Density Recursive Convolution Finite-difference Time-domain Research Articles

Analysis of weakly ionized ablation plasma flows for a hypersonic vehicle

Hypersonic vehicles are enveloped by a plasma sheath that affects the data transmission and object identification. This paper develops a numerical methodology based on Magnetohydrodynamics equations to study the electromagnetic environment of hypersonic vehicles under the condition of carbon-based thermal protection material ablation. A surface ablation model considering the oxidation and sublimation ablation process is coupled with a Navier–Stokes solver by a gas–solid interaction method to simulate the ablation plasma flows. A piecewise linear current density recursive convolution finite-difference time-domain method is applied to further analyze the interaction between the incident electromagnetic wave and the plasma sheath. The computational results for an HTV-2 type vehicle indicate that both ablation and non-ablation plasma sheaths have significant effects on the electromagnetic environment of the vehicle. Compared with a non-ablation plasma sheath, ablation results in a decrease in the number of electrons and increases the number of neutral particles and therefore changes characteristic parameters of the plasma. Details of the electromagnetic scattering characteristics are reported to highlight the influences of ablation on the reflectivity, penetrability, and absorptivity of the plasma sheath for incident electromagnetic waves over different bands.

Defect mode properties of two-dimensional unmagnetized plasma photonic crystals with line-defect under transverse magnetic mode

The piecewise linear current density recursive convolution finite-difference time-domain method of plasma is used to study the defect mode properties of transverse magnetic wave propagation in the two-dimensional unmagnetized plasma photonic crystals with a line-defect layer. In frequency domain, the transmission coefficients of electromagnetic differential Gaussian pulses are computed, and the effect of lattice constant, dielectric column radius, periodic constant, parameters of plasma and parameters of line-defect layer on defect mode properties of two-dimensional unmagnetized plasma photonic crystals are analyzed. The results illustrate that the frequency of defect mode cannot be tuned by changing periodic constant, position of the defect layer and plasma collision frequency, but be tuned by changing relative permittivity and radius of dielectric column in the defect layer, and central distance between defect layer and dielectric layer with the width of prohibit band gaps fixed. Furthermore, the defect mode and the width of prohibit band gaps can also be tuned by changing lattice constant, dielectric column radius and plasma frequency.

含单缺陷层的一维可调谐磁化等离子体光子晶体滤波特性研究

The plasma rising time, plasma temperature and plasma density are taken as the tunable parameters, under the isothermal hypothesis. The piecewise linear current density recursive convolution finite-difference time-domain method for magnetized plasma is applied to study the filtering properties of one dimensional tunable magnetized plasma photonic crystals with single defective layer. The electro-magnetic propagation process of a Gaussian pulse through a magnetized plasma photonic crystal is investigated. The transmission coefficients through magnetized plasma photonic crystals are calculated based on which the effects of the plasma rising time, plasma temperature and plasma density on characteristic of filtering are analyzed. The results illustrate that the filter channel can be tuned by changing rising time and plasma density and the resonant frequency can not be tuned by changing plasma temperature.

Tunable filter using plasma defect in one-dimensional microwave photonic crystal

A tunable filter is formed when a plasma defect is introduced in the one-dimensional dielectric-air microwave photonic crystal. Plasma is a dispersive medium and its equivalent refractive index is related to the frequency of the incident electromagnatic wave and the plasma frequency， so it is feasible to shift the syntonic frequency of plasma defect by changing the plasma parameters, which behaves as a tunable filter. In the numerical simulation， the finite-difference time-domain method and the piecewise linear current density recursive convolution finite-difference time-domain method are applied to the dielectric and plasma， respectively. The results show that the filter channel of this microwave photonic crystal can be tuned in a wide band in the photonic band-gap by changing the plasma frequency.

FINITE-DIFFERENCE TIME-DOMAIN ANALYSIS OF UNMAGNETIZED PLASMA PHOTONIC CRYSTALS

The plasma photonic crystal is a periodic array composed of alternating thin unmagnetized (or magnetized) plasmas and dielectric materials (or vacuum). In this paper, the piecewise linear current density recursive convolution finite-difference time-domain method for the simulation of isotropic unmagnetized plasma is applied to model unmagnetized plasma photonic crystal structures. A perfectly matched layer absorbing material is used in these simulations. In time-domain, the electromagnetic propagation process of a Gaussian pulse through an unmagnetized plasma photonic crystal is investigated. In frequency-domain, the reflection and transmission coefficients through unmagnetized plasma photonic crystals are computed and their dependence on plasma frequency, plasma thickness, collision frequency is studied. The results show theoretically that the electromagnetic bandgaps of unmagnetized plasma photonic crystals are tuned by the plasma parameters.

Numerical dispersion and dissipation error of the 2-D PLCDRC-FDTD method for plasmas

Recently, a new finite-difference time-domain method for dispersive media called the piecewise linear current density recursive convolution finite-difference time-domain (PLCDRC-FDTD) method has been published. The numerical dispersion relation of the 2-D PLCDRC-FDTD method for plasma is derived. With the numerical dispersion relation, the numerical dispersion error and dissipation error caused by the PLCDRC-FDTD method are investigated by comparing the real part and imaginary part of a numerical index of refraction with those of an analytic index of refraction. The relationships between the numerical dispersion, dissipation errors and different parameters (i.e. EM wave frequency, plasma frequency, collision frequency) are studied.