2-bit Coding Research Articles

Polarization insensitive non-interleaved frequency multiplexed dual-band Terahertz coding metasurface for independent control of reflected waves

Independent control of electromagnetic (EM) waves by metasurfaces for multiple tasks are highly desired and is the recent hot topic of research. In this work we contribute a polarization insensitive frequency multiplexed 2-bit coding metasurface to control the Terahertz (THz) waves in the two operating bands independently. In this regard, as a first step a cascaded meta-atom composed of square rings and/or square metallic patches separated by two polyimide substrates is designed and optimized that provides sixteen independent distinct discrete phases in the reflection geometry. These meta-atoms are then distributed with distinct coding sequences in the two-dimensional spatial plane to realize various bi-functional metasurfaces. As a proof of the concept various full structures are designed and simulated to realize a series of bi-functionalities including anomalous reflection/beam shaping, beam shaping/anomalous reflection, beam deflection/Orbital angular momentum (OAM) beam generation with distinct modes and propagating wave to surface wave (PW–SW) conversion/PW beam manipulation in the lower and higher THz bands, respectively. All the simulation results are in excellent agreement with their theoretical equivalents. We envision that the proposed meta-designs have potential applications for the multi-spectral control of EM waves in THz band. The idea can be further extended to design frequency dependent tri-functional and multi-functional THz meta-devices.

Bidirectional beam generation by metasurface for 6G communication

This paper presents a bidirectional metasurface that is polarization dependent and consists of 2-bit coding reflect-transmit (RT) elements. The proposed metasurface can transmit the vertical polarized (VP) incident wave and reflect the horizontal polarized (HP) wave with the same focal length. The 2-bit coding passive RT elements, named UC0 to UC3, have 0°, 90°, 180°, and 270° phase responses for both vertical and horizontal incidences. The array samples were fabricated using standard print circuit board (PCB) technology. The results of both numerical and experimental investigations demonstrate that the proposed metasurface is capable of beam control with an angular range of ±30° in the xoy, xoz, and diagonal planes. The reflected and transmitted beams have been found to exhibit peak gains of 22 dBi at 94.5 GHz with 7% 3-dB gain bandwidth and 22.1 dBi at 93 GHz with 14.8% 3-dB gain bandwidth, respectively. The proposed metasurface shows great potential for use in 6G wireless communication applications.

2-битные метаповерхности Патчаратнама-Берри с генерацией, интерференцией и гашением орбитального углового момента для широкополосного снижения ЭПР

The radar cross-section (RCS) reduction using non-absorbing digital Patcharatnam-Berry (PB) metasurfaces (MSs), consisting of 2-bit modules with generation, interference and cancellation of vortex electromagnetic waves with orbital angular momentum (OAM) is studied. Each module has a helical PB-phase profile and possesses vortex scattering. Module unit cells contain a shielded dielectric substrate and meta-particles in the form of triple-coupled split-ring resonators. The modules are distinguished by 2-bit coding of the initial tilt angle of the meta-particles 0º, 45º, 90º and 135º. The purpose of the work is to numerically analyze the generation of antiphase vortex beams (VBs) by OAM-modules and to assess the influence of interference and cancellation of antiphase vortices on the structure and order of OAM in the resulting field and the RCS reduction of three digital MSs in the form of 2´2 lattice of 2-bit OAM-modules of different sizes with different topological charges. The scattering characteristics are studied using HFSS for normally incident circularly polarized waves using of the finite element method. The simulation showed that the interference of phase vortices of four OAM-modules forms the main axial vortex and N additional interference side near and far vortices (N depends on the size of the MS). Interference vortex beams create phase singularities and zero the resulting far field in N side directions over the entire forward hemisphere. The intense OAM modes of the main vortex beams are of the fourth or eighth order. The OAM modes of adjacent interference VBs, as a rule, differ in sign. The proposed 2-bit MSs provide wider-angle phase cancellation of vortex fields (compared to 1-bit MSs) and, as a consequence, wider-angle diffuse scattering of the resulting field of the MS, which is important for RCS reduction.

Compact 1- and 2-bit coding metamaterial for RCS reduction application in terahertz frequency

This work focuses on 1- and 2-bit coding metamaterials by designing unit cell structures, also known as binary elements, that possess 0-, 90-, 180-, and 270-degree phase responses. Several parametric studies are mainly investigated, for instance, various coding sequence patterns and a few numbers of lattices likely 4, 8, and 12 in each bit. The RCS reduction analysis revealed a promising outcome where the distinct coding sequences exhibited way better reduction behaviour than others. For instance, coding sequences likely CS3, CS4, and CS5 exhibit excellent reduction behaviour when the lattices increase from 4 to 12. However, the 2-bit coding metamaterial exhibits superior reduction behaviours in RCS values, where the maximum points reached when adopting the CS5 design ranged from −75.2 to −55.6 dBm2.Concisely, the proposed coding metamaterial satisfied the target of this investigation to gain optimal RCS reduction by adopting both 1- and 2-bit design structures for terahertzfrequency.

Multifunctional 2-bit coded reconfigurable metasurface based on graphene-vanadium dioxide

In this paper, a graphene-vanadium dioxide-based reconfigurable metasurface unit structure is proposed. Using the change at a graphene Fermi energy level on the surface of the unit structure to satisfy the 2-bit coding condition, four reflection units with a phase difference of 90∘ can be discovered. The modulating impact of the multi-beam reflection wave with 1-bit coding is then confirmed. Then we study the control of a single-beam reflected wave by metasurfaces combined with a convolution theorem in a 2-bit coding mode. Finally, when vanadium dioxide is in an insulating condition, the structure can also be transformed into a terahertz absorber. It is possible to switch between a reflection beam controller and a terahertz multifrequency absorber simply by changing the temperature of the vanadium dioxide layer without retooling a new metasurface. Moreover, compared with the 1-bit coded metasurface, it increases the ability of single-beam regulation, which makes the device more powerful for beam regulation.

Pattern-reconfigurable integrated array antenna based on a coding metasurface.

An electrically tunable pattern-reconfigurable integrated array antenna based on a 1-bit digital coding metasurface is proposed in this paper. The array antenna consists of 8 × 8 unit cells which is divided into the radiation antenna and the phase control metasurface. The rectangular microstrip patch antenna is used as the radiation source. The phase control metasurface includes three stacked layers of square slot units loaded with varactor diodes and a biasing circuit layer. The metasurface regulates the transmission phase of the quasi-plane wave generated by the radiation antenna. The pattern reconfigurability is achieved by switching coding sequences of the metasurface which can be regulated by the capacitance of varactor diodes. The measured results show the design has the capability of pencil-beam radiation, beam deflection, and multi-beam radiation at 5 GHz. The proposed array antenna preserves the coding metasurface without requiring the additional horn antenna. This highly integrated design is more concise and reduces the profile height. This article offers what we believe is a new method for the design of high integration, multi-unit, and electrically tunable reconfigurable array antenna.

Optimization-Driven design of a 2-bit coding based metasurface absorber for enhanced EMI shielding and RCS reduction

In this paper, a 2-bit optimized coding based metasurface absorber (CMA) is designed for electromagnetic interference (EMI) shielding and radar cross section (RCS) reduction. The 2-bit CMA comprises four digital elements using triple circular ring resonators to represent ‘00′, ‘01′, ‘10′ and ‘11′, through optimized coding sequences obtained via particle swarm optimization (PSO) algorithm applied to array theory. The simulation results demonstrate that optimized pattern performs better, achieving an RCS reduction exceeding −10 dB across 7.5 to 17.5 GHz frequency range, with additional evidence from 3D scattering patterns at 9.76, 11.90, 13.84, and 16.80 GHz confirming its remarkable ability to suppress bistatic RCS. The optimized pattern also demonstrates high shielding effectiveness with near unity absorption. A prototype is fabricated and experimentally tested to validate the optimized pattern performance, with both simulation and experimental results confirming the optimized pattern as a viable option for achieving enhanced EMI shielding and RCS reduction.

Genetic algorithm based terahertz multifunctional reconfigurable Dirac semi-metallic coded metasurface

Digitally encoded hypersurfaces show great potential in the field of electromagne-tic wave modulation. Currently, digitally encoded hypersurfaces in the terahertz band are mainly classified into two types: structure-encoded and controllable material-encoded. Once a structure-encoded hypersurface is fabricated, its function is fixed, which makes it difficult to adapt to changing application requirements. In contrast, the controllable material-encoded hypersurfaces can achieve dynamic regulation and multifunctional switching of terahertz beams by changing the external excitation, which shows good reconfigurability. To address this challenge, a Dirac semimetal-based encoded hypersurface is proposed in this paper. The Fermi energy level of the Dirac semimetal is varied by changing the bias voltage, which in turn dynamically adjusts its relative permittivity to obtain the coded unit. Besides, the traditional gradient-phase method encodes arrays by periodically arranging the cell structure, but there are limitations in the flexibility and accuracy of beam modulation. In order to break through these limitations, this paper employs a genetic algorithm for the inverse design of hypersurface coding arrays, which effectively improves the initiative and flexibility of beam modulation. In this paper, a three-layer terahertz-encoded hypersurface unit with a “back” structure composed of Dirac semimetallic materials is firstly designed, and the Dirac semimetallic dielectric constant is dynamically adjusted by using an applied bias voltage, so that the hypersurface unit is at 1.95 THz when the Fermi energy levels are 0.01 eV, 0.05 eV, 0.09 eV, and 0.55 eV can achieve 2bit coding. The results show that, for beam configuration, single-beam and multi-beam (two-beam to five-beam) modulation can be achieved at 1.95 THz within 40° pitch angle and 360° azimuth angle; for vortex beam generation, single-vortex beams with ±1 and ±2 topological charges can be generated, with mode purity exceeding 60%, and single-vortex, double-vortex and triple-vortex beams in pitch angle and 360° azimuth angle can be realised with the vortex-phase convolution. In terms of RCS reduction, in the frequency range of 1.72–2.51 THz, the hypersurface is able to achieve more than 10 dB of RCS reduction, especially in the frequency range of 1.82 THz, the maximum reduction value is up to 27.5 dB. achieves the diversity of functions, but also has a high degree of reconfigurability to meet the needs of complex application scenarios.

Binary coding metasurface for broadband and flexible generation of acoustic vortex beams

Considerable efforts have recently focused on sound vortices imprinted with orbital angular momentum (OAM) yet whose generation generally relies on sophisticated phase modulation, whether through traditional phased arrays or emerging metamaterial methods. Here, we propose and numerically demonstrate a mechanism for broadband generation of acoustic vortices in a simple, flexible, and high-efficiency way through binary-phase-based chirality modulation enabled by building a binary coding metasurface. The metasurface with a theoretically derived phase profile that is implemented with two types of meta-structures is capable of twisting the incident plane wave into a vortex beam with a desired order in a broad band and at the same time enables steering the vortices' propagation direction freewheelingly. The effectiveness of our proposed mechanism is verified by numerically demonstrating the broadband generation of vortex beams carrying different OAMs through a monolayered binary coding metasurface. We further demonstrate the generality and flexibility of our mechanism for generating the multiplexed vortex beams as well as modulating the propagation direction of the output beam by judiciously designing the 1-bit coding sequences of the metasurface. We anticipate our design with capability and simplicity to have far-reaching implications in OAM-enabled applications ranging from high-capacity acoustic communication to contactless particle manipulation.

2-bit coding metasurface with a double layer random flip structure for wide band diffuse reflection and reciprocity protected transmission.

Coding metasurfaces based on random-flip structures have attracted great attention due to their ability to achieve distortion-free transmission and diffuse reflection simultaneously. However, previous implementation based on 1-bit coding metasurface has a narrow bandwidth and insufficient bandwidth coverage in the near infrared region. Here, we propose a novel vertical 2-bit coding metasurface composed of double-layer random-flip meta-atoms (DLRFM). while the main transmission lobe is unchanged, the zero-order diffraction intensity of DLRFM's reflection direction is less than 10% of the total reflection in the range of 0°∼ 30° incidence angle, which proves its excellent diffuse reflection and distortion-free transmission effect. Such design strategy can be extended to multiple wide band coverage in near-infrared regime by tailoring the geometric parameters, which indicates good application potential in advanced display and lens designs.

Design of Anomalous Reflectors by Phase Gradient Unit Cell-Based Digitally Coded Metasurface

In this letter, we propose the designs of 1-bit and 2-bit digitally coded metasurfaces, which achieve anomalous reflection-based beam-steering. First, we demonstrate the systematic design flow of coded metasurface using phase gradient digital unit cells to achieve anomalous reflection in the preferred direction for a normally incident plane wave. Initially, the design procedure is analytically implemented to get the phase profiles for 1-bit and 2-bit digitally coded metasurfaces having equal sizes of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$10\lambda _{0} \times 10\lambda _{0}$</tex-math></inline-formula> (where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> is the free space wavelength at 5.9 GHz) for a specific reflection angle, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(\theta _{r}=30^{0},\phi _{r}=0^{0})$</tex-math></inline-formula> , and subsequently, the far-field plots are generated. Furthermore, these phase profiles are used to generate 3D-CAD models of the 1-bit and 2-bit metasurfaces using CST, and the desired far-field patterns are obtained having half-power beamwidth (HPBW) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$5^{0}$</tex-math></inline-formula> . It is observed that the 1-bit coded metasurface produces additional side-lobe levels, which are minimized by use of 2-bit coding. Finally, the proposed 1-bit and 2-bit coded metasurfaces are fabricated, and the anomalously reflected far-field beam is detected by the received power at desired reflection angle and comparing the results with a perfect electric conductor (PEC). The proposed design is suitable for V2X communications and can be scaled to other frequencies.

Rapid design of hybrid mechanism metasurface with random coding for terahertz dual-band RCS reduction.

In this paper, a hybrid mechanism metasurface (HMM) employing 1-bit random coding is proposed to achieve polarization-insensitive and dual-wideband monostatic/bistatic radar cross section (RCS) reduction under a wide range of incident angles. The anisotropic unit cell is designed by the combination of the multi-objective particle swarm optimization (MOPSO) algorithm and Python-CST joint simulation, which facilitates the rapid acquisition of the desired unit cell with excellent dual-band absorption conversion capability. The unit cell and its mirrored version are used to represent the units "0" and "1", respectively. In addition, the array distribution with random coding of the units "0" and "1" is optimized under different incident angles, polarizations and frequencies, which enables better diffusion-like scattering. Simulation results demonstrate that the proposed coding HMM can effectively reduce the monostatic/bistatic RCS by over 10 dB within the dual-band frequency ranges of 2.07-3.02 THz and 3.78-4.71 THz. Furthermore, the specular and bistatic RCS reduction performances remain stable at oblique incident angles up to 45° for both TE and TM polarizations.

Real-time programmable metasurface for terahertz multifunctional wave front engineering

Terahertz (THz) technologies have become a focus of research in recent years due to their prominent role in envisioned future communication and sensing systems. One of the key challenges facing the field is the need for tools to enable agile engineering of THz wave fronts. Here, we describe a reconfigurable metasurface based on GaN technology with an array-of-subarrays architecture. This subwavelength-spaced array, under the control of a 1-bit digital coding sequence, can switch between an enormous range of possible configurations, providing facile access to nearly arbitrary wave front control for signals near 0.34 THz. We demonstrate wide-angle beam scanning with 1° of angular precision over 70 GHz of bandwidth, as well as the generation of multi-beam and diffuse wave fronts, with a switching speed up to 100 MHz. This device, offering the ability to rapidly reconfigure a propagating wave front for beam-forming or diffusively scattered wide-angle coverage of a scene, will open new realms of possibilities in sensing, imaging, and networking.

Rapid deep-learning-assisted design method for 2-bit coding metasurfaces.

This paper proposes a deep-learning-assisted design method for 2-bit coding metasurfaces. This method uses a skip connection module and the idea of an attention mechanism in squeeze-and-excitation networks based on a fully connected network and a convolutional neural network. The accuracy limit of the basic model is further improved. The convergence ability of the model increased nearly 10 times, and the mean-square error loss function converges to 0.000168. The forward prediction accuracy of the deep-learning-assisted model is 98%, and the accuracy of inverse design results is 97%. This approach offers the advantages of an automatic design process, high efficiency, and low computational cost. It can serve users who lack metasurface design experience.

On-chip beam steering through reprogrammable integrated coding metasurfaces

Coding metasurfaces have found many applications in free space optics, but have not been used for integrated photonic applications. This can partly be attributed to the lack of implements to usefully implement such a framework in practice. The advent of low-loss phase change materials such as Sb2S3 has changed this by enabling the implementation of reprogrammable integrated metasurfaces. This manuscript presents Sb2S3 based 1-bit and 2-bit coding metasurfaces that can potentially also be practically implemented. These metasurfaces can achieve functionalities such as beam focusing, beam splitting, and beam steering through the rearrangement of the material phase of Sb2S3. This can find potential applications in numerous fields including integrated photonic computational platforms.

Active modulation of terahertz vortex beams by Dirac semimetals-based space–time-coding​ metasurface

Coding metasurfaces have developed rapidly in the last few years because of the digital thought. Recently, spatiotemporal metasurface have attracted considerable attention for the additional degrees of freedom they provide when manipulating electromagnetic waves in space and time domains. This study proposed Dirac semimetal based space–time-coding metasurfaces in the terahertz band. The conversion from a low- to high-bit programmable metasurface was achieved using a spatiotemporal metasurface, that is, 2-bit coding was equated to 3-bit coding. Space–time-coding metasurfaces facilitated the realization of the function of wide-band terahertz vortex beam generator switching according to the vortex phase arrangement, and were combined with the convolution theory for the successful realization of the modulation of terahertz vortex deflection and beam splitting under space–time coded modulation. The modulation of the equivalent 3-bit vortex beam produced under space–time coded modulation considerably reduced the gain of the side lobes and achieved precise modulation of the terahertz vortex beam. Moreover, the principle and method proposed in this study are also applicable to microwave and visible wavelengths. The results of this study are expected to result in promising applications in future terahertz high-data-capacity communication systems and multi-target precision tracking and guidance.

1-bit Coding Reconfigurable Array for 2-D Wide-Angle Scanning

In this article, an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\,\,{\times }$ </tex-math></inline-formula> 8 array with 2-D wide-angle scanning is proposed and studied. By integrating two p-i-n diodes on the feeding line, the radiated electric field of the element can present two different phase states of 0° and −180°. By introducing the elaborately designed two groups of fixed phase delay (FPD) in horizontal and vertical directions, the grating lobe of the 1-bit array is effectively mitigated. Simulated and measured results indicate that the proposed array can cover the beam from −60° to 60° with no grating lobe within a 2-D scanning scope from 9 to 10 GHz. The peak gain of the array is 17.3 dBi and the cross-polarization level at the main lobe is less than −20 dB. The proposed array has the advantages of being lightweight, low-cost, and easy to integrate. These features enable its applications in space-limited scenarios such as base stations and unmanned aerial vehicles.

Transmission-type coding metasurface with ultra-broadband polarization conversion

The advent of coding metasurfaces (MSs) has established a bond between electromagnetic scattering and digital control. Given that most of the current coding MSs are based on reflection-type, we investigate a novel transmission-type MS that can achieve ultra-wideband and efficient polarization conversion. A new double diagonal split ring resonator structure is designed to mainly constitute the unit. The 1-bit and 2-bit coding arrays are constructed using the proposed polarization rotation mechanism of the MS unit combined with the dimensional transformation to achieve beam focusing, beam deflection, and beam splitting. Finally, the broadband focusing characteristic of the coding MS is also demonstrated. Numerical simulation results demonstrate that the transmission coefficient of the proposed MS is above 90% in the frequency range of 0.4 to 2 THz, with a relative bandwidth of 133.3%. Asymmetric transmission phenomenon is observed in the range of 0.4 to 2 THz, with coefficients remaining above 80% in all ranges.The proposed coding MS can be used in terahertz polarization converters and unidirectional transmission devices due to its superior polarization conversion performance.

Improving Stability of Roll-to-Roll (R2R) Gravure-Printed Carbon Nanotube-Based Thin Film Transistors via R2R Plasma-Enhanced Chemical Vapor-Deposited Silicon Nitride.

Single-walled carbon nanotubes (SWCNTs) have an advantage in printing thin film transistors (TFTs) due to their high carrier mobility, excellent chemical stability, mechanical flexibility, and compatibility with solution-based processing. Thus, the printed SWCNT-based TFTs (pSWCNT-TFTs) showed significant technological potential such as integrated circuits, conformable sensors, and display backplanes. However, the long-term environmental stability of the pSWCNT-TFTs hinders their commercialization. Thus, to extend the stability of the pSWCNT-TFTs, such devices should be passivated with low water and oxygen permeability. Herein, we introduced the silicon nitride (SiNx) passivation method on the pSWCNT-TFTs via a combination of roll-to-roll (R2R) gravure and the roll-to-roll plasma-enhanced vapor deposition (R2R-PECVD) process at low temperature (45 °C). We found that SiNx-passivated pSWCNT-TFTs showed ± 0.50 V of threshold voltage change at room temperature for 3 days and ±1.2 V of threshold voltage change for 3 h through a Temperature Humidity Test (85/85 test: Humidity 85%/Temperature 85 °C) for both p-type and n-type pSWCNT-TFTs. In addition, we found that the SiNx-passivated p-type and n-type pSWCNT-TFT-based CMOS-like ring oscillator, or 1-bit code generator, operated well after the 85/85 test for 24 h.

High-Sensitivity Liquid Dielectric Characterization Differential Sensor by 1-Bit Coding DGS

This paper presents two devices to detect the liquid dielectric characterization. The differential method was used to enhance the robustness and reduce tolerance. A basic sensor based on defected ground structure (DGS) was designed and the optimization for the squares of the DGS via adaptive genetic algorithm was applied to enhance the performance of the microwave sensor, which was shown by the difference of the two resonant frequencies. Furthermore, the electric field distribution was enhanced. Glass microcapillary tubes were used to hold samples to provide an environment of non-invasive. The optimized device exhibited the sensitivity of 0.076, which is more than 1.52 times than the basic structure. It could be considered a sensitive and robust sensor with quick response time for liquid dielectric characterization.