Smart Processing in Materials Tectonics:Fabrication of Photonic Crystals for Terahertz Wave Control by Using Micro-Stereolithography

Photonic crystals with three-dimensional dielectric structures were fabricated to control terahertz waves effectively by using micro-stereolithography of a CAD/CAM process. The photonic crystals with a diamond structure composed of acrylic lattice with nanosized alumina particles were fabricated. Dense alumina structures were obtained by successive dewaxing and sintering in an air atmosphere. The electromagnetic wave properties of these samples were measured by using a terahertz spectroscopy device. The micro periodic structures exhibited perfect band gaps in the terahertz range. To control terahertz waves, micrometer sized electromagnetic devices for cavities, filters, and antennas will be necessary.     

多层电磁超材料在太赫兹技术中的应用研究进展

基于电磁超材料的电磁谐振通过合理设计可以实现太赫兹波段的频率响应,为太赫兹波调控开辟了新的道路,特别是利用多层电磁超材料设计的太赫兹功能器件.本文综述了当前国内外基于多层电磁超材料在太赫兹波段技术的应用研究进展,分类介绍了其在太赫兹滤波器、吸收器、偏振器等方面的应用,最后对多层超材料在太赫兹技术应用的发展趋势作了探讨.     

Active terahertz metamaterial devices

The development of artificially structured electromagnetic materials, termed metamaterials, has led to the realization of phenomena that cannot be obtained with natural materials. This is especially important for the technologically relevant terahertz (1 THz = 10(12) Hz) frequency regime; many materials inherently do not respond to THz radiation, and the tools that are necessary to construct devices operating within this range-sources, lenses, switches, modulators and detectors-largely do not exist. Considerable efforts are underway to fill this 'THz gap' in view of the useful potential applications of THz radiation. Moderate progress has been made in THz generation and detection; THz quantum cascade lasers are a recent example. However, techniques to control and manipulate THz waves are lagging behind. Here we demonstrate an active metamaterial device capable of efficient real-time control and manipulation of THz radiation. The device consists of an array of gold electric resonator elements (the metamaterial) fabricated on a semiconductor substrate. The metamaterial array and substrate together effectively form a Schottky diode, which enables modulation of THz transmission by 50 per cent, an order of magnitude improvement over existing devices.     

基于纳米复合材料的太赫兹滤波器研究

为了克服高阻硅片过低的太赫兹透过率和激光阈值,通过放电等离子体烧结(SPS)工艺制备了一种新型纳米复合材料,可以作为透过太赫兹波、隔离飞秒激光的高效太赫兹滤波器件.器件整体设计原理主要基于瑞利散射,粒径100nm左右的纳米颗粒可以选择性地使太赫兹波高效透过,透过率最多达90%,远超高阻硅片50%的透过率,并且可以散射掉大部分波长为800nm的高能激光.器件由太赫兹频段吸收率很低的金刚石纳米颗粒和真空球磨得到的高阻硅颗粒组成,金刚石的高熔点提高了激光阈值,疏松多孔的结构进一步减少了太赫兹波段菲涅尔反射损失,器件整体性能优异.     

准周期光子晶体的传输特性

本文利用数值模拟和实验的方法研究了准晶光子晶体的传输特性和局域特性.能流和态密度的计算结果都表示十二重准晶光子晶体具有光子带隙.但是,和周期性的光子晶体不同,具有确定频率的电磁波局域在无缺陷的十二重准晶光子晶体中.理论分析表明,这种局域模是由准晶光子晶体结构中的无序性和自相似性相互竞争的结果.     

2022年太赫兹人工表面等离激元科技热点回眸

随着第六代通信技术（6G）、空间态势感知等系统对高通量、高带宽要求的进一步提高,太赫兹技术成为国际学术界和工业界的研究热点。2022年,太赫兹人工表面等离激元研究在国际上受到很大的关注,盘点了该领域的关键热点与新进展,包括基于太赫兹人工表面等离激元的无源器件、有源器件、传感器、通信系统以及生物医药应用等。人工表面等离激元对传输的电磁波具有亚波长的电场束缚能力和非线性色散特性,为太赫兹功能器件和系统应用的实现带来了新机遇。     

Fabrication of photonic crystals for the visible spectrum by holographic lithography

The term 'photonics' describes a technology whereby data transmission and processing occurs largely or entirely by means of photons. Photonic crystals are microstructured materials in which the dielectric constant is periodically modulated on a length scale comparable to the desired wavelength of operation. Multiple interference between waves scattered from each unit cell of the structure may open a 'photonic bandgap'--a range of frequencies, analogous to the electronic bandgap of a semiconductor, within which no propagating electromagnetic modes exist. Numerous device principles that exploit this property have been identified. Considerable progress has now been made in constructing two-dimensional structures using conventional lithography, but the fabrication of three-dimensional photonic crystal structures for the visible spectrum remains a considerable challenge. Here we describe a technique--three-dimensional holographic lithography--that is well suited to the production of three-dimensional structures with sub-micrometre periodicity. With this technique we have made microperiodic polymeric structures, and we have used these as templates to create complementary structures with higher refractive-index contrast.     

电磁超材料吸收器在太赫兹波段的研究进展

基于电磁超材料的太赫兹吸收器通过合理设计结构尺寸和材料参数能够实现近完美吸收,因而受到学术界的关注,近几年对太赫兹吸收器的研究发展很快.本文综述了基于电磁超材料的太赫兹吸收器的研究进展,分别从理论、结构和性能对太赫兹吸收器的研究进行了介绍,最后对太赫兹吸收器的未来发展和待解决的问题进行了探讨.     

探地雷达检测混凝土含水率试验研究

混凝土含水率对混凝土材料和结构性能有很大影响,但其无损检测技术不能满足实际需要.雷达电磁波的传播速度主要由材料介电常数决定,而影响混凝土材料介电常数主要是其含水率.本文对探地雷达检测混凝土含水率技术进行研究,采用干燥法得到混凝土试块含水率,利用探地雷达测得雷达波在混凝土板中的波速,得到了探地雷达波速和混凝土含水率的关系,发现探地雷达波速和混凝土含水率具有良好的线性关系.     

Research of the terahertz dual-band notch filter based on FSS structures

In this paper, a dual-band notch filter for two-layer frequency selective surface （FSS） at terahertz （THz） frequency with high fil- tering performance has been realized on high-resistivity silicon substrates. With periodic metallic resonators patterned on the sili- con wafer, the designed filter can provide two tunable resonant frequencies for terahertz application. The transmission response was improved by introducing an extra surrounding pattern around the T-shaped structure, and the location of transmission drop was tuned independently with geometric parameters. Simulated by finite-integral time-domain method, the filter is designed to operate between 0.2 and 0.6 THz with dual-band band-stop performance, a salient feature of this design is making the low sensi- tivity of its frequency response to the incident angles, which allows to place the filter close to the radiation source with spherical wave fronts. The proposed structures were fabricated using photolithography and tested by THz time-domain spectroscopy system Experimental results show that the transmission response has more than 12 and 32 dB rejections near 285 and 460 GHz respectively, which is in good agreement with the simulation result.     

Low frequency dispersion law for two-dimensional metallic photonic crystals

Using the rigorous multiple-scattering theory, we study the dispersion relation of electromagnetic （EM） waves in two dimensional dielectric photonic crystals （PCs） and metallic photonic crystals （MPCs） in the low-frequency limit. Analytic formula for the effective velocity of EM waves in PCs and MPCs is obtained. Accuracy of our formula is checked by comparing the results with rigorous calculations. For PCs, our result is exactly the same as the coherent potential approximation （CPA）, which is accurate even when the filling fraction is high. But for MPCs, our approach demonstrates special advantages, while the CPA theory fails, in predicting the effective velocity of EM waves in MPCs at low frequency.     

利用光子晶体的禁带特性实现无源电磁屏蔽

为了实现一维二元光子晶体的全方位禁带,利用传输矩阵法,对于不发生Brewester效应的一维光子晶体的禁带结构特点进行了研究,获得了TE波和TM波的反射率随频率和入射角的变化关系图,分析了TE波和TM波光子禁带特征.根据全方位禁带特性,提出了一种新的光子晶体的无源电磁屏蔽设计,并指出了在给定屏蔽频段范围内,两种介质光学厚度的选取范围.数值计算表明了只要TM波满足屏蔽条件就能实现电磁屏蔽.     

可重构的硅基等离子体通道的辐射性能研究

表面PIN二极管导通时可以形成固态硅基等离子体通道,这种通道具有类金属性并能够传递电磁波.当由上述通道单元耦合形成特定的结构时,它将对外辐射电磁波信号.本文简要阐述了此种通道的形成机理,通过软件设计并导通表面PIN二极管阵列上不同单元,构造形成单极、双频、八木天线等结构.期望通过以上不同结构实现对硅基等离子体通道辐射性能的研究.仿真结果表明,利用动态调控表面PIN二极管阵列的方法,硅基等离子体通道能够实现对电磁波的辐射,并能改变辐射频率、多频段的调节及辐射方向图的动态可重构等.因此,硅基等离子体阵列天线具有可重构、智能化、隐身等诸多优点.这些系统的理论研究进一步促进了人们对硅基固体等离子通道的理解,为此类天线的设计和加工提供理论指导.     

光子晶体及其应用研究

对光子晶体的性质和应用,如光局域化或光子晶体波导,甚至于是沿着一个很尖锐的弯曲的光子晶体波导能力,以及光子晶体激光器,进行了讨论.在这一技术领域,有许多基础方面的特点被认为是正确的,但却没有给出严格的证明.这是由于下列两方面的原因,第一是这个新领域发展的非常迅速,第二是由于在光子晶体中分析电磁波是很困难的,除了使用计算机去得到定量结果外,没有别的选择.板型的光子晶体(带有一个周期性空洞系统的高折射率板片),对高集成的光电路器件来说,也许是最佳结构.     

埋藏导体表面电磁波散射特性研究

根据几何绕射理论,利用时域有限差分方法研究了导体球表面电磁波的散射和绕射,分析了导体表面爬行波的特点,并计算了埋藏在沙土中的不同电导率金属球表面电磁波的散射特征。计算及图像分析结果表明,在介质外接收到的电磁波是多次反射波的叠加;利用散射电磁波峰值之间的关系,可以预测埋藏金属物的深度。     

基于超材料的太赫兹角度滤波器研究

提出了一种基于超材料的太赫兹低通角度滤波器,该角度滤波器是一种仅允许法向入射太赫兹波透过而将其他方向传播太赫兹波滤除的器件,其结构为螺旋的左右对称开口的金属双环.仿真结果表明,在0.94 THz频率处,该器件的透射效果随着入射角的增大明显降低,且对法向入射的透射率达到94.4％,3 dB角域带宽达到25.0°.所提出的太赫兹角度滤波器在角度波谱分析、雷达数据处理、隐私保护、高信噪比检测器等领域具有重要的应用前景.     

电磁带隙结构滤波特性

电磁带隙(EBG)结构是一种周期性结构,存在明显的禁带效应.为了解其特性,研究了二维平面电磁带隙结构,该装置采用在接地金属板上光刻出阵列小孔的方法制作.在对EBG结构进行仿真和计算时,利用了完全匹配层(PML)吸收边界条件的时域有限差分法(FDTD).设计的程序采用C 和Matlab语言混合编制,既简化了程序又保持了C语言速度快的特点.最后通过大量实验和研究,提出了一种新型EBG结构,在此基础上设计出宽阻带并具有双频段带隙特性的滤波电路.     

多孔氧化铝膜色彩特性研究进展

 介绍了利用阳极氧化法制备的氧化铝膜板（AAM）的色彩特性。利用阳极氧化法制备的AAM,其色彩分布于整个可见光区,不同的色彩主要来源于光的干涉现象。AAM 的这种特性可广泛应用于染色、彩色显示、装饰装潢、防伪、纺织工业等。人工制备AAM 彩色膜板得到研究人员的广泛关注,其制备方法包括：AAM 多层膜结构、金属覆盖AAM 结构、碳纳米管复合AAM 结构、沉积纳米线的AAM 结构等。从周期性氧化电压法制备周期性多层结构AAM 光子晶体开始,按照改善AAM 色彩饱和度方法的不同分为5 个部分,综述了近年来对AAM 色彩特性的研究进展。     

一种电波折射订正方法及其在高空风探测中的应用

为提高无线电测风的精度,在根据二维射线追踪法的基础上,建立了适用于球面分层大气的电波折射高精度在线订正方法,并对电波折射误差及高空风探测误差进行了模拟计算和分析.结果表明,电波折射产生的仰角、斜距和高度误差通常为正值,3类误差均随仰角减小和斜距增大而增大;在低仰角和大斜距的条件下,电波折射误差大于定位设备误差,当仰角低...     

溶胶-凝胶法制备超细三氧化铝粉末工艺条件研究

采用溶胶-凝胶(sol-gel)法制备超细高纯A12O3粉末,通过考察pH值、以及煅烧温度对制备超细粉末的粒度和性态的影响,进一步确定了制备氧化铝超细粒子的较佳工艺条件.