孔缝箱体屏蔽效能电磁拓扑分析模型

基于Robinson等效电路法,提出了一种电磁拓扑模型,用于任意平面波入射条件下的孔缝箱体屏蔽效能分析。该模型将孔缝及其所在平面等效为连接自由空间(等效为特性阻抗为Z0的传输线)和剩余箱体(等效为特性阻抗为Zg的短路矩形波导)的二端口网络,并通过等效电路模型计算了该二端口网络的散射矩阵,进而推导出描述孔缝耦合的广义BLT(Baum-Liu-Tesche)方程。设计了4组实验模型用于电磁拓扑理论(EMT)算法、Robinson算法和CST软件的对比分析,仿真结果证明:EMT算法较Robinson算法具有更高的准确率,尤其是在高频域;EMT算法继承了Robinson算法简洁高效的特性,且能直观反映箱体参数、孔逢参数对屏蔽系数的影响,较CST软件实用性更强。     

腔体内传输线耦合的电磁仿真软件与传输线方程的混合算法

研究了一种有限积分法软件与传输线方程相结合的混合算法,用于解决复杂电磁环境下屏蔽腔体内传输线的电磁耦合问题。利用有限积分法软件实现屏蔽腔体的建模,仿真得到腔体内部空间电磁场分布,并设置电场探针提取出传输线的激励场。利用传输线方程建立腔体内传输线的耦合模型,将得到的传输线激励场引入到传输线方程作为等效分布电压和电流源。利用时域有限差分(FDTD)格式对传输线方程进行离散,从而迭代求解出传输线终端负载上的电压和电流响应。通过与文献以及传统数值算法的计算结果进行对比,验证混合算法的正确性。研究表明,该混合算法在模拟电大尺寸腔体内传输线的电磁耦合方面,具有较高的精度和计算效率。     

自动波竞争神经网络及其在单源最短路问题中的应用

将竞争机理引入网络的自动波产生与传播过程中，提出自动波竞争神经网络(ACNN)模型，并成功地应用于求解单源最短路问题，给出了基于ACNN的最短路求解算法. 与其他神经网络最短路算法相比，基于ACNN的最短路算法具有网络所需的神经元数目少、神经元及网络的结构简单、易于软硬件的实现、以及全并行方式计算等特点，可用于求解非对称赋权图的最短路径树问题，且其计算时间(迭代次数)仅正比于最短路径上的跃点数，与赋权图的复杂度、路径总长、边长的精度、通路总数等因素无关. 计算机仿真结果表明该算法的有效性和快速求解能力. 关键词： 单源最短路问题 自动波竞争神经网络 脉冲耦合神经网络     

开孔矩形腔体电磁泄漏特性的解析研究

本文提出了一种用于计算开孔矩形腔体电磁泄漏场的解析理论模型.该理论模型先基于模式展开法求解封闭腔场,进而依据Bethe小孔耦合理论将泄漏场与封闭腔场用等效偶极子关联.该模型可以考虑波频率、场源位置、开孔位置及场强观测点位置等因素的影响,计算结果与全波仿真结果一致.本文计算分析了相关因素对电磁屏蔽效能的影响规律,并给出了物理解释.结果表明近场屏蔽效能小于远场屏蔽效能,且近场区电场屏蔽效能与磁场屏蔽效能并不相同.     

开孔屏蔽腔内传输线负载所受电磁干扰的解析算法

外界电磁场通过孔缝耦合进入屏蔽腔,并经由线缆对腔内电子设备造成干扰,这是电磁兼容中需要考虑的重要问题,而数值法分析此类尺寸跨度大的电磁问题效率过低。基于电磁拓扑和等效电路法,提出一种快速计算外界平面波辐照下开孔屏蔽腔内传输线负载所受电磁干扰的解析算法。首先利用电磁拓扑将整个耦合问题分解为两个独立的子问题:外界平面波辐照下开孔空腔内的耦合场问题与耦合场辐照下孤立传输线的响应问题,然后提出基于等效电路法求解空腔内耦合电场的计算方法,最后利用场线耦合BLT方程求解耦合电场对孤立传输线负载造成的电磁干扰。经CST仿真验证,该解析算法能有效计算任意位置开(多)孔屏蔽腔内任意放置传输线负载所受的电磁干扰。相比于数值法,该解析算法不仅花费更少的计算时间与资源,且能用于参数影响规律的研究。     

开孔矩形腔体的近场电磁屏蔽效能研究

基于扩展的等效电路方法, 建立了电偶极子和磁偶极子天线近场照射下开孔矩形腔体电磁屏蔽效能计算的近似解析模型, 计算分析了场源–腔体距离对电场和磁场屏蔽效能的影响规律. 结果表明在近场区, 屏蔽效能随场源–腔体距离的减小而明显减小, 近场屏蔽效能小于远场屏蔽效能. 基于Bethe小孔耦合理论, 得出了描述近场和远场屏蔽效能关系的解析公式, 并用该公式检验了等效电路方法计算结果的可信性. 关键词： 电磁屏蔽 矩形腔体 近场 Bethe 理论     

平面波照射下开孔矩形腔体的电磁耦合与屏蔽效能研究

基于Bethe小孔耦合理论和腔内电磁场的本征模展开, 建立了平面波照射下开孔矩形腔体电磁场分布的近似解析模型. 该模型物理意义清晰, 可以考虑开孔的形状、 尺寸、 个数及位置和入射波的传播与极化方向等参数的影响. 该模型的计算结果优于传统的等效电路方法, 与实验结果的一致性更好. 计算分析了相关因素对电磁屏蔽效能的影响规律, 所得结果对电磁屏蔽腔体的设计有指导意义.     

中等导电性材料覆盖的金属腔体的电磁屏蔽效能研究

基于传输线和波导理论, 提出了一种用于计算覆盖中等导电性材料的金属腔体电磁屏蔽效能的解析理论模型, 并通过和全波电磁模拟结果的比较检验了该模型的有效性. 计算分析了屏蔽体屏蔽效能的位置效应和谐振效应. 建议了一种评价导电材料电磁屏蔽效能的方法, 能很好的削弱谐振效应和位置效应的影响, 直接反映出材料本身的电磁屏蔽效能. 关键词： 电磁屏蔽 导电材料 金属腔体 屏蔽效能     

表面平整目标的电磁散射快速预估

针对表面基本由平面构成的散射体,在传统弹跳射线法的基础上,对射线跟踪以及射线求交测试方法进行改进,使得该方法对于分析隐身飞行器等有更好的应用。研究了单根射线与三角形的快速求交方法,同时与弹跳射线法相结合,使用三角形对目标进行两次表面拟合,分别得到用于求交测试的稀疏三角面元,以及用于射线追踪的起始三角面元,利用快速求交方法,完成射线追踪,进行物理光学积分,完成目标远场电磁散射的快速预估,将该方法的计算结果与文献结果进行对比,验证了该方法的可靠性,通过计算不同拟合面元密度下情况下的结果,验证了该算法的高效性。     

建筑物墙壁电磁耦合截面建模及应用

电磁波照射下的建筑物室内电磁环境具有混响效果,因此可采用功率平衡法（PWB）快速评估室内电磁环境水平。然而目前PWB方法中电大腔壁耦合截面（CCS）的计算模型建立在腔内电磁波不穿透腔壁的条件下,无法直接用于电磁波可穿透室内建筑物墙壁的耦合截面计算。为此,提出了一种适用于电磁波穿透有限厚度建筑物墙壁的CCS计算新模型。该模型考虑实际建筑物墙体的厚度和材料电磁特性,能够充分反映电磁波因有限厚度墙壁多次反射对室内电磁环境水平的影响。将该模型应用于室内电场水平的快速评估,预测结果与实际测量结果吻合较好,证明了所提有限厚度建筑物墙壁CCS模型的合理性。     

Efficient packet routing strategy in complex networks

We investigate a new efficient packet routing strategy which mitigates traffic congestion on complex networks. In order to avoid congestion, we minimize the maximum betweenness, which is a measure for concentration of routing paths passing through a node in the network. Danila et al. propose a packet routing strategy in which, instead of shortest paths, they used efficient paths, which are the paths with the minimum total summations of weights assigned to nodes in the respective paths. They use a heuristic algorithm in which the weights are updated step by step by using the information of betweenness of each node in every step and the respective total summations of weights for paths through the nodes with large degrees become comparatively large. Thus passage through such nodes, where congestion almost occurs, is likely to be avoided in their algorithm. The convergence time by their algorithm is, however, quite long. In this paper, we propose a new efficient heuristic algorithm which balances traffic on networks by achieving minimization of the maximum betweenness in the much smaller number of iteration steps for convergence than that by the algorithm of Danila et al.     

Reaction rate calculation by parallel path swapping

The efficiency of path sampling simulations can be improved considerably using the approach of path swapping. For this purpose, we devise a new algorithmic procedure based on the transition interface sampling technique. In the same spirit of parallel tempering, paths between different ensembles are swapped, but the role of temperature is here played by the interface position. We test the method on the denaturation transition of DNA using the Peyrard-Bishop-Dauxois model. We find that the new algorithm gives a reduction of the computational cost by a factor of 20.     

On the concepts of complex networks to quantify the difficulty in finding the way out of labyrinths

Labyrinths have been a tradition and part of the imagination of the human kind for centuries, and were probably built either as a challenge to make it difficult for someone to find the way out, or for aesthetic purposes. They are conventionally classified according to the country they were built, to the style (Roman, classic and contemporary) or to the construction site. In this study, we show that labyrinths can be modeled as complex networks, whose metrics can be used to classify them in terms of their difficulty to find the way out. This is performed by calculating the absorption time, defined as the time it takes for a particle on an internal node to reach an output node through a random walk. The absorption time correlates well with the shortest paths and length of the networks, as expected, and has a very high correlation (Pearson coefficient of 0.97) with the betweenness, therefore allowing one to quantify the level of complexity of any labyrinth. It is shown that the conventional classification is inappropriate to distinguish between labyrinths, because some with very similar properties exist in different countries or were built in distinct time periods. A refined analysis in 77 famous labyrinths indicated that the majority were built for aesthetic purposes, with relatively small absorption times. Furthermore, with the expectation maximization algorithm, we could combine the complex network metrics to identify four clusters of labyrinths that differ in terms of density and shape.     

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.     

Transport in weighted networks: partition into superhighways and roads

Transport in weighted networks is dominated by the minimum spanning tree (MST), the tree connecting all nodes with the minimum total weight. We find that the MST can be partitioned into two distinct components, having significantly different transport properties, characterized by centrality--the number of times a node (or link) is used by transport paths. One component, superhighways, is the infinite incipient percolation cluster, for which we find that nodes (or links) with high centrality dominate. For the other component, roads, which includes the remaining nodes, low centrality nodes dominate. We find also that the distribution of the centrality for the infinite incipient percolation cluster satisfies a power law, with an exponent smaller than that for the entire MST. The significance of this finding is that one can improve significantly the global transport by improving a tiny fraction of the network, the superhighways.     

半导体器件多物理场计算中的热边界条件北大核心CSCD

基于半导体器件的物理模型,联立并求解由电磁场、半导体物理及热力学方程构成的多物理场方程组,实现半导体器件及电路的电磁效应计算。为了更加准确地仿真半导体器件的温度变化,深入研究了多物理场计算中的热边界条件。以肖特基二极管HSMS-282c为例,采用多物理场算法仿真并对比了器件在相同激励(幅值为2V的阶跃脉冲)、不同边界条件下的温度变化情况。实际测量了器件在正向偏置下的表面温度,并于多物理场计算结果进行对比。结果表明,采用热对流边界可以准确仿真半导体器件的热效应。     

基于电磁拓扑的多腔体屏蔽效能快速算法

提出基于电磁拓扑理论计算开孔多腔体屏蔽效能的快速方法.首先给出双腔体等效电路和电磁拓扑信号流图,并推导孔缝节点处的散射矩阵,给出拓扑网络的散射矩阵方程和传输矩阵方程,获得双腔体的广义Baum-Liu-Tesche(BLT)方程.在此基础上研究了开孔三腔体,包括串型级联三腔体和串并型混合级联三腔体的广义BLT方程.对于串型级联三腔体,其电磁拓扑网络和广义BLT方程在双腔体基础上直接扩展即可获得.而对于串并型混合级联三腔体,通过将位于三腔体公共面上的孔缝等效为三端口网络节点,并根据三端口网络散射参数定义推导获得该节点的散射矩阵,最终得到串并型混合级联三腔体的广义BLT方程.本文方法对双腔体的计算结果与文献结果和实验结果相符合,对3组不同类型和尺寸开孔腔的屏蔽效能的计算结果与时域有限差分法计算结果符合较好.该算法不仅效率高,通过对所有计算结果和实验结果的误差统计分析,表明该算法具有较高的计算准确度.     

Local adaptive sampling for wireless sensor network powered by energy harvesting

For a sensor network, energy limitation is always a key factor to affect the continuous work of a sensor node. A good idea is harvesting energy from the environment to support the node to work continuously. However, energy from environment is varied with time, weather and season. So in order to use the varied environment energy, it is necessary to find a way to achieve real-time monitoring and adaptive working. In this paper, an algorithm called “Adaptive Sampling” was proposed to adapt the sample mode to the present energy condition. Simulation proves that the algorithm can make the CO₂ sensor flexibly achieve adaptive sampling under different energy condition with the least MSE 2.7767. This algorithm can be widely used in wireless sensor network power by energy harvesting for local adaptive sampling.     

一种改进的基于信息传播率的复杂网络影响力评估算法

评价网络中节点的信息传播影响力对于理解网络结构与网络功能具有重要意义.目前,许多基于最短路径的指标,如接近中心性、介数中心性以及半局部(SP)指标等相继用于评价节点传播影响力.最短路径表示节点间信息传播途径始终选择最优方式,然而实际上网络间的信息传播过程更类似于随机游走,信息的传播途径可以是节点间的任一可达路径,在集聚系数高的网络中,节点的局部高聚簇性有利于信息的有效扩散,若只考虑信息按最优传播方式即最短路径传播,则会低估节点信息传播的能力,从而降低节点影响力的排序精度.综合考虑节点与三步内邻居间的有效可达路径以及信息传播率,提出了一种SP指标的改进算法,即ASP算法.在多个经典的实际网络和人工网络上利用SIR模型对传播过程进行仿真,结果表明ASP指标与度指标、核数指标、接近中心性指标、介数中心性指标以及SP指标相比,可以更精确地对节点传播影响力进行排序.     

智能光网络中一种新型的分布式恢复方法

提出了一种基于固定备用路由和目的端触发的智能光网络中的分布式恢复方法,所选择的任一对源端节点和目的的端节点之间的固定备用路由包括该节点对之间的k条最短路径路由和基于部分链路无关的路由.目的端节点一旦探测到业务通道的失效将立即启动恢复进程,根据网络当前的资源使用情况,在这些备用路由中按照一定的次序选择一条恢复路由并为此分配一条可用的波长(对于没有波长变换器的光网络),然后将恢复通道的建立请求消息发送给该恢复通道的相关节点,这些相关节点可以锁定相关的网络资源,以避免来自其他恢复通道的竞争.所提出的算法增加了固定备用路由的数量,从仿真结果可以看出,该方法明显改善了失效连接的阻塞性能.