Experimental two-layer adaptive phase-switched screen

An experimental two-layer planar phase-switched screen is described. The screen is designed to provide controlled phase modulation of electromagnetic energy reflected from its surface, and can be configured to synthesise the time-averaged reflectivity response of a microwave absorber. Measured results are presented to show that the experimental system exhibits dynamic reflectivity null steering capabilities over an 8 to 15 GHz frequency range     

Principles of minimum variance robust adaptive beamforming design

Robustness is typically understood as an ability of adaptive beamforming algorithm to achieve high performance in the situations with imperfect, incomplete, or erroneous knowledge about the source, propagation media, and antenna array. It is also desired to achieve high performance with as little as possible prior information. In the last decade, several fruitful principles to minimum variance distortionless response (MVDR) robust adaptive beamforming (RAB) design have been developed and successfully applied to solve a number of problems in a wide range of applications. Such principles of MVDR RAB design are summarized here in a single paper. Prof. Gershman has actively participated in the development and applications of a number of such MVDR RAB design principles.     

Principles of gyrotron powered electromagnetic wigglers for free-electron lasers

The operation of free-electron lasers (FEL's) with axial electron beams and high-power electromagnetic wiggler fields such as those produced by high-power gyrotrons is discussed. The use of short wavelength electromagnetic wigglers in waveguides and resonant cavities can significantly reduce required electron beam voltages, resulting in compact FEL's. Gain calculations in the low- and high-gain Compton regime are presented, including the effects of emittance, transverse wiggler gradient, and electron temperature. Optimized scaling laws for the FEL gain and the required electromagnetic wiggler field power are discussed. Several possible configurations for FEL's with electro-magnetic wigglers powered by millimeter wavelength gyrotrons are presented. Gyrotron powered wigglers appear promising for operation of compact FEL's in the infrared regime using moderate energy (<10 MeV) electron beams.     

大屏幕彩电枕校电路原理与设计

详细介绍了大屏幕彩电图像枕形失真校正电路的原理,并对单频（16kHz）及倍频（32kHz)扫描条件下关键器件的参数选择提出了指导意见。     

The scattering of electromagnetic pulses by a slit in a conducting screen

A direct method for calculating the impulse response of a slit in a conducting screen is presented. The method may be used to study the scattering of electromagnetic pulses by conducting objects with planar boundaries and straight edges. The impulse response is obtained by assuming that the total response is composed of two sequences of diffracted waves. The solution is determined for the first two diffracted waves in one sequence by using Green's functions and the equivalence principle. The method is applied iteratively to obtain the solution for additional waves in the sequence. The solution for the other sequence is obtained by a transformation of coordinates. The total response is the sum of the two sequences of waves. The cases ofE-polarization andH-polarization are considered. Curves are presented to depict 1) the successive diffractions of the pulses by the edges of the slit, and 2) the impulse response of the slit.     

Backscattering of electromagnetic waves by the vertex area of a thin conducting screen

The backscattering of the electromagnetic waves by the vertex area of a thin metal screen is investigated. A special case when the magnetic field of the incident wave is perpendicular to the diagonal of the vertex area is considered. The dependence of the vertex-scattered signal on the grazing angle is experimentally found. At a certain angle, an extremum in the radar scattering is discovered. At the extremum, good agreement between the results predicted by the asymptotic theory and the experimental results is observed.     

三维目标电磁散射的自适应积分方法

应用自适应积分方法并结合邻近组预条件求解三维导电目标的电磁散射.通过建立辅助基函数将三角形分域基函数映射到矩形网格中,并将格林函数离散变换为具有Toeplitz特性的矩阵.用快速傅立叶变换加速迭代求解中的矩阵和矢量相乘,该方法极大的减少了内存需求和CPU时间,其存储量和运算复杂度分别为低于O(N1.5)和O(N1.5logN)量级.应用邻近组预条件技术进一步降低了迭代求解所需的迭代次数.数值结果表明了该方法的准确性和高效性.     

频率选择表面电磁特性的多元自适应采样分析

将自适应频率采样法扩展为多元函数的自适应采样法,并应用于频率选择表面(FSS)的电磁特性分析。依据FSS的散射参数与多个变量的函数关系建立多元有理函数模型,通过在各维变量中查找误差最大点选择采样点,并通过依次将一维内插值作为下一维内插拓扑关系的初始值,将一维内插扩展为多维内插,结合矩量法分析频率、入射方向等参数对FSS电磁特性的影响。计算分析了十字形贴片单元、方形孔径单元FSS散射特性曲线和口径天线-FSS罩系统的方向图,计算结果与直接矩量法结果吻合,计算效率得到显著改善,验证了方法的有效性。     

基于稳健自适应频率采样的宽频电磁数值仿真

已有的基于Stoer-Bulirsch有理函数插值的自适应频率采样算法往往对插值间隔、收敛精度等参数非常敏感,算法稳定性差,甚至会出现伪收敛等问题.针对已有算法的上述缺陷,通过采用极点判断、插值区域二分、参数变换和多次收敛性检验等措施,提出了一种逐一增加采样点的自适应策略.形成了一种通用性强、稳定性好的自适应频率采样算法,可以用较少的采样点插值重构未知函数响应.并结合多层快速多极子方法,对宽频带目标电磁散射进行计算分析,实现采样频点的自适应选取,减少了计算量极大的精确数值计算的次数,提高了仿真效率.     

Efficient electromagnetic source imaging with adaptive standardized LORETA/FOCUSS

Functional brain imaging and source localization based on the scalp's potential field require a solution to an ill-posed inverse problem with many solutions. This makes it necessary to incorporate a priori knowledge in order to select a particular solution. A computational challenge for some subject-specific head models is that many inverse algorithms require a comprehensive sampling of the candidate source space at the desired resolution. In this study, we present an algorithm that can accurately reconstruct details of localized source activity from a sparse sampling of the candidate source space. Forward computations are minimized through an adaptive procedure that increases source resolution as the spatial extent is reduced. With this algorithm, we were able to compute inverses using only 6% to 11% of the full resolution lead-field, with a localization accuracy that was not significantly different than an exhaustive search through a fully-sampled source space. The technique is, therefore, applicable for use with anatomically-realistic, subject-specific forward models for applications with spatially concentrated source activity.     

The research of new electromagnetic screen system of the 300-kWsuperconducting homopolar DC machine

An analysis is made of the original configuration of the 300-kW superconducting homopolar machine (SHM) and a novel electromagnetic screen system for this machine is presented. Numerical computation is made of the magnetic field of the 300-kW SHM for a ship. The high-Tc superconducting magnetic screen is tested with a microtester. All data and the analysis for this magnetic screen system of the superconducting machine are discussed     

A new approach to the electromagnetic diffraction problem of a perfectly conducting half-plane screen

It is well known that the magnetic vector potential of an electromagnetic (EM) field incident upon a perfectly conducting thin plate satisfies, on the plate, an inhomogeneous Helmholtz equation. Rahmat-Samii, Mittra et al., and also Wilton and Dunaway applied this fact to the numerical solution of the thin-plate EM diffraction problem, using a modified version of the electric field integral equation. They pointed out that the Helmholtz equation alone determines the vector potential on the plate only up to an unknown term which expresses the coupling of the current-density components, which is due to the influence of the edge of the plate. It is demonstrated that their method is applicable in the theoretical analysis of some EM plate diffraction problems as well. The method will be applied, in combination with the Wiener-Hopf method, to reproduce the well-known solution of the classical problem of diffraction of plane electromagnetic waves by perfectly conducting half-plane screens. This approach can be done directly in vector form for general, three-dimensional incident waves. The result is applied to the discussion of grazing incidence.     

Unified quality assessment of natural and screen content images via adaptive weighting on double scales

In multimedia communication systems, digital images may contain various visual contents, among which the natural scene images (NSIs) and screen content images (SCIs) are two important and common types. The existing full-reference image quality assessment (IQA) metrics are designed for only one type of images, but cannot precisely perceive the visual quality of another type. It is still unclear what the different characteristics are between NSIs and SCIs resulting in this failure. Inspired by some psychological studies, we figure out that it is due to the different structural scale levels between NSIs and SCIs. Given this observation, this paper introduces the gradient degradation of Gaussians (GDoG) to analyze the images’ structural scale level, proposes a fast unified IQA index for both NSIs and SCIs by incorporating an adaptive weighting strategy on double scales. Experimental results conducted on several databases verify the effectiveness and efficiency of the proposed unified IQA index for both types of images, also demonstrate that the adaptive weighting strategy based on GDoG can improve the existing models for cross-content-type images.     

多功能计数器的设计

该系统由单片机89S52控制模块,程控宽带放大模块,整形模块,FPGA内频率、相位差测量模块等构成,采用等精度测频法测出频率和周期.可测量有效值为0.01～5 V,频率范围1 Hz～20 MHz信号的频率、周期信号,精度高达10-6.采用计数法测量相位差,该系统可测量有效值0.5～5 V,频率10 Hz～100 kHz信号的相位差,精度为1°.系统功能由按键控制,测量结果奕时显示,人机界面友好.     

多功能计数器的设计

该系统由单片机89S52控制模块,程控宽带放大模块,整形模块,FPGA内频率、相位差测量模块等构成,采用等精度测频法测出频率和周期,可测量有效值为0.01～5 V,频率范围1 Hz～20 MHz信号的频率、周期信号,精度高达10-6。采用计数法测量相位差,该系统可测量有效值0.5～5 V,频率10 Hz～100 kHz信号的相位差,精度为1°。系统功能由按键控制,测量结果实时显示,人机界面友好。     

Sparse parameterisation of electromagnetic scattering data using genetic algorithm with adaptive feeding

A method is presented to parameterise scattering data from complex targets. Based on a global model with both scattering centres and resonances, a genetic algorithm with adaptive feeding is proposed for a sparse representation. The algorithm is tested with measurement data and shows better performance than non-global parameterisation methods.     

An adaptive first-order polarization-mode dispersion compensationsystem aided by polarization scrambling: theory and demonstration

An adaptive polarization-mode dispersion (PMD) compensation system has been developed to cancel the effects of first-order PMD by producing a complementary PMD vector in the receiver. Control parameters for the PMD compensation system comprised of a polarization controller and a PMD emulator are derived from the nonreturn-to-zero (NRZ) signal in the channel to be compensated. Estimates of the link's differential group delay (DGD) and principal states of polarization (PSPs) based on this signal are reliable when the signal power is equally split between the link's two PSP's; however this condition cannot be assumed. To meet this requirement, we scramble the state of polarization (SOP) of the input signal at a rate much greater than the response time of the PMD monitor signal so that each sample represents many different SOP alignments. This approach allows the effective cancellation of the first-order PMD effects within an optical fiber channel     

基于自适应局部增强的手机TFT-LCD屏Mura缺陷自动检测

针对手机屏幕图像整体亮度不均以及Mura缺陷对比度低等特点,提出一种基于自适应局部增强的Mura缺陷自动在线检测方法。首先对CCD相机采集的手机屏幕原始图像进行感兴趣区域提取、几何校正、滤波等预处理,获取图像中的屏幕区域,然后将屏幕区域划分为多个不重叠的像素块,并根据每个像素块的灰度分布特征,采用自适应局部增强算法自动识别并定位图像中的Mura区域,最后考虑到Mura缺陷大小的不确定,提出采用多层级分块的方式对屏幕区域进行检测,提高算法鲁棒性。实验结果表明,相较现有多种屏幕缺陷自动检测算法,本文方法能更准确有效地识别手机屏幕中的Mura缺陷,且覆盖率和误检率分别为91.17%和5.84%。     

Diffraction of electromagnetic plane wave by an infinite slit in a screen with surface impedance

Diffraction of an electromagnetic plane wave by an infinite slit in a screen with surface impedance is solved analytically as a boundary value problem under the assumption that the plane of incidence is normal to the slit in a screen of zero thickness surrounded by a homogeneous medium. The field expressions and the transmission coefficient are derived asymptotically, and their numerical solutions are presented for a special case of perfect conducting screen.