Research And Design Of Internal Electromagnetic Field Probes In Plasma

When the high-speed aircraft re-enters the atmosphere and the high-speed target will fly at high speed in the adjacent space,it will frictionally with the atmosphere,and its kinetic energy will be continuously converted into heat.The high temperature will continuously ionize the atmosphere into a large number of neutral particles,positive ions and free electrons.Covered on the surface of a high-speed aircraft to form a "plasma sheath." This layer of "plasma sheath" will absorb,reflect and refract and so on the electromagnetic waves injected into it,thereby affecting the propagation of electromagnetic waves,causing communication "black obstacles",restricting the development and utilization of adjacent spaces.The nature of these problems involves the electromagnetic science of high-speed target plasmas.In order to study the interaction mechanism between electromagnetic wave and plasma,the electromagnetic field probe technology is applied to apply the coupling principle to design an electromagnetic field probe suitable for internal measurement of plasma to accurately obtain the amplitude and phase of the electromagnetic field distribution inside the plasma.To provide a scientific research and measurement platform for further study of the electromagnetic wave propagation process inside the plasma and the interaction mechanism between plasma and electromagnetic waves.This paper first introduces the basic electromagnetic radiation theory,analyzes the basic working principle of the electromagnetic field probe,and gives the four performance index parameters of the electromagnetic field probe,including: sensitivity,isolation,bandwidth and resolution,and respectively for each performance.The parameters were introduced to provide calibration criteria for the study design of the probe.Subsequently,the plasma characteristics were analyzed.Since the conventional coaxial structure probe could not be applied to the complex working environment inside the plasma,the probe structure was converted,the coaxial structure was converted into a coplanar waveguide structure,and further the improvement is to protect the metal layer in the high temperature resistant dielectric substrate to avoid direct contact with the plasma.At the same time,the overall design of the probe is given.The design makes the probe tail lengthened and lengthened so that the probe can penetrate deep into the plasma for electromagnetic field scanning measurement.In this paper,the 3D electromagnetic simulation software CST is used to model and simulate the electric field probe and magnetic field probe of the coplanar waveguide structure.The effects of different inner conductor length and frequency on the performance parameters of the probe are studied.Aiming at the unbalanced structure of the coplanar waveguide magnetic field probe,the left and right peak asymmetry of the Y-direction magnetic field distribution on the surface of the microstrip line is scanned and measured,and a feasible structural improvement scheme is proposed.The simulation results verify the good measurement results.After comprehensive consideration of the parameters of the probe,the length of the inner conductor of the electric field probe designed in this paper is 3mm,the receiving power is-36.6dBm,and the resolution is 1.5mm.The improved magnetic field probe receiving power is-35.5dBm,and the resolution is 1.5mm.Finally,the probe was physically processed,and an electromagnetic field scanning measurement system was built.The electric field probe and the magnetic field probe were respectively measured on the surface of the microstrip line.The measured results are basically consistent with the simulation results,which verify the good performance of the probe and meet the engineering application requirements.