基于新型对偶复合左右手传输线的高性能带阻滤波器设计

 利用交指螺旋线结构和枝节贴片设计了一种新型对偶复合左右手传输线结构.采用电磁全波仿真软件和Bloch-Floquet 理论对其进行研究,计算并提取了其色散曲线,研究结果表明该对偶复合左右手传输线结构具有良好的带阻特性,并且阻带内2个传输零点独立可控．在此基础上采用2个单元结构级联的方式设计了一款具有小型化特性的性能优越的带阻滤波器,进行实物加工并使用适量网络分析仪测试,测量结果与仿真结果吻合较好,表明所设计的带阻滤波器中心频率为3.56 GHz,阻带带宽为39.3%,阻带矩形度为0.85,通带带宽为4.47~8.42 GHz,整体性能优越．此外所设计的带阻滤波器整体尺寸为0.237λ×0.145λ（λ为中心频率在自由空间波长）,小型化优势明显．     

小型化频率选择表面研究现状及其应用进展

频率选择表面是一种在平面内排布的二维周期阵列,由金属贴片单元或孔径单元构成,其对不同频率电磁波呈现不同的滤波响应,被广泛应用于雷达隐身、卫星通讯和电磁兼容等领域。随着应用对技术的要求不断提高,传统频率选择表面难以满足实际应用。原因有:(1)传统频率选择表面较大的单元尺寸会导致单元谐振时栅瓣过早出现,对传输特性产生不良影响;(2)传统频率选择表面较大的单元尺寸导致其很难在有限空间的区域内以及不规则天线罩上使用,且大尺寸使得现有工艺很难完成贴装布阵。而单元尺寸远小于工作波长的小型化频率选择表面MEFSS的出现为解决上述问题提供了新的思路,其优势日益凸显了自身的价值,逐渐发展成为新的研究方向。最初的小型化频率选择表面通过结构上的交叉、旋绕、连接等模式来达到缩小单元尺寸的目的,最典型的方法就是单元的卷曲、交指设计。为了突破"单元尺寸与谐振波长一致"这一限制,实现小尺寸结构可以控制长波长谐振,通过金属贴片和网格经介质级联,产生了基于容性表面与感性表面耦合技术的小型化频率选择表面。该频率选择表面通过减小单元的有效电尺寸来实现小型化。耦合型双屏小型化频率选择表面主要分为:网栅及其互补结构、网栅和方环贴片阵列结构、方环贴片及其互补结构。这三种典型的耦合双屏结构是研究复杂耦合型小型化频率选择表面结构的基础。由于前两类频率选择表面在实现小型化特性时都无法摆脱周期单元尺寸的制约,若需要更高的小型化需求时则难以实现。而加载无源集总元件(电容器、电感器)的频率选择表面可以增大等效电感L以及等效电容C的值,能够更大程度地缩小单元的有效电尺寸,使得频率选择表面小型化程度更高。为了拓展小型化频率选择表面的功能,在普通小型化频率选择表面单元或介质衬底上加入有源器件(变容二极管和PIN二极管等)或采用特征媒质作为介质衬底等组成有源小型化频率选择表面。该频率选择表面在实现小型化特性的同时,通过对有源器件的调节来控制该频率选择表面的通带开关和变频特性等。本文从单元卷曲和交指设计、基于容性表面与感性表面耦合技术设计、加载无源/有源集总元件技术设计等方面综述了小型化频率选择表面的研究状况。随后,对小型化频率选择表面在实际中的应用进行了介绍并对其未来发展方向进行了展望。     

频率选择表面的研究与应用现状

主要介绍了频率选择表面在雷达罩、空间电磁滤波器等领域的应用以及频率选择表面级联结构设计和多频FSS设计的研究进展和现状,阐述了为满足实际应用和技术支持的需要,FSS结构设计在小型化和可调性方面的最新进展,FSS结构设计与加工还存在较大的发展空间.     

十字型电阻贴片频率选择表面吸收体吸波性能研究

本工作用有限元法对十字型电阻贴片频率选择表面(FSS)吸收体的吸波性能进行了研究,结果表明:改变十字型电阻贴片FSS的周期排列方式、周期尺寸、FSS单元的尺寸、FSS的方阻、介质层厚度均可对其吸收峰的位置、峰值以及带宽进行调节,并且调节范围较大,计算结果与实验结果基本吻合.研究表明这种结构具有传统Salisbury吸收体所不具有的优势.     

Investigation of self-assembly growth and thermal stability of Au nano-particles on atomic-layer-deposited Al2O3 film

在原子层淀积的Al₂O₃薄膜表面自组装生长Au纳米颗粒,研究了Au纳米颗粒的自组装过程和热稳定性. 结果表明,原子层淀积的Al₂O₃薄膜表面很容易吸附氨丙基三甲基硅烷(APTMS), 有利于Au纳米颗粒的自组装, 生长出的Au纳米颗粒尺寸为5--8 nm, 密度约为4×10¹¹cm^-2. 在300℃氮气中退火使Au纳米颗粒的尺寸增大, 但是没有改变APTMS的吸附状态和Au的化学组成. 当退火温度提高到450℃时, Au纳米颗粒发生明显的团聚, 且分布变得极不均匀.     

PIMNT单晶弯曲圆盘换能器设计

新型弛豫铁电单晶材料铌铟酸铅-铌镁酸铅-钛酸铅晶体(Pb(In_1/2Nb_1/2) O₃-Pb(Mg_1/3Nb_2/3) O₃-PbTiO₃, PIMNT)的压电系数是陶瓷材料的 6 倍以上,应变量高出压电陶瓷 10 倍以上,具有较高的机电耦合系数,压电性能优于传统 PZT 材料。文章将单晶材料应用于带空气腔的弯曲圆盘换能器中,利用 ANSYS 仿真软件优化换能器结构,确定换能器尺寸,设计制作 PIMNT 压电单晶换能器和PZT4压电陶瓷换能器,并进行了水池实验。换能器实测结果与仿真结果保持一致,单晶换能器的谐振频率为 2.85 kHz,最大发送电压响应为 136.3 dB。结果表明,相比于同尺寸的陶瓷换能器,将 PIMNT 压电单晶应用于弯曲圆盘换能器可降低谐振频率,提高发送电压响应,提升换能器的工作性能,为进一步改善单晶换能器综合性能提供参考。     

新型陶瓷基复合超疏水涂层的制备及其性能

为了研究开发新型超疏水涂层的制备方法,改善涂层的结构与性能,以Al₂O₃-40%TiO₂(AT40)、PFA(全氟烷氧基乙烯基醚共聚物)粉末为原始材料,采用大气等离子喷涂(APS)技术,并调整电流、氩气流量等喷涂参数,在铝合金基体表面制备了两种不同的AT40/PFA复合超疏水涂层。利用相对应的测试仪器及分析手段对喷涂态涂层的相组成、显微结构、摩擦系数及基本性能等进行了表征分析。结果表明,两种涂层的相组成均为C₂₀F₄₂、Al₂TiO₅及少量的γ-Al₂O₃、α-Al₂O₃相;涂层表面均为圆形和椭圆形的粒状突起结构,其中突起结构的表面均存在类似荷叶表面结构的二元微纳米乳突结构,其表面粗糙度为9.3 μm和12.41 μm;所得涂层具有良好的综合性能,与水的静态接触角均达到了150°以上,滚动角为4~5°;在其他参数不变的情况下,随着电流的增大及氩气流量的减小,涂层中的陶瓷相含量增加,涂层的粗糙度、摩擦系数、显微硬度及结合强度均增大。     

双金属AunCu0- (n=1~9) 团簇结构、稳定性、电子及光学性能研究

为了探究铜掺杂金团簇的结构及特性,依据密度泛函理论对Au_nCu^{0/-(n=1~9)团簇的结构、稳定性、电子及光学性能进行了系统分析。基于卡利普索结构预测程序,在B3LYP/Lanl2dz水平下优化得到了不同尺寸的基态结构。研究表明,除Au₇Cu和Au₈Cu-呈现三维结构外,其它尺寸下的基态均呈现二维平面结构。而且,Au_nCu0/-的基态可通过在Aun-1Cu0/-}基态基础上添加一个Au原子得到。稳定性分析确定了Au₅Cu和Au₂Cu-团簇在各自体系中拥有相对强的稳定性。磁性分析发现,闭壳层电子结构体系的总自旋磁矩为零;开壳层电子结构体系分别具有1 μB的总磁矩。分析极化率表明,Au₉Cu和Au₉Cu-团簇对外场的各向异性响应最强,AuCu和Au₃Cu-团簇对外场的各向异性响应最弱。AdNDP分析发现,众多σ键连通了整个分子骨架,促进了整个团簇的稳定。基于Multiwfn程序,拟合的光电子能谱、红外谱、拉曼谱和紫外可见光谱可为实验上鉴别Au_nCu^0/-团簇的结构提供帮助。     

基于“双法多程式”的悬架橡胶衬套力学性能估算与试验验证简

 为估算验证橡胶衬套的力学性能,以促进衬套对车辆性能影响研究工作的有效开展,将轿车麦弗逊悬架的衬套作为研究对象,先推导相关应变能密度函数方程,再采用Yeoh,Van der Waals,Ogden (N=3)方程为主的多种本构模型,对衬套NR55橡胶进行材料力学性能估算并与其基础试验结果作对比验证,确定Ogden (N=3)方程为衬套结构力学性能估算的较优本构模型.设定多材料系数μ₁,μ₂,μ₃,α₁,α₂,α₃为优化变量并赋初值,初步估算衬套结构力学性能并分析与结构试验结果的一致性,优化目标是“面积重合”和“位移相等”的四类函数,选择自适应响应面法,经过10次迭代,识别出一组能较好估算衬套结构力学性能的本构模型方程系数值.利用最后一次估算值,求解拟合出新曲线,与基础试验估算拟合曲线、结构试验本身刚度曲线进行比较后发现,径(轴)向的刚度值误差均在9.1%以内,考虑各种因素,工程上属可接受范围,说明所述方法可行,能被推广。     

浮动凹弧底推杆-盘形凸轮组合机构的运动保真性研究

 浮动凹弧底推杆-盘形凸轮组合机构的Ⅰ类综合问题即是其综合理论的重要内容,又是其工程推广应用的重要准备.然而,机构的Ⅰ类综合问题是一个十分复杂的问题,难以一次性解决.“运动保真条件”是Ⅰ类综合问题必须首先保证的重要前提性条件.将“支撑函数法”应用于浮动凹弧底推杆-盘形凸轮组合机构,成功解决了预设凸轮轴心O₁（x_O1,y_O1）条件下,凸轮曲率半径的通用公式和“运动保真条件”.在为未来解决该类机构Ⅰ类综合问题奠定重要前提基础同时,还将“支撑函数法”推广拓展为适用于新型组合机构的一种通用有效方法.     

Effect of crystallite size and calcination temperature on the thermal stability of single nanocrystalline chromium oxide: expressed by novel correlation

   The thermal reaction of chromium acetylacetonate in various organic solvents at 300 °C for 2 h yielded an amorphous product. Single nanocrystalline chromium oxide was obtained after being calcined at 300 °C for 1 h. The crystallite size of product is in the range of 16–26 nm. In this work, the thermal stability of product was given by BET/BET₀. It was found that the crystals of large crystallite size show higher thermal stability than the crystals of small crystallite size. Thermal stability of chromium oxide can be presented by the correlation of the BET surface area after calcination, crystallite size of as-synthesized product and calcination temperature (500–900 °C) as shown below.

Effect of photoelectrode morphology of single-crystalline anatase nanorods on the performance of dye-sensitized solar cells

TiO₂ terpineol-based pastes with nanorods (NRs) of over 25 μm thickness have been prepared for the photoactive electrodes of the dye-sensitized solar cells (DSSCs). The NRs, with a length of approximately 80 nm and an aspect ratio of about 3, are made by a two-step hydrothermal process. They have the single crystalline anatase structure and can be dispersed well in water and ethanol. With a high thermal stability and larger surface area (47.2 m² g^− 1) than commercial TiO₂ particles (P25, 39.1 m² g^− 1), the well-dispersed anatase NR films with aggregate-free morphology are transparent. For the photocurrent-voltage measurements, the NR cell exhibits high short-circuit photocurrent (J_SC) under 1 Sun AM 1.5 simulated sunlight due to the higher surface area and transmittance. The open-circuit voltage (V_OC) of NR films is not obviously reduced with incremental thickness, which results from the one-dimensional single crystalline structure of NR due to less surface defects. As compared with the P25 cell, DSSCs made with NRs have a higher fill factor (FF) because of the uniform void spaces. An enhancement of conversion efficiency from 4.88% for P25 to 5.67% for NR is achieved. The P25 particles are incorporated in NR films as light-scattering centers, while the R1P1 containing 50 wt.% of P25 has a high V_OC and FF as compared with P25, but the J_SC is still lower than that of the NR.     

Structural, microstructural and dielectric studies of tin-doped barium niobate perovskite

Monophasic oxides of the type Ba(Nb_1-x Sn _x ) O₃ (0 ≤ x ≤ 1) have been synthesized by solid-state reaction method. All these compounds are found to have tetragonal structure except x = 1. The cell parameters and their variation with composition x have been determined. The X-ray density is found to increase gradually with increase of dopant concentration. Tolerance factor and volume of unit cell was found to be almost constant for all the compositions. Scanning electron microscopy showed the presence of grains of approximately 1 μm in size. Dielectric measurements in the frequency range 100 Hz to 1 MHz and in the temperature range from − 100°C to 500°C has been carried out to determine the dielectric parameters. A strong frequency dependence of both dielectric constant (ɛ′) and dielectric loss (D) is observed in the frequency range 100 Hz to 100 kHz. At low frequency, the piling up of mobile charge carriers at the grain boundary produces interfacial polarization giving rise to high dielectric constant. Dielectric loss showed a typical behaviour in the temperature and frequency range studied.     

Face-centered cubic (Al1 − xCrx)2O3

We report the discovery of a face-centered cubic (Al_1−xCr_x)₂O₃ solid solution [0.60 < x < 0.70] in films grown onto Si substrates using reactive radio frequency magnetron sputtering from Al and Cr targets at 400 °C. The proposed structure is NaCl-like with 33% vacancies on the metal sites. The unit cell parameter is 4.04 Å as determined by X-ray diffraction. The films have a <100> preferred crystallographic orientation and exhibit hardness values up to 26 GPa and an elastic modulus of 220-235 GPa.     

Growth of strained La1 − xSrxCoO3 films and multilayers using layer-by-layer growth

Pulsed laser deposition was used in combination with real time reflection high energy electron diffraction to prepare layer-by-layer grown La_1 − xSr_xCoO₃ films on single terminated substrates. The films exhibit an epitaxially and completely strained film growth resulting in an atomic flat surface with terrace structure. The films were compared to similar layers grown by off-axis laser deposition under higher oxygen partial pressure. With decreasing oxygen pressure an increased unit cell volume and decreasing magnetic moment was observed. Furthermore, we exemplarily show the preparation of layer-by-layer grown LaCoO₃|SrTiO₃ multilayers.     

Rietveld refinement and switching properties of Cr substituted NiFe2O4 ferrites

A series of ferrite samples of the chemical formula NiCr_xFe_2 − xO₄ (x = 0.0 to x = 1.0) were prepared by a wet chemical co-precipitation method and annealed at 600 °C for 4 h. The prepared samples were shown to have the cubic spinel structure by applying the full pattern fitting of the Rietveld method using the Full Prof program. The unit cell dimension, discrepancy factor and interatomic distance have been determined. It was observed that the unit cell dimensions decrease with an increase in Cr³⁺ content x. The grain size of the synthesized powder has been determined from XRD data and strain graph. The grain size of all samples is in the range of 26 to 40 nm. The IR spectra show three absorption bands in the wave number range of 200 to 800 cm^− 1. All samples were studied for electrical switching. Current controlled negative resistance type switching was observed for all samples.     

Frequency-selective surfaces for GPS and DCS1800 mobile communication. 1. Quad-layer and single-layer FSS design

In the paper, frequency selective surfaces (FSS) composed of quad-layer FSS with staggered tuning are designed, to allow signals to pass through at the frequency range of the global positioning system (GPS) cum DCS1800 mobile communications operation, while rejecting signals at the higher frequencies. The FSS is analysed by visualising the transformation of the admittance locus on the Smith chart, on subsequent additions of material layers to the multilayer stack-up. In addition, a single-layer FSS with convoluted loop elements (with interelement spacing of 6.08 cm) is designed to yield a similar band-pass response at 1.575 GHz (wavelength lambda=19.05 cm). This relatively close spacing is achieved by convoluting the conventional 1lambda square-loop element at its four corners. The convoluted segment provides a short-circuit response when the segment length is lambda/4 long. This provides a reflection to the electromagnetic energy at the selected band-stop frequency range. The performance of the quad-layer and single-layer FSS are compared     

Zirconium and hafnium oxide interface with silicon: Computational study of stress and strain effects

Computations of the periodic double-interface MO₂/Si (M = Zr and Hf) systems using density functional theory (DFT) demonstrate that very thin epitaxial MO₂ layers at silicon (1 0 0) surface adopt anatase-like structure with six-coordinate M atoms, while tetragonal-like MO₂ structure with seven-coordinated M atoms has a lower stability (metastable). This results from a closer match between Si(1 0 0) surface unit cell and anatase-like ZrO₂ and HfO₂ leading to the overall stress reduction if MO₂ adopts the anatase-like structure on silicon. In agreement with the previous study of Gavartin et al. [Gavartin, Fonseca, Bersuker, Shluger, Microelectron. Eng. 80 (2005) 412–415] formation of oxygen vacancy at the interface is demonstrated to be lower than in bulk film. This result appears to be independent from the film or interface structure but originates from the energy balance between M–O, M–M, Si–O and M–Si bonds, as revealed by a simple molecular model.     

Structure, hardness and thermal stability of TiAlBN coatings grown by alternating deposition of TiAlN and BN

Hardness and thermal stability of TiAlBN coatings prepared by alternating deposition of TiAlN and BN with high rotation speed of substrate holder (∼7 rpm) have been investigated. The TiAlN and BN were deposited by reactive sputtering of Ti_0.5Al_0.5 and BN targets with N₂ and Ar reactive gases, respectively. Despite alternating deposition, the TiAlBN coating did not show layered structure due to high rotation speed of substrate holder. By TEM analysis, the TiAlBN coating was observed to be nanocomposite with grain less than 10 nm in size. Compared to TiAlN coating, the TiAlBN nanocomposite coating showed superior hardness. Furthermore, the hardness of the coating increased after the heat-treatment in N₂ atmosphere up to 800 °C. By comparison with TiAlN/BN nanoscale multilayered coating prepared by the same deposition method except the lower rotation speed of substrate holder (∼1 rpm), the hardness enhancement after annealing, ‘self-hardening’, of the TiAlBN nanocomposite coating is believed to be due to the sharpness in chemical composition at the interface between TiAlN and BN phase.