Geophysical Investigation Using Time Domain Electromagnetic Method (TDEM) at Wadi Deir Al-Kahaf Area/Jordan for Groundwater Artificial Recharge Purposes

In this study, Ten Time Domain Electromagnetic (TDEM) measuring points have been conducted at four pre-selected sites along Wadi Deir Al-Kahaf in order to investigate the potential of the near subsurface deposits and aquifer for groundwater artificial recharge applications. The surveyed results suggest well resolved geological layers such as alluvial mudflat, basalt layers and their saturation states. In addition a hydrogeophysical cross section along the studied sites was constructed which permits to locate the lateral variations in rock properties due to water saturation and or facies changes. The saturated thickness of the Upper Aquifer System in the study area was found to be changed from 5 m near TEM 1 to about 120 m near TEM 4 in thickness. The Abed Basalt Aquifer (AOB) has an average saturation thickness of about ~60 m, and forming the main aquifer (~100 m thickness) near surface to the north of the study area. TEM-3 and TEM-4 sites were found to be potential sites for groundwater artificial recharge based on the constructed hydro-geophysical model. This study recommends implementing detailed geophysical investigations particularly in the most northern parts of the study area.

Prediction study of hydrocarbon reservoir based on time-frequency domain electromagnetic technique taking Ili Basin as an example

The time-frequency domain electromagnetic(TFEM)sounding technique can directly detect oil and gas characteristics through anomalies in resistivity and polarizability.In recent years,it has made some breakthroughs in hydrocarbon detection.TFEM was applied to predict the petroliferous property of the Ili Basin.In accordance with the geological structure characteristics of the study area,a two-dimensional layered medium model was constructed and forward modeling was performed.We used the forward-modeling results to guide fi eld construction and ensure the quality of the fi eld data collection.We used the model inversion results to identify and distinguish the resolution of the geoelectric information and provide a reliable basis for data processing.On the basis of our results,key technologies such as 2D resistivity tomography imaging inversion and polarimetric constrained inversion were developed,and we obtained abundant geological and geophysical information.The characteristics of the TFEM anomalies of the hydrocarbon reservoirs in the Ili Basin were summarized through an analysis of the electrical logging data in the study area.Moreover,the oil-gas properties of the Permian and Triassic layers were predicted,and the next favorable exploration targets were optimized.

Finite Time Domain Dynamics of Dirac Fields

In the present paper we consider the case of a Dirac field in a finite time domain and coupled to an external field. We decompose the field and its Hamiltonian in terms of creation and annihilation operators and path integrate it via Grassmannian variables techniques. In that way we obtain its finite time domain Green function. We use it in the perturbative study of the interaction of Dirac particles with classical electromagnetic waves.

A Hybrid Method for Electromagnetic Coupling in Large Spaces

A hybrid method combining finite difference time domain(FDTD)with topology network was presented to treat with electromagnetic couplings and transmissions in large spaces A generalized matrix euqation expressing the relations among wave vectors at every port of the network nodes was give Scattering characteristics and electromagnetic distributions of every node was calculated independently using FDTD A structure of irises in a waveguide was taken as numerical examples This hybrid method has more advantages than the traditional FDTD method which includes saving calculation time,saving memory spaces and being flexible in setting up FDTD grids

Reducing the calculation workload of the Green function for electromagnetic scattering in a Schwarzschild gravitational field

When the finite difference time domain(FDTD) method is used to solve electromagnetic scattering problems in Schwarzschild space-time, the Green functions linking source/observer to every surface element on connection/output boundary must be calculated.When the scatterer is electrically extended, a huge amount of calculation is required due to a large number of surface elements on the connection/output boundary.In this paper, a method for reducing the calculation workload of Green function is proposed.The Taylor approximation is applied for the calculation of Green function.New transport equations are deduced.The numerical results verify the effectiveness of this method.

RESEARCH ON INDOOR ELECTROMAGNETIC RADIATION FIELD OF MULTIPLE ANTENNA SYSTEM

The complexity of the indoor environment brings great challenges to predict the electromagnetic radiation field of multiple antenna systems. Based on the Finite Difference Time Domain (FDTD) algorithm, using the mobile phone shielding device as the multiple antenna systems example, the mobile phone shielding device's indoor electromagnetic radiation field is researched by measurment method and simulation method. The effectivity of prediction method is verified by comparing the prediciton results with the measurment results. About 80% of the error can be controlled less than dB. The quantitative research has certain guiding significance to the prediction of the multiple antenna systems radio wave propagation.

ERROR IMPROVEMENT OF TEMPORAL DISCRETIZATION IN TDFEM FOR ELECTROMAGNETIC ANALYSIS

Integral method is employed in this paper to alleviate the error accumulation of differential equation discretization about time variant t in Time Domain Finite Element Method (TDFEM) for electromagnetic simulation. The error growth and the stability condition of the presented method and classical central difference scheme are analyzed. The electromagnetic responses of 2D lossless cavities are investigated with TDFEM; high accuracy is validated with numerical results presented.

Polarization insensitivity electromagnetically induced reflection in graphene metasurface

The electromagnetically induced reflection(EIR)effect of graphene metamaterials has been investigated by finite difference time domain(FDTD)method.In this study,a metamaterial sandwich structure composed of silica(SiO2),gold and graphene on terahertz band is designed.By changing the width of the two ribbons of graphene length and the incident angle of electromagnetic wave,the EIR effect of the structure is discussed,and it can be found that SiO2 is a kind of excellent dielectric material.The simulation results show that graphene metamaterial is not sensitive to polarized incident electromagnetic wave.Therefore,such EIR phenomena as insensitive polarization and large incident angle can be applied to optical communication filters and terahertz devices.

HIGHER-ORDER NODE-BASED TDFEM FOR TRANSIENT ELECTROMAGNETIC ANALYSIS IN RECTANGULAR WAVEGUIDE

Higher-order Time Domain Finite Element Method (TDFEM) based on the nodal inter- polation is proposed for two-dimensional electromagnetic analysis. The detailed algorithms of the method are presented firstly, and then the accuracy, CPU time and memory consumption of the higher-order node-based TDFEM are investigated. The high performance of the presented approach is validated by numerical results of the transient responses of Transverse Electric (TE) field and Transverse Magnetic (TM) field in a rectangular waveguide.

Time-Domain Analysis of a Rectangular Reflector Antenna

Rectangular reflector antennas have motivated the time-domain analysis of electromagnetic scattering problems. The asymptotic time domain physical-optics (TDPO) is applied to the analysis of a rectangular reflector illuminated by a Gaussian-impulse. The effects of time-delayed mutual coupling between points on the surface will be ignored as a result of utilizing the TDPO method for determining the equivalent surface-current density on the reflector. Finally, in this work the scattered signals at the specular reflection point, at the edges, and at the corners can be clearly distinguished.

Analysis of Electromagnetic Environment Effect Using TDIE-FDTD-MNA Hybrid Algorithm

It is important but difficult to analyze the electromagnetic environment effect(E3) in the designing of modern airborne,sea,space,and ground systems.Thus a hybrid algorithm of time domain integral equation,finite difference time domain and modified nodal analysis(TDIE-FDTD-MNA) is developed to analyze the E3 of complex systems with cables and nonlinear circuit structures.The plane wave time domain(PWTD) enhanced TDIE method is adopted to solve field problems.The higher order FDTD(2,4) is adopted to solve cable problems.The MNA is adopted to obtain the response of complex circuits(with nonlinear structures).Numerical examples demonstrate the effectiveness of the proposed algorithm.

Characteristic Analysis of Transient Electromagnetic Disturbance Data in Substation

Characteristic analysis of transient electromagnetic disturbance data is very important. In this paper, the time-domain and frequency-domain characteristics of transient electromagnetic disturbance caused by switching operations in substations are analyzed. Two methods are adopted in time-domain analysis. One method is histogram and the other one is normality test. An appropriate procedure for the normality test is proposed. Furthermore, the method used in frequency- domain analysis is to obtain overall envelope. These statistical characteristic analysis methods are showed to be of great value in analyses of the measured samples. The simulation results showed that these methods are effective.

架空配电线路故障电弧的电磁辐射特性及故障定位应用

针对架空配电线路电弧接地故障点定位难题,该文研究架空配电线路故障电弧的电磁辐射特性,探索基于电磁辐射信号的电弧故障定位方法的可行性。通过10 k V配网真型故障模拟试验平台,分析接地电弧电磁辐射的时域与频域特性及传播衰减规律,结果表明:电弧电流的电磁辐射特征频段为20~30 MHz,该特征频段不会受到中性点接地方式、电弧接地介质与线路结构参数的显著影响,且特征频段内辐射信号在传播过程中衰减较慢。在此基础上,设计一种小型化三角形单极子–环形组合平面天线,工作频率为20~500 MHz。利用自制天线开展小型电弧故障定位实验,为后续配网电弧故障定位的应用研究提供基础。

一种新型可移动TEM喇叭辐射波模拟器的模拟优化

为改善基于TEM喇叭的辐射波模拟器的低频辐射特性从而展宽其辐射近场半高宽,首次提出了在指数型TEM喇叭上/下两个极板的端口加上2个金属直板、并通过倾斜金属板和并联电阻相连的新型可移动模拟器的设计方案。基于FDTD方法模拟分析了该新型模拟器的特性参数对其近场辐射性能的影响,并给出了优化后的模拟器及其阵列的辐射特性。计算结果表明:尺寸为6 m×6 m×6.24 m的优化后的新型模拟器在距离口面3 m的中心位置的辐射近场脉宽能达到18.95 ns,而达到相同低频辐射性能的常规模拟器尺寸为9 m×12 m×6.8 m。且与常规模拟器相比,优化后的模拟器的场峰值更大。与前人的研究相比,优化后的模拟器场在保持高峰值的同时,时域波形后延震荡的幅度与主峰的比值明显减小。优化后的模拟器2×2阵列模型的测试平面中心点场峰值最大,且在测试平面上满足6 dB均匀性要求的有效测试区最大;有效测试区在横向上范围最大的是2×2阵列模型,其次是2×1阵列模型;在纵向上范围最大的是2×2阵列模型及1×2阵列模型。

介质粗糙面与组合目标宽带电磁散射特性研究

文中对介质粗糙面和组合目标的宽带复合电磁散射特性进行研究,通过数值计算得到了复合散射系数频率响应曲线。分析结果显示,后向复合散射系数在宽频带范围内随着频率的变化而产生振荡,粗糙面的高度均方根、介电常数、组合目标尺度、目标介电常数等因素对复合散射系数有显著的影响,且影响规律较为复杂。相比之下,粗糙面的相关长度对复合散射系数的影响较为微弱。当目标是理想导体时,频率响应曲线近似呈现出准周期性的振荡形态。

汽车组合仪表有意电磁干扰空时域联合分离系统设计

有意电磁波与汽车仪器电磁传输波产生的混合干扰,降低了汽车组合仪表的稳定运行能力,造成仪表设备失灵;为避免上述情况的发生,设计汽车组合仪表有意电磁干扰空时域联合分离系统;在步进电机驱动电路中,设置汽车组合仪表控制器、分离电源与PCB电路板、有意电磁干扰数字传感器;分配有意电磁波空时域源地址,通过计算干扰信号平坦度的方式,确定脉冲参数的取值范围,实现汽车组合仪表有意电磁的空时域干扰效应分析;估算有意电磁波干扰信号的数目,按照信号分解的处理原则,求解联合分离修正函数,实现电磁干扰的联合分离;在设置频率范围在100 MHz~1 GHz之间、幅度范围为0.5~5 V、脉冲宽度范围为10~100 ns区间后,通过实验结果表明,设计系统应用后可以在混合信号中,按照空域、时域标准的不同分离有意电磁波,且分离后的信号波长、信号频率依然在1.0μm、300 Hz左右,不会因混合干扰降低汽车组合仪表的稳定运行能力。

基于同步提取变换的地空频率域电磁信号幅度提取方法

地空频率域电磁法探测信号为多频非平稳信号,为了解决应用传统傅里叶变换方法提取其幅度时分辨率较差的问题,本文提出了基于同步提取变换(SET)的地空频域电磁信号幅度提取方法。该方法对电磁数据进行SET,得到高分辨率时频图,并利用能量算子使电磁数据时频谱能量更为集中;采用贪心算法提取脊线,得到时频图的高能量带;通过自回归模型自适应地补充了脊线中的0值,解决了由窗函数引起的端点效应问题。根据脊线位置的时频图复数值,得到各频率分量幅度随时间的变化,研究了不同信噪比情况下基于SET的地空频率域电磁信号幅度提取结果的准确性。结果表明:当信噪比≥10 dB时,幅度提取结果的平均相对均方根误差均小于5%;当信噪比<10 dB时,幅度提取结果的平均相对均方根误差在10%以内。提取效果良好。将此方法应用于新疆霍拉山隧道工程地空频率域电磁法探测中,成功提取了多频电磁信号各频率分量的幅度,与采用傅里叶变换提取非平稳信号幅度的方法相比,该方法有效地提高了幅度提取结果的分辨率。

弱导电薄层介质材料电磁耦合等效计算方法研究

面向核电磁脉冲等强电磁环境下复合材料壳体平台的电磁环境效应分析需求,根据Maxwell-Ampere定理的积分形式,分析得到了时域有限差分方法在处理弱导电薄层介质材料参数时的等效计算方法,即当介质等效波长远大于模型厚度时,可将薄层模型适当增厚,同时等比例减小其电导率,参数等效前后模型的电磁耦合特性基本相同。该方法通过等效增厚薄层材料从而实现增大空间离散步长,减少网格量的目的,不需要改变传统时域有限差分方法的时间步进格式,不会破坏计算的稳定性。无限大有耗介质薄板、薄层球体、含薄层壳体无人机电磁耦合等算例表明,在包含毫米级厚度弱导电介质薄层壳体平台的核电磁脉冲耦合模拟中,该方法具有较好的适用性。

基于G-TF/SF方法的分层地表电磁环境研究

本文将基于广义总场散射场(generalized total-field/scattered-field,G-TF/SF)方法的时域有限差分(finite-difference time-domain,FDTD)方法用于分层地表的电磁环境计算中,四周采用卷积完全匹配层(convolutional perfectly matched layer,CPML)吸收边界条件。G-TF/SF方法可有效削减由地面四周截断产生的边缘效应,提高分层地表电磁环境计算精度且G-TF/SF边界只需要加载入射场,无需计算反射场与透射场。G-TF/SF方法将部分边界埋在完全匹配层(perfectly matched layer,PML)区域中,对埋在PML层中G-TF/SF边界的入射波乘以相应的系数,保证将合适的入射波等效到主网格区域进行计算。本文用G-TF/SF方法模拟计算了水平单层地表及不同分层地表情形下的电磁环境,并将水平单层地表结果与用解析法计算的结果进行对比;将不同分层情形与采用有限积分技术得到的结果对比,验证了G-TF/SF方法计算结果的正确性。

电磁干扰多通道时域快速测量与信号计算方法

针对复杂电磁环境和复杂大型系统电磁干扰测量参数、测量点位及测量工况多的特点,采用传统扫频式频域测量方法具有代价高、耗时长等现实问题,提出了一种低频电磁干扰的多通道时域快速测量与信号计算方法,并研制出低频电磁干扰多通道时域快速测量系统,实验验证表明提出的测量、计算方法和研制出的测量系统可以准确得到复杂电磁环境和大型系统的低频电磁干扰特性,且测量速度快、成本低。