A Bayesian approach based on the vulnerability distribution is proposed to estimate the confidence limits of the state probability and the threat level of multistate electronic systems interfered by intentional electromagnetic interference (IEMI). The vulnerability distribution is used to describe the state probability function of the multi-state system (MSS) for a given IEMI threat level. When a small number of test samples are under a specific threat level and prior MSS information is known, the posterior estimation of the state probability function can be obtained based on Bayesian theory. Furthermore, to effectively apply the state probability function to assess the vulnerability of the MSS, the uncertainty of the state probability function is discussed. Considering state probabilities under the same threat level as random variables, all these state probabilities also follow the Dirichlet distribution. Thus, the confidence limits of the posteriori state probability and the threat level can be inferred by the marginal distribution of the state probability, which is induced by combining the Dirichlet and vulnerability distributions. Finally, a case study is given to demonstrate the details of the calculation process of the vulnerability distribution, the state probability function, and the confidence limits under a lognormal distribution.

In this paper, we simulated the space-charge effect current by the full electromagnetic particle-in-cell (PIC) code UNIPIC in a planar gap. Compared with Lau’s numerical work, we introduce the applied voltage $U$ , gap separation $D$ , suppression magnetic field $B$ , electron-injection energy spectra $f(E)$ and temporal profiles $f(t)$ as the factors affecting the current densities and the particle distributions. It is shown that $U$ and $D$ could change the particle distribution significantly, causing the electrons’ escape, while they bring little impact on the ratio of 2-D Child-Langmuir current to the classical 1-D value $J_{\mathrm {CL}}(2)/J_{\mathrm {CL}}$ (1). Considering the temporal profile, it is interesting that the transported current density is inversely going to decrease when the injection rise time is much smaller than the transit time, which explores the smaller temporal profile numerically compared with Valfells’s experiments. Last, the preliminary simulation of the combined effect of temporal profile and initial electron energy spectra is presented, and it is evident that the thermal electrons obeying the Boltzmann distribution generate a larger transported current density than the photoelectron under exponential distribution, which might be an inspiration to the engineering application.

针对复杂环境下多探测传感器网络难以准确协同定位的问题,提出了一种多传感器协同定位优化布站方法.基于后验克拉美罗下界构建了目标定位精度几何稀释因子评价指标,考虑复杂外界环境,分析了起伏地形、杂波干扰和光照对传感器探测定位能力的影响.建立了多传感器协同定位优化布站模型,并采用智能优化算法进行快速求解.仿真实验结果表明:所提方法能够有效提高多探测传感器网络的协同定位能力,对多传感器协同优化布站具有指导意义.

针对激光大气传输湍流效应不确定度量化中采用蒙特卡罗(MC)方法计算效率低的问题,提出了一种基于多项式混沌(PC)的不确定度量化方法.该方法采用拉丁超立方抽样随机抽取少量样本,经过数值模拟后通过多项式混沌构造代理模型,并依据代理模型进行不确定度量化.以准直Gauss光束的地空垂直上行传输为例,不确定度计算中考虑了激光器出口光束质量和大气相干长度对远场功率密度的影响,并以大样本量MC方法的不确定度量化结果作为基准,对PC方法进行了验证.结果表明,PC方法只需对少量样本进行数值模拟计算,便可快速构建远场功率密度的代理模型,得到的不确定度量化结果与MC方法的量化结果吻合较好.

The research on the space-charge limited current is of great importance for developing insight into the high current diodes. The Child-Langmuir law presents one-dimensional (1D) space-charge limited current density by considering a full electrostatic solution. Jaffe investigated the 1D space-charge limited current density modified by the uniform initial velocity of electrons emitted from the cathode by using the equation of motion for the individual electron. Luginsland et al. presented the two-dimensional (2D) space-charge limited current density by using the particle-in-cell (PIC) codes neglecting initial velocity distribution of the emitted electrons. In this Letter, the effects of initial electrons with the uniform energy distribution and thermal equilibrium distribution on the space charge limited current density are studied by using the full electromagnetic PIC method; the 2D modification factors to the space charge limited current density for the two cases are presented and discussed.

This paper presents a virtual-force-based guidance law (VFGL) for path following and obstacle avoidance in unmanned aerial vehicles. First, a virtual spring force and a virtual drag force are designed for straight-line following; then, the dynamic of the cross-track-error is equivalent to a spring mass system, which is easy to tune to acquire stability and non-overshoot convergence. Secondly, an additional virtual centripetal force is designed to counteract the influence of the curvature of the planned path so that the guidance law can accurately track a curve with a time-varying curvature. Thirdly, an extra virtual repulsive force is designed directly according to the sensor inputs; the virtual repulsive force pushes the vehicle away to move around obstacles. The use of artificial physics means the guidance law is founded on solid physical theory and is computationally simple. The physical meanings of the parameters are definite, and the VFGL has a large parameter adaptation. These make the guidance law easy to tune in application. Both the numerical and hardware-in-the-loop simulation results demonstrated the effectiveness of the proposed guidance law for path following and obstacle avoidance in unmanned aerial vehicles.

将二维轴对称柱坐标系中基于MPI平台的并行FDTD (MPI-FDTD)方法与基于基尔霍夫表面积分表达式(KSIR)的场变换相结合,实现“MPI-FDTD+MPI-KSIR”的混合并行技术,并应用于无电阻加载的大型垂直极化电磁脉冲(EMP)辐射波模拟器时域辐射近场的快速预估.验证算例所得辐射近场不仅与商用软件及并行FDTD的整体模拟符合很好,且与并行FDTD整体模拟相比可以节约80％的计算时间.给出并行加速比和并行效率的测试结果.该方法可用于其它大型垂直极化EMP辐射波模拟器时域辐射近场和辐射远场的快速预估.

Parallelized finite-difference time-domain (FDTD) method combined with mirror image theory is used for simulating the leakage of flat-plate bounded wave electromagnetic pulse (EMP) simulator with hybrid configuration. Considering the simulator has the symmetric characteristic and the tangential electric fields are symmetrical at the two sides of the simulator's symmetry plane, perfectly magnetic conductor (PMC) boundary is applied for the FDTD computing. The results of the method agree well with those of normal FDTD method. The results show that the leakage field from the simulator is affected by the ground conductive characteristic evidently, and the leakage fields near the ground should be concerned specially. The method in this paper is useful for the simulation of other bounded wave EMP simulators. And the method has the advantages of saving computing time and CPU storage.

The electromagnetic resonance of IEMP in a cavity is studied by numerical modeling using 3-D Particle in Cell (PIC) codes combined with MCNP providing electron emission states. Two cylindrical cavity models of different sizes are computed, and then the condition of resonance is given. Moreover, the distribution of radial electronic field along the axial direction, as well as the distribution of electrons in the cavity is analyzed.

A new wire-grid transverse electromagnetic (TEM) horn as an electromagnetic pulse (EMP) radiating-wave simulator, with resistors, two PEC vertical plates and two sloping PEC plates loaded, are given. And the radiation fields of the new horn are simulated by parallel finite-difference time-domain (FDTD) method. The EMP's effects of the new horn are numerically studied and analyzed. The results show that the full width at half maximum (FWHM) of electric field increases as the total resistance of each wire increases and the tail effect of waveform weaken efficiently. The low-frequency characteristic of the new horn is improved greatly comparing with the normal TEM horn antenna.

采用将大地设置为均匀有耗介质,并用单轴完全匹配层(UPML)吸收边界截断的方式,对离散电阻加载的地面上方大型水平极化电磁脉冲(EMP)有界波模拟器的时域辐射场进行并行时域有限差分模拟.给出大地电导率和相对介电常数及模拟器圆锥的锥半径不同时模拟器辐射场的时域波形,分析三者对辐射场的影响,并给出模拟器内有10m长的效应物时耦合场的时域波形.并行模拟时,计算网格总数达18亿.研究表明:大地相对介电常数和电导率越大,近地面测点接收到的地面反射作用越大;测点场的峰值受锥半径的影响最大,且随着锥半径的增大,同一水平面内的场也越不均匀;对地面上方1 m处的几个测点,其脉冲峰值及半高宽受地面反射及地面损耗的影响较大,而地面上方5 m处的几个测点则受地面影响较小;当效应物开孔位置位于模拟器场泄露一侧时耦合进入圆筒内的电磁波能量较多.

A hybrid mode of one- and two-surface multipactor on the grooved dielectric surface is studied in detail using both an analytical approach and two-dimensional particle-in-cell (2D PIC) simulations. When the groove width L< eE(0)/(4 pi m(e)f(2)), there are one-surface multipactor and one-order two-surface multipactor on the grooved dielectric surface, and only one slope of the groove has the multipactor anytime. When L > eE(0)/(4 pi m(e)f(2)), both slopes may have the multipactors. The electron surface density of the multipactor discharge has a sharp increase at the length L = eE(0)/(4 pi m(e)f(2)).

Multipactor discharge on the rectangular grooved dielectric surface is simulated self-consistently by using a two-and-a-half dimensional (2.5 D) electrostatic particle-in-cell (PIC) code. Compared with the electromagnetic PIC code, the former can give much more accurate solution for the space charge field caused by the multipactor electrons and the deposited surface charge. According to the rectangular groove width and height, the multipactor can be divided into four models, the spatial distributions of the multipactor electrons and the space charge fields are presented for these models. It shows that the rectangular groove in different models gives very different suppression effect on the multipactor, effective and efficient suppression on the multipactor can only be reached with a proper groove size.

The multipactor plays a key role in the surface breakdown on the feed dielectric window irradiated by high power microwave. To study the suppression of multipactor, a 2D electrostatic PIC-MCC simulation code was developed. The space charge field, including surface deposited charge and multipactor electron charge field, is obtained by solving 2D Poisson's equation in time. Therefore, the simulation is self-consistent and does not require presetting a fixed space charge field. By using this code, the self-consistent simulation of the RF multipactor on the periodic micro-grooved dielectric surface is realized. The 2D space distributions of the multipactor electrons and space charge field are presented. From the simulation results, it can be found that only half slopes have multipactor discharge when the slope angle exceeds a certain value, and the groove presents a pronounced suppression effect on the multipactor.

Radiation near-fields of 10m height TEM antenna are computed by parallelized finite-difference time-domain(FDTD) method. The effects of the source's excitation ways, terminator load, below plate's shape and the ground to the near-fields of that TEM antenna are discussed. And the regularity of simulation is agreed well with that of experiment. The simulation analysis shows that the simulation results of the TEM antenna with hard source are closer to the experimental results than those with soft source; the fields at the points near the antenna's end are affected by the terminator load greatly; the rise-time of some testing points increases as the rectangle below plate replaced by trapezoid one; the peak-value of testing points decreases and the rise-time increases as the ground around the below plate is considered.

This paper presents a relativistic coaxial overmoded surface wave oscillator (SWO) working at the terahertz band in the double-ring metamaterial slow wave structure (SWS). A relativistic electron beam passes through the SWS between the inner and outer rings. A coaxial overmoded SWS made up of metal metamaterial is designed to generate the high-power terahertz wave by increasing the beam-wave interaction efficiency and enlarging the transverse size of the terahertz device. It consists of double rings periodically arrayed along the z-direction, and a coaxial conductor with a radius of 2.4 mm. By its dispersive relation the proposed device is studied, from which we choose the 0.14 THz as the operating frequency of the device. Then the parameters of the geometric structure and the electron beam are optimized; the transitional section for extracting the terahertz signal is designed of the largest propagation coefficient. Particle simulation code UNIPIC is employed to verify the initial expectation and potential advantages. When the beam voltage and current are increasing, the operating frequency of the device remains almost constant, and this is the typical characteristic of the SWO. Particle simulation results show that the coaxial inner conductor has a stable operating mode of double-ring metamaterial SWS and can increase the beam-wave interaction efficiency of the SWO at the terahertz band. For a guiding magnetic field of 2.0 T, with the electron beam of 600 kV and a current of 1.0 kA, a 0.141 THz wave output power of 316.8 MW is obtained.

Based on the secondary electron emission avalanche (SEEA) model, the SEEA discharge on the vacuum insulator surface is simulated by using a 2D PIC-MCC code developed by ourselves. The evolutions of the number of discharge electrons, insulator surface charge, current, and 2D particle distribution are obtained. The effects of the strength of the applied electric field, secondary electron yield coefficient, rise time of the pulse, length of the insulator on the discharge are investigated. The results show that the number of the SEEA electrons presents a quadratic dependence upon the applied field strength. The SEEA current, which is on the order of Ampere, is directly proportional to the field strength and secondary electron yield coefficient. Finally, the electron-stimulated out-gassing is included in the simulation code, and a three-phase discharge curve is presented by the simulation, which agrees with the experimental data. (C) 2015 AIP Publishing LLC.

This paper presents a new kind of device for generating the high power terahertz wave by using a coaxial overmoded surface wave oscillator with metamaterial slow wave structure (SWS). A metallic metamaterial SWS is used to avoid the damage of the device driven by a high-voltage electron beam pulse. The overmoded structure is adopted to make it much easy to fabricate and assemble the whole device. The coaxial structure is used to suppress the mode competition in the overmoded device. Parameters of an electron beam and geometric structure are provided. Particle-in-cell simulation results show that the high power terahertz wave at the frequency of 0.14 THz is generated with the output power 255 MW and conversion efficiency about 21.3%.

For fast estimating the time-domain near-fields of flat-plate bounded wave electromagnetic pulse(EMP) simulator with vertical polarization, scattering transfer function method is used in time-domain simulation of this kind of simulator. A Gaussian pulse, whose effective frequency domain is wider than that of a given pulse source, is found firstly. And the time-domain response of electric fields at some testing points in the simulator excited by the Gaussian pulse source can be got by finite-difference time-domain (FDTD) method. Then the transient response of electric field at each testing point as the simulator excited by the given pulse source can be computed by Fourier transform, system transfer function and inverse Fourier transform. The results are well consistent with those got by FDTD method as the simulator is excited by the given pulse source directly. The method in this paper is useful for fast estimating radiation near-fields of a fixed simulator with different exciting sources. It has the advantages of reducing FDTD simulation time, saving much computing time and CPU storage especially for medium or large simulators.

将并行时域有限差分方法用于分布式负载平行板有界波电磁脉冲模拟器模拟,并给出模拟器的尺寸参数对工作空间半高处几个测试点场的影响。研究结果表明:与源在x轴向距离上越靠近的点,其电场的上升沿越小;模拟器传输线最大宽度和最大高度之比为2,且下金属板宽度与传输线最大宽度相同时,测试点场的上升沿较小,半高宽较大;随着传输线在x方向投影长度的增加,与源位置x轴向等距离的测试点场的峰值增大,场的上升沿减小,但减小的量趋于平缓。且同轴线馈电时得到的各测试点场脉冲的上升沿要比直接加平面电场源的方式更大一点,半高宽则要小一点,但两者波形相似。