面向超短波接收机射频前端的电磁脉冲效应仿真与效应分级方法

针对接收机射频前端在电磁脉冲环境作用下的电磁损伤过程模拟问题,以超短波接收机为具体研究对象,基于超外差式接收机电路功能模型,采用Verilog-a和SPICE网表联合建模方法,建立了射频前端低噪声放大器（LNA）电磁脉冲效应仿真模型(Extended LNA Model),并通过S参数仿真和瞬态仿真验证了LNA电磁脉冲效应模型具备正常功能仿真能力;为验证该模型的电磁脉冲损伤模拟能力,以标准电磁脉冲波形作为激励,以偶极子天线作为简化的天线前门耦合通道,在不同强度电磁脉冲作用下,接收机中频电路信号输出表现出了无影响、干扰、损毁的电磁脉冲效应过程,说明了建模方法的有效性;最后以EMP-天线耦合电压峰值作为阈值指标,分析得到了超短波接收机不同电磁脉冲效应等级对应的电压峰值阈值数据。     

基于GABP神经网络曲线拟合的快沿电磁脉冲信号源模型求解

为给电子设备的电磁脉冲效应仿真提供准确的快沿电磁脉冲(fast rise-time electromagnetic pulse,FREMP)信号源模型,提出一种基于遗传算法优化BP神经网络(GABP-NN)曲线拟合的信号源模型求解方法;该方法通过示波器对脉冲信号进行采集,利用GABP神经网络对波形曲线进行高精度拟合,提取网络参数建立信号源模型;为进一步获得BP神经网络拟合规律设置对比实验,采用隐含层神经元数为10的GABP神经网络对FREMP信号源进行建模,所得模型拟合度为91.64%;仿真结果表明该方法运算速度快、精度高。     

油气管道数据采集与监视控制系统电磁脉冲效应实验

为研究油气管道数据采集与监视控制(SCADA)系统的电磁脉冲易损性和防护措施,搭建了具有数据采集、数据通信、远程控制等功能的典型油气管道SCADA模拟实验系统,进行了峰值场强最高为50kV/m的典型高功率电磁波形作用下的电磁脉冲效应试验。利用实验数据,对目前油气管道SCADA系统面临强电磁脉冲威胁的机理和规律进行了初步分析,发现电磁脉冲对油气管道SCADA系统具有一定程度的威胁,获得了效应现象和效应阈值结果。     

基于重要度的分级贝叶斯网络诊断模型研究

为了提高复杂系统故障检测和诊断的准确性,从数据的不确定性、诊断的不确定性以及特征参数选择的不确定性三方面展开研究。在贝叶斯网络解决不确定性问题优势的基础上,提出了基于重要度的分级贝叶斯网络模型。以往基于贝叶斯网络的方法无法做到系统地选择参数,建立的模型都是全模型。虽然全模型没有遗漏关键的参数,但包含了很多不必要的参数,这些多余参数不仅会对诊断造成不良影响,导致拖尾效应。仿真结果表明,提出方法可以获得更佳的故障特征,有利于提高故障识别能力,验证了模型的有效性。     

有界波电磁脉冲模拟器下短线缆效应的理论和实验研究

 研究了有界波电磁脉冲模拟器下短线缆效应的理论建模和实验方法。基于传输线模型计算了线缆在有界波电磁脉冲模拟器辐照下的电流响应。建立了有界波电磁脉冲模拟试验环境,其前沿时间小于5 ns,脉冲半高宽约200 ns。开展了短线缆的效应实验验证研究,短线缆负载端响应电流的测量和计算结果吻合得很好,表明应用改型有界波电磁脉冲模拟器开展短线缆效应实验在理论和实验上都是可行的。这种线缆实验方法具有效应实验空间电磁场分布规范均匀、参数指标可控、监测技术成熟等优点。     

PIN限幅器电磁脉冲效应数值模拟与验证

基于电磁脉冲对半导体器件效应的电-热多物理场模型,利用Sentaurus-TCAD仿真器建立了PIN限幅器电磁脉冲效应数值模型,研究了不同峰值功率的电磁脉冲作用下限幅器的输入/输出特性,以及大功率电磁脉冲注入PIN器件热损伤阈值与脉冲宽度的关系。模拟与实验结果表明:基于器件热效应影响载流子输运过程的电-热多物理模场型,模拟限幅器在大功率电磁脉冲注入下输入/输出功率的结果与实验结果吻合较好;模拟大功率电磁脉冲注入PIN器件热损伤阈值与脉冲宽度的关系式,与Wunsch-Bell半经验关系式符合较好。     

考虑参数不确定性的高空电磁脉冲E1分量环境计算及分析

高空电磁脉冲的早期分量幅值高、频谱宽、分布范围广,是高空核爆的电磁效应的重要组成部分。分析了国内外高空电磁脉冲早期分量仿真计算法的研究进展,并选取基于高频近似并考虑电子与电磁场自洽作用的EXEMP算法进行详细介绍,通过数值计算结果总结了高空电磁脉冲的时域波形和空间分布随场源当量、爆高等参数变化的规律,与IEC标准约定的波形时域和空间特征一致。针对HEMP计算中部分参数的不确定性,分析参数取值偏差和波动对电磁脉冲计算结果的影响,使用多项式混沌方法联合Sobol全局敏感度指标对其进行不确定量化,得到电磁脉冲关键值可能分布的上下界、分布的概率密度等信息,分析各参数在特定取值范围内对电磁脉冲特征参数的影响及联合影响。     

强电磁脉冲(激光、微波)在高温离解氮气中的击穿效应

 通过对电子能量分布函数所满足的Boltzmann方程的求解，在理论上分析了强电磁脉冲(激光、微波)在高温氮气中的击穿效应。高温气体的一个主要特征是其中的部分气体分子会离解为原子，这一离解效应会对强电磁脉冲在气体中发生电离击穿的阈值产生影响。计算表明：随着温度的升高，氮分子的离解度增大，强电磁脉冲的击穿阈值下降；击穿阈值的下降幅度与电磁波的频率有关，对频率较高的红外激光，击穿阈值下降明显；而对微波，击穿阈值所受影响较小。     

能量选择表面的瞬态响应

为实现强电磁脉冲防护和信号收发的兼容,研究了一种基于能量选择机制的强电磁防护结构,即能量选择表面。该防护表面利用半导体压控导电特性,实现了强场辐照时防护表面由高阻态向低阻态的转变,具有能量低通特性和超宽带特性。利用场路协同仿真方法,分析了能量选择表面瞬态响应与PIN二极管阻抗特性、强电磁脉冲峰值场强及脉冲前沿的关系,结果显示:尖峰泄漏功率和响应时间与Ⅰ层厚度、强电磁脉冲峰值场强成正比,与少数载流子寿命成反比变化。     

GaN高电子迁移率晶体管强电磁脉冲损伤效应与机理

提出了一种新型GaN异质结高电子迁移率晶体管在强电磁脉冲下的二维电热模型,模型引入材料固有的极化效应,高场下电子迁移率退化、载流子雪崩产生效应以及器件自热效应,分析了栅极注入强电磁脉冲情况下器件内部的瞬态响应,对其损伤机理和损伤阈值变化规律进行了研究.结果表明,器件内部温升速率呈现出"快速-缓慢-急剧"的趋势.当器件局部温度足够高时(2000 K),该位置热电子发射与温度升高形成正反馈,导致温度急剧升高直至烧毁.栅极靠近源端的柱面处是由于热积累最易发生熔融烧毁的部位,严重影响器件的特性和可靠性.随着脉宽的增加,损伤功率阈值迅速减小而损伤能量阈值逐渐增大.通过数据拟合得到脉宽τ与损伤功率阈值P和损伤能量阈值E的关系.     

混响室雷达地杂波统计特性模拟

为实现混响室中威布尔分布杂波的有效模拟,营造逼真的雷达电磁环境,基于广义平稳非相关散射电磁环境下混响室信道衰落特性,通过控制幅度调制信号对衰落系数进行补偿,提出一种基于时域波形设计的混响室地杂波模拟方法。通过调节输入信号序列中大、小幅度脉冲比例,改变混响室传统输入信号的零均值幅度特性,以实测地杂波统计特性为参考,最终得到与实测数据统计特性参数一致的混响室杂波电磁环境。用最大似然估计和KS检验法对实验数据作参数估计和假设检验,实测地杂波数据拟合于标准威布尔模型,混响室实验数据拟合于实测地杂波幅度统计模型,从而实现了实测地杂波起伏特性的混响室有效模拟。     

The Weibull-log Weibull transition of the interoccurrence time statistics in the two-dimensional Burridge-Knopoff Earthquake model

In analyzing synthetic earthquake catalogs created by a two-dimensional Burridge-Knopoff model, we have found that a probability distribution of the interoccurrence times, the time intervals between successive events, can be described clearly by the superposition of the Weibull distribution and the log-Weibull distribution. In addition, the interoccurrence time statistics depend on frictional properties and stiffness of a fault and exhibit the Weibull-log Weibull transition, which states that the distribution function changes from the log-Weibull regime to the Weibull regime when the threshold of magnitude is increased. We reinforce a new insight into this model; the model can be recognized as a mechanical model providing a framework of the Weibull-log Weibull transition.     

The distribution of first-passage times and durations in FOREX and future markets

Possible distributions are discussed for intertrade durations and first-passage processes in financial markets. The view-point of renewal theory is assumed. In order to represent market data with relatively long durations, two types of distributions are used, namely a distribution derived from the Mittag-Leffler survival function and the Weibull distribution. For the Mittag-Leffler type distribution, the average waiting time (residual life time) is strongly dependent on the choice of a cut-off parameter t_max, whereas the results based on the Weibull distribution do not depend on such a cut-off. Therefore, a Weibull distribution is more convenient than a Mittag-Leffler type if one wishes to evaluate relevant statistics such as average waiting time in financial markets with long durations. On the other hand, we find that the Gini index is rather independent of the cut-off parameter. Based on the above considerations, we propose a good candidate for describing the distribution of first-passage time in a market: The Weibull distribution with a power-law tail. This distribution compensates the gap between theoretical and empirical results more efficiently than a simple Weibull distribution. It should be stressed that a Weibull distribution with a power-law tail is more flexible than the Mittag-Leffler distribution, which itself can be approximated by a Weibull distribution and a power-law. Indeed, the key point is that in the former case there is freedom of choice for the exponent of the power-law attached to the Weibull distribution, which can exceed 1 in order to reproduce decays faster than possible with a Mittag-Leffler distribution. We also give a useful formula to determine an optimal crossover point minimizing the difference between the empirical average waiting time and the one predicted from renewal theory. Moreover, we discuss the limitation of our distributions by applying our distribution to the analysis of the BTP future and calculating the average waiting time. We find that our distribution is applicable as long as durations follow a Weibull law for short times and do not have too heavy a tail.     

Strength statistics and the distribution of earthquake interevent times

The Weibull distribution is often used to model the earthquake interevent times distribution (ITD). We propose a link between the earthquake ITD on single faults with the Earth’s crustal shear strength distribution by means of a phenomenological stick–slip model. For single faults or fault systems with homogeneous strength statistics and power-law stress accumulation we obtain the Weibull ITD. We prove that the moduli of the interevent times and crustal shear strength are linearly related, while the time scale is an algebraic function of the scale of crustal shear strength. We also show that logarithmic stress accumulation leads to the log-Weibull ITD. We investigate deviations of the ITD tails from the Weibull model due to sampling bias, magnitude cutoff thresholds, and non-homogeneous strength parameters. Assuming the Gutenberg–Richter law and independence of the Weibull modulus on the magnitude threshold, we deduce that the interevent time scale drops exponentially with the magnitude threshold. We demonstrate that a microearthquake sequence from the island of Crete and a seismic sequence from Southern California conform reasonably well to the Weibull model.     

Amplitude Statistics of Sea-Ice Clutter Using a Millimeter Wave Radar

Sea-ice clutter was measured using a millimeter wave radar with frequency of 34.86GHz and pulse length of 30ns. To determine the sea-ice clutter amplitude statistics, we investigated the log-normal, Weibull, log-Weibull and K-distributions using the Akaike Information Criterion (AIC), which is more rigorous fit of the distribution to the data than the least-squares method. It is shown that the amplitude of sea-ice clutter obeys almost a log-Weibull distribution.     

The Weibull-log Weibull distribution for interoccurrence times of earthquakes

By analyzing the Japan Meteorological Agency (JMA) seismic catalog for different tectonic settings, we have found that the probability distributions of time intervals between successive earthquakes-interoccurrence times-can be described by the superposition of the Weibull distribution and the log-Weibull distribution. In particular, the distribution of large earthquakes obeys the Weibull distribution with the exponent α₁<1, indicating the fact that the sequence of large earthquakes is not a Poisson process. It is found that the ratio of the Weibull distribution to the probability distribution of the interoccurrence time gradually increases with increase in the threshold of magnitude. Our results infer that Weibull statistics and log-Weibull statistics coexist in the interoccurrence time statistics, and that the change of the distribution is considered as the change of the dominant distribution. In this case, the dominant distribution changes from the log-Weibull distribution to the Weibull distribution, allowing us to reinforce the view that the interoccurrence time exhibits the transition from the Weibull regime to the log-Weibull regime.     

Suppression of Sea-Ice Clutter Observed by a Millimeter Wave Radar Using a New Log-Weibull/CFAR System

Sea-ice clutter was measured using a millimeter wave radar with frequency of 34.860GHz, beamwidth of 0.25° and pulse length of 30ns. To determine the sea-ice clutter amplitude statistics, we investigated the log-normal, Weibull, log-Weibull and K-distributions using the Akaike Information Criterion (AIC), which is more rigorous fit of the distribution to the data than the least-squares method. It is shown that the amplitude of sea-ice clutter obeys the log-Weibull distribution with shape parameters of 2.36 to 2.93 for both entire data and data within the beam width of an antenna. We propose a new log-Weibull/CFAR system uses a modified cell-averaging LOG/CFAR system. It is found that this log-Weibull/CFAR procedure is effective for suppression of sea-ice clutter and detection of target.     

高反射膜激光零几率损伤阈值的实验研究

 在确定光学薄膜激光损伤阈值的实验数据处理过程中，发现一些样品的数据点分布偏离直线型式。对此，用国际标准规定的零几率来确定损伤阈值的同时，对测试数据点采用了不同的非直线拟合，也得到一个零几率损伤阈值。比较两者差异，并与实验测试结果对照，发现这些样品采用非直线拟合得出的零几率损伤阈值与实际情况更接近一些。