FDTD Simulation of Electromagnetic Pulse Interaction with a Switched Plasma Slab

This paper deals with the Finite Difference Time Domain (FDTD) simulation of interaction of an electromagnetic wave with a switched plasma slab. In formulating the simulation the well-known concepts of (a) total-field/scattered-field formulation (b) and PML lattice truncation are adapted to suit the simulation under consideration.FDTD is particularly well suited to handle the switched (time-varying) medium (including sudden switching) since the time varying parameters of the medium can be easily interpreted in the algorithm. The technique is applied to the difficult problem of interaction of an electromagnetic pulse source wave of frequency ₀ and a gaussian envelope with a newly created plasma slab of time-varying and space varying electron density profile. The creation of a pulse of Wiggler magnetic field in the slab is illustrated.     

银薄膜对光学基底表面粗糙度及光散射的影响

为了研究金属银薄膜与光学基底表面粗糙度和光散射的关系,提出了通过对光学薄膜矢量散射公式积分来获得界面粗糙度完全相关模型和完全非相关模型下其表面的总反射散射的方法.理论计算了光学基底上两种模型在不同厚度银膜下的总反射散射和双向反射分布函数.结果表明,当沉积在光学基底上的银薄膜的厚度大于80 nm后,两种模型下计算的银薄膜的表面总反射散射都等于基底的总积分散射,银薄膜能较好地复现出基底的粗糙度轮廓.实验研究表明为了复现基底的粗糙度,银薄膜的最佳厚度应在80~160 nm之间.     

A novel unsplit perfectly matched layer for the second-order acoustic wave equation

When solving acoustic field equations by using numerical approximation technique, absorbing boundary conditions (ABCs) are widely used to truncate the simulation to a finite space. The perfectly matched layer (PML) technique has exhibited excellent absorbing efficiency as an ABC for the acoustic wave equation formulated as a first-order system. However, as the PML was originally designed for the first-order equation system, it cannot be applied to the second-order equation system directly. In this article, we aim to extend the unsplit PML to the second-order equation system. We developed an efficient unsplit implementation of PML for the second-order acoustic wave equation based on an auxiliary-differential-equation (ADE) scheme. The proposed method can benefit to the use of PML in simulations based on second-order equations. Compared with the existing PMLs, it has simpler implementation and requires less extra storage. Numerical results from finite-difference time-domain models are provided to illustrate the validity of the approach.     

Unconditionally Stable Z-Transform ADI-PML Algorithm for Lorentzian Double Negative Meta-Materials

Unconditionally stable formulations of the anisotropic perfectly matched layer (APML) are presented for truncating double negative (DNG) meta-material finite difference time domain (FDTD) grids. In the proposed formulations, the Z-transform theory is employed in the alternating direction implicit FDTD (ADI-FDTD) scheme to obtain update equations for the field components in the DNG meta-material domains. Numerical examples carried out in one dimensional Lorentzian type DNG meta-material domains are included to show the validity of the proposed formulations.     

Eigenmodes of index-modulated layers with lateral PMLs

Maxwell equations are solved in a layer comprising a finite number of homogeneous isotropic dielectric regions ended by anisotropic perfectly matched layers (PMLs). The boundary-value problem is solved and the dispersion relation inside the PML is derived. The general expression of the eigenvalues equation for an arbitrary number of regions in each layer is obtained, and both polarization modes are considered. The modal functions of a single layer ended by PMLs are found, and their orthogonality relation is derived. The present method is useful to simulate scattering problems from dielectric objects as well as propagation in planar slab waveguides. Its potential to deal with more complex problems such as the scattering from an object with arbitrary cross section in open space using the multilayer modal method is briefly discussed.     

Efficient and stable perfectly matched layer for CEM

An efficient unsplit perfectly matched layer for numerical simulation of electromagnetic waves in unbounded domains is derived via a complex change of variables. In order to surround a Cartesian grid with the PML, the time-dependent PML requires only one (scalar) auxiliary variable in two space dimensions and six (scalar) auxiliary variables in three space dimensions. It is therefore cheap and straightforward to implement. We use Fourier and energy methods to prove the stability of the PML. We extend the stability result to a semi-discrete PML approximated by central finite differences of arbitrary order of accuracy and to a fully discrete problem for the ‘Leap-Frog’ schemes. This makes precise the usefulness of the derived PML model for longtime simulations. Numerical experiments are presented, illustrating the accuracy and stability of the PML.     

Effects of shaded facets on the performance of metal-coated etched diffraction grating demultiplexer

A finite-difference time-domain (FDTD) method combined with a periodic boundary condition is used to analyze the diffraction efficiency of an etched diffraction grating (EDG) demultiplexer coated with a metallic film at the backside. The numerical results show that the diffraction loss is mainly due to the scattering effect of shaded facets of a metal-coated grating at both the polarizations. However, the same shaded facets can produce a higher loss for a TM polarization than that for a TE polarization, which induces a higher polarization dependent loss (PDL) of the demultiplexer.     

吸收边界条件和完美匹配层

证明了一个Maxwell方程的完美匹配层的的充要条件.条件的核心是吸收边界条件.这个判据可以用来检验文献中的各个模型,也可用来设计一些新的模型.最后给出了一些例子.     

吸收边界条件和完美匹配层

证明了一个Maxwell方程的完美匹配层的的充要条件.条件的核心是吸收边界条件.这个判据可以用来检验文献中的各个模型,也可用来设计一些新的模型.最后给出了一些例子.     

Electromagnetic MUSIC-type imaging of perfectly conducting, arc-like cracks at single frequency

We propose a non-iterative MUSIC (MUltiple SIgnal Classification)-type algorithm for the time-harmonic electromagnetic imaging of one or more perfectly conducting, arc-like cracks found within a homogeneous space R²${\mathbb{R}}^2$. The algorithm is based on a factorization of the Multi-Static Response (MSR) matrix collected in the far-field at a single, nonzero frequency in either Transverse Magnetic (TM) mode (Dirichlet boundary condition) or Transverse Electric (TE) mode (Neumann boundary condition), followed by the calculation of a MUSIC cost functional expected to exhibit peaks along the crack curves each half a wavelength. Numerical experimentation from exact, noiseless and noisy data shows that this is indeed the case and that the proposed algorithm behaves in robust manner, with better results in the TM mode than in the TE mode for which one would have to estimate the normal to the crack to get the most optimal results.