高空核爆电磁脉冲E2部分对架空管道的影响

高空核爆电磁脉冲会通过管道的耦合作用,对各种电子设备和系统造成严重的影响和破坏.为了研究高空核爆电磁脉冲对架空管道的影响,首先通过麦克斯韦方程给出了高空核爆电磁脉冲对架空管道的耦合方程,然后应用格林函数法求解微分方程得到管道上感应电流和电压的频域表达式,再应用傅里叶反变换得到电流和电压的时域波形.最后计算了基于IEC标准波形的高空核爆电磁脉冲E₂部分作用下架空管道的感应电流和电压.     

近地电缆屏蔽层对高空核电磁脉冲响应的研究

为了研究近地面电缆屏蔽层对高空电磁脉冲的耦合规律,依据传输线理论,计算了在高空核电磁脉冲作用下损耗大地上电缆屏蔽层上的感应电流。利用快速傅立叶变换技术,首先得到近地面电缆屏蔽层感应电流的频域解,然后采用快速傅立叶逆变换技术得到时域解。得到了感应电流随电缆长度、电缆架设高度、电磁脉冲极化角、方位角、俯仰角、端接阻抗和大地电导率等的变化规律。     

V-conical antenna

A new angular antenna called the V-conical antenna was investigated. The characteristics of the antenna are frequency-independent, and the electromagnetic fields are pure spherical waves (transverse electromagnetic mode) even in the near region. The theoretical analysis makes use of conformal mapping. Closed-form solutions for the fields, currents, and characteristic parameters are obtained. The formulas are simple and precise. An experimental study of the antenna was conducted under pulse excitation. The shape of the measured electric-field pulses is the same as that of the source pulse from a picosecond pulse generator. The measured field patterns are very close to those predicted by the theory. Such a structure with a tapered resistive termination is an ideal directional pulse antenna or electromagnetic pulse simulator     

T2 -Selective Magnetization Preparation Pulses

The purpose of this work was to present and evaluate a new method for directly designing T₂-selective preparation pulses. Using a modified Shinnar-Le-Roux (SLR) transform, the design of T₂-selective pulses becomes equivalent to designing a pair of polynomials one of which represents the longitudinal magnetization and the other the transverse magnetization. The polynomials enable one to directly analyze the various tradeoffs involved in the design. To evaluate the new method, a short-T₂-selective magnetization preparation pulse was designed. Following the preparation pulse, a 2D Fourier transform (2DFT) multislice gradient echo sequence was used for imaging. For verification Bloch equation simulations were performed along with both in vivo and phantom scans. Phantom scans showed good signal suppression of long-T₂ species. This is supported by good long-T₂ signal suppression seen on the in vivo images. Simulations indicate that the pulse is robust to plusmn150 Hz B₀ inhomogeneities and plusmn10% B₁ inhomogeneities.     

The Tradeoff Between Processing Gains of an Impulse Radio UWB System in the Presence of Timing Jitter

In time hopping impulse radio, N_f pulses of duration T_c are transmitted for each information symbol. This gives rise to two types of processing gains: (i) pulse combining gain, which is a factor Nf, and (ii) pulse spreading gain, which is N_c = T_f/T_c, where T_f is the mean interval between two subsequent pulses. This paper investigates the tradeoff between these two types of processing gains in the presence of timing jitter. First, an additive white Gaussian noise (AWGN) channel is considered, and approximate closed-form expressions for bit error probability (BEP) are derived for impulse radio systems with and without pulse-based polarity randomization. Both symbol-synchronous and chip-synchronous scenarios are considered. The effects of multiple-access interference (MAI) and timing jitter on the selection of optimal system parameters are explained through theoretical analysis. Finally, a multipath scenario is considered, and the tradeoff between processing gains of a synchronous impulse radio system with pulse-based polarity randomization is analyzed. The effects of the timing jitter, MAI, and interframe interference (IFI) are investigated. Simulation studies support the theoretical results.     

The use of the frequency-dependent finite-difference time-domainmethod for induced current and SAR calculations for a heterogeneousmodel of the human body

This paper describes the use of the previously formulated frequency-dependent finite-difference time-domain ((FD)²TD) method for analysis of an anatomically based heterogeneous man model exposed to ultra-wide-band electromagnetic pulse sources. The human tissues' electrical permittivities, ϵ_i*(ω) are described by Debye equations with two relaxation constants, and the equation D(t)=ϵ*(ω))E(t) is converted to a finite-difference equation along with the Maxwell's equations used by the standard FDTD method. Using a single run with a broad-band pulse excitation, the (FD) ²TD method is used to calculate mass normalized rates of energy deposition (specific absorption rates or SARs) and induced currents in the man model over a broad band of frequencies. Time-domain coupling of a representative ultrashort pulse of subnanosecond rise time and nanosecond pulse duration to the human body is also examined     

Gyrotron coaxial cylindrical resonators with corrugated innerconductor: Theory and experiment

Gyrotron coaxial resonators with a longitudinally slotted inner cylinder are examined analytically using a surface impedance model, from which expressions for the electromagnetic field, ohmic quality (Q) factor, and characteristic equation of the transverse eigenvalues χ _m,p are obtained. The major attributes of such resonators are expressed by the dependence of χ_m,p on the parameter C-defined as the ratio of the outer to inner radii of the coaxial structure. In that connection, the effect of the corrugation parameters on χ_m,p is particularly investigated on the basis of an expression derived for the slope function dχ_m,p,p/dC. It is shown that the χ_m,p(C) curve may either exhibit oscillatory behavior or present a flat portion over a wide range of C depending on the corrugation parameters chosen. The theory is checked against experiment in which resonant frequencies and total Q factors were measured for TE modes operating in the range of 8-16 GHz in a coaxial cavity with 40 slots. Good agreement is found in that the magnitude of the relative error in frequency is less than 0.5%. Corrugated coaxial resonators prove to be relevant to megawatt gyrotrons where highly selective cavities are required to ensure high conversion efficiency     

Electromagnetic field near rail guns

The field in the neighborhood of an electromagnetic rail gun is computed for the case of constant current. The analysis centers on the Westinghouse EMACK launcher in which two rails of 2-m length carry a peak current of 2.1 MA, while a peak power of over 10 GW is delivered to the rails. Expressions are derived for electric field strength and magnetic flux density as functions of gun parameters. These formulas can be used to compute the electromagnetic pulse produced by a rail gun of any given characteristics     

相参脉冲序列频率估计的小波变换方法

在单站无源定位与跟踪系统中,接收信号的多普勒频率变化率信息对运动目标的状态估计和定位非常重要。对于脉冲体制的雷达来说,信号持续时间较短,很难精确测量多普勒频率变化率。小波变换在时频域同时具有良好的局域特性和较低的信噪比门限。文章引入了小波变换方法实现单站无源定位与跟踪系统的参数估计,推导了相参脉冲序列的小波变换方法。数值仿真证明该方法能实现脉冲的相参积累,大幅提高参数的估计精度。     

Transient behavior of the kink effect in partially-depleted SOIMOSFET's

The behavior of transients in the drain current of partially-depleted (PD) SOI MOSFET's down to L_eff=0.2 μm is examined as a function of drain bias, gate pulses of varying magnitude (V_GS), pulse duration, and pulse frequency. At fixed V_DS, the gate is pulsed to values ranging from 0.1 V above V_T to V_GS=V_DS. A slow transient is seen when the drain is biased at a V_DS where the current kink is observable. This slow transient can be on the order of microseconds depending on the relative magnitude of the impact ionization rate. For short times after the pulse edge or for very short pulses at low frequencies, it is shown that the subthreshold drain current value can be very different from the corresponding DC, and that the kink characteristic of PD MOSFET's disappears. However, the kink values can be approached when the pulse frequency and/or duration applied to the gate is increased, due to the latent charge maintained in the floating body at higher frequencies. No transient current effects were observed in fully-depleted SOI MOSFET's     

Optimal data-based kernel estimation of evolutionary spectra

Complex demodulation of evolutionary spectra is formulated as a two-dimensional kernel smoother in the time-frequency domain. First, a tapered Fourier transform, y_v(f, t), is calculated. Then the log-spectral estimate, is smoothed. As the characteristic widths of the kernel smoother increase, the bias from the temporal and frequency averaging increases while the variance decreases. The demodulation parameters, such as the order, length, and bandwidth of spectral taper and the kernel smoother, are determined by minimizing the expected error. For well-resolved evolutionary, spectra, the optimal taper length is a small fraction of the optimal kernel halfwidth. The optimal frequency bandwidth, w, for the spectral window scales as w²~λ/τ, where τ is the characteristic time and λ_F is the characteristic frequency scalelength. In contrast, the optimal halfwidths for the second stage kernel smoother scales as h~1/(τλ_F )¹(p+2)/ where p is the order of the kernel smoother. The ratio of the optimal-frequency halfwidth to the optimal-time halfwidth is determined     

强激光打靶产生电磁脉冲特性与传导防护研究

为了降低电磁脉冲的场强大小,加强强激光打靶产生电磁脉冲的传导防护性能,提出了强激光打靶产生电磁脉冲特性与传导防护研究.由于强激光打靶产生电磁脉冲对各种电子设备和电气设备都会造成一定威胁,采用双指数函数,分析了强激光打靶产生电磁脉冲的时域波形频谱,完成了强激光打靶产生电磁脉冲的特性研究;为了消除强激光打靶产生的电磁脉冲波...     

通道参数对MPCA传播特性的影响分析

该文针对现有高功率微波武器辐射天线的不足,提出了将磁化等离子体通道用作电磁脉冲辐射天线的思想磁化等离子体通道天线(MPCA),分析了MPCA周围为有耗气体媒质时MPCA所传播的一般模式。简单阐述了MPCA的具体实现方法,根据MPCA的工作原理,建立了MPCA的几何模型,导出了广义柱坐标系下磁化等离子体中纵向场所满足的波动方程及纵-横的关系,利用边界条件导出了MPCA严格的特征方程。重点讨论了MPCA的传播常数随等离子体通道参数(等离子体频率和通道半径)的变化。结果表明,强磁场时等离子体频率对天线衰减常数影响增大,且有一极值出现。     

The behavior of electromagnetic localized waves at a planarinterface

In this paper, we investigate the behavior of electromagnetic localized waves [LW's], which are concentrated moving pulses of energy, at an interlace between two electrically different media. We employ a previously given Fourier transform domain representation of LW's that is geometric in nature; the Fourier transform of an LW consists of a support line on a particular surface together with a weighting associated with this line. The behavior of electromagnetic LW's at an interface is somewhat involved owing to their broadband nature, but this behavior has a lucid pictorial representation in terms of the transform domain geometry and, in this paper, we exploit this representation. If an LW strikes the interface obliquely then a different LW is reflected, but the pulse transmitted into the second medium is not a LW. We give analytical and graphical evidence of this behavior. Moreover, we show that if one desires a particular LW to be propagated into the second medium, one can in some cases design the necessary non-LW pulse one needs to launch at the interface to achieve this goal     

A Broadband and Scalable Lumped Element Model for Fully Symmetric Inductors Under Single-Ended and Differentially Driven Operations

A broadband and scalable 2-T model is developed to accurately simulate fully symmetric inductors with various dimensions. The 2-T model is defined to reflect the structure of an equivalent circuit with two identical T-model circuits. Two-step de-embedding is assisted by open and through pads for extraction of intrinsic characteristics. The accuracy is validated by 3-D full- wave electromagnetic simulation. A novel parameter extraction flow is established, and a single set of model parameters is derived to be valid for both single-ended and differentially driven topologies. The broadband accuracy is proven by a good match with S-parameters, L(omega), Re(Z_ln(omega)), and Q(omega) over frequencies up to 20 GHz. The scalability is justified by good fitting with either a linear or a parabolic function of spiral coil radii. Furthermore, all model parameters are frequency independent so as to ensure computation efficiency. This 2-T model consistently predicts the enhancement of Q_max by 20%-30% for the symmetric inductors under a differential excitation. The Q improvement is even better than 100% over broader frequencies beyond f_m (Q_max).     

联合多维特征的干扰识别技术研究

干扰识别是通信电子防御系统的重要组成部分，针对复杂电磁环境的干扰识别问题，本文研究了联合多维特征的干扰识别技术，从时域、频域和变换域提取了一组对干扰参数、噪声敏感度低且复杂度较低的特征参数，给出了联合多维特征且基于决策树和支持向量机（Support Vector Machine，SVM）的两种干扰识别器结构，并进行了干扰识别性能仿真对比分析。仿真结果表明，这两种识别器对典型电磁干扰均具有良好的识别性能，对于瞄准式干扰、部分频带噪声干扰、噪声调频干扰和脉冲干扰，二者识别性能很接近；对于梳状多音干扰和线性调频干扰，SVM识别器比决策树识别器具有更好的识别性能。      

Real-time human blood pressure measurement based on laser self-mixing interferometry with extreme learning machine

In this paper, we present a method based on self-mixing interferometry combing extreme learning machine for real-time human blood pressure measurement. A signal processing method based on wavelet transform is applied to extract reversion point in the self-mixing interference signal, thus the pulse wave profile is successfully reconstructed. Considering the blood pressure values are intrinsically related to characteristic parameters of the pulse wave, 80 samples from the MIMIC-II database are used to train the extreme learning machine blood pressure model. In the experiment, 15 measured samples of pulse wave signal are used as the prediction sets. The results show that the errors of systolic and diastolic blood pressure are both within 5 mmHg compared with that by the Coriolis method.     

屏蔽室接地位置不同对其屏蔽效能的影响研究

为分析屏蔽室不同接地位置对其屏蔽效能的影响,应用并行时域有限差分算法,对雷电电磁脉冲和高空核电磁脉冲与开孔屏蔽室的耦合问题进行了数值模拟。计算了屏蔽室在两种接地位置下(前点接地、后点接地)内部的耦合电场,并进行了局部实验验证。研究结果表明:接地点与屏蔽室开孔位置间的距离远,屏蔽效能高;距离近则屏蔽效能低。     

An improved Gaussian approximation for probability of bit-erroranalysis of asynchronous bandlimited DS-CDMA systems with BPSK spreading

This paper analyzes probability of bit-error (P_e) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of P_e analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low P_e (< 10^-3) or a prohibitively large computational complexity. The paper presents an alternate method of P_e analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P _e performance, user capacity and the accuracy of the proposed method     

电磁环境中电子器件的失效分析

以现在应用较广泛的电子器件-MOS器件在电磁环境中的失效建模为例,针对MOS器件受到电磁脉冲和周期脉冲的冲击后,所表现出来的失效特征,得出它符合基于随机过程的退化失效模型所描述的结论.根据结论和两种电应力的特点,分别提出基于随机过程的失效建模和动态应力-强度干涉建模.通过模型的建立和分析,初步制定出电子器件失效的试验方案.