Research On Electromagnetic Wave Propagation Loss Based On Plasma Generator

When a high-speed aircraft reenters the atmosphere,a layer of plasma is generated and covered on the its surface due to air ionization caused by the friction with aircraft,known as plasma sheath.The communication signal is greatly weakened and even totally blocked by plasma sheath,known as"blackout"phenomenon.It severely influenced the safety of aircraft during reentry and landing.Therefore,the study of electromagnetic wave propagation in plasma is of vital importance in space aircraft research.In this thesis,through simulation and experiment,a plasma electromagnetic wave experimental system is designed and the propagation loss of electromagnetic wave in plasma is studied,in order to provide technical support for the research of the blackout problem.The main work of the research is as follows:(1)The plasma parameters are analyzed,and the reasons of electromagnetic wave propagation attenuation in the plasma are discussed,and the plasma model is further analyzed.(2)In the view of experiment,the plasma generation equipment is discussed,a plasma generator using plate discharge is designed based on the glow discharge principle.The feasibility of the generator is verified with COMSOL simulation.The simulation results show that it can produce uniform plasma with high density,and the maximum plasma density reaches 1.5×10⁹m^-3.(3)Based on the plasma density distribution obtained above,the electromagnetic wave propagation model in Drude type plasma is established with CST,and the transmission features of electromagnetic wave with frequency 1-30GHz is simulated and analyzed.Besides,the influence of external electric field,magnetic field and electromagnetic field on the electromagnetic wave transmission in plasma is also researched.The simulation results show that the transmission loss of electromagnetic wave in plasma increases significantly when the working frequency is below 1.2GHz,but has no change in the frequency above 1.2GHz.At the same time,an external electric field is able to help reduce the transmission loss when frequency is below 1.5GHz.Besides,the electromagnetic wave loss characteristics of thin layer plasma are simulated.The simulation results show that the transmission loss of electromagnetic wave in plasma is very large when the working frequency is below 0.85GHz,but is small in the frequency above 0.85GHz.At the same time,an external electric field is able to help reduce the transmission loss when frequency is above 0.70GHz.(4)A plasma generator is designed and fabricated,and the plasma density is measured.The results show that the generated plasma density can reach 1.64×10¹⁵/m³.Based on the plasma generator,an experimental system of electromagnetic wave propagation is established.And the transmission features are experimentally examined.The influence of external magnetic field on the transmission feature is also studied.The experimental results show that when the working frequency is below 5GHz,the plasma strongly affects the propagation of electromagnetic wave in the plasma,with the maximum transmission loss increasing up to 20.9d B,and it has little influence in the frequency above.Apart from that,the decrease of the transmission loss reaches 8.8d B when applied with external magnetic field.