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.     

基于遗传算法的介电梯度碳纳米管/环氧树脂吸波材料优化设计

将碳纳米管吸波剂超声分散到环氧树脂中,制备了碳纳米管/环氧树脂吸波材料。采用同轴法测试了2%、5%、9%(质量分数)碳纳米管/环氧树脂吸波材料电磁参数。随碳纳米管含量的增加,吸波材料的复介电常数不断增大。遗传算法优化设计的介电梯度碳纳米管/环氧树脂吸波材料最优结构为双层5%、9%(质量分数)碳纳米管/环氧树脂复合材料,其厚度分别为0.5146、1.3255mm,多层吸波材料反射率-5dB频带宽最大,为8.48GHz。     

掺天然磁铁矿水泥基复合材料电磁波吸收性能研究

以天然磁铁矿粉为低成本吸收剂制备了水泥基吸波材料,采用矩形波导法测试了不同磁铁矿掺量试样的复介电常数与复磁导率,并基于传输线与阻抗理论计算了试样的反射率。结果表明,掺天然磁铁矿水泥复合材料在8.2~12.4GHz频率范围内具有较高的电磁参数,表现出明显的电损耗与磁损耗。磁铁矿水泥复合材料存在2.5和8.5 mm两个匹配厚度。随磁铁矿掺量的增加,吸收峰向低频方向移动。当试样厚度为2.5mm时,磁铁矿掺量15%时,复合材料吸波性能最好,吸收峰值达到-14.8dB,反射率低于-10dB的频带达到2.1 GHz,而试样厚度为8.5mm时吸收峰值较低,但是吸收频带较窄。     

聚苯胺纳米纤维/锂锌铁氧体复合吸波材料的制备与性能

采用溶胶-凝胶法制备锂锌铁氧体(Li_0.435Zn_0.195Fe_2.37O₄,LZFO),界面聚合法制备纯聚苯胺(PANI)和PANI纳米纤维/LZFO复合材料。通过SEM、XRD、FTIR和矢量网络分析(PNA)等对材料的物相、结构和吸波性能进行了表征和分析。结果表明:制备出的样品分别为PANI、LZFO和不同配比的PANI纳米纤维/LZFO复合材料。在2~18 GHz范围内,PANI纳米纤维/LZFO复合材料的电磁波反射率<-10 dB的波段有2个,吸波性能较纯PANI和LZFO有了很大提高,并且拓宽了吸波频带,当PANI纳米纤维/LZFO复合材料中PANI纳米纤维的质量分数为10%,其综合吸波性能最佳,电磁波反射率<-10 dB的波段分别为2.5~5.5 GHz波段和14.5~16.5 GHz波段,最大吸收峰可达到-33.8 dB。而PANI和LZFO在电磁波反射率<-10 dB的波段只有1个。因此通过PANI纳米纤维接枝铁氧体,可调节电磁参数,提高材料的吸波性能。      

复合材料中碳纤维的铺设方式对吸波性能的影响

实验采用东华大学自制的碳纤维作为吸波剂，在基体环氧树脂中平行排列，制备出了吸波复合材料。采用矢量网络分析仪在2~18GHz波段，对复合材料的吸波性能进行测试。结果表明：复合材料的吸波性能不仅与碳纤维含量有关，还与碳纤维在基体中的排列方式有关，当碳纤维含量为3．2％（质量分数）时，吸波复合材料最大反射衰减为-18．64dB，反射率〈-10dB的频率带宽为2．6GHz，同时采用电磁理论对材料的吸收机理进行了探讨。     

双层结构型吸波复合材料的制备与吸波性能研究

依据传输线理论和阻抗匹配原则,设计并制备了一种以磁性金属微粉为面层、多壁碳纳米管为底层、玻璃纤维布为环氧树脂基体增强体的低频段双层结构型吸波复合材料。采用透射电镜和扫描电镜对多壁碳纳米管和磁性金属微粉的微观形貌进行了表征,采用HP8722ES矢量网络分析仪测量了材料在2～18GHz频率范围内的复介电常数和复磁导率,采用弓形法测试了复合材料在2～8GHz扫频范围内的反射率特性。研究表明,该双层结构型吸波复合材料在低频S波段具有良好的吸波效果,当其匹配厚度为dm=4.0mm时,最大吸收峰在3.08GHz时达到-17dB,反射率小于-10dB的频宽为1.82GHz。     

碳纤维增强莫来石陶瓷的介电性能和吸波性能研究

采用模压成型工艺和固相反应烧结制备了碳纤维/莫来石（Cf /Mullite）复合材料。对Cf /Mullite复合材料的物相组成、微观结构进行了表征,使用矢量网络分析仪研究了碳纤维（Cf）含量对莫来石（3Al2O3 2SiO2）陶瓷在X波段（8.2~12.4 GHz）的介电性能和吸波性能的影响。结果表明：Al2O3和SiO2在高温下充分反应生成了莫来石陶瓷,Cf /Mullite复合材料具有相对致密结构,Cf /Mullite复合材料的介电常数和介电损耗角正切值（tan δ）均随碳纤维添加量的增加而增大,且Cf的加入使得莫来石陶瓷具有更优的电磁波吸收性能。Cf体积分数为1.2%、Cf /Mullite复合材料厚度d=1.5 mm时,反射损耗最大吸收峰为-33.3 dB,反射损耗优于-5 dB的吸收频宽达3.675 GHz,反射损耗优于-10 dB的频宽达到2.205 GHz。Cf的加入显著提高了莫来石陶瓷的吸波性能。     

多壁碳纳米管/环氧有机硅树脂吸波涂层的介电和吸波性能研究

研究了不同直径和含量多壁碳纳米管填充环氧有机硅树脂吸波涂层在2~18GHz频率范围内的介电和吸波性能.可以得到吸波涂层的介电常数随着碳纳米管含量的增加而增大.当碳纳米管含量相同时,吸波涂层介电常数随着碳纳米管直径的增加而增大.当碳纳米管含量大于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:当涂层中多壁碳纳米管含量为10wt%、厚度为2mm时,吸波涂层的最大吸收峰随碳纳米管直径的增大向低频移动.多壁碳纳米管填充环氧有机硅树脂吸波涂层的吸波性能在7~14GHz范围内可达到-10dB,具有较好的吸波效果.     

碳纳米管/镍铁氧体涂层的吸波性能及吸波机理

采用柠檬酸络合物形成的溶胶凝胶制备了镍铁氧体,并将所得镍铁氧体与碳纳米管混合均匀,得到不同碳纳米管质量分数的复合材料。采用微波矢量网络分析仪测量了复合材料的电磁参数,根据电磁参数研究了1mm厚涂层在2~18GHz频段的微波反射率。结果表明:复合材料的吸波性能明显优于单纯的镍铁氧体材料,而且复合材料中碳纳米管含量对吸波性能有明显的影响。对于厚度为1mm的薄涂层,当碳纳米管的质量分数为20%时,涂层具有最优的吸波性能,最大吸收峰值达-14.02dB,小于-10dB的有效带宽达3GHz;然后通过电损耗功率密度分析了复合材料的微波吸收机理,并给出了厚度为1mm的薄涂层,当其中的碳纳米管含量为20%时,吸波效果最佳的理论解释。     

铁氧体/石墨复合吸波涂层的微波吸收性能

本文将固相法制备的磁损耗型Ba0.9Sm0.1Co2Fe16O27铁氧体与电损耗型石墨相结合,通过测试两者的电磁参数,采用YRcomputor软件模拟计算了双层复合吸波涂层的反射率。结果表明：铁氧体/石墨复合吸波涂层在2～8 GHz频段有较好的吸波性能;其中,下层为含量80 wt%的Ba0.9Sm0.1Co2Fe16O27,厚度1.5 mm,上层为10 wt%的石墨,厚度1.5 mm时,该复合涂层表现出优良的微波吸收特性,反射率损耗RL〈-10 dB时,带宽约为3 GHz（3.5～6.5 GHz）,最大吸收值约为-27 dB。     

The enhanced microwave absorption property of CoFe(2)O(4) nanoparticles coated with a Co(3)Fe(7)-Co nanoshell by thermal reduction

CoFe(2)O(4) nanoparticles were fabricated by a sol-gel method and then were coated with Co(3)Fe(7)-Co by means of a simple reduction process at different temperatures under 2% H(2) with the protection of argon to generate the dielectric-core/metallic-shell structure. The optimum reflection loss (RL) calculated from permittivity and permeability of the 80 wt% CoFe(2)O(4)/Co(3)Fe(7)-Co and 20 wt% epoxy resin composites reached - 34.4 dB, which was much lower than that of unreduced CoFe(2)O(4) and epoxy resin composites, at 2.4 GHz with a matching thickness of 4.0 mm. Moreover the RL exceeding - 10 dB in the maximum frequency range of 2.2-16 GHz was achieved for a thickness of composites of 1.0-4.5 mm with 600?°C thermal reduction process. The improved microwave absorption properties are a consequence of a proper electromagnetic match and the enhanced magnetic loss besides its dielectric loss due to the existence of the core/shell structure in CoFe(2)O(4) composites. Thus, the reductive CoFe(2)O(4) nanoparticles have great potential for being a highly efficient microwave absorber.     

Microwave absorption characteristics of CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>PbI<Subscript>3</Subscript> perovskite/carbon nanotube composites

The CH₃NH₃PbI₃ (MAPbI₃) and CH₃NH₃PbI₃/carbon nanotube (MC) composite have been successfully synthesized by a facile in situ solution method, which are investigated as the microwave absorption materials. For the MAPbI₃ particles, the minimum reflection loss is only ?4.9 dB around 16.4 GHz due to the poor relative complex permittivity. Then, the relative complex permittivity of MC composites could be adjusted by changing the mass fraction of CNTs in composite, which is a vital role for the dielectric loss. The reflection loss of MC-5 composite (MAPbI₃/CNT, 5:1 wt%) can be improved to ?35.7 dB with thickness of 1.3 mm at 13.1 GHz. When the thickness is <3.0 mm, the microwave absorption bandwidth of MC-5 is 11.8 GHz (5.0–16.8 GHz) under the reflection loss lower than ?20 dB. The quarter-wavelength (λ/4) matching model is used to discuss the microwave absorption mechanism of MC composites. These results indicate that MC-5 composite could be used as the microwave absorption materials with strong reflection loss, lightweight and broad bandwidth.     

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.     

螺旋形炭纤维的吸波性能

通过气相催化裂解法分别制得了螺径约为4μm、螺距为0.5μm～0.8μm的炭纤维（简称为coils-A）和螺径为20μm左右、螺距为1μm～4μm的炭纤维（简称为coils-B）.以coils-A和coils-B为掺杂体与石蜡制成复合材料在8.2 GHz～124 GHz范围内通过反射传输系统测量其电磁参数,结果表明该等微米级螺旋形炭纤维磁损耗为零,其中coils-B的介电参数的虚部及其损耗正切值tanδε较coils-A的高.分别以coils-A和coils-B为手性掺杂体制得填充有手性材料的夹芯蜂窝板复合材料,研究发现coils-A的吸波效果较好,在10 GHz～15 GHz的范围内对电磁波的反射衰减量大于10 dB,在4.6 GHz～18 GHz 的范围内对电磁波的反射衰减量均大于5 dB,在12.4 GHz时最大的反射衰减量为18 dB,其结果与藉由电磁参数所预测的结果相反.经计算,coils-A的手性参数ξ较大.因此,手性参数ξ对于提高吸波性能的影响大于介电参数ε的影响.     

Al2O3填料对SiCf/BN/SiC复合材料弯曲强度和高温吸波性能的影响

用有机先驱体浸渍裂解(PIP)法制备SiC_f/BN/SiC复合材料,研究了微米Al₂O₃粉体对其弯曲强度、高温介电和高温吸波性能的影响。结果表明,随着Al₂O₃的含量从5%提高到20%,SiC_f/BN/SiC的弯曲强度呈现出先升高后降低的趋势,最大值达到295 MPa;随着温度的升高复合材料复介电常数的实部和虚部均逐渐增大,加入Al₂O₃填料能降低高温复介电常数及其随温度增大的幅度。无填料复合材料的室温和高温吸波性能均较差,而添加20% Al₂O₃的复合材料在8.2~12.4 GHz频段的室温反射损耗均低于-8 dB,且适用厚度为3.0~3.5 mm,700℃时厚度为3.0 mm的反射损耗为-5~-8 dB,在实际工程应用中具有较强的可设计性。     

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.     

粉煤灰磁珠Fe含量和研磨粒径对Fe3C@C-CNTs复合材料结构和吸波性能的影响

以粉煤灰磁珠作为原料,采用化学气相沉积(CVD)方法制备纳米结构铁/碳复合材料。该复合材料呈现良好的吸波性能,但存在磁珠性质不均一、结构调控难等问题。本文采用摇床方法对磁珠进行分选,并进行研磨处理,考察了磁珠Fe含量和研磨粒径对CVD生成产物的影响。结果表明,富铁磁珠CVD生成产物为碳包覆磁性颗粒与碳纳米管组成的复合材料(Fe₃C@C-CNTs),该复合材料呈现多孔团簇球形结构。磁珠Fe含量增加,复合材料的相对碳沉积量(C/Fe值)减小,石墨化程度降低(D峰和G峰面积比I_D/I_G值升高),导致材料阻抗匹配值升高,吸波性能获得提升。磁珠Fe含量为71.43wt%时,复合材料有效吸收频带达到4.5 GHz,最小反射损耗(RLmin)达到-16.1 dB。对磁珠进行研磨后,CVD生成产物的C/Fe值不变,但碳沉积速率增大,I_D/I_G值升高,电磁波衰减常数下降,但阻抗匹配明显提高,吸波性能大幅度提升。研磨粒径为18.23μm时,复合材料有效吸收频带达到4.8 GHz,RLm_i...     

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。     

纳米SiC纤维改性短切碳纤维增强Si_3N_4陶瓷介电响应及吸波性能

以甲基三氯硅烷为原料,采用催化化学气相沉积(CCVD)工艺在短切碳纤维(C_(fd))表面制备了纳米SiC纤维(nano SiC_f)改性层,并采用凝胶注模-无压烧结工艺制备了nano SiC_f-C_(fd)/Si_3N_4和C_(fd)/Si_3N_4复合材料。使用矢量网络分析仪研究了nano SiC_f-C_(fd)和C_(fd)对Si_3N_4陶瓷在X波段(8.2~12.4GHz)的介电响应和吸波性能的影响。结果表明:nano SiC_f-C_(fd)/Si_3N_4和C_(fd)/Si_3N_4复合材料的复介电常数和介电损耗角正切值(tanδ)均随纤维添加量增加而增大;相同纤维含量时,nano SiC_f-C_(fd)/Si_3N_4复合材料的介电常数实部比C_(fd)/Si_3N_4复合材料有所降低,但损耗角正切升高。反射损耗结果表明:nano SiC_f-C_(fd)/Si_3N_4复合材料拥有更优的电磁波吸收效果。nano SiC_f-C_(fd)含量为2wt%、d=2.5mm时,出现最大吸收峰-14.95dB,反射损耗优于-5dB,波段频宽达3.5GHz。nano SiC_f界面改性能有效提高C_(fd)/Si_3N_4复合材料的吸波性能。