Research On The Propagation Characteristics Of Microwave In Plasma Photonic Crystals

Plasma have a series of effects on microwaves such as total reflection,scattering,and absorption loss.As an important branch in the field of microwave signal transmission,the propagation of microwaves in plasma has always been an active issue.Plasma photonic crystals(PPCs)are a kind of periodic structure materials containing plasma.It inherits the electromagnetic(EM)properties of photonic crystals,and strengthens the effect of plasma on microwaves through EM resonance.PPCs can be used to build applications such as microwave absorbers,narrowband filters,and microwave antennas,etc.Therefore,PPCs have huge application prospects in aerospace,radar wave stealth,microwave communications and other fields.This thesis the related transmission problems of microwaves in PPCs,mainly studying the influence of non-uniform plasma on the EM properties of PPCs,the band cross in PPCs and the principles of related applications,and the non-reciprocal transmission properties of microwaves in magnetized PPCs.The specific content of this article is as follows:(1)H-polarized microwaves can excite SPPs in a non-uniform plasma.These modes are localized inside the plasma,and their frequency is approximately equal to the plasma frequency in the region where they are located.Therefore,there are a large number of lowfrequency absorption peaks in the transmittance curve,and these absorption peaks evolve over time.This evolution reflects the dynamics of the plasma density distribution.(2)Plasma inhomogeneity can cause multiple reflections,which makes the transmittance curve of high frequency microwaves oscillate.At the same time,for Epolarized microwaves,the plasma non-uniformity is equivalent to reducing the plasma frequency,causing the cut-off frequency to decrease;the high-frequency band gap becomes narrower.For H-polarized microwaves,plasma non-uniformity is equivalent to introducing more plasma frequencies.Therefore,there are more zero index band gaps in the transmittance curve of 1D PPCs;more low-frequency SPPs absorption peaks appear in the transmittance curve of 2D PPCs.In general,the plasma non-uniformity has a greater impact on the transmission of H-polarized microwaves.(3)There are two mechanisms for closing the band gap in PPCs,one is related to wave phase and the other is related to wave impedance.For binary 1D PPCs,the condition for closing the band gap is that the optical thickness of the two media are equal and equal to an integer multiple of the half-wavelength in vacuum.In order to obtain a closed band gap,the incident angle and the dielectric constant and thickness of the medium should be reduced as much as possible.For multi-element 1D PPCs,the condition for closing the band gap is that the impedance of the scattering material is equal to the impedance of the background medium.In particular,for the discharge tube array in the air,as long as the dielectric constant of the tube wall is greater than that of air,a closed band gap can be obtained.(4)When the sum of the effective impedances of the two photonic crystals is zero,a narrow-band transmission peak appears in the common band gap.The closer the sum of the two band gaps effective parameters is to 0,the higher the peak transmittance.On the other hand,filters based on 1D PPCs are more sensitive to plasma parameters.Increasing the plasma collision frequency can easily cause filter loss,but reducing the number of cycles can reduce this effect.In comparison,filters based on 2D PPCs have better resistance to plasma loss,which is mainly related to the difference in electric field distribution between the two.(5)Only when the dielectric constants of the incident medium and the exit medium are different,and the H polarized wave is perpendicular to the applied magnetic field,will the phenomenon of non-reciprocal transmission occur.The introduction of periodic structures in the plasma can enhance the non-reciprocal properties.The surface state of the nonreciprocal transmission of the magnetized 1D PPCs has a certain resistance to plasma loss,because it can be expressed locally in a lossless medium.The waveguide mode in magnetized 2D PPCs not only has good directivity,but also has good resistance to defects in the waveguide.