基于TE-TM模变换的新型相位自补偿磁光隔离器

讨论了由45°非互易模变换器与45°互易模变换器构成波导型光隔离器时两者之间须满足的条件,并由此设计了一种新型的相位自补偿磁光隔离器. 利用全矢量有限差分光束传输法对隔离器进行仿真,得到了插入损耗为-12dB,隔离度为-34dB的结果. 关键词： 集成光学 磁光隔离器 非互易模变换器 互易模变换器     

Anomalous magnetic properties of an iron film system deposited on fracture surfaces of α-Al2O3 ceramics

An iron film percolation system is fabricated by vapour-phase deposition on fracture surfaces of α-Al2O3 ceramics. The zero-field-cooled （ZFC） and field-cooled （FC） magnetization measurement reveals that the magnetic phase of the film samples evolve from a high-temperature ferromagnetic state to a low-temperature spin-glass-like state, which is also demonstrated by the temperature-dependent ac susceptibility of the iron films. The temperature dependence of the exchange bias field He of the iron film exhibits a minimum peak around the temperature T=5 K, which is independent of the magnitude of the cooling field Hcf. However, for T 〉 10K, （1） He is always negative when Hcf=2kOe and （2） for Hcf= 20 kOe （1Oe≈80 A/m）, He changes from negative to positive values as T increases. Our experimental results show that the anomalous hysteresis properties mainly result from the oxide surfaces of the films with spin-glass-like phase.     

Two-dimensional ultrashort echo time imaging using a spiral trajectory

Tissues with very short transverse relaxation time (T2) cannot be detected using conventional magnetic resonance (MR) sequences due to the rapid decay of excited MR signals. In this work, a multiecho sequence employing half-pulse excitation and spiral sampling was developed for ultrashort echo time (UTE) imaging of tissues with short T2. Spiral readout gradients were measured and precompensated to reduce gradient distortions due to eddy currents and gradient anisotropy. The effects of spatial blurring due to fast signal decay were investigated experimentally through spiral UTE (SUTE) imaging of rubber bands with different spiral sampling duration. The unwanted long T2 signals were suppressed through the use of an inversion pulse and nulling, and/or subtraction of a later echo image from the initial one. This technique has been applied to imaging of the short T2 components in brain white matter, knee cartilage, bone and carotid vessel wall of normal volunteers at 1.5 T. Preliminary results show high spatial resolution and excellent image contrast for a variety of short T2 tissues in the human body under a relatively short scan time. A quantitative comparison was also made between radial UTE and SUTE in terms of signal-to-noise ratio efficiency.     

基于光电准直虚拟扩展成像的姿态角测量系统的误差分析

建立了基于光电准直原理的姿态角测量系统,提出一种虚拟扩展成像面技术,应用于测量系统中,对图像传感器成像面进行复用,虚拟扩大系统的测量视场.介绍了系统的主要工作原理,在系统模型下,对可能影响系统测量精度的误差源进行了分析,建立其数学关系,对精度影响因素进行了定量仿真实验.按照仿真结果,对系统设计方案进行了分析验证.结果表...     

单目摄像机-激光测距传感器位姿测量系统

在单目视觉测量中,由于模型自身的限制,沿摄像机光轴方向上的位移测量精度一般远低于垂直光轴方向上的位移测量精度.首先,从数学模型上分析了单目视觉位姿测量在沿光轴方向上位移测量精度低的原因;然后,为了提高沿摄像机光轴方向上的位移测量精度,通过在沿摄像机光轴方向上加装一个高精度的激光测距传感器,设计了一种单目摄像机-激光测距...     

含有源频率选择表面可调复合吸波体

基于传输线等效理论,设计了含有源频率选择表面(active frequency selective surface,AFSS)的三层可调复合吸波体,第一层是表面层,为AFSS衬底;中间层是AFSS层,由频率选择表面(frequency selective surface,FSS)和PIN二极管阵列构成;第三层是介质层.反射率测量结果表明,通过调节PIN二极管阵列偏置电压可以动态调节吸波体反射特性,在偏置电压为5 V时,可获得最佳吸波性能,在5—15 GHz和5.3—13 GHz频段分别可获得-8 dB和- 关键词： 频率选择表面 复合吸波材料 反射率 PIN二极管     

基于OH自由基A2Σ + →X2Πr 电子带系发射光谱的温度测量技术

本文基于OH自由基所固有的分子结构特征,通过分子光谱理论系统地分析和计算了OH自由基A²Σ ⁺ →X²Π_r 电子带系发射光谱的谱线跃迁频率、能级分布以及爱因斯坦自发发射跃迁概率等重要参数.同时结合实际的光谱实验,分析了谱线的自然展宽、碰撞展宽、多普勒展宽以及仪器展宽等各种展宽因素对谱线线型的影响,从理论上计算了任意转动温度、振动温度以及谱线展宽条件下OH自由基A²Σ ^{关键词： 发射光谱 转动温度 振动温度 自发发射爱因斯坦跃迁概率}     

PdCO分子结构与势能函数

用密度泛函理论的B3LYP方法,对钯原子采用LANL2DZ收缩价基函数,碳原子和氧原子采用AUG-cc-pVTZ基组,对PdC,PdO和PdCO体系的结构进行优化,计算表明：PdC分子基态为¹Σ⁺态,键长为R_e=0.17285nm,离解能为4.919eV.PdO分子基态的平衡核间距为0.18546nm,其电子态为³Π,离解能为2.455eV,并拟合得到Murrell-Sorbie势能函数;PdCO分子有两 关键词： PdCO 分子结构 势能函数     

第一性原理研究Fe掺杂SnO2材料的光电性质

采用基于第一性原理的线性缀加平面波(FP-LAPW)方法,研究Fe掺杂SnO₂材料电子结构和光学性质,包括电子态密度、能带结构、介电函数和其他一些光学图谱. 研究结果表明,掺Fe后材料均属于直接跃迁半导体,且呈现半金属性;随掺杂浓度增加,费米能级进入价带,带隙逐渐减小,Fe原子之间耦合作用增强;通过掺杂能够在一定程度上改变成键性质,使其具有金属键性质. 光学谱线(吸收谱、消光系数等)与介电函数虚部谱线相对应,均发生蓝移,各峰值与电子跃迁吸收有关,从理论上指出光学性质和电子结构的内在联系. 关键词： 能带结构 态密度 光学性质 介电函数