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The rough structure may affect the flow field and electromagnetic (EM) scattering characteristics of a hypersonic vehicle. In this study, the EM scattering characteristics of the hypersonic vehicle RAM C-II with a microrough surface were investigated in the millimeter wave band. We first simulated the flow field of a smooth RAM C-II vehicle and calculated the radar cross section (RCS) in the wideband using the physical optics method. The calculation results show that many factors contribute to the variation in the RCS; however, it is occasionally difficult to predict. We then used a one-dimensional Gaussian random rough surface to generate a RAM C-II with a microrough surface through a point-coordinate transformation and simulated its flow field. The electron density flow field of the rough surfaced aircraft fluctuates greatly on the wall. Finally, we calculated the RCS of RAM C-II with different values of roughness in the millimeter wave band. The change of surface structure can be reflected in millimeter waves, and the RCS is determined by both plasma and rough structure. [ABSTRACT FROM AUTHOR]

Electron density is one of the most important parameters for characterizing plasma properties, so obtaining accurate electron density is a prerequisite for studying the interaction between plasma and the electromagnetic waves. This paper presents the effects of different electron densities on the electric field distribution of a microstrip antenna with a center frequency of 2.45 GHz. Then, on the basis of the integrated model of plasma and the microstrip antenna, the Bayesian regularization neural network (BRNN) is used to retrieve the electron density of inhomogeneous plasma. Furthermore, the performance of the proposed approach is evaluated and analyzed by comparison with Levenberg–Marquardt (LM) and Scaled Conjugate Gradient (SCG) neural networks. The results show that the BRNN provides better performance than LM and SCG neural networks to retrieve plasma electron density based on the electric field intensity at fewer spatial positions. The accurate distribution of the electron density of inhomogeneous plasma can be obtained using BRNN. In addition, the greater the range variation of electron density, the greater the relative inversion error. This study provides an important theoretical basis for the diagnosis of electron density for inhomogeneous plasma in experiments. [ABSTRACT FROM AUTHOR]

The attenuation characteristics of obliquely incident electromagnetic (EM) wave in L-Ka frequency band in weakly ionized dusty plasma are analyzed based on the modified Bhatnagar–Gross–Krook (BGK) collision model. According to the kinetic equation and the charging theory, the total complex dielectric constant of the weakly ionized dusty plasma is derived by considering that the minimum velocity of the electron accessible to the dust particle surface is non-zero and the second potential part of the collision cross-section contributes to the charging. The attenuation characteristics within the modified model are compared with those within the traditional model. The influence of the dusty plasma parameters and the incident angle of EM waves on the attenuation in weakly ionized dusty plasma is further analyzed. Finally, the influence of different reentry heights on the attenuation characteristics of the obliquely incident EM wave is discussed. The results show that the effect of the minimum electron velocity and the second term of the collision cross-section on the attenuation characteristics of EM waves cannot be ignored. When the dust density and dust radius are changed, the trends of the attenuation of obliquely incident EM waves are consistent, but the influence of dust density is weaker than that of dust radius due to the constraint of orbit-limited motion (OLM) theory. The plasma thickness, electron density, and incident angle are proportional to the attenuation amplitude of EM waves. The effect of different reentry heights on the attenuation obliquely incident EM waves is related to the electron density and plasma thickness. [ABSTRACT FROM AUTHOR]

A new electromagnetic (EM) calculation model, the inhomogeneity zonal medium model (IZMM) (based on the physical optics (PO) method), is proposed to calculate and analyze the EM scattering characteristics of hypersonic vehicle covered with a plasma sheath. First, the flow field of the plasma sheath is divided into nonuniform calculation subregions with different spacing sizes. The shape of the external flow field of the aircraft is modeled by fitting with a paraboloid and circular platform with different radii. Then, the electron density, temperature, and pressure distribution are obtained by collecting data from different points in the flow field of the sheath. Finally, a piecewise PO method is used to calculate the backscattering radar cross section (BRCS) of the hypersonic vehicle covered with plasma sheath from $L$ -band to $X$ -band. The numerical results show that the EM scattering characteristics of a target spacecraft covered with a plasma sheath can be described more accurately by using zoned medium model simulation. Under different flying conditions, the BRCS of hypersonic vehicle covered with a plasma sheath appears to be reduced to different degrees in the $S$ -band and the band range of 7–11 GHz, and a large attenuation of BRCS occurs in the head area of the aircraft. The research results enrich the EM modeling method of hypersonic vehicles, overcome some shortcomings of the existing PO method, and provide technical support and innovative ideas for the accurate analysis of the EM scattering characteristics of hypersonic targets. [ABSTRACT FROM AUTHOR]

3-D time-varying and spatially nonuniform plasma is applied using the finite-difference time-domain algorithm in investigating the effects of electromagnetic (EM) wave scattering in the plasma sheath. The plasma sheath is stratified in space, and three types of electron density in time-varying forms are assumed. The characteristics of different time-varying forms are analyzed using radar cross section (RCS). In addition, the effects of RCS change with time at S - and L -bands are investigated using electron density as the time variable. In the condition of time-varying and spatially nonuniform plasma sheath, the attenuation of EM wave is affected by different time-varying regularities of electron density ( ne ). The RCS varying with time is related to the change rate of ne . [ABSTRACT FROM PUBLISHER]