Reflection Phase Shift Research Articles

Downlink Power Minimization in Intelligent Reflecting Surface Aided Security Classification Wireless Communications System

User privacy protection is considered a critical issue in wireless networks, which drives the demand for various secure information interaction techniques. In this paper, we introduce an intelligent reflecting surface (IRS)-aided security classification wireless communication system, which reduces the transmit power of the base station (BS) by classifying users with different security requirements. Specifically, we divide the users into confidential subscribers with secure communication requirements and general communication users with simple communication requirements. During the communication period, we guarantee the secure rate of the confidential subscribers while ensuring the service quality of the general communication users, thereby reducing the transmit power of the BS. To realize such a secure and green information transmission, the BS implements a beamforming design on the transmitted signal superimposed with artificial noise (AN) and then broadcasts it to users with the assistance of the IRS's reflection. We develop an alternating optimization framework to minimize the BS downlink power with respect to the active beamformers of the BS, the AN vector at the BS, and the reflection phase shifts of the IRS. A successive convex approximation (SCA) method is proposed so that the nonconvex beamforming problems can be converted to tractable convex forms. The simulation results demonstrate that the proposed algorithm is convergent and can reduce the transmit power by 20\% compared to the best benchmark scheme.

User Scheduling and Trajectory Optimization for Energy-Efficient IRS-UAV Networks With SWIPT

This paper investigates user scheduling and trajectory optimization for a network supported by an intelligent reflecting surface (IRS) mounted on an unmanned aerial vehicle (UAV). The IRS is powered via the simultaneous wireless information and power transfer (SWIPT) technique. The IRS boosts users uplink signals to improve the network longevity and energy efficiency. It simultaneously harvests energy with a non-linear energy harvesting circuit and reflects the incident signals by controlling its reflection coefficients and phase shifts. The trajectory of the UAV impacts the efficiency of these operations. We minimize the maximum energy consumption of all users by joint optimization of user scheduling, UAV trajectory/velocity, and IRS phase shifts/reflection coefficients while guaranteeing each user minimum required data rate and harvested energy of the IRS. We first derive a closed-form solution for the IRS phase shifts and then address the non-convexity of the critical problem. Finally, we propose an alternating optimization (AO) algorithm to optimize the remaining variables iteratively. We demonstrate the gains over several benchmarks. For instance, with a 50-element IRS, min-max energy consumption can be as low as 0.0404 (Joule), a 7.13% improvement over the No IRS case (achieving 0.0435 (Joule)). We also show that IRS-UAV without EH performs best at the cost of circuit power consumption of the IRS (a 20% improvement over the No IRS case).

A Novel RIS-Aided Code Index Modulation Scheme With Low-Complexity Detection

In order to achieve high throughput and low-power consumption of the transmitter and improve the error performance of the receiver, a novel reconfigurable intelligent surface (RIS)-aided code index modulation (RIS-CIM) is proposed in wireless communications. RIS-CIM utilizes the index of a spreading code to convey additional information, which further improves the spectral efficiency (SE) and error performance of the receiver by adding and adjusting the reflected phase shift of low-cost reflective elements at the RIS-aided relay. To reduce the computational complexity incurred by the maximum likelihood (ML) detection, we propose two low-complexity detections, namely the match correlation (MC) detection and the optimal low complexity (OLC) detection. MC and OLC approaches separate the dispreading from the demodulation in the detection, which achieves a significant reduction of the computational complexity over ML detection demonstrated by the analysis of the computational complexity measurements. We present a thorough analysis for the upper bound on the average bit error probability (ABEP) of the ML detection and the bit error probability (BEP) of the OLC detection of RIS-CIM, which is verified by numerical simulations. Numerical simulations also demonstrate that the proposed RIS-CIM performs better in terms of the error performance of ML detection than several existing CIM and RIS-related schemes at a given SE setting. In addition, the proposed ML and OLC detections achieve an error performance close to the ML detection under various measures of signal-to-noise ratio (SNR) and the increasing SE in the simulations. Moreover, RIS-CIM can utilize a large number of reflective elements at the RIS-aided relay to offset the performance degradation caused by the improvement of SE.

Joint transmission design for IRS-assisted MISO SWIPT systems

In this paper, we investigate the transmission design for an intelligent reflecting surface (IRS)-assisted multiple-input single-output (MISO) simultaneous wireless information and power transfer (SWIPT) system, where an IRS adjusts its reflection phase shifts to facilitate information transfer and energy harvesting. Two types of input signals, i.e., Gaussian signals and finite-alphabet signals, are both considered. Our goal is to maximize the mutual information between the access point (AP) and the information receiver (IR) by jointly optimizing the transmit beamforming at the AP and the phase shifts of the IRS under the constraints of transmit power at the AP and required harvested energy at the energy harvesting receiver (ER). We show that the transmission designs for these two types of signals actually can be unified into a common optimization problem. Although the formulated problem is an intractable non-convex problem, the solving frameworks in cases of perfect and imperfect channel state information (CSI) are provided, respectively. For the perfect case, an efficient algorithm, which combines semidefinite relaxation (SDR) and penalty-based manifold optimization (PMO), is proposed. For the imperfect case, we study the worst-case transmission design and develop an algorithm based on SDR. Numerical results show the superiority of our proposed algorithms.

Inspection of Steel Bars Corrosion in Reinforced Concrete Structures by Nondestructive Ground Penetrating Radar

In this study, the degree of corrosion of steel reinforcement is compared to the reflected voltage of electromagnetic waves and the ASTM C876 specification. This study conducted some tests on steel bars with different degrees of corrosion by transmitting electromagnetic waves in the reinforced concrete. In the test, a corrosion potentiometer was used to analyze and compare the experimental results. The electromagnetic wave reflection signals from the image generated by the ground penetrating radar were used to capture the different media in the concrete components. The reflection coefficient method was used to analyze the calculated relative dielectric constant of the media and to obtain the reflection energy and phase changes on the medium interface. We compared and discussed the corrosion potential and the reflected voltage from the corroded steel bars in the reinforced concrete. The reflected voltage analysis of the ground penetrating radar showed that the average corrosion potential on the corroded plate on the 3rd floor was −280 m V (Area C). According to ASTM C876, the steel bars in the concrete were moderately corroded. The reflected voltage analysis of the electromagnetic waves concluded that areas A and B were moderately corroded, which is consistent with the conclusion from ASTM C876. Using the innovative method, this study has established a reference standard for the degree of corrosion of steel bars based on ASTM C876 and has calculated the quantitative state of corroded steel bars. The variations of the electromagnetic wave reflected voltage of the ground penetrating radar can mark the changes in the corrosion interface of concrete and steel reinforcement with different degrees of corrosion and different thicknesses of the protective layer.

Multiuser beamforming optimization for IRS‐aided systems with discrete phase shifts

Here, the beamforming design for multiuser multiple-input and multiple-output (MIMO) downlink transmission aided by an intelligent reflecting surface (IRS) with discrete phase shifts is studied. The authors deduce a minimum signal-to-interference-plus-noise-ratio (SINR) maximization fairness problem with the transmit beamformer, the receive beamformer and IRS phase shifts as optimization variables, which is generally NP-hard. Hence, an alternating optimization algorithm based on the gradient extrapolated majorization-minimization (GEMM) approach is employed to solve the above problem. Specifically, when the transmit beamformer and reflective phase shift are fixed, the authors give an optimal closed expression for the receive beamformer. Then, the receive beamformer is fixed, and the minimum SINR maximization problem at the transmitter is transformed into a power minimization problem. Finally, under the zero-forcing (ZF) transmitter beamformer, the GEMM algorithm is used to optimize the reflective phase shift. Simulation results show that by comparing to existing methods, the proposed GEMM algorithm can almost achieve the same performance with lower complexity.

Maximizing the Rate of IRS-Assisted Downlink NOMA Systems

Nonorthogonal multiple access (NOMA) techniques and intelligent reflecting surface (IRS) are being explored as potential essential technologies for future wireless communications. Accordingly, this paper provides a network framework for IRS-aided downlink NOMA transmission, in which IRS is employed to improve the NOMA system’s transmission performance, and optimization problems are raised to maximize the achievable rate. Given the fractional structure of multivariate coupling as presented in this study, the fractional problem first converts to a linear form; then, the semidefinite relaxation (SDR) algorithm is proposed to address nonconvex issues for a single-user scenario. As for a multiuser scenario, the alternating optimization (AO) algorithm is raised based on transmit beamforming and reflection phase shift matrix to settle relevant issues and mitigate computational complexity. The simulation results suggest that the algorithm described in this paper can significantly increase the signal’s achievable rate compared to the nondeployed IRS and IRS random phase-shifting schemes.

Capability of commercial trackers as compensators for the absolute refractive index of air

A procedure is presented which calibrates a wavelength/refractive-index tracker, so that it can compensate for the absolute refractive index of air within 3 × 10−8 ⋅ n. The procedure employs ultrahigh-purity helium and argon as reference gases of known n(p, T) to deduce the two unknown parameters in the working equation of the tracker: gas pathlength and pressure-induced distortion error. The performance of the gas calibration procedure is evaluated by comparing the corrected tracker against a master refractometer based on a Fabry–Perot cavity in nitrogen, a third reference gas of known n(p, T). In nitrogen, the calibrated trackers demonstrate accuracy at the level of 4 × 10−9 ⋅ n. Testing in a fourth reference gas—water vapor—reveals that the working equation of the trackers must include a third unknown parameter: an end-effect caused by a moisture-dependence of the reflection phase-shift. Correcting for this moisture-related error represents the largest contribution to measurement uncertainty, and explains why performance of the calibrated trackers is an order-of-magnitude worse in moist air than in pure gas. In air, the Fabry–Perot cavity-based refractometer performs within 5 × 10−9 ⋅ n, but is not a commercially-available device.

RIS-Assisted SSK Modulation: Reflection Phase Modulation and Performance Analysis

In this letter, we present a reconfigurable intelligent surface (RIS)-assisted space shift keying (SSK) modulation and reflection phase modulation (RPM) scheme, where RIS embeds its own information in the reflection phase shift of the reflected radio frequency (RF) signal. More specifically, the RIS simultaneously performs two tasks: i) reflecting the impinging RF signal with a discrete phase shift and ii) embedding the information bits in the phase shift. We perform joint detection for the RPM and SSK symbols using a maximum likelihood detector, and a unified analytical framework is presented for theoretical analysis of the average bit error rate (ABER) and ergodic capacity of the proposed scheme. All numerical results are thoroughly verified through Monte Carlo simulation. Numerical results reveal that the proposed scheme outperforms the conventional SSK scheme.

Tunable photonic bandgap and reflection phase shift properties of 1D binary photonic crystal consisting of double negative and magnetic cold plasma materials

In this manuscript, by using alternate layers of double negative and magnetic cold plasma materials, we have studied the reflection and reflection phase shift properties of 1D binary photonic crystals. The simulations of the proposed work have been carried out by using the transfer matrix method with the help of MATLAB software. It has been found that the combination of the angle of incidence and external magnetic field under both right hand polarized and left handed polarized configurations can be used for right and left tuning of photonic bandgap (PBG) of the proposed structure under consideration. Under the aforementioned circumstances, the reflection phase shift corresponding to TE and TM waves can be smoothly switched between 0 to π and –π to 0, respectively, across PBGs of the proposed structure. The variation in external magnetic field values from 0 to 6 T and angle of incidence from 0° to 80° can be used for precise tuning of PBG and reflection phase shift between –π and π depending upon TM and TE polarization cases, respectively. This study may open a new gateway for designing externally tunable microwave devices like single to multichannel band-stop filters, buffers that can hold data temporarily, tunable wave plates, and tunable phase retarders.

IRS-aided SWIPT systems with power splitting and artificial noise

Intelligent reflecting surface (IRS) is regarded as a promising technology because it can achieve higher passive beamforming gain. In particular, the IRS assisted simultaneous wireless information and power transfer (SWIPT) system can make the information decoding receivers (IDRs) have a higher signal-to-noise ratio (SNR), and the energy harvesting receivers (EHRs) have the guarantee of minimum harvested energy threshold. Motivated by the above, in this paper, we use the power splitting (PS) at the user and introduce artificial noise (AN) into the access point (AP), so that the user in system can harvest energy and decode information simultaneously, further improve the security of user. We jointly optimize the beamforming matrix at AP, the reflection phase shift at IRS and the PS ratio, in order to maximize the user's achievable secrecy rate, subject to the user's minimum harvested energy threshold and AP's transmission power. Due to the introduction of PS ratio, the coupling between variables is increased, and the complexity of the problem is significantly increased. Furthermore, the problem is non-convex, so we propose an efficient algorithm based on Taylor Formula, semi-definite relaxation (SDR) and alternating optimization (AO) to get the solution. Numerical results show that the proposed IRS-SWIPT system with PS and AN achieves significant performance improvement compared with other benchmark scheme.

Coupled Solid and Inverse Antenna Stacks Above Metal Ground as Metamaterial Perfect Electromagnetic Wave Absorbers with Extreme Subwavelength Thicknesses

AbstractThe ability to completely absorb an electromagnetic (EM) wave with a material much thinner than the wavelength is a prerequisite for achieving ultracompact, flexible, and lightweight EM devices. Herein, a metamaterial microwave perfect absorber is demonstrated as thin as 1/1250 of the target wavelength by coupling an array of metal patches to inverse cross metal antennas through a dielectric separator and with a reflector placed underneath. Compared to a conventional three‐layer absorber, the modified design reduces the resonance frequency by up to tenfolds without altering the patch and dielectric layers, but by reconfiguring the induced current pathways that reorient the dipolar magnetic fields and dramatically boost the magnetic flux. With the reflector, the stack is framed for perfect absorption at the critical coupling condition, which is identified by monitoring the reflection phase shift across the resonance frequency. The study provides guidelines for shrinking the thickness further and can be extended to other frequencies.

A novel miniaturized, multiband, AMC-integrated CPW-fed antenna operating at millimetric wave frequencies suitable for IoT applications

PurposePlanar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate, and they introduce a zero-degree reflection phase shift to incident waves. The antenna designers have new challenges while designing the AMC structure. The steps followed in designing the structure are as follows: 1) Designing the antenna, aimed to operate at millimetric wave frequencies, (2) Designing the AMC at desired frequencies, (3) Integrating the antenna design and AMC to resonate at millimetric wave frequencies and (4) Validate the output parameters of the antenna to be suitable for Internet of Things (IoT) applications.Design/methodology/approachThe antenna is integrated with artificial material known as high impedance surface (HIS) for performance enhancement. A miniaturized, multiband, enhanced gain, AMC-integrated CPW-fed antenna is proposed and aimed to operate at millimetric wave frequencies, which is most suitable for IoT applications. The developed antenna operates at an extremely high range (30–300 GHz), i.e. from 40 to 60 GHz with the return loss values at lesser than −20 dB, and gain is greater than 10. The antenna is developed and simulated by using HFSS software.FindingsAn extensive research study has been carried out to develop a low profile, high gain and optimized antenna. The first two steps are separately designing the antenna and the AMC unit cell at the desired frequencies. The third step is finding the antenna or AMC radiating parts responsible for each resonant frequency by analysing the surface current distribution. CPW fed along with AMC integration has made the antenna feasible to achieve the extremely high frequency (EHF) range, i.e. 40–60 GHz, which is highly adoptable in IoT applications.Originality/valueThe result represented that the developed antenna is resonating at EHF rank with high gain and good imped matching when it is being compared with the previous models and has only CPW fed without having AMC structure integration. It is evident that the antenna which has only CPW fed has resonated at lower frequency than EHF range and justified output characteristics. But when it is embedded with the AMC structure, it resonates at the EHF range, which makes the antenna highly suitable for IoT applications, with more accuracy and high data rate possibility.

Analysis and Design of an X-Band Reflectarray Antenna for Remote Sensing Satellite System.

This paper presents the analysis and design of an X-band reflectarray. The proposed antenna can be used for a medium Earth orbit (MEO) remote sensing satellite system in the 8.5 GHz band. To obtain a nearly constant response along the coverage area of this satellite system, the proposed antenna was designed with a flat-top radiation pattern with a beam width of around 29° for the required MEO system. In addition, broadside pencil beam and tilted pencil beam reflectarrays were also investigated. The feeding element of the proposed reflectarray antennas is a Yagi–Uda array. The amplitude and phase distribution of the fields due to the feeding element on the aperture of the reflectarray antenna are obtained directly by numerical simulation without introducing any approximation. The required phase distribution along the aperture of the reflectarray to obtain the required flat-top radiation pattern is obtained using the genetic algorithm (GA) optimization method. The reflecting elements of the reflectarray are composed of stacked circular patches. This stacked configuration was found to be appropriate for obtaining a wide range of reflection phase shift, which is required to implement the required phase distribution on the reflectarray aperture. The antenna was fabricated and measured for verification.

Effect of acoustic diffraction phase shift on caustic structure in deep sea convergence zone

The constant phase shift <inline-formula><tex-math id="M1">\begin{document}$- {{\text{π}}}/{2}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20220763_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20220763_M1.png"/></alternatives></inline-formula> generated by a turning point is an ideal approximation under high frequency conditions. In fact, when sound waves pass through a turning point, it will travel horizontally for a certain distance in the form of inhomogeneous plane wave and then be refracted back. At this time, a functional phase shift should also be included at the turning point. In addition, a refracted ray will bring about reflection phase shift when the turning point is close to the waveguide edge. These two kinds of phase shifts which are associated with the diffraction phenomenon are called diffraction phase shifts in this paper and are more notable when the frequency goes down. In order to accurately obtain the caustic structure at low frequency, the diffraction phase shift is used to correct the classical ray theory in calculating ray skip distance, traveling time, and group velocity in this work. On this basis, a simple and explicit analytical model is proposed which is suitable for calculating the low frequency deep water caustics. The numerical study of the first upper convergence zone in the complete deep water sound channel shows that there are three caustic lines in the refracted-refracted (RR) convergence zone and four caustic lines in the refracted surface-reflected (RSR) convergence zone under the condition of high frequency hypothesis. When the diffraction phase shifts at low frequency are included, and compares with high frequency results, it is found that the horizontal beam displacement caused by the reflection phase shift will make the RR caustics horizontally move towards the source and also lead the RSR rays to generate several new caustics, while the beam displacement caused by sound propagating in the form of inhomogeneous plan wave will make the RR caustics horizontally move away from the sound source. Accompanied with the increased frequency, the diffraction effect will decrease, and the caustic structure gradually tends to the classical ray theory results. The reliability of the correction results is verified by the normal mode theory. The model proposed in this work makes up for the deficiency of classical ray theory.

Fullerite C60 optical constants in the C 1s NEXAFS region

Using data on the absorption cross sections the refraction coefficient spectral dependence n(E) and the spectra of the remaining optical coefficients (reflection coefficient, phase shift, and atomic form factor) in the fullerite C60 C 1s near edge X-ray absorption fine structure (NEXAFS) region (280–350 eV) were determined. For the n(E) calculations the Kramers-Kronig integral relations (KKRs) were used. The KKR computations were performed using data on atomic carbon absorption cross sections in the 10–30000 eV range and on solid and gaseous C60 – in the 0–120 eV. Absorption cross section spectrum in the fullerite C60 C 1s NEXAFS region were measured.

Environmental Sensitivity of Fabry-Perot Microcavities Induced by Layered Graphene-Dielectric Hybrid Coatings

We propose a fiber-based environmental sensor that exploits the reflection phase shift tunability provided by the use of layered coatings composed of dielectric slabs spaced by conducting membranes. A transfer matrix study is done in a simplified theoretical model, for which an enhanced sensitivity of the reflection interference pattern to the output medium is demonstrated, in the typical refractive index range of liquid media. An experimental configuration using a cascaded Fabry-Perot microcavity coated by a graphene oxide/polyethylenimine (GO/PEI) multilayered structure is demonstrated. Its cost effective chemical production method makes graphene oxide-based hybrid coatings excellent candidates for future real-life sensing devices.

Aerial intelligent reflecting surface-enhanced cell-free massive MIMO for high-mobility communication: joint Doppler compensation and power optimization

Intelligent reflecting surfaces (IRSs) are considered one of the core technologies in sixth-generation (6G) mobile communication. In this paper, we investigate an aerial IRS (AIRS)-enhanced cell-free (CF) massive multiple-input-multiple-output (MIMO)system where multiple APs serve a high-speed mobile user simultaneously. The mobility of the user leads to fast time-varying and nonnegligible Doppler frequency offsets (DFOs), which cause a serious threat to link performance. To overcome the influence of the Doppler effect and reduce the energy consumption of the system, we propose a Doppler compensation and transmission method by using the AIRS. Specifically, we divide the AIRS reflection phase shift vector into two parts: one part is used for Doppler compensation, and the other is used for transmission. First, we propose an angle-sensing algorithm to obtain the user angle in each coherent time (CT) and use it to design a Doppler compensation vector. Then, we propose an angle information-aided transmission strategy to design the transmission reflecting vector, the beamforming vector, and the power allocation coefficient of each AP to minimize the transmission power of all APs at a required achievable rate. The simulation results show that we can significantly reduce the total transmission power by using the proposed method.

Intelligent Reflecting Surface (IRS)-Aided Covert Communication With Warden’s Statistical CSI

This work considers covert communications with the aid of an intelligent reflecting surface (IRS). We jointly design the transmit power and IRS's reflection phase shifts and amplitudes to enhance covert communication performance. To this end, we first derive the total detection error rate at a warden. We then determine the IRS's optimal phase shifts and develop an effective one-dimensional search method to identify the IRS's optimal amplitudes. We show that the IRS can significantly improve the achievable covertness. In addition, optimizing the IRS's amplitudes on top of its phase shifts significantly outperforms fixing them as unit in covert communications.

Graphene Nanoribbon Gap Waveguides for Dispersionless and Low-Loss Propagation with Deep-Subwavelength Confinement.

Surface plasmon polaritons (SPPs) have been attracting considerable attention owing to their unique capabilities of manipulating light. However, the intractable dispersion and high loss are two major obstacles for attaining high-performance plasmonic devices. Here, a graphene nanoribbon gap waveguide (GNRGW) is proposed for guiding dispersionless gap SPPs (GSPPs) with deep-subwavelength confinement and low loss. An analytical model is developed to analyze the GSPPs, in which a reflection phase shift is employed to successfully deal with the influence caused by the boundaries of the graphene nanoribbon (GNR). It is demonstrated that a pulse with a 4 μm bandwidth and a 10 nm mode width can propagate in the linear passive system without waveform distortion, which is very robust against the shape change of the GNR. The decrease in the pulse amplitude is only 10% for a propagation distance of 1 μm. Furthermore, an array consisting of several GNRGWs is employed as a multichannel optical switch. When the separation is larger than 40 nm, each channel can be controlled independently by tuning the chemical potential of the corresponding GNR. The proposed GNRGW may raise great interest in studying dispersionless and low-loss nanophotonic devices, with potential applications in the distortionless transmission of nanoscale signals, electro-optic nanocircuits, and high-density on-chip communications.