宽频带碳团簇型吸波涂层的制备与性能

为满足对吸波涂层薄、轻、宽的要求,通过吸波涂层的优化设计,制备了密度较低的宽频带碳团簇型吸波涂层.该涂层为三层结构,总厚度为2.10 mm,在8～12.4GHz频率范围内,对微波的最小反射率为-42dB,其中反射率小于-10dB的工作频带达90%以上,且性能稳定,有较好的实用前景.     

四针状纳米氧化锌电磁波吸收特性

将四针状纳米ZnO作为吸收剂、环氧树脂为粘结剂制备成吸波涂层,分析了吸波涂层中的四针状纳米氧化锌含量及涂层厚度对吸波性能的影响,当涂层厚度为15mm时,吸收主要集中在15—18GHz波段;当涂层厚度增加到35mm后,样品的吸波性能提高明显,特别在6—11GHz之间的吸波性能提高显著,样品反射率小于-5dB的频率宽度达到136GHz(44—18GHz),其吸波性能相比较微米级ZnO有显著提高. 最后对四针状纳米氧化锌的吸波机理进行了讨论. 所研究的涂层在电磁波屏蔽方面具有较大的应用价值. 关键词： 四针状纳米ZnO 吸波性能 反射率 吸波机理     

圆环单元FSS对改善吸波体雷达吸波特性的影响

设计了圆环单元的频率选择表面（FSS）结构,并将该结构置于吸波材料中构成了复合吸波结构。利用谱域法对该结构进行数值模拟,计算出频率为2～16GHz微波波段的反射系数,并研究了圆环单元尺寸和排布周期对其吸波特性的影响。结果表明：当圆环单元FSS的单元间距为10mm,单元尺寸为3．3mm时,其共振频率的反射率由-8．15dB降低为-14．54dB,-5dB吸波带宽由1．2GHz拓展为3．05GHz;且随圆环单元尺寸增大,共振反射率增加;随单元排列周期增加,吸波材料带宽增大。结果表明,利用FSS可以明显改善吸波材料涂层的吸波性能,通过凋整相关参数可以获得所需的复合吸波结构,拓展FSS在吸波材料中的应用范围。     

基于超材料吸波体的低雷达散射截面微带天线设计

设计了一种高吸波率、宽入射角、无表面损耗层的超材料吸波体, 并将其用于微带天线的带内雷达散射截面(radar cross section, RCS)减缩.实验结果表明: 设计的吸波体的厚度为0.3 mm, 吸波率达99.9%, 相比普通微带天线, 加载该吸波体后的天线在工作频带内法向RCS减缩都在3 dB以上, 最大减缩16.7 dB, 单站RCS在-30°–+30° 角域、双站RCS在-90°–+90°角域减缩超过3 dB, 且天线辐射性能保持不变. 证实了该吸波体具有良好的吸波效果, 可以应用于微带天线的带内隐身. 关键词： 超材料吸波体 微带天线 雷达散射截面     

四针状氧化锌/炭黑复合吸波材料吸波性能的研究

利用四针状氧化锌和炭黑为吸收剂,硅橡胶为基体,制备了一种复合吸波材料,并探究了不同含量的炭黑、四针状氧化锌以及复合材料的厚度对其吸波性能的影响。同时使用了扫描电子显微镜、矢量网络分析仪等仪器对不同质量分数的复合吸波材料样品进行微观形貌和电磁性能的表征。结果表明,在一定范围内,样品的厚度、炭黑的含量和四针状氧化锌的含量增加,会提高样品的吸波性能,当样品的厚度为2 mm,碳粉和四针状氧化锌的质量分数含量分别为8%和10%时,复合吸波材料的最小反射损耗值可以达到-14.68 dB,符合当下吸波材料轻薄宽频的发展趋势。该复合材料具有吸收剂含量低、轻薄、弹性大等优点,在电磁屏蔽领域具有潜在的应用前景。     

微弧等离子喷涂碳纳米管/纳米Al2O3-TiO2复合涂层的吸波性能研究

将碳纳米管与纳米Al₂O₃-TiO₂陶瓷粉末超声共混制备了碳纳米管/纳米Al₂O₃-TiO₂复合粉末,测试了复合粉末在2—18GHz波段的电磁参数.研究表明：随着碳纳米管质量分数的增加,碳纳米管/纳米Al₂O₃-TiO₂复合粉末的复介电常数和损耗角不断增大.当碳纳米管质量分数和厚度增加时,复合粉末对电磁波的反射率峰值先增加后减小,而谐振频率不断向低频移动.采用微弧等离子喷涂制备了7wt%碳纳米管/纳米Al₂O₃-TiO₂复合吸波涂层,当厚度为1.5mm时,涂层最小反射率为-24.0dB,当厚度为2.0mm时,涂层小于-10dB的频带宽为3.60GHz,当温度为500℃高温时,1.0mm厚的涂层最小高温反射率为-12.2dB,小于-10dB频带宽为2.0GHz.复合涂层的实际厚度D与理论厚度d呈线关系：d=0.898D+0.515. 关键词： 等离子喷涂 碳纳米管 2O₃-TiO₂')" href="#">纳米Al₂O₃-TiO₂ 吸波性能     

碳纳米管复合吸波涂层微波吸收性能的模拟计算

如何利用碳纳米管复合吸波涂层的参数进行吸波性能优化是电磁屏蔽研究的热点之一.涂层参数对吸波性能影响的研究主要停留在实验探索阶段,而碳纳米管的结构参数对吸波性能影响的研究鲜有报道.因此,从微观结构层次研究涂层参数对吸波性能的影响有重要意义.基于多壁碳纳米管的等效电路,利用碳纳米管结构参数与等效电路各元件参数的关系,研究了碳纳米管损耗微波的机理,建立了碳纳米管结构参数与微波反射率的关系式.根据此关系式,利用Matlab软件模拟计算了碳纳米管管长、管径、涂层中碳纳米管的含量以及涂层厚度对微波反射率的影响.模拟计算结果表明:涂层的微波反射率随碳纳米管含量变化的模拟曲线与实验结果符合;碳纳米管含量和厚度是影响吸收峰位置和吸收强度的重要参量,而碳纳米管直径和长度是主要影响吸收峰强度的参量.     

含有源频率选择表面可调复合吸波体

基于传输线等效理论,设计了含有源频率选择表面(active frequency selective surface,AFSS)的三层可调复合吸波体,第一层是表面层,为AFSS衬底;中间层是AFSS层,由频率选择表面(frequency selective surface,FSS)和PIN二极管阵列构成;第三层是介质层.反射率测量结果表明,通过调节PIN二极管阵列偏置电压可以动态调节吸波体反射特性,在偏置电压为5 V时,可获得最佳吸波性能,在5—15 GHz和5.3—13 GHz频段分别可获得-8 dB和- 关键词： 频率选择表面 复合吸波材料 反射率 PIN二极管     

基于超材料的吸波体设计及其波导缝隙天线应用

设计了一种基于超材料电磁特性的吸波体, 并将其应用于波导缝隙天线. 该吸波体是由两层金属及其中间的有耗介质组成, 上层金属是由刻蚀交叉缝隙的贴片形成的电谐振器, 下层金属不刻蚀, 作为整个金属地板. 通过优化结构参数, 得到了一种极化不敏感、宽入射角的超薄吸波体, 吸波率达到99.1%, 厚度只有约0.01λ. 将该吸波体应用与波导缝隙天线, 在5.48-5.7 GHz工作频段内, 天线雷达散射截面减缩都在3 dB以上, 在鼻锥方向的-25°-+25°范围的角度上, 天线雷达散射截面减缩均在5 dB以上, 雷达散射截面减缩最大超过12 dB, 而天线前向增益仅降低了0.53 dB. 实验结果与仿真结果符合得较好, 证实了该吸波体具有好的天线雷达散射截面减缩效果, 可以应用于天线目标的隐身.     

涂层球体混合体系的等效介电常数计算及应用

采用一定的包覆工艺制备了炭黑包覆发泡型聚苯乙烯(EPS)颗粒，用包覆的颗粒作为填料制备了环境适应性强的吸波材料. 将涂层球体混合体系作为密实整体考虑，计算了炭黑含量1%时的等效介电常数，并用计算结果预测了吸波性能. 与实验值对比表明，计算值是基本准确的，可以应用于新型微波暗室用吸波材料的设计和优化. 关键词： 炭黑 吸波材料 等效介电常数 吸波性能     

Strain rate effects on compressive behavior of covalently bonded CNT networks

In this study, strain rate effects on the compressive mechanical properties of randomly structured carbon nanotube (CNT) networks were examined. For this purpose, three-dimensional atomistic models of CNT networks with covalently-bonded junctions were generated. After that, molecular dynamics (MD) simulations of compressive loading were performed at five different strain rates to investigate the basic deformation characteristic mechanisms of CNT networks and determine the effect of strain rate on stress–strain curves. The simulation results showed that the strain rate of compressive loading increases, so that a higher resistance of specimens to deformation is observed. Furthermore, the local deformation characteristics of CNT segments, which are mainly driven by bending and buckling modes, and their prevalence are strongly affected by the deformation rate. It was also observed that CNT networks have superior features to metal foams such as metal matrix syntactic foams (MMSFs) and porous sintered fiber metals (PSFMs) in terms of energy absorbing capabilities.     

Fabrication of Fe/Fe<Subscript>3</Subscript>C-functionalized carbon nanotubes and their electromagnetic and microwave absorbing properties

Fe/Fe₃C-functionalized carbon nanotubes (CNTs) have been prepared by the floating catalyst chemical vapor-deposition method. It is demonstrated that the Fe and Fe₃C nanostructures are both encapsulated in the CNTs or decorated on the surface of CNTs. The Fe/Fe₃C content in the composites can easily be adjusted by changing the ferrocene concentration in the preparation. The electromagnetic properties of the CNTs have been evaluated in the frequency range of 2–18 GHz, and the nanocomposites exhibit excellent microwave absorbing performance. The CNT composites with higher Fe/Fe₃C content show enhanced microwave reflection losses. The significant influence of the Fe/Fe₃C nanostructures on the microwave absorption is realized by tuning the characteristic impedance of the nanocomposites. With increasing thickness, the maximum reflection loss peak shifts to lower frequency. The microwave absorbing performance of the composites is mainly caused by dielectric loss, resulting from the continuous CNT networks with excellent electrical conductivity.     

Control of morphology for energy dissipation in carbon nanotube forests

This study focuses on the effect of carbon precursor on the carbon nanotube (CNT) morphology and energy dissipation. Benzene, toluene, and m-xylene were used as carbon precursors for the synthesis of CNT forests following a chemical vapor deposition process. The results indicate that substituents on the benzene ring increase entanglement in the CNT forests. The absorbed energy was slightly greater for CNT forests synthesized using m-xylene than for toluene, but was much smaller for benzene. When compressed to a strain of 0.67, the toluene CNTs absorbed more energy than the m-xylene CNTs. The restitution was much higher for the forests synthesized with m-xylene than toluene while it further decreased for the forests made with benzene. A strong correlation is also observed between the average diameter of the CNTs and the number of methyl substituents on the benzene ring. The control of the entanglement of the CNT forests can potentially be used to design high energy absorbing composites for blast energy dissipation.     

Super-hydrophobic transparent surface by femtosecond laser micro-patterned catalyst thin film for carbon nanotube cluster growth

In this work, super-hydrophobic surfaces were fabricated by femtosecond laser micro-machining and chemical vapor deposition to constitute hybrid scale micro/nano-structures formed by carbon nanotube (CNT) clusters. Nickel thin-film microstructures, functioning as CNT growth catalyst, precisely control the distribution of the CNT clusters. To obtain minimal heat-affected zones, femtosecond laser was used to trim the nickel thin-film coating. Plasma treatment was subsequently carried out to enhance the lotus-leaf effect. The wetting property of the CNT surface is improved from hydrophilicity to super-hydrophobicity at an advancing contact angle of 161 degrees. The dynamic water drop impacting test further confirms its enhanced water-repellent property. Meanwhile, this super-hydrophobic surface exhibits excellent transparency with quartz as the substrate. This hybrid fabrication technique can achieve super-hydrophobic surfaces over a large area, which has potential applications as self-cleaning windows for vehicles, solar cells and high-rise buildings.     

On the thermal expansion of CNT/Cu composites for electronic packaging applications

Carbon nanotubes (CNTs) exhibit both excellent high thermal conductivity and low coefficient of thermal expansion (CTE), which are an ideal reinforcement in composite materials for high performance electronic packaging applications. In the present study, CNT/Cu composites containing CNTs varying from 0 vol.% to 15 vol.% are prepared, and their CTE behavior is studied in detail. The results indicate that the CTE of 0–10 vol.% CNT/Cu composites is significantly decreased with increasing CNT content. However, as the CNT content increases to 15 vol.%, the decrease in CTE of the composites is pronouncedly reduced. Possible mechanisms are discussed in combination with CTE model predictions.     

Absorption of Long Waves by Nonresonant Parametric Microstructures

Using simple acoustical and mechanical models, we consider the conceptual possibility of designing an active absorbing (nonreflecting) coating in the form of a thin layer with small-scale stratification and fast time modulation of parameters. Algorithms for space-time modulation of the controlled-layer structure are studied in detail for a one-dimensional boundary-value problem. These algorithms do not require wave-field measurements, which eliminates the self-excitation problem that is characteristic of active systems. The majority of the considered algorithms of parametric control transform the low-frequency incident wave to high-frequency waves of the technological band for which the waveguiding medium inside the layer is assumed to be opaque (absorbing). The efficient use conditions are found for all the algorithms. It is shown that the absorbing layer can be as thin as desired with respect to minimum spatial scale of the incident wave and ensures efficient absorption in a wide frequency interval (starting from zero frequency) that is bounded from above only by a finite space-time resolution of the parameter-control operations. The structure of a three-dimensional parametric black coating whose efficiency is independent of the angle of incidence of an incoming wave is developed on the basis of the studied one-dimensional problems. The general solution of the problem of diffraction of incident waves from such a coating is obtained. This solution is analyzed in detail for the case of a disk-shaped element.     

Low-voltage soft robots based on carbon nanotube/polymer electrothermal composites

Nowadays, soft robots have become a research hot spot due to high degree of freedom, adaptability to the environment and safer interaction with humans. The carbon nanotube (CNT)/polydimethylsiloxane (PDMS) electrothermal composites have attracted wide attention in the field of flexible actuations due to large deformation at low voltages. Here, the preparation process of CNT/PDMS composites was designed and optimized, and electrothermal actuators (ETAs) were fabricated by cutting the CNT/PDMS composite films into a "U" shape and coating conductive adhesive. The deformation performance of the ETAs with different thicknesses at different voltages was studied. At a low voltage of about 7 V, the ETA has a deformation rate of up to 93%. Finally, two kinds of electrothermal soft robots (ETSRs) with four-legged and three-legged structures were fabricated, and their inchworm-like motion characteristics were studied. The ETSR2 has the best motion performance due to the moderate thickness and three-legged electrode structure.     

介质涂覆位置对双S弯排气系统电磁散射特性影响研究

尾喷管作为飞行器后向强散射源之一, 可通过特殊结构设计和介质涂覆缩减其雷达散射截面(RCS). 本文采用迭代物理光学法和阻抗边界条件的混合计算模型, 研究了6种涂覆方案和不涂覆时双S弯排气系统的电磁散射特性, 采用所提出的射线行程追踪方法提高了几何消隐计算效率, 利用前后向迭代方法加速收敛并采用openMP和MPI并行技术缩短计算时间, 获得了在X波段下7种模型的RCS随探测角度的变化规律. 研究结果表明, 介质涂覆能够有效抑制双S弯排气系统的RCS; 合理的介质涂覆方案不仅具有明显的抑制效果, 同时又具有经济性好、重量轻及涂覆方便等优势; 相比全涂覆方案, 仅在喷管出口附近涂覆的方案, 可减少73.6%的涂覆材料, 且其RCS的最大增幅不超过15.6%, 相比未涂覆方案, RCS 至少降低18.5%. 同时所开发的计算程序可用于任意腔体电磁散射特性的计算, 可为带介质涂覆腔体试验提供技术支撑.