured in laboratory. The system can dynamically control the reflection spectrum in 5.1–6.5 GHz according to what it sees. Both the simulation and experiment results verify this framework. This work provides a perceptron-algorithm-metasurface framework with robust extendibility for intelligent EM manipulation and may find wide applications in camouflage and wireless communication.

Reconfigurable three multi-mode terahertz metasurface.

We designed a three reconfigurable multi-mode terahertz metasurface based on a concentric elliptical ring structure. The proposed unit cell is a concentric elliptical ring composed of copper, vanadium oxide and photosensitive silicon from the inside ring to the outside ring. The conductivity of photosensitive silicon and vanadium oxide can be adjusted by changing the external operating temperature and pump light intensity. The same unit cell can reconstruct three kinds of states with different properties, and they have completely different transmission characteristics in various terahertz bands. By encoding the arrangement, through changing external stimulus and operating frequencies, the reconfigurable terahertz metasurface can achieve multiple functions including terahertz focusing with adjustable focal length, vortex beam with different topological charge, and near-field imaging with different patterns. It provides what we believe to be a new idea for the field of information security and the design of multifunctional and multifrequency terahertz devices.

Flexible wavefront modulation of Rayleigh surface waves by mechanically reconfigurable elastic metasurface

The expression of the generalized Snell's law for modulating the Rayleigh surface wave was derived. Based on the generalized Snell's law and the reconfigurability of the screw-and-nut structure, a reconfigurable elastic metasurface was proposed to modulate the wavefront of the Rayleigh surface wave. Flexible switching between different frequencies and functions, such as abnormal refraction, point focusing, beam focusing and self-bending beam can be realized just by adjusting the screw-in depths of the nuts. The flexibility and effectiveness of the reconfigurable metasurface were verified by numerical simulations. The study in this paper is expected to have a guiding significance for the design of new surface wave devices, and at the same time provides a new idea for modulation of seismic waves.

Active Matrix Integrated Metasurface for 2D Electromagnetic Modulation

AbstractReconfigurable metasurfaces have attracted widespread attention owing to their dynamic, multifunctional, and intelligent manipulation ability of electromagnetic waves. However, most previous reconfigurable meta‐devices work in one‐dimension (1D) due to the complex electrical wires and control circuits for two‐dimensional (2D) modulation. Here, an active matrix circuit composed of a MOSFET chip and a storage capacitor is introduced into the meta‐atom design to realize 2D control of reconfigurable metasurfaces. The number of the control circuits is reduced from M × N to M + N by applying sequential voltage and selecting the row/column. As proof of the scheme, a 10 × 10 active matrix integrated reconfigurable metasurface operating in X‐band is experimentally demonstrated. 2D beam scanning and point focusing with focal lengths of 60 mm & 120 mm are verified through 2D phase modulation. The scheme for 2D modulation has great potential in the construction of high‐frequency large‐scale compact reconfigurable metasurfaces and promises unprecedented progress for wireless telecommunication and microwave detection.

Spatiotemporal modulations in acoustics: From nonreciprocity to mechanical computing

Spatially graded materials have been a cornerstone of acoustic metamaterials for decades, enabling wave manipulation across different length scales. Likewise, structures with time-varying material properties have gained traction in wave filtering applications. Put together, systems exhibiting concurrent spatial and temporal modulations of one or more parameters (e.g., stiffness or phase) can unlock an array of new features ranging from nonreciprocal propagation to frequency-dependent wave beaming. In this talk, we will introduce the notion of dynamic phase gradients, i.e., a spatial phase shift between neighboring elements (of a metasurface) or transducers (of a phased array) which also varies in time. Through theory and experiments, we will demonstrate that the resultant systems are capable of (a) generating multiple scattered harmonics of a single input which simultaneously propagate in different directional lanes, each carrying a unique frequency footprint, and (b) exhibiting non-identical beaming patterns in transmission and reception by breaking time invariance. We will present an application of this concept in the development of a mechanical neural network via reconfigurable elastic metasurfaces, designed to perform a computational task. Since the frequency channels of a spatiotemporally-modulated metasurface are independently tunable, they can be assigned distinct tasks, thus allowing parallel operations in mechanical computing systems.

Transmission and reflection bidirectional terahertz coding metasurface based on thermally switchable materials

Metasurface, with its powerful and flexible terahertz(THz) wave manipulation capability, has become a key component of beamforming and imaging systems in the THz band. However, its practical application is limited by fixed properties and propagation mode on a single metasurface. In this paper, we propose a coding metasurface with tunable characteristics and bidirectional working modes. The complete 2π phase compensation can be realized by rotating the InSb unit according to the Pancharatnam-Berry phase concept, and eight meta-atoms are selected to regulate the wavefront of terahertz waves using phase compensation. By increasing the temperature of the InSb from 290 K to 370 K, the working frequency permits wideband coverage from 1.7 to 4.5 THz. As the temperature reaches 341.15 K, which is required for vanadium dioxide's(VO2) phase transition, the metasurface's propagation direction mode will switch from transmission to reflection. The proposed metasurface can perform beam deflecting, splitting, and focusing functions when VO2 is in a dielectric state. Meanwhile, beam deflecting, splitting, and radar scattering surface (RCS) reduction can also be achieved when VO2 is in a metallic state. Furthermore, a near-field image of the letter P is presented as verification. Numerous potential applications for the reconfigurable metasurfaces include polarization beam splitters, imaging, and terahertz switching.

Multifunctional active terahertz metasurface with electromagnetically induced transparency, perfect absorption, and circular dichroism

Navigated by the continued demand for design integration and miniaturization, incorporating multiple diversified operations into a single metasurface hybridized with the tunable metasurface is highly demanding at the terahertz (THz) range. However, up to now, because of the limitation of the reconfigurable metasurface at the terahertz range, most metasurfaces only feature a single function or process similar functionalities at a single frequency. A multi-functional terahertz metasurface based on vanadium dioxide (VO2) is proposed in this paper, which consists of a gold layer, a VO2 bridge, a SiO2 spacer, and a VO2 layer on the back of the spacer. Under different conductivity of different VO2 layers, the proposed metasurface achieves various terahertz device functions, including single-band perfect terahertz absorption, circular dichroism (CD) for the reflected and transmitted fields, and electromagnetically induced transparency (EIT) effect. Furthermore, the proposed metasurface exhibits robust response against oblique incidences. The mechanisms of perfect absorption, chiral-selective absorption and EIT are illustrated by impedance matching theory, surface current and electric field distributions, respectively. The function-switching ability of proposed metasurface provides more options for the design of terahertz devices in the future.

A two‐dimensional beam steering Fabry–Pérot antenna employing a liquid‐based reconfigurable metasurface

AbstractA novel 2‐D beam steering technology using a Fabry–Pérot antenna with a liquid‐based reconfigurable metasurface is presented. The antenna employs a reconfigurable partially reflecting surface to regulate phase distribution and adopts a microstrip antenna as feed to realise 2‐D beam steering. The antenna beam can be tilted in four different directions by injecting liquid metal into the specific area of the microfluidic channels embedded in the metasurface. Moreover, the antenna has a simple and compact structure with a low profile. A prototype is manufactured, and good agreement between simulated and experimental results verifies the correctness of the design. The measured results of the manufactured antenna prototype demonstrate that the main beam tilts to maximum values of ±15° and ±28° in the yoz and xoz planes, respectively, between 9.5 and 9.7 GHz.

Continuous beam steering with a varactor-based reconfigurable intelligent surface in the Ka-band at 31 GHz

Varactor diodes have been proposed as active tuning elements of reconfigurable metasurfaces in the Ka-band. However, their experimental realization in this frequency range has not been demonstrated yet. We report the implementation of such a reconfigurable intelligent surface (RIS) made of 20×20 unit cells. By active tuning of the bias voltage of the varactors, the phase of the backward diffracted wave can be continuously tuned between 0° and 180°. Thus, the phase tuning can be independently controlled for each unit cell. The frequency working range of the RIS is 1.1 GHz (from 30.6 to 31.7 GHz). As an illustration of the practical use, we demonstrate continuous beam steering of microwave radiation at 31 GHz in a defined propagation plane.

A 1-bit electronically reconfigurable beam steerable metasurface reflectarray with multiple polarization manipulations

A 1-bit electronically controlled metasurface reflectarray is presented to achieve beam steering with multiple polarization manipulations. A metsurface unit cell loaded by two PIN diodes is designed. By switching the two PIN diodes between ON and OFF states, the isotropic and anisotropic reflections can be flexibly achieved. For either the isotropic reflection or the anisotropic reflection, the two operation states achieve the reflection coefficients with approximately equal magnitude and 180° out of phase, thus giving rise to the isotropic/anisotropic 1-bit metasurface unit cells. With the 1-bit unit cells, a 12-by-12 metasurface reflectarray is optimally designed and fabricated. Under either y- or x-polarized incident wave illumination, the reflectarray can achieve the co-polarized and cross-polarized beam scanning, respectively, with the peak gains of 20.08 dBi and 17.26 dBi within the scan range of about ±50°. With the right-handed circular polarization (RHCP) excitation, the left-handed circular polarization (LHCP) radiation with the peak gain of 16.98 dBic can be achieved within the scan range of ±50°. Good agreement between the experimental results and the simulation results are observed for 2D beam steering and polarization manipulation capabilities.

Reconfigurable High-Efficiency metadevice using Kirigami-Inspired phase gradient metasurfaces

Kirigami-inspired metasurface has attracted great attention in electromagnetic (EM) wave manipulations, due to its unprecedented and tailorable structural transformations via mechanical approaches. However, it is still challenging for wavefront control because of its unfeasibility in forming a phase gradient at different folding angle β. Here, we report a strategy of kirigami-inspired reconfigurable phase gradient metasurfaces to efficiently control beam steering of scattering wave through mechanically changing β, where the control range of β is theoretically derived based on EM diffraction and generalized Snell’s law. For demonstration, reconfigurable anomalous reflectors with high efficiency are demonstrated in both dual-element and tri-element tunable metadevices. In former case, the reflection angle varies within 37°∼47° under polarization along y axis by changing β within the range of 10°∼40°, whereas it varies within 36°∼50° under that along x axis when β is changed within 10°∼39°, and numerical and experimental results show measured efficiency of beam steering over 78.6%. In latter case, the reconfigurable tri-element metadevice with various folding states are also experimentally characterized to further verify our strategy. Compared with available metasurfaces, our reconfigurable strategy using maneuverable structures to control EM wave is more versatile and shows great potential in engineering applications.

3-bit reconfigurable THz metasurface based on structured light illumination for vortex beams and holographic imaging

Metasurfaces have attracted widespread attention due to their excellent control ability of terahertz wavefronts. Terahertz metasurfaces have made rapid progress in areas such as biological detection, high-speed communication, and imaging. However, terahertz metasurfaces currently have a single function, and the primary goal of this research is to create a reconfigurable and multifunctional terahertz metasurface. In this work, we designed a novel eight-gaps-splits-ring resonator (EGSRR). The EGSRR is filled with photosensitive semiconductor material, and the metasurface unit's amplitude-phase characteristics are controlled by different encodings of structured light. Finally, under the incidence of right-handed circularly polarized (RCP) waves, 3-bit phase encoding of its reflected wave with cross-polarization is achieved. To verify the ability of metasurface to control terahertz wavefronts, the 3-bit metasurface units are assembled into an array to achieve different-order vortex beams and reconfigurable holographic images. The novel optically controlled reconfigurable metasurface not only has promising applications in generating vortex beams and holographic imaging, but it also represents a novel approach to designing multifunctional and programmable terahertz metamaterials.

Light‐Driven Thermo‐Optical Effects in Nanoresonator Arrays

AbstractThermonanophotonics, that is the study of photothermal effects in optical nanoantennas, has recently attracted growing interest. In particular, going beyond thermoplasmonic designs, thermo‐optical modulation of dielectric nanoantennas opens new opportunities for reconfigurable and non‐reciprocal metasurfaces. However, understanding light‐driven thermo‐optical effects in large arrays of nanoantennas remains challenging. In this work, for the first time the impact of thermo‐optical effects beyond the single nanoresonator is analyzed. By performing photo‐thermo‐optical computations of large nanoantenna arrays (more than 105 elements), the complex interplay of thermo‐optical effects with self‐ and collective‐heating in 1D, 2D, and 3D systems are explored. The results show that collective heating contributions strongly alter the local absorption cross‐section and, in return, also the self‐heating term. Therefore, both terms must be carefully accounted for in large arrays. Importantly, by controlling the nanoresonator size, array periodicity and illumination wavelength, thermo‐optical effects enable the realization of non‐trivial spatial temperature profiles. In particular, ways to counteract collective heating effects and obtain flat temperature profiles in 2D arrays of dissimilar silicon nanoresonators are demonstrated. Overall, this work paves the way to the design of light‐driven reconfigurable metasurfaces, supporting the development of advanced thermonanophotonic functionalities.

Switchable metasurface for high-efficiency absorption and broadband polarization conversion based on vanadium dioxide in the terahertz frequency.

High-performance devices with superior execution will facilitate the practical application of terahertz (THz) technology and foster THz innovation. In this paper, taking advantage of the phase transition characteristics of vanadium dioxide (V O 2), a reconfigurable metasurface with absorption and polarization conversion capacities is proposed. The metallic condition of V O 2 results in the formation of a wideband absorber. It provides more than 90% absorption over a broad spectral range from 3.32 to 5.30THz. Due to the regularity of the meta-atom, the absorber is not polarization-delicate and keeps a high retention rate in the scope of incoming angles from 0° to 45°. When V O 2 is in the insulating condition, the calculated outcomes demonstrate that the cross-polarization conversion rate can reach more than 90% in the range of 2.29-7.85THz when x-polarized or y-polarized waves are incident vertically. The proposed metasurface is likely to be used in the fields of emitters, sensors, imaging systems, and wireless communication.

Dual-Degree-of-Freedom Multiplexed Metasensor Based on Quasi-BICs for Boosting Broadband Trace Isomer Detection by THz Molecular Fingerprint

The metasurface is a powerful tool for trace analyte sensing in a label-free manner by amplifying their THz molecular fingerprint signals. However, current technologies are still facing the problems of high background noise and narrow working bandwidth. Here, we propose a broadband dielectric metasurface sensor based on guided mode resonances (GMRs) with a dual-degree-of-freedom configuration, which boosts the generation of multiplexed quasi-bound states in the continuum (quasi-BICs). Our design shows the extraordinary sensing performance on molecular fingerprint identification of two trace explosive isomers whose distinctive spectral characteristics span an ultrawide THz band. In comparison to the conventional sensing method, the metasensor demonstrates that the signal enhancement factors of over 19 dB in the entire frequency range from 0.9 THz to 1.6 THz, and is capable of precisely analyzing the sample composition ratios of the two mixed isomers. Our study explores the multiplexing mechanism of quasi-BICs based on the reconfigurable GMR metasurface and facilitates its application on high-sensitivity broadband THz molecular fingerprint retrieval, which is promising for nondestructive detection of trace-amount analytes.

Detecting Angle of Arrival on a Hybrid RIS Using Intensity-Only Data

Reconfigurable reflective metasurfaces—or reconfigurable intelligent surfaces (RISs)—can redirect incident signals toward desired directions, an ability that allows for sculpting wireless communication channels with desired characteristics. This smart radio environment, however, necessitates the information about the transmitter(s) and the receiver(s) to be available at the RIS. One possible solution to this need is to add sensing capability to the RIS. However, sensing complex wireless signals (i.e. both amplitude and phase) often requires complicated setups. In this paper, we propose and numerically demonstrate a reconfigurable reflective metasurface that uses intensity-only samples of the incident signal to retrieve desired information about the propagation environment. To do that, we will randomly tune the metasurface elements to multiplex information incident on all of them. The phaseless multiplexed data is then processed using computational ghost imaging algorithm to retrieve the desired information. As a demonstrative example, we present the detection of the incident angle from a user in a free-space environment. This simplified sensing process can pave the way for incorporation of RISs with integrated sensing capabilities in future wireless communication or sensing systems.

Switchable dual-mode nanolaser: mastering emission and invisibility through phase transition materials

Abstract The principle of detailed balance states that objects efficiently emitting radiation at a specific wavelength also efficiently absorb radiation at the same wavelength. This principle presents challenges for the design and performance of photonic devices, including solar cells, nanoantennas, and lasers. A design that successfully integrates the properties of an efficient emitter in one state and invisibility in another state is essential for various applications. In this work, we propose a novel nanolaser design based on a semiconductor nanoparticle with gain enveloped by a phase transition material that enables switching between lasing and cloaking (nonscattering) states at the same operating frequency without modifying the pumping conditions. We thoroughly investigate the operational characteristics of the nanolaser to ensure optimal performance. Our nanolaser design can function with both optical and electric pumping and exhibits the features of a thresholdless laser due to its high beta-factor and strong Purcell enhancement in the tightly confined Mie resonance mode. Additionally, we develop a reconfigurable metasurface comprising lasing-cloaking metaatoms capable of transitioning from lasing to a nonscattering state in a fully reversible manner.

A Low-Cost Multibeam Switching Antenna Using Reconfigurable Hybrid Metasurface for Beamforming Applications.

In this paper, we proposed a multibeam switching antenna based on a low-cost reconfigurable hybrid metasurface applied for beamforming systems. The antenna consists of two parts: a microstrip feed antenna and a transmission hybrid metasurface. The latter is composed of three types of units with different amplitude and phase responses to electromagnetic waves so as to control the beams of the feed antenna. Sixteen PIN diodes are arranged in the metasurface with a simple bias network. When two different direct-current voltages are applied to the PIN diodes, the antenna can dynamically switch between two beams and four beams. For demonstration, the proposed antenna is fabricated, and the measured results show that the antenna operates at 9.07-9.42 GHz (-10 dB bandwidth) with a total size of 1.80λ0 × 1.52λ0 × 0.22λ0 (λ0 corresponds to the wavelength of 9.28 GHz in free space). With the merits of a compact structure, low cost and good radiation performance, the proposed design is suitable for beamforming applications.