一维带限Weierstrass分形粗糙地面电磁散射的FDTD研究

采用一维带限Weierstrass分形函数模拟了实际的粗糙地面,应用时域有限差分方法研究了一维分形粗糙地面电磁散射特性,计算了分形粗糙地面散射的双站散射系数,得出了散射系数随散射角和入射波频率变化的曲线,讨论了高度起伏均方根、分维数、土壤湿度、入射波频率、入射角等参数对散射系数的影响,得到了一维带限Weierstrass分形粗糙地面电磁散射的特性。数值计算结果表明各参数对散射系数均有显著影响,入射波不同极化方式下的散射系数也有明显的变化。     

CST软件在计算双层球粒子散射场中的应用

如何精确计算双层球的散射特性,尤其是不规则双层球的散射场,受到越来越多人的关注.利用Mie理论等解析方法可以精确的求解双层球的散射场,但是对于不规则双层球的情况则无能为力.通过用基于有限积分法的CST微波工作室对双层球散射场进行计算,所得结果与经典Mie理论所得结果进行比较,二者的计算结果基本吻合.模拟仿真表明:随着商...     

基于抛物方程的湍流散射研究

在远距离的电磁信号传输过程中,大气散射会对微波传输产生不可忽视的影响。为了定量分析这种影响,从大气湍流的结构出发,在同时考虑湿度以及温度的基础上得到电波波段的湍流大气结构常数,然后基于统计随机理论建立了湍流大气散射模型,采用抛物方程模拟并分析了大气湍流对微波传输的影响。仿真结果表明,大气湍流引起的散射效应在超视距区域才趋于明显;随着传播距离的增加,沿传播方向的场强幅度出现随机的起伏;大气散射效应会随着高度的增加而减弱。     

Toward Integrated Circuit Size Reduction

In this article, voltage-basis, current-basis, and normalized scattering matrices were introduced and it was shown that three different scattering matrices are the same only with equal termination impedances but only the normalized scattering matrix is correct with arbitrary termination impedances. The scattering matrices can be calculated from impedance, admittance, or ABCD matrices characterizing a network. However, if the network has more than three ports, the calculation process from the admittance or impedance matrices is not simple. For this, conversion formulas of the ABCD parameters into the normalized scattering parameters were presented for the impedance-transforming directional couplers. If one can have any choice of the termination impedances of the directional couplers as shown in this article, the total size of a microwave integrated circuit can be reduced.     

基于ADS的复杂目标雷达回波模型库ADS-RTBS

复杂目标电磁散射特性研究是军事电子领域的关键性技术,在雷达、制导、识别、电子对抗等领域有着广泛应用, Agilent系统级仿真工具ADS和先进的测试仪表为目标电磁散射特性在上述领域的实际应用提供了一个灵活、统一的软硬件协同设计平台。本文综述了当前用于高效分析复杂目标电磁散射特性的数值精确方法、高频近似方法和美国军方专用电磁建模仿真软件,介绍了我们自主开发的基于矩量法和多层快速多极子方法的精确电磁建模仿真软件FASTEM(Fast and Accurate Simulation Tools for Electromagnetics)和高频电磁仿真软件。重点介绍了与Agilent联合开发的基于ADS的雷达回波模型库- ADS-RTBS,并给出实例。     

基于米氏散射理论的粒度测试算法研究

在光散射法测量微粒体系粒度分布技术中,反演算法的选择及其正确使用是很关键的。介绍了基于米氏散射理论的粒度测试,对其求解方法进行了详细分析,力图通过算法的改进提高激光粒度仪的粒度测试精度。综合采用了直接法NNPT和迭代法LMS的优点,在稳定性和准确性方面得到了一定程度的改进,并对算法进行了验证。     

Scattering effect in optical microring resonators

In this paper we present an investigation of detrimental effects due to roughness-induced scattering and their influence on the properties of both passive and active optical microring resonators. The theoretical analysis involves different mathematical models, such as the volume current method to determine the scattering influence, and the quantum mechanical approach based on density matrix to investigate the active ring dynamics.     

A Non Perturbative Model of Surface Roughness Scattering for Monte Carlo Simulation of Relaxed Silicon n-MOSFETs

In the present paper the problem of interface roughness scattering is treated non-perturbatively by incorporating the effects of scattering as a boundary condition for the Boltzmann transport equation (BTE). This provides a basis for the development of a semi-classical model of the interface roughness scattering mechanism applicable to the Monte Carlo (MC) simulations of electron transport in the Si n-MOSFET. The model is based on the Boltzmann-Fuchs method for the solution of the BTE. This method has shown to be computationally efficient and is naturally suited to the semi-classical spirit of the BTE and its direct solution via the MC method.     

Single Gold Nanorod Detection Using Confocal Light Absorption and Scattering Spectroscopy

Gold nanorods have the potential to be employed as extremely bright molecular marker labels for fluorescence, absorption, or scattering imaging of living tissue. However, samples containing a large number of gold nanorods usually exhibit relatively wide spectral lines. This linewidth limits the use of the nanorods as effective molecular labels, since it would be rather difficult to image several types of nanorod markers simultaneously. In addition, the observed linewidth does not agree well with theoretical calculations, which predict significantly narrower absorption and scattering lines. The discrepancy could be explained by apparent broadening because of the contribution of nanorods with various sizes and aspect ratios. We measured native scattering spectra of single gold nanorods with the confocal light absorption and scattering spectroscopy system, and found that single gold nanorods have a narrow spectrum as predicted by the theory, which suggests that nanorod-based molecular markers with controlled narrow aspect ratios, and to a lesser degree size distributions, should provide spectral lines sufficiently narrow for effective biomedical imaging.     

LED单边侧入式导光板的网点设计

单边侧入式导光板可降低其设计成本和制作成本,为了获得均匀的表面照度,本文介绍了LED为光源的单边侧入式导光板散射网点设计方法。建立了相应模型,得到这种导光板散射网点的一种排布公式和计算方法,并用TracePro软件进行模拟仿真,验证了网点设计方法的正确性。模拟和实验结果表明通过这种网点设计方法可获得均匀度优于90%的表面照度分布。     

Modeling Decoherence Effects on the Transport Properties of Mesoscopic Devices

In this paper we present a Monte Carlo technique aimed at including the effects of decoherence in mesoscopic electron transport in the scattering matrix of the system such technique is based on a phenomenological microscopic model, that captures the effect of elastic interactions in terms of a random term added to the phase of the single particle wave function. Given the random character of scattering events, each Monte Carlo run provides a particular occurrence of the reduced single particle scattering matrix. Average transport properties are obtained from large samples of Monte Carlo runs. We focus on the simulation of magnetoconductance in Aharonov-Bohm rings, and relate the amplitude of the h/e oscillations to the strength of dephasing mechanisms.     

多重散射对含有气体和颗粒的燃烧介质中辐射传热的影响

该文采用蒙特卡洛方法研究包括吸收性气体和具有一定浓度颗粒的燃烧环境中的辐射传热。在蒙特卡洛程序被验证之后，研究了多重散射对辐射传热的影响。定义了一个临界颗粒体积份额f^cv，作为区分单次散射区和多重散射区的分界。当颗粒云的体积份额位于单次散射区和多重散射区时，其辐射通量的变化表现出不同的行为。在单次散射区，平板的辐射通量随着离子浓度增加而剧烈增长，辐射行为受到颗粒单次散射的影响。在多重散射区，离子浓度的增加不会引起辐射通量的增长，辐射通量趋近于一个固定值，辐射行为受到气体吸收和多重散射的双重影响。     

分形地面与半埋矩形截面目标复合电磁散射FDTD研究

采用一维带限分形函数模拟实际的粗糙地面,应用时域有限差分法研究了一维分形地面与半埋矩形截面目标复合电磁散射特性,得出了复合散射系数随散射角变化的曲线,分析了分形地面粗糙度参数、土壤介电参数、目标几何参数等对复合散射系数的影响,得到了分形地面与半埋目标复合电磁散射的特性.数值计算结果表明复合散射系数受地面粗糙度参数影响明显,目标表面散射波对表面镜反射方向复合散射系数影响较大.     

雷达属性散射中心的快速目标分类和参数估计

雷达属性散射中心模型的属性参数能够提供目标更为丰富的重要信息,属性散射中心参数估计对解析雷达目标有着极其重要的研究意义。针对雷达属性散射中心模型,提出了基于深度学习的雷达属性散射中心快速目标分类和参数估计的技术。首先利用ViT (vision transformer)深度学习网络将雷达属性散射中心分类为局部式和分布式两类,然后基于TS2Vec框架构建针对属性散射中心参数估计的卷积神经网络(convolutional neural network for attribute scattering centers, ASCNN),最后分别对两种数据进行训练以实现局部式和分布式属性散射中心的参数估计。基于属性散射中心模型展开数值实验,实验结果表明,该方法对雷达属性散射中心目标分类的准确率高达99%以上;雷达属性散射中心参数估计的速度超过传统方法的10 000倍以上,且精度更高,验证了所提方法的有效性和优越性。     

Shadow-corrected bistatic scattering from randomly very rough surfaces

Contents  The like- and cross-polarized scattering coefficients of electromagnetic waves from random rough surfaces corrected by shadowing functions are studied in this paper. Due to the use of approximate tangential surface fields in the derivative of all the wave scattering from randomly rough surfaces, the shadowing functions should be added to correct the scattering especially from surfaces with large rms surface slope. For correct prediction to the scattering characteristics we apply the suitable angular shadowing function to the single and multiple scattering coefficients respectively. The comparisons of scattering coefficients with or without shadowing functions are shown in this paper to evaluate the conditions of angular shadowing functions and the effect of shadowing function for the scattering from random very rough surfaces. We also compare the shadow-corrected scattering coefficients with the measured data and find the good agreements between them. Received: 12 December 2000     

Comparison of Non-Equilibrium Green’s Function and Quantum-Corrected Monte Carlo Approaches in Nano MOS Simulation

In this paper, we present a comparative study between non-equilibrium Green’s function and quantum-corrected Monte Carlo approaches for an ultra-short channel MOSFET. As a result, we have found that the both models are equivalent in the simulation of quantum transport in a nano-scale MOSFET. We will also demonstrate that impurity scattering in the source region and plasmon scattering at the drain-end of the channel especially influence the drain current based on the quantum-corrected Monte Carlo approach.     

Carrier scattering and impact ionization in bilayer graphene

Transport properties of carriers in bilayer graphene (BLG) were studied. Several analytical models were developed for drift velocity, scattering rate and ionization coefficient of BLG for the first time. Then, the joint effect of temperature and potential difference of layers were addressed on the modeled parameters. The accuracy of the proposed models for drift velocity and scattering rate was verified by the simulation results of published works. In addition, the analytical results of ionization coefficient of BLG were compared with those of silicon.     

Determination of epithelial tissue scattering coefficient using confocal microscopy

Most models of light propagation through tissue assume the scattering properties of the various tissue layers are the same. The authors present evidence that the scattering coefficient of normal cervical epithelium is significantly lower than values previously reported for bulk epithelial tissue. They estimated the scattering coefficient of normal and precancerous cervical epithelium using measurements of the reflectance as a function of depth from confocal images. Reflectance measurements were taken from ex vivo cervical biopsies and fit to an exponential function based upon Beer's law attenuation. The mean scattering coefficients derived were 22 cm/sup -1/ for normal tissue and 69 cm/sup -1/ for precancerous tissue. These values are significantly lower than previously reported for bulk epithelial tissues and suggest that scattering of bulk tissue is dominated by the stroma. They also suggest that computational models to describe light propagation in epithelial tissue must incorporate different scattering coefficients for the epithelium and stroma. Further, the lower scattering of the epithelium suggests greater probing depths for fiber optic probes used by optical diagnostic devices which measure reflectance and fluorescence in epithelial tissue. The difference in scattering between normal and precancerous tissue is attributed to increased nuclear size, optical density, and chromatin texture. The scattering coefficients measured here are consistent with predictions of numerical solutions to Maxwell's equations for epithelial cell scattering.     

Trapping and Manipulation of Biological Particles Through a Plasmonic Platform

Enhanced optical radiation force can be induced through the resonant scattering field from a single plasmonic nanoparticle or a randomly distributed plasmonic nanoparticle array. In this paper, we utilized the dipole approximation for the Mie scattering field to analyze such radiation force in both far-field and near-field regime. This force can be utilized to develop noninvasive probes for trapping and manipulation of single biological particles. The trapping of single yeast cells is also demonstrated as an application of this approach.     

日盲紫外光霾粒子光散射测量方法研究

针对光散射粒子测量方法中测量结果受到外界杂散光干扰这一问题,提出将日盲紫外光应用于光散射粒子测量方法中。利用Mie散射理论仿真了日盲紫外光不同粒径粒子的散射光分布函数,结果表明,日盲紫外光对粒径较小的粒子散射特性良好,能够应用于光散射粒子测量方法之中。利用T矩阵方法计算了日盲紫外光椭球粒子的散射特性,结果表明,在日盲紫外光248 nm处,椭球粒子的消光截面相比等效球形粒子偏小2.82%,散射截面偏小1.95%。最后分析了椭球粒子形变参数与复折射率对其散射相函数的影响,这些分析为光散射粒子测量方法提供了一定的理论依据。