源搅拌混响室的仿真分析与实验研究

根据谐振腔理论,分析了理想情况下影响源搅拌混响室性能的主要因素,通过数值计算对其进行仿真验证,确定了影响混响室场均匀性的主要因素有激励天线的极化方向,摆放位置以及激励源的位置数等;在此基础上提出了一种可行的源搅拌方案,通过实验的方法,在满足一定采样数情况下,实现了混响室较好的场均匀性;同时借助K-S拟合对源搅拌混响室测量场值的统计特性进行了分析,结果表明:源搅拌混响室的一维场分布服从瑞利分布。     

双发射天线对混响室场性能影响的数值分析

提出了双天线激励混响室的方法,研究了双天线激励对混响室场性能的影响。分析了双天线改善混响室场均匀性的原理,对单天线激励下的混响室模型以及处于不同位置的双天线激励下的混响室模型进行了仿真计算,从场均匀性和场强两个方面研究了双天线对混响室场性能的影响,对双天线影响场强的机理进行了分析。研究表明:采用双天线激励改善了混响室工作区域的场均匀性;采用双天线可以降低对功率放大器的要求,降低大型混响室测试成本。最后对双发射天线在大型混响室中的应用进行了探讨和展望。     

2012 IEEE EMC国际学术研讨会——混响室

Validation of a One-Antenna Reverbera-tion-Chamber Technique for Estimatingthe Total and Radiation Efficiency of anAntenna摘要:使用单天线激励方式分析估计混响室中天线的总效率和散射效率,与其他测试方式及不同天线类型的测试结果进行了比较,验证了此方法的有效性。关键词:混响室;单天线激励;辐射效率视点:使用单天线技术估计天线效率。混响室非常适合对天线或待测设备进行散射功率测量,因此也很容易用于确定其散射效率     

Validation of a One-Antenna Reverberation-Chamber Technique for Estimating the Total and Radiation Efficiency of an Antenna

使用单天线激励方式分析估计混响室中天线的总效率和散射效率,与其他测试方式及不同天线类型的测试结果进行了比较,验证了此方法的有效性.     

电磁兼容试验的本征混响室技术

本征电磁混响室既继承了混响室的优点,又能克服机械搅拌混响室效率低、电子搅拌混响室不能进行辐射发射测试和低频性能较差的问题,是大型装备系统/设备级EMC试验场地最有希望的研究方向之一。根据本征电磁混响室的基本结构和工作原理,分析了本征电磁混响室在理论研究、结构设计和测试应用中需要解决的本征电磁混响室电磁场的模式理论与统计分布规律、腔体几何外形与散射器的结构优化、性能指标分析与评估、数值仿真、测试应用方法与流程等方面的关键技术及其研究思路和方法,为本征电磁混响室技术的研究提供一定的参考和借鉴。     

混响室发射天线指向对场均匀性影响研究

采用基于矩量法的电磁仿真软件FEKO建立了混响室仿真模型,并对步进模式下的混响室模型进行了数值计算.将混响室数值计算与遗传算法相结合,通过仿真计算与理论分析研究了混响室发射天线指向对场均匀性的影响.研究结果表明:改变发射天线指向,其本质是改变混响室各模式前的加权系数,导致表征混响室工作区域场均匀性的电场标准偏差随之发生改变.发射天线指向处于最优配置时,工作区域各轴向电场标准偏差较初始状态有所下降,说明通过优化提高了工作区域场均匀性.     

EMC混响室电磁场模态研究

混响室谐振腔激励的三维电磁场的推导一般采用并矢格林函数的方法,物理意义不太明显。用本征函数迭加的方法推导混响室有源激励的电磁场分布公式,有利于正确建立混响室电磁结构模型,树立正确的物理概念。并根据公式及其推导过程,分析了混响室EMC电磁工作机理,以此将EMC混响室电磁工作状态按模式状况进行了系统地分类,为混响享研究设计提供理论指导。     

电场传感器校准的等效天线系数法

针对电场传感器在1 GHz以上频段高于200 V/m场强的校准需求,提出了等效天线系数法.该方法借用了天线系数的概念,在混响室中首先通过现有场强标准装置传递得到小场强时接收天线的等效天线系数,再利用等效天线系数对混响室中的大场强定标,从而实现电场传感器的大场强校准.混响室中采用等效天线系数法定标的大场强与采用统计方法计算得到的大场强相比较,场强偏差满足系统不确定度要求,说明了等效天线系数法的合理性.该方法借助混响室的特点和天线系数概念,将电场传感器校准幅度提升至200 V/m以上,为大场强测量的准确性提供了依据.     

混响室随机多径衰落电磁环境的实验研究

混响室内的电磁波经搅拌器和室壁多次反射,形成了多径衰落,利用混响室模拟了实际无线通信中2种常见的多径衰落环境。对混响室内的发射天线、接收天线以及损耗物进行配置,设置了6组实验。其中一组是经典混响室(发射天线不可直接辐射接收天线)的实验,实验结果表明,当工作频率、搅拌器转速控制得当时,混响室能够模拟各向同性的瑞利衰落场环境。另外5组是发射天线直接辐射接收天线的实验。实验结果表明,当发射天线和接收天线存在直接耦合分量时,混响室能够模拟莱斯衰落场环境,并且通过控制天线正对距离、工作频率以及损耗物加载量可改变直射波和反射波强度的占比,使混响室内的电场获得不同的莱斯K因子。其中损耗物加载量对莱斯K因子的影响最大,不仅会降低混响室的品质因数,还使混响室内电磁场的边界条件更为复杂,从而使混响室内的环境更接近于真实的无线通信环境。     

Aspects of Field Statistics inside Nested Frequency-stirred Reverberation Chambers

在一个单一机械搅拌的混响室中,电场分量的幅度服从瑞利分布;但是对于嵌入在大型混响室中的箱体内部场的概率分布函数(PDF)却是未知的。通过研究频率搅拌的混响室,假设场的PDF为已知的,然后通过一系列拟合良好性检验(K-S检验)进行验证。     

Experimental determination of the higher electric field level inside an overmoded reverberation chamber using the generalized extreme value distribution

Reverberation chamber (RC), in which a complex electromagnetic environment is created, is of great interest as a versatile test and measurement tool, and its performance is conveniently evaluated through the field statistics. Following a previous paper in which the generalized extreme value (GEV) distribution was proposed to model the maximum field inside an RC, this work presents an experimental validation of the GEV use for the overmoded RC. The electric field is measured with a small sensor for a large number of points inside the RC, and the GEV parameters are accurately estimated. Since the maximum field distribution for this overmoded RC is found to be of reverse Weibull type, the field distribution is right bounded by a higher level that can be determined.     

时域有限差分法分析混晌室中场的均匀性

针对目前仿真分析混响室内的场分布过程中计算量大、耗费时间长和对计算机配置要求高的现状,用在一定的约束条件下随机分布于球面上的一组等效源辐射的平面电磁波叠加而成的一维推进的重叠平面渡模拟搅拌器搅拌过程中混响室内的电磁波,并采用时域有限差分法(FDTD)法对基于上述模型的混响室内的场分布进行了仿真计算,得出了使混响室内场分...     

顶角设置QRD散射体的混响室内场均匀性分析

提出了混响室内设置散射体的一种新方法。用FDTD方法对该结构混响室内的场进行了仿真分析,并与无搅拌器及散射体结构的混响室内的场均匀性、散射体位于混响室内6个壁面时混响室内的场均匀性进行了分析比较。结果表明:本文所提出的8个顶角处均设置QRD散射体的方法可有效提高混响室内的场均匀性,实现了进一步提高混响室内场均匀性的目的。     

Maximum Field Inside a Reverberation Chamber Modeled by the Generalized Extreme Value Distribution

Classically, the statistical model of the maximum field inside a reverberation chamber (RC) is derived from the field magnitude model that is only known for the overmoded RC. We propose in this paper to model the maximum field by the generalized extreme value (GEV) distribution, as an application of the Fisher-Tippett theorem that formulates the asymptotic distributions of sample maximum. As the knowledge of the parent distribution (field magnitude) is not required, the GEV distribution is suitable for both overmoded and undermoded regimes (few modes excited). A Monte Carlo simulation illustrates the use of the GEV distribution for the overmoded RC. Modal FEM analysis of the RC extends the application to the undermoded regime. Special attention is brought to the issue of GEV parameter estimation: The so-called L-moments technique is advantageously employed to estimate the parameters from the small data sample. Dispersion of the estimated parameters is approximated and reduced by averaging uncorrelated values obtained from a narrow frequency band     

Modeling of the Reverberation Chamber Method for Determining the Shielding Properties of a Coaxial Cable

The paper considers the reverberation chamber (RC) method for the measurement of the shielding effectiveness (SE) of coaxial cables with braided shields. In particular, the voltage at the cable termination is numerically computed and compared to that measured in an RC. The RC field is represented by a finite summation of random plane waves, and a finite-difference time-domain (FDTD) code is used to calculate the outer shield current induced by the RC field. The knowledge of the shield current distribution allows the determination of the voltage at the cable termination's internal circuit after a proper numerical averaging. It is then compared to the measured voltage averaged over stirrer rotations. The method is applied to a commercially available cable model RG58, and using the nominal value for the transfer impedance of this cable type gives results in a satisfactory agreement with the measurements. Finally, the possibility of recovering the transfer impedance from the measured SE of the RC is discussed.     

Numerical and experimental analysis of the field to enclosure coupling in reverberation chamber and comparison with anechoic chamber

This paper presents a study of coupling between an external field and a metallic enclosure with a long aperture in the frequency range which includes several box resonances. A reverberation chamber (RC) and an anechoic chamber (AC) are considered as a field generation structure. In both cases, a customized FDTD code is used to calculate the current induced by the external field in a loop placed inside the enclosure. In order to simulate the AC facility, a single plane wave is used to represent the test field, whereas for the RC, the field is represented by a proper superposition of random plane waves. Numerical results are experimentally validated. The proposed method is useful to investigate the performance of the enclosure during its early design stage before the realization of a prototype.     

Differential method for Hall-coefficient measurements in an a.c. magnetic field

A compensation method for Hall-coefficient measurements with an audiofrequency magnetic field and a direct sample current is described. An a.c. magnetic field is generated in a ferritecored coil working in a series-resonance circuit.1 Compensation is achieved over a wide frequency range of the magnetic field by the use of RC bridges and a differential amplifier. The method eliminates spurious e.m.f.s and after small modifications permits the (pulsed) changes of Hall coefficient to be measured with high sensitivity.     

Statistical model of an undermoded reverberation chamber

Weibull distribution is adopted to model the electric field component of a Reverberation Chamber (RC). Its first property is to include the asymptotic laws, such as Rayleigh and exponential, and its main advantage lies in the fact that the Weibull shape parameter enables a model of the departure from overmoded to undermoded RC regime. Applications are given, such as an RC modal finite element modeling and a Monte Carlo simulation: they prove that the Weibull two-parameter distribution correctly models the quality factor influence. Moreover, the relevance of the use of this extreme value distribution is illustrated.     

腔体形状对混响室内场均匀性的影响

针对高功率微波(HPM)激励下的混响室,研究了不同腔体形状对混响室内电场分布的影响。根据理想封闭矩形腔体内电磁场表达式,分析了腔体形状对混响室内场特性的重要影响,并确立以时间窗为研究单元的统计计算方法描述混响室内的瞬态场特征。重点研究腔体形状对腔体内场均匀性的影响效果,主要对比电场的最大值、分布标准差以及各向同性等指标。研究结果表明:在矩形谐振腔中引入复杂结构能够降低场分布标准差,提高能流分布的均衡性,实现均匀的电磁场环境。     

Dynamically Driven Emergence in a Nanomagnetic System

Emergent behaviors occur when simple interactions between a system's constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring-shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field-dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays’ properties (e.g., non-linear behavior, “fading memory” to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers.