Co含量对轻质微波吸收剂C/Co纳米纤维吸波性能的影响

采用静电纺丝法结合热处理制备了一种可应用于2~18 GHz频段的高性能轻质微波吸收剂C/Co纳米纤维, 详细研究了金属Co含量对纳米纤维的电磁特性及微波吸收性能的影响。相对于纯碳纳米纤维, C/Co纳米纤维的微波吸收性能得到显著加强, 其主要吸波机制仍是介电损耗。随着Co含量的增加, C/Co纳米纤维的电磁衰减能力逐渐下降, 而微波吸收却先增强后减弱, 含37.8wt% Co的C/Co-5纳米纤维因金属Co粒子和纳米碳纤维的良好结合与协同效应, 以及纤维中特殊的Co粒子@石墨核壳结构所带来的良好阻抗匹配与足够高的电磁衰减能力而表现出最好的吸波性能。模拟计算结果表明, 涂层厚度在1.1~5.0 mm间变化时, 填充5wt% C/Co-5纳米纤维的硅胶吸波涂层的反射损耗(RL)值超过-20 dB的频率范围在3.2~18 GHz, 最小RL值达到-78.8 dB, 其中当涂层厚度仅为1.5 mm时, RL值低于-20 dB的吸收带宽可达6.0 GHz (12~18 GHz)。C/Co纳米纤维优异的微波吸收性能表明, 这些磁性碳杂化纳米纤维有望成为一种极具应用前景的新型吸波材料。     

非连续体吸波平板的设计制备及吸波机理分析

通过吸波体内导电媒质的“孤岛”化设计, 制备了单层非连续体平板吸波材料, 并分析了不同炭黑含量和不同试样厚度对吸波效能的影响以及电磁波的损耗机理。发现随着CB/ ABS 颗粒中炭黑含量和试样厚度的增加, 在8～18 GHz 频段内, 非连续体试样的反射损耗增加。当炭黑质量含量达到30 %时, 平板的反射损耗在8. 5～18 GHz 宽频范围内都超过- 10 dB , 在15～18 GHz 均高于- 15 dB。当试样厚度达到20 mm 时, 其反射损耗在8～18 GHz 频率范围内超过- 15 dB。结果表明, 非连续体试样较热压致密试样吸波效能有较大提高, 是很有潜力的吸波结构。      

Microwave-absorbing properties of de-aggregated flake-shaped carbonyl-iron particle composites at 2-18 GHz

We have investigated the microwave-absorbing properties for different shapes and aggregated states of carbonyl-iron particles dispersed in epoxy resin matrix at various volume concentrations. Here, we discuss the requirements of lower reflection coefficient for the microwave permittivity /spl epsiv//sub r/=/spl epsiv/'-j/spl epsiv/' and permeability /spl mu//sub r/=/spl mu/'-j/spl mu/'. Compared to the aggregated sphere-shaped particles (SS), the de-aggregated flake-shaped carbonyl iron particles (FS) have higher permeability, lower permittivity, better filling characteristics in epoxy resin, and better absorbing properties in the frequency range of 2-18 GHz. For the FS composite with volume fraction of 0.60 at single-layer thickness of 1 mm, the calculated reflection loss at 2 GHz reaches -4.04 dB and the minimum reflection loss is -12.2 dB at 4.4 GHz, which indicates that the FS composite can be applied as a thinner microwave absorber in the S-band than if SS particles are used. The results also show that different volume concentrations can have high absorption at different wave bands, a fact on which the design of absorbing material can be based.     

低密度Fe3O4/中孔炭微球复合材料的可规模制备及吸波性能

采用喷雾干燥法制备出中孔炭微球(MCMSs), 进一步通过液相浸渍得到磁性Fe₃O₄/MCMSs纳米复合材料, 系统研究了复合材料的形貌结构和吸波性能。结果发现, Fe₃O₄/MCMSs复合材料具有优异的流动性和低密度(0.24~0.33 g/cm³)特征, 其中Fe₃O₄纳米颗粒高度分散在MCMSs中孔孔道内。复合材料具有较高的比表面积(548~735 m²/g), 可以促进多种介电弛豫的形成。在2~18 GHz范围内, 复合材料以介电损耗为主, 在12.6 GHz处具有最大反射率-25 dB, 小于-10 dB的带宽达4.7 GHz。复合材料优异的吸波性能可以归因于均相分布的Fe₃O₄纳米颗粒和中孔炭微球的协同作用, 在增大界面弛豫和电磁波散射的同时, 改善了阻抗匹配, 减少了电磁波在吸波层表面的反射。     

Synthesis of core–shell FeCo@SiO<Subscript>2</Subscript> particles coated with the reduced graphene oxide as an efficient broadband electromagnetic wave absorber

The FeCo@SiO₂@RGO composites were prepared by combining liquid-phase reduction reaction in Argon atmosphere with hydrothermal reaction. The crystal structure, chemical composition and morphology of the as-prepared composites have been investigated in detail. SEM and TEM results illustrate that the FeCo@SiO₂ composites are of core–shell structure with a diameter of about 150–200 nm. Compared with FeCo@SiO₂ and FeCo@RGO composites, the as-prepared FeCo@SiO₂@RGO composites exhibit excellent electromagnetic (EM) wave absorption properties. As an EM wave absorber, the maximum R_L reaches ?52.9 dB at 9.12 GHz with a thickness of 3.0 mm, and the absorption bandwidth with the reflection loss below ?10 dB was up to 5.36 GHz (from 8.8 to 14.16 GHz) with a thickness of 2.5 mm. It is believed that the FeCo@SiO₂@RGO composites can serve as an excellent microwave absorbent and can be widely used in the microwave absorbing area.     

Controllable synthesis of Ni/NiO@porous carbon hybrid composites towards remarkable electromagnetic wave absorption and wide absorption bandwidth

The reasonable design of the composition of the composite materials is of great significance to optimized the electromagnetic (EM) wave absorption performance.Herein,the Ni/NiO@C hybrid composites with tunable Ni proportion were successfully synthesized through a two-step process.With the assistance of X-ray diffraction with refinement treatment,the specific proportion of Ni of as-obtained hybrid com-posites could be obtained.Employing controlling calcination time to adjust the Ni content of Ni/NiO@C hybrid composites,it has been found that the composite carbonized at 500 ℃ exhibited remarkable EM wave absorption with the minimum reflection loss (RLmin) of-49.1 dB at 4.9 mm and the widest effective absorption bandwidth (EABmax) of 4.56 GHz at 2.1 mm.Moreover,by adjusting the Ni source,the optimal EM wave absorption performance could be achieved.Results illustrated that the N3PC with the Ni pro-portion of 13.17 ％ showed the RLmin as low as-51.1 d B at 2.4 mm and the EABmax was 5.12 GHz at 2.7 mm.It is worth noting that this work demonstrates the relevance of the composition and EM wave absorption performance of hybrid composites,which offers a feasible reference for the absorption mechanism of absorber.     

镀镍碳纳米管的微波吸收性能研究

用竖式炉流动法制备了碳纳米管,碳纳米管的外径40nm～70nm,内径7nm～10nm,长度50μm～1000μm,呈直线型,用化学镀法在碳纳米管表面镀上了一层均匀的金属镍。碳纳米管吸波涂层在厚度为0.97mm时,在8GHz～18GHz,最大吸收峰在11.4GHz(R=-22.89dB),R<-10dB的频宽为3.0Hz,R<-5dB的频宽为4.7GHz。镀镍碳纳米管吸波涂层在相同厚度下,最大吸收峰在14GHz(R=-11.85dB),R<-10dB的频宽为2.23Hz,R<-5dB的频宽为4.6GHz。碳纳米管表面镀镍后虽然吸收峰值变小,但吸收峰有宽化的趋势,这种趋势对提高材料的吸波性能是有利的。碳纳米管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,从而雷达波能量被转换为其它形式的能量。     

碳/氧化铝/二氧化硅涂层的介电和吸波性能研究

研究了炭黑或碳纤维填充氧化铝/二氧化硅吸波涂层在X波段范围的介电和吸波性能. 结果表明: 吸波涂层的复介电常数随着炭黑或碳纤维含量的增加而增大. 当吸收剂含量相同时, 填充碳纤维的吸波涂层比填充炭黑的吸波涂层具有更大的复介电常数. 当吸收剂含量大于5wt%时, 吸波涂层的介电常数在低频急剧增加, 且随频率增大而减少, 出现频散效应. 反射率测试结果表明: 吸波涂层的最大吸收峰随涂层厚度的增大向低频移动, 当涂层中炭黑含量为2wt%、厚度为1.8 mm时, 吸波涂层在9.2~12.4 GHz范围内反射率小于-10 dB, 具有较好的吸波效果.     

Nickel/carbon hybrid nanostructures as microwave absorbers

Magnetic metal/carbon hybrid nanostructures are novel materials having multifunctional properties. Here we report the microwave absorbing properties of nickel/carbon nanostructures synthesized by a controlled pyrolysis method. Their complex dielectric permittivity and magnetic permeability were measured at different microwave frequencies using the technique of cavity perturbation. Reflection losses were evaluated and found to be less than −10 dB over the entire X-band (8-12 GHz) for a thickness of 2.2-2.8 mm. A minimum reflection loss of −45 dB was attained for an absorber thickness of 6.6 mm at 3.13 GHz.     

Microwave absorption properties of FSS-impacted composites as a broadband microwave absorber

The development of a cost-effective microwave absorber with wide bandwidth corresponding to reflection loss (RL)?≤??10 dB is still a very challenging task. A sugarcane bagasse-based agricultural waste composite has been analyzed for its elemental contents. The combination of elements is suitable for its possible usage as a cost-effective microwave absorbing material. Therefore, this composite has been subjected to morphological and electromagnetic studies to analyze its microwave absorbing behavior. The frequency dependent complex dielectric permittivity and complex magnetic permeability values were obtained using a transmission/reflection waveguide approach in the X-band. Furthermore, the effect of the Minkowski loop frequency selective surface (FSS) was studied over the absorption capability of the composite. It was found that the application of FSS leads to a reduction in thickness up to 2.9 mm and an enhancement in absorption bandwidth up to 3.6 GHz. The FSS patterned composite shows a remarkable performance with peak RL of ?28.4 dB at 10.7 GHz and absorption bandwidth of 3.6 GHz.     

空心微珠铁氧体复合粉体的改性与吸波性能

研究了柠檬酸盐溶胶-凝胶方法制备空心微珠-钡、锶、钴镍钡铁氧体复合粉体的微观形貌, 采用化学添加剂改善铁氧体的包覆性能. SEM、EDS分析表明铁氧体在空心微珠表面的包覆状态与铁氧体种类无关; 在前驱体中加入乙二醇或聚乙二醇可以使铁氧体对空心微珠的包覆更加完整、牢固致密. 用网络分析仪测试了C波段5.0～6.5GHz、X波段8.2～12.4GHz、Ku波段12.5～18.0GHz内1.8mm厚铁氧体空心微珠复合粉体制备的吸波涂层的微波损耗. 试验表明：铁氧体空心微珠复合粉体具有良好的电磁吸波性能, 吸波涂层在5～18GHz内微波反射损失总体上大于单纯铁氧体涂层; 加入乙二醇或聚乙二醇有助于提高涂层的吸波效果.     

Si/C/N纳米粉体的吸波特性研究

采用ＸＲＤ研究了氮原子百分含量为１１．６１%的Ｓｉ/Ｃ/Ｎ纳米粉体的相组成,并测定了粉体介电常数根据介电常数,分别优化设计了单层和双层的吸波徐层,设计的吸波涂层对８~１８ＧＨｚ范围的电磁波有较好的吸收作用．设计厚度为２．７ｍｍ的单层吸波涂层,在８~１５ＧＨｚ范围内反射率＜－５ｄＢ设计厚度为２．８ｍｍ的双层吸波涂层,在８~１８ＧＨｚ频率范围内电磁波的反射率均＜－５ｄＢ,反射率＜－８ｄＢ的频带为６ＧＨｚ．针对纳米粉体的吸波特性,提出了Ｓｉ/Ｃ/Ｎ纳米粉体的吸波机理．     

Synthesis of covalently bonded reduced graphene oxide-Fe3O4 nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic (EM) wave absorbers,covalently bonded reduced graphene oxide-Fe3O4 nanocomposites (rGO-Fe3O4),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe3O4 nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe3O4 nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe3O4 is 2∶1 (sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss (RL) reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth (RL＜-10 dB) is 6.32 GHz (11.68-18.0 GHz) with a matching thickness of 2.1 mm.Furthermore,radar cross section (RCS) simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption performance.This work provides a possible method for preparing efficient EM wave absorbers.     

Enhanced microwave absorption performance of graphene/doped Li ferrite nanocomposites

In the present study, Microwave absorbing Li-Sr, Li-Co ferrite nanoparticles and RGO/Li-Sr, RGO/Li-Co ferrite nanocomposites containing Li ferrite and reduced graphene oxide (RGO) were synthesized to further improve the microwave absorption performance of Li ferrite nanoparticles (LiFe₅O₈). The Li-Sr and Li-Co nanoparticles were synthesized by thermal treatment method, the RGO/Li-Sr and RGO/Li-Co nanocomposites were obtained by a polymerization method and were characterized by different techniques. The electromagnetic wave absorption properties of the samples were evaluated by vector network analyzer (VNA) in the frequency range of 2–18 GHz. The magnetic and dielectric loss, impedance matching, and electromagnetic wave absorption of the samples are significantly improved through the addition of RGO. Experimental results revealed that the RGO/Li-Co nanocomposite considerably increased microwave absorption. The minimum reflection loss (RL) of RGO/Li-Co also was found to reach −46.80 dB at the thickness of 3 mm and the effective absorption bandwidth (≤-10 dB) amounted to 6.80 GHz (from 10.52 to 17.32 GHz), which was much higher in comparison with pure Li and Li-Co ferrites nanoparticles. Due to the synergistic effect between magnetic loss and dielectric loss and the good impedance matching, the RGO/Li-Co nanocomposite may be regarded as a new candidate for microwave absorbing materials characterized with a broad effective absorption bandwidth at thin thicknesses.     

Ferromagnetic and microwave absorption properties of copper oxide/cobalt/carbon fiber multilayer film composites

The copper oxide/cobalt/carbon fiber multilayer film composites were synthesized by thermal oxidation route. In order to investigate the intrinsic reasons for microwave absorption properties of absorbers, the complex permittivity, complex permeability and the microwave absorption properties of composites were studied in the 1-18 GHz range. The strongest reflectivity loss (RL) of microwave absorber was further enhanced to − 42.7 dB (microwave absorption rate > 99.9%) at 10.8 GHz for a layer of 2.0 mm thickness, and the strong absorption (RL < − 10 dB) was obtained between 8.72 and 18 GHz for the thickness of 1.3-2.2 mm. The results indicated that the dielectric loss and magnetic loss led to the excellent microwave absorption property of CuO/Co/CF composites. It is believed to be ideal for making a lightweight, strong absorption and wide-frequency microwave absorbing material.     

Ni0.4Co0.2Zn0.4Fe2O4/BaTiO3纳米纤维双层吸波涂层的微波吸收特性研究

采用静电纺丝法制备了平均直径分别为180 nm和220 nm的BaTiO₃(BTO)和Ni_0.4Co_0.2Zn_0.4Fe₂O₄(NCZFO)纳米纤维, 使用X射线衍射(XRD)、场发射扫描电镜(FESEM)和矢量网络分析仪(VNA)对纤维的物相结构、表面形貌和微波电磁参数进行了表征, 并根据传输线理论分析评估了以BTO和NCZFO纳米纤维为吸收剂的硅橡胶基单层和双层结构吸波涂层在2~18 GHz范围内的微波吸收性能。结果显示, 由于BTO纳米纤维的介电损耗与NCZFO纳米纤维的磁损耗的有机结合和阻抗匹配特性的改善, 以NCZFO纳米纤维/硅橡胶复合体(S1)为匹配层、BTO纳米纤维/硅橡胶复合体(S2)为吸收层的双层吸波涂层比相应单层吸波涂层表现出更为优异的吸收性能。通过调节匹配层与吸收层的厚度, 在4.9~18 GHz范围内反射损耗可达–20 dB以下; 当吸收层和匹配层的厚度分别为2.3 mm和0.5 mm时, 最小反射损耗位于9.5 GHz达–87.8 dB, 低于–20 dB的吸收带宽为5 GHz。优化设计的NCZFO/BTO纳米纤维双层吸波涂层有望发展成为一种新型的宽频带强吸收吸波材料。     

Enhanced microwave absorption performance of nitrogen-doped porous carbon dodecahedrons composite embedded with ceric dioxide

CeO₂/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO₂ was first prepared by introducing CeO₂ into the precursor of ZIF-67 and then CeO₂/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO₂. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO₂/Co/C exhibited a minimum reflection loss of ?68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO₂ effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO₂/Co/C composite is a promising microwave absorber material with high performance.     

Double layer microwave absorber based on Cu dispersed SiC composites

The present work has been focused on designing an efficient and cost-effective double layer microwave absorber in 8.2–12.4?GHz frequency range. For the same, Cu particles were dispersed in SiC to achieve enhanced microwave absorption by combining the excellent dielectric characteristics of SiC with highly conductive Cu. Cu dispersed SiC composites were prepared by dispersing various weight fractions of Cu particles in the SiC matrix using planetary ball mill. The Cu dispersion in SiC yielded excellent relative complex permittivity values translating into a decrease in the reflection loss (RL) values of dispersed composites as compared to the pristine counterpart. The minimum RL of ?17.18?dB has been observed for 2?wt% Cu dispersed SiC composite at 11.81?GHz with a thickness of 1.3?mm and bandwidth corresponding to ?10?dB is 1.77?GHz. Genetic algorithm approach has been implemented to design double layer microwave absorber to further enhance the microwave absorption of the prepared composites for realizing a cost-effective solution. The optimum double layer results show the RL of ?32.16?dB at 11.05?GHz with 1.67?mm total thickness and bandwidth corresponding to ?10?dB is 2.35?GHz.     

Fabrication of Graphdiyne/Graphene Composite Microsphere with Wrinkled Surface via Ultrasonic Spray Compounding and its Microwave Absorption Properties

Advanced carbon materials are constantly being used in the field of microwave absorption. Herein, in order to enrich the variety and expand the application fields of graphdiyne (GDY), the wrinkled graphene (RGO) nanosheet coated and embedded with GDY porous microspheres (RGO/GDY) are prepared by GDY synthesis, ultrasonic spray, and pyrolysis. The study finds that RGO and GDY have effective synergistic effects. The suitable pores and composition, conductive network formed by overlapping 0D and 2D materials, special surface and internal morphology design, and high-temperature activation process make RGO/GDY exhibit excellent impedance matching and attenuation capabilities. Under the best amount of GDY (20 mg), the particle sizes of the microspheres (≈6 µm), and filler content (27.5%), the minimum reflection loss (RL_min) is −58 dB@8.3 GHz, and the corresponding matching thickness is 2.7 mm. The effective absorption bandwidth is 4.3 GHz as the thickness is 1.9 mm. By adjusting the thickness, the absorber can completely absorb microwaves of all the C, X, and Ku bands. The microwave absorbing mechanisms are elucidated. GDY materials are first applied to the field of microwave absorption, enhancing the absorption performance of RGO/GDY. It provides a new way to manufacture electromagnetic wave absorbers with satisfactory performance.     

氧化硅包覆铁“壳/核”型纳米复合粒子的制备及其吸波特性研究

采用非平衡物理气相蒸发法在氢气氩气混合气氛下制备了氧化硅包覆铁“壳/核”型纳米复合粒子. 通过X射线衍射(XRD)、透射电子显微镜(TEM)和能谱分析(EDS)等方法表征了纳米复合粒子的相组分、结构以及颗粒形貌. 结果表明,制备的氧化硅包覆铁纳米复合粒子的尺寸在50nm左右,在铁纳米粒子的表面还出现了非晶态的氧化硅纳米棒,长度为150~200nm. 利用电磁参数模拟微波吸收特性得出,涂层厚度为1.79mm时,在15.4GHz频率处达到最小反射损耗值为-14.5dB,反射损耗在8~18GHz的频段低于-10dB,且损耗机制为自然共振.