交替隐式时域方法精确实现理想导体边界

为了准确求解交替方向隐式时域有限差分(Alternating Direction Implicit Fi-nite-Difference Time-Domain,ADI-FDTD)方法实现理想电导体边界和理想磁导体边界的待求场分量系数,通过在获得该系数前应用理想导体边界条件,推导出了相应的修正系数.计算了单个金属立方体和对称的两个金属立方体的双站雷达散射截面.结果表明:理想导体边界作为理想导体表面,采用修正系数的计算结果与时域有限差分(Finite-Differ-ence Time-Domain,FDTD)方法计算结果更为吻合;理想导体边界作为截断计算空间对称面,采用修正系数的计算结果与ADI-FDTD方法计算结果相同,与理论推导结论一致.     

螺旋皱纹导体同轴电缆特性阻抗不均匀性研究

本文建立了关于螺旋皱纹内、外导体同轴电缆特性阻抗不均匀性的理论。从缓变的近似圆截面导体模型出发,利用区域变分法和黎卡迪方程,推导出计算特性阻抗和电压反射系数的近似解析表达式,系统分析了电缆设计、制造和安装等实际问题。     

一种分析复杂导体目标瞬态特性的快速方法

将渐进波形估计技术引入到频域矩量法中,并结合傅立叶逆变换和自适应复频率跳跃技术,快速而准确地分析任意形状导体目标的瞬态特性,大大提高了计算效率.在分析中,脉冲波形和导体目标的几何形状可以任意.分别以理想导体方形平板、理想导体立方体、理想导体球体和理想导体锥体为例,并将计算结果与频域矩量法的结果进行了比较.它们之间良好的一致性说明了所提出方法的正确性和有效性.     

基于轴对称四边形薄导体模型的电阻估算法

本文提出一种利用轴对称薄片导体模型近似等效处理不规则的薄片导体转角电阻的估算方法。首先从理论出发,论证了所有轴对称的四边形薄片导体,其对边之间的电阻等于其方阻。以该结论为依据,得到了一种以近似划分为手段的薄片电阻估算法。作为实例,将该方法应用于L型薄片电阻的估算,并对这种估算的有效性和精确性进行了分析和讨论。     

时域电场积分方程的稳定求解

提出了一种基于时域电场积分方程的稳定精确数值方法计算任意形状理想导体的时域散射.矢量位的时间导数采用中心差分近似,而标量位采用时间平均表示,并且标量位和矢量位在单元上随时间变化采用单元中心处的值来计算.将该方法与隐式方法相结合可以得到稳定精确的求解结果,而不必对电流密度进行时间或空间平均的处理过程.从模拟结果证明了该方法的稳定性和精确性.     

边界条件微扰法计算非理想波导的传播常数

考虑到非理想导体波导壁金属损耗对传播常数的影响,对理想金属边界条件进行一阶近似微扰,得到了非理想波导的传播常数。和传统微扰法相比,能够在截止频率附近较为精确地计算衰减常数,也适用于导体损耗较大的情况;同时能给出非理想导体波导壁对相位常数的影响。将结果与Ansoft HFSS软件的仿真结果进行比较,两者具有较好的一致性。同时给出了边界条件微扰法解与解析解及传统微扰法解在一定条件下的联系,表明边界微扰法比解析法实现简单,比传统微扰法具有更广泛的适用性。     

THz频段粗糙导体圆锥的极化成像特性

太赫兹频段下粗糙导体表面会对电磁散射回波的幅度、相位、极化状态产生影响,为分析这一影响,以导体圆锥为例,研究了不同粗糙参数表面电磁散射在雷达图像中的表现规律。基于谱方法和坐标变换对粗糙圆锥面进行建模,利用高频电磁计算方法获得不同粗糙度导体圆锥样本多角度、多频点、全极化的单站散射场,基于转台模型,利用二重积分法获得目标二维像。从仿真结果可以看出,粗糙与理想光滑导体的圆锥图像存在明显差异,粗糙圆锥图像中能量分布偏离理想光滑情况下的强散射区域;随着粗糙度的增加,图像能量分布愈加均匀;相比于同极化图像,交叉极化图像更具反映目标轮廓信息的潜力。     

电磁场与微波技术

0441,TN385 00020794星用固放电磁兼容设计/王玉田,张友(电子部13所)11半导体情报.一1999,36(4).一59一61,50介绍了星用固放的电磁兼容设计,主要从结构设计角度分析和解决了电磁兼容性问题,并给出试验结果.图7参2(午)27(9)一35一36文中讨论半空间中目标后向散射计算的一次反射近似方法.并且利用互易原理和等效偶极子模型进一步简化八十算.数值例子验证了所述近似方法的适用性该方法可应用于短波超视距雷达海上目标散射特性的分析咚}3参4(金)0441.1()0020795带电双导体球之间的静电作用/莫克威(长沙交通学院)11长沙交通学院学报.一1999,15(3…     

导电高分子能带的Wannier函数方法

导电高分子的Peierls不稳定性会在费米面上产生能隙,它将半满能带分裂成价带和导带,并使体系变为半导体.本文给出了在二聚化的基础上利用Wannier函数来计算导电高分子能带的一般方法,由此可改进紧束缚近似下的SSH 模型.我们把这一方法应用于聚乙炔链并采用二聚化的一维方势阱模型,其结果是极为令人满意的.     

半导体技术

TN301 00010455半导体组子点的形状对受限激子的影响/罗莹,王若祯,马本kun(北京师范大学),,物理学报.一1999,48(7).一1320一1326在有效质量近似范围内,采用有限深势阱模型,考虑介电受限、计入表面极化效应的情况下,研究了球形、立方形半导体量子点的形状对受限激子的影响.结果表明量子点的形状效应不可忽略.图2参10(午)的结果.图7参3(木)TN301.4 00010456PN结压变电容特性的应用研究/成立(江苏理工大学)11半导体杂志.一1999,24(1).一8一13首先提出了PN结压变电容特性表达式,并绘制出其实验曲线,然后导出了PN结结电容的几个近似计算式,最…     

渐近波形估计技术应用于导体柱RCS方向图的快速获取

本文基于渐近波形估计(AWE)技术和矩量法(MOM)快速预测任意形状导电柱体(PEC)的单站RCS方向图.首先采用矩量法求解导体柱的电场积分方程,得到导体柱在某一给定方向入射波照射下的表面电流的低阶矩量,然后利用AWE技术求出在任意方向入射波照射下用有理分式函数表示的表面电流,进而计算出RCS方向图.计算结果表明AWE完全能逼近MOM精确计算的曲线,同时在计算速度上可加快几十倍.     

预处理结合AWE技术求解导体目标RCS

采用渐近波形估计技术(AWE)和预处理技术求解导体目标的宽带雷达散射截面(RCS)。应用矩量法求解导体目标的电场积分方程,通过构造预条件算子,使由矩量法得到的阻抗矩阵稀疏化,从而计算导体表面电流时变得简便,再结合渐近波形估计(AWE)技术计算导体目标的宽带雷达散射截面(RCS)。实例结果表明,该方法在计算电大导体目标时具有较高的计算效率和很好的精度。     

一种解决MOO算法求解任意形状导电目标 瞬态散射稳定性的方法

本文通过对Hertz矢量展开系数的误差逼近提出了一种新的计算方法用来确定u的值.该方法确保了MOO算法的稳定性且在编码中更具有通用性.用此算法对金属球体和飞机、导弹缩比模型进行了仿真计算并与频域数据进行了比较,验证了算法的有效性.     

Analysis of Optical Losses in a Photoelectrochemical Cell: A Tool for Precise Absorptance Estimation

Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar‐to‐hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscopic measurements is presented. Specifically, photoelectrodes using transparent conductive substrates such as F:SnO₂ coated with thin absorber films are focused. The optical model is verified for hematite photoanodes fabricated by atomic layer deposition and successfully used to determine wavelength‐dependent reflection, transmission, layer absorptances, and charge generation rates. Furthermore, the calculated absorptances enable 20–30% more accurate calculations of the absorbed photon‐to‐current efficiency of PEC cells. Our optical model is a powerful tool for the optimization of the optical performance of PEC cells focusing on single absorber or tandem configurations and represents a cornerstone of a complete (optical and electrical) model for PEC water splitting cells.     

An efficient multiregion model for electromagnetic scattering and radiation by PEC targets

An efficient multiregion model has been proposed for the fast implementation of the electromagnetic scattering by perfectly electrical conducting (PEC) targets and the radiation of point sources or wire antennas near PEC targets. In the multiregion model, the PEC target under consideration is divided by multiple regions depending on the position of point source/antenna or the incident direction of plane waves. Then the method of moments (MoM) is used on the first region, which is close to the source or is the illuminated region, to obtain the accurate electric current. The mutual coupling between different regions are considered approximately based on the magnetic-field integral equation, from which closed-form approximations for electric currents on other regions are derived. Because MoM is only performed on the first region, the number of unknowns in the new model is much fewer than that in the full MoM analysis, making the new model much more efficient. Compared with the published hybrid methods, the multiregion model gives a more reasonable physical explanation, and provides a better accuracy in both currents and scattered fields. Numerical simulations for two-dimensional (2-D) problems (transverse-magnetic/transverse-electric) and 3-D problems are given to test the validity and efficiency of the proposed modeling.     

The Gilbert-Holland FDTD thin slot model revisited: an alternative expression for the in-cell capacitance

This paper proposes an alternative expression for the in-cell capacitance of a photoelectrical cell (PEC)-mounted slot, which is the conceptual cornerstone of the Gilbert-Holland subcell finite difference time domain (FDTD) model. By treating a slightly modified electrostatic problem, the extraneous charge singularity on the PEC edges touching the cell, which is characteristic of the originally proposed model, is removed. The latter offers better physical grounds for a new expression of the capacitance and the effective permittivity used in the update equations. High resolution standard FDTD simulation results are presented in support of the new expression.     

Magnetic field integral equation at very low frequencies

It is known that there is a low-frequency breakdown problem when the method of moments (MOM) with Rao-Wilton-Glisson (RWG) basis is used in the electric field integral equation (EFIE); it can be solved through the loop and tree basis decomposition. The behavior of the magnetic field integral equation (MFIE) at very low frequencies is investigated using MOM, where two approaches are presented based on the RWG basis and loop and tree bases. The study shows that MFIE can be solved by the conventional MOM with the RWG basis at arbitrarily low frequencies, but there exists an accuracy problem in the real part of the electric current. Although the error in the current distribution is small, it results in a large error in the far-field computation. This is because a big cancellation occurs during the far field computation. The source of error in the current distribution is easily detected through the MOM analysis using the loop and tree basis decomposition. To eliminate the error, a perturbation method is proposed, from which a very accurate real part of the tree current has been obtained. Using the perturbation method, the error in the far-field computation is also removed. Numerical examples show that both the current distribution and the far field can be accurately computed at extremely low frequencies by the proposed method.     

A fictitious domain method for conformal modeling of the perfectelectric conductors in the FDTD method

We present a fictitious domain method to avoid the staircase approximation in the study of perfect electric conductors (PEC) in the finite-difference time-domain (FDTD) method. The idea is to extend the electromagnetic field inside the PEC and to introduce a new unknown, the surface electric current density to ensure the vanishing of the tangential components of the electric field on the boundary of the PEC. This requires the use of two independent meshes: a regular three-dimensional (3-D) cubic lattice for the electromagnetic field and a triangular surface-patching for the surface electric current density. The intersection of these two meshes gives a simple coupling law between the electric field and the surface electric current density. An interesting property of this method is that it provides the surface electric current density at each time step. Furthermore, this method looks like FDTD with a special model for the PEC. Numerical results for several objects are presented     

计算细理想导电圆柱RCS的物理模式基矩量法

根据GTD—MOM技术给出一种物理模式基的概念 ,并用之分析细理想导电圆柱的电磁散射 ,求解其雷达散射截面积 (RCS)。圆柱表面上的电流假设由三部分组成 :入射波的感应电流和圆柱两端的反射电流。该方法较传统的全域基矩量法减小了计算机内存 ,加快了计算速度 ,而且数值计算结果与全域基的结果吻合较好。     

一种粗粒度可重构体系结构多目标优化映射算法

针对多约束下的行流水粗粒度可重构体系结构的硬件任务划分映射问题,提出了一种多目标优化映射算法.该算法根据运算节点执行时延、依赖度等因素构造了累加概率权值函数,在满足可重构单元面积和互连等约束下,通过该函数值动态调整就绪节点的映射调度次序,当一块可重构单元阵列当前行映射完毕后,就自动换行,当一块阵列被填满,就切换到下一块,当一个数据流图映射完毕后,就自动计算划分块数等参数.实验结果表明,与层贪婪映射算法相比,文中算法平均执行总周期降低了8.4%(RCA_4×4)和5.3%(RCA_6×6),与分裂压缩内核映射算法相比,文中算法平均执行总周期降低了20.6%(RCA_4×4)和21.0%(RCA_6×6),从而验证了文中提出算法的有效性.