单轴各向异性球对任意方向入射平面波的散射

基于球矢量波函数的正交完备性,给出了具有任意传播方向两种极化模式的平面波用球矢量波函数展开的形式,导出了其展开系数的具体表达式.研究了单轴各向异性介质球对任意方向入射平面波的散射,利用球矢量波函数及傅里叶变换方法得到了各向异性介质球的内场展开式,结合切向连续边界条件给出了散射系数.数值分析了介电常数张量元、有耗、无耗、尺寸参数、入射角和方位角等对单轴各向异性介质球的雷达散射截面的影响.

在轴零阶贝塞尔波束对手征介质球的散射特性分析(英文)

贝塞尔波束自产生以来,凭借其无衍射、自修复特性已经获得了越来越多学者的关注。基于广义洛伦兹米理论,将在轴贝塞尔波束与手征介质球相互作用的入射场及散射场展开为球矢量波函数的表达式。结合球矢量波函数的正交完备性及电磁场的连续性边界条件,推导出了在轴零阶贝塞尔波束对手征介质球电磁散射的解析解。数值模拟了散射强度随散射角的分布,将在轴贝塞尔波束退化为平面波照射手征介质球的散射结果与文献比较,吻合得较好。分析了波束及介质球参数、介质球偏离波束中心位置对散射强度的影响。该理论为手征材料和手征涂覆目标在微波工程及目标隐身中的应用提供了很好的理论应用价值。

双零阶贝塞尔波束的传播及对单轴各向异性球的散射特性

基于广义洛伦兹Mie理论,研究了单轴各向异性球形粒子对两束具有任意传播和极化方向的零阶贝塞尔波束的传播和散射特性,并与单零阶贝赛尔波束入射单轴各向异性球形粒子时的传播和散射特性进行了对比研究.利用球矢量波函数的正交关系及坐标旋转定理,导出了任意传播和极化方向零阶贝塞尔波束的球矢量波函数的展开形式,通过矢量叠加得到了总入射场的展开系数.基于傅里叶变换方法和切向连续的边界条件,得到了单轴各向异性球内部电磁场的球矢量波函数展开式,并导出了散射系数解析表达式.将零阶贝塞尔波束退化成平面波,通过将其入射到单轴各向异性球形粒子的雷达散射截面角分布与文献结果进行对比,验证了本文理论及程序的正确性.数值分析了入射角、锥角及极化角等参数对雷达散射截面角分布的影响.本文理论和数值结果希望能应用于多波束入射下各向异性粒子、生物细胞等复杂粒子体系的散射、粒径分析以及光学俘获等特性的研究中.

钝头锥目标对太赫兹波背景辐射的反射特性研究

为克服大气衰减对太赫兹波应用距离的限制,充分发挥太赫兹波探测的优势,文中对空气稀薄的对流层顶高度上的太赫兹波辐射传输特性进行了研究,探索太赫兹波在卫星及飞行器平台的应用如被动探测技术等.选择7.147 THz,8.839 THz与10 THz三个频率较高、吸收衰减较小的窗口频率,计算和分析不同频率和海拔高度上大气背景亮度及目标对背景辐射的反射辐射.结果表明,在所有高度上,大气背景在向上方向上的辐射比向下方向上的辐射小,这种趋势在海拔高度高于5 km时更为明显.对于平行与地面放置的钝头锥目标来说,在高于5 km的高度上出现反射辐射的不对称性,反射的辐射在约80°和190°时达到峰值.

Paraxial propagation of cosh-Airy vortex beams in chiral medium

Propagation dynamics of the cosh-Airy vortex(CAiV) beams in a chiral medium is investigated analytically with Huygens–Fresnel diffraction integral formula. The results show that the CAiV beams are split into the left circularly polarized vortex(LCPV) beams and the right circularly polarized vortex(RCPV) beams with different propagation trajectories in the chiral medium. We mainly investigate the effect of the cosh parameter on the propagation process of the CAiV beams.The propagation characteristics, including intensity distribution, propagation trajectory, peak intensity, main lobe's intensity, Poynting vector, and angular momentum are discussed in detail. We find that the cosh parameter affects the intensity distribution of the CAiV beams but not its propagation trajectory. As the cosh parameter increases, the distribution areas of the LCPV and RCPV beams become wider, and the side lobe's intensity and peak intensity become larger. Besides, the main lobe's intensity of the LCPV and RCPV beams increase with the increase of the cosh parameter at a farther propagation distance, which is confirmed by the variation trend of the Poynting vector. It is significant that we can vary the cosh parameter to control the intensity distribution, main lobe's intensity, and peak intensity of the CAiV beams without changing the propagation trajectory. Our results may provide some support for applications of the CAiV beams in optical micromanipulation.

Factors influencing electromagnetic scattering from the dielectric periodic surface

The scattering characteristics of the periodic surface of infinite and finite media are investigated in detail.The Fourier expression of the scattering field of the periodic surface is obtained in terms of Huygens’ s principle and Floquet’s theorem.Using the extended boundary condition method(EBCM) and T-matrix method, the scattering amplitude factor is solved,and the correctness of the algorithm is verified by use of the law of conservation of energy.The scattering cross section of the periodic surface in the infinitely long region is derived by improving the scattering cross section of the finite period surface.Furthermore, the effects of the incident wave parameters and the geometric structure parameters on the scattering of the periodic surface are analyzed and discussed.By reasonable approximation, the scattering calculation methods of infinite and finite long surfaces are unified.Besides, numerical results show that the dielectric constant of the periodic dielectric surface has a significant effect on the scattering rate and transmittance.The period and amplitude of the surface determine the number of scattering intensity peaks, and, together with the incident angle, influence the scattering intensity distribution.

Estimation of co-channel interference between cities caused by ducting and turbulence

With the rapid development of the fifth-generation(5 G)mobile communication technology,the application of each frequency band has reached the extreme,causing mutual interference between different modules.Hence,there is a requirement for detecting filtering and preventing interference.In the troposphere,over-the-horizon propagation occurs in atmospheric ducts and turbulent media.The effects of both ducting and turbulence can increase the probability of occurrence of long-distance co-channel interference(CCI),in turn,severely affecting the key performance indicators such as system access,handover and drop.In the 5 G era,to ensure communication channels and information security,CCI must be reduced.This paper introduces a scattering parabolic equation algorithm for calculating signal propagation in atmospheric ducts on irregular terrain boundaries.It combines Hitney’s radio physical optical model and Wagner’s nonuniform turbulent scattering model for calculating the tropospheric scattering in an evaporation duct or a surface-based duct.The new model proposes a tropospheric scattering parabolic equation algorithm for various tropospheric duct environments.Finally,as a specific case,the topographical boundaries between several cities in the East China Plain were considered,and the over-the-horizon propagation loss was simulated for various ducting and turbulent environments.The simulation results were used to evaluate whether CCI would occur between cities in a specific environment.

Reflection and transmission of an Airy beam in a dielectric slab

The reflection and transmission of a finite-power Airy beam incident on a dielectric slab are investigated by an analytical method.Based on the plane-wave angular spectrum expansion and Fresnel approximation,the analytical expressions of the reflected field,internal field as well as transmitted field in each region are obtained.Through numerical simulations,the intensity distributions of the incident beam,reflected beam,internal beam as well as transmitted beam are presented at oblique incidence.Besides,we also compare the intensity distributions of the geometrical-optics beam field,the first order beam mode field and the actual beam field,which indicates that the contribution of each order beam mode field to the actual beam field is related to the refractive index of the dielectric slab.Meanwhile,the reflection characteristics of the Airy beams in the special cases of Brewster incidence and total reflection are investigated.Finally,the effects of the optical thickness and refractive index of the dielectric slab on the peak intensity distributions and beam shifts of the reflected and transmitted beams are also discussed in detail.The analytical and numerical results will be useful to analyze the propagation dynamics of Airy beam in the dielectric slab and provide some theoretical supports to the design of optical film.

拉盖尔高斯涡旋光束对生物细胞的散射特性分析

采用强度矩量分析法得到拉盖尔高斯涡旋光束的波束宽度及发散角。利用复源点方法得到厄米高斯光束的球矢量波函数展开形式，结合厄米多项式与拉盖尔多项式的转换关系，推导得到拉盖尔高斯涡旋光束展开为球矢量波函数的表达式。利用广义洛伦兹Mie理论，研究了拉盖尔高斯涡旋光束对癌细胞的散射特性。数值分析了不同模阶数及不同传输距离的拉盖尔高斯涡旋光束在垂直于传播方向横截面的强度和相位分布。结果表明：随着径向、方位向模阶数及传输距离的增加，拉盖尔高斯涡旋光束的光斑尺寸变大，另外随着传输距离的增加，拉盖尔高斯涡旋光束的相位结构呈现不同于源平面的特点。利用拉盖尔高斯涡旋光束的强度分布特征来解释不同模光束入射的散射强度的角分布特点。

厄米-高斯光束对手征介质球的远场散射

利用复源点方法将厄米-高斯光束展开为球矢量波函数的形式。基于广义洛伦兹米氏理论,应用手征介质球与自由空间分界面处电磁场切向连续的边界条件以及球矢量波函数的正交性,得到手征介质球远区散射场展开系数。研究了厄米-高斯光束对手征介质球的散射特性。数值计算了厄米-高斯光束对手征介质球的远区散射场分布,分析了波束模式、手征参数和手征球尺寸等对散射特性的影响。

Geometric optics interpretation for rainbow scattering of a chiral sphere

Research on light scattering from a large chiral sphere shows that the rainbow phenomenon is different from that of an isotropic sphere. A chiral sphere with certain chirality generates three first-order rainbows. In this Letter,we present a geometric optics interpretation for the phenomenon and make a calculation of the rainbow angles.The ray traces inside the sphere are determined by the reflection and refraction laws of light at the achiral–chiral interface and the chiral–achiral interface. The calculated rainbow angles achieve good agreements with those obtained by the analytical solutions. The effects of chirality and the refractive index of the sphere on rainbow angles are analyzed.