Shift Operator Finite-difference Time-domain Method Research Articles

Research on Transmission Characteristics of Two-Dimensional Superconducting Photonic Crystal in THz-Waves

In this paper, the transmission characteristics of two-dimensional photonic crystal with Hg-1223 cylindrical array in transverse magnetic mode are studied in terahertz-waves by shift operator finite-difference time-domain method. The effects of external temperature and pressure and the period and radius of the dielectric cylinders on the transmission properties of superconducting photonic crystal in terahertz-waves are studied. The simulation results show that external temperature and pressure can be used to change the plasma frequency of superconductor, thus adjusting band gap width of superconducting photonic crystal. The decreasing of the external temperature or the increasing of the pressure have resulted in the increasing of the band gap width of superconducting photonic crystal, while increasing external temperature or decreasing the pressure can decrease the band gap width, which gradually becomes apparent as temperature increases or pressure decreases. In addition, the increasing of the periods and radius of superconducting cylinders can also broaden the band gap of superconducting photonic crystal in terahertz-waves. The research in this paper is in terahertz-waves, and all the cutoff frequencies of band gap are between 0.1 and 6 THz, which provides references for practical application of superconducting photonic crystal.

Effect of the plasma sheath on the propagation of low frequency radio waves

The plasma sheath formed around a hypersonic vehicle traveling through the atmosphere will affect the quality of wireless signals. To fully grasp this effect, it is necessary to comprise the vehicle antennas in the investigations, which is considered in our work. Firstly, the discrete plasma sheath data is generated by using COMSOL. Then, combining the shift-operator Finite-Difference Time-Domain method and numerical methods such as the high-dimensional Lagrange interpolation, an electromagnetic algorithm designed for the discrete plasma sheath data is developed. Based on this, the influence of the plasma sheath on the radio wave propagation is studied under different flight condition. Results show that, due to the influence both of the plasma sheath and of the vehicle antenna, the radio waves exhibit rich propagation behaviors, such as the frequency-band shift and the tail diffraction, etc. Compared with other studies, the results in this paper more approximately reflect the propagation characteristics of radio waves in the hypersonic environment, and can provide a reference for the related applications.

Propagation characteristics of THz waves in space-time inhomogeneous and fully ionized dusty plasma sheath

When a hypersonic vehicle flies in near-space, the electron density of the plasma surrounding the aircraft is inhomogeneous and varies with time. Ablation occurs around the vehicle as the temperature rises. Therefore, investigating the propagation characteristics of electromagnetic (EM) waves in a space/time inhomogeneous and fully ionised dusty plasma sheath is important. In this article, a space/time inhomogeneous dusty plasma sheath model is first established. The expression of the dielectric coefficients of weakly collisional and fully ionised dusty plasma sheath is adopted. The shift-operator finite difference time-domain method is used to calculate the reflection and transmission coefficients of different dusty particle concentrations and radii, changes in electron density with time, electron temperatures and ion charges in the terahertz (THz) band. Finally, the propagation characteristics of THz waves with different electron density distributions at eight re-entry heights are analysed. Results show that increasing the incident wave frequency can effectively improve the effects of dusty particle concentration and radius, electron temperature and ion charge on the transmission of the EM wave. Different electron density change forms and electron density distributions significantly influence the propagation properties of THz waves.

An improved cascaded SO-FDTD method for high temperature magnetized plasma

An improved cascaded shift operator finite-difference time-domain method is put forward for high temperature magnetized plasma. The calculation formulas of iterative coefficients of this method are given. These results show that the improved method can let the mathematical formula reduce math order and the computational complexity. This is contributed to the derivation of the formula and the compilation of the calculation program. The absorption and reflection characteristics of high temperature magnetized plasma on electromagnetic wave are studied by using this improved CSO-FDTD method. The effects of external magnetic field and temperature on the attenuation coefficient and absorption coefficient of the plasma are discussed. A new phenomenon is found, namely, a sharp transmission peak emerged in the physics band formed by a terahertz wave passing through the monolayer plasma. By studying the effects of external magnetic field and temperature, the phenomenon can be simply produced by monolayer high temperature plasma.

Plasma Passive Jamming for SAR Based on the Resonant Absorption Effect

The resonant absorption effect between plasma and electromagnetic waves makes the plasma a potential efficient passive jamming method for synthetic aperture radar. In this paper, the validity of plasma passive jamming is verified by comparing the echoes with and without plasma. First, the shift operator finite-difference time-domain method is utilized to numerically calculate the echoes from different plasma parameters. Then, the images of point target with and without plasma are obtained and compared. The image of point target with plasma is partly focused and the geometry character of point target is destructed. The simulation and analysis results validate the effectiveness of the proposed plasma passive jamming method.

Research on the scattering characteristics of electromagnetic waves in time‐varying and weakly collisional and fully ionized dusty in plasma

In this study, a three-dimensional (3D) time-varying dusty plasma iterative finite-difference time-domain (FDTD) algorithm is deduced by combining the relative permittivity of fully ionised dusty plasma and the shift-operator FDTD method. Then, a 3D time-varying dusty plasma model is established. The scattering characteristics of electromagnetic (EM) waves are analysed by calculating the backward radar cross-sections (RCSs) of different parameters in time-varying dusty plasma. The results show that the RCS will increase when the dust particles are considered in plasma. The values of RCS increase with the dust radius dust concentration relaxation time of charge and electron density increasing. In dusty plasma, the electron temperature has a different effect on the incident wave frequency bands. Finally, the effects of dust to electron density ratio on RCS are analysed and as the increase of the incident frequency, the absorption of dusty plasma on EM wave will reduce.

Evaluations of Plasma Stealth Effectiveness Based on the Probability of Radar Detection

To overcome the limitations of radar cross section characteristic, a method using detection probability as an indicator to evaluate plasma stealth effectiveness is proposed in this paper. Based on shift operator finite-difference time-domain method, the distorted waveform of linear frequency modulation radar echo is obtained when the targets coated with plasma. Then, by making a comparison between outputs of pulse compression with and without plasma, the peak instantaneous signal-to-noise ratio (SNR) loss is calculated. According to the signal detection theory, the relationship between plasma parameters and radar detection probability is built up through the SNR loss, in which the attenuation of radar echo and the mismatch loss of pulse compression are both considered. Finally, effects of plasma parameters including electron density, collision frequency, and radar frequency on the probability of detection have been studied systematically. By adopting detection probability $P_{d }\le 0.1$ as a valid criterion, the effective plasma parameters for different radar frequencies are given as a guide when using plasma for stealth application.

Finite-difference time domain method for the analysis of radar scattering characteristic of metal target coated with anisotropic ferrite

A metal cylinder coated with anisotropic ferrite material is analyzed using the finite-difference time-domain method (FDTD) in this paper, and the bistatic radar cross-section (RCS) is obtained. The new method of electromagnetic scattering by magnetized ferrite medium is analyzed in detail based on the FDTD. To exemplify the availability of the algorithm, bistatic RCS of a magnetized ferrite cylinder is computed, and the numerical results are the same as the shift operator FDTD (SO-FDTD), which shows that the proposed FDTD method is correct and efficient.

A high efficient SO-FDTD method for magnetized collisional plasma

Based on the Maxwell formulae and the auxiliary differential equation of polarized current density, this paper presents a high efficient shift-operator finite difference time-domain (SO-FDTD) method for simulating magnetized cold plasma, which combines time-domain shift operators with a memory-minimized algorithm. This method is applied to calculate the reflection and transmission of the electromagnetic waves incidence in a magnetized plasma layer, and its accuracy is validated by the analytical method. The bistatic radar cross section of magnetized plasma sphere is also calculated by this method. Numerical experiment demonstrates that the new method is more efficient than the improved SO-FDTD methods proposed in the recent references based on the same accuracy. Moreover, the recursion formulae of the new SO-FDTD method avoid huge expenses of computer resource arising from complicated convolutions and complex or exponential variables, so the computations for magnetized plasma are simpler than other FDTD methods based on recursive convolution or transformation principle such as piecewise-linear current density recursive convolution-FDTD method and Z-transformation-FDTD method proposed in former references.

SO-FDTD method of analyzing the reflection and transmission coefficient of weakly ionized dusty plasma layer

The complex permittivity of weakly ionized dusty plasma is presented as a fractional polynomial in j. A frequency-domain constitutive relation of weakly ionized dusty plasma is given by shift operator finite-difference time-domain (SO-FDTD) method in time domain. Also the recurrence relation on the electromagnetic properties of weakly ionized dusty plasma is deduced by the SO-FDTD. The reflection and transmission coefficients of the weakly ionized dusty plasma layer are calculated, and the influences which is caused by the change of the dust particle concentration and radius on reflection and transmission coefficients are also analyzed by the SO-FDTD method. The result shows that the reflection coefficient in the presence of dust particles is smaller than in the absence of dust particles, while the transmission coefficient in the former case is larger than in the latter case. Besides, it is found that the reflection coefficient decreases as the concentration or radius of dust particle increases.

Shift operator method and Runge-Kutta exponential time differencing method for plasma

In this paper, the shift operator finite difference time domain (SO-FDTD) method and Runge-Kutta exponential time differencing (RKETD) method are introduced. The high accuracy and efficiency of the two methods are verified by calculating the reflection and transmission coefficients of electromagnetic waves through a collisional plasma slab. A comparison of computational efficiency of the two methods is presented by simulating the electromagnetic wave propagation in homogeneous non-magnetized plasma. The numerical results indicate that the calculation time using SO-FDTD method is less than that using RKETD method with almost the same accuracy.

Finite-difference time-domain studies of low-frequency stop band in superconductor-dielectric superlattice

The transmission coefficients of electromagnetic (EM) waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain (SO-FDTD) method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.

The comparison of the CPU time between SO-FDTD method and PLCDRC method for dispersive media

The precision and computational efficiency of the shift operator finite-difference time-domain (SO-FDTD) method are compared with those of the piecewise linear current density recursive convolution (PLCDRC) method by simulating the electromagnetic wave at different frequency propagation in homogeneous unmagnetized plasma in this paper. The results show that the two methods almost have the same precision, but the CPU time of the SO-FDTD method is less than that of the PLCDRC method, this is because the SO-FDTD method eliminates many convolution operations of the PLCDRC method.

A modificatory algorithm for electrically thin dispersive layers base on shift operator finite-difference time-domain method

A novel technique for treating electrically thin dispersive layer with the finite difference time domain (FDTD) method is introduced. The proposed model is based on modifying the node update equations to account for the layer, where the electric and magnetic flux densities are locally averaged in the FDTD grid. Then, based on the characteristics that the complex permittivity and complex permeability of three kinds of general dispersive media model, i.e. Debye model, Lorentz model, and Drude model, may be described by rational polynomial fraction in jω, the shift operator method is then applied to obtain the recursive formulation for D and E, B and H available for FDTD computation is obtained. The model is validated with several numerical examples. The computed results illustrate the generality, memory and time step economy and the precision of presented scheme.

Improved finite difference time-domain method for anisotropic magnetised plasma based on shift operator

Based on the dispersion characteristic of magnetised plasma, an improved shift-operator finite difference time-domain (SO-FDTD) method for anisotropic medium is proposed. The constitutive relations between the polarised current density J and the electric field intensity E in the frequency-domain are written as a rational polynomial function, and the constitutive relations are deduced in the time-domain. Through a shift operator, the constitutive relations in the time-domain are transformed to the discrete time-domain. Thus, the recursion difference equations are obtained for each field component. Compared to the analytical method, current-density (JE) convolution finite difference time-domain method and the original SO-FDTD method, the high accuracy and efficiency of this method are verified by calculating the reflection and transmission coefficient of electromagnetic waves through a magnetised plasma slab.

New FDTD-based method for computing the Lorentz dispersive media

We apply the shift-operator finite-difference time-domain (SO-FDTD) method to the calculation of the Lorentz dispersive media. The Lorentz-medium permittivity is written as a rational fractional function, and the relation between D and E is derived in a time domain. The high efficiency and accuracy of the method is demonstrated by calculating the reflection and transmission of the electromagnetic plane wave impinging on a Lorentz-dispersive-medium slab. The results obtained with the help of the SOFDTD method are compared with analytical results. The SO-FDTD method is proved to have high efficiency and accuracy in computing the Lorentz dispersive media.

Analysis on the Calculation of Plasma Medium with Parallel SO-FDTD Method

This paper introduces a novel parallel shift operator finite-difference time-domain (SO-FDTD) method for plasma in the dispersive media. We calculate the interaction between the electromagnetic wave of various frequencies and non-magnetized plasma by using the parallel SO-FDTD method. Then, we compare the results, which are calculated with serial and parallel SO-FDTD executions to obtain the speedup ratio and validate the parallel execution. We conclude that the parallel SO method has almost the same precision as the serial SO method, while the parallel approach expands the scope of memory and reduces the CPU time.

An improved shift operator finite-difference time-domain method based on digital signal processing technique for general dispersive medium

An improved shift operator finite-difference time-domain （SO-FDTD） method for general dispersive medium based on the implementation of infinite impulse response filter in digital signal processing technique is presented. Compared with the commonly used SO-FDTD, the storage variables in the improved SO-FDTD are reduced by 33% and computational efficiency is also increased. Finally, the generality and the feasibility of the presented scheme are validated by calculations of scattering by first order and second order dispersive objects.