2-bit Coding Research Articles

Design of a 2-Bit wide-angle coding metasurface for bistatic RCS reduction

A 2-bit wide-angle coding metasurface is proposed to decrease the bistatic radar cross section (RCS) in this study. Each meta-atom of the designed coding metasurface is composed of a wide-beamwidth microstrip antenna whose feeding port is loaded with an open stub. There are globally four phase-coding states, namely, “00,” “01,” “10,” and “11,” which are achieved in a wide-angle range through an elaborate design of the lengths of the open stubs. Simulation results indicate that, for each meta-atom, the reflective amplitude is above −1 dB, and the reflective phase difference between two adjacent coding states is limited in the range of 90° ± 25° at 8 GHz at incident angles, 0°, 20°, 40°, and 60°. In addition, the generalized Rudin–Shapiro (RS) polynomial is applied to design the coding sequence of the metasurface array to reduce bistatic RCS. A 16 × 16 metasurface array is simulated, manufactured, and measured to validate the bistatic RCS reduction. The simulated results perfectly agree with the experimental results when the incidence angle of the 8 GHz plane wave is within 60°, which shows that the coding metasurface is practical and valid.

Programmable VO2 metasurface for terahertz wave beam steering

SummaryProgrammable vanadium dioxide (VO2) metasurface is proposed at THz frequencies. The insulating and metallic states of VO2 can be switched via external electrical stimulation, resulting in the dynamical modulation of electromagnetic response. The voltages of different columns of the metasurface can be controlled by the field-programmable gate array, and thus the phase gradients are realized for THz beam steering. In 1-bit coding, we design periodic and nonperiodic 24 × 24 coding sequences, and achieve wide-angle beam scanning with the deflection angles from −60° to +60°. In 2-bit coding, we use two different meta-atoms to design 18 × 18 coding sequences. Compared with 1-bit coding, 2-bit coding has more degree of freedom to control the optical phase, and 3 dB diffraction efficiency is improved by generating a single deflection angle. The proposed programmable metasurfaces provide a promising platform for manipulating electromagnetic wave in 6G wireless communication.

Drone Movement Control by Electroencephalography Signals Based on BCI System

Brain Computer Interface enables individuals to communicate with devices through ElectroEncephaloGraphy (EEG) signals in many applications that use brainwave-controlled units. This paper presents a new algorithm using EEG waves for controlling the movements of a drone by eye-blinking and attention level signals. Optimization of the signal recognition obtained is carried out by classifying the eye-blinking with a Support Vector Machine algorithm and converting it into 4-bit codes via an artificial neural network. Linear Regression Method is used to categorize the attention to either low or high level with a dynamic threshold, yielding a 1-bit code. The control of the motions in the algorithm is structured with two control layers. The first layer provides control with eye-blink signals, the second layer with both eye-blink and sensed attention levels. EEG signals are extracted and processed using a single channel NeuroSky MindWave 2 device. The proposed algorithm has been validated by experimental testing of five individuals of different ages. The results show its high performance compared to existing algorithms with an accuracy of 91.85% for 9 control commands. With a capability of up to 16commands and its high accuracy, the algorithm can be suitable for many applications.

Broadband and Programmable Amplitude-Phase-Joint-Coding Information Metasurface.

Information metasurfaces have attracted much attention in recent years due to the capability to link the physical world and information science. However, most of the current information metasurfaces are either phase-only coding or amplitude-only coding, limiting their functions and applications. Here, a broadband and programmable amplitude-phase-joint-coding (APJC) information metasurface is proposed and experimentally demonstrated, from which the phase and amplitude of reflected electromagnetic waves can be independently controlled by adjusting the bias voltage of PIN diode integrated in the meta-atom. In particular, the reflection amplitude can be continuously controlled from 0.1 to 0.9, and the reflection phase can be switched between two states with about 180° phase difference. Thus, the proposed metasurface is capable of realizing independent 1-bit or multibit amplitude coding and 1-bit phase coding, and both of them can be reprogrammed in real time in broad band from 8 to 13 GHz. The abilities of the programmable APJC information metasurface in manipulating the electromagnetic waves are demonstrated by both numerical simulations and experiments, including to suppress the sidelobes of scattering beam, generate the diffractive waves with arbitrary magnitudes, and so on. These results show unique advantages of APJC information metasurface in real-time independent controls of energy allocation and wavefront tailoring of the electromagnetic waves in a wide frequency band.

Digital Polarization Programmable Metasurface for Continuous Polarization Angle Rotation and Radar Applications

Polarization angle manipulation has been a vital technic in radar applications. This paper proposes and demonstrates a digital polarization programmable metasurface for continuous polarization angle rotation and radar applications. By coding “0” and “1” elements with the two orthogonally polarized waves having 180° phase difference, the polarization angle of electromagnetic (EM) waves can be continually and arbitrarily manipulated. The designed metasurface adopts a patch-transmission and line-patch structure and integrates two polarization channels to carry out 1-bit coding. By rotating the azimuth angle of the designed metasurface mechanically, a continuous rotation of the polarization angle of the transmitted wave can be achieved. Moreover, the transmission around 9.4 GHz can reach higher than 95%. The metasurface sample with optimized structure parameters has been fabricated and tested, where the measurement agrees well with the simulation results. In addition, a radar detection experiment was implemented with an anisotropic target, demonstrating the practical use of the proposed metasurface for polarimetric radar.

Broadband tunable coding metasurfaces based on a metal patch and graphene for beam control at the terahertz frequencies.

We present a broadband tunable coding metasurfaces structure using a cruciate metal patch and circular graphene on a multilayer substrate. By changing the Fermi level of the graphene, we can achieve obvious reflection phase variation to design multi-bit coding metasurfaces. In the research of 1-bit coding metasurfaces, we combine the advantages of graphene and copper to realize the real-time adjustment of the reflected waves in four broadband frequency bands. In this case, we can control the number of far-field reflected waves in the frequency range of 5.45-6.45 THz. Then, we create 2-bit and 3-bit coding modes on the basis of 1-bit coding metasurfaces to obtain a single beam of reflected waves. Finally, we use the convolution calculation to realize the real-time adjustment of the single beam reflection direction from 0° to 360° in the azimuthal plane. Research of the 2-bit and 3-bit coding modes also provides a way to control the number and direction of the reflected beam, specifically in the 1-bit coding mode. The present coding metasurfaces structure provides inspiration for the design of functional devices in future-oriented intelligent communication.

Transmission‐type 1‐bit coding metasurfaces with linear‐to‐circular polarization conversion using coupling‐propagation‐decoupling unit cells

In this paper, a coupling-propagation-decoupling unit cell is designed to independently manipulate the transmission phase and polarization of a linearly polarized electromagnetic wave by adjusting only two geometry parameters respectively. Utilizing this kind of unit cell structure, two 1-bit transmissive coding metasurfaces were proposed to efficiently realize the wavefront control and linear-to-circular polarization conversion from 7.90 to 8.20 GHz. By arranging two types of unit cells in different coding sequences, the designed two coding metasurfaces can split a linearly polarized incident wave into two and four transmitted beams, respectively. The proposed coding metasurfaces demonstrated the independent phase and polarization manipulation characteristic of the designed structure.

A 1-Bit Coding Metasurface With Polarization Conversion in X-Band

Polarization conversion metasurfaces are widely used in optical devices, microwave devices and communication systems, owing to their unique polarization modulation characteristics. However, in some applications (such as folded reflectarrays), the unit cell must be capable of polarization conversion and phase modulation. To the best of our knowledge, there are only a few related designs with both the functionalities. In this paper, we propose a well-performing 1-bit reconfigurable coding metasurface with polarization conversion. It realizes linear-to-linear polarization conversion in a 1.32 GHz bandwidth, and the conversion loss is within 1 dB. Simultaneously, the metasurface achieves a phase difference of approximately 180° by switching the working state of the PIN diodes. This metasurface has great potential for radar detection, folded reflectarrays, and other fields.

Dual-band multifunctional coding metasurface with a mingled anisotropic aperture for polarized manipulation in full space

Integrated metasurfaces with diversified functionalities have demonstrated promising prospects for comprehensive implementations in compact 5G/6G communication systems by flexibly manipulating electromagnetic (EM) waves. Increasingly emerged multifunctional metasurfaces have successfully revealed integrated wavefront manipulations via phase gradient arrays, coding apertures, independent polarization control, asymmetric transmission/reflection, etc. However, multifunctional metasurfaces with more degrees of freedom in terms of multi-band/broadband operation frequencies, full-space coverage, and computable array factors are still in dire demand. As a step forward in extending manipulation dimensions, we propose and corroborate a dual-band multifunctional coding metasurface for anomalous reflection, radar cross-section reduction, and vortex beam generation through full-wave analysis and experiment. Our tri-layer meta-device comprises a shared coding aperture of split-ring and cross-shaped resonators sandwiched between two layers of orthogonal wire gratings. With an approach of independent control of a reflection–transmission wavefront under orthogonal polarization states and Fabry–Perot-like constructive interference, the low-cross-talk shared coding aperture features a smooth phase shift and high efficiency for 3-bit coding in the K-band and 1-bit coding in the Ka-band. Both numerical and measured results verify that the proposed coding metasurface can effectively realize full-space EM control and improve the capacity of the information channel, which could be developed for potential applications in multifunctional devices and integrated systems.

Multi‐path separation and parameter estimation by single DMA in fading channel

The propagation of electromagnetic waves will produce multi-path fading of wireless channel, which degrades communication performance substantially. If multi-path can be separated, better signal transmission and reception strategies can be designed to weaken or eliminate fading and improve signal transmission performance. However, it is challenging for communication nodes with limited number of antennas. A general multi-path separation and measurement framework based on single dynamic metasurface antenna is established which rapidly changes patterns within a single pilot symbol period so that equivalent multi-dimensional received signals can be obtained. Based on the framework, a multi-path channel estimation scheme is proposed. Specifically, the parameter estimation problem is formulated and present the algorithm based on atomic norm minimisation to estimate parameters including angle of arrival and complex gain of each propagation path. Simulation results illustrate that single dynamic metasurface antenna can approach the capability of a conventional multi-antenna array, and even using single dynamic metasurface antenna with 1-bit coding can estimate angle of arrivals and complex gains of multi-path components accurately.

Active beam manipulation and convolution operation in VO2-integrated coding terahertz metasurfaces.

Coding metasurfaces have received tremendous interest due to their unprecedented control of beams through the flexible design of coding sequences. However, realizing tunable coding metasurfaces with scattering-pattern shifts in the terahertz range is still challenging. Here, we propose a VO2-integrated coding metasurface to realize a thermally controlled scattering-pattern shift by convolution operation. The required phase profiles and high amplitudes of 1-bit and 2-bit coding metasurfaces are easily obtained only by changing the length of the VO2 cut-wires. The insulator-metal phase transition of the VO2 cut-wires leads to an ultrafast switching effect between multiple deflected scattering beams and one normally reflected beam. In particular, the VO2 phase transition contributes to dynamical convolution operations of the 2-bit coding metasurface. The proposed VO2-integrated coding metasurfaces are important for realizing tunable terahertz beam manipulation as well as arbitrary required scattering beams.

Efficient Electronic Patient Information Hiding Scheme With Tamper Detection Function for Medical Images

With the rapid development of the electronic medical information systems and Internet technology, the frequency of electronic medical records (EMRs) and electronic patient information (EPIs) transmitted over the Internet and shared among authorized medical parties is gradually increased. Reversible data hiding in medical images is an efficient technique to embed an EPI or EMR into a medical image, such as X-ray, MRI etc. In this paper, a reversible data hiding scheme by using enhanced neighbor mean interpolation (ENMI) technology is proposed to expand each <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> block in the original image to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times 3$ </tex-math></inline-formula> block. The four original pixels remaining at the four corners in each expanded block. Five derived pixels by using the ENMI interpolation algorithm are used to carry 4-bits secret data and a 1-bit authentication code with our proposed efficient data hiding strategy. Experimental results confirm that the detection performance and the robustness of the hidden data with our proposed scheme are significantly higher than that of the Geeth & Geeth scheme and other six representative schemes.

Feasibility of a Plasma-Based Intelligent Reflective Surface

Gaseous Plasma Antennas are devices in which an ionized gas (i.e., plasma) is exploited to transmit and receive Electro-Magnetic waves. Their main advantage over metallic systems is the possibility to reconfigure the antenna performance (e.g., radiation pattern) by electronically varying the plasma parameters (e.g., density). Recently, Intelligent Reflecting Surfaces (IRSs) have been proposed to control the environment between transmitting and receiving antennas manipulating the signals reflected. In this work, the feasibility of a plasma-based IRS is investigated. A theoretical model has been developed to assess the use of plasma as a reflecting medium. Numerical simulations have been performed to preliminary design plasma-based IRSs. Two designs of IRSs, relying on plasma properties consistent with the technology at the state-of-the-art, are proposed. The former enables beam steering operations depending on the continuous control of the phase of the reflected wave. The latter exploits a 1-Bit coding strategy to produce specific diffraction patterns. The main advantage of a plasma-based IRS with respect to the metallic counterpart is the possibility to control the phase of the reflected wave, maintaining the magnitude of the reflection coefficient close to the unit. The main drawback of plasma-based systems is the necessity of using thick plasma elements (in the order of the wavelength in the air) to control the phase of the reflected wave over 360 deg. This constraint can be relaxed if digital plasma elements are adopted.

Electromagnetic wave beam manipulator based on an all-dielectric THz coding metasurface.

In this paper, we proposed an all-dielectric THz coding metasurface that can effectively manipulate electromagnetic waves. This structure was composed of sub-wavelength coding units with different reflection phases. The encoding unit is composed of a rectangular base with a cross dielectric column. Different encodings were designed by changing the thickness of the X arm of the dielectric column. We designed a variety of coding modes and implemented the modulation of the number of far-field reflection beams and the angle of reflection direction at 0.85 THz by 1- and 2-bit coding. Our theoretical calculations and numerical simulations of the structure suggested that the far-field scattering obtained by full-wave simulation matched the theoretical calculation when the incident direction of electromagnetic wave was perpendicular to the metasurface. We chose all-dielectric materials to design the coding unit due to the low cost, strong corrosion resistance, and low internal electromagnetic loss. As a result, the all-dielectric materials avoided the serious internal loss of metal materials and demonstrated the flexibility to regulate the reflected beam in the THz band to realize abnormal refraction and beam splitting.

Experimental and Numerical Investigations of Backscatter Patterns of the Blocks of Masking Digital Two-Bit Meta-covers

Introduction. The scattering patterns of non-absorbing coded checkerboard-like meta-coatings (MCs) applied for reducing the radar cross section (RCS) of metal surfaces inevitably contain side diffraction lobes. Therefore, the development of MCs with a low level of diffraction lobes is relevant. For this purpose, it is proposed to use checkerboard-like MCs in the form of a set of several basic flat blocks with the same dimensions. The paper discusses two such basic MC blocks with different coding matrices. The cells of the metasurface contain two coupled elliptical ring resonators and are distinguished by a 2-bit coding of the tilt angle of the anisotropy axis. Coding matrices of the MC blocks are built according to the block principle.Aim. To investigate experimentally and numerically backscatter patterns (BSP) for consonant (co-) and orthogonal (cross-) polarizations of the two developed flat blocks of the 2-bit digital nonabsorbing anisotropic MCs for different planes and polarizations of irradiation.Materials and methods. Full-wave simulation of the MC blocks was carried out using the HFSS software by the finite element method. BSP measurements of the fabricated MC layouts were performed in an anechoic chamber of the Center for Collective Usage “Applied Electrodynamics and Antenna Measurements” of the Southern Federal University using an automated information and computing complex.Results. The RCS reduction for the two blocks under normal irradiation is approximately the same and not less than 12 dB over the 9.8…21 GHz band. A good matching between the simulation and measurement results of backscattering patterns of the blocks in the region of the central lobes for various planes and polarizations of the irradiation is noted. In the principal planes, the blocks cancel the central lobes of the BSP by 10…25 dB; in the sector of angles of around ±40°, the backward RCS of the blocks is lower than that of the reference. In the diagonal planes, there is a cancellation of the RCS by 13…15 dB and an expansion of the central lobe of the BSP for copolarizations, as well as a bifurcation of this lobe for crosspolarizations in the sector of angles ±9°; outside of this sector the RCSs of the blocks are commensurate with the RCS of the reference.Conclusion. The developed blocks of the 2-bit digital nonabsorbing anisotropic MCs can be used for broadband cancellation of the RCS of metal surfaces.

Underwater Acoustic Stealth by a Broadband 2-Bit Coding Metasurface

Underwater acoustic stealth is of significance for hiding targets. Since perfect cloaking achieved by carpet cloaks or metasurface carpet cloaks may only be suitable for static targets, here we propose a broadband 2-bit coding metasurface to reduce the scattering cross section (SCS) of an object by the destructive interferences among waves scattered by different coding elements. A simple and easy fabricated design is developed by drilling square holes into a steel plate. Utilizing the antiresonance induced by couplings among four square holes of the unit cell, we achieve an approximate $95.62\mathrm{%}$ fractional bandwidth of acoustic stealth with the SCS reduction below $\ensuremath{-}10\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$, which has been confirmed by both the theoretical prediction and experimental measurement. Compared with the previously proposed underwater acoustic carpet cloaks by the transformation acoustics, the bandwidth of SCS reduction is greatly expanded by the destructive interferences. In addition, simulations have demonstrated that the proposed metasurface may also be suitable for an object with a nonplanar surface.

Three-dimensional shape measurement based on spatial-temporal binary-coding method

Binary coding methods have been widely used for three-dimensional (3D) shape measurement. However, traditional binary coding methods always require a sequence of binary patterns to encode the fringe order. This paper presents a spatial-temporal binary coding (STBC) method for 3D shape measurement with three binary patterns, including a spatial pattern and two temporal patterns. Specifically, the spatial pattern is used to encode a 4-bit spatial code, and the temporal patterns are used to encode the 2-bit temporal code. By combining the spatial code and the temporal code, 6-bit code words can be obtained that distinguish fringe periods of sinusoidal phase-shifting patterns. A robust dual-region labeling decoding scheme is also developed to extract the 6-bit code word for fringe order determination, and then absolute-phase unwrapping can be carried out. Experiments have been conducted, and their results confirm that the STBC method can reliably reconstruct the 3D shapes of measured objects with only three binary patterns.

Anisotropic digital metasurfaces relying on silicon Mie resonance

We propose an anisotropic terahertz metasurface based on silicon Mie resonance for achieving terahertz wave beam deflection manipulation. The presented coding metasurface can achieve various functions for two orthogonal linear polarized terahertz waves incidence. By elaborately designing 1-bit and 2-bit anisotropic coding metasurface with different coding matrix, we verify the anisotropic coding metasurface having excellent performance on manipulation reflection beam numbers and beam deflection angles under different polarization waves incidence. The proposed anisotropic terahertz metasurface provides an efficient and flexible method for regulation terahertz wave and has the potential for the promising applications of terahertz MIMO communication systems.

Single-Shot Phase Measuring Profilometry Based on Quaternary Grating Projection

In this paper, we propose a new single-shot three-dimensional (3D) measuring method based on quaternary grating projection. In traditional binary grating phase measuring profilometry (PMP), a multi-step or color fringe pattern are usually used to extract the sinusoidal fringes. In our proposed method, by using the DLP4500’s 2-bit gray coding mode, the grayscale is quaternary. The three non-zero grayscales cyclically arranged in equal width, and the fourth grey value is 0 which is not encoded in the fringe pattern but represents the shadow information in the deformed pattern, where a quaternary grating is encoded. When the DLP4500 projects the quaternary grating onto the measured object, the charge coupled device (CCD) captures the corresponding deformed pattern synchronously. Three frames of binary deformed patterns with 1/3 duty cycle and a relative displacement of 1/3 period can be decomposed by the segmentation algorithm proposed in this paper. Three sinusoidal deformed patterns with a 2π/3 shift-phase can be obtained by extracting the fundamental frequency of the three binary deformed patterns correspondingly, and the 3D shape of the object can be reconstructed by PMP. Experimental results show the effectiveness and feasibility of the proposed method. Because the DLP4500 only needs 2-bit coded grating for projection, the refresh rate of the projected grating is as high as 1428 Hz, which will have a broad application prospect in real time and fast online measurement.

An Efficient Design of Binary to Gray Code Binary Converter using QCA

An upcoming Quantum Dot Cellular Automata (QCA) technology promises the incomparable compactness, high-speed operation and the features of ultralow-power utilization. In QCA, fault-tolerance is a significant feature to be considered in order to explore and manufacture quantum dots. For the reason of its high density and its inbuilt substantial properties. In this paper, the QCA based 2-bit, 3-bit, 4-bit, and 5-bit gray code converter have been proposed. The proposed converter designs reduce the number of cells (57.5% for 2-bit, 62.19% for 3-bit, 64.28% for 4-bit) and area (50% for 2-bit, 63.63% for 3-bit and 53.33% for 4bit) as compared to the earlier existing circuit, and also design a 5-bit converter. An integrated parameter, Area Utilization Factor (AUF) is also calculated for all the designs.