碳基纳米吸波材料制备的研究进展

为探索民用电磁屏蔽和军用隐形碳基高性能吸波材料的制备,研究了碳纳米管和磁性金属复合,碳纳〖JP2〗米管和铁氧体复合,碳纳米管/聚合物复合,碳、石墨基复合等碳基吸波材料的不同复合和制备方法,比较了其反射损耗等不同的特点、影响因素和性能特点及其相关应用。结果表明,多元复合、低维化、工艺优化是其制备的有效途径。     

Structural, Magnetic, and Microwave Properties of SrFe12−x (Ni0.5Co0.5Sn) x/2O19 Particles Synthesized by Sol–Gel Combustion Method

This study is intended to evaluate the structural, magnetic, and microwave properties of Ni-Co-Sn-doped strontium hexaferrite SrFe_12?x (Ni_0.5Co_0.5Sn) _x/2 O₁₉ particles with x = 0 to 2.5 synthesized by a sol–gel combustion method. These particles were evaluated to characterize the structural, magnetic, and reflection loss properties of prepared samples by use of x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared (FTIR) spectroscopy, vibrating-sample magnetometer (VSM), and vector network analyzer. The XRD results confirmed the presence of strontium ferrite phase with magnetoplumbite structure in all synthesized samples. The results of FTIR analysis indicated the formation of functional groups such as metal-oxygen (Sr-O and Fe-O) and carboxylic groups during the sol–gel process. In addition, FE-SEM micrographs indicated that submicron particles with different morphologies such as spherical, pyramidal, irregular, and hexagonal platelet shapes appeared in the structure. According to hysteresis loops, magnetization and coercivity decreased due to occupation of Ni-Co-Sn cations at low levels of substitutions. The microwave absorption characteristics of this ferrite were investigated in the 8 GHz to 12 GHz frequency range. The sample with 80 wt.% ferrite content showed a maximum reflection loss of ?29 dB at 9.6 GHz with 4 GHz bandwidth through the entire frequency range of 8 GHz to 12 GHz for absorber thickness of 1.5 mm. Based on microwave measurements of reflectivity, this material with the expressed chemical composition could be proposed as a good choice for electromagnetic compatibility and other practical applications such as microwave absorption at high frequencies.     

P-GN/Ni复合材料的制备及其微波吸收性能研究

本文采用一步溶剂热法成功制备了磷掺杂石墨烯/Ni纳米复合材料(P-GN/Ni),并系统研究了其微纳结构和微波吸收性能。透射电镜(TEM)结果显示Ni纳米颗粒呈海胆状,并均匀地负载在半透明褶皱的磷掺杂石墨烯(P-GN)上。相比单独的海胆状Ni纳米颗粒,P-GN/Ni纳米材料表现出优异的微波吸收能力。在厚度仅为1.5 mm时,复合材料在17.3 GHz下反射损耗值(RL)达到了-34.8 dB且有效吸收带宽(RL<-10 dB)为3.7 GHz。复合材料的厚度为1.5-5.0 mm时,其有效吸收带宽为14.9 GHz(3.1-18 GHz),覆盖S波段到X波段,在微波吸收领域具有潜在的应用价值。微波吸收机制研究表明P-GN的引入,一方面利用磁损材料与电损材料的协同效应优化了阻抗匹配,另一方面极大地增加了材料的电导率和界面极化能力,提高了复合材料对电磁波的衰减能力。     

Microstructure and microwave absorption properties of MWCNTs reinforced magnesium matrix composites fa- briccated by FSP

Multiwall carbon nanotubes (MWCNTs) reinforced magnesium matrix (MWCNTs/Mg) composites were successfully fabricated by friction stir processing (FSP). Microstructure and microwave-absorption properties of WCNTs/Mg composites are studied. The results show that with increasing the MWCNTs content to 7.1% in volume fraction, the agglomeration of MWCNTs is found in the WCNTs/Mg composites. The addition of MWCNTs has little effect on microwave-absorption properties. With increasing the frequency from 2 GHz to 18 GHz, the microwave absorption of the composites decreases. Compared with the absorption loss of the MWCNTs, the reflection loss of base material takes the most part of the loss of the microwave, and the increase of the reflection loss can promote electromagnetic shielding properties of the composites. Moreover, the electromagnetic shielding properties of the composites are less than ?85 dB in the lower frequency range from 0.1 MHz to 3 GHz. With increasing the content of MWCNTs, the electrical conductivity of the composites is decreased, and the electromagnetic shielding properties is slightly enhanced.     

Enhanced Microwave Absorption Performance from Magnetic Coupling of Magnetic Nanoparticles Suspended within Hierarchically Tubular Composite

The microwave absorption (MA) performance of carbon materials is severely hindered by their drawbacks of lacking magnetic loss ability and mismatched electromagnetic impedance. In this work, utilizing sustainable biomass kapok as a template, the hierarchically tubular C/Co nanoparticle composite is rationally constructed to acquire the enhanced MA performance for the first time. The fruit‐tree‐like hierarchical structure is composed from a “trunk” of kapok‐derived carbon microtubes, a “branch” of entangled carbon nanotubes, and “fruit” of Co nanoparticles embedded in the nanotubes. Such a hierarchically tubular structure offers the composite: i) a submillimeter‐scale 3D magnetic coupling network and reinforced magnetic loss ability, ii) a hierarchical dielectric carbon network, iii) better matched impedance, confirmed by the off‐axis electron holography and micromagnetic simulation. Accordingly, the as‐prepared hierarchically tubular carbon composite demonstrates impressive MA performance, with a maximum reflection loss of as much as ?52.3 dB and a broad absorption bandwidth of 5.1 GHz. These encouraging achievements light the way to the development of the hierarchical microstructure of magnetic absorbents.     

石墨烯/铜镍铁氧体复合材料的制备及性能研究

为制备出宽波段磁波衰减材料,采用水热法制备得到了石墨烯/铜镍铁氧体复合材料（CNFRGO）,并对其进行SEM、XRD、红外光谱和拉曼光谱表征分析;然后测量其2~18 GHz的电磁参数,并计算其损耗角正切值和反射损耗,进而分析其微波衰减性能;最后,测量其中远红外波段的复折射率,利用测量数据和T矩阵法计算分析其红外波段消光和吸收性能。结果表明,尖晶石型铜镍铁氧体纳米颗粒吸附在还原石墨烯上,粒径大部分约为20 nm;CNFRGO同时具有介电损耗和磁损耗两种机制,其反射损耗低于-10 dB的频宽为3.7 GHz,在11.8 GHz处有峰值-14.7 dB;CNFRGO在近红外波段消光较强主要由散射引起,中远红外波段则主要由吸收决定,而其吸收能力在近红外和中红外波段较强,但在远红外大气窗口内相对较弱。因此,CNFRGO可同时吸收微波和红外辐射,是一种良好的微波与红外兼容材料。     

石墨表面化学镀Ni-P非晶的制备与电磁性能

为了提高石墨吸收剂的阻抗匹配能力,改善其吸波性能,采用化学镀法对石墨表面进行镀Ni-P改性。研究了镀层的相组成、形貌、成分和样品的电磁吸波性能。结果表明:石墨表面包覆了一层非晶态Ni-P镀层;与原始石墨相比,在2GHz时,镀Ni-P非晶石墨复合材料的ε′和ε″分别明显降低至6.6和0.4,μ′和μ″分别略微增加至1.08和0.26,其吸收频带得到展宽,在14GHz的最小反射率为–7.0dB,反射率小于–5dB的吸收频带宽达4GHz。     

Electronic Materials Based on Co0.5Zn0.5Fe2O4/Pb(Zr0.52Ti0.48)O3 Nanocomposites

The reduction of the radar cross-sectional area achieved in stealth technology has been a major challenge since the Second World War, being accomplished by covering the metallic surfaces of aircraft, ships, tanks, etc. with radar-absorbing materials. Nowadays, the development of lightweight microwave-absorbing materials with reduced thickness has a greater impact due to their excellent microwave-absorbing properties. In this study, the microwave-absorbing properties of nanocomposites based on Zn-substituted cobalt ferrite and lead zirconium titanate have been investigated in the X-band (8.2 GHz to 12.4 GHz) region. Zn-substituted cobalt ferrite (CZF) and lead zirconium titanate (PZT) nanoparticles were prepared by the coprecipitation and homogeneous precipitation method, respectively. Nanocomposites were developed by dispersing these nanoparticles with different compositions into an epoxy resin matrix. All the composite materials showed more than 90% microwave absorption in the X-band region. The nanocomposite containing CZF/PZT (3:1) with 2 mm thickness displayed maximum return loss of ?47.87 dB at 12.23 GHz. The microwave absorbers based on epoxy resin polymeric matrix exhibited better absorbing properties when the dielectric contribution matched the magnetic contribution, and the loss mechanisms were mainly due to the dielectric loss.     

螺旋形碳纤维结构吸波材料的制备及性能研究

用基板法以乙炔为碳源,镍板为催化剂,PCI,为助催化剂,通过化学气相沉积制备了螺旋形碳纤维手性吸收剂,并研究了其在2～18GHz的微波电磁特性：具有较高的介电损耗,电磁参数随频率的增大有减小的趋势,有利于实现宽频吸波。以螺旋形碳纤维作为吸收剂制备了Nomex蜂窝夹芯结构吸波材料,复合材料的厚度为9．5mm时,在3．76～18GHz反射率R小于-10dB,反射率小于-10dB的频宽为14．24GHz;最大吸收峰在10．4GHz,反射率R为-21．62dB。探讨了螺旋形碳纤维的吸波机理,螺旋形碳纤维是一种非常有发展前景的手性吸收剂和吸波材料。     

镀镍中间相沥青基碳纤维的吸波性能

为了改善中间相沥青基碳纤维的磁性能和吸波性能,通过化学镀工艺在中间相沥青基碳纤维表面均匀包覆了金属镍,研究了镀镍中间相沥青基碳纤维的磁性能和微波吸收性能。以镀镍中间相沥青基碳纤维作为吸收剂,环氧树脂为基体制备了单层吸波涂层,涂层的厚度为1.02 mm时,吸波涂层在15.4~18 GHz反射率R小于-10 dB,最大吸收峰在18 GHz,反射率R为-20.74 dB。探讨了镀镍中间相沥青基碳纤维的吸收机理,在含镀镍中间相沥青基碳纤维的吸波涂层中,镀镍中间相沥青基碳纤维作为偶极子在电磁场的作用下,会产生耗散电流,在周围基体作用下,耗散电流被衰减,从而电磁波能量转换为其它形式的能量,主要为热能,这是镀镍中间相沥青基碳纤维偶极子吸波涂层的主要吸波机理。     

Structural,Magnetic, and Reflection Loss Characteristics of Ni/Co/Sn-Substituted Strontium Ferrite/Functionalized MWCNT Nanocomposites

Ni/Co/Sn-substituted strontium ferrite [SrFe_12?x (Ni_0.5Co_0.5Sn) _x/2O₁₉]/multiwalled carbon nanotube (MWCNT) nanocomposites were produced by assembling ferrite particles on the external surfaces of MWCNTs. Various techniques including x-ray diffraction (XRD) analysis, transmission electron microscopy, field-emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared (FTIR) spectroscopy were used to demonstrate the successful attachment of ferrite particles onto the external surfaces of the MWCNTs. XRD analysis and FTIR spectroscopy confirmed the presence of strontium ferrite and carbon nanotube phases in ferrite and nanocomposite samples, respectively. FE-SEM micrographs indicated the formation of ferrite particles on the outer surfaces of MWCNTs in nanocomposite samples. Furthermore, vibrating-sample magnetometer (VSM) and reflection loss (RL) measurements were performed to assess the magnetic and microwave characteristics of the synthesized samples. VSM loops confirmed a relatively strong dependence of the saturation magnetization and coercivity on the volume percentage of MWCNTs. With the introduction of MWCNTs or an increase in the substitution, the saturation magnetization and coercivity were decreased. The RL properties of the nanocomposites were investigated in the 8 GHz to 12 GHz frequency range. The sample with 80 wt.% nanocomposite content showed a maximum RL of ?35 dB at 8.3 GHz with a 4 GHz absorption bandwidth over the extended frequency range of 8 GHz to 12 GHz for absorber thickness of 1.8 mm. The RL evaluations indicated that these nanocomposites have high potential for application as wide-band electromagnetic wave absorbers at GHz frequencies.     

Linear and Non-Linear Inserts for Genuinely Wideband Continuous Frequency Tunable Coaxial Gyrotron Cavities

We consider two continuous frequency tunable CW coaxial gyrotron oscillators, one 330 GHz with 3 GHz bandwidth and output power 50 – 400 W for scientific applications and one 30 GHz with 0.4 GHz bandwidth and output power 40 – 140 kW for industrial applications. The continuous tuning of both gyrotrons is achieved by moving the linearly tapered inner conductor in the axial direction in combination with the proper adjustment of the operating magnetic field. We consider also a non-linear tapering, which makes it possible to reduce the length of the insert and to improve efficiency of the device.     

基于三维石墨烯的可拉伸太赫兹吸波材料

通过将三维石墨烯材料与聚二甲基硅氧烷薄膜相结合,设计并研制了一种宽带可拉伸的太赫兹波吸收材料,设计结构可以使三维石墨烯在聚二甲基硅氧烷层的保护下实现大幅度拉伸。实验结果表明,该吸波材料在0.2~1.1 THz的测试范围内有最高90%的吸收率,同时在20%的拉伸量下复合结构对太赫兹波吸收率基本保持不变,并且在去掉外力时材料样品的结构和性能均可恢复至原始状态。可拉伸太赫兹吸波材料具有带宽大、吸收率高、加工简单以及可大面积制备等优点,在太赫兹吸收器等领域中具有潜在的应用价值。     

Direct Growth of Edge‐Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High‐Performance Microwave Absorption

High‐performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave‐transmitting matrices is of paramount importance to bring it to real‐world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge‐rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si₃N₄ ceramics using only methyl alcohol (CH₃OH) as precursor is reported. The large O/C atomic ratio of CH₃OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si₃N₄ hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide‐based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.     

Ka Band Broadband Fourth Harmonic Image Rejection Mixer

This paper presents the design and implementation of Ka band broadband hybrid integrated image rejection mixer with a fourth harmonic mixer as unit mixer. Detailed design and analysis have been carried out. The mixer was fabricated by hybrid microwave integrated circuit (HMIC) process based on the thin film ceramic substrate which can reduce the cost compared to monolithic microwave integrated circuit (MMIC). The measured results showed conversion loss less than 11.2 dB and image rejection ratio (IRR) more than 20 dB in 4 GHz RF bandwidth. It can also play the role of up-converter from the test data.     

不同形状特征的碳基复合材料吸波性能分析

基于短切碳纤维、碳纳米纤维、石墨烯及炭黑,分析研究碳基复合材料中吸收剂形状比对电磁特性,尤其是吸波性能的影响。采用矢量网络分析仪测试基于不同形状比吸收剂形成碳基复合材料的电磁参数,并且计算出样品理论反射损耗。结果发现,随着频率的增加,碳基复合材料的介电常数逐渐减小;碳纳米纤维样品厚度为2 mm,在8 GHz时反射损耗达到-8 d B;炭黑与石墨烯质量比为1∶1时,在0. 5~12. 8 GHz频段内损耗角正切tanδ随频率的增大而增大且样品厚度为2mm时,其在12~16. 2 GHz反射损耗小于-10 d B,且在12. 8 GHz时反射损耗达到-22. 5 d B。通过对不同形状比吸收剂形成碳基复合材料的电磁参数分析,发现具有一定长径比或较大比表面积的吸收剂复合有利于提升碳基复合材料的吸波性能。     

二维材料调制的掺铥脉冲光纤激光器的研究进展

2μm波段掺铥脉冲光纤激光器由于在人眼安全、激光雷达、生命科学、光通信和医疗等领域有着重要的应用,近年来成为新型光纤激光器的研究热点。以石墨烯为代表的二维材料因其优良的可饱和吸收特性引起人们的广泛关注。分析了碳纳米管、石墨烯、黑鳞及拓扑材料等二维材料作为可饱和吸收体在掺铥脉冲激光器中的应用和发展。对国内外基于二维材料的掺铥脉冲光纤激光器的研究进展进行了综述,并对其未来的发展前景进行了展望。     

On artificial magnetodielectric loading for improving the impedance bandwidth properties of microstrip antennas

The effect of artificial magnetodielectric substrates on the impedance bandwidth properties of microstrip antennas is discussed. We review the results found in the literature and then focus on practically realizable artificial magnetic media operating in the microwave regime. Next, a realistic dispersive behavior of a practically realizable artificial substrate is embedded into the model. It is shown that frequency dispersion of the substrate plays a very important role in the impedance bandwidth characteristics of the loaded antenna. The impedance bandwidths of reduced size patch antennas loaded with dispersive magnetodielectric substrates and high-permittivity substrates are compared. It is shown that unlike substrates with dispersion-free permeability, practically realizable artificial substrates with dispersive magnetic permeability are not advantageous in antenna miniaturization. This conclusion is experimentally validated.     

激光诱导碳纳米管制备石墨烯纳米带及其电学性能分析

通过将纳米管解压缩可以很容易地生产石墨烯纳米带,因为碳纳米管结构可以被认为是卷起的石墨烯筒。这是一种特殊的2D石墨结构,具有出色的性能。应用领域广泛,包括晶体管、光学和微波通信设备、生物传感器、化学传感器、电子存储和处理设备以及纳米机电系统和复合材料。通过扫描电子显微镜（SEM）观察薄膜的形貌,通过拉曼光谱法表征石墨烯的性质,并通过半导体参数测量系统测量薄膜的电导率。拉曼光谱表明,通过优化工艺可以增强石墨烯的拉曼特性。碳纳米管制备石墨烯带的两个重要参数是激光能量密度和辐照时间。在这项研究中,通过准分子激光辐照碳纳米管薄膜来生产石墨烯纳米带。实验结果表明,在150 mJ的激光能量下,观察到连接时碳纳米管没有打开。在450 mJ的能量下,可以有效地破坏碳纳米管,并且使其部分地形成石墨烯带。此时,膜的电导率达到最大值。由于蓄热作用,在碳纳米管壁上出现大量的多孔结构。     

碳基气凝胶复合材料电磁波吸收材料研究进展

随着无线电通信技术和各种电子设备的广泛应用,电磁污染日益严重,具有三维多孔结构的电磁波吸收材料成为科学研究的热点。总结了碳基气凝胶复合材料的研究进展,详细介绍了石墨烯气凝胶、生物质衍生的碳气凝胶和聚合物衍生的碳气凝胶的多种制备方法,碳气凝胶与磁性颗粒、碳化硅、碳纳米管和MXene复合而成的复合碳基气凝胶吸波材料的吸波性能。简要阐述了吸波材料的损耗机理,讨论了碳基气凝胶复合材料的组分、微观结构和损耗机制对吸波性能的影响。最后,就目前研究现状总结了碳基气凝胶复合材料在制备和性能提升方面的挑战,展望了碳基气凝胶复合材料的研究重点和发展方向。