Electrically Controlled Liquid Crystal Phase Grating for Terahertz Waves

This work demonstrates the feasibility of electrically controlled liquid-crystal-based phase grating for manipulating the terahertz (THz) waves. This device can be utilized as a THz beam splitter and the beam splitting ratio of the zeroth- to the first-order diffractions can be tuned from 10 : 1 to 1 : 1.      

液晶红外ECB效应的研究

液晶的红外ECB效应应用广泛，但是目前国内在这一领域的研究没有考虑液晶分子的吸收效应。在考虑液晶红外吸收效应的前提下，以向列相液晶BL－009为例研究了液晶的红外电控双折射效应，得到了入射光波长1300nm和1550nm下液晶双折射随电压变化关系曲线，同时得到了吸收系数随电压变化关系曲线。     

基于液晶的太赫兹可调谐超材料吸波体

文中设计了一种液晶太赫兹电控超材料吸波体,通过外部电场改变液晶层的等效介电常数,实现对于太赫兹反射波的调控。对器件的传输性能进行计算,分析了谐振频点处的表面电流分布和能量损耗密度情况。采用紫外光刻以及湿法刻蚀技术,制作了30×30单元超材料吸波体阵列并对其进行测试验证。结果表明,当偏置电压在0~30 V之间变化时,吸波体的谐振频点可实现101.5~117.95 GHz范围内的动态调控,综合可调率达到13.9%,整个工作频段内,吸收率始终维持在90%以上。     

Electrically Tunable Reflective Terahertz Phase Shifter Based on Liquid Crystal

We present a reflective spatial phase shifter which operates at terahertz regime above 325 GHz. The controllable permittivity of the nematic liquid crystals was utilized to realize a tunable terahertz (THz) reflective phase shifter. The reflective characteristics of the terahertz electromagnetic waves and the liquid crystal parameters were calculated and analyzed. We provide the simulation results for the effect of the incident angle of the plane wave on the reflection. The experiment was carried out considering an array consisting of 30?×?30 patch elements, printed on a 20?×?20 mm quartz substrate with 1-mm thickness. The phase shifter provides a tunable phase range of 300° over the frequency range of 325 to 337.6 GHz. The maximum phase shift of 331° is achieved at 330 GHz. The proposed phase shifter is a potential candidate for THz applications, particularly for reconfigurable reflectarrays.     

Photo-Doped Active Electrically Controlled Terahertz Modulator

We demonstrate an electric-controlled terahertz (THz) modulator which can be used to realize amplitude modulation of terahertz waves with slight photo-doping. The THz pulse transmission was efficiently...     

基于液晶空间光调制器的光束偏转控制

液晶空间光调制器(LCSLM)通过实时调制波前倾斜实现光束偏转,与传统的快反镜相比,具有非机械调制、体积小、功耗低、轻巧灵敏等优点,可应用于空间光通信中。简单介绍了液晶实现光束偏转的原理,并测试了LCSLM的调制特性,根据调制特性设计基于LCSLM的光束偏转闭环系统。实验结果表明LCSLM能有效地抑制光束抖动,使相对误差小于±1.75%。分析了LCSLM的衍射效率对于光束质量的影响及液晶响应速度、系统传输时延和算法复杂度对控制系统带宽的制约。     

电控位相型液晶菲涅耳波带片的特性

利用电场中液晶分子的可控双折射效应对制成电场可调的位相型衍射式菲涅耳波带片。对菲涅耳波带片的原理做了理论分析,测试了其最大衍射效率,给出不同电压Ｆ的不同衍射图像,并对衍射图像的周期性变化做了理论分析。     

Characterization of an Electrically Controlled Metamaterial Terahertz Modulator Using Dynamic Measurement Method

The characterization results of a typical electrically controlled metamaterial terahertz (THz) modulator obtained by the dynamic measurement method are presented and are in good agreement with the theoretical results predicted by a first-order model. The dynamic measurement method can characterize the modulation depth and modulation speed simultaneously. The reliability of the method is verified by terahertz time-domain spectroscopy (THz-TDS), and the current response method, which show that the more intuitive and comprehensive dynamic measurement method, can be used to characterize the electrically controlled metamaterial THz modulator accurately.     

液晶光学相控阵光束偏转效率研究(英文)

液晶光学相控阵(LCOPA)的光束偏转效率(OSE)定义为一级衍射光强与总入射光强的比值,它受很多因素的影响,因此建立一个数值分析的模型来分析光束偏转效率。这个模型将液晶光学相控阵器件当作一个相位光栅和一个振幅光栅的组合体,可控变量既包括几何结构参数又包括相位分布的参数。理论研究了光束偏转效率和三类因素即偏转角、器件参数及理想与实际相位分布误差之间的关系,提出了改善光束偏转光效率的方法。结果表明随着偏转角的增大光束偏转效率将会减小,而增大填充因子、减小像素大小会提高光束偏转效率。均匀排布像素并不能获得最佳偏转效率,需要使用如时域有限差分等方法来得到最佳的像素分布。减小相邻相移器之间的间隔、提高相位回置值可以明显提高光束偏转效率。     

Rewritable Electrically Controllable Liquid Crystal Actuators

Conductive structures determine the functions and actuation modes of electrically responsive soft actuators. The rewritability of conductive structures is highly desirable but has not been realized in electro-driven actuators. Typically, once conductive pathways are established, they can hardly be modified; thus, the function of the actuator is permanently fixed. In this study, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is developed as a rewritable conductive coating for actuators composed of liquid crystalline elastomers (LCEs). This enables reconfigurable, adaptive, and precisely controllable electro-driven motions and the repeated use of the same actuator for various purposes without disposal. Moreover, different PEDOT:PSS layers can be coated onto different regions, thus enabling the assembly of different actuation behaviors in a monolithic actuator under a single input voltage. Unlike all previously reported soft actuators that respond to electricity and light, opposite shape changes in an actuator with a series circuit can be performed under these two stimuli. Furthermore, when combining LCEs with dynamic covalent bonds, the PEDOT:PSS-coated LCE (PEDOT:PSS-LCE) actuator can be reprogrammed based on two different mechanisms: rewriting the conductive PEDOT:PSS patterns and re-aligning the LCEs. This versatile method can be adapted to other types of actuators.     

一种平面印刷电控波束扫描天线阵

该文设计了一种平面印刷偶极子波束扫描寄生阵列天线,可用于移动终端设备以提高通信质量和系统容量。通过改变加载在寄生单元中的电抗值可以控制天线的最大辐射方向。天线基本结构用电磁场全波软件设计,所需加载的电抗值通过差分进化算法(DE)优化得出。实测的天线主波束方向在xoy平面内-34~38之间扫描;在各方向上,中心工作频率上的增益在3.6~4.9 dBi之间变化,反射系数小于-10 dB的频带在5.63~5.96 GHz之间,带宽为330 MHz。实测结果表明,天线具有良好的波束扫描性能,采用的设计和优化方法准确高效。     

基于铁电液晶电控双折射的调谐滤波器的研究

将铁电液晶作为缺陷层引入一维光子晶体中,基于液晶的电控双折射,形成快速窄带调谐滤波器.用传输矩阵法研究了铁电液晶缺陷光子晶体的可调谐滤波特性,计算了电场对滤波器透射峰的位置、强度、个数和带宽的影响,结果表明该滤波器呈现良好的滤波功能.     

国外毫米波电扫描技术

综述了国外近年来提出、实施或实现的各种毫米波电扫描技术,并指出我国发展毫米波电扫描装备应该注意的五个方面,即:新的电扫描原理;新的天线形式;毫米波MMIC芯片;集成封装技术;毫米波馈电技术.     

宾主效应原理测试液晶分子电控倾角

液晶分子的预倾角测试技术对研究液晶器件电光特性十分重要,现有的晶体旋转法不适合测试20°￣70°之间的倾角,本文提出一种利用宾主效应原理测试液晶分子电控倾角的实验方法。推导出液晶盒中液晶分子倾角与透射光强的关系式,制备出加二色性染料液晶盒,对样品施加电场,观测液晶盒电光特性。对实验结果进行分析,认为该实验方法对于测试15°￣75°之间的液晶分子电控倾角具有一定的可行性。     

宽带调谐光子晶体光纤多功能太赫兹器件

基于液晶分子的指向矢随外加电场改变而变化的特点,设计了一种新型电场调制液晶太赫兹器件。利用全矢量平面波展开法和光束传播法分别研究了光子晶体光纤的带隙位置和传输光谱的电场分布。同时,利用时域有限差分法计算了液晶分子指向矢随外电场的变化关系。结果显示该器件不仅可以在0.55 THz的宽带范围内实现开关功能,且具有耦合损耗低、消光比高等优点,消光比为30.78 dB。当太赫兹波的入射频率满足光纤的单偏振条件时,该器件还具有偏振控制功能,能够改变传输模式的偏振状态。     

Discrete Cosine Transform for Driving Liquid Crystal Displays

Despite rapid advances in science and technology of liquid crystal display (LCD); elimination of motion-related artifacts and preservation of color purity in moving images have remained elusive because gray-scale to gray-scale response time, i.e., time taken to switch pixels from one gray-scale to another depends on the initial and final gray shades. A technique wherein gray scale to gray scale response times are less dependent on the initial and final gray shades as compared to other addressing techniques for driving matrix LCD is reported. We also found that the response times are about the same as that of a pixel driven with simple square waveforms and, therefore, the effect of duty cycle due to matrix addressing is minimal with distributed waveforms of this technique.      

Beam Steering with Linear Arrays

The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.     

Elimination of Fresnel Reflection Boundary Effects and Beam Steering in Pulsed Terahertz Computed Tomography

For the past few decades there has been tremendous innovation and development of Terahertz (THz) science and imaging. In particular, the technique of 3-D computed tomography has been adapted from the X-Ray to the THz range. However, the finite refractive index of materials in the THz range can severally refract probing THz beams during the acquisition of tomography data. Due to Fresnel reflection power losses at the boundaries as well as steering of the THz beam through the sample, refractive effects lead to anomalously high local attenuation coefficients near the material boundaries of a reconstructed image. These boundary phenomena can dominate the reconstructed THz-CT images making it difficult to distinguish structural defect(s) inside the material. In this paper an algorithm has been developed to remove the effects of refraction in THz-CT reconstructed images. The algorithm is successfully implemented on cylindrical shaped objects.     

OCB模式液晶显示器件的膜补偿模拟优化

研究了OCB模式液晶显示器件的膜补偿方式,给出了4种膜补偿结构的优化参数以及4种膜补偿结构下的等对比度视角图和响应时间。4种膜补偿结构通过模拟与研究都得到了很好的优化结果,最大对比度都可以达到2 200以上,响应时间在2ms以下。     

琉醇/丙烯酸脂聚合物稳定的铁电液晶显示器件

采用琉醇和丙烯酸的混合物作为反应单体,制备了单体含量为4%的聚合物稳定铁电液晶器件.琉醇的引入使丙烯酸聚合反应由自由基链式自聚转变为自由基逐步共聚,碳碳双键的转化率由30%提高到84%,较丙烯酸自聚反应有了大幅提高,降低了残留在液晶中的单体.在器件内部形成了沿着摩擦方向的聚合物网络,得到了具有"V"字型电光特性、对比度高、响应速度快、稳定性好的铁电液晶器件.