矩形线圈检测导体板缺陷的阻抗仿真及实验分析

金属表面缺陷电磁场分布情况是影响电涡流探测器灵敏度的主要原因~([1])。在测试导电结构时,矩形线圈由于其本身的非对称性特征,会比圆形线圈更有效~([2])。矩形线圈放置在带缺陷的导体板上方,并与之平行。根据有限元建模理论建立传感器的有限元模型,通过ANSYS仿真得到传感器磁力线和线圈阻抗值。最后通过搭建硬件实验平台进行实验验证。     

物联网感知线圈电感量设计与阻抗匹配

阐述了13.56 MHz工作频率线圈的电感、电容满足一定条件下实现电磁振荡的原理,设计了线圈的电感量,提出了并联谐振电路电容、电阻混合阻抗匹配的计算公式.通过计算,矩形PCB微带线线圈和矩形空心线圈电感值分别约1 ìH和2 μH.根据线圈电感量,理论计算与Smith圆图仿真相结合确定电容、电阻混合阻抗匹配参数值.匹配电路简单,经单个参数和系统测试,测量值与理论值相符,且线圈能正常使用.该设计成果可广泛应用于13.56 MHz的RFID等物联网系统中.     

时域积分方程MOT算法的推迟位时间卷积数值积分新方法

通过变量代换平滑三角形上推迟位（标量位函数和矢量位函数）并消除推迟矢量位旋度的奇异性,使得采用数值积分法就能够精确快速地计算任意正则时间基函数与推迟位函数及推迟矢量位旋度之间的时间卷积运算,可用于基于任意类型时间基函数的时域电场、时域磁场及其混合场积分方程时间步进（MOT ）算法。与时间卷积运算的解析法对比分析表明,该时间卷积数值积分方法能够精确快速地计算基于任意类型时间基函数和不同时间步长条件下时域积分方程MOT算法的阻抗矩阵元素;而具体的计算实例也表明,阻抗矩阵的精确计算显著地提升了时域积分方程MOT算法的后时稳定性和求解精度。     

阻抗劈的UTD公式(TM情形)

本文给出了TM平面波被一照射面为阻抗表面的导体劈绕射的一致性几何绕射公式.利用该公式,我们计算了涂覆有耗介质的矩形平板的后向雷达散射截面,计算结果与测量值吻合较好.     

半空间跨界面目标电磁散射的精确建模与高效计算

利用混合位积分方程对跨界面导体目标电磁散射进行精确建模与高效计算.通过引入适当的半空间并矢格林函数来满足目标跨界面时要求的特殊边界条件,从而简化数值离散过程.对阻抗矩阵的生成过程进行优化,并结合格林函数的列表与空间插值,来提高阻抗矩阵的生成速度.上述方法可以用来对跨界面目标电磁散射进行精确建模,同时很大程度上克服了由于目标跨界面而导致的数值计算上的困难.     

有耗半空间斜架对数周期天线的MPIE-MoM 分析

以平面分层媒质为物理模型,利用混合位积分方程(MPIE)结合矩量法(MoM)对有耗半空间斜架对数周期天线进行了严格的理论分析。推导了阻抗矩阵元素的计算公式,利用分层媒质中格林函数关于场点纵坐标连续的性质,将对标量位格林函数的微分运算转移到电流基函数上,有效降低了运算的奇异性,加快了计算速度,利用微波网络理论处理馈源问题,采用一种快速方法计算了远区辐射场,最后仿真计算了天线方向图,分析了地质参数对天线辐射特性的影响。研究结果表明,地质电导率值的变化对斜架LPDA 方向图的影响比较明显,而地质介电常数的变化对此天线方向图的影响较小。本文对有耗半空间上斜架对数周期天线辐射场的计算有一定的参考价值。     

时域电场积分方程的稳定求解

提出了一种基于时域电场积分方程的稳定精确数值方法计算任意形状理想导体的时域散射.矢量位的时间导数采用中心差分近似,而标量位采用时间平均表示,并且标量位和矢量位在单元上随时间变化采用单元中心处的值来计算.将该方法与隐式方法相结合可以得到稳定精确的求解结果,而不必对电流密度进行时间或空间平均的处理过程.从模拟结果证明了该方法的稳定性和精确性.     

张量人工阻抗单元的阻抗计算及应用

提出了一种张量人工阻抗单元的表面阻抗分析计算方法,主要对矩形形状单元的表面阻抗开展了研究。通过仿真软件Ansys-HFSS提取了人工阻抗单元表面的入射散射场,再利用等效传输线技术计算出表面的张量阻抗。利用张量阻抗与表面场的关系,给出了人工阻抗单元的标量阻抗与传播方向的关系,验证了计算的准确性。最后作为实例,设计了一种基于张量阻抗单元的圆极化全息天线,天线具有较好的圆极化特性,增益大于21 dB。     

相关阴影Rician信道上广义矩形MQAM的性能

本文使用矩生成函数方法推导了相关视距(LOS)分量和独立散射分量条件下的多输入多输出阴影Rician衰落信道上采用正交空时分组编码(OSTBC)的广义矩形M进制正交幅度调制(MQAM)的平均误符号率(SEP)的精确闭合表达式.利用该表达式可计算信道衰落参数以及天线间的相关性对广义矩形MQAM平均SEP性能的影响.数值计算结果阐明,天线间的相关性恶化了广义矩形MQAM的平均SEP性能,广义矩形MQAM的平均SEP性能随着信道衰落参数的增大而得到改善.     

互连封装结构电特性分析中的改进PEEC三维建模

本文提出了一种改进的PEEC模型,为便于在大规模互连封装结构分析中利用规模缩减技术,它以描述系统的状态方程代替了具体的等效电路.为此它以矢量磁位的积分表达式和洛仑兹规范代替了矢量磁位和标量电位的积分表达式,对积分方程进行展开.这样做可以避免复杂介质结构中的电容矩阵提取,大大节省了计算时间.这一模型可方便地嵌入更大的系统进行分层次的综合分析和利用PVL等规模缩减技术.数值计算的结果与其他文献吻合较好,表明该方法有较高的可靠性.     

On the aperture and pattern space factors for rectangular and circular apertures

A consequence of a recently discovered edge condition for planar apertures is that all planar aperture distributions are separable physically into a product of an edge factor and an aperture space factor, analogous to the way in which the radiation pattern separates into a product of an element factor and a pattern space factor. An exact relationship between these aperture and pattern space factors for physically realizable vector fields is derived here for rectangular and for circular apertures. For rectangular apertures it leads to a two-dimensional set of doubly orthogonal functions that are characteristic of the aperture geometry. Characteristic functions for circular apertures, however, are shown to exist only if the vector fields are circularly symmetric, although for scalar fields they exist for completely arbitrary aperture distributions with arbitrary edge taper. For rectangular apertures the characteristic functions consist of products of spheroidal functions and for circular apertures they are obtained from a generalization of the spheroidal functions. Some of the properties of these generalized spheroidal functions are developed here.     

Finite-difference analysis of cyclic H-plane waveguide three-port circulators with an arbitrary-shape lossy ferrite post

A finite difference method (FDM) with an analytical truncation boundary condition is developed for the analysis of cyclic H-plane waveguide three-port circulators with an arbitrary shape ferrite post. The method is based on scalar wave equations and the analytical field distribution in the rectangular waveguides. A general boundary field equation for an arbitrarily shaped ferrite or dielectric interface is derived. To verify the validity of the present method, the eigenvalue phases of the cyclic three-port empty junctions and the characteristics of H-plane waveguide Y-junction circulators with lossless, lossy cylindrical, composite and triangular ferrite post are calculated. Good agreements with previously published experimental and theoretical results have been achieved. The performance of a Y-junction circulator with a hexagonal ferrite post and the characteristics of a cyclic three-port circulator with a ferrite rod are also investigated.     

The signal-to-noise ratio of nuclear magnetic resonance surfacecoils and application to a lossy dielectric cylinder model. I. Theory

Surface coils are used in magnetic resonance imaging (MRI) for their high signal-to-noise ratio (S/N) when placed near the-region to be imaged. However, their optimization for high field MRI systems is hampered by the lack of understanding of the electromagnetic effects taking place at high frequencies when a coil is placed near the human body. The aim of this work was to calculate the S/N of surface coils using complete solutions to Maxwell's equations and also to study the high frequency effects and parameters determining the S/N. Here the authors present a general approach to the computation of the S/N of surface coils using the reciprocity principal and the complex Poynting vector for arbitrary coil and body geometries. This approach is then applied to the case of the human body modeled as an infinitely long homogeneous dielectric cylinder exhibiting both conductive and dielectric losses. The S/N of a coil of unspecified geometry facing the cylinder is derived using a dyadic Green's function. Complete solutions for the fields of a dipolar source arbitrarily located in the cylinder are first derived, and applying the reciprocity principle, the authors deduce the fields created at the dipole position by a coil excited with a unit radiofrequency current. These yield the expressions for the power dissipated in the cylinder, for its reciprocal the noise picked up by the coil, and also for the signal received. Any coil geometry and any coil or source position can be evaluated with this infinite cylinder model. It is valid at all frequencies and for any tissue parameter. The general approach to the computation of the S/N of MRI coils can be applied to other body geometries as well     

任意槽形矩形慢波结构高频特性分析

矩形慢波结构及其变态具有易于微加工、横向尺寸大、散热好等优点,是一种有潜力工作于毫米波段或亚毫米波段的高频系统.文中利用场匹配的方法推导出了任意槽形状开放式矩形波导慢波结构的统一色散方程,并利用数值计算方法分析了几种特殊槽形状加载慢波结构的色散特性及耦合阻抗,得到三角形结构色散和耦合阻抗均最弱,而倒梯形结构色散最强,耦合阻抗最大.     

Electromagnetic scattering from vibrating penetrable objects using a general class of time-varying sheet boundary conditions

Calculation of electromagnetic (EM) scattering from vibrating penetrable cylinders of arbitrary cross-section is presented using a general class of time-varying sheet boundary conditions (SBCs) in conjunction with the method of moments (MoM). Sheet impedance and admittance expressions are first derived from the exact scattering solution for a penetrable circular cylinder with perturbed radius. Then, using the SBCs, integral equations are derived and solved numerically so that vibrating cylinders with arbitrary cross-section can be treated. Cylinder vibrations are assumed to be non-relativistic, allowing a simplified calculation of the scattered Doppler spectrum. A critical factor in the calculation of the potentially small Doppler components is that the time-varying nature of the cylinder boundary, contained within the sheet impedance and admittance expressions, can be isolated from the unperturbed terms in the scattered field. Comparison with exact and analytical perturbation solutions are presented to demonstrate the accuracy of the numerical solution.     

Time-averaged behaviour of single and dual flying capacitor converters

The Single Flying Capacitor Converter (SFCC) and Dual Flying Capacitor Converter (DFCC) are two-quadrant power supplies for energy storage and transfer systems. They have applications in nuclear research and pulsed power systems in which superconductive coils are used. In this paper analytical expressions for the time-averaged behaviours of SFCC and DFCC are derived by using averaging technique. Because large superconductive magnet coils are used, time constants of the switched circuits are large enough compared to the switching period. Therefore, an averaged PWM switch equivalent circuit is substituted into the original converter circuits to find the averaged system equations. With this new insight in the averaged dynamics, their design and control can be optimized. Although DFCC has less coil current ripple compared to SFCC, the analysis will show that the averaged behaviours of both converters are the same.     

Electric-Type Dyadic Green's Functions for a Corrugated Rectangular Metaguide Based on Asymptotic Boundary Conditions

The Green's functions for the mixed potential electric field integral equation are derived for a rectangular waveguide with dielectric-filled corrugations supporting left- as well as right-hand propagation. Under the asymptotic boundary conditions assumption, the expressions of the Green's dyadic components can be decomposed into terms that represent conventional waveguide modes and others that represent hybrid metaguide modes. A simple approach is used to find the poles of the spectral domain expressions before obtaining the spatial domain expressions using the inverse Fourier transform. The dispersion diagram reflects very interesting characteristics for the structure and the deviation from the conventional case. The derived Green's function is verified by considering the problem of a probe excitation and comparing the input impedance obtained using a moment method procedure based on the present theory and the finite-difference time-domain method     

Radiation from dielectric-loaded arrays of parallel-plate waveguides

The problem of calculating the reflected and transmitted fields as a function of scan angle in an infinite phased array of parallel-plate waveguides is studied on an analytical basis. Two infinite sets of simultaneous linear equations are derived for the scattered fields internal and external to the waveguides. These sets of equations are attacked by a newly developed modified residue calculus method. Application of the results to the problem of designing rectangular waveguide arrays with improved impedance performance over a wide range ofH-plane scan angles is discussed. It is indicated that the present analysis may serve as a first step toward investigating the more general problem of phased arrays scanning at an arbitrary angle.