| When a hypersonic vehicle is flying at high speed in the adjacent space,the vehicle will violently rub against the air,causing a plasma sheath of complex structure composed of dozens of chemical components to be generated around the vehicle.The plasma sheath on the periphery of the aircraft will cause effects such as scattering and attenuation of incident electromagnetic waves.In severe cases,communication will be interrupted and the outside world cannot communicate with the aircraft,which is a "black barrier" phenomenon.In addition,the existence of the plasma sheath will also affect the radar cross section of the aircraft,which puts forward higher requirements for radar detection and radar warning.Based on the inductively coupled plasma generator,this paper carries out ground simulation measurement,and simulates and analyzes the electromagnetic wave propagation and scattering problems in inhomogeneous plasma,and provides basic analysis for the communication,navigation,positioning and other technologies of hypersonic aircraft.The main work of the thesis is as follows:1.Non-uniform plasma electron density measurement and simulation analysis.Based on the inductively coupled plasma generator,argon is used as the working gas,and the electron density on the central axis of the cavity under different powers,pressures,and different air intakes is measured and analyzed by the probe method.A two-dimensional axisymmetric inductively coupled plasma model was established according to the actual size,and the plasma electron density and electron temperature distribution under different power,different pressure,and different intake air volume in the cavity were obtained by calculation and compared with the experimental results.2.Research on the transmission characteristics of electromagnetic waves in inductively coupled plasma has been carried out.Based on the ICP plasma device,five sets of patch antennas are used to measure the S21 parameters of the antennas when electromagnetic waves of different frequencies are transmitted in plasmas with different densities and different distributions.The equivalent transmission line method is used to calculate the reflection coefficient and transmission coefficient under different electron density distributions.Finally,the influence of the presence or absence of dust in the cavity and the plasma under different dust sizes and dust densities on the electromagnetic wave transmission characteristics is analyzed.3.A numerical simulation model of the ICP cavity was established,and the influence of the blunt-nosed cone and pointed cone model in the cavity on the distribution of plasma electron density,electron temperature,and gas flow velocity was analyzed.The JEC-FDTD method was used to calculate the different frequencies.The electromagnetic scattering characteristics of plasma-coated targets under different pressures,and the influence of different plasma parameters on RCS is analyzed.4.Based on the support vector machine method,the inversion research of electromagnetic parameters in inhomogeneous plasma is carried out.The two-dimensional plasma cylindrical scattering cross-section calculated by the numerical method is used as the characteristic value,and the parameters to be inverted are used as the target value,and the inversion model of the two-dimensional plasma electron density and the collision frequency is established.Using TE and TM wave incidence models,the inversion model of the plasma with the linear and parabolic distribution of electron density was simulated and verified. |
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