Investigation of phase modulation and propagation-route effect from unmatched large-scale structures for Doppler reflectometry measurement through 2D full-wave modeling

To interpret the common symmetric peaks caused by the large-scale structure in the complex S(f)spectrum from the heterodyne Doppler reflectometry(DR)measurement in EAST,a 2D circular-shaped O-mode full-wave model based on the finite-difference time-domain method is built.The scattering characteristics and the influences on the DR signal from various scales are investigated.When the structure is located around the cutoff layer,a moving radial or poloidal large-scale structure k_(θ)k_(θ),match(k_(θ),match is the theoretic wavenumber of Bragg scattering)could both generate an oscillation phase term called‘phase modulation’,and symmetrical peaks in the complex S(f)spectrum.It was found that the image-rejection ratio A_(−1)/A_(+1)(A_(±1)represents the amplitudes of±1 order modulation peaks)could be a feasible indicator for experiment comparison.In the case when the structure is near the cutoff layer with the same arrangement as the experiment for the edge DR channel,the curve of A_(−1)/A_(+1)versus kθcan be divided into three regions,weak asymmetrical range with k_(θ)/k_(0)0.15(k_(0)is the vacuum wavenumber),harmonics range with 0.15k_(θ)/k_(0)0.4,and Bragg scattering range of 0.4k_(θ)/k_(0)0.7.In the case when the structure is located away from the cutoff layer,the final complex S(f)spectrum is the simple superimposing of modulation and Bragg scattering,and the modulation peaks have an amplitude response nearly proportional to the local density fluctuation,called the‘propagationroute effect’.Under the H-mode experiment arrangement for the core DR,a critical fluctuation amplitude Amp(n_(e,Mod.@route))/Amp(n_(e,Tur.@MSA)∼1.3–4.1(Amp(n_(e,Mod.@route))refers to the pedestal large-scale structure amplitude and Amp(ne,Tur.@MSA)refers to turbulence amplitude at the main scattering area)is needed for the structure in the pedestal to be observed by the core DR measurement.The simulations are well consistent with the experimental results.These effects need to be carefully considered during the DR signal analyses as the injecting beam passes through the plasma region with large-scale structures.

Investigation of nonlinear effects in Doppler reflectometry using full-wave synthetic diagnostics

In this work,Doppler reflectometry(DR)and radial correlation DR(RCDR)nonlinear scattering effects are studied using full-wave modeling with a set of representative FT-2 tokamak turbulence as inputs.Narrowing of the RCDR correlation function and widening of the DR poloidal wavenumber spectrum are demonstrated.An effect on the dependence of the DR signal frequency shift on the probing wavenumber is found,namely,this dependence‘linearizing’in the nonlinear scattering regime.Nonlinear effects are shown to be weaker for O-mode probing than for X-mode probing,while a faster transition to nonlinear regime is demonstrated for RCDR compared to DR in both probing scenarios.

Full-wave Analyses of Scattering of Electromagnetic Wave from the Weakly Ionized Plasma in Plane Geometry

The purpose of the present work is to present a full-wave analysis of scattering from the weakly ionized plasma in the plane geometry. We have yielded an approximate solution in an analytic form to the electromagnetic wave scattering from the weakly ionized plasma. In the normal and oblique incidence, the analytic solution works well, as compared with the exact solution and the solution based on the Wenzell-Kramers-Brillouin-Jeffreys (WKBJ) approximation to the uniform density profile.

Quasi-Dynamic Green’s Functions for Efficient Full-Wave Integral Formulations for Microstrip Interconnects

Integral formulations are widely used for full-wave analysis of microstrip interconnects. A weak point of these formulations is the inclusion of the proper planar-layered Green’s Functions (GFs), because of their computational cost. To overcome this problem, usually the GFs are decomposed into a quasi-dynamic term and a dynamic one. Under suitable approximations, the ?rst may be given in closed form, whereas the second is approximated. Starting from a general criterion for this decomposition, in this paper we derive some simple criteria for using the closed-form quasi-dynamic GFs instead of the complete GFs, with reference to the problem of evaluating the full-wave current distribution along microstrips. These criteria are based on simple relations between frequency, line length, dielectric thickness and permittivity. The layered GFs have been embedded into a full-wave transmission line model and the results are ?rst benchmarked with respect to a full-wave numerical 3D tool, then used to assess the proposed criteria.

A Simplified Full-Wave Analysis for Microstrip Patch Antennas

The spectral domain integral equation(SDIE) provides an accurate and efficient method for computing the resonant frequency, radiation patterns, etc . Using continuous Fourier transform, the formulation utilizes the singular integral equations via the Glerkin's method to derive the deterministic equation with fewer mathematical manipulations. In contrast, discrete Fourier transform(DFT) requires intricate mathematical labor. The present scheme requires a small size, i.e ., (2×2) matrix, and it is possible to extract higher order modal solutions conveniently. Moreover, computation is reduced with the same convergence properties. Based on the present scheme, some results for resonant frequency and radiation patterns compared with available data and computed current distribution on the patch are presented.

A New Current Conveyor Full-Wave Rectifier for Low Frequency/Small Signal Medical Applications

This paper presents a new current conveyor (CCII+) full-wave rectifier for low frequency/small signal medical applications. The proposed rectifier is based on the current conveyor full-wave rectifier proposed previously, but the proposed rectifier is better in view of no need diodes to rectify, and no need bias sources to overcome the zero crossing error. It needs only two CCII+s, two resistors, and three simple current mirrors, which is easy for IC implementation and for building in many countries. The PSPICE simulation with the current conveyor CCII+ in the current feedback opamp AD844 IC and the 2N2222 bipolar current mirror shows the good low frequency/small signal rectification, the operation voltage of down to 6 .

Precision Full-Wave Rectifier Using Two DDCCs

A new precision full-wave rectifier employing only two differential difference current conveyors, which is very suitable for CMOS technology implementation, is presented. The proposed rectifier is the voltage-mode circuit, which offers high-input and low-output impedance hence it can be directly connected to load without using any buffer circuits. PSPICE is used to verify the circuit performance. Simulated rectifier results based-on a 0.5 μm CMOS technology with ±2.5 V supply voltage demonstrates high precision rectification and excellent temperature stability. In addition, the application of proposed rectifier to pseudo RMS-to-DC conversion is also introduced.

Recent Advances in Reconfigurable Electromagnetic Surfaces:Engineering Design,Full-Wave Analysis,and Large-Scale Optimization

This paper presents a comprehensive review of recent advances in reconfigurable electromagnetic(EM)surfaces.The discussion is organized around three key aspects of reconfigurable EM surfaces:unit cell engineering design,full-wave numerical analysis,and large-scale optimization techniques.Numerous references are provided to facilitate further exploration of this compelling and timely subject.To address the above three key aspects,we conduct an extensive examination of the design process for metasurfaces in reconfigurable devices.This involves evaluating the design methodology of unit cells,EM simulation techniques tailored for highly complex structures,and innovative optimization methods suitable for scenarios with numerous variables.In scenarios featuring reconfigurability for real-time manipulation of EM waves to meet the requirements of emerging communication environments,the optimization cost function is defined with multiple variables,exhibiting intricate behavior in the design space.Consequently,it necessitates an optimization methodology capable of handling high-dimensional functions without getting trapped in local minima.Moreover,the intricate geometries of metasurface devices preclude analytical solutions,necessitating high-performance full-wave solvers capable of providing highly accurate simulations with minimal computational expense.Key concepts and details pertaining to the aforementioned design stages are presented in a unified manner,along with representative examples.

Efficiency-loss analysis of monolithic perovskite/silicon tandem solar cells by identifying the patterns of a dual two-diode model’s current-voltage curves

In this work,we developed a simple and direct circuit model with a dual two-diode model that can be solved by a SPICE numerical simulation to comprehensively describe the monolithic perovskite/crystalline silicon(PVS/c-Si)tandem solar cells.We are able to reveal the effects of different efficiency-loss mechanisms based on the illuminated current density-voltage(J-V),semi-log dark J-V,and local ideality factor(m-V)curves.The effects of the individual efficiency-loss mechanism on the tandem cell’s efficiency are discussed,including the exp(V/VT)and exp(V/2VT)recombination,the whole cell’s and subcell’s shunts,and the Ohmic-contact or Schottky-contact of the intermediate junction.We can also fit a practical J-V curve and find a specific group of parameters by the trial-and-error method.Although the fitted parameters are not a unique solution,they are valuable clues for identifying the efficiency loss with the aid of the cell’s structure and experimental processes.This method can also serve as an open platform for analyzing other tandem solar cells by substituting the corresponding circuit models.In summary,we developed a simple and effective methodology to diagnose the efficiency-loss source of a monolithic PVS/c-Si tandem cell,which is helpful to researchers who wish to adopt the proper approaches to improve their solar cells.

A Rigorous Analysis of Vehicle-to-Vehicle Range Performance in a Rural Channel Propagation Scenario as a Function of Antenna Type and Location via Simulation and Field Trails

Vehicle-to-Everything(V2X) communications will be an essential part of the technology in future autonomous drive decision systems.A fundamental procedure is to establish a robust communication channel between end-to-end devices.Due to the antenna placed at different positions on vehicles,the existing cellular electro-magnetic(EM) wave propagation modelling does not fit properly for V2X direct communication application.In order to figure out a feasible understanding of this problem,this paper focuses on the propagation channel analysis in a rural Vehicle-to-Vehicle(V2V) scenario for vehicular communication with antenna position experiments at different heights.By adopting the ray-tracing algorithm,a rural scenario simulation model is built up via the use of a commercial-off-the-shelf(COTS) EM modelling software package,that computes the path loss received power and delay spread for a given propagation channel.Next,a real-world vehicle measurement campaign was performed to verify the simulation results.The simulated and measured receiver power was in good agreement with each other,and the results of this study considered two antenna types located at three different relative heights between the two vehicles.This research provides constructive guidance for the V2V antenna characteristics,antenna placement and vehicle communication channel analysis.

应用改进的矩阵束方法加速混响室时域仿真

为了减少混响室时域全波仿真的计算量,首次对混响室时域响应的预测做出探索研究。以改良矩阵束方法为基础,提出一种计算效率更高的矩阵束方法,并验证了该方法的正确性与稳定性。用复指数幂求和式对混响室的时域波形进行拟合,利用该方法能够高效求解出拟合式中的各极点,实现了对混响室时域响应的近似外推。由电场强度的前20 000步计算结果,可快速预测得到后20 000步响应,发现束参数比例取0.62左右时,对多个采样点的电场均可得到良好的预测效果,可保证仿真与预测相结合得到的结果与真实结果的频域相对误差小于15%。这种结合预测的仿真算法可节省计算量约50%。

Anisotropy of Thermal-expansion for β-Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine： Quantum Chemistry Calculation and Molecular Dynamics Simulation

Molecular dynamics simulations on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine （HMX） at 303-383 K and atmospheric pressure are carried out under NPT ensemble and COMPASS force field, the equilibrium structures at elevated temperatures were obtained and showed that the stacking style of molecules don＇t change. The coefficient of thermal expansion （CTE） values were calculated by linear fitting method. The results show that the CTE values are close to the experimental results and show anisotropy. The total energies of HMX cells with separately increasing expansion rates （100%-105%） along each crystallographic axis was calculated by periodic density functional theory method, the results of the energy change rates are anisotropic, and the correlation equations of energy change-CTE values are established. Thus the hypostasis of the anisotropy of HMX crystal＇s thermal expansion, the determinate molecular packing style, is elucidated.

Comparison of Adsorption of Proteins at Different Sizes on Pristine Graphene and Graphene Oxide

Using all-atom molecular dynamics （MD） simulations, we have investigated the adsorption stability and conformation change of different proteins on the surface of pristine graphene （PG） and graphene oxide （GO）. We find that： （i） with the cooperation of the electrostatic interactions between proteins and oxygen-containing groups, GO shows better adsorption stability than PG; （ii） the peptide loses its secondary structure on both PG and GO surface, and the a-helix structure of the protein fragment is partially broken on PG surface, but is well preserved on GO surface, while the secondary structure of globular protein has no distinct change on both PG and GO surface. In general, GO presents better biocompatibility than PG. Our results are of significant importance to understand the interactions between proteins and PG/GO and the applications of PG/GO in biotechnology and biomedicine.

Design and theoretical study of a polarization-insensitive multiband terahertz metamaterial bandpass filter

We report the design of a novel multiband metamaterial bandpass filter （BPF） in the terahertz （THz）-wave region. The designed BPF is composed of a metal-dielectric-metal sandwiched structure with three nested rings on the top surface and a cross structure on the bottom surface. Full-wave simulation results show that the designed BPF has three transmission peaks at frequencies of 0.42, 1.27, and 1.86 THz with transmission rates of-0.87,-1.85, and-1.83 dB, respectively. Multi-reflection interference theory is introduced to explain the transmission mechanism of the designed triple-band BPF. The theoretical transmission spectrum is in good agreement with the full-wave simulated results. The designed BPF can maintain a stable performance as the incident angle varies from 0 to 30 for both transverse electric and transverse magnetic polarizations of the incident wave. The designed BPF can be potentially used in THz devices due to its multiband transmissions, polarization insensitivity, and stable wide-angle response in the THz region.

ANALYSIS OF LEVER ARM EFFECTS IN GPS／IMU INTEGRATION SYSTEM

Disturbance specific force caused by the lever arm ef-fects in integration navigation system is investigated,Navigation errors eaused by the lever arm effects have been demonstrated under three flinght scenarios of the air-craft.Analytical under three flight scenarios of the ari-craft.Analytical results show that disturbance specific force resulted from lever arm effects may become one of the major error sources while an aircraft undertakes the maneuvers,and mavigation errors caused by the lever arm effects accumulate rapidly with time.Therefore,a com-pensation method must be taken into account to eliminate the disturbance specific force caused by the lever arm ef-fects in integration navigation system.

Numerical simulations of stress wave propagation and attenuation at arc-shaped interface inlayered SiC/Al composite

The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.

Scattering center modeling for low-detectable targets

The scattering centers(SCs)of low-detectable targets(LDTs)have a low scattering intensity.It is difficult to build the SC model of an LDT using the existing methods because these methods mainly concern dominant SCs with strong scattering contributions.This paper presents an SC modeling approach to acquire the weak SCs of LDTs.We employ the induced currents at the LDT to search SCs,and the joint time-frequency transform together with the Hough transform to separate the scattering contributions of different SCs.Particle swarm optimization(PSO)is applied to improve the estimation results of SCs.The accuracy of the SC model built by this approach is verified by a full-wave numerical method.The validation results show that the SC model of the LDT can precisely simulate the signatures of high-resolution images,such as high-resolution range profile and inverse synthetic aperture radar(ISAR)images.

Performance improvement of blue InGaN light-emitting diodes with a specially designed n-AlGaN hole blocking layer

Blue InGaN light-emitting diodes （LEDs） with a conventional electron blocking layer （EBL）, a common n-A1GaN hole blocking layer （HBL）, and an n-A1GaN HBL with gradual A1 composition are investigated numerically, which involves analyses of the carrier concentration in the active region, energy band diagram, electrostatic field, and internal quantum efficiency （IQE）. The results indicate that LEDs with an n-AIGaN HBL with gradual AI composition exhibit better hole injection efficiency, lower electron leakage, and a smaller electrostatic field in the active region than LEDs with a conven tional p-A1GaN EBL or a common n-A1GaN HBL. Meanwhile, the efficiency droop is alleviated when an n-A1GaN HBL with gradual A1 composition is used.

Length estimation of extended targets based on bistatic high resolution range profile

The approach to estimate the length of extended targets by using the bistatic high resolution range profile（ H RRP） is analyzed in this paper. The relationship between the bistatic H RRP and the monostatic H RRP of extended targets are investigated. It is demonstrated by simulations that the target length measured by the bistatic H RRP is more meaningful and accurate than that by the monostatic HRRP,though the monostatic H RRP has been well developed and widely used in target recognizing and classification. The estimation results of a cone shaped target are present and compared at the end of the paper. To assure the reliability of the simulation,the bistatic H RRP is obtained through the scattering field data calculated by a fullwave numerical method,FE-BI-MLFMA.