微螺旋炭纤维手性复合吸波材料的研究

微螺旋炭纤维独特的螺旋手性结构赋予其优异的吸波性能,本文结合自身实验,综述了微螺旋炭纤维复合吸波材料的研究进展,并分析其吸波机理在螺旋手性结构引起的电磁波交叉极化,同时对发展更好的微螺旋炭纤维手性复合吸波材料提出了可行建议.     

炭纤维吸波复合材料结构设计的研究进展

总结了炭纤维吸波性能的电磁改性方法,重点介绍了结构设计对炭纤维吸波复合材料吸波性能的影响,包括短切炭纤维、炭纤维排布结构、炭纤维电路模拟结构以及含炭纤维的混杂纤维排布对炭纤维复合材料吸波性能的影响.提出了炭纤维吸波复合材料今后的研究方向.     

水泥基多孔复合材料吸波性能

对发泡型聚苯乙烯(expanded polystyrene,EPS)填充普通硅酸盐水泥制备的水泥基多孔复合材料的吸波性能进行了研究.为废弃的EPS二次开发利用以及建筑物的电磁波防护提供了新的途径.在微波暗室中用弓形反射法进行测试,研究了EPS的填充率、球径大小和样品厚度对吸波性能的影响.结果表明:EPS的填充率(体积分数)为60%,样品厚度为20 mm时的反射率最小,在8～18 GHz范围内,小于-10 dB的带宽达6 GHz,在18 GHz最小反射率达-15.27 dB.在EPS表面包覆一层导电薄膜后,有助于提高多孔材料的吸波性能.     

水泥基复合材料的吸波性能

对普通硅酸盐水泥与吸波材料制成的复合材料的吸波性能进行了研究。为军事掩体、军用机场及其它固定军用目标干扰雷达探测找到了一种合适的方法,也为大型建筑物的电磁波防护提供了一种新途径。研究了羰基铁粉、氧化镍和纳米氧化钛3种吸波材料与水泥制成的复合材料的吸波性能,并分析了纳米氧化钛的用量、分散方式及试样厚度对电磁波反射衰减的关系。结果表明：在8～18GHz频率范围内。纳米氧化钛与水泥制成的复合材料的反射率均小于-7dB,在16．24GHz时其反射率达-16．34dB,反射率小于-10dB的带宽达4．5GHz。     

炭纤维/环氧树脂结构吸波材料电磁特性研究

采用真空CVD炉分别在600,630,660℃对炭纤维进行了热处理,制备了3种不同的炭纤维,然后制备出炭纤维/环氧树脂结构吸波复合材料,最后采用波导法对材料的电磁特性进行了测试,并对其吸波性能进行了模拟。结果表明:炭纤维的热处理温度对材料的介电常数有较大影响。从实验中得出,通过控制炭纤维的热处理温度,可有效地调节炭纤维的介电常数,从而制备出具有良好的吸波性能的结构吸波材料。     

短切导电纤维填充的复合材料吸波性能研究

本文研究了不同含量的短切导电纤维、吸收剂以及不同含量吸收剂/短切导电纤维混合体系对复合材料吸波性能的影响,并在此基础上确定了合理的吸收剂混合比例,研制出8～18GHz频率范围内反射率小于-10dB的结构吸波材料.     

聚苯胺复合材料的电磁吸波性能研究

本文叙述了以过硫酸胺为氧化剂,在盐酸介质中用化学方法制备聚苯胺粉末的方法以及采用镀镍碳毡与聚苯胺填充环氧树脂复合得到复合材料的过程,并讨论了镍电镀层、碳毡、聚苯胺对吸波性能的作用。     

炭黑-矿棉基双层吸波材料的微波吸收性能

单层结构吸波材料只在较窄的频率范围内具有较好的吸波性能,采用多层结构可以有效改善吸波性能。根据阻抗匹配原理以及电磁波传输规律,设计制备了具有阻抗渐变特性的双层结构吸波矿棉板,并采用弓形反射法测试了在2~18 GHz范围的吸波性能。结果表明:阻抗匹配设计是吸波材料设计中的重要环节;双层结构吸波矿棉板的吸波性能随匹配层中炭黑含量的增加而降低,随吸收层中炭黑含量的增加而增强;当匹配层中炭黑含量为1%,吸收层炭黑含量为5%时,样品的反射率在2~18GHz范围内全部小于-10dB;当匹配层中炭黑含量为1%,吸收层炭黑含量为4%时,最小反射率可以达到-41.5dB。该吸波矿棉板具有一定的工程应用价值。     

Electromagnetic and electromagnetic wave‐absorbing properties of the SrTiO3–Epoxy composite

The effects of SrTiO₃ content on the electromagnetic properties and electromagnetic wave‐absorbing characteristics of SrTiO₃–epoxy composites were investigated. Also, the frequency dispersion behavior of the complex permittivity of composites was demonstrated. The complex permittivity and permeability were measured using a network analyzer in the frequency range of 130 MHz to 10 GHz. As the SrTiO₃ content increased, it was found that the complex permittivity and permeability of the composites increased and the resonance frequency moved toward low frequency range. The logarithmic model coincided with the effective permittivity of composite as a function of SrTiO₃ content comparatively well. The resonance frequency of composites was found to show good agreement with the theoretical values calculated by the equation proposed in this article. The electromagnetic wave‐absorbing behavior showed that the center frequency of attenuation curve was shifted to a lower frequency band with increasing the amount of SrTiO₃ and the thickness of composite. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 75–83, 1999     

Microwave absorbing properties of a radar absorbing structure composed of carbon nanotube papers/glass fabric composites

In this study, carbon nanotube papers were employed in fabricating thin and broadband radar absorbing structures (RAS). Different concentrations of the CNT papers have been made by using a vacuum filtration method, with 20 × 20 cm in size and 21-27 μm in thickness. An epoxy resin was added into the CNT paper and then cured to become a composite with 1-5 wt.% of CNTs and 83-309 μm in thickness. The complex permittivity and permeability (ε′, ε″, μ′, μ″) of the CNT paper composites were measured using the transmission/reflection method in the frequency range of 2-18 GHz. The results reveal that the real (ε′) and imaginary (ε″) parts of the complex permittivity are increased with the CNT concentration. The ε′ of 5 wt.% CNT sample reaches 323 at 2 GHz and then decreases to 49.0 at 18 GHz. The ε″ reaches 321 at 2 GHz and decreases to 26.0 at 18 GHz. The CNT paper composite combined with a glass fabric composite used for a dielectric spacer is fabricated for an innovative RAS and the reflection loss is measured using the arch method in a microwave anechoic chamber. The results show that the 5 wt.% CNT paper composite/glass fabric composite absorbers attain maximum reflection loss of −13.3 dB at 12.0 GHz, −13.8 dB  at 10.0 GHz, and −16.0 dB at 7.5 GHz for spacer thickness of 1.5, 2.0, and 3.0 mm, respectively.     

Microwave absorbing properties of ternary linear low‐density polyethylene/carbonyl iron powder/carbon black composites

Linear low‐density polyethylene (LLDPE) was used as polymer matrix, carbonyl iron powder (CIP) and carbon black (CB) were used as fillers, and ternary composites with microwave absorbing properties were prepared by melt blending. Transmission electron microscopy was used to characterize the prepared samples. The absorbing ability (reflection loss) of the prepared composites was measured using the arch method, and the electromagnetic parameters of composites were determined by the transmission/reflection method. The filler contents of CIP and CB have effects on the absorbing peak positions and reflection loss, and there is the optimum filler content in composites to obtain the maximum microwave absorbing. The microwave absorption of LLDPE/CIP/CB composites comes from the combining contributions of the dielectric loss and the magnetic loss. The synergistic effects of CIP and CB effectively improve the microwave absorbing properties of polymer composites. CIP and CB are uniformly distributed in the polymer matrix. The theoretical calculation results of the absorbing ability are in agreement with the experimental results using the transmission line theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

多孔Al2O3/SiC、MoSi2/SiC复合材料的制备及吸波性能

以Si、Al₂O₃、MoSi₂微粉和生物竹材为原料,采用包埋烧结法分别制备出SiC多孔材料、Al₂O₃/SiC、MoSi₂/SiC复合材料。采用XRD、SEM及波导法测试其物相组成、显微结构及吸波性能。结果表明：MoSi₂/SiC复合材料的厚度为2 mm时有明显的吸波特性,有效吸收带宽在X波段的9.65~12.4 GHz频率范围内达2.75 GHz,且最低反射损耗为-38.27 dB。Al₂O₃/SiC复合材料孔道内的Al₂O₃与SiC晶须交缠,形成大量电偶极矩,产生介电损耗;MoSi₂/SiC复合材料除介电损耗外还存在电阻损耗,使得复合材料电磁损耗增加,是较有前途的结构功能吸波材料。     

Properties and potential applications of carbon microcoils/nanocoils

The carbon microcoils (CMCs) were prepared by the Ni-catalyzed pyrolysis of acetylene containing a small amount of H₂S, the morphology and some properties of the CMCs were examined, and the potential applications were discussed. It was found that super-elastic CMCs, which could be extended and contracted by 3–15 times of the original coil length, could be obtained by controlling the reaction conditions. The electrical resistivity (R) of these super-elastic CMCs increased by extending and decreased by contracting. Furthermore, it was found that inductance (L) and capacitance (C) extensively changed with extending and contracting motions. Accordingly, CMCs could be used as high sensitive tactile sensors based on the noble LCR composite hybrid resonance, as well as in MEMS.     

聚醚酰亚胺对炭黑填充环氧树脂复合材料导电性能和吸波性能的影响

利用反应诱导方法设计制备了炭黑(CB)包覆环氧树脂(EP)微球/聚醚酰亚胺(PEI)(EP/PEI/CB)复合材料。研究了该复合材料的微观结构,测量了其导电性能及在Ka波段的吸波性能,并与CB填充EP(EP/CB)复合材料进行了对比。结果表明,在EP/PEI/CB中,CB选择性分布在PEI相中并形成较规则的立体网状连续相,EP为30μm左右大小的微球分散相,与EP/CB相比具有更低的体积电阻率。EP/PEI/CB属于一种谐振腔式吸波体,在33～40 GHz范围具有较好的吸波性能且优于EP/CB,最大吸收峰出现在35.61 GHz,峰值反射率(R)为–17.40 dB,吸收带宽3.22 GHz(R–10 dB).     

Fabrication and microwave absorbing property of WO3@WC with a core-shell porous structure

Special microstructure can significantly improve the microwave absorption property of rare materials. In this paper, porous WC powders were successfully synthesized by spray granulation method. Then, WO₃@WC materials with core-shell porous structure can be prepared after 410 °C heating treatment at different time to form the outer WO₃ oxidation layer. In addition, the microstructure, morphology, phase analysis and electromagnetic property were fully studied by investigating the WC-based materials in different structures. For WO₃@WC core-shell porous materials, when the coating thickness was 2.1 mm, the maximum reflection loss can reach ?19.4 dB at 12.6 GHz, which shows quite good microwave absorbing effects. The core-shell porous structure enhances the original microwave absorption performance due to the multiple reflection reflections and polarizations.     

Effect of various dielectric and magnetic nanofillers on microwave absorption properties of carbon fiber reinforced composites structures

Carbon fiber reinforced unidirectional composite (CFRC) structures were developed by impregnating various dielectric and magnetic nanofillers at a 2% loading concentration of the weight of the matrix. Microwave absorption properties were studied in a broad frequency range of 0.1–13.6 GHz covering the L, S, C, and X frequency ranges. The variation of radar absorption properties with frequency were studied in detail. The effect of dielectric and magnetic materials on microwave absorption properties was also investigated. The results shows that the microwave absorption properties increases with increasing the measuring frequency and maximum absorption was at X frequency range (8.2–12.4 GHz). The Dielectric nanoparticles showed better absorption properties compared with magnetic nanoparticles. Among dielectric nanoparticles, silicon carbide showed maximum reflection loss properties of ?15.32 dB with an absorptance value of 97.06%. Among magnetic nanoparticles, ferric oxide showed a maximum reflection loss of ?9.14 dB with an absorptance value of 87.81%. The addition of nanoparticles significantly improved the complex permittivity, permeability, and loss tangent properties.     

Microwave dielectric properties of polytetrafluoroethylene‐polyacrylate composite films made via aerosol deposition

Few studies have examined the deposition of polytetrafluoroethylene (PTFE) using additive manufacturing and their subsequent properties in microwave devices. The present study examines polytetrafluoroethylene‐polyacrylate (PTFE‐PA) composite films made via aerosol deposition to assess the potential use of PTFE in additive manufacturing processes. The composites are composed of PTFE‐PA core ? shell nanoparticles, synthesized using a seeded emulsion polymerization, containing various PTFE weight fractions up to 50%. The synthesized nanoparticles were sprayed onto a heated glass substrate and subsequently annealed at a temperature above the glass transition temperature of PA and below that of PTFE, rendering a solid film approximately 40 µm thick. A cavity perturbation resonance technique was employed to determine the complex permittivity of the films. As the volume fraction of PTFE increased, the real part of the permittivity ?′ decreased while the imaginary part of the permittivity ?″ showed little variation. The results demonstrate a promising approach for incorporating PTFE into additive manufacturing processes, particularly for microwave devices. © 2016 Society of Chemical Industry