个性化头相关传输函数的近似获取——现状和问题

虚拟听觉重放采用头相关传输函数(HRTF)合成双耳声信号,并用耳机重放,以产生所需的空间听觉事件。理想的虚拟听觉重放需要个性化HRTF。个性化HRTF可通过实验测量或数值计算相对地准确获得。然而,测量每个潜在使用者的高空间分辨率HRTF是困难的,而数值计算HRTF的频段往往受限于计算机性能。近年发展了多种HRTF的近似获取方法,并成为热门研究课题,但效果有待验证和提高。本文评述了个性化HRTF近似的研究进展,指出了存在的问题和今后的方向。     

Photoracemization broadening of selective reflection and polarization band of glassy chiral-nematic films

Glass-forming liquid crystals consisting of a cyclohexane central core with (S)-1-phenyl-ethylamine and (4-cyanophenyl)naphthalene pendants were synthesized as hosts for racemizable (R)-dinaphtho[2,1-d:1',2'-f][1,3]dioxepin, a chiral dopant. Chiral-nematic films 14, 22, and 35 mum thick were prepared for thermal and photoinduced racemization at temperatures from 95 to 130°C, i.e. in the mesomorphic temperature range, over a period of hours to days. Spatially modulated photoracemization was accomplished with an insignificant contribution from the thermal process at temperatures around 100°C over a period of up to 3 h. With an absorbance per unit thickness of 6.2 mum^-1 at 334 nm, the photochemical process was essentially confined to the irradiated surface, thereby setting up counter-diffusion of the two enantiomers through the film, and hence the pitch gradient as visualized by atomic force microscopy. The significantly widened selective reflection band was interpreted with the Good-Karali theory extended for a gradient-pitch film. Furthermore, the bandwidth was found to increase with decreasing racemization temperature or with increasing film thickness, further validating the presence of a pitch gradient as a result of controlled photoracemization.     

Comparison of electro-optical switching between polymer-stabilised cubic and amorphous blue phases

We prepared polymer-stabilised cubic and amorphous blue phase liquid crystals consisting of the same materials at different UV-curing temperatures using photopolymerisation. Then we investigated the effects of polymer stabilisation on their physical properties. The UV-curing temperature does not affect phase stabilisation of the polymer-stabilised amorphous BPIII (PS-BPIII). Temperatures of the PS-BPIII were found to be extended to more than 50 K. However, a critical temperature exists in the polymer stabilisation process for the PS-cubic BP. Although no substantial difference in response speed was found between the polymer-stabilised cubic and amorphous structures, larger hysteresis and higher residual birefringence were observed in the PS-cubic BP than in the PS-BPIII. Amorphous BPIII with an amorphous network of disclination lines has no critical temperature for the polymer stabilisation and realises a high-performance display.     

Dielectric and electro-optical properties of a nematic liquid crystalline material with gold nanoparticles

ABSTRACT

We have prepared the composites of a room temperature nematic liquid crystalline material namely 4-(trans-4′-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and gold nanoparticles (GNPs). Thermodynamic, electro-optical and dielectric properties have been investigated. Effect of dispersion of GNPs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters such as threshold voltage, dielectric anisotropy and splay elastic constant have altered for composite systems. Due to the dispersion of GNPs, nematic to isotropic transition temperature is significantly increased. Relaxation frequency corresponding to flip-flop motion of the 6CHBT molecules about their short axes has increased due to the presence of GNPs.     

Fast switching and luminance-controlled fringe-field switching liquid crystal device for vehicle display

ABSTRACT

Liquid crystal displays (LCDs) for vehicle displays should exhibit a fast response time in wide temperature range and wide-viewing angle in horizontal and downward directions without grey-scale inversion but limited brightness in the upward direction because the display images can be reproduced in the front window glass of a vehicle, affecting driver’s front visibility. Currently, fringe-field switching (FFS) liquid crystal device is widely commercialised for high resolution and wide-viewing-angle LCD; however, it needs to improve response times and limit the display brightness in the upward direction. As a solution, we propose a homogeneously aligned liquid crystal device in which liquid crystal director does tilt as well as twist deformation in a confined area by both vertical- and fringe-electric fields, exhibiting about two times faster decay response time than that of conventional FFS mode with suppressed luminance in the upward direction. The proposed liquid crystal device can be applied to LCDs for vehicle displays.     

分光计电子显示系统的研制

介绍了我院针对分光计实验的实际情况,自行研制了CCD电子显示系统,解决了实验教学中的难题,收到了很好的教学效果。     

Enhanced electro-optical properties of a nematic liquid crystals in presence of BaTiO3 nanoparticles

Composites of nematic liquid crystals (NLCs) and ferroelectric barium titanate (BaTiO₃) nanoparticles (NPs) have been prepared. The alignments of NPs in the host medium have been demonstrated. Effect of NPs doping on various display parameters of NLCs, namely, threshold voltage, dielectric anisotropy and splay elastic constant has been studied using electro-optical and dielectric studies. The nematic ordering of host supports alignment of NPs parallel to the director which consequently improves electro-optical parameters in the composite system. The dielectric and electro-optic properties of LC–NPs composites have been discussed in frame of conventional theories of NLCs.     

数字微镜器件动态红外场景投影技术

动态红外场景投影(DIRSP)技术是考察和评估红外成像测量跟踪系统性能指标的主要方法。本文回顾了国内外DIRSP技术的发展现状及应用,概述了几种主要的DIRSP技术及其特点。在详细介绍数字微镜器件(DMD)的工作原理及机械结构的基础上,总结了灰度等级控制的方法及其特点。通过对3种数字光处理(DLP)显示系统投影原理的对比,指出了各自的特点和应用场合。重点分析了基于DMD的DIRSP系统—微镜阵列投影系统(MAPS)的工作原理、系统结构、性能指标及技术优势,并讨论了将DMD应用于DIRSP所采用的6大关键技术。最后,结合DIRSP技术的应用背景和国内外研究现状,对下一步的研究工作做了展望。     

数字电视的光色计量及其装置

结合市面上常见数字电视器件CRT,LCD,PDP等的显示原理及特性，具体讲解光色计量指标测量方法及原理，系统量值传递是通过国家色度和亮度基准标准灯来完成的。利用虚拟仪器技术建立的数据采集及分析系统，可对待测仪器的参数进行实时数据检测和数据分析。整个测试系统亮度和色坐标不确定度小于2%和0.005. 通过对市场主流电视产品的集中检测，将其相对光谱功率分布、亮度、色坐标、亮度不均匀性及对比度等综合参数进行对比，给出了测试结果及各种电视性能分析，为数字彩色电视计量工作提供了参考。     

基于硅基液晶微显示立体投影光学引擎的设计

从平衡两路图像对比度的角度,采用双硅基液晶(LCoS)芯片设计了一种实用的微型立体投影光学引擎。光学引擎中双LCoS芯片分别用于调制左右眼的图像,一个白光LED作为投影光源,两个标准的MacNeille偏振分光棱镜(PBS)用于产生两路偏振方向相互垂直的高偏振度光束。整个引擎设计简单,结构紧凑,其尺寸约为105mm×28mm×25mm。测量了本设计中光学引擎的各部件的实际参数值,根据所测量的数据通过理论计算得到:左右两光路的对比度完全平衡且均为64…1,光效率均为3.61%,整机的光通量为20lm。