Iterative physical optics method based on efficient occlusion judgment with bounding volume hierarchy technology

This paper builds a binary tree for the target based on the bounding volume hierarchy technology,thereby achieving strict acceleration of the shadow judgment process and reducing the computational complexity from the original O(N^(3))to O(N^(2)logN).Numerical results show that the proposed method is more efficient than the traditional method.It is verified in multiple examples that the proposed method can complete the convergence of the current.Moreover,the proposed method avoids the error of judging the lit-shadow relationship based on the normal vector,which is beneficial to current iteration and convergence.Compared with the brute force method,the current method can improve the simulation efficiency by 2 orders of magnitude.The proposed method is more suitable for scattering problems in electrically large cavities and complex scenarios.

基于矩阵降维的MoM-PO电磁散射混合算法

针对包含精细结构的电大尺寸目标电磁散射快速计算问题,提出了一种计算包含精细结构的电大尺寸目标电磁散射问题的基于矩阵降维的混合算法。该方法在Rao-Wilton-Glisson基函数矩量法(method of moment,MoM)的基础上,对目标区域进行划分,完成阻抗矩阵的分块和未知量的分离,再由矩量区与物理光学(physical optics,PO)区之间的电流相互作用构造耦合转移矩阵和激励转移矩阵,从而建立两个区域未知量之间的线性关系,进而完成对阻抗矩阵的降维,最终从矩阵运算角度构建了一种MoM-PO混合算法。其中,使用等效电偶极子模型简化双重积分计算,进一步减少矩阵元素的计算量;阻抗矩阵的阶数大幅减少,避免了大规模矩阵方程的求解计算。算例结果表明,与传统的低频算法相比,该算法既保证了计算精度,又提高了计算效率。

Modified physical optics algorithm for near field scattering

A novel modified physical optics algorithm is proposed to overcome the difficulties of near field scattering prediction for classical physical optics. The method is applied to calculating the near field radar cross section of electrically large objects by taking into account the influence of the distinct wave propagation vector, the near field Green function, and the antenna radiation pattern. By setting up local reference coordinates, each partitioned facet has its own distinct wave front curvature. The radiation gain for every surface element is taken into consideration based on the modulation of the antenna radiation pattern. The Green function is refined both in amplitude and phase terms and allows for near field calculation. The scattered characteristics of the near field targets are studied by numerical simulations. The results show that the approach can achieve a satisfactory accuracy.

Optical Band Gap, Oxidation Polarizability, Optical Basicity and Electronegativity Measurements of Silicate Glasses Using Ellipsometer and Abbe Refractometer

The values of refractive index (n) for silicate glasses (silica, soda lime and borosilicate 7059) are decreased from 1.5119 to 1.5111, 1.5086 to 1.5065 and 1.5296 to 1.5281, respectively;and the optical band gap (Eg) is increased from 9.8 to 9.81 eV, 9.845 to 9.88 eV and 9.56 to 9.58 eV, respectively over the temperature range 295 - 473 K using ellipsometer at wavelength 632.8 nm. While n is decreased from 1.5276 to 1.5274, 1.5074 to 1.5070 and from 1.5283 to 1.5281, respectively;and Eg is increased from 9.59 to 9.592 eV, 9.862 to 9.870 eV, and 9.574 to 9.58 eV, respectively over the temperature range 297 - 322 K using Abbe refractometer at wavelength 589.3 nm. The values of oxide ion polarizability [αo2- (n) and αo2-(Eg)] regarding silica, soda lime and borosilicate 7059 glasses are decreased from 1.3427 to 1.3408, 1.6014 to 1.5941, 1.4329 to 1.4193, respectively over the temperature range 295 - 473 K using ellipsometer;and are decreased from 1.3786 to 1.3764, 1.5991 to 1.5969, 1.4297 to 1.4191, respectively over the temperature range 297 - 322 K using Abbe refractometer. Similarly, the values of optical basicity [A (n) and A (Eg)] of silica, soda lime, and borosilicate 7059 glasses are decreased from 0.4272 to 0.4245, 0.6271 to 0.6224, 0.5045 to 0.4933, respectively over the temperature range 295 - 473 K using ellipsometer;and are decreased from 0.4586 to 0.4567, 0.6256 to 0.6242, 0.5018 to 0.4930, respectively over the temperature range 297 - 322 K using Abbe refractometer. Further, we have found that for silica, soda lime and borosilicate 7059, the values of electronegativity (ξ1av) QUOTE ζ1av) using Zahidnumerical model [based on αO2- (n) and A (n)] are increased from 5.1035 to 5.5504, 4.0393 to 4.830, 4.8143 to 5.0111, respectively over the temperature range 295 - 473 K using ellipsometer;while these values are increased from 5.0657 to 5.2149, 5.0657 to 5.2149, 4.8357 to 5.0111, respectively over the temperature range 297 - 322 K using Abbe refractometer. It is very clear from this research report that both refractive index and optical band gap-based-oxide ion polarizability and optical basicity have the same decreasing trend as the temperature is increased, and this trend indicates that the reported glasses have a very small amount of electronic polarizability. Moreover, this decreasing trend occurs due to the decreasing amount of non-bridging oxygen (NBO) which in turn caused a decrease in refractive index within the silicate glass system at higher temperature. Since the calculated values of electronegativity are found to be in the range 4.0393 - 5.5504 for the reported silicate glasses, so all these glasses have an ionic character. Moreover, low values of optical basicity and of oxide ion polarizability suggest that the silicate glasses are not novel glasses (optical functional glasses) for non-linear optical (NLO) devices or for three dimensional displays.

The Effect of Annealing Treatments on Spherulitic Morphology and Physical Ageing on Glass Transition of Poly Lactic Acid (PLLA)

Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The morphology of spherulite of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The effect of both annealing temperature and crystallization temperature on the formation of cracks was described by polarized optical microscope (POM). Non banded spherulite (fibrils) with cracks was detected in PLLA film after annealing at 160°C (180 min.) and isothermal crystallization temperatures at 140°C and 150°C. With increasing temperature after annealing treatment the size of spherulite is increased and more cracks are formed. The maximum growth rate of spherulites was found at 130°C. The physical ageing was carried out by annealing the PLLA sample at room temperature for several annealing time (ta) from 0 h to 720 h. The enthalpy relaxation has been studied by differential scanning calorimetry (DSC) through analysis of the endothermic peak of glass transition temperature, which increased and shifted towards higher temperature as the annealing time increased.

Ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer using a beam collimator and its application for ultrasonic imaging of seismic physical models

An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer(FPI) is proposed and employed for ultrasonic imaging of seismic physical models(SPMs). The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber(MMF), both of which are enclosed in a ceramic tube. The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity, leading to an increased spectral fringe visibility and thus a steeper spectral slope. By using the spectral sideband filtering technique, the collimated FPI shows an improved ultrasonic response. Moreover, two-dimensional images of two SPMs are achieved in air by reconstructing the pulse-echo signals through using the time-of-flight approach. The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.

Optical nonlinearity measurement of 4-(N-methyl,N-hydroxyethl)amino,4'-nitroazobenzene using a transmittance technique with a phase object(T-PO) with top-hat beams at 600-nm wavelength

The transmittance technique with a phase object(T-PO),for measuring optical nonlinear coefficients is proposed with a top-hat beam.The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam.The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid,CS 2 at 532-nm wavelength.The ease of use of this method has been proved by measuring a new compound 4-(N-methyl,N-hydroxyethyl)amino,4'-nitroazobenzene(ANAB) at 600-nm wavelength,indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.

Photoinduced Reorientation Process and Nonlinear Optical Properties of Ag Nanoparticle Doped Azo Polymer Films

有或没有 Ag nanoparticles 做的偶氮苯聚合物电影被准备。photoinduced 重取向过程被使用 Nd 调查: 在 532 nm 的 YVO4 泵横梁和在 650 nm 的一根低半导体激光横梁。偶氮的聚合物电影的重取向率与 2.2 g/ml 的 Ag 集中面对偶氮的聚合物电影的 Ag nanoparticles，和率被提高比有 1.1 g/ml 和 4.4g/ml 的 Ag 集中的偶氮的聚合物电影的大。Ag/azo 合成电影的第三顺序的非线性的光性质被 Z 扫描技术在 532 nm 的波长获得，并且测量非线性的折射索引是 9.258 ?????????????? ㈠ ? 渭 ? 潴 ? 楓吗？？

Corrections to atomic ground state energy due to interaction between atomic electric quadrupole and optical field

We study the ground state energy of an atom interacting with an oscillating optical field with electric dipole and quadrupole coupling.Under the rotating wave approximation,we derive the effective atomic Hamiltonians of the dipole/quadrupole coupling term within the perturbation theory up to the second order.Based on the effective Hamiltonians,we analyze the atomic ground-state energy corrections of these two processes in detail.As an application,we find that for alkali-like atoms,the energy correction from the quadrupole coupling is negligible small in comparison with that from the dipole coupling,which justifies the so-called dipole approximation used in literatures.Some special cases where the quadrupole interaction may have considerable energy corrections are also discussed.Our results would be beneficial for the study of atom–light interaction beyond dipole approximation.

Iterative physical optics model for electromagnetic scattering and Doppler analysis

An iterative physical optics(IPO) model is proposed to solve extra large scale electric electromagnetic(EM) scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation(Fa FFA) in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle(LGA).

RIS辅助的混合RF/FSO系统物理层安全性能分析

【目的】针对自由空间光(FSO)链路和射频(RF)链路的保密信息容易被外部窃听者窃听的问题,为提升混合RF/FSO通信系统的保密性能,同时考虑到实际工程中FSO链路往往无法满足视距条件且不同天线分支之间会由于收发模块小型化产生相关性,需要对可重构智能表面(RIS)辅助的混合RF/FSO系统的安全性能进行研究,以得到系统安全性能与RIS部署位置和天线相关性程度等参数的关系。【方法】文章考虑单个窃听者,分别针对RF和FSO链路进行窃听,RF链路服从任意相关的Nakagami-m分布,FSO链路服从Gamma-Gamma分布。采用解码转发协议,推导得到了两种窃听场景下通信系统的安全中断概率(SOP)和严格正安全容量概率(SPSC)的闭合表达式,并对SOP进行了渐近分析。此外还利用Matlab软件进行了仿真实验,通过蒙特卡洛仿真来验证所推导公式的准确性。【结果】仿真结果表明,将RIS部署在靠近接收端的位置可以降低系统的SOP,RF主信道的信道质量与窃听信道相比较好时,天线相关性程度的增加会使系统的SOP上升。【结论】RIS辅助的FSO链路相比RF链路具有更好的安全性,虽然多天线分集技术能够有效提高系统的安全性能,但是类似指向误差和大气湍流引起的衰落,天线相关性也会对系统的安全性能造成损害,通过降低天线相关性程度能有效提升系统的安全性。

霍尔效应实验教学设计及内容拓展探索

从霍尔效应的发现及历史发展出发,介绍了磁感应强度、载流子浓度及迁移率的测量原理,进而拓展引入了前沿科学研究内容——光场调控霍尔效应及动力学演化过程。教学内容由浅入深、由古及今,引发学生的思考,拓宽学生的视野,使学生对霍尔效应有一个全面的认识,为培养追求卓越、引领未来的领军人才奠定基础。

大学物理中光学与工程相结合的实例设计

大学物理是理工科专业的一门基础课。将大学物理课程与工程实践相结合,是培养工程技术人才的重要内容。以光学为例,深入研究工程中的物理理论,从复杂的工程实例中提炼与课程知识点相关联的模型融入教学,设计了光纤传光原理、光纤陀螺仪、磁致旋光效应、线性电光效应等教学实例。用工程实例讲述物理理论,为大学物理教学改革提供思路。

利用UTD修正的MoM-PO混合算法研究

介绍了利用矩量法 (MoM )和物理光学 (PO)混合方法处理复杂线体结构的电磁散射问题 ,提出利用 pulse基函数对线电流进行展开 ,使得处理复杂线体结构问题变得简化 ,并推导出一般的矩阵方程。然后针对PO在阴影区域失效等问题 ,利用UTD(一致性几何绕射 )对该简化模型结构下的PO区域电流进行了修正 ,使得其应用范围得到扩展、计算精度得到提高。文中的实例结果与传统的MoM很好的一致 。

线面结构天线辐射的MoM-PO混合法分析

介绍了利用矩量法求解线面复杂结构目标的电磁散射问题,并给出了一般的矩阵方程.并在以平面三角形电流为基展开的物理光学表面电流基础上,对矩量法和物理光学的混合方法的理论进行了细致和深入的研究,推导出了一般的矩阵方程表达式.仿真实例说明了该混合方法的精确性和高效性.

基于PO-EEC的各向同性介质薄层涂覆目标电磁散射

基于阻抗边界条件,将介质薄层涂覆目标等效为无厚度阻抗表面,应用三维各向同性阻抗面电磁散射的物理光学(physical optics,PO)算法,并通过各向同性阻抗劈的一致性几何绕射理论导出各向同性阻抗边缘的等效边缘流(equivalent edge currents,EEC),从而以边缘波场修正物理光学场,实现各向同性介质薄层涂覆三维导电目标电磁散射的高频预估。给出两个典型算例,与矩量法精确结果吻合良好,验证该各向同性PO-EEC算法的精度和效率。

基于HPP/PO的舰船与海面耦合散射快速算法

针对粗糙海面上舰船类超电大尺寸复杂目标电磁散射问题,提出了一种基于混合面元投影(HPP)和物理光学法(PO)的计算目标与海面耦合散射的快速算法。首先建立基于海谱的海面几何模型,并考虑海面面元的微粗糙特性,修正海面反射系数,然后针对目标和海面的结构特点,形成两种尺度面元混合的目标与海面模型,对电磁波在海面和目标之间的多次反射按照GO原理进行快速投影运算,并利用PO计算投影区域的散射贡献,最后给出了几组典型实例的计算结果。数值计算表明,该方法对于海面舰船类目标的散射计算是高效、准确的。

基于两平晶三面互检的折射率均匀性测量方法

结合奇偶函数理论,提出了一种基于两平晶三面干涉测量平晶折射率均匀性的方法。该方法通过两块平晶3个表面之间的组合测量,对折射率均匀性引入的误差进行分部求解,生成4个随机波面作为初始3个表面面形和折射率均匀性误差,对其中的均匀性误差复原,结果与初始值仅相差0.6×10-6,残差与平晶表面面形的低频信息无关,仅取决于折射率均匀性本身的旋转不变项。在100 mm口径Zygo干涉仪上完成了两平晶折射率均匀性检测实验。同时通过三平晶透射法对同一块平晶的折射率均匀性进行检测,将两种方法的测量结果进行对比。结果表明两平晶方法获得的折射率均匀性结果与透射法获得的折射率均匀性波面形状相同,指标结果仅相差0.2×10-6,波面偏差峰谷值相差3 nm。分析了影响评估精度的误差项,旋转角度误差与对准误差的影响在实验精度条件下,均方根偏差均小于1 nm。实验结果表明所提出的两平晶三面互检方法能够有效地对平晶的折射率均匀性进行测量。

HFSS/PO混合分析飞行器放电对雷达目标特性的影响

为精确计算飞行器在飞行过程中静电放电对雷达散射截面(radar cross section,RCS)的影响,采用高频电磁仿真软件Ansoft HFSS与物理光学(physic-optics,PO)法相混合。用HFSS计算放电产生的等离子体所覆盖的局部机翼的散射场,用物理光学法计算飞行器其余部分引起的散射场,将二者的等相位面重合,保持飞行器各散射体之间的相位关系,进而计算出飞行器的宽带雷达散射截面。