Study Of Plasma Sheath Parameter Fluctuation And Its Influences On Electromagnetic Wave

When an aircraft is flying in the atmosphere with a high speed,the aircraft will impact the air around and heat the air.When the temperature of the air is up to thousands of Kelvin,it will ionize and produce plenty of charged particles.These charged particles form the plasma.The plasma restrained by the hypersonic flow of the aircraft forms a sheath enveloping the aircraft.This sheath is called the plasma sheath.The plasma sheath interacts with the electromagnetic(EM)waves and interferences the TT&C signals.At worst,the TT&C signals will be cut off by the plasma sheath which is known as the blackout and threatens the safety of the aircraft.For remitting and overcoming the blackout,it's necessary to study the influences of the plasma sheath to the EM waves.Essentially,it is because the enormous charged particles that the plasma sheath can influences the EM waves.These particles are subjected by the force of the hypersonic flow and present the characteristics of time-varying and fluctuation.Thus,it is necessary to study the influences of plasma sheath fluctuation on the EM waves.This paper combined the theory of plasma physics and the characteristics of the plasma sheath to study the relation of several major plasma parameters including temperature,pressure,density,electron number density and collision frequency.Then,on this basis,this paper studied the relation of fluctuations of these parameters and contacted them with the fluctuation of the permittivity of the plasma sheath.Based on these relations of fluctuations,this paper studied the influences of plasma sheath fluctuation on the EM waves.In addition,this paper introduced the theory of random medium with EM waves to study the influences of the random properties of plasma sheath on EM waves.The major results are listed below:1.This paper presented a computing method for the collision frequency of plasma sheath.Combing the plasma kinetic theory,and the condition of hypersonic plasma sheath,this paper analyzed the influences of different collision modes and got the computing method suiting the condition of hypersonic plasma sheath.In addition,this paper introduced the influence of EM waves to the particle collisions into the computing method.2.This paper connected the parameters of hypersonic plasma sheath,including temperature,pressure,density,electron number density and collision frequency,studied the relation of fluctuations of these parameters and contacted them with the fluctuation of the permittivity of the plasma sheath.On this basis,this paper analyzed the varying tendencies of these parameter fluctuations in different plasma sheath conditions.3.This paper analyzed the influences of the plasma sheath parameters fluctuations on the propagation properties and polarization properties of EM waves.This paper taken the fluctuations of plasma sheath temperature as example,combing the data of the RAM C fly test,to study the influences of plasma sheath fluctuations in the region of antenna window adjoin the aft of the craft on the propagation properties and polarization properties of EM waves.In addition,the paper studied the variation tendency of the influences with the flight altitude.4.This paper analyzed the influences of the random properties of plasma sheath parameter fluctuations on the propagation and scattering properties of EM waves.This paper taken the fluctuations of plasma sheath temperature as example,combing the data of the RAM C fly test,to study the influences of the random properties of plasma sheath fluctuations in the region of antenna window adjoin the aft of the craft on the scattering and propagation properties of EM waves.In addition,the paper studied the variation tendency of the influences with the flight altitude.The results of this paper provides an approach to analyze the influences of plasma sheath fluctuations and references for the designing of the TT&C systems.