Jin-Sheng Zhang

Combined IE-FDTD Algorithm for Long-Range Loran-C Ground-Wave Propagation

The integral equation (IE) method and finite-difference time-domain (FDTD) method are combined for the prediction of long-range Loran-C ground-wave propagation. Being capable of modeling the topography details, the combined IE-FDTD algorithm has much better accuracy than the integral equation method. On the other hand, it saves computational resources dramatically as compared to a full FDTD solution. Measurement results along two paths between Xuancheng and Songshan China are used to validate the proposed algorithm.

A New Method for Loran-C ASF Calculation over Irregular Terrain

The finite-difference time-domain (FDTD) method is employed to improve the prediction accuracy of the Loran-C additional secondary factors (ASFs) over irregular terrains. The FDTD method is validated by comparing the results with the theoretical method with flat Earth formula, and then the ASFs are studied as functions of the mountains slope gradient, height, and width, respectively. The cases with multiple mountains in the propagation paths are also studied. Numerical results show that when the gradient of the mountain is low, the FDTD and integral equation methods both perform well. However, when the gradient of the mountain is rather high, before the mountain area, the FDTD method predicts the ASFs oscillation caused by the reflected and scattered wave from the terrains, whereas the integral equation method is not applicable. Therefore, the FDTD method is better than the integral equation method in predicting Loran-C signals propagating over the region with serious irregularities. The measured ASFs of Loran signals are taken along two real paths between Pucheng and Qinling Mountains in Shaanxi Province, China. It is found that most of the measured and FDTD results have good agreement while some still have certain errors due to the model approximation measured. The ASFs change rapidly in the region with serious irregularities.

An Effective CFS-PML Implementation for Cylindrical Coordinate FDTD Method

The stretched coordinate (SC) perfectly matched layer (PML) absorbing boundary in cylindrical coordinate system is implemented using the bilinear transform technique. The proposed PML performs much better in attenuating low frequency evanescent waves as compared to the conventional UPML (anisotropic medium). Numerical results show the efficiency of the proposed algorithm.

Combined Piecewise Linear Recursive Convolution-Bilinear Transform Implementation of the CFS-PML for Unmagnetized Plasma

The complex frequency shifted (CFS) perfectly matched layer (PML) has been proven to be more efficient in attenuating evanescent waves and reducing late-time reflections than the original PML. In this letter, the piecewise linear recursive convolution (PLRC) method is combined with the bilinear transform (BT) to implement the CFS-PML for unmagnetized plasma simulation. Compared to the original bilinear transform implementation, the computational cost of the PLRC CFS-PML is greatly reduced with the same absorbing performance.

FDTD Simulation for Wave Propagation in Anisotropic Dispersive Material Based on Bilinear Transform

The finite-different time-domain (FDTD) method is applied to solve wave propagation in anisotropic dispersive materials by means of bilinear transform (BT) technique. The frequency-dependent and anisotropic constitutive relation is translated into time-domain update equations with coupled x- and y-components of electric fields. The proposed algorithm has a simple formulation and is easy to apply to general dispersive anisotropic or isotropic material. The transmission and reflection coefficients of a 9-mm magnetized plasma slab are calculated and compared to analytical solutions for validation purpose. Very-good agreements are found in both amplitude and phase of these coefficients.

An Unconditionally Stable WLP-FDTD Model of Wave Propagation in Magnetized Plasma

The weighted Laguerre polynomials-based finite-difference time-domain algorithm is applied for modeling wave propagation in a magnetized plasma medium. Its anisotropic property is treated by solving a set of tightly coupled current densities components implicitly at each iteration step. The equations are formulated in a stretched-coordinate system for the implementation of perfectly matched layer. Numerical examples validate the accuracy and efficiency of the developed algorithm.

Tridiagonalized WLP-FDTD Implementation for Wave Propagation in Magnetized Plasma

We present an efficient implementation of the unconditionally stable finite-difference time-domain (FDTD) algorithm based on the weighted Laguerre polynomials (WLPs) for the modeling of wave propagation in magnetized plasmas. The sparse matrix equation is tri-diagonalized by using a factorization-splitting (FS) scheme, leading to a significant reduction in computational time. The algorithm is validated by numerical experiments.

An Effective CFS-PML Implementation for the Cylindrical ADI-FDTD Method

A perfectly matched layer (PML) with complex-frequency-shifted (CFS) constitutive parameters is introduced to the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method in cylindrical grids. The new CFS-PML is based on complex stretching methodology and implemented using bilinear transform. Numerical results show the effectiveness of the proposed implementation.

An Iterative WLP-FDTD Method for Wave Propagation in Magnetized Plasma

We previously developed a tri-diagonalized finite-difference time-domain (FDTD) algorithm based on the weighted Laguerre polynomials (WLPs) for modeling wave propagation in magnetized plasma. The algorithm demonstrated dramatic CPU time reduction in comparison with the original WLP-FDTD algorithm. However, a splitting error was caused owing to the additional perturbation term. In this paper, an iterative scheme is introduced to the tri-diagonalized WLP-FDTD algorithm to further reduce the splitting error. Numerical example shows the accuracy and effectiveness of the proposed algorithm.

Modeling of Wave Propagation in Isotropic Cold Plasma Using Iterative WLP-FDTD Algorithm

In this letter, an efficient implementation of the iterative unconditionally stable finite-difference time domain (FDTD) based on weighted Laguerre polynomials (WLPs) algorithm is presented for isotropic cold plasma. The iterative scheme is employed to reduce the splitting error in WLP-FDTD with factorization-splitting procedure. Meanwhile, a stretched-coordinate perfectly matched layer with a complex-frequency-shifted factor is used as the absorbing boundary condition. Numerical example demonstrates the accuracy and efficiency of the proposed algorithm.