Precision time-domain measurement system

For an accurate comparison of two pulse signals on one channel of a sampling system, an alternating pretrigger shift is used. Simultaneously, a quartz-stable c.w. sine gives a precise time reference. A programmable data-acquisition system performs control and output operations. After averaging, the usable dynamic range is 70 dB with noise and drifts below 0.2 mVeff     

Power line filter design for conducted electromagnetic interference using time-domain measurements

A time-domain technique for the design of passive power line conducted electromagnetic interference (EMI) filters in the frequency range 150 kHz-30 MHz is described. A digital storage oscilloscope (DSO) with adequate sampling, storing and processing features is sufficient for the design using the proposed technique. Accordingly, Agilent's Infiniium Oscilloscope (Model 54810A) has been used. The signals from LISN are directly fed into the two channels of the DSO where they are added and subtracted to separate the CM and DM components, thereby eliminating the need for common-mode-differential mode (CM-DM) separator. These components are stored in the DSO. A specially designed filter design software (FDS), residing in the DSO, estimates the noise spectrum by computing the Bartlett and Welch periodograms. It also computes the filter component values. Thus, the sampling of the conducted noise, separation of CM and DM components, signal processing, and filter value computations are all done using one DSO. A spectrum analyzer is not required. Bartlett periodograms have been preferred over Welch periodograms due to low memory storage requirements of the former. The proposed technique has been applied to the design of power line filter for a switched mode power supply (SMPS), and satisfactory results have been obtained. The proposed measurement scheme is compact, economical, and convenient. All the details of this work are presented.     

High-frequency periodic time-domain waveform measurement system

A system is presented for the accurate measurement of high-frequency periodic time-domain voltage and current waveforms of a nonlinear microwave device. The measurements are performed in the time domain using a high-speed sampling oscilloscope. The results are Fourier-transformed into the frequency domain for error correction and then back into the time domain. An error-correction algorithm is presented that makes it possible to obtain accurate waveforms in spite of nonideal system components. Practical difficulties in measurement-system characterization are also discussed. An accurate circuit model for the measurement fixture is developed and its element values are determined. Measurement results are given showing the waveforms in a microwave transistor operated in the nonlinear region. The errors caused by signal processing are discussed     

A review of electromagnetic compatibility/interference measurement methodologies

This paper presents a review summary of radiated emission and susceptibility measurement methodologies currently used for assessing the electromagnetic compatibility/interference (EMC/EMI) characteristics of electronic devices and systems. In particular, measurement methods using open sites, transverse electromagnetic (TEM) cells, reverberating chambers, and anechoic chambers are discussed, in light of their technical justifications and bases, their strengths and limitations, and interpretation of the measured results.     

Quasi-peak detector model for a time-domain measurement system

In this paper, a quasi-peak detector mode for a time-domain electromagnetic interference (TDEMI) measurement system is described. Measurements were performed in the 30-1000-MHz range. The digital signal processing of EMI measurements can emulate in real time the modes of conventional analog equipment, e.g., peak, average, rms, and quasi-peak detector. With the presented time-domain measurement system, the measurement time can be reduced by a factor of ten. A novel signal recording routine for TDEMI measurements and quasi-peak detection is described. Measurement results obtained from the investigation of a drill machine, monitor, and laptop obtained with the TDEMI measurement system are discussed. The comparison of the results obtained with the described TDEMI measurement system and measurements performed with a conventional EMI receiver show an average deviation over the whole frequency range less than 3 dB.     

A low-noise multiresolution high-dynamic ultra-broad-band time-domain EMI measurement system

A time-domain electromagnetic interference (EMI) measurement system allows to reduce measurement time by several orders of magnitude in comparison with conventional systems. This will considerably reduce the costs of compliance tests. In this paper, a novel multiresolution time-domain EMI measurement system is presented. The multiresolution time-domain EMI measurement system exhibits several channels with limiters, amplifiers, and analog-to-digital converters. The amplitude range of the signal is subdivided into several intervals. In each interval the analog-to-digital conversion is performed with an amplitude discretization proportional to the width of the amplitude interval. The signal-to-noise ratio of the multiresolution time-domain EMI measurement system compared with a conventional time-domain measurement system for transient signals is enhanced by at least 50 dB. It is shown that the multiresolution time-domain EMI measurement system has a higher overload factor than conventional systems working frequency domain. The noise floor is 5 dB lower than the noise floor of a conventional EMI receiver. The multiresolution time-domain EMI measurement system shows a higher 1-dB compression point than conventional EMI receivers. Measurements were performed in the frequency range from 30 MHz to 1 GHz and compared with results obtained by an EMI receiver.     

Antenna time-domain measurement techniques

The results of an experimental study, in which time-domain pulses are used to measure the far-field characteristics of an antenna, are presented. Pulses with duration and rise time of the order of 50 ps are generated, in order to characterize the complete frequency (1-18 GHz) behavior of an antenna. An X-band standard-gain horn has been used to verify the overall performance of the measurement system. Excellent agreement between the time-domain and the frequency-domain measurements has been observed. This paper describes the antenna time-domain measurement (ATDM) technique, time-domain gating, the error sources, and the advantages and the disadvantages of such a measurement technique     

电子整流与逆变系统中电磁干扰分析

针对电子整流与逆变系统设计应用中的电磁干扰问题,详细介绍了电磁干扰特性以及常用电路的电磁兼容方法,通过对整流与逆变系统的干扰测试,提出了已经生产的产品形成干扰的抑制方法.测试结果表明该方法能够极大的减小系统中的电磁干扰.     

低频/甚低频电磁脉冲测量系统研究

为了准确地测量电磁脉冲（electromagnetic pulse,EMP）的波形,开展低频/甚低频（low-frequency/very low-frequency,LF/VLF）EMP的形成和传播机理研究,识别不同EMP的特征,并以此为依据来识别、确认雷电及核爆炸等现象,提出了一种高分辨率的EMP原始波形测量系统方案,同时针对LF/VLF这一较低的频段提出了一套有效的系统标校方法,实现了对EMP的连续、准确测量和快速有效判别,并能通过网络实时上传数据.系统采用正交环磁场天线和平板电容电场天线实现信号的接收,设计了低噪声高保真的信道调理电路和高速数据采集电路来实现信号的采集,利用高精度的授时模块为EMP信号标记时间戳,最后结合多点监测波形实现EMP定位估计.实测结果表明:该系统能够给出高分辨率、高精度的LF/VLF EMP波形;利用该系统组网可以实现远距离EMP源的定位,定位精度与目前近距离的定位手段相当.通过长期的运行,验证了该系统具有高可靠、低失真、判别准确、实时性强等特点.     

飞行器惯性测量组合的电磁敏感度评估

采用双因素等重复试验方差分析(ANOVA)方法实现对惯性测量组合的电磁敏感度试验评定.将惯性测量组合(IMU)参数标定测试与电磁敏感度试验相结合,克服了单独进行电磁敏感度试验难以区分评定等级的难题,从而获得参数标定位置因素与电磁干扰强度因素对惯性测量组合输出脉冲个数的单独影响和交互作用.     

基矛电磁波的低流速测量中干扰因素分析研究

介绍了电磁渡测量流速的基本原理一多普勒效应．分析了影响低流速测量的主要干扰因素一发射泄漏干扰和旁瓣干扰。根据接收信号中发射泄漏干扰不变的特性,提出了去均值滤波的方法来消除干扰,对数据进行预处理;根据旁瓣干扰的信号特性,提出了通过频谱加窗和二次加权平均法构造频域带通滤波器来抑制干扰的方法,在仿真比较完各个窗函数的性能之后,选定布莱克曼窗来进行频谱加窗。仿真分析表明,旁瓣干扰经频域带通滤波后得到了很好的抑制。最后通过实验测试验证了这些方法在流速测量中的显著效果。     

基矛电磁波的低流速测量中干扰因素分析研究

介绍了电磁渡测量流速的基本原理一多普勒效应．分析了影响低流速测量的主要干扰因素一发射泄漏干扰和旁瓣干扰。根据接收信号中发射泄漏干扰不变的特性,提出了去均值滤波的方法来消除干扰,对数据进行预处理;根据旁瓣干扰的信号特性,提出了通过频谱加窗和二次加权平均法构造频域带通滤波器来抑制干扰的方法,在仿真比较完各个窗函数的性能之后...     

A time-domain differential solver for electromagnetic scatteringproblems

The authors' objective is to extend computational fluid dynamics (CFD) based upwind schemes to solve numerically the Maxwell equations for scattering from objects with layered non-metallic sections. After a discussion on the character of the Maxwell equations it is shown that they represent a linearly degenerate set of hyperbolic equations. To show the feasibility of applying CFD-based algorithms, first the transverse magnetic (TM) and the transverse electric (TE) waveforms of the Maxwell equations are considered. A finite-volume scheme is developed with appropriate representations for the electric and magnetic fluxes at a cell interface, accounting for variations in material properties in both space and time. This process involves a characteristic subpath integration known as the `Riemann solver'. An explicit-Lax-Wendroff upwind scheme, which is second-order accurate in both space and time, is employed to solve the TM and TE equations. A body-fitted coordinate transformation is introduced to treat arbitrary cross-sectioned bodies with computational grids generated using an elliptic grid solver procedure. For treatment of layered media, a multizonal representation is employed satisfying appropriate zonal boundary conditions in terms of flux conservation. The computational solution extending from the object to a far-field boundary located a few wavelengths away constitutes the near-field solution. A Green's function based near-field-to-far-field transformation is employed to obtain the bistatic radar cross section (RCS) information     

Wide bandwidth time-domain electromagnetic sensor for metal targetclassification

A portable, wide bandwidth, time-domain electromagnetic sensor system has been developed and used extensively to measure the eddy current time-decay response of a wide variety of metal targets. The sensor has demonstrated the ability to measure metal target decay times starting approximately 3 to 5 μs after the transmitter current is turned off and target decay time constants as short as 1.4 μs. The sensor has demonstrated the potential for detecting very low-metal content mines due to the void they create in some types of electrically lossy soils. The development of the sensor is described in detail, and time-decay data are shown for a variety of metal targets, including low metal antitank and antipersonnel mines     

A path integral time-domain method for electromagnetic scattering

A new full wave time-domain formulation for the electromagnetic field is obtained by means of a path integral. The path integral propagator is derived via a state variable approach starting with Maxwell's differential equations in tensor form. A numerical method for evaluating the path integral is presented and numerical dispersion and stability conditions are derived and numerical error is discussed. An absorbing boundary condition is demonstrated for the one-dimensional (1-D) case. It is shown that this time domain method is characterized by the unconditional stability of the path integral equations and by its ability to propagate an electromagnetic wave at the Nyquist limit, two numerical points per wavelength. As a consequence the calculated fields are not subject to numerical dispersion. Other advantages in comparison to presently popular time-domain techniques are that it avoids time interval interleaving and it does not require the methods of linear algebra such as basis function selection or matrix methods     

干涉法测量中的信噪比

本文根据现代随机介质中波的传播理论,从二阶互相干函数出发导出了干涉图信噪比的分析表达式,对不同情况下的结果作了讨论,表明信噪比决定于光束的波长与宽度,传播距离和湍流强度等因素。在一定条件下信噪比将趋向于一个常数,可以用强度起伏的饱和效应来解释这个现象。     

基于两步相移干涉的微表面形貌检测系统

为了精确稳定地测量物体微表面形貌,设计了一种基于改进迈克尔逊结构的空间两步相移干涉系统。该系统在泰曼-格林偏振干涉仪的基础之上,使用改进的迈克尔逊结构实现分光,采用偏振方向分别为0和45的两偏振片作为相移器件,在单个CCD相机中同时记录两幅具有90相移的干涉图像,然后由离散希尔伯特变换法提取相位,获取物体表面形貌信息。搭建了两步相移干涉光路,并通过对玻璃平板表面的检测,验证了该系统的可行性。结果表明,在实验室环境下系统重复测量结果的均方根误差小于0.02,在实际微表面测量中具有良好的稳定性。     

Pastes for electromagnetic interference shielding

A paste has been developed for electromagnetic interference shielding by mixing stainless steel fibers (8-μm diameter) and graphite flakes (5 μm) in a water-based graphite colloid (containing submicron graphite flakes and a binder) in a volume ratio 0.5:20:100. The resulting coating of thickness 0.1–0.2 mm after drying exhibits shielding effectiveness of 34 dB at 1 GHz, primarily due to reflection. The paste is superior to those containing graphite flakes or carbon filaments (0.1-μm diameter), due to the higher shielding effectiveness of the steel fibers. The graphite flakes in the paste serves to help suspend the steel fibers, in addition to contributing to shielding.     

基于时域光谱系统的太赫兹圆柱RCS 测量

雷达散射截面（RCS）测量对于太赫兹雷达系统论证设计具有重要意义。详细描述了时域光谱（TDS）系统测量RCS 的原理,以及实验方案的设计。基于TDS 系统对太赫兹频段圆柱RCS 进行了测量实验,获得光滑和粗糙圆柱在太赫兹频段下的回波,对光滑圆柱回波进行傅里叶变换得到其宽带 RCS,与理想圆柱RCS 的物理光学解进行比较,发现RCS 理论值与测量值基本一致,验证了TDS 系统可用于太赫兹频段目标RCS 的测量;同时将光滑圆柱和粗糙圆柱的RCS 测量值进行对比分析,结果表明:太赫兹频率越高,粗糙面对RCS 的影响越大,粗糙度大于八分之一波长为粗糙面的传统定义须重新考虑。     

电磁场时域数值算法的新进展

电磁场时域计算方法由于一次计算可以获得目标的时域响应,结合傅里叶变换得到宽带信息等的优势越来越受到关注.本文介绍了近年来时域有限差分（finite-difference time-domain,FDTD）法和时域有限元（finite element time-domain,FETD）无条件稳定算法方面的研究进展以及FETD算法的更新方案——时域非连续伽辽金（discontinuous Galerkin time-domain,DGTD）方法的新进展.