MPSTD算法中子域分界面匹配条件的比较研究

针对多区域伪谱时域算法(MPSTD)中子域分界面两侧为不同介质的情形,提出了特征变量-物理边界(CV-PB)子域分界面匹配条件,然后在总结现有子域分界面匹配条件的基础上,分别比较了子域分界面两侧为相同和不同介质时各种子域分界面匹配条件的稳定性.数值仿真表明,在子域分界面两侧为相同介质材料时采用特征变量法匹配条件,而在子域分界面两侧为不同介质材料时采用CV-PB匹配条件,可使得MPSTD算法稳定性最好.     

基于半解析谱元法的各向异性介质PBG结构传输特性的研究

将精细积分方法与谱单元法结合,对含有各向异性介质的波导介质层光子带隙(PBG)结构的传输特性进行了研究.从矢量波动方程相对应的单变量变分形式出发,对含有各向异性介质波导横截面采用谱单元进行离散,引入对偶变量,将单变量变分原理导入到哈密顿体系,利用精细积分法求出出口刚度矩阵.数值算例将半解析谱元法与常规有限元法、半解析有限元法进行了比较,表明本文方法具有高精度、高效率的特点,而且计算精度随着谱单元阶数的增加呈指数增长.     

PECVD氮氧化硅膜的初始瞬态过程与其特性关系的研究

AES分析表明,PECVD SiON-Si界面处存在一个很薄的富Si区域。本研究表明,它与介质膜的界面特性密切相关,对不同组分、不同工艺的介质膜,其界面富Si区域情况不同,从而使界面特性不同。本文给出了PECVD介质膜界面贫H的机理。实验中采用了俄歇能谱、红外光谱,C—V测试等分析手段,研究了膜内部结构。     

金属散射问题的积分方程区域分解法

研究了区域分解法在求解金属散射体的积分方程时的应用。积分算法可以精确地求解各种电磁场问题,但因为受限于格林函数,需要求解较为复杂的矩阵。区域分解法是一种迭代算法,把原来较大的求解区域划分成若干个相对独立的子区域,将原问题的求解转化为在各子区域上分别进行求解,并利用某种数据交换条件在子区域之间传递信息,最后得到原电大区域上的解。由于每个子区域相互独立并且单独划分网格,区域分解法更加适合解决多尺度的电磁散射问题。最后通过与商业软件的对比验证了算法的正确性。     

损耗介质周期加载圆柱波导场分析

本文利用傅立叶级数将损耗介质周期加载圆柱波导结构的场展开,通过分界面上场匹配的模式分析方法得出了TMOn模的色散曲线、电磁场分布以及品质冈数等特性参量.编写了程序DDET-TM并计算TM01模的各特性参量,得到的结果与HFSS的仿真结果吻合较好,验证了本方法的适用性.     

手征Ω介质偶极子天线研究

本文首先探讨了用手征Ω介质作为微带天线基片的可能性。应用广义谱域指数矩阵方法,分析了单层和双层手征Ω介质中所有Ω单元的三种不同取向对偶极子天线辐射特性的影响,以及偶极子方向图随手征Ω介质损耗正切的变化情况。     

电磁波同周期介质相互作用与系统的能带结构

电磁场同物质相互作用问题可以归结为电磁场同不同折射率形成的"势场"相互作用问题。当电磁场(光子)在周期"势场"中传播时,能量将分裂成带。文章从麦克斯韦方程出发,讨论了电磁场与周期介质的相互作用,并用转移矩阵方法导出了系统的色散关系,描述了周期介质中布洛赫波的传播及系统的稳定性。     

MPSTD算法子域分界面上的CV-PB匹配条件

针对多域伪谱时域算法(MPSTD)中子域分界面两侧为不同介质的情形,将特征变量法与物理边界条件相结合提出一种新的子域分界面匹配条件:特征变量-物理边界(CV-PB)匹配条件,并推导得到一般3D曲线坐标系中子域分界面上的场值更新关系.最后给出的数值实例将其与传统分界面匹配条件在算法稳定性、计算精度方面做了比较.多种情形下的数值仿真表明,该匹配条件比传统匹配条件的数值稳定性更好、精度更高.     

分析多层介质多导体传输线的区域分解法

本文利用区域分解法 ,将直线法和有限差分法结合起来 ,用于计算多层介质中具有任意截面形状多导体传输线的电容和电感矩阵。通过在纯介质区域使用直线法 ,导体所在区域使用有限差分法分别进行求解 ,充分发挥两种方法各自的优越性。直线法中快速傅里叶变换的引入进一步提高了算法的计算效率。数值结果表明 :该方法是有效的 ,且计算时间与介质层的厚度无关。文中还研究了介质层分界面的不平整性对传输线电磁参数的影响。     

电磁场中分界面上的位与场的关系及其应用

文章讨论了电磁场中两种介质的分界面上电位与电场的关系以及矢量磁位与磁场的关系,通过分析说明了在分界面上如何依据电位分析出电场的分布规律,并从矢量分析的角度出发证明了矢量磁位的边值关系.     

A numerical solution to full-vector electromagnetic scattering bythree-dimensional nonlinear bounded dielectrics

This paper deals with electromagnetic scattering by nonlinear dielectric objects. In particular, a numerical approach is developed that is aimed at determining the distributions of the electromagnetic field vector inside a three-dimensional nonlinear, inhomogeneous, isotropic scatterer illuminated by a time-periodic incident electric field vector. An integral-equation formulation for the full-vector scattering problem is considered, and the nonlinear effect is taken into account by introducing equivalent sources and a Fourier-series representation. A system of integral equations (for each harmonic vector component and for the static term) is obtained that includes the internal electric field distribution as the unknown. After discretization, the solution is reduced to solving an algebraic system of nonlinear equations. Some preliminary numerical results are reported concerning scatterers that exhibit a specific (quadratic) dependence of the dielectric permittivity on the total electric field. The harmonic components of the scattered electric field outside the objects are also computed     

An optimization approach to time-domain electromagnetic inverseproblem for a stratified dispersive and dissipative slab

The one-dimensional electromagnetic inverse problem for a stratified dispersive and dissipative slab is considered in the time domain. An optimization approach is used to reconstruct the parameters using the measured reflected field and/or transmitted field. Wave-splitting is used, and an explicit expression for the gradient is derived by introducing dual functions. The reconstruction algorithm is tested with both synthetic and experimental data     

A quasi-static model for the ring capacitor applicator

The electromagnetic heat dissipation in a radially layered biological tissue inside a ring capacitor (RC) applicator has been investigated. A quasi-static model is introduced to compute the relevant electromagnetic field quantities. The method of computation employs the spatial Fourier transform of all field quantities with respect to the axial coordinate. After an iterative solution of a dual boundary value problem for the electric potential and the current density at the electrodes, an inverse Fourier transform is carried out to compute the quantities that are of interest to the deep-body system at hand. Comparison of numerical results with phantom measurements shows excellent agreement.     

Scattering from a chirally coated DB elliptic cylinder

An exact analytic solution to the problem of scattering of a plane electromagnetic wave from a chirally coated elliptic cylinder defined by a DB boundary has been obtained, by expanding the different electromagnetic fields associated with the problem in terms of suitable elliptic vector wave functions and a set of expansion coefficients. The incident field expansion coefficients are known, but the expansion coefficients associated with the fields scattered outside the coated cylinder and the fields transmitted inside the coating are unknown. These unknown coefficients are obtained by imposing appropriate boundary conditions at the two boundaries. Results have been presented as normalized bistatic and backscattering widths for a variety of admittances, permeabilities, and permittivities of the chiral materials used for the coating, to show their effects on scattering from the chirally coated cylinder.     

Analysis of waveguide antenna arrays with protruding dielectricelements

The two-dimensional problem of radiation of TE and TM waves from a waveguide array with protruding smooth dielectric elements of arbitrary shape is considered, and solution algorithms are suggested. The algorithms are based on applying the method of auxiliary sources for the representation of electromagnetic fields outside and inside the protrusions in combination with the method of integral equations for the electric field at the waveguide aperture. The point matching of the field tangential components on the protrusion-to-free-space boundary and at the waveguide aperture is used to reduce the problem to a system of linear algebraic equations for the amplitudes of the auxiliary filamentary currents and of the waveguide aperture electric field, which is assumed to be piecewise constant. The amplitudes obtained from the solution of the system are used for computing the array reflection coefficient and element pattern, which are shown in some cases to be significantly dependent on the protrusion shape. Examples of arrays with flat-topped element patterns resulting from array geometry numerical optimization are also presented     

BCGs-FFT结合BP神经网络反演金属介质复合柱体目标参数

利用双共轭梯度-快速傅里叶变换方法（BCGs-FFT）结合BP神经网络技术研究了金属介质复合结构柱体目标的电磁逆散射问题.先用BCGs-FFT方法计算了复合结构目标的正散射问题,得到不同目标参数下的多个观测点上的散射电场,以此作为训练样本提供给BP网络,经过适当的离线训练,再以新的散射电场作为网络的输入,实时重构了金属介质复合结构目标的几何、电磁参数.数值结果显示了该方法的有效性.     

Solving satisfiability problems using reconfigurable computing

This paper reports on an innovative approach for solving satisfiability problems for propositional formulas in conjunctive normal form (SAT) by creating a logic circuit that is specialized to solve each problem instance on field programmable gate arrays (FPGAs). This approach has become feasible due to recent advances in reconfigurable computing and has opened up an exciting new research field in algorithm design. SAT is an important subclass of constraint satisfaction problems, which can formalize a wide range of application problems. We have developed a series of algorithms that are suitable for a logic circuit implementation, including an algorithm whose performance is equivalent to the Davis-Putnam procedure with powerful dynamic variable ordering. Simulation results show that this method can solve a hard random 3-SAT problem with 400 variables within 1.6 min at a clock rate of 10 MHz. Faster speeds can be obtained by increasing the clock rate. Furthermore, we have actually implemented a 128-variable 256-clause problem instance on FPGAs     

High-frequency electromagnetic field coupling to long terminatedlines

We present a theory for the EMC problem of electromagnetic field coupling to a long line with arbitrary terminations. The theory is applicable for the high-frequency plane wave electromagnetic field excitations, when the transmission line approximation is no longer valid. Analytical expressions are derived for the induced current along the line, and at the two-line terminals. The coefficients of these expressions are determined using a procedure based on the exact solutions of the integral equation for two similar line configurations, but having a significantly shorter length. The method is, therefore, particularly efficient when considering the electromagnetic field coupling to very long lines. The advantage of the proposed approach is that, in contrast with transmission line approximation, it takes into account high-frequency radiation effects. Furthermore, it allows a considerable reduction in computation time and storage requirements with respect to conventional numerical solutions based on the thin-wire approximation     

Electromagnetic Field-Responsive and Accurate Control of Bending in VO2 Based Micro-Pillar Array

Electromagnetic field-responsive mechanical deformation enables remote control of dynamic devices including micro-robotic machines and smart surfaces. Metal–insulator transition (MIT) of vanadium dioxide (VO₂) is developed for micro devices that are electrically or optically activated, but none of these is electromagnetic field-responsive. Herein, a micro-pillar array composed of epitaxial VO₂ nanobeams that are asymmetrically coated with Cr, Au, and silicon oxide layers is demonstrated. Localized Joule heat, induced by the eddy current effect within the Cr or Au metal layer under an electromagnetic field, provides a high-sensitive thermal response that triggers MIT of VO₂, thus activates bending and relaxing of the micro-pillars. For accurate and site-specific control of the bending, layers of amorphous silicon oxide are added to the structure to endow tunable stiffness through electron beams-matter interaction. These micro-pillars are optimized to be a 2D, tractable surface on which directional transportation by remote control of the electromagnetic field in a liquid medium is realized. This discovery provides novel ideas for the design of electromagnetic field-responsive structures.     

An effective near-field far-field transformation technique fromtruncated and inaccurate amplitude-only data

A general approach to the near-field far-field transformation from amplitude only near-field data is presented. The estimation of the far field is stated as an intersection finding problem and is solved by the minimization of a suitable functional. The difficulties related to the possible trapping of the algorithm by a false solution (common to any nonlinear inverse problem) are mitigated by setting the problem in the space of the squared field amplitudes (as already done in a number of existing papers) and by incorporating all the a priori knowledge concerning the system under test in the formulation of the problem. Accordingly, the a priori information concerning the far field, the near field outside the measurement region and the accuracy of the measurement setup and its dynamic range are properly taken into account in the objective functional. The intrinsic ill conditioning of the problem is managed by adopting a general, flexible, and nonredundant sampling representation of the field, which takes into account the geometrical characteristics of the source. As a consequence, the number of unknowns is minimized and a technique is obtained, which easily matches the available knowledge concerning the behavior of the field. The effectiveness of the approach is shown by reporting the main results of an extensive numerical analysis, as well as an experimental validation performed by using a very low cost near field facility available at the Electronic Engineering Department, University of Napoli, Italy