Research On The Mechanism Of Electromagnetic Wave Propagation In Plasma Sheath

The simulation of electromagnetic wave propagation plays an important role in solving the problem of"communication interruption".The result of"communication interruption"is that when the frequency of electromagnetic waves is close to or lower than the oscillation frequency of plasma,electromagnetic waves(EMW)will decay sharply.Therefore,a deep understanding of the propagation characteristics of electromagnetic waves in the plasma sheath plays an important role in solving the problem of"communication interruption".This paper models the propagation of electromagnetic waves in cold plasma sheaths and warm plasma sheaths respectively,and then analyzes the propagation characteristics of electromagnetic waves by observing the field distribution.At present,most of the related work is almost carried out based on the cold plasma sheath model,ignoring the plasma temperature and spatial dispersion effects.Therefore,this article focuses on the electron temperature term in the electromagnetic wave propagation model under the plasma sheath,and compares with the traditional cold plasma model to study the mode conversion and spatial dispersion effects of electromagnetic waves in warm plasma.In addition,the energy dissipation and power deposition characteristics of electromagnetic waves propagating in the plasma sheath are analyzed in detail.In the cold plasma,the difference in coefficients between s-polarized waves and p-polarized waves can be further explained by the presence or absence of mode conversion.The s-polarized electromagnetic wave decays exponentially from the cut-off position.When the real part of the plasma relative permittivity is close to 0,the non-normally incident p-polarized wave will undergo mode conversion.In addition,this article also calculated and analyzed the frequency response of reflection coefficient,transmission coefficient and absorption coefficient in detail.In the warm plasma,the p-polarized wave with oblique incidence is intensively simulated,because the spatial dispersion has no effect on the s-polarized wave or the p-polarized wave with normal incidence in which the Langmuir wave is completely decoupled from the electromagnetic wave.Compared with cold plasma,the maximum values of|E_1y|and|ne1|in warm plasma are significantly reduced.Both|E_1x|and|E_1y|are modulated near the resonance region,which is caused by the propagation of Langmuir waves converted from electromagnetic waves.For the p-polarized wave with a proper incident angle in the entire inhomogeneous plasma sheath,two typical cases are considered,there is resonance(min{?_pe}<?<max{?_pe})and there is no resonance(?>max{?_pe}):(1)When resonance occurs(min{?_pe}<?<max{?_pe}),it can be observed that|E_1y|has two reduced and broadened peaks in warm plasma,and the reflection coefficient in the frequency range where resonance occurs The absorption coefficient and the absorption coefficient are also affected accordingly,while the transmission coefficient is not affected.This is because the Langmuir wave can only propagate in the plasma region and does not contribute to the transmission wave.(2)When the resonance condition(?>max{?_pe})is not satisfied,the field distribution in warm plasma is almost the same as that in cold plasma except for the slight modulation in|E_1y|.The interaction between electromagnetic waves and plasma is very weak and can be ignored.The reflection coefficient and absorption coefficient outside the resonance region are also not affected by the electron temperature.The power deposition curve of s polarization is divided into three categories:f<Min(f_pe/cos?),Min(f_pe/cos?)<f<Max(f_pe/cos?)and f>Max(f_pe/cos?)?When f<Min(f_pe/cos?),EMW does not exist in the entire plasma sheath,and the power deposition is concentrated near the left boundary of the plasma sheath.If f>Max(f_pe/cos?),the power deposition can cover the entire plasma sheath and maximize near the center of the plasma sheath.When Min(f_pe/cos?)<f<Max(f_pe/cos?),the power deposition can penetrate into a certain depth of plasma sheath.When the resonance between EMW and electron plasma oscillation occurs in the frequency range of Min(f_pe/cos?)<f<Max(f_pe/cos?)the power deposition profile with p-polarization and oblique incident angle is concentrated at the left resonance position.When the electron collision frequency increases,the resonant absorption peak of the power deposition profile decreases and becomes wider.The power deposition without resonance is similar to the case of s-polarized EMW.The volume integral of power deposition is the absorption coefficient.For s and p-polarized EMW,the characteristics of the absorption coefficient are different.For s polarization,the absorption coefficient is maximized near the frequency of Max(f_pe/cos?).As the electron density gradient decreases,the absorption bandwidth becomes narrower.However,increasing the electron collision frequency will not only increase the amplitude peak of C_A,but will increase the frequency bandwidth of the absorption coefficient.