Efficient implicit FDTD algorithm based on locally one-dimensional scheme

The locally one-dimensional (LOD) scheme is introduced into the implicit FDTD method. The LOD-FDTD provides simple implementation of the algorithm and reduced computational time. For facet reflectivity analysis of an optical waveguide, the computational time is reduced to 80 and 50% of those of the ADI-FDTD and the conventional FDTD, respectively.     

Higher-order alternative direction implicit FDTD method

A second-order in time and fourth-order in space alternative direction implicit (ADI) finite difference time domain (FD-TD) method has been developed. The dispersion relation is derived and compared with the ADI-FDTD method. Numerical results demonstrated that the higher-order ADI-FDTD has a better accuracy compared to the ADI-FDTD method.     

A new FDTD algorithm based on alternating-direction implicit method

In this paper, a new finite-difference time-domain (FDTD) algorithm is proposed in order to eliminate the Courant-Friedrich-Levy (CFL) condition restraint. The new algorithm is based on an alternating-direction implicit method. It is shown that the new algorithm is quite stable both analytically and numerically even when the CFL condition is not satisfied. Therefore, if the minimum cell size in the computational domain is required to be much smaller than the wavelength, this new algorithm is more efficient than conventional FDTD schemes in terms of computer resources such as central-processing-unit time. Numerical formulations are presented and simulation results are compared to those using the conventional FDTD method     

Unconditionally-stable FDTD method based on Crank-Nicolson scheme for solving three-dimensional Maxwell equations

The approximate-factorisation-splitting (CNAFS) method as an efficient implementation of the Crank-Nicolson scheme for solving the three-dimensional Maxwell equations in the time domain, using much less CPU time and memory than a direct implementation, is presented. At each time step, the CNAFS method solves tridiagonal matrices successively instead of solving a huge sparse matrix. It is shown that CNAFS is unconditionally stable and has much smaller anisotropy than the alternating-direction implicit (ADI) method, though the numerical dispersion is the same as in the ADI method along the axes. In addition, for a given mesh density, there will be one value of the Courant number at which the CNAFS method has zero anisotropy, whereas the Crank-Nicolson scheme always has anisotropy. Analysis shows that both ADI and CNAFS have time step-size limits to avoid numerical attenuation, although both are still unconditionally stable beyond their limit.     

Stability of the FDTD scheme containing macromodels

Stability analysis of the finite difference time domain scheme containing macromodels is presented. It is shown that for a stable macromodel, the stability of the combined scheme depends on the field interpolation at the macromodel boundary. The maximal allowable time step is shown to be much larger than for subgridding.     

A three-dimensional horizontally wide-angle noniterative beam-propagation method based on the alternating-direction implicit scheme

A three-dimensional horizontally wide-angle beam-propagation method is proposed on the basis of the alternating-direction implicit scheme, in which the Pade/spl acute/ approximant is applied only to the horizontal direction. The present formulation reduces the splitting error to the first order without an iteration procedure. The effectiveness is demonstrated through the wide-angle propagating beam analysis of a tilted optical waveguide.     

基于FDTD的环形孔缝电磁耦合规律研究

为提高电子设备及系统在复杂电磁环境下工作的稳定性,应用时域有限差分方法对不同脉宽电磁脉冲通过带有不同形状（方形环,圆环,矩形环）环形孔缝屏蔽腔体的耦合规律进行了分析.研究结果表明：电磁脉冲通过环形孔缝耦合现象明显,其通过圆环的耦合能量最小;对于矩形环,当入射波极化方向与环形孔缝的短边平行时,若矩形环孔缝纵横比越大,则耦合能量也越大,当极化方向与短边垂直时,则纵横比越大,耦合能量越小;入射电磁脉冲脉宽越短,电磁脉冲越容易耦合进入环形孔缝;腔体壁的反射及谐振会增强耦合效应.     

Analysis of the numerical dispersion of the 2Dalternating-direction implicit FDTD method

The numerical dispersion property of the two-dimensional alternating-direction implicit finite-difference time-domain (2D ADI FDTD) method is studied. First, we notice that the original 2D ADI FDTD method can be divided into two sub-ADI FDTD methods: either the x-directional 2D ADI FDTD method or the y-directional 2D ADI FDTD method; and secondly, the numerical dispersion relations are derived for both the ADI FDTD methods. Finally, the numerical dispersion errors caused by the two ADI FDTD methods are investigated. Numerical results indicate that the numerical dispersion error of the ADI FDTD methods depends highly on the selected time step and the shape and mesh resolution of the unit cell. It is also found that, to ensure the numerical dispersion error within certain accuracy, the maximum time steps allowed to be used in the two ADI FDTD methods are different and they can be numerically determined     

Inexact alternating direction method based on Newton descent algorithm with application to Poisson image deblurring

The recovery of images from the observations that are degraded by a linear operator and further corrupted by Poisson noise is an important task in modern imaging applications such as astronomical and biomedical ones. Gradient-based regularizers involving the popular total variation semi-norm have become standard techniques for Poisson image restoration due to its edge-preserving ability. Various efficient algorithms have been developed for solving the corresponding minimization problem with non-smooth regularization terms. In this paper, motivated by the idea of the alternating direction minimization algorithm and the Newton’s method with upper convergent rate, we further propose inexact alternating direction methods utilizing the proximal Hessian matrix information of the objective function, in a way reminiscent of Newton descent methods. Besides, we also investigate the global convergence of the proposed algorithms under certain conditions. Finally, we illustrate that the proposed algorithms outperform the current state-of-the-art algorithms through numerical experiments on Poisson image deblurring.     

Determination of the direction that has maximum phase-velocity for the 2-D and 3-D FDTD methods based on Yee's algorithm

To easily evaluate the performance of the numerical dispersion of the FDTD method, a simple and efficient manner to theoretically determine the special direction that has the maximum phase-velocity for arbitrarily shaped two-dimensional (2-D) and three-dimensional (3-D) Yee's cells is proposed. It is found that the wave propagating along the special direction obeys the following physical rule: the time that the wave takes to traverse the spatial step sizes along each of the main axes of the cell is identical. It is demonstrated that this special direction is closely related to the aspect ratio(s) of the cells, rather than the diagonals of the cells. Moreover, the mathematical expressions for the maximum phase-velocity of the 2-D and 3-D cells with arbitrary aspect ratios are derived for the first time.     

Mobile platform continuous authentication scheme based on gait characteristics

The popularity of smart phones renders people extremely high requirements for safety.But the traditional one-time authentication method can’t continuously guarantee the security of equipment.To solve the problem,a continuous authentication scheme based on gait characteristics was proposed to realize the identification of current visitors.Moving average filtering,threshold-based useful information interception method and other operations were adopted to reduce noise interference.Template interception was used to maximize the utilization of information,and an optimal combination of time domain features and frequency domain features were proposed to reduce the storage space requirement of users’ information.Finally,the support vector machine realized the identity authentication function.Experiments show that the proposed scheme can effectively authenticate the identities of visitors.     

Adaptive predistorter for power amplifier based on real-timeestimation of envelope transfer characteristics

A new adaptation technique for digital predistortion is presented. The proposed method employs the real-time input and output signals of a high power amplifier (HPA) to estimate the complex envelope transfer characteristics. Therefore, a look-up table update can be performed without Interrupting the normal transmission of messages through an HPA     

基于交替光栅光纤复合结构折射率传感特性研究

基于D型多模光纤表面沉积交替光栅构成了一种 光纤结构折射率传感器。利用传输矩阵法和时域 有限差分法FDTD协同研究了传感器透射光谱特性及共振吸收峰产生的机理。在优化设计结构 基础上探究 了折射率和温度双参量传感特性。研究结果证明,光纤复合结构具有双通道和超窄线宽双重 光谱特性;基 于两种共振模式折射率和温度的差异敏感性,选择两共振峰峰位波长作为信息载体,借助矩 阵方程获得温 度补偿后的折射率传感灵敏度和品质因数分别为562.8 nm/RIU和24.14/RIU。 该传感器结构简单,体积小,易于集成,同时可消除温度交叉敏感的干扰,更具实用性。     

基于FDTD算法的天线设计

在无线通信中,天线是很重要的角色,它可以增强或者减弱系统性能。模拟工具可以准确模拟基本的天线系统拓扑结构。提出了时域有限差分算法(FDTD)。根据时域有限差分单元尺寸和外吸收之间的距离的影响对边界和天线的精度进行了探索。根据MATLAB代码,通过插槽和确定几何参数,形成了一个运作于双频带(800MHz~1800MHz)的单极子天线。     

基于改进Yee网格的FDTD差分格式及程序实现

Yee网格中电场各分量或磁场各分量不在同一点,若要计算一点的电矢量或磁矢量,必须借助各种插值方法。对传统的Yee网格作必要的改进,克服了Yee网格的不足,而且用基于这种改进网格的差分格式计算任一电磁分量时,用到了其周围更多的数据,使计算精度得到了提高。     

基于时域有限差分法的广义传输矩阵的研究

文章研究了基于时域有限差分法的时域广义传输矩阵方法,时域广义传输矩阵在包含散射体的惠更斯等效面上计算和提取,通过时域积分方程和时域有限差分法的混合应用计算得出。本文同样给出了一个在等效面上RWG基函数和FDTD网格上的变换算法。基于时域有限差分法的时域广义传输矩阵方法比基于时域步进法（MOT）和积分方程的广义传输矩阵方法更加稳定。     

海面环境信号传播特性的FDTD算法研究

海浪是影响海面环境下信号传播特性的重要因素。文中采用FDTD算法对海面环境下信号衰落和时延特性进行了研究。模型中采用修正的PM谱模拟随机海浪,生成随风速变化的成熟海浪。文中设置了不同的仿真环境,得到不同观测点的瞬时电磁分量,通过数据分析,得到在固定发射机和接收机位置的情况下,路径损耗和时延随浪高的变化曲线。     

Analysis of the resonant cavities using the FDTD scheme with effective permittivities formulae

An efficient expression of the effective permittivities along x-, y-, z-direction is obtained by analogy with the circuit concept of series–parallel connection of capacitance. Under the condition of numerical stability, the approximate formulae of effective permittivities for various inhomogeneous cell mesh are combined with the Finite Difference Time Domain (FDTD) scheme of arbitrary spatial cell size to calculate resonant frequency of 3-D cavity. The results are in agreement with that of conventional FDTD method, but the proposed method can save computing time and memory.     

基于图形处理器的时域有限差分算法研究

如何提高时域有限差分算法（FDTD）的运算效率一直是FDTD数值运算研究的核心问题之一。针对近年来图形处理器（GPU）运算能力的高速增长及GPU通用运算概念提出的背景,对GPU加速FDTD运算的潜力与研究现状进行了总结,并对GPU加速FDTD运算的并行实现原理进行了阐述,通过将其与其他典型硬件加速方式进行比较,指出了GPU加速具有低成本易于开发移植等特点。通过GPU加速FDTD的实例运算,初步验证了GPU运算的可行性与高速性,证实了GPU加速运算FDTD运算存在广阔应用的前景,并对现有问题进行了总结。     

一种基于信道特征参数的无线通信密钥生成方法

无线通信由于自身传输信道的开放性,其安全问题相对于有线通信更为突出。物理层安全技术利用无线通信信道天然的多径时变特性,可为无线传输提供物理层加密,因而近年来得到快速发展。针对传统物理层安全中密钥生成速率低、频分双工系统不适用等问题,提出了一种基于信道特征参数的无线通信密钥生成方法。基于宽带信号对多径的辨识力,利用各径间相对时延生成初始密钥,结合码本进行密钥长度扩展,从而生成最终密钥。通过数值分析证明,相对于传统物理层密钥生成方式,所提方法能显著提高密钥生成速率,同时,基于时延信道特征的互易性,该方法可适用于时分双工和频分双工无线通信系统的物理层加密。