无限长非均匀圆柱对任意入射平面波的散射特性

基于无限长非均匀介质圆柱对斜入射平面波散射场公式推导,研究发现当入射角为90°时,斜入射散射公式可以简化为垂直入射的散射公式,所用的算法也可以统一.并用已有算法模拟了无限长非均匀柱粒子对任意入射平面波散射场的强度分布,并且与已有文献结果进行比较,验证了上述结论的正确性.     

水中双层无限长圆柱壳体声散射

研究水下双层无限长圆柱壳体的声散射。采用弹性薄壳理论和Fourier变换方法导出了散射声场的解析解。并分别计算了平面波正横和斜入射单层和双层无限长圆柱壳体的远场散射形态函数。计算表明在不同的入射角,由于不同类型的弹性波被激励,散射波呈现不同的特性。通常双层无限长圆柱壳体的散射特性由外壳、内壳和中间耦合水层共同作用决定。但外壳很薄、内壳较厚、水层较薄时,无限长充水双层圆柱壳体的低频散射特性主要由单层内壳决定。当然这时外壳的共振特性也不能忽略。     

均匀外电场中无限长介质圆柱壳的场分布的计算和讨论

用圆柱坐标系中的分离变量法计算了位于均匀外电场中的无限长介质圆柱壳各区域的电势和电场,由计算结果分析了无限长介质圆柱壳对外电场的屏蔽效果,并指出均匀外电场中的无限长导体圆柱壳、无限长介质圆柱体、无限长导体圆柱及无限大均匀电介质中开有一无限长的圆柱形空腔的电势和电场都可以由均匀电场中的无限长介质圆柱壳电势及电场给出.     

在轴高斯波束入射无限长多层圆柱散射的德拜级数解

不均匀柱形粒子的光散射特性研究对复杂结构粒子参量的反演具有重要意义。基于德拜理论,对在轴高斯波束垂直入射无限长多层圆柱的散射特性进行了讨论。获得了散射系数的德拜级数展开式;并利用该公式分别计算了均匀和双层圆柱的总散射强度角分布,德拜级数单阶散射强度角分布;总散射强度结果与广义米氏理论(GLMT)进行了比较,两者吻合很好。分析表明圆柱散射强度不同散射角区间的值来自德拜级数不同阶的散射强度贡献;双层圆柱各层半径和折射率的值对德拜级数二阶散射强度角分布中峰值的出现起决定作用。当双层圆柱的外层较薄时,在120°~150°之间会出现两个明显峰值,即出现双重一阶彩虹峰值;反之,当外层厚度大于内层时,只有一个峰值存在。     

新型光学聚合物——Topas环烯烃共聚物微结构光纤的设计及特性分析

以新型光学聚合物Topas 环烯烃共聚物（折射率为1.53）为基质,设计了四种微结构聚合物光纤.应用有限元方法对各种光纤在波长0.5—2.0 μm范围内的基模有效折射率、模场面积和数值孔径进行了计算.研究了结构参数对模场分布、单模特性和色散特性的影响.得出了具有极大/小模场面积、无限单模传输和平坦近零色散的光纤结构参数.与石英、聚甲基丙烯酸甲酯基质的微结构光纤相比,该光纤具有更大的数值孔径和较宽的平坦近零色散范围.为光纤的制备提供了理论指导. 关键词： 微结构聚合物光纤 有限元方法 传输特性 Topas 环烯烃共聚物     

空心圆柱微腔谐振模式研究

基于分离变量法研究了平面波斜入射时,空心无限长介质圆柱微腔的光学特性,通过计算散射场展开系数分析了入射角度、空心部分的尺寸等因素对谐振廓线的影响。研究结果表明,当空心部分的尺寸参数较大时将使微腔的形貌共振(Morphology Dependent Resonances,MDR)峰值产生偏移,当空心部分尺寸参数较小时,圆柱仍然可以产生MDR共振,且位置和均匀圆柱重合。当平面波斜入射时,MDR峰也会产生偏移,并且随着入射角度的减小,MDR峰值减小,直至完全消失。     

椭圆截面的无限长金属棒对任意平面电磁波在有损耗的均匀各向同性无限媒质中的散射

本文利用椭圆柱形坐标系,严格地分析了具有任意偏心度的椭圆截面的无限长理想导电的金属棒,放在有损耗的均匀各向同性的无限介质中,对从任意方向入射的均匀平面波的散射问题;并将散射场表示为马许函数。     

脉冲平面波斜入射旋转对称体电磁散射的FDTD算法

提出一种应用时域有限差分算法求解脉冲平面波斜入射时旋转对称体散射问题的方法.对斜入射脉冲平面波在圆柱坐标系下进行分解、应用总场/散射场连接边界、PML吸收边界条件.通过与矩量法分析结果的比较,验证了该方法的有效性.     

用耦合波理论求解渐变折射率光纤的传播常数和模式场

本文应用耦合波理论来计算任意渐变折射李光纤的传播常数和模场分布.将无限伸展的抛物型折射率分布光纤作为一个理想波导,任意径向不均匀折射率分布光纤便可以视作该理想波导的微扰,其模场可以展开成一组完备的理想波导模的叠加.然后,模场和传播常数可以通过耦合波方程求得.进一步将一阶微分方程组形式的耦合波方程变换成线性方程组,使计算过程大大简化.文中给出了数值计算结果,并将其与准确值进行了比较.     

结合计算层析与光学相干层析测量折射率分布

通过将计算层析技术与光学相干层析技术相结合,测量散射介质非均匀折射率分布。该方法测量散射样品折射率分布时,通过光学相干层析技术测量散射样品折射率分布在多个方向上的投影,采用计算层析技术实现对样品折射率分布的层析重建,克服了传统折射率光学测量方法如单纯的基于光学相干层析原理的焦点追迹法和光程匹配法,不能测量散射介质非均匀折射率分布的缺点。采用该方法在实验中对梯度折射率棒的径向相对折射率分布进行层析重建,取得了较好的实验结果。     

Solution of problem of electromagnetic waves scattering on inhomogeneously layered scatterers using pattern equation method

In this paper, the pattern equation method (PEM) is used to solve the problems of electromagnetic waves scattering by inhomogeneously layered scatterers. The numerical algorithm based on PEM for multilayered scatterers of arbitrary geometry is developed. The numerical results are presented for magneto-dielectric objects coated with magneto-dielectric materials to demonstrate the stability, accuracy, and efficiency of the proposed method. A comparison of the results obtained by the present method and by the other methods are shown and the limits of applicability of method are outlined.     

离轴多层球对高斯波束的光散射

根据广义米氏理论，将入射的高斯波束按矢量球谐函数展开，获得了波束因子（展开系数）ｇｍｎ，ＴＭ和ｇｍｎ，ＴＥ的一般表达式。应用ｇｍｎ的局域近结果和散射系数ａｎｍ和ｂｎｍ的迭代公式与算法，研究了多层有耗介质球的光散射。讨论了波束宽度与球形粒子的尺寸和位置对散射系数和散射强度角分布的影响。     

Prediction of sound transmission loss through multilayered panels by using Gaussian distribution of directional incident energy

In this study, a new prediction method is suggested for sound transmission loss (STL) of multilayered panels of infinite extent. Conventional methods such as random or field incidence approach often given significant discrepancies in predicting STL of multilayered panels when compared with the experiments. In this paper, appropriate directional distributions of incident energy to predict the STL of multilayered panels are proposed. In order to find a weighting function to represent the directional distribution of incident energy on the wall in a reverberation chamber, numerical simulations by using a ray-tracing technique are carried out. Simulation results reveal that the directional distribution can be approximately expressed by the Gaussian distribution function in terms of the angle of incidence. The Gaussian function is applied to predict the STL of various multilayered panel configurations as well as single panels. The compared results between the measurement and the prediction show good agreements, which validate the proposed Gaussian function approach.     

Exact analytical representations for broadband transmission properties of quarter-wave multilayers

The formalism of the scattering matrix is applied to describe the transmission properties of multilayered structures with deep variations of the refractive index and arbitrary arrangements of the layers. We show that there is an exact analytical formula for the transmission spectrum, which is valid for the full spectral range and which contains only a limited number of parameters for structures satisfying the quarter-wave condition. These parameters are related to the poles of the scattering matrix, and we present an efficient algorithm to find them, which is based on considering the ray propagation inside the structure and subsequent application of the harmonic inversion technique. These results are significant for analyzing the reshaping of ultrashort pulses in multilayered structures.     

静电场中无限长均匀双层圆柱体的拉普拉斯方程解及其在纳米光学中的应用

应用拉普拉斯方程求解静电场中无限长均匀双层圆柱体的电势及电场,并基于散射理论获得该结构颗粒的光学散射、吸收及消光系数.进一步计算了金纳米管的远场光谱和近场分布,其结果与经典的Mie散射理论计算结果完全一致.因此,该理论结果可以很好的被应用于纳米光学研究.     

嵌入线型缺陷的石墨纳米带的热输运性质

采用非平衡格林函数方法研究了嵌入有限长、半无限长、 无限长线型缺陷的锯齿型石墨纳米带 (ZGNR)的热输运性质.结果表明, 缺陷类型和缺陷长度对ZGNR的热导有重要影响. 当嵌入的线型缺陷长度相同时, 包含t5t7线型缺陷的石墨纳米带比包含Stone-Wales线型缺陷的条带热导低. 对于嵌入有限长、同种缺陷的ZGNR, 其热导随线型缺陷的长度增加而降低, 但是当线型缺陷很长时, 其热导对缺陷长度的变化不再敏感.通过比较嵌入有限长、半无限长、无限长线型缺陷的ZGNR, 我们发现嵌入无限长缺陷的条带比嵌入半无限长缺陷的条带热导高, 而后者比嵌入有限长线型缺陷的条带热导高. 这主要是因为在这几种结构中声子传输方向的散射界面数不同所导致的. 散射界面越多, 对应的热导就越低. 通过分析透射曲线和声子局域态密度图, 解释了这些热输运现象. 这些研究结果表明线型缺陷能够有效地调控石墨纳米带的热输运性质. 关键词： 石墨烯 线型缺陷 热导     

On the electromagnetic cloaking of (Nano)particles

We theoretically study the electromagnetic cloaking of small (nano)particles in optical or IRbands by means of multilayered coating simultaneously providing the shielding of cloaked volume and minimizing scattering. Within a quasi-static approximation in sphe rical geometry, we show that two kinds of shielding shells exist with zero and with infinitely large (in the lossless case) values of the dielectric constant. We demonstrate that narrowing of the shielding shell at zero dielectric permittivity leads to the effect of electric field superlocalization when an infinite amount of energy is concentrated inside an infinitesimal volume.     

Extraction of optical scattering parameters and attenuation compensation in optical coherence tomography images of multilayered tissue structures

A recently developed analytical optical coherence tomography (OCT) model [Thrane et al., J. Opt. Soc. Am. A 17, 484 (2000)] allows the extraction of optical scattering parameters from OCT images, thereby permitting attenuation compensation in those images. By expanding this theoretical model, we have developed a new method for extracting optical scattering parameters from multilayered tissue structures in vivo. To verify this, we used a Monte Carlo (MC) OCT model as a numerical phantom to simulate the OCT signal for heterogeneous multilayered tissue. Excellent agreement between the extracted values of the optical scattering properties of the different layers and the corresponding input reference values of the MC simulation was obtained, which demonstrates the feasibility of the method for in vivo applications. This is to our knowledge the first time such verification has been obtained, and the results hold promise for expanding the functional imaging capabilities of OCT.     

Efimov Trimers Near the Zero-crossing of a Feshbach Resonance

Near a Feshbach resonance, the two-body scattering length can assume any value. When it approaches zero, the next-order term given by the effective range is known to diverge. We consider the question of whether this divergence (and the vanishing of the scattering length) is accompanied by an anomalous solution of the three-boson Schrödinger equation similar to the one found at infinite scattering length by Efimov. Within a simple zero-range model, we find no such solutions, and conclude that higher-order terms do not support Efimov physics.     

The three-boson system with short-range interactions

We discuss renormalization of the non-relativistic three-body problem with short-range forces. The problem is non-perturbative at momenta of the order of the inverse of the two-body scattering length. An infinite number of graphs must be summed, which leads to a cutoff dependence that does not appear in any order in perturbation theory. We argue that this cutoff dependence can be absorbed in one local three-body force counterterm and compute the running of the three-body force with the cutoff. This allows a calculation of the scattering of a particle and the two-particle bound state if the corresponding scattering length is used as input. We also obtain a model-independent relation between binding energy of a shallow three-body bound state and this scattering length. We comment on the power counting that organizes higher-order corrections and on relevance of this result for the effective field theory program in nuclear and molecular physics.