地下SLF/ELF水平电偶极子在球形地-电离层中产生的场

在非理想导电地面与电离层条件下,导出了地下SLF/ELF水平电偶极子在地上、地下及电离层中产生的电磁场的球谐级数表达式.并提出了一种加速收敛算法,算出了大气层及电离层中的电磁场分布.计算结果表明:地下几十公里的水平电偶极子产生的场除了增加了一个固定衰减外,与地面上的水平电偶极子产生的场分布完全相似,它产生的电磁场可理解为电波首先垂直地透过土壤,然后在地一电离层腔体中传播.在SLF频段,地一电离层空腔中的电磁场可理解为两个"行波"的叠加.在ELF频段,空腔中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

电离层中ELF辐射源向下传播衰减理论分析

利用大功率高频（HF）电波调制加热电离层可在电离层中有效形成辐射源,并用于辐射ELF电磁波.本文基于磁流体力学的基本方程通过对电离层中极低频（ELF）辐射源的辐射场分析,获得ELF电磁波在电离层中传播的色散关系式,建立电离层中的ELF辐射源向下传播衰减模型.并依据建立的传播衰减模型,分析不同纬度地区传播衰减的差异,以及传输频率和背景电离层参数对传播衰减的影响.     

高纬极区电离层离子速度分布函数的多项式解

考虑高纬极区电离层,采用麦克斯韦分子碰撞模型来描述玻耳兹曼方程的碰撞项,通过求解麦克斯韦分子碰撞模型下的输运方程,得到了离子分布函数的16矩近似.将麦克斯韦分子碰撞模型和驰豫碰撞模型下输运方程的解进行了对比,同时论证了麦克斯韦分子碰撞模型下的16矩近似偏离双麦克斯韦分布的程度.鲒果表明:相对于麦克斯韦分子碰撞模型,驰豫碰撞模型下得到的输运方程的解高估了离子温度的各向异性、应力张量项、热流矢量项以及离子分布函数的大小.     

地震ELF/SLF辐射源在地面及电离层中产生的场

针对地震电磁辐射与传播,将地下辐射源理想化为水平ELF/SLF电偶极子,传播介质理想化为地层-大气层-电离层三层平面分层介质,其中地层和电离层都看作均匀有耗介质.在此物理模型下,导出了电磁场在大气层和电离层中的积分表达式,更由留数定理得出了电磁场的级数表达式.计算结果表明:ELF/SLF电波从辐射源出发后,首先以最短的垂直向上路径渗透出地层进入大气层,然后在地-电离层波导中以若干个"波模"叠加的方式向外传播到达大气层中的接收点,并进一步渗透电离层被卫星上的接收点接收.     

ELF/SLF电磁波传播的FDTD和GIS结合建模与分析

首次采用三维时域有限差分(3D-FDTD)经纬度模型和地理学信息系统技术(Geographic Information System,GIS)对地球-电离层波导系统进行几何建模,并对闪电、舒曼谐振中的极低频/超低频(ELF/SLF)的电磁辐射进行仿真实验.计算结果表明,当激励源放置在高空模拟闪电发生时,电磁波通过波导系统传播到观测点,并继续绕地球多次经过同一位置,直到完全衰减,其谐振频点与舒曼谐振点基本一致.发现地形地貌对于地表电磁波的电场分布有较大影响,而对地表电磁波的磁场分布几乎没有影响.     

地基ELF线天线在地-电离层壳体中产生的场

为了研究地震产生的机理, 需要分析和研究地基极低频(Extreme-Low Frequency, ELF)电磁波的传播特性.地基任意ELF线天线产生的电磁场可由ELF点源产生的电磁场进行叠加.通过地基ELF点源电磁场的表达式导出了ELF线天线在地-电离层壳体中电磁场的表达式.利用加速收敛算法得到了单条和两条ELF线天线产生电磁场的场强空间分布图, 用色标表示场强值在空间分布的强弱.电场水平分量的场强值要比垂直分量的场强值小, 磁场水平分量的场强值要比垂直分量的场强值大.而且两条线天线产生的场强值要比单条线天线产生的场强值大.     

地下ELF线天线在地-电离层壳体中产生的场

为了研究地震产生的机理,需要分析和研究地下任意ELF线天线在地-电离层壳体中产生的电磁场。地下任意ELF线天线产生的电磁场可由地下ELF点源产生的电磁场进行叠加。首先导出了地下ELF点源在地-电离层壳体中产生的电磁场表达式,然后得到了地下任意ELF线天线在地-电离层壳体中产生的电磁场的表达式。分别讨论了地下单条和两条ELF线天线在地面上产生电磁场的场强空间分布图,用色标表示了场强值在空间分布的强弱。电磁场的水平分量在地面上产生电磁场的场强值要比垂直分量产生的场强值大,单条线天线在地面上产生电磁场的场强值要比两条线天线产生的场强值小。     

大地-电离层谐振腔中极低频电磁波传播的数值模拟

随着极低频探地技术的发展,极低频电磁波在大地和电离层组成的腔体中的传播成为人们感兴趣的研究课题.基于时域有限差分算法,建立了地-电离层腔体中极低频电磁场的时间步进迭代公式,并分别计算了时谐振荡源和高斯脉冲源所激励的极低频电磁场及其传播特性,给出了可视化的计算结果,演示了球面导波结构对电磁波的汇聚效应以及地-电离层腔体中的舒曼谐振效应.     

极低频/超低频/甚低频宽带磁传感器技术研究

分析了极低频/超低频/甚低频(ELF/SLF/VLF)宽带磁传感器的工作原理,解决了磁天线低噪声、放大器低噪声、传感系数标校等关键技术问题,研制了ELF/SLF/VLF宽带磁传感器的样机并对其幅度特性、相位特性进行了测试,测试结果表明:设备性能达到了预期研究目标。     

SLF/ELF垂直电偶极子在理想导电地-电离层中的场

在理想导电地面与电离层条件下,我们导出了SLF/ELF垂直电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,并提出了一种加速收敛算法。利用此算法分别算出了电场分量随传播距离、高度及工作频率的变化,所得计算结果与Barrick方法所得结果基本吻合。由于地面和电离层没有吸收损耗,地面与电离层之间产生的场是＂驻波＂,在ELF频段,其频率变化规律能正确反映出＂舒曼＂谐振现象。     

SLF/ELF水平电偶极子在地-电离层波导中的场

在非理想导电地面与电离层条件下,导出了SLF/ELF水平电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,采用一种加速收敛算法,算出了波导中的电磁场分布.根据计算结果,在SLF频段,地面与电离层之间的电磁场可理解为两个"行波"的叠加,且与SLF频段的球面二阶近似算法计算结果吻合很好.在ELF频段,壳体中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

Propagation of ELF waves below an inhomogeneous anisotropic ionosphere

The ionospheric anisotropy is considered with horizontal magnetic field either for transverse (East-West or West-East) or for longitudinal (South-North) propagation. For transverse propagation in a vertically stratified medium the differential equations of the various field components are uncoupled and a closed form solution is given for identical exponential height variation of the components of tensor conductivity. For arbitrary height variation of the tensor conductivity numerical solutions are obtained after expressing the surface impedance below the ionosphere in terms of a Riccati-type differential equation. The West-East direction of propagation exhibits a lower attenuation constant than the East-West direction forf < 1000cps. This is contrary to the expectations based on a model of a homogeneous anisotropic ionosphere. For longitudinal propagation the differential equations of the various field components are coupled, with the coupling being particularly strong above theDregion. The differential equations are simplified by assuming no coupling in the lower ionosphere and strong coupling above a pre-selected altitudey_{1}. For exponential height variation of the tensor conductivity components the closed form solution differs negligibly from the isotropic case. For arbitrary height varition of the tensor conductivity numerical solutions are obtained similarly as for the transverse propagation. Over most of the frequency range the attenuation figures for South-North propagation are intermediate between the corresponding figures for West-East and East-West propagation.     

Fast Convergence Algorithm for Earthquake Prediction Using SLF/ELF Horizontal Electric Dipole during Day and Night and Schumann Resonance

Electromagnetic wave radiation from a SLF/ELF horizontal electric dipole (HED) related to seismic activity is discussed. In order to estimate the effects on the electromagnetic waves associated with the seismic activity, SLF/ELF waves on the ground radiated from a possible seismic current source modeled as a electric dipole, are precisely computed by using a speeding numerical convergence algorithm. A theoretical calculation of the VLF/SLF electric wave propagating among the Earth-ionosphere cavity generally utilizes the full wave method to solve the model equation. The field in the cavity is comprehended as the sum of each wave mode. However, this method is very complex, and unsuitable to the ELF frequency band. In 1999, Barrick proposed an algorithm, which was only suitable to solve the electromagnetic problems under the ideal electric conductor condition. To solve the problems under the non-ideal electric conductor condition, we have further developed Barrick??s method and proposed a speeding numerical convergence algorithm. The spherical harmonic series expressions of electromagnetic fields excited by SLF/ELF HED in non-ideal Earth-ionosphere cavity are derived. The speed of this algorithm is faster thirty times than it of calculating directly the sum of the series. If it calculates directly the sum of the series, it needs 1,000 series items, while it needs only 200 series items by this algorithm. Our algorithm is compared with the second order spherical surface approximate algorithm, and two algorithms agree with each other very well. Therefore, our algorithm is correct. Schumann resonance is also verified.     

Reduction of common-source inductance in FET/HEMT structuresutilizing wave-propagation effects

In this paper, a novel high-frequency/high-power field-effect-transistor structure is presented to reduce gain degradation caused by common-source inductance. In this structure, the reduction in common-source inductance is achieved without the need for using very thin substrates or very complicated fabrication technology, such as vias under each source finger. Using detailed transmission-line modeling, it is shown that a significant reduction in common-source inductance and improvement in RF performance can be achieved even for moderately high values of source grounding via inductance. The new structure allows simpler fabrication technology and is expected to be particularly useful to reduce the cost and improve the performance of high-power microwave and millimeter-wave devices and circuits     

Fast Convergence Algorithm for Earthquake Prediction Using Electromagnetic Fields Excited by SLF/ELF Horizontal Magnetic Dipole and Schumann Resonance

In order to estimate where the electromagnetic radiation associated with the seismic activity comes from, the propagation characteristics of the SLF/ELF electromagnetic waves on the ground should also be studied. The radiation source may also be modeled as a horizontal magnetic dipole (HMD), and it is precisely calculated by using a speeding numerical convergence algorithm. A theoretical calculation of the VLF/SLF electric wave propagating among the Earth-ionosphere cavity generally utilizes the full wave method to solve the model equation. The field in the cavity is comprehended as the sum of each wave mode. However, this method is very complex, and unsuitable to the ELF frequency band. To solve the problems under the non-ideal electric conductor condition, we have further developed Barrick’s method. The approach we employ below subtracts and adds appropriate identical terms to the original exact series. The subtraction accelerates significantly its numerical convergence. The added terms sum to simple closed-form expressions. The spherical harmonic series expressions of electromagnetic fields excited by SLF/ELF HMD in non-ideal Earth-ionosphere cavity have been derived. The speed of our algorithm is faster twenty eight times than it of calculating directly the sum of the series. If it calculates directly the sum of the series, it needs 1,200 series items and takes 17 min, while it needs only 300 series items and takes 0.6 min. Moreover, under the ideal electric conductor condition, we have verified the correct of our algorithm that the result coincides with that of Barrick’s method. Schumann resonance is also verified.