镜像对称结构对多馈源混响室场性能的影响

为解决混响室大体积与场性能高要求之间的矛盾,提出了一种基于镜像原理的多馈源混响室的设计思想,从原理上分析了镜像多馈源混响室的可行性和有效性,并通过仿真计算研究了镜像双馈源混响室的场性能.结果表明,在输入功率一定时,两个单混响室系统组合成镜像双馈源混响室后,在工作区域的场均匀性能不下降的基础上,不但可用于电磁兼容测试的工作区域体积大幅度增大,而且测试区域的电场强度也得到了提高.同时,对镜像多馈源混响室进行了进一步的扩展分析,得出了组成镜像多馈源混响室的单混响室系统数量的理论表达式.     

Comparison Between Different Criteria for Evaluating Reverberation Chamber Functioning Using a 3-D FDTD Algorithm

This paper is devoted to the comparison between different criteria used to evaluate the functioning of a mechanically stirred reverberation chamber. Usual criteria based on power or electric fields are considered, and we also propose a criterion based on the Kolmogorov-Smirnov test, called in this paper ldquosuccess ratio to Kolmogorov-Smirnov testrdquo (SRKS). The SRKS represents the acceptation ratio of this test applied at several points of the working volume, when considering a field component and its associated theoretical distribution. After a presentation of the criteria and of the studied chamber, data issued from 3-D finite-difference time-domain simulations and measurements are used to analyze the chamber functioning by the use of these criteria. This study is performed on a large frequency band, in the lossless case as well as with a lossy chamber, and for several stirrer shapes, to emphasize the influence of these parameters. The comparison of the usual criteria with the SRKS shows the SKRS is an accurate test to estimate the lowest usable frequency of a given reverberation chamber.     

Use of Reverberation Chambers to Determine the Shielding Effectiveness of Physically Small, Electrically Large Enclosures and Cavities

With the proliferation of small electric devices in recent years, along with various other applications, there is a growing need to test and determine the shielding properties or shielding effectiveness (SE) of physically small (but electrically large) enclosures or cavities. In this paper, we discuss how a reverberation chamber technique can be used to measure the SE of such enclosures. The approach consists of placing the small enclosure inside a reverberation chamber and using frequency stirring to excite the reverberation chamber. A small surface probe (i.e., a monopole) is mounted on the inside wall of the small enclosure to measure the power level inside the small enclosure. We present measured data from various other reverberation chamber approaches obtained from various enclosure configurations. The data from these other reverberation chamber approaches are used to validate the proposed approach. We also compared measured data to theoretical calculations of the SE for two small enclosures with circular apertures. These various comparisons illustrate that the proposed technique is a valid approach for determining the SE of physically small (i.e., cubic enclosure dimensions of the order of 0.1 m and smaller), but electrically large enclosures (that support several modes at the lowest frequency of interest).      

A Topology Control Approach Reducing Construction Cost for Lossy Wireless Sensor Networks

In lossy wireless sensor networks, many links suffer from significant quality variation with time and environments. Topology control approaches need to consider such stochastic nature to yield different topologies for different application requirements. However, the metric of links must be timely obtained to speed up the topology construction. In fact, the existing approaches address it by passive monitoring, which is not timely adaptive to link quality variation. Also, timely access to the metric of all links at all power levels causes a large burden on topology control operation. We do not insist on getting the link metrics of all power levels at a time. Most urgently needed link metrics are firstly obtained by an active probing mode in this paper. If these link metrics do not meet the topology performance requirements, sub-urgently needed link metrics will be obtained on demand. At the same time, each node performs a topology control process based on the information in a smaller range (e.g., 1-hop neighborhood). Therefore, our approach has the low construct cast, which is proved in this paper. The simulation results also show that our approach outperforms the existing typical works in terms of average transmission power level, though it is slightly less efficient in terms of average delivery rate, average end-to-end delay and total energy consumption. In addition, our approach has advantage in terms of standard deviation of remaining energy under the relatively smaller required path quality bound or lower node density.     

Shielding effectiveness measurements of materials using nested reverberation chambers

The use of reverberation chambers for determining the shielding effectiveness has the advantage over other techniques in that the reverberation chamber exposes the material to a more realistic environment. That is, in a reverberation chamber, the fields are incident on the material with various polarizations and angles of incidence. There are various reverberation chamber techniques found in the literature and international standards. These techniques can give incorrect results because aperture and cavity-size effects are not correctly accounted for. In fact, we show that for no sample in the aperture, these techniques give a nonzero result for shielding effectiveness. In this paper, we review existing techniques and present a new technique for determining the shielding effectiveness of materials from nested reverberation-chamber measurements. The new approach accounts for aperture, cavity size, and chamber loading effects. Various examples are presented to illustrate the utility of the new approach, and a discussion on edge treatments of the materials is given.     

混响室条件下的辐射敏感度测试新方法

提出了一种基于统计平均思想的新的辐射敏感度测试方法,在大量实验的基础上验证其可靠性。两种工作模式分别采用位于测试区域内的接收天线在统计平均时间内接收环境场的平均值和所有步进位置测试结果的平均值作为最终测试结果。实验结果表明该方法测试过程简单,能够得到给定设备在任意敏感频点的辐射敏感度阈值,且具有良好的测试可重复性。将国际电工委员会(IEC)颁布的IEC61000-4-21第二版新标准与旧版本中关于步进模式最少独立采样位置的数量做了简要对比,通过实验数据验证了新版本的测试结果。     

A closer look at reverberation Chambers - 3-D Simulation and experimental verification

This paper presents three-dimensional (3-D) full-wave simulations of the electromagnetic field inside a medium-sized reverberation chamber. A frequency-domain method-of-moments approach based on the electric field integral equation is used. A synopsis of the computational challenges particular for reverberation chambers is described and a detailed overview on the chamber modeling procedure is given. The electric field inside the chamber is computed and the influence of small geometric details and asymmetries is investigated as well as the effect of different excitations and stirrers. It is demonstrated that a statistics-based validation of reverberation chamber simulations is insufficient. To validate simulation results, therefore extensive near-field measurements inside the prototype reverberation chamber are performed. The complete 3-D reverberation chamber simulation, considering stirrers, door, and various practical excitations, accurately predicts the fields within the chamber in the important lower-to-medium frequency range and thus represents a reliable tool facilitating reverberation chamber optimization.     

On sequential frame synchronization in AWGN channels

We present a framework for the analysis of frame synchronization based on synchronization words (SWs), where the detection is based on the following sequential algorithm. The received samples are observed over a window of length equal to the SW; over this window, a metric (e.g., correlation) is computed; an SW is declared if the computed metric is greater than a proper threshold, otherwise the observation window is time-shifted one sample. We assume a Gaussian channel, antipodal signaling, equally distributed data symbols, and coherent detection, where soft values are provided to the frame synchronizer. We state the problem starting from the hypothesis testing theory, deriving the optimum metric [optimum likelihood ratio test (LRT)] according to the Neyman-Pearson lemma. When the data distribution is unknown, we design a simple and effective test based on the generalized LRT (GLRT). We also analyze the performance of the commonly used correlation metric, both with "hard" and "soft" values at the synchronizer input. We show that synchronization can be greatly improved by using the LRT and GLRT metrics instead of correlation and that, among correlation-based tests, sometimes hard correlation is better than soft correlation. The obtained closed-form expressions allow the derivation of the receiver operating characteristic (ROC) curves for the LRT and GLRT synchronizers, showing a remarkable gain with respect to synchronization based on correlation metric.     

Limit distributions for imperfect electromagnetic reverberation

Investigates departures from ideal circular Gauss normality for the statistical distribution of complex fields in undermoded mode-tuned or mode-stirred reverberation chambers. A physical nonlinear model is developed, in which the energy density of the interior field is expressed as a functional of energy densities for equivalent boundary sources associated with a partitioning of the cavity surface. This results in Meijer G and Bessel K limit distributions which extend the well-known Gauss normal, chi and chi-squared asymptotic distributions for ideal reverberation fields, their magnitude and energy density, respectively. The additional distribution parameter permits graduation of the distribution, allowing one to incorporate chamber imperfections and operating at lower frequencies. The role of entropy, mode migrations, mode mutations, and the link with doubly stochastic random walks and cavity ensembles are outlined. In an alternative model based on cavity feedback, a powered gamma distribution is obtained for the field magnitude and energy density, exhibiting one further distribution parameter. Theoretical results are illustrated with measured and numerically simulated data, and include results on eigenfrequency dynamics.     

Seizure detection using the phase-slope index and multichannel ECoG

Detection and analysis of epileptic seizures is of clinical and research interest. We propose a novel seizure detection and analysis scheme based on the phase-slope index (PSI) of directed influence applied to multichannel electrocorticogram data. The PSI metric identifies increases in the spatio-temporal interactions between channels that clearly distinguish seizure from interictal activity. We form a global metric of interaction between channels and compare this metric to a threshold to detect the presence of seizures. The threshold is chosen based on a moving average of recent activity to accommodate differences between patients and slow changes within each patient over time. We evaluate detection performance over a challenging population of five patients with different types of epilepsy using a total of 47 seizures in nearly 258 h of recorded data. Using a common threshold procedure, we show that our approach detects all of the seizures in four of the five patients with a false detection rate less than two per hour. A variation on the global metric is proposed to identify which channels are strong drivers of activity in each patient. These metrics are computationally efficient and suitable for real-time application.     

Reconciling statistical models with practical experience of reverberation chambers

Presented are novel theoretical probability density functions (PDF) for the magnitude and phase of electromagnetic fields inside reverberation chambers (RC) operating in a `good-but-imperfect regime?. The derivation is based on considering two Gaussian random variables with mean values, variances and correlation between them that depart from the ideal assumptions. A multivariate approach using a complete joint Gaussian distribution of these variables is defined. Marginal distributions obtained by integration of this twodimensional joint PDF are compared with theoretical PDFs for ideal situations, and significantly lower rejection rates are experienced for field data measured in real RCs. Additionally, these novel marginal PDFs are highly general since they are able to describe both ideal and non-ideal stirred fields.     

An energy efficient and QoS aware routing protocol for wireless sensor and actuator networks

Wireless sensor and actuator networks are composed of sensor and actuator nodes interconnected via wireless links. The actuators are responsible for taking prompt decisions and react accordingly to the data gathered by sensor nodes. In order to ensure efficient actions in such networks, we propose a new routing protocol that provides QoS in terms of delay and energy consumption. The network is organized in clusters supervised by CHs (Cluster-Heads), elected according to important metrics, namely the energy capability, the riches of connectivity, which is used to select the CH with high node density, and the accessibility degree regarding all the actuators. The latter metric is the distance in number of hops of sensor nodes relative to the actuator nodes. This metric enhances more the network reliability by reducing the communication delay when alerting the actuator nodes, and hence, reducing the energy consumption. To reach efficiently the actuator nodes, we design a delay and energy sensitive routing protocol based on-demand routing approach. Our protocol incurs less delay and is energy efficient. We perform an evaluation of our approach through simulations. The obtained results show out performance of our approach while providing effective gain in terms of communication delay and energy consumption.     

Validation of a Three-Dimensional Transmission Line Matrix (TLM) Model Implementation of a Mode-Stirred Reverberation Chamber

Reverberation chambers are attractive electromagnetic compatibility test facilities, both economically and technically. Careful design and analysis of these facilities are important, if the results obtained are to be treated with a high level of confidence. Numerical modeling is an important part of the process of reverberation chamber design and analysis. Hence, it is important that the modeling techniques to be used are appropriately validated. Much of the published work to date takes either a statistical or a deterministic view of validation. This paper provides validation evidence for a low-resolution transmission line matrix (TLM) model of a reverberation chamber in a manner approximating the way in which the chamber is used, i.e., validating based on the effects of a simple device under test. A variety of statistical and heuristic approaches have been used to quantify the level of agreement, intending to set the likely lower bound for the quality of comparisons between simulations and measurements. While not drawing any "universal" conclusions about the veracity of the TLM technique, the paper concludes that a relatively simple model of a reverberation chamber provides a useful analysis of the chamber with close comparisons between modeled and measured data.     

Maximizable routing metrics

We present a simple theory for maximizable routing metrics. First, we give a formal definition of routing metrics and identify two important properties: boundedness and monotonicity. We show that these two properties are both necessary and sufficient for a routing metric to be maximizable in any network. We show how to combine two (or more) routing metrics into a single composite metric such that if the original metrics are both bounded and monotonic (and, hence, maximizable), then the composite metric is also bounded and monotonic (and, hence, maximizable). We present several applications of our theory. We show that the composite routing metric used in the inter-gateway routing protocol (IGRP) is not maximizable and we show that enhanced IGRP (EIGRP) does not behave as expected for nonmonotonic metrics. We also show that a technique for scalable link-state routing does not work correctly when applied to composite metrics. A common theme throughout the paper is that the intuitions generated by using distance metrics to produce shortest paths do not carry over to other routing metrics.     

Efficiency measurement of UWB antennas using time reversal in reverberation chambers

Using the reverberation chamber to obtain antenna radiation efficiency is considered. The reverberation chamber, which has for many years been used for electromagnetic compatibility measurements, can also be used with great advantage for antenna measurements since it simulates effectively a uniform multipath propagation environment. How a reverberation chamber can be used to measure the ultra-wideband (UWB) antenna efficiency in a very short time is described. The procedure based on time domain is described and some experimental results are given and compared to measurements obtained by the Wheeler cap method extended by Schantz to UWB antennas.     

乐器笙的声功率级谱

笙是中国具有悠久历史的簧管乐器,在民族管弦乐队中占有重要位置,曾被誉为最受欢迎的中国管风琴.但迄今为止,笙的声功率级尚未予以测定.介绍了在混响室内对笙声功率级所进行的测试工作.由2位资深乐师分别用不同的笙在混响室中演奏,采用多通道实时分析技术测量笙的声功率级和动态范围.获得笙在不同演奏力度下典型的平均声功率级数值;详细介绍了24簧传统笙的声功率级测试过程,同时给出了高音键笙、低音抱笙和排笙的声功率级谱.     

基于四元数奇异值分解的视频质量评价方法

准确的客观视频质量评价方法对于视频应用发展是至关重要的.近年来,图像质量评价方法已经比较成熟,而视频质量评价方法与图像质量评价方法在性能上的差距仍然较大.本文提出一种基于四元数奇异值分解的客观视频质量评价方法,该方法将像素的亮度、色度、边缘能量和残差能量作为四元数的四个部分,并用熵作为视觉感兴趣系数对块加权.在视频质量...     

Perceptual blur and ringing metrics: application to JPEG2000

We present a full- and no-reference blur metric as well as a full-reference ringing metric. These metrics are based on an analysis of the edges and adjacent regions in an image and have very low computational complexity. As blur and ringing are typical artifacts of wavelet compression, the metrics are then applied to JPEG2000 coded images. Their perceptual significance is corroborated through a number of subjective experiments. The results show that the proposed metrics perform well over a wide range of image content and distortion levels. Potential applications include source coding optimization and network resource management.     

Shielding Measurements of Equipment Enclosures in the Radiating Near Field

To evaluate the shielding performance of an equipment-level enclosure, a new measure termed shielding power ratio is proposed, which includes the average shielding power ratio (AS) and a statistically based enhancement factor. Two measurement environments, the anechoic chamber and the reverberation chamber, are considered and compared. To achieve a quick estimate of such measure, the reverberation chamber is proposed to measure the AS. The enhancement factor can be derived from the statistical analysis on both measurement results and simulation results. Based on the enhancement factor and the total radiated power, the maximum power density radiated from the enclosure can be estimated accurately. The paper is informing new developments in IEEE Standard 299.     

Scattering Cross Section Measurement in Reverberation Chamber

Reverberation chambers are now common test facilities used in electromagnetic compatibility. Objects loaded in the chambers, such as antennas and reflectors, can affect the measurement because they absorb and scatter the diffuse field. Thus, it is important to know the scattering and absorbing cross sections of these objects. In this paper, we propose a new technique to measure the scattering cross sections averaged over all angles of incidence and both polarizations in a reverberation chamber. It is based on stacking time-dependent fields generated by a repetitive pulsed source while the objects are moving. The fields recorded by wire antennas are averaged over the object positions. The square of the averaged field is shown to decrease exponentially with the time spent by the wave in the chamber. The cross section is deduced from the exponential factor. The technique has been experimentally validated in a 1 m³ reverberation chamber at 2.45 GHz with metallic spheres of several radii. The experimental cross sections are found to be in agreement with the theoretical ones.