石墨烯/钡铁氧体复合材料的制备及微波吸收性能的综合实验设计

电磁波污染已经严重威胁到信息安全和人体的健康,微波吸收材料被认为是解决电磁波污染问题最可行的措施之一。通过水热法获取氧化石墨烯/钡铁氧体纳米复合物,利用X-射线衍射仪、扫描电子显微镜、振动样品磁强计和矢量网络分析仪等分析技术对所制备的材料进行了表征。结果显示,当复合材料的厚度为2 mm时,其有效带宽可达6.8 GHz,当频率在12.64 GHz时,反射损耗最小为-41.66 dB。通过此综合实验设计,从实验的角度对纳米复合材料吸波机理进行了研究,有助于提高学生的科研兴趣,启发学生创新思维。     

还原石墨烯与片状氧化镍复合材料的隐身性能

采用一锅法制备还原石墨烯与片状氧化镍复合材料。复合材料的结构形貌、晶型和电磁参数分别通过扫描电镜、透射电镜、X射线衍射仪以及HP8722ES型矢量网络分析仪进行表征、测试与分析。结果表明,还原石墨烯与片状氧化镍复合材料同纯还原石墨烯相比在低频段(2.0~6.6 GHz)有更佳的吸收宽度和微波吸收能力,还原石墨烯与氧化镍片复合材料的介电损耗显著增加。大尺寸氧化镍片与还原石墨烯紧密复合提高了材料的载流子迁移率,从而提高了材料的吸波特性。     

基于EMSIW的互补裂缝环多频带谐振天线设计

文中设计了一个谐振频率在17.1GHz、27.6GHz和30GHz的多频带天线.该天线加载在八分之一基片集成波导(EMSIW)上,在EMSIW进行金属银过孔并在表面金属薄片上蚀刻一个互补裂缝环.天线尺寸占传统基片集成波导(SIW)的12.5%.利用HFSS软件进行仿真,获得了它的回波损耗、驻波比及三维增益图等参数.在谐振频率为17.1GHz时,回波损耗小于-10dB的相对带宽达到了1.9%,增益最高达到了4.4dB;在谐振频率为27.6GHz处和30GHz处,回波损耗小于-10dB的两个有效频带出现了无缝衔接,使得总相对带宽达到了15.2%,最大增益可达7.68dB.     

X波段宽带极低噪声低温放大器

介绍了8～9GHz极低噪声低温放大器的研制。在≤15K的工作温度下,实测放大器的主要性能指标如下:等效噪声温度≤7.9K;增益>31dB,带内起伏≤1dB;输入反射损耗<-21dB;输出反射损耗<-23dB。它的研制成功,实现了深空探测、天文观测等X波段宽带低温接收机的核心器件国产化。     

方环结构的宽频可调超材料滤波器

采用微控制电路加载技术控制超材料的等效介电常数和等效磁导率在不同时间的空间分布形式,实现空间滤波器中心频率的可调.设计了一种方环缝隙结构超材料滤波器,单元结构尺寸为18.5mm×18.5mm,通过在单元结构上加载变容二极管实现X波段内的连续可调.当变容二极管电容值从0.15pF增大到0.70pF时,仿真结果表明滤波器的中心频率从11.8GHz逐渐减小到10.5GHz,工作带宽为16.3%(10.2~12.0GHz),通带内的回波损耗最小值为22dB,插入损耗最大值为0.6dB.测试结果表明滤波器的中心频率从11.7GHz逐渐减小到10.3GHz,工作带宽为17.2%(10.1~12.0GHz),且通带内的回波损耗最小值为25dB,插入损耗最大值为0.5dB.     

基于H型谐振器的Ku波段高温超导滤波器设计

高温超导滤波器已在移动通信、射电天文、雷达探测等多个领域获得了重要应用.当前高温超导滤波器的研究和应用主要集中于10GHz以下的频段,针对超高频段(>10GHz)高温超导滤波器的研究很少.本文设计优化了具有无载Q值高、耦合强、尺寸短等特点的H型阶跃阻抗谐振器,并讨论了超高频段滤波器端口激发源的电容效应对滤波器响应的影响,最后采用优化的H型谐振器,应用去嵌入(De-Embed)设计方法消除端口效应,设计了中心频率为16GHz,相对带宽12.5%的6节高温超导滤波器.研制的超导滤波器在未经调谐的情况下,测试结果与仿真结果符合得很好,插入损耗小于0.3dB,反射损耗优于-14dB,带外抑制达到了-70dB.     

一种T形高功率微波功率合成器

提出了一种新型功率合成器,其工作原理为:通过在两个相互垂直的过模矩形波导中放置两组相互垂直的金属插板,对具有不同极化方向的矩形波导TE10模进行隔离传输,实现高功率微波的双路通道功率合成。基于这一原理初步设计了一个中心频率为9.55 GHz的功率合成器,并进行了数值模拟。模拟结果表明:这种功率合成器可以承受高功率,单通道工作时的功率容量分别大于7.31 GW和6.83 GW,中心频率上两个通道的单模功率传输效率分别达到了98%和99%,反射损耗分别小于-36 dB和-21 dB,通道之间的耦合损耗分别小于-30 dB和-45 dB。     

高温超导滤波器的低温调谐技术

本文给出了高温超导滤波器的一种低温机械调谐方法,通过调谐滤波器的电场来达到优化性能的目的.此方法可以很好的改善滤波器的性能和提高产品的合格率,使基片厚度的不均匀性以及介电常数的误差对高温超导滤波器性能的影响降到最低,从而最大程度地使测试结果和计算机仿真结果相一致.文中以一个4节的高温超导微带滤波器为例,叙述了该方法的实现过程.其带宽为15MHz,中心频率为2.868GHz,带内插损为-0.04dB,反射损耗为-21dB.文中给出了带外抑制,带内特性等的调谐结果.制备完成的超导滤波器在调谐前的性能较设计结果有较大的偏差.主要表现在带内插入损耗、反射损耗特性和带外抑制的偏差.通过调谐,带内特性和带外抑制有明显的改善.带内插入损耗由调谐前的-0.44dB改善到-0.21dB;反射损耗由调谐前低端带边的-8.2dB改善到-14.27dB,但在高频端没有改善;带外抑制由实测的-28dB最大可以改善为-47dB.理论预测该调谐方法会使通带中心频率向低频端移动,我们也观察到了该现象,中心频率向低频端最大偏移了大约3.1MHz.综合各项参数,调谐后,整体性能更接近设计结果.     

基于高阻抗表面的多频带Salisbury屏设计

为进一步提高传统Salisbury屏的吸波性能, 本文提出了利用高阻抗表面在特定频率同相反射的特性, 替代原有结构中的金属平板设计多频带Salisbury屏的方法. 通过分析不同频率电磁波经高阻抗表面反射后空间电磁场的场强分布, 说明可以通过共用Salisbury屏的损耗层, 在高阻抗表面同相反射的特征频率附近引入新的吸收带. 以不同尺寸方形周期结构的单频和双频高阻抗表面为例, 从仿真和实验两个方面验证了多频带Salisbury屏设计的可行性, 且实验和仿真结果十分符合. 结果表明, 多频带Salisbury屏基本保留了原有的吸波性能, 同时又引入了新的吸收峰, 吸收峰的位置和数量与高阻抗表面同相反射的频带位置和数目有关. 与传统的Salisbury屏相比, 在材料增加厚度不足1 mm 的情况下, 多频带Salisbury屏的设计使反射率小于-10 dB的吸波带宽由8.5 GHz增加到10.1 GHz, 且实现了向长波方向的拓展, 最低频率由7.5 GHz拓展到5.98 GHz.     

140 GHz带状注弯折波导SU-8工艺与传输特性(英)

对140 GHz 带状注弯折波导的色散特性和耦合阻抗进行了仿真。CST微波工作室的仿真表明该波导在140 GHz时,波导内电磁波的轴向相速度为0.227c,且140 GHz频率附近色散特性平坦。波导的耦合阻抗在140 GHz时为5 左右。CST粒子工作室注波互作用的仿真结果表明该弯折波导在140 GHz处的功率增益为24.6 dB。该弯折波导带状电子注的设计保证了该波导的加工工艺与MEMS微加工工艺兼容。通过SU-8 UV-LIGA工艺实现了对该波导的微型加工。测试结果表明该波导的反射损耗S11与插入损耗S21分别为-28 dB和-1.2 dB。实测的输出功率增益达到23 dB。测试结果和仿真结果的一致性表明该弯折波导设计的合理性,同时也验证了多步SU-8 UV-LIGA工艺可以实现对该波导的高精度加工。     

Development of Novel Graphene/g‐C3N4 Composite with Broad‐Frequency and Light‐Weight Features

In this study, a novel graphene/g‐C₃N₄ microwave absorber is developed to solve the electromagnetic wave interference problem. Graphene/g‐C₃N₄ composite is synthesized by loading g‐C₃N₄ nanosheets on graphene through a simple liquid‐phase approach. High‐performance electromagnetic absorption performance can be achieved. The optimal reflection loss value is up to ?29.6 dB under a thin coating layer of 1.5 mm. At the same time, the corresponding absorption bandwidth of this composite can reach 5.2 GHz (12.8–18 GHz). Excellent electromagnetic absorption property may be attributed to the current attenuation theory which has been proven by replacing graphene with porous graphene or graphene oxide. The results reveal that free electron numbers and loading mass of g‐C₃N₄ on graphene play the key roles in the intensity of current attenuation and resistance value.     

Surface modification of M-Ba-ferrite powders by polyaniline: Towards improving microwave electromagnetic response

A composite of polyaniline (PANI)-coated M-type hexagonal barium ferrite (M-Ba-ferrite) powder was prepared by an in situ polymerization of an aniline monomer in the presence of M-Ba-ferrite particles. The obtained composite was characterized by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The structure and microwave response properties were investigated. The continuous coverage of polyaniline has been produced on the platelet M-Ba-ferrite particle surface, and a core–shell structure has been formed. The results show that the coverage of polyaniline has a great influence on microwave response of M-Ba-ferrite particles. A polyaniline thin layer formed on the surface of a barium ferrite particle changes the character of frequency dispersion of microwave absorption. The results indicate the existence of an interaction at the interface of polyaniline macromolecule and barium ferrite particle, which influences the physical and chemical properties of the composite. The interaction and interfacial polarization are seen as important factors contributing to the influence on microwave response of the PANI-coated ferrite composite powders.     

Microwave absorption properties of composite powders with low density

The composites of barium ferrite coated on hollow ceramic microspheres were prepared using sol-gel technique. The crystal structure, morphology and microwave absorption properties of composite powders with different weight ratio of microspheres were studied with XRD, EDS, FESEM and vector network analyzer. The results show that the microwave absorption properties of composite powders are greatly improved. The maximum microwave loss of composite powders reaches 31 dB with an amount of 50 wt.% microspheres, and its density is only about 1.80 g/cm³. The effect of hollow ceramic microspheres on the microwave absorption property is also discussed.     

Synergistic effect of polypyrrole/BST/RGO/Fe3O4 composite for enhanced microwave absorption and EMI shielding in X-Band

Present study focus on the designing of high performance microwave absorbing material against electromagnetic pollution. Herein we synthesize conducting polymer based composite encapsulated with Barium strontium titanate (BST), reduced graphene oxide (RGO), and Fe₃O₄ nanoparticles via chemical oxidative polymerization of pyrrole. The synthesized composite materials were thoroughly characterized using SEM, FTIR, XRD, TGA, and VSM techniques. The presence of filler materials in conducting polymer matrix leads to absorption dominated shielding effectiveness value of 48 dB in the frequency range of 8.2–12.4 GHz (X-band). Moreover, presence of dielectric and magnetic fillers increases the thermal and chemical stability of the composite material. The obtained shielding effectiveness value is above the recommended limit (30–40 dB) required for the commercial applications, therefore these composite material could be used as effective shield against EM pollution.     

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles

A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy(TEM) and Fourier transform infrared spectroscopy(FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/ GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss(RL) of GO/PANI/GAunano with a thickness of 2 mm is up to-24.61 d B at 15.45 GHz, and the bandwidth corresponding to RL at-10 d B can reach 4.08 GHz(from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.     

碳纳米管/聚苯胺纳米复合管的制备及其微波介电特性研究

用原位乳液聚合法在碳纳米管表面包覆聚苯胺，制备出了碳纳米管/聚苯胺一维纳米复合管.复合管的直径为50—80 nm，聚苯胺包覆层的厚度为20—30 nm，聚苯胺在碳纳米管表面以层状和枝晶状两种形态生长.研究了碳纳米管/聚苯胺复合管在2—18 GHz的微波介电特性.与纯碳纳米管相比，碳纳米管/聚苯胺复合管的介电常数的实部ε′和虚部ε″在2—18 GHz随频率变化较小，在低频波段介电常数值较小，作为微波吸收剂容易实现与自由空间的阻抗匹配，而且它的介电损耗角正切(tanδ=ε″/ε′)较高，是一种很好的微波吸收剂. 关键词： 碳纳米管 聚苯胺 微波介电特性 微波吸收剂     

Synthesis, infrared and microwave absorbing properties of (BaFe12O19+BaTiO3)/polyaniline composite

The (BaFe₁₂O₁₉+BaTiO₃)/polyaniline composite was synthesized by in situ polymerization and introduced into epoxy resin and polyethylene to be a microwave and infrared absorber. The spectroscopic characterizations of the formation processes of (BaFe₁₂O₁₉+BaTiO₃)/polyaniline composite were examined using Fourier transform infrared, ultraviolet-visible spectrophotometer, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron spin resonance. Microwave absorbing properties were investigated by measuring reflection loss in 2-18 and 18-40 GHz microwave frequency range using the free space method. Thermal extinction measurements in the 3-5 and 8-12 μm were done to evaluate the shielding effectivity of infrared. The results showed that a significant absorption frequency range shifting and thermal extinction could be obtained by adding polyaniline to the BaFe₁₂O₁₉+BaTiO₃ blend.     

Enhanced gas sensing performance of polyaniline incorporated with graphene: A first-principles study

Conducting polymers such as polyaniline (PANI) are potential sensing materials for ammonia due to their fast response and low cost, however, the corresponding sensing mechanism needs to be studied further. In this paper, molecular dynamic and first-principles simulations are carried out to investigate ammonia sensing mechanisms of polyaniline/graphene heterostructure. The adsorption of ammonia at different locations of pure polyaniline and graphene/PANI composites is analyzed. The band gap for graphene/PANI system shows more significant change after adsorption than that of pure polyaniline, which indicates higher sensitivity for detecting ammonia, and the results of sorption isotherm imply that graphene/PANI system exhibits more adsorption capacity for ammonia. Moreover, diffusion coefficient of ammonia in polyaniline/graphene system is much large than that of pure polyaniline, demonstrating that gas diffusion occurs more easily in the heterostructure. The results are verified by experimental data, and the proposed computational frame can be used to evaluate and design nanocomposite materials for gas sensor.     

双层螺旋环超表面复合吸波体等效电路模型及微波损耗机制

针对超材料吸波频带窄的问题,采用金属螺旋环超表面与碳纤维吸波材料相复合的方式,设计了宽频高性能复合吸波体.研究发现,在碳纤维吸波材料中引入双层螺旋环超表面能显著增强吸收峰值和吸波带宽,且适当增加螺旋环初始线长和吸收层厚度有利于提高复合吸波体的吸波性能, 9.2—18.0 GHz频段的反射损耗均优于–10 dB (带宽达8.8 GHz),吸收峰值达–14.4 dB.利用S参数计算得到螺旋环-碳纤维复合吸波体的等效电磁参数和特征阻抗呈现多频点谐振特性,通过构建双层螺旋环超表面等效电路模型,定量计算了复合吸波体的电磁谐振频点,发现由等效电路模型获得的谐振频点计算值与仿真值基本相符,说明该复合吸波体多频点电磁谐振是宽频电磁损耗的主要机制.