微波混沌腔体中的散射特性研究

以计算机机箱为研究目标,开展了电磁波耦合入计算机机箱腔体的散射问题研究.通过对其散射矩阵元的讨论和分析发现:可以通过辐射散射测量得到系统散射矩阵的系综平均;随着腔体损耗的增加,腔体散射系数的波动性减小;随着腔体损耗的进一步增加,插入相移分布逐渐趋于均一分布.通过Dyson圆系综讨论了归一化散射矩阵,计算机机箱腔体中存在波混沌散射.根据随机矩阵理论,微波混沌腔体的归一化阻抗矩阵具有统计通用性,且只与系统的损耗有关.     

微波腔内波混沌散射的初步研究

 通过建立的微波腔模拟产生大量腔体散射矩阵和辐射散射矩阵,并转化得到归一化散射矩阵和阻抗矩阵。利用戴桑环系综对归一化散射矩阵的本征值和本征相位进行了统计分析,其本征值的模和本征相位具有统计独立性,且本征相位近似均一分布,验证了腔体中波混沌散射的存在。对数值模拟和随机矩阵理论预测得到的归一化阻抗的统计特性进行了比较,其结果基本一致,说明随机矩阵理论对归一化阻抗具有一定的预测功能。     

2H-1P多重散射关联及自屏蔽效应对17O和15O能谱的贡献

本文利用格林函数方法和多重散射理论考察了2H(空穴)-1P(粒子)多重散射关联及自屏蔽效应对¹⁷O和¹⁵O能谱的贡献.计算中采用了Paris位导得的G矩阵,计算结果表明2H-1P多重散射关联的贡献是重要的,而自屏蔽效应的影响可以忽略.     

火灾烟雾颗粒532 nm光散射矩阵实验研究

基于自主研制的结合偏振调制和锁相检测技术的光散射实验装置,测量了两种典型火灾烟雾颗粒(棉绳阴燃烟雾和正庚烷池火烟雾)及超声雾化水滴颗粒的532 nm光散射矩阵元素随散射角的分布. 通过水滴颗粒测量结果与数值计算结果的比较验证了实验装置的可靠性. 对比分析了棉绳阴燃烟雾和正庚烷池火烟雾光散射矩阵元素随散射角的分布特征,讨论了该特征在颗粒区分上的应用. 研究了烟雾颗粒微观形貌特征对光散射矩阵的影响,发现可以利用Lorenz-Mie理论描述棉绳阴燃烟雾的光散射,表明其形貌为球形,并利用模拟退火拟合的方法得到了棉 关键词： 光散射 散射矩阵 烟雾     

不同近远场外推方案对MRTD散射模型穆勒矩阵计算精度的影响分析

非球形气溶胶穆勒散射矩阵的不确定性是影响偏振遥感精度的重要因素。在自主研制的时域多分辨率(MRTD)气溶胶散射模型中,穆勒散射矩阵的计算需要以远场电场值为基础,因此近远场外推过程成为制约其模拟精度的重要环节。为确定适用于MRTD散射模型的最佳近远场外推方案,在球形和非球形粒子情形下,系统地对比分析了基于惠更斯原理的表面积分方案以及基于电介质亥姆霍兹方程的体积积分方案所对应的穆勒散射矩阵的模拟精度。结果表明,虽然两种近远场外推方案均可有效准确地实现近远场外推,但从穆勒矩阵的计算误差分布上看,基于体积积分原理的近远场外推方案性能更优。     

推广t-J模型的坐标Bethe Ansatz方法

利用坐标Bethe Ansatz方法,研究了推广的t—J模型的精确解,导出了两组Bethe Ansatz方程;同时证明了在两体散射问题中的散射矩阵正是三角型的非对称六顶角R矩阵.     

氢分子在磁场中回归谱的散射矩阵理论研究

利用散射矩阵理论,结合扩展的半经典闭合轨道理论和多通道量子亏损理论,计算了磁场中高里德堡H2分子的回归谱.该方法使用了两个空间散射矩阵来描述里德堡电子的动力学性质,计算中可以包括所有阶的实散射的作用.回归谱的每一个尖峰对应着一条闭合轨道,新的额外峰是由于弹性散射和非弹性散射所引起的通道内和通道间的轨道组合,进一步证明了体系通道间和通道内的散射具有同等的重要性.     

氢分子在磁场中回归谱的散射矩阵理论研究

利用散射矩阵理论,结合扩展的半经典闭合轨道理论和多通道量子亏损理论,计算了磁场中高里德堡H2分子的回归谱.该方法使用了两个空间散射矩阵来描述里德堡电子的动力学性质,计算中可以包括所有阶的实散射的作用.回归谱的每一个尖峰对应着一条闭合轨道,新的额外峰是由于弹性散射和非弹性散射所引起的通道内和通道间的轨道组合,进一步证明了体系通道间和通道内的散射具有同等的重要性.     

含有周期球腔的黏弹性覆盖层消声性能分析

利用散射矩阵法分析了单个球状空腔在黏弹性橡胶中的Mie散射特性以及振动模式.以此为基础，利用多重散射法分析了不同背衬条件下，含有单层周期球状空腔的橡胶覆盖层(厚度为8mm)的消声性能.结果表明，单个球腔的径向共振对覆盖层的低频消声性能有重要贡献，覆盖薄层在共振区具有良好的消声性能.最后，设计了双层消声覆盖层(厚度为20mm)，有效拓展了消声带宽. 关键词： Mie散射 多重散射法 消声材料 声子晶体     

任意方位双球粒子体系散射极化特征与单个球的比较

本文用T矩阵与场方程叠加相结合的方法，系统研究任意方位双球粒子体系散射矩阵各元素随两球球心的间距变化规律。 详细推导了双球粒子体系T矩阵的具体形式，并将T矩阵所求得的散射矩阵与单个球的情况作了比较。数值计算表明，球心间间距的增加对该体系的散射矩阵影响不大，得出任意方位即对方位求平均的情况下，双球粒子体系的散射矩阵与体系中有较大尺寸参数的单球相似的结论.     

多重散射方法研究轴对称空腔覆盖层的声学特性

发展了一种多重散射方法研究声学覆盖层的半数值半解析模型,分析了影响轴对称空腔结构声学性能的主要能量耗散机制。在球坐标条件下推导出轴对称空腔结构的位移和应力场基函数,通过对空腔表面基函数的数值积分,得到散射波和入射波之间的传输矩阵方程,结合分层介质声传播理论计算了周期性空腔结构覆盖层的反射、透射和吸声性能。研究结果表明;空腔共振是低频能量耗散的主要形式,边界条件对材料空腔结构的谐振特性影响很大,利用双空腔耦合共振可以拓宽材料的低频吸声频带;背衬对材料的高频吸声影响较小,材料的高频能量损耗取决于空腔的散射和波型转换特性。      

Scattering Properties of Cylindrical Ferrite Posts and Their Applications

The scattering field of a ferrite post and a cylindrical ferrite post containing conducting post illuminated by a plane wave is analyzed. The special interest is the scattering property of the ferrite posts, which is resonating at certain modes such as TM₁₁ mode. We hope to know the speciality it shows and find its applications. It is found that the scattering field pattern of a resonating ferrite post is similar to the rotation of the scattering field pattern of a dielectric cylindrical post, which has the same dimension as ferrite. The scattering properties of the ferrite may give us some inspirations to explore its applications in microwave components. This property is utilized to explain the mechanism of the operation of the circulators. It also may be used in microstrip patch antenna, coupler and filter to control their properties. Other applications may be possible too. Some calculation results are presented.     

Wave scattering functions and their application to multiple scattering problems

Scattering functions arise naturally in standard treatments of the effects of a material object or surface embedded in a uniform field. The most commonly used scattering function describes the far-field modulation imparted at large distances to a spherical wavefront eminating from the scatterer. The purpose of this is to develop the properties of the spectrum of scattered plane waves as an exact generalized scattering function. The linearity of the wave equations guarantees that such a representation exists; moreover, it is possible to derive the generalized scattering function from the far-field scattering function by analytic continuation. Although these properties are known, recent theoretical developments have motivated us to reexplore the interrelations among the far-field scattering function, the Green's function and various forms of the generalized scattering function as well as the symmetry properties of the generalized scattering function imposed by reciprocity. For multiple-scattering objects that can be separated by parallel planes, a system of difference equations is developed that fully accommodates the mutual interaction among the scatterers. The mutual interaction equations were developed earlier, but we show here that they can be transformed into the form that would be obtained by using the Foldy-Lax-Twersky formalism. This reinforces the equivalence between wave-space and configuration space formulations of the scattering problems.     

Theoretical analysis and measurements on near specular scattering

In scattering measurement it is important and also difficult to separate instrument scattering from the scattering of a sample. Particularly at angles near the specular reflection, it is believed that the small angle limit for scattering measurement is determined not only by detector proximity to the specular beam, but also by the sample scattering. When the scattering angles are smaller than a certain limit, the total scattering combining the instrument scattering and the sample scattering is lower than the instrument scattering. This prevents us from discriminating the instrument scattering and the sample scattering at angles smaller than this limit. In this paper a data processing method is reported that enables us to distinguish the instrument scattering at angles smaller than this limit. Based on this method, we can measure the scattering at angles restricted only by the performance of the instrument.     

Statistical properties of resonance widths for open quantum graphs

We connect quantum compact graphs with infinite leads, and turn them into scattering systems. We derive an exact expression for the scattering matrix, and explain how it is related to the spectrum of the corresponding closed graph. The resulting expressions allow us to get a clear understanding of the phenomenon of resonance trapping due to over-critical coupling with the leads. Finally, we analyse the statistical properties of the resonance widths and compare our results with the predictions of random matrix theory. Deviations appearing due to the dynamical nature of the system are pointed out and explained.     

Statistical properties of resonance widths for open quantum graphs

We connect quantum compact graphs with infinite leads, and turn them into scattering systems. We derive an exact expression for the scattering matrix, and explain how it is related to the spectrum of the corresponding closed graph. The resulting expressions allow us to get a clear understanding of the phenomenon of resonance trapping due to over-critical coupling with the leads. Finally, we analyse the statistical properties of the resonance widths and compare our results with the predictions of random matrix theory. Deviations appearing due to the dynamical nature of the system are pointed out and explained.     

SS-HORSE Method for Analysis of Resonances: Charged-Particle Scattering

The method for analyzing resonance states based on the harmoni©oscillator representation of scattering equations (HORSE) and on analytic properties of partial-wave scattering amplitudes which has been proposed earlier, is generalized to the case of charged-particle scattering. The method in question is tested by applying it to the model problem of pα scattering and can be used to study resonance states on the basis of microscopic calculations within various versions of the shell model.     

Wavelet transforms in estimating scatterer spacing from ultrasound echoes

Ultrasound echoes from organs such as the liver display resolvable periodicity due to regular scattering centers within tissue. The spacing among such scattering centers has been proposed as a signature to characterize diffuse and focal diseases of the liver. Even though it is highly desirable to be able to estimate an inter-scatterer-spacing (ISS) distribution, current methods can estimate only the mean value of scatterer spacing (MSS) over a tissue length. In this paper, we propose a wavelet transform-based technique that is capable of estimating the location of each scattering center, making it possible to obtain the ISS distribution. We represent liver tissue with a point scatterer model, and show, via computer simulations, that the use of multi-scale information in the wavelet scale-space allows us to estimate the locations of regular scattering centers. We show that both the observation noise and random ultrasound returns from unresolvable tissue microstructure can be removed successfully in the wavelet domain via the properties of the modulus maxima sequence of observation across different scales.