High Frequency Electromagnetic Wave Propagation Research Articles

Mixed Spectral Element Method for Electromagnetic Secondary Fields in Stratified Inhomogeneous Anisotropic Media

The spectral element method (SEM) is widely used for analyzing high frequency electromagnetic wave propagation and scattering in complex structures. At low frequencies, however, the primary (direct) fields are usually much larger than the secondary fields caused by scattering, thus making it much more difficult to accurately simulate the secondary (scattered) fields because of the source singularity in the primary fields. To more effectively and accurately simulate the low-frequency secondary fields in subsurface structures, in this work the vector Helmholtz equation for the scattered fields is used to directly obtain the secondary field data in inhomogeneous anisotropic media. The computational method for the secondary electromagnetic fields is based on the mixed spectral element method (mixed SEM) for anisotropic objects in a layered anisotropic background medium. The electromagnetic field is separated into the background fields that are evaluated analytically using the dyadic Green's functions (DGFs) of a layered uniaxially anisotropic medium, and the secondary fields caused by anomalous bodies with arbitrary shapes are numerically computed by the mixed SEM. This avoids the source singularity, and allows the transmitters to be located outside the computational domain. By enforcing Gauss' law as the constraint condition, the mixed SEM efficiently eliminates the low frequency breakdown problem. Numerical results verify the proposed method over the traditional SEM in low-frequency scattering from objects in subsurface layered anisotropic media.

Numerical simulation of the propagation of electromagnetic waves in ionospheric irregularities

The characteristics of high-frequency (HF) electromagnetic (EM) wave propagation can be affected when EM waves propagate in the ionosphere. When ionospheric irregularities appear in the ionosphere, they can have a serious impact on the propagation of HF EM waves. In this study, the propagation of HF EM waves in ionospheric irregularities was investigated by numerical simulation. First, a two-dimensional model of plasma bubbles was used to produce ionospheric irregularities in the ionosphere. A ray-tracing method was then utilized to simulate the propagation of HF radio waves in these ionospheric irregularities. Results showed that the propagation of HF radio waves in the ionosphere was more complex in ionospheric irregularities than without ionospheric irregularities. In addition, corresponding ionograms were synthesized by radio rays propagated in the ionosphere with these irregularities. The synthesized ionograms were then compared with the experimental ionograms recorded by an ionosonde. Results showed that spread F could be simulated on the ionograms when ionospheric irregularities occurred in the ionosphere. This result was consistent with the ionosonde observations.

Numerical Simulation Modeling of GPR on Road Disease

Numerical simulation of ground penetrating radar is an effective way of analyzing and studying high frequency electromagnetic wave propagation rules in the underground media. In this paper, Finite-Difference Time-Domain (FDTD) method is used for numerical simulation to form radar records reflection profile about road disease such as loose disease. The purpose is to study and sum up the radar wave propagation rules and reflection signal characters in this diseases media, in order to provide reliable theory support for road maintenance and evaluation.

FDTD Numerical Simulation of Absorption of Microwaves in an Unmagnetized Atmosphere Plasma

Numerical simulations based on the finite-difference-time-domain (FDTD) approximation to multi-fluid equations for positive ions, negative ions and electrons are used to study high frequency electromagnetic wave propagation and absorption in an unmagnetized plasma layer. The interaction between the incident high frequency wave and the plasma layer shows that the existence of negative ions and the nonlinear effect reduces the power absorption capability of the plasma. Parameter dependences of the effects are calculated and discussed.

Modeling High Frequency Propagation in Tunnel Environments by IterativePhysical Optics Method

A new formulation of the Iterative Physical Optics (IPO) method, including waveguide wall loss effects, has been developed to model high frequency electromagnetic wave propagation in tunnel environments. The lossy behavior of the tunnel walls has been considered throughout the inclusion of the Impedance Boundary Condition (IBC) model in the formulation of the IPO. Different arched tunnels have been studied, showing that this approach has a convergent behavior and providing accurate results for realistic tunnel models. Moreover, the computational cost associated with the analysis of long tunnels has been significantly reduced by using a connection scheme which splits the tunnel into a set of short sections that can be more easily analyzed. Some results are shown, illustrating the capability of the proposed method.

Theoretical and experimental approach of the propagation of high frequency waves in road tunnels

Characterization of high frequency electromagnetic wave propagation in tunnels has important applications in the field of mobile communication. In long tunnels, the amplitude of the electric field radiated by a retransmitting antenna can be easily calculated from ray theory. However, for short tunnels, one of the most critical points is either the radiation towards free space of a mobile station emitting in the tunnel or, on the contrary, the penetration of an external wave inside the tunnel. This coupling between the inside and the outside is treated through the uniform theory of diffraction. By comparing theoretical and experimental results, it is shown that this theory leads to adequate prediction of the field variation and allows the authors to point out the influence of parameters, such as the position of the mobile in the tunnel and the influence of the angle of incidence, on the entrance plane of an incoming external wave.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>