基于聚合物网络液晶的近红外波段快响应相位调制器

相位型液晶空间光调制技术已经广泛应用于自适应光学、信息光学等领域,然而一直存在着响应速度较低的问题。为了提高相位型液晶空间光调制器的响应速度,采用聚合物网络液晶制备近红外波段亚毫秒响应相位调制器,并对其光散射特性和瞬态响应特性进行了研究。通过降低聚合反应温度并提高紫外(UV)固化照度,可以降低器件的光散射强度,实现较好的相位调制。在此基础上,初步研究了聚合物网络形貌对最大光散射强度的影响。在高电压加载下,聚合物网络的电致伸缩效应会极大降低聚合物网络液晶的响应速度,使其达到秒级,经分析认为通过采用高介电各向异性的液晶材料可以降低阈值电压,提高器件的响应速度。     

Effect of trabecular bone material properties on ultrasonic backscattering signals

In this study, ultrasonic backscattering signals in cancellous bones were obtained by finite difference time domain （FDTD） simulations, and the effect of trabecular material properties on these signals was analyzed. The backscatter coefficient （BSC） and integrated backscatter coefficient （IBC） were numerically investigated for varying trabecular bone material properties, including density, Lame coefficients, viscosities, and resistance coefficients. The results show that the BSC is a complex function of trabecular bone density, and the IBC increases as density increases. The BSC and IBC increase with the first and second Lame coefficients. While not very sensitive to the second viscosity of the trabeculae, the BSC and IBC decrease as the first viscosity and resistance coefficients increase. The results demonstrate that, in addition to bone mineral density （BMD） and microarchitecture, trabecular material properties significantly influence ultrasonic backseattering signals in cancellous bones. This research furthers the understanding of ultrasonic backscattering in cancellous bones and the characterization of cancellous bone status.     

一种紫外-可见光谱法检测水质COD的浊度影响实验研究

消除浊度影响是直接光谱法检测水质COD的关键技术问题。此源于紫外-可见光谱法检测水质参数的关键依赖于化学计量法所建立的准确的水质参数分析模型,而浊度是影响其建模的一个重要参数。为此,选取福尔马肼浊度液和邻苯二甲酸氢钾标准溶液,开展了紫外-可见吸收光谱法检测水质COD的浊度影响实验研究,获得了选定溶液在245,300,360和560 nm几个特征波长点的吸光度随浊度变化的最小二乘法拟合曲线,分析了吸光度随浊度的变化规律。研究结果表明,在240～380 nm的紫外光谱段,由于引起浊度的颗粒物对有机物产生了吸附,致使浊度对水样的紫外光谱影响较为复杂;在380～780 nm的可见光谱区域,浊度对光谱的影响则是随着波长的增大而减弱。基于此,开展了多元散射校正法对受浊度影响的水样光谱进行校正试验。对某溪水水样的紫外-可见吸收光谱进行多元散射校正,通过处理前后光谱对比表明,浊度引起各个波长点的基线偏移都得到了有效的校正,而在紫外区域特征并未减弱。接着对选取的三种液体的紫外-可见吸收光谱进行多元散射校正,实验结果表明：该方法可在不影响水样紫外-可见吸收光谱特征的前提下对其吸收曲线进行有效的校正,这不仅提高了光谱法检测水质COD的信噪比,而且还为化学计量法建立准确、有效的水质检测COD分析模型进行数据预处理提供了一种新途径。     

雨滴对电磁波的散射特性研究

由于重力和向上气流的作用,高速摄影显示较大的雨滴在降落过程中表现为一底部扁平、顶部圆滑的非球形对称体,已有的模型中BC模型(由Beard和Chuang提出)被认为能准确描述雨滴的形状。本文利用沿降落方向旋转对称的扁椭球体和均匀球体模拟降落中的雨滴,扁椭球体的短轴(旋转轴)与BC模型的相等,长轴通过与BC模型截面积等效法确定;利用T矩阵方法研究了水平取向的旋转扁椭球体和BC雨滴模型的散射特性,利用Mie理论计算了均匀球的散射特性,比较了半径分别为2 mm和3 mm大小的三种雨滴模型对94 GHz电磁波斜入射时的单次散射相矩阵,以及对频率为30 GHz~100 GHz电磁波的单次散射反照率,最后讨论了半径为0.5 mm~3.5 mm雨滴对35 GHz和94 GHz的后向散射函数。计算结果表明,利用均匀球模拟雨滴将带来较大误差,而利用截面积等效的旋转扁椭球体模型可以较好地模拟雨滴的散射特性。     

Surface Plasmon Resonance and Raman Scattering Activity of the Au/AgxO/Ag Multilayer Film

The nanostructured Au/AgxO/Ag sandwich multilayer films on quartz substrates are prepared by the magnetron sputtering method. The morphology, plasmon resonance and surface enhanced Raman scattering （SERS） activi- ties of the multilayer films are studied. The resonant absorption wavelength of localized surface plasmon is tuned in a wide range from 618nm to 993nm by controlling the density of nanoparticles of Au and Ag. The SERS activity of the Au/AgxO/Ag multilayer films are enhanced over -10 times compared with those of bare Ag and bare Au films. These properties may find a potential application in biosensor and bioimaging.     

Impact of CHFa Plasma Treatment on A1GaN/GaN HEMTs Identified by Low-Temperature Measurement

We investigate the impact of CHFa plasma treatment on the performance of AIGaN/GaN HEMT （F-HEMT） by a temperature-dependent measurement in the thermal range from 6 K to 295 K. Tlle temperature dependence of the transconductance characteristics in F-HEMT declares that the Coulomb scattering and the optical phonon scattering are effectively enhanced by the fluorine ions in the A1GaN layer. The fluorine ions not only provide immobile negative charges to deplete 2DEG, but also enhance the Schottky barrier height of the metal gate. Thermal activation of the carrier traps induced by CHF3 plasma for F-HEMT contributes to the negative shift of the threshold voltage by -3.4mV/℃ with the increasing temperature. The reverse gate-leakage current of F-HEMT is decreased by more than two-order magnitude in comparison with that of conventional A1GaN/GaN HEMT （C-HEMT） without fluorine ions.     

Design of the Coordinate Transformation Function for Cylindrical Acoustic Cloaks with a Quantity of Discrete Layers

Acoustic cloak based on coordinate transformation is of great topical interest and has promise in potential appli- cations such as sound transparency and insulation. The frequency response of acoustic cloaks with a quantity of discrete homogeneous layers is analyzed by the acoustic scattering theory. The effect of coordinate transforma- tion function on the acoustic total scattering cross section is discussed to achieve low scattering with only a few layers of anisotropic metamaterials. Also, the physics of acoustic wave interaction with the interfaces between the discrete layers inside the cloak shell is discussed. These results provide a better way of designing a multilayered acoustic cloak with fewer layers.     

光子晶体光纤中去极化型声波导布里渊散射频移和散射效率研究

利用矢量有限元法,数值模拟了不同结构参数下光子晶体光纤中空气孔填充率与去极化型声波导布里渊散射频移的关系,以及布里渊散射频移与布里渊散射效率的关系。研究结果表明,空气孔填充率的增大会导致扭转径向模式的去极化型声波导布里渊散射频移下移。空气孔节距或纤芯直径一定时,高阶模式的频移对空气孔填充率的变化更为敏感。扭转径向模式的去极化型布里渊散射效率都随布里渊散射频移的增大而增大。     

旋转粗糙目标微运动特征识别技术

基于动态散斑技术的微运动特性识别在目标探测领域具有重要的研究价值.以粗糙面散射理论为基础,研究了旋转粗糙凸体目标的动态散斑时间相关函数,给出了旋转圆锥体目标动态散斑时间相关函数.将数值结果与相同条件下实验结果进行比较,验证了圆锥体目标时间相关长度的有效性.利用粒子群算法,反演出旋转圆锥体的旋转角速度和视线角.结果表明,该方法可识别旋转圆锥体范围为20°—90°之间的视线角值和范围为0.5—6 r/min的角速度值,为微运动特征识别提供理论和实验依据.     

含泡沫面元模型的海面电磁散射研究

传统计算海面电磁散射的方法都是通过求集平均的方法来统计得到不同输入参数下海面总回波系数的均值曲线,并不需要具体的几何样本.随着合成孔径雷达以及雷达成像的发展,为了充分描述海面各点的分布特征,需要得到海面具体面元的散射结果,同时随着海面上方风速的增大,海面泡沫层的出现会对散射结果产生相当大的影响.本文采用海面模型面元化的思想,将海面散射的贡献面元化,同时考虑泡沫层对大入射角下散射结果的影响,计算了不同风速下海面的后向散射系数,并与实测数据做对比分析,验证了方法的准确性.