Partially prism-gridded FDTD analysis for layered structures oftransversely curved boundary

In this paper, a partially prism-gridded finite-difference time-domain (FDTD) method is proposed for the analysis of practical microwave and millimeter-wave planar circuits. The method is featured by hybridizing the flexible prism-based finite-element method to handle the region near the curved metallization boundary and the efficient rectangular-gridded FDTD method for most of the regular region. It can be used to deal with shielded or unshielded planar components such as patch antennas, filters, resonators, couplers, dividers, vias, and various transitions between planar transmission lines. Although only representative structures, e.g., grounded via, through hole via, and coplanar waveguide to coplanar stripline transition, are analyzed in this paper, the underlined formulation is applicable to layered structures with arbitrary curved boundary in the transverse direction. The accuracy of this method is verified by comparing the calculated results with those by other methods. Also, by the analysis of computational complexity, the present method is shown to be as efficient as the conventional FDTD method, with negligible overhead in memory and computation time for handling the curved boundary     

FDTD analysis of dielectric resonators with curved surfaces

In this paper, the finite-difference time-domain (FDTD) method is applied to calculate the resonant frequency of dielectric resonators (DRs) with curved surface. The contour-path integral FDTD (CFDTD) is modified to deal with the curved surface of the dielectric body while the traditional rectangular cells are maintained. Results are compared with theoretical values and staircase approximation, and show that the present method is more accurate than the staircase approximation     

Transient analysis of waveguides with curved boundaries

The transmission-line-matrix method of numerical analysis is modified to allow boundary points to fall anywhere between nodes on the mesh. Results are obtained for circular and elliptical waveguide cross-sections on a cartesian mesh.     

FDTD electromagnetic and thermal analysis of interstitialhyperthermic applicators

The electromagnetic and thermal behavior of interstitial applicators was analyzed by using the finite-difference time-domain method. Two configurations were considered: a simple insulated dipole antenna radiating in a layered tissue, and an air cooled applicator radiating in a tissue-equivalent phantom. The proposed approach allows a detailed modeling of the complete structure of the applicator. Furthermore, specific absorption rate and temperature distributions can be determined considering real clinical or experimental conditions. The temperature distribution for the air cooled applicator has been compared with experimental results     

基于高阶时域有限差分算法的电磁波传播计算

利用FDTD(2,4)高阶时域有限差分(Finite-Difference Time-Domain,FDTD)算法并结合滑动窗口的思想,对电磁波传播特性进行了仿真计算. 采用的高阶FDTD算法在空间上达到四阶精度,与二阶精度的传统FDTD算法相比,在相同每波长采样数的条件下,数值色散误差能得到进一步的减少. 在源脉冲传播较长距离时,数值色散的减少使得时域下脉冲扩展现象得到改善,滑动子窗口仍然能包含着激励源脉冲的全部信息,从而可更加准确地计算长距离电波传播特性. 另外,在相同的数值色散误差容限下,每波长采样数比传统二阶FDTD方法有所减少,从而节省存储空间,加快计算速度.     

An unsplit formulation of the Berenger's PML absorbing boundary condition for FDTD meshes

An unsplit formulation of the Berenger's perfectly matched layer absorbing boundary condition (PML ABC) for finite-difference time-domain (FDTD) meshes is presented. This unsplit formulation uses the conventional E-H algorithm, but does not require the E and H fields to be split. The proposed formulation is memory-efficient like that of the previous unsplit PML following the theory of Sacks. This unsplit formulation is easy to be implemented, and many useful modification to the Berenger's PML can also be done to it.     

一种分析探针加载微带天线的局部共形FDTD法

提出一种局部共形时域有限差分法(LCFDTD),对短路探针加载的小型微带贴片天线进行了精确的数值分析.该方法对任意尺寸和位置的同轴探针和短路探针都可精确模拟,并且可用来模拟多探针加载情况.计算结果和实验结果相一致,证明了本文方法的有效性.     

Median and mean filters produce similar shifts on curved boundaries

The author considers the shifts produced by median filters on curved boundaries and contours, and shows that mean and Gaussian filters produce similar but generally slightly smaller shifts, the cases of linear intensity variations and of step edges being somewhat different and at opposite extremes of a continuum. In all cases, the shifts are zero for straight edges and contours, and are proportional to the angle turned through within the filter neighbourhood.<>     

基于石墨烯一维太赫兹光子晶体电磁特性研究

采用时域有限差分(Finite Difference Time Domain FDTD)和表面边界条件对单层石墨烯的太赫兹电磁特性进行研究.首先计算了其反射和透射系数, 并与解析解对比验证了该理论的正确性.接着研究了一维光子晶体表面石墨烯在太赫兹光谱范围的吸收.通过改变模型中石墨烯的位置, 得到了一维石墨烯吸收特性与石墨烯位置的关系.结果表明:当石墨烯位于光子晶体表面时, 由于石墨烯和间隔层在光子晶体表面构成了表面缺陷, 从而导致光的局域化, 这种局域化增强了石墨烯对太赫兹范围光的吸收.     

Novel FDTD simulation method using multiple-analysis-space for electromagnetic far field

Wide-band undesired electromagnetic noise near electronic systems, which includes small noise source like the printed circuit board (PCB), is a current problem in the field of electromagnetic interference. However, the estimation method for the electromagnetic noise near a system under test has not been established. This paper proposes a newly developed estimation method of the electromagnetic noise for a wide area, from near to far field, using the finite difference time-domain (FDTD) method. The proposed FDTD simulation method is an estimation technique for near to far field with multiple analysis spaces (MAS). The MAS has an internal analysis space (IAS) and an external analysis space (EAS). The analysis near a radiation source can be calculated in the IAS. The EAS is the outside space from IAS, which is for calculation of the far field. It is expected that the proposed FDTD method by MAS (FDTD-MAS) decrease in the calculation cost in terms of computational time and memory costs, especially for estimation of radiation from PCB. The principle procedure of the FDTD-MAS method is described in the first part of this paper. As example of advantages of the calculation and confirmation of the calculation accuracy, the electric field distributions radiated from a 1-GHz half-wavelength dipole antenna in an IAS of 0.3/spl times/0.3 m/sup 2/ area and an EAS of 7/spl times/7 m/sup 2/ area are used as examples. When the cell size ratio of IAS to EAS is changed from 6 to 20, the FDTD and theoretical values show good agreement. It is indicated that the FDTD-MAS simulation method is one of the most powerful tools for the estimation of electromagnetic noise from near field to far field from small and thin source.     

FDTD analysis of electromagnetic wave radiation from systemscontaining horn antennas

The application of the finite-difference time-domain (FDTD) method to various radiating structures is considered. These structures include two- and three-dimensional waveguides, flared horns, a two-dimensional parabolic reflector, and a two-dimensional hyperthermia application. Numerical results for the horns, waveguides, and parabolic reflectors are compared with results from using the method of moments (MM). The results for the hyperthermia application are shown as extensions of the previously validated models. This new application of the FDTD method is shown to be useful when other numerical or analytic methods cannot be applied     

Convergence of FDTD and wavelet-collocation modeling of curved dielectric interface with the effective dielectric constant technique

The convergence of the effective dielectric constant (EDC) model of curved dielectric surfaces has been investigated precisely for the finite-difference time-domain (FDTD) as well as for the interpolet-collocation time-domain (ICTD) methods. The EDC is computed by solving the Laplace equation of static electric potential by a finite-difference (FD) method for each cell located on the interface of arbitrary dielectric media. The FD solution of the Laplace equation provides an accurate EDC for arbitrary curved interface with even high contrast of the dielectric constants. It has been demonstrated in this paper that the precisely chosen EDC allows both the FDTD and the wavelet-collocation methods to exhibit second-order convergence for the analysis of not only planar but also curved dielectric interfaces.     

Novel high-power laser structures incorporating curved gratings

We present a theoretical investigation of a novel type of distributed-feedback high-power diode laser with a “curved-groove” diffraction grating (c-DFB), which is predicted to give enhanced spectral and spatial output characteristics. Analyzed spectral properties of the proposed device are found to be identical to the conventional DFB laser of the same length and coupling. It has been also shown that the lateral optical modes of the proposed c-DFB laser are the cylindrical symmetry, which implies that the power generated by such a device can be brought to a common focus     

Analyzing low-frequency electromagnetic scattering from a compositeobject

In this paper, we present a method for solving electromagnetic scattering from a composite object at low frequencies using the method of moments (MoM) and loop-tree basis. Many applications involve composite objects which consist of several homogeneous regions. The loop-tree basis used for analyzing scattering from a homogeneous body at low frequencies could not be directly applied to analyze the low-frequency scattering from a composite object. In general, it is very difficult, if not impossible, to find a set of loop-tree basis functions that is valid for the structures on both sides of the interfaces. In this paper, we treat a composite object as a limiting case of multibody problem so that we could setup the MoM equation using the loop-tree basis found on each single body. A process is then developed to eliminate the redundant unknowns. The proposed method makes it possible to analyze low-frequency scattering from an arbitrary composite object. The validity and applications are illustrated with representative numerical examples     

Fabrication of curved structures by electron-beam lithography

The suitability of electron-beam lithography for the fabrication of curved structures, of interest for integrated optical devices, can be limited by the available pattern data formats. Extensions to the input format of a Cambridge Instruments electron-beam microfabricator are reported, which have allowed complex patterns to be easily specified for both mask making and direct writing.     

FDFD analysis of electromagnetic scattering in anisotropic mediausing unconstrained triangular meshes

A method using finite differences in the frequency domain (FDFD) for modeling field interaction and propagation in anisotropic media with generalized tensor permittivity and permeability, and with complex geometry, is presented. The method uses an unconstrained mesh with triangular cells, which provides an efficient discrete approximation of curved surfaces. The two-dimensional problem with transverse field excitation is studied. Computed results comparing this algorithm to published data for the former case show excellent agreement. The analysis provides information for all view angles simultaneously at a single frequency. The method can be adapted to a time-domain formulation to analyze the effects of wave pulses and multiple frequencies at a single observation angle     

基于OpenMP的电磁场FDTD多核并行程序设计

探讨了基于OpenMP的电磁场FDTD多核并行程序设计的方法,以期实现该方法在更复杂的算法中应用具有更理想的性能提升。针对一个一维电磁场FDTD算法问题,对其计算方法与过程做了简单描述。在Fortran语言环境中,采用OpenMP＋~粒度并行的方式实现了并行化,即只对循环部分进行并行计算,并将该并行方法在一个三维瞬态场电偶极子辐射FDTD程序中进行了验证。该并行算法取得了较其他并行FDTD算法更快的加速比和更高的效率。结果表明基于OpenMP的电磁场FDTD并行算法具有非常好的加速比和效率。     

洛伦兹介质电磁特性分析的通用FDTD方法

针对窄带、宽带及其临界情况时洛伦兹介质对应不同时域表达式而导致的递归卷积、Z变换等常用色散介质FDTD方法的更新公式无法通用问题,提出一种改进的移位算子FDTD方法,该方法保持了原方法概念简明、推导简单的优点,减少了内存占用,提高了计算速度,对窄带、宽带及其临界情况洛伦兹介质具有完全相同的更新公式。最后,通过具体算例验证了算法的有效性。     

用数值方法分析室内电磁环境

提出了利用数值方法计算钢筋混凝土墙包围的室内电磁环境的方法.在该方法中,首先要将整个墙体的复杂结构分成若干小的单元块.对于每个小的单元块而言,针对其具体结构的细节计算其电磁特性,并记录在相对应的特性矩阵中.基于这些矩阵建立表面积分方程进行求解,将大大提高计算的效率.     

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.