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Microwave Doppler spectra of sea return at small incidence angles: specular point scattering contribution 下载免费PDF全文
<正>It is well known that the sea return echo contains contributions from at least two scattering mechanisms.In addition to the resonant Bragg scattering,the specular point scattering plays an important role as the incidence angle becomes smaller(≤20°).Here,in combination with the Kirchhoff integral equation of scattering field and the stationary phase approximation,analytical expressions for Doppler shift and spectral bandwidth of specular point scattering,which are insensitive to the polarization state,are derived theoretically.For comparison,the simulated results related to the two-scale method(TSM) and the method of moment(MOM) are also presented.It is found that the Doppler shift and the spectral bandwidth given by TSM are insufficient at small incidence angles.However,a comparison between the analytical results and the numerical simulations by MOM in the backscatter configuration shows that our proposed formulas are valid for the specular point scattering case.In this work,the dependences of the predicted results on incidence angle,radar frequency,and wind speed are also discussed.The obtained conclusions seem promising for a better understanding of the Doppler spectra of the specular point scattering fields from time-varying sea surfaces. 相似文献
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基于矩量法、互易性定理及镜像理论,提出了一种新的混合方法用于研究水平分界面上方二维介质目标对垂直入射高斯波束的差值散射场.应用镜像理论,介质水平分界面可被原始目标相对于该分界面的镜像目标所替代,从而给出散射问题的等效模型.在等效模型中,应用矩量法求解了原始目标及镜像目标对高斯波束的散射场,同时结合互易性定理得到了原目标与其镜像目标之间的耦合散射场.数值计算结果与相关文献方法及MoM所得结果进行了比较,验证了该混合方法的有效性.
关键词:
互易性定理
电磁散射
高斯波束
二维目标 相似文献
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基于等效原理和互易性定理,研究了N个相互平行二维柱体对平面波/高斯波束的电磁散射特性,给出了求解N阶散射场公式.一阶散射可通过求解单个柱体的散射场得到,但对于高阶散射场而言,由于耦合散射的复杂性,很难给出精确的解析解.为了解决这一问题,借助等效原理和互易性定理给出了求解N阶散射场的面积分公式.只要给出柱体的i-1阶散射场及相关目标表面上的等效电流和(或)等效磁流,就可应用此公式求解i阶散射场.应用该近似方法计算了相互平行非均匀等离子体涂层导体圆柱的单/双站散射宽度,讨论了束腰半径、等离子体涂层厚度、电子密度、碰撞频率及雷达频率等对散射结果的影响. 相似文献
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两个相邻目标对平面波、高斯波束的光散射 总被引:3,自引:0,他引:3
基于等效原理和互易性定理研究了两个靠近目标对平面波、高斯波束的光散射问题,给出了这一复合光散射模型的二阶散射结果。通常一阶散射结果容易求解,但由于耦合效应的复杂性,很难给出二阶散射结果的解析形式。为了解决这一问题,应用互易性定理给出了求解任意相邻介质目标二阶散射场的公式,同时借助等效原理将求解散射场公式中的体积分简化为面积分的形式,从而降低了求解难度。求解了两相邻球形粒子的复合散射场,并将求解结果与应用时域积分方程法求得的结果进行了比较。同时,还讨论了束腰半径、目标位置对散射截面及偏振度的影响。 相似文献
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Modified Two-Scale Model for Electromagnetic Scattering from the Non-Gaussian Oceanic Surface 下载免费PDF全文
Based on the skewness of sea waves, a modified two-scale model is developed for the non-Gaussian sea surface scattering. In this new model, a complementary term is added to the first-order scattering coefficient of the classical small perturbation method (SPM), the additional part is proportional to the surface bispectrum and it is the critical part in explaining the scattering difference between upwind and downwind observations. Meanwhile, the effects of the shadowing function of the anisotropic surface, the curvature of the surface are also taken into account. The numerical results show the theoretical estimates obtained are consistent with the experimental result, and the influence of the wind speed, the trend and the incident frequency on the backscattering coefficients from the non-Gaussian oceanic surface is discussed in detail. 相似文献
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细胞壁模板诱导介观尺寸生物SiO~2材料合成 总被引:2,自引:0,他引:2
在人工培养年下施用正硅酸乙酯(TEOS)在结缕草叶外表皮细胞间隙,以细胞壁为模板生物矿化合成介观尺寸有序SiO~2材料,植物吸收和矿化构筑单元的硅化学形态显著影响有序SiO~2结构的形成,这反映出TEOS和细胞壁模板分子作用时有较强的结构控制能力和缓慢的凝聚硅化过程。X-ray(EDX)能谱分析显示一根完整的硅柱是含有SiO~2和C元素,表明TEOS部分水解后在植物外表皮细胞间隙合成了不同于自然的地球化学条件下形成SiO~2。 相似文献
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生物体利用生物矿化作用,在有机分子模板上协同合成有种间差异的生物SiO2材料。具有精确形态可控的固态SiO2结构是在蛋白和多糖生物分子诱导下,在水相、中性pH和室温等温和反应条件下形成的,然而,利用化学合成方法,使SiO2的前体分子聚合形成具有一定模式结构的SiO2则需要极端的pH值或表面活性剂诱导。在人工培养条件下施用硅酸钠(Na2SiO3)时,在芦荟植物叶刺内,以细胞壁为模板生物矿化合成微米尺寸有序SiO2材料。X-ray(EDX)能谱分析显示一根硅针中含有Si,O和C元素,表明Si(OH)4吸收进入植物体内后Si-OH与细胞壁多糖和糖蛋白上的羟基(OH)组分,通过界面分子识别、细胞水平调控和再加工作用,聚合形成了有序的无定形(电子衍射确定)SiO2针状结构体。 相似文献
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