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.     

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.     

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。     

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.     

FDTD模拟SLF\ELF水平电偶极子在非均匀地-电离层波导中的场

在SLF/ELF频段,已有的解析算法对于研究其在非均匀电离层模型下的电磁特性有很大的局限性。采用三维球坐标时域有限差分方法(FDTD)计算了非均匀电离层模型下(考虑电离层白天和黑夜不对称),水平电偶极子产生的SLF/ELF波在球形地-电离层腔体中的传播特性。计算了电场分量和磁场分量沿地面随传播距离的变化,以及随方位角的变化。和均匀电离层模型对比,非均匀电离层模型的计算结果更具有实际意义。     

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。     

离子对SLF／ELF电磁波在电离层中传播的影响

在SLF/ELF频段,离子的磁回旋频率接近甚至高于电波频率,其对电波传播的影响不能忽略.深入分析了SLF/ELF电磁波在电离层中传播时,离子对折射指数、极化因子等参数的影响.研究结果表明:在离地高度大于200 km的高电离层,由于电子与离子的碰撞频率远小于磁回旋频率和电波的频率,离子对电波传播的影响很大.在离地高度70 km左右的低电离层,电子与离子的碰撞频率远大于磁回旋频率,离子对电波传播的影响就可忽略.因此,就SLF/ELF对电离层的反射而言,可不计离子的作用;但对于透射传播,应该考虑离子的作用.     

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.     

中低纬调制高频加热电离层ELF／VLF辐射模拟

从基本的电子能量方程出发,改进了幅度调制HF电波加热低电离层模型.计算了低电离层电子温度和电导率随加热时间的变化,以及不同高度上加热产生ELF/VLF Hall电流大小.根据实际的电离层参数,在一定加热条件下,计算了北京、上海、昆明和海口所产生ELF/VLF Hall总电偶极矩大小.结果表明:利用幅度调制HF电波加热中低纬度地区低电离层,可以有效形成ELF/VLF电波辐射源.     

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.     

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.     

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.     

ELF and VLF fields of a horizontal electric dipole

The waves in the spherical guide between the earth and ionosphere are excited by a horizontal electric dipole. The guide boundaries are characterized by surface impedances and the resulting waves are expressed as a superposition of TM and TE modes. The wavenumbers, excitation factors, height-gain functions, and height-dependent impedances are examined for both types of modes. A thin-shell approximation of the radial wave functions is shown to be adequate for phase velocity estimates; but other propagation parameters are of restricted validity in the VLF range where Airy integral approximations provide more reliable data. A horizontal electric dipole is shown to provide a nearly omnidirectional coverage of horizontal field components in the frequency range of the lower Schumann resonances. For an elevated source the horizontal fields are essentially omnidirectional also in the VLF range. Near fields are expressed as a summation of waveguide modes. The vertical field components vanish at the antipode, but the horizontal components remain of finite magnitude.     

Primary VLF/ELF currents produced by heating the lower ionospherein parts of China

A new iterative method is employed to calculate the primary ELF/VLF currents produced by heating the lower ionosphere with powerful modulated waves. The calculations are mainly for parts of China, as well as For Tromso, Norway for comparison. The results indicate that first, there are many similar characteristics for Beijing and Tromso, secondly the ELF/VLF currents in Haikou are much larger than those in Beijing and Tromso if the natural electric fields are equal