镀镍石墨烯的微波吸收性能

用化学还原液相悬浮氧化石墨法制备了石墨烯, 经亲水处理后, 利用化学镀镍法在其表面镀上均匀镍颗粒层. 采用SEM、EDX、振动样品磁强计等对样品的形貌、元素成分与磁性质进行了表征, 并用矢量网络分析仪测试了样品在2~18GHz频带内的复磁导率和复介电常数, 利用计算机模拟出不同厚度材料的微波衰减性能. 结果表明, 材料的微波吸收峰随着样品厚度的增加向低频移动, 材料的电磁损耗机制主要为电损耗, 未镀镍石墨烯的吸波层厚度为1mm时, 在7GHz左右最大衰减值?为?6.5dB, 镀镍石墨烯的吸波层厚度为1.5mm时, 在约12GHz时最大值为-16.5dB, 并且在频带9.5~14.6 GHz的范围内达到-10dB的吸收.     

二氧化锰涂覆EPS方法与效能分析

采用直接涂覆法将二氧化锰涂覆在EPS表面制成吸波球体。实验证实，这种方法有能力涂覆大密度导电粉末，且效果良好。在反射阻抗的测试中，当试样厚度为10mm时，其反射损耗在8～18GHz频率范围内为-7～-15dB，发现随着吸波颗粒中二氧化锰含量和试样厚度的增加，在8～18GHz频段内，试样的反射损耗增加。二氧化锰层吸波球体效能略低于同等导电层厚度的炭粉层吸波球体。     

三维织物石膏基微波吸收材料的制备及性能

采用浸渍工艺在三维织物表面包覆炭黑,并将其与石膏复合制备石膏基微波吸收材料。利用弓形反射法测试了该复合材料在2~18GHz内的吸波性能,结果表明吸波性能随炭黑含量的增加而增强,三维织物的最佳厚度为6mm。三维织物厚度为6mm、乙炔炭黑含量为24%的复合材料在2~18GHz内对电磁波的反射损耗均低于-5dB,最低反射损耗可达-28.3dB。三维织物的特殊结构不仅能够有效改善材料的阻抗匹配,还能够增加材料的电磁波损耗路径,从而达到增强损耗能力、拓宽吸波频宽的目的。此外,三维织物还能够明显增强石膏基材料的抗折性能。     

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。      

磁功能化多孔生物质炭复合材料的制备及吸波性能

采用高温炭化和水热法制备了兼具介电损耗和磁损耗特性的磁功能化生物质炭(Fe_3O_4/多孔生物质炭)吸波材料。在200℃水热条件下,随着FeCl_3浓度的增加,PLSC表面生成的聚集态Fe_3O_4纳米晶粒有所增加,颗粒大小规整,平均粒径约为200 nm。通过矢量网络分析仪探讨了磁材料含量、复合材料的形貌结构对吸波性能的影响,并分析了多重损耗吸波机理。结果表明,在2～18 GHz范围内,当FeCl_3浓度为4 mmol时制备的磁功能化生物质炭复合吸波材料具有最佳的吸波性能,在厚度为2 mm时,其在11.42 GHz处的最大反射损耗值可达-42.2 dB,有效频宽达3.14 GHz (反射损耗小于-10 dB)。     

多元助剂改性羰基铁粉雷达波低频吸波性能研究

采用三种处理剂对羰基铁粉样品进行表面复合改性,研究了多元助剂对羰基铁粉样品表面改性后的微观结构及电磁参量的影响。结果表明,多元助剂的使用使羰基铁粉表面形成了一层致密的有机绝缘薄膜,能有效降低羰基铁粉的复介电常数,增加复磁导率虚部,提高吸波材料的电磁匹配性能,改善吸收剂的低频吸收效果。根据传输线理论计算吸波材料的反射损耗(Reflection loss,RL),在厚度为2mm时,三元助剂改性羰基铁粉的反射损耗峰值在2GHz附近达到-15dB,在RL-10dB的有效吸收频宽为1GHz(1.6~2.6GHz),具有较好的雷达波低频吸波性能。     

制备时间对CIPs/Fe_3O_4吸波性能的影响

通过表面柔性氧化技术在羰基铁粉(CIPs)表面改性制备了CIPs/Fe_3O_4材料。利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、X射线光电子能谱分析(XPS)和矢量网络分析仪对改性前后的CIPs进行测试分析,研究了不同处理时间对CIPs/Fe_3O_4材料微观形貌、物相、元素组成和价态、电磁性能及吸波性能的影响。结果表明:随着表面氧化处理时间的延长,CIPs表面生成的Fe_3O_4颗粒越来越多。模拟反射率结果表明:当反应时间为90 min、材料厚度为1.8 mm时,CIPs/Fe_3O_4材料在测试频段内的吸收值低于-20 dB的频宽为1.7 GHz,最低吸收峰值为-29.6 dB;而原始CIPs材料在测试频段内的吸收值低于-20 dB的频宽为1.5 GHz,最低吸收峰值为-24.1 dB。这说明通过对CIPs的表面进行氧化改性处理,可以提高其吸收效率和吸收频宽。     

高能球磨对Al_8Mn_5粉体微波吸收特性的影响

采用真空悬浮熔炼和高能球磨工艺制备了Al8Mn5合金粉体,使用SEM、XRD和网络矢量分析仪研究高能球磨对Al8Mn5合金粉体微波吸收特性的影响。结果表明,随着球磨时间的增加,粉体的颗粒及晶粒变细,粉体吸收峰频率向低频移动;样品厚度为1.5mm时,未经球磨的粉体在13~18GHz频段内有3个吸收率90%的吸收峰,呈现出较好的频宽效果;经24h球磨后粉体在13.2GHz频率处有最大吸收峰,其反射率最小值约为-37.5 dB(吸收率为99.98%);Al8Mn5粉体对电磁波的吸波机理与吸波涂层内的电磁损耗和涂层厚度对电磁波的干涉损耗影响有关。     

膨胀石墨基纳米镍、铁、钴化学镀制备复合吸波材料

为了获得薄、轻、宽、强等性能理想的吸波材料,采用化学镀的方法在膨胀石墨表面镀覆纳米镍、镍钴、镍铁钴,制备了复合吸波材料.SEM和EDs分析证实,膨胀石墨表面镍层、镍钴层、镍铁钴层的镀覆厚度约为70～150 nm.采用HP8722ES矢量网络分析仪测量了复合吸波材料在2～18 GHz内的复介电常数(ε=ε'-jε")和复磁导率(μ=μ'-jμ").用吸收屏理论公式计算了反射率损耗(R.L)、匹配频段(fm)及匹配厚度(dm).结果表明,当dm=0.3 mm时,镀覆镍铁钴层的复合吸波材料最低的反射损耗达-28 dB,对应的fm=13.5 GHz,R>L<-10 dB时频宽达7.5 GHz.本法制备的复合吸波材料符合"轻、薄、宽、强"的现代要求.     

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。     

Effects of Multi-walled Carbon Nanotubes on the Electromagnetic Absorbing Characteristics of Composites Filled with Carbonyl Iron Particles

The electromagnetic(EM) wave absorbing property of silicone rubber filled with carbonyl iron particles(CIPs) and multi-walled carbon nanotubes(MWCNTs) was examined.Absorbents including MWCNTs and spherical/flaky CIPs were added to silicone rubber using a two-roll mixer.The complex permittivity and complex permeability were measured over the frequency range of 1-18 GHz.The two EM parameters were verified and the uniform dispersion of MWCNTs and CIPs was confirmed by comparing the measured reflection loss(RL) with the calculated one.As the MWCNT weight percent increased,the RL of the spherical CIPs/silicone rubber composites changed insignificantly.It was attributed to the random distribution of spherical CIPs and less content of MWCNTs.On the contrary,for composites filled with flaky CIPs the absorption bandwidth increased at thickness 0.5 mm(RL value lower than-5 dB in 8-18 GHz) and the absorption ratio increased at lower frequency(minimum-35 dB at 3.5 GHz).This effect was attributed to the oriented distribution of flaky CIPs caused by interactions between the two absorbents.Therefore,mixing MWCNTs and flaky CIPs could achieve wider-band and higher-absorption ratio absorbing materials.     

Microwave absorption of gamma'-Fe2.6 Ni1.4N nanoparticles derived from nitriding counterpart precursor

Gamma-Fe2.6Ni1.4 nanoparticles were prepared by the arc-discharge method as the precursor and its nitride counterpart of gamma'-Fe2.6Ni14N nanoparticles was synthesized directly through a thermal ammonolysis reaction at the temperature of 673 K for two hours. The resultant product was identified as a homogeneous ternary nitride with nearly spherical shape and average size of about 60.0 nm. The electromagnetic characteristics of gamma'-Fe2.6Ni1.4N derivant and gamma-Fe2.6Ni1.4 precursor have been studied in the frequency range of 2-18 GHz. Compared with the precursor, gamma'-Fe2.6Ni1.4N nanoparticles exhibits an enhanced electromagnetic absorption property resulted from the increased dielectric loss by nitriding process. The optimal reflection loss (RL) of gamma'-Fe2.6Ni1.4N nanoparticles/paraffin composite can reach -39.9 dB at 5.2 GHz in a thickness of 2.29 mm, and the frequency band corresponding RL < -10 dB is over 2.6-18 GHz in the thickness range of 0.78-4.20 mm.     

Influence of SiO2 fillers on microwave absorption properties of carbonyl iron/carbon black double-layer coatings

Epoxy resin (ER) based double-layer composite coatings were prepared with the thickness of 1.2 mm, employing carbonyl iron (CI) and carbon black (CB) as absorbents in the matching layer and absorption layer respectively. Especially, SiO₂ was introduced into the matching layer as wave-transmission material to improve the matching impendence. The complex permittivity, complex permeability and absorption properties were investigated in 2–18 GHz. With increasing SiO₂ content in the matching layer, the reflection loss (RL) was enhanced in the range 2–18 GHz. When the coating with the optimized SiO₂ and CI weight concentration (SiO₂:CI:ER) of 2:5:1, the optimal RL got to −17.3 dB and the effective absorption band (RL better than −4 dB) reached 5.7 GHz. In comparison, the minimum RL value was only −5.9 dB and the bandwidth (RL better than −4 dB) was just 4.1 GHz for the SiO₂-free composite coating.     

Magnetic and Microwave-absorption Properties of Graphite-coated (Fe, Ni) Nanocapsules

The structure, magnetic and microwave-absorption properties of graphite-coated (Fe, Ni) alloy nanocapsules, synthesized by the arc-discharge method, have been studied. High-resolution transmission electron microscopy shows that the nanocapsules have a core/shell structure with (Fe, Ni) alloy as the core and graphite as the shell. All (Fe, Ni) alloy nanocapsules/paraffin composites show good microwave-absorption properties. The optimal reflection loss (RL) was found for (Fe70Ni30)/C nanocapsules/paraffin composites, being -47.84 dB at 14.6 GHz for an absorber thickness of 1.99 mm, while the RL values exceeding -10 dB were found in the 12.4- 17.4 GHz range, which almost covers the Ku band (12.4-18 GHz). For (Fe70Ni30)/C nanocapsules/paraffin composites, RL values can exceed -10 dB in the 11.4-18 GHz range with an absorber thickness of 1.91 mm, which cover the whole Ku band.     

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.     

天然尖晶石型铁氧体(铁砂)基复合吸波涂料特性研究

天然尖晶石型铁氧体（铁砂）与聚氨脂粘结剂制成的吸波涂料在7～12GHz频段有两个吸收峰，涂层厚度1．25mm时，吸收量5．2～8．5dB，在基础吸波材料(铁砂)中添加尖晶石型铁氧体、顺磁性稀土材料和六角铁氧体制成复合吸波涂料，使其吸收量达18～25aB，匹配厚度1．1～1．2mm，两吸收峰间距＞4．4GHz，它加工简单，价格低廉。     

Microwave measurements on oilshale rocks

Characterization of some structural and electrical properties of oilshale deposit are studied in the X-band (8 to 12 GHz) through measuring the insertion loss (IL), return loss (RL), and the material equivalent input impedance, Z_m. X-ray diffraction and scanning electron microscopy show that the deposit contains a number of minerals and oil pores. Measurements at microwave frequency show that the IL for the rock specimen of 5.1 mm thickness ranges between 2 and 4.5 dB; and the value of the RL for the same specimen ranges between 2 and 5.8 dB over the whole X-band. A particular surface deposit specimen of thickness 7.15 mm shows a high value of RL of about 38 dB at around 11.2 GHz, which seems almost transparent at this frequency. The overall behaviour of the measured impedance as a function of frequency shows a relatively strong dependence on the specimen thickness and weak dependence on both deposit depth and composition. Analysis of the obtained data of impedance indicates that the deposit has an inductive behaviour.     

Enhanced microwave absorption of ZnO-coated planar anisotropy carbonyl-iron particles in quasimicrowave frequency band

For the aim of thin electromagnetic wave absorbers used in quasimicrowave frequency band, planar anisotropy carbonyl-iron (PACI) particles coated with ZnO nanoshells were prepared by ball milling technique and chemical precipitation method. Compared with the as-milled PACI/paraffin composite, lower dielectric constant was obtained for the composite containing PACI at ZnO particles, and hence a dramatic enhancement of reflection loss (RL) was obtained. The minimum RL of PACI at ZnO composite reaches −31.93 dB at 1.96 GHz with the matching thickness of 2.5 mm. Furthermore, the absorbing property is further improved after the PACI at ZnO composite was rotationally oriented in an external magnetic field. The minimum RL of the oriented PACI at ZnO composite reaches −40.06 dB and the matching thickness reduces to 2.2 mm with a slight variation of matching frequency. The PACI at ZnO core-shell particles exhibit great potential in application of the thin absorber in the 1–4 GHz frequency range.     

Effect of ball milling and moderate surface oxidization on the microwave absorption properties of FeSiAl composites

Commercially available irregular FeSiAl alloys were used as raw materials. The microwave absorption properties of FeSiAl/paraffin composites were improved by ball milling the alloys and moderately oxidizing their surfaces. Permittivity and permeability of the as-milled composites distinctly increased compared with those before milling. Moderate surface oxidization significantly reduced permittivity whereas permeability almost maintained its initial value compared with those of as-milled composites. Consequently, the microwave absorption properties were significantly improved. The minimum reflection loss (RL) of the absorber with 35 vol% surface-oxidated flake reached −39.67 dB at 1.40 GHz at a thickness of 4 mm. Effective microwave absorption (RL < −10 dB) was achieved within the range of 0.73–3.94 GHz at the thickness of 2–5 mm, which may be applied to the L- and S-bands.     

Microwave absorbing behavior of metal dispersed TiO2 nanocomposites

Metal dispersed TiO₂ nanocomposites were prepared by milling process. The microwave absorbing characteristics of the prepared nanocomposites with epoxy were studied in the 8.2–12.4 GHz frequency range for the microwave absorption application. The measured relative complex permittivity of metal dispersed nanocomposite-epoxy indicates higher values in comparison to the pure TiO₂-epoxy nanocomposite. The Reflection loss (RL) values were calculated for thickness from 0.1 to 2.2 mm with an interval of 0.1 mm and the maximum value of RL found for TiO₂-epoxy nanocomposite was −4.96 dB at 10.21 GHz frequency for 2.0 mm thickness. Whereas, RL value is improved to a maximum value of −13.67 dB at 10.13 GHz with Al dispersion (1.8 mm thickness) and −7.24 dB at 10.38 GHz with Ni dispersion (1.3 mm thickness). This study suggests the effectiveness metal particles dispersion for the development of thin microwave absorbers as well as increasing the level of RL.