On the Interplay Between the Equipment Under Test and TEM Cells

In all applications of the gigahertz transverse electromagnetic (GTEM) cell, there is an interplay between the equipment under test (EUT) and the cell reflecting metal walls, as represented by images of the EUT. Moreover, owing to the multiple reflections within the cell and to its tapering structure, the phenomenon of illumination and reillumination of the EUT can hardly be avoided. These problems, known as reactive effects of the cell, are investigated in this paper. A simple new approach for an efficient investigation of the interactions between the EUT and the cell is provided. Closed-form expressions for the reflection coefficient, the relative deviation in field, and the relative error in the induced current caused by the reactive effect of the cell are derived. Each of these expressions encompasses both the mutual influence of the EUT's radar cross section (RCS) and the reactive effects of the cell. It is shown that depending on the frequency-dependent phase factor e^jpsi, strong and weak test conditions may occur since the overall incident field will exhibit maxima and minima. Hence, evidence showing that the total incident field impinging on the EUT generally deviates from the primary excited TEM field is provided. Moreover, the relative deviation in the field and the relative error in the induced current are quantified. Finally, the frequency dependence of the well-known one-third-rule of thumb is demonstrated.     

TEM传输室置入金属EUT后场分布的边界元分析

横电磁波传输室广泛应用于电磁兼容试验中，当置入受试设备后，其中的场分布会发生扰动。本文采用边界元法分析了横电磁波传输室中置入金属箱体的受试设备后场分布的规律，对受试设备所受暴露场的场强进行了计算，并提出了具体的估算方法。对空载时横电磁波传输室的场分布进行了测量，测量结果证实了计算方法的正确性。     

加载横电磁传输室中的电场分布计算

用“准静脉法”研究了当工作频率远低于截止频率时,放置于横电磁传输室中的被测物体中的电场分布。文中使用的是有限差分法,给出了在三维空间中不同介质交界面上拉普拉斯方程的差分格式。计算结果表明当把ＥＴＵ放入ＴＥＭＣｅｌｌ的中心时,ＥＵＴ横截面上的电场分布是均匀的。     

Impedance of TEM cells with equipment under test

A quasi-Tem approach based on conformal transformation is used to determine the characteristic impedance of a TEM cell with symmetric equipment under test (EUT), for efficient operation of the TEM cell. Some numerical results are presented.<>     

Investigation of radiated susceptibility during EFT tests

The aim of this paper is to focus on a problem: during an electrical fast transient (EFT) conducted susceptibility test, a very strong radiated field is produced and a radiated coupling with the internal circuitry of the equipment under test (EUT) occurs. Therefore in case of EUT malfunctions, it is difficult to understand whether the resulting failures are due to the injected conducted current (requiring a filtering action) or to the impinging radiated EM field (requiring a shielding action). A model to describe the EM radiation, coming from the current flowing along the EUT power cord, is presented as well as its experimental validation     

Current‐Induced Restructuring and Chemical Modification of N‐Doped Multi‐walled Carbon Nanotubes

Multi‐walled carbon nanotubes (MWCNTs) have long been anticipated as candidates for electrical components in an increasingly miniaturized electronics industry due to their inherent electrical properties. It is possible to manipulate and control these properties by introducing dopants such as N, B, and P. Although some current‐induced structural changes in MWCNTs have been observed, no systematic study has been carried out to explore the correlation of changes in the internal structure with the electronic behavior of doped‐MWCNTs in terms of the current densities present. In situ transmission electron microscopy (TEM) investigations are presented here of individual, N‐doped MWNCT (N‐MWCNTs) using the in situ TEM/scanning tunneling microscopy (TEM/STM) Nanofactory© holder. It is observed for the first time that N‐MWCNTs not only undergo current‐induced structural transformation; i.e., from the typical bamboo structure of N‐MWCNTs to the stacked cones, but also—and most importantly—the complete removal of the dopant causes a significant change in the electronic behavior. This has serious implications for the use of doped CNTs as electronic components, especially since tremendous efforts are being made to synthesize CNTs with controlled dopant concentrations.     

基于频域块LMS算法的实时虚拟暗室测试方法

针对电磁辐射现场测试被测设备信号和干扰未知的情况,提出了一种基于频域块最小均方算法的实时虚拟暗室测试方法。该方法采用双通道接收机,根据测试通道和背景通道中干扰信号的相关性设计自适应滤波器,在频域对背景通道信号滤波以趋近测试通道中的干扰分量,采用瞬时双通道信号迭代更新滤波器系数,滤波器系数收敛后系统输出中只有被测设备信号。仿真与分析表明,该方法在背景通道有无被测设备信号泄露的情况下都能有效抑制干扰,与基于时域最小均方算法的方法相比,在滤波器长度相同的情况下其计算复杂度更低,适用于实时现场测试。     

定向辐射式核电磁脉冲场模拟器的研制

针对大型受试设备核电磁脉冲抗扰度试验评估要求，研制了基于Marx发生器脉冲源和横电磁波（Transverse Electro Magnetic，TEM）喇叭天线的可移动、极化方向可调的定向辐射式核电磁脉冲模拟器.实验分析了不同极化方向和终端负载对脉冲波形的影响，确定了定向辐射式核电磁脉冲模拟器的均匀区域.结果表明:辐射电磁脉冲场可用区域为近场区域，随着与口径面距离的增大，峰值场强近似按1/d2衰减，脉冲宽度显著减小；与传输式模拟器相比，辐射式核电磁脉冲模拟器具有更大的均匀区域，更适合大型设备电磁脉冲抗扰度试验.     

Maximum power available to stress onto the critical component in the equipment under test when performing a radiated susceptibility test in the reverberation chamber

We show, by theory and experiment, that the stress put onto the equipment under test (EUT) when performing a radiated susceptibility test in a reverberation chamber (RC) is not affected by either the directivity pattern or the receiving polarization pattern of the EUT. The stress put onto the EUT will differ from the stress measured by a reference antenna in the RC. We have developed distribution functions for this discrepancy.     

A Method to Minimize Emission Measurement Uncertainty of Electrically Large EUTs in GTEM Cells and FARs Above 1 GHz

This paper presents an emission measurement technique with reduced uncertainties for electrically large equipment under test (EUTs) in gigahertz transverse electromagnetic (GTEM) cells and fully anechoic rooms (FARs) above 1 GHz. A small and a large EUT were measured and the results obtained in the GTEM cell were validated against those obtained in a FAR. Measurements in a FAR were made, for the small EUT, in the conventional way with an azimuth scan and, for the large EUT, with a limited antenna height scan. Key findings are that similar scanning is required in the GTEM cell and that the three-orthogonal-position (TOP) method of EN61000-4-20 is not appropriate for EUTs that have multilobed radiation patterns. In other words, GTEM cells and FARs are sensitive to directional properties of EUTs, and both methods require further scanning for electrically large EUTs     

Induced foot-currents in humans exposed to VHF radio-frequency EMfields

In order to limit the specific absorption rate (SAR) in the ankles of a person exposed to an electric field at frequencies below 100 MHz, induced current limits are prescribed in the 1992 ANSI/IEEE safety standard. The authors have measured the induced currents passing through the feet of nine subjects exposed to vertically polarized electric fields from nearby antennas, transmitting at frequencies between 90 and 104 MHz (in the FM broadcast band). The experimental results are in excellent agreement with the results obtained analytically for frequencies up to 110 MHz. The analytical results were obtained by applying the finite difference time domain (FDTD) method to an anatomically-based model of an average height male (1.75 m) and to a model of the tallest subject in the study (1.91 m). For the mean height of the nine subjects (1.75 m), the measured induced foot current for a unit strength vertically polarized electric field varied with frequency from 4.46 to 3.45 mA/(V/m) for frequencies between 90-104 MHz. For the tallest subject (1.91 m), the corresponding values ranged from 5.42 to 4.45 mA/(V/m), Foot currents in excess of the induced current limits in RF safety guidelines for both the controlled and uncontrolled environments could result even when the vertical component of the incident electric fields comply with the corresponding field limits. It is important, therefore, to not only measure the E- and H-fields, but also the induced currents up to the recommended maximum frequency of 100 MHz, and perhaps up to the upper frequency of the FM broadcast band (108 MHz)     

Theoretical investigation of the field conditions in a vibrating reverberation chamber with an unstirred component

In this paper, we examine the use of a vibrating reverberation chamber in which an equipment under test (EUT) is directly illuminated by a source antenna. A three-dimensional theoretical model, based on a simplified ray tracing method has been applied on a reverberation chamber whose dimensions were varied. The field distribution together with the field homogeneity was investigated, introducing the Rice distribution due to the presence of the line-of-sight component between the antenna and the EUT.     

A treatment of the phase properties of GTEM to open-area test-sitecorrelation techniques

The gigahertz transverse electromagnetic (GTEM) cell is a very attractive environment for the measurement of radiated emissions from electrically small equipment under test (EUTs). However, the GTEM is only accepted by the relevant measurement standards as long as the measurements in a GTEM can be used to predict the field that a particular EUT would produce on an open-area test site (OATS). Techniques for predicting equivalent OATS radiated fields from measurements in a GTEM have been developed. The techniques include the assumption that the dipole moments, which represent the radiation of an EUT, are all in phase. We analyze the case where the EUT dipole moments are not in phase and propose a new upper limit for the predicted OATS radiated field. Our new limit is up to 5 dB greater than the maximum predicted by the existing techniques, but over most of the frequency range the difference with the existing technique is about 3 dB     

Targeted Resonance Control in a TEM Cell

We investigate extending the upper frequency limit of an asymmetric ldquoCrawford-style' transverse electromagnetic (TEM) cell with targeted resonance control. Focusing on the fundamental TE cavity resonance, an active feedback cancellation system is applied with the aim of reducing the resonant field amplitude without affecting the desired TEM mode. A half loop J-dot current probe is positioned with a vertical polarization on one wall of the TEM cell to measure the wall currents generated from the TE resonance. An identical probe is placed on the facing wall that is connected to the first through a negative feedback chain. The second loop's purpose is to excite a field that has the appropriate magnitude and phase to attenuate the TE resonance amplitude. Experimental application achieved a 17-dB reduction in the amplitude of the resonance field. The method is also outlined with respect to the TE resonance. This system is planned for full-scale implementation into a hybrid reverberation/TEM whole-aircraft electromagnetic vulnerability testing facility.     

Correlation Between EUT Failure Levels and ESD Generator Parameters

Some system-level electrostatic discharge (ESD) tests repeat badly if different ESD generators are used. For improving repeatability, ESD generator specifications have been changed, and modified generators have been compared in a worldwide round robin test. The test showed up to 1 : 3 variations of failure levels. Multiple parameters that characterize ESD generators have been measured. This paper correlates the parameters to test result variations trying to distinguish between important and nonrelevant parameters. The transient fields show large variations among different ESD generators. A correlation has been observed in many equipment under tests (EUTs) between failure levels and the spectral content of the voltage induced in a semicircular loop. EUT resonance enhances the field coupling, and is the dominate failure mechanism. The regulation on the transient field is expected to improve the test repeatability.      

The Detection of Induced Polarization with a Transient Electromagnetic System

The study of two-dimensional TEM models consisting of a cylinder in a conductive host using measured rock properties show that TEM surveys are capable of detecting induced polarization (IP) effects. A case history showing a comparable type of response is presented. The IP effects manifest themselves in extreme cases as negatives in the response and in other cases as anomalously high apparent resistivities. The models used allow a study of the variation of responses produced by varying the Cole-Cole constant for the cylinder properties. The results suggest that the different parameters produced distinct effects in the response. If the rock properties reported in the literature are correct, it appears quite feasible to observe IP effects via TEM using an ungrounded system. There may also occur a set of negatives in the response of a cylinder which are associated with high-conductivity contrasts and geometrical effects. In the cases studied these two groups are readily distinguished. IP effects might be interpreted from a family of zero responses (when these occur), apparent resistivity/time sections or by stripping away the host rock response and comparison with a uniform polarizable ground. There is a great deal of geometrical information about the scattering body at early times our of reach of many contemporary instruments.     

On the Measurement of Total Radiated Power in Uncalibrated Reverberation Chambers

A novel experimental procedure to measure the total radiated power of an equipment under test (EUT) placed in a reverberation chamber (RC) is presented. In contrast to the well-established method of the IEC 61000-4-21, this new procedure does not rely on information obtained during the empty chamber calibration or the calibration with the EUT in place. Thus, the method is simpler, faster, and may have a smaller uncertainty budget.     

Electromagnetic-Field Distortion Due to a Conducting Rectangular Cylinder in a Transverse Electromagnetic Cell

This paper deals with the distortion effects in a TEM cell resulting from loading by the object under test. To insure that higher order modes are ruled out as contributing factors, a brief discussion of the cutoff frequencies of these modes is presented. The paper then proceeds to a theoretical and experimental analysis of the loading effects. In the theoretical analysis for the loading effects, i.e., the electromagnetic-field distortion caused by an object under test in a TEM cell, the frequency-domain integral equation for the magnetic field, or equivalently, the current density on the surface of a perfectly conducting cylinder in a parallel-plate waveguide, is solved by the method of moments to predict the degree of magnetic-field distortion. The experimental investigations are performed by mounting a number of electrically small half loops on the surface of the conducting cylinder in a TEM cell. The loading effects in terms of magnetic-field distortion are analyzed as the ratio of one of the object dimensions (height) to the separation distance between the inner conductor and the ground plane of the TEM cell. Also, the response of an electrically small loop to both the magnetic and electric components of the electromagnetic field is used to measure the phase relation between the magnetic and electric fields, which in turn can be used to determine the degree of degradation of the TEM mode due to the presence of the conducting cylinder. These theoretical and experimental results are compared with the available quasi-electrostatic results.     

Induced current in a Bi2Sr2CaCu2Ox superconductor tube

Experiments were conducted to measure the induced current in a high-temperature Bi₂Sr₂CaCu₂O_x superconductor tube that was excited by an external coil driven by an AC sinusoidal voltage source. Experimental data were obtained for tests without and with an iron core inside the superconductor tube. All of the tests were conducted at 77 K and an excitation frequency of 60 Hz. The results showed that immediately after field penetration, the induced current (RMS value) decreased from the critical current, then began to recover, and eventually approached the critical current again at a high excitation current. Before field penetration, the induced current was mainly shielding current, which is 180 ° out of phase with the excitation current. After field penetration, the induced current consisted of two parts, a shielding current that led the excitation current by 180 ° and an inductive current (Faraday's law) that led the excitation current by 90 °. The presence of the iron core amplified the drop in induced current immediately after field penetration and delayed the growth of the inductive current after field penetration.