碳纳米管材料低频电磁参数及吸波产热特性

微波的热利用技术促进了吸波材料的应用研究。碳纳米管(CNTs)是近年来新兴的强吸波材料,具有密度小、比表面积大、量子尺寸效应的特点。对碳纳米管吸波材料的复介电常数和复磁导率随碳纳米管含量的变化进行探究。在此基础上,以石蜡油为蓄热介质探究了碳纳米管材料在微波辐照下吸波产热特性。同轴传输法适用于小型样品的测量,具有误差小的优点,故采用此种方法作为测量电磁参数手段。对碳纳米管电磁参数测量实验结果表明,碳纳米管吸波材料在低频下对于微波能的损耗兼具电损耗和磁损耗。对碳纳米管吸波产热特性实验结果表明,碳纳米管是一种强吸波材料。     

吸波材料的微波损耗机理及结构设计

就吸波材料与电磁波的相互作用及其损耗机理进行了阐述。通过对吸波材料与电磁波相互作用的研究和不同类型吸波材料微波损耗机理的详细探讨，对研制高宽频、质轻、红外微波隐身兼容复合型吸波材料进行了展望，并提出了材料结构设计的思路。     

环氧树脂/碳纤维吸波涂层电磁特性的实验研究

对环氧树脂/碳纤维吸波涂层的电磁特性进行了研究,包括对体系电磁参数及反射率的测量,纤维长径比、体积含量对电磁参数及吸波性能的影响,以及电磁参数与吸波性能的关联。结果表明,在8～18GHz频段内,随碳纤维长度的增大其介电常数实部与虚部值均增大,磁导率虚部值增大,吸收效果逐渐增强;随碳纤维体积含量的增加,其介电常数实部与虚部值均显著提高,吸收效果逐渐增强,吸收峰向低频方向移动。     

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。     

聚苯胺包覆短碳纤维的制备及电磁性能研究

对短碳纤维(SCF)硝酸氧化处理后,采用聚苯胺原位氧化聚合法对其进行包覆改性,制备聚苯胺包覆改性SCF,以改善SCF的电磁性能.采用XPS、SEM对聚苯胺包覆的SCF进行了微观结构和形貌的分析,结果显示聚苯胺层包覆完整、致密,且聚苯胺和SCF表面之间存在化学键合作用.采用PNA-LN5230A微波网络测试仪测定了聚苯胺包覆SCF的电磁性能(复介电常数和复磁导率),并对2mm厚度下的吸收和反射损耗进行了分析,研究了以此为填料制备的涂膜的电磁屏蔽性能和导电性.结果表明,在50 MHz～2 GHz频率范围内,相对于未包聚改性的短碳纤维,导电聚苯胺/碳纤维(PASCF)的复介电常数实部和虚部都有所提高,磁损耗正切为O,为电损耗型材料,而不导电聚苯胺/碳纤维(NPASCF)的复介电常数实部和虚部都有所下降,而磁损耗止切高达O.09,显示出弱电磁性;采用Matlab 6.5软件进行屏蔽性能分析,导电聚苯胺包覆碳纤维的吸收损耗可达4.654 dB,不导电聚苯胺包覆碳纤维(NPASCF)的吸收损耗为1.105 dB:以PASCF为填料制备的涂膜表面电阻率为1.02 Ω·m-2,电磁屏蔽效能值约为17 dB,以NPASCF为填料制备的涂膜表面电阻率为2.32×1011Ω·m-2,电磁屏蔽效能值可达8 dB.     

TiO2/SiO2/NiFe2O4介孔材料的制备和电磁特性

NiFe2O4纳米粒子做磁性载体,苯乙烯、正硅酸乙酯为原料,KH-570为交联剂,采用乳液聚合法制备了PS/SiO2/NiFe2O4磁性微球材料。以PS/SiO2/NiFe2O4磁性微球为核,十二烷基磺酸钠和聚乙烯吡咯烷酮作模板剂,钛酸丁酯做钛源,制备得到多层介孔复合微粒TiO2/SiO2/NiFe2O4。通过XRD、SEM对磁性复合微粒的结构进行了表征,结果表明,TiO2/SiO2/NiFe2O4是具有核壳结构的中空介孔微粒。采用矢量网络分析仪测试了NiFe2O4、SiO2/NiFe2O4、TiO2/NiFe2O4、TiO2/SiO2/NiFe2O4复合材料的微波电磁参数,SiO2、TiO2对磁性微粒的电磁参数有明显的改善,可较好的解决吸波涂层设计中的阻抗匹配问题。     

环氧树脂/玻璃纤维/石墨烯复合材料的电磁吸波性能

为了制备具有一定电磁吸波性能的结构型吸波材料,采用喷涂法制备了负载石墨烯微粒的玻璃纤维预浸料,并通过热压罐成型工艺进行固化,制备了环氧树脂/玻璃纤维/石墨烯吸波复合材料。研究了石墨烯含量对吸波复合材料电磁性能、吸波性能和力学性能的影响。通过三点弯曲测试结果可知,随着石墨烯含量的增加,环氧树脂/玻璃纤维/石墨烯吸波复合材料的弯曲强度先增大后减小,弯曲弹性模量增大,但总体变化幅度较小。矢量网络分析仪测试结果表明,随着石墨烯含量的增加,环氧树脂/玻璃纤维/石墨烯复合材料的介电常数逐渐增大,磁导率几乎不变,介电损耗正切角值逐渐增大。分析反射损耗计算结果可知,环氧树脂/玻璃纤维/石墨烯吸波复合材料的吸波性能主要由复合材料的厚度和石墨烯含量决定,随着复合材料厚度的增大,反射损耗峰值逐渐朝低频移动;随着石墨烯含量的增加,复合材料的吸波性能逐渐增大。当石墨烯质量分数为2.5%、复合材料厚度为1.7 mm时,环氧树脂/玻璃纤维/石墨烯复合材料具有最佳的吸波效果,此时反射损耗峰值为-11.8 dB,有效带宽为1.45 GHz。     

聚氨酯掺杂铜粉涂层的电磁特征及其涂层织物的吸波性能

将掺杂了不同含量微米铜粉的聚氨酯（PU）涂料通过涂层工艺涂敷在棉织物上制成吸波涂层织物,并利用扫描电子显微镜、红外光谱和矢量网络分析仪等测试了不同铜粉含量聚氨酯涂层的介电常数、磁导率和电磁损耗等电磁性能,同时还探讨不同铜粉含量涂料对涂层织物电磁吸收性能的影响。结果表明,在 8~13 GHz 的频段范围内,随着涂层中铜粉含量增加,涂层介电常数实部与虚部均增大,铜粉具有良好的介电性能,在外加电场的作用下产生极化,对电磁波产生介电损耗;铜粉不属于磁损耗材料,对电磁波产生磁损耗较小;当铜粉的含量较低（3 %,质量分数,下同）时,涂层材料的吸波与电磁屏蔽性能较弱,当含量由5 %增加至11 %时,在9.0、10.5、12.8 GHz处反射损耗最低分别为-20.4、-28.3、-25.6 dB,有效吸收带宽分别为0.2、1.3、1.1 GHz,电磁屏蔽效能分别由12.24、16.59、21.1 dB增加至25.92 dB。     

CB/MnO2/ABS复合平板材料的吸波效能

通过在CB／ABS复合材料中加入MnO2发现,在2～18GHz频率范围内,MnO2能有效吸收电磁波。分析表明MnO2片状和针状颗粒形状以及较高的介电常数是损耗电磁波的主要原因。     

Comprehensive study of electromagnetic wave absorption properties of GdMnO3-MoSe2 hybrid composites

Recently, the public does not avoid the use of RF/microwave communication and non-communication devices, which means they will be constantly exposed to radiation from those devices, which will worsen their health in the long term, as well as there will be interference and coupling effects between devices. In this paper, a novel and high-performance absorber material is created and analyzed. The microscopic and macroscopic properties of Gadolinium Manganite (GdMnO₃), Molybdenum Diselenide (MoSe₂), and three mixtures of GdMnO₃-MoSe₂ (GdMo) with 20, 30, and 40% filler loading were investigated. The procedure for producing the five materials was explained and described in detail. The mixture of GdMo with 20, 30, and 40 wt% filler loading has the features of GdMnO₃ and MoSe₂. For macroscopic analysis, the measured relative complex permittivity and permeability of the five synthesized materials are modeled using the Lorentz dispersion model. Among the five study materials, GdMo with 40 wt% filler loading shows the highest electric and magnetic losses with loss tangent, tan δ_e ≈ 0.228 and tan δ_m ≈ 0.38 where the absorption performance is better compared to its pristine components, namely GdMnO₃ and MoSe₂. Based on the transmission theory of metal plate backing materials, the GdMo with 40 wt% filler loading and thicknesses ranging from 0.0014 m to 0.0021 m, which is terminated by a metal plate on the back side, exhibited the optimum microwave absorption performance with a minimum reflection loss value better than ?20 dB at X-band operating frequency. Without a metal backing, a 0.008 m thickness of GdMo with 40 wt% can achieve reflection loss, RL of ?10 dB from 9.2 GHz to 12.4 GHz, and RL of ?20 dB from 11.1 GHz to 12.4 GHz.     

无填料热源塔吸热效率实验

建立无填料热源塔热泵系统实验平台,研究不同进风位置、喷嘴位置、室外空气干球温度、相对湿度、风量、溶液入口温度下无填料热源塔吸热效率的变化规律。结果表明：进风位置和喷嘴位置对热源塔的吸热效率会产生影响,下喷式无填料热源塔吸热效率高于上喷式无填料热源塔;干球温度与吸热效率无明显相关性,但干球温度升高,热源塔从空气中吸收的总热量增加;相对湿度和风量升高,吸热效率提高;溶液入口温度升高,热源塔的吸热效率明显提高。与其他参数相比,溶液入口温度对热源塔的吸热效率影响最大。     

Continuous growth of carbon nanotubes on the surface of carbon fibers for enhanced electromagnetic wave absorption properties

As electromagnetic wave (EMW) pollution has become a serious problem in daily life, lightweight, efficient, and mass-produced EMW-absorbing materials are urgently needed. Herein, we developed a novel method for the continuous growth of carbon nanotubes (CNTs) on the surface of polyacrylonitrile (PAN)-based carbon fibers (CFs) by chemical vapor deposition (CVD), which can be applied to mass production. The obtained CF/CNT composites demonstrate outstanding EMW absorption capability, exhibiting a -58.75 dB reflection loss (RL) at a thickness of 1.54 mm. An effective absorption bandwidth (RL < -10 dB) of 4.24 GHz (13.76–18.00 GHz) was achieved at a thickness as low as 1.25 mm, which almost covers the entire Ku band. The excellent EMW-absorbing performance can be attributed to the 3D conductive network constructed by the CNT forest, which effectively promotes multiple reflections and scattering, and further favors dipole and interface polarizations. The mechanical properties of CF, CF-electrochemical anodic oxidation (EAO), and CF/CNT composites were examined, the results showed that the single-filament tensile strength of CF/CNT@0.07 and CF/CNT@0.09 was effectively improved. Our work suggests that the novel CF/CNT composite is a promising material for EMW absorption and strength enhancement owing to its light weight, high strength, low thickness, and good scale-up ability.     

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     

Enhanced dielectric and microwave absorption properties of LiCoO2 powders by magnesium doping in the X-band

The solid-state reaction was adopted to prepare a series of LiCo_1−xMg_xO₂ powders doped with different amount of Mg²⁺. The XRD patterns reveal single phase for all the prepared materials. The shift of the electronic structure of LiCo_1−xMg_xO₂ has been investigated by X-ray photoelectron spectroscopy to confirm the single phase for material. Influence of dopant amount on the electromagnetic properties of LiCoO₂ powders was analyzed. The dielectric and the microwave absorption properties were evaluated. Results showed that with the increase in Mg the complex permittivity decreased after increasing. Maximum values of both real part (ε′ = 16.2 at 8.2 GHz) and imaginary part (ε″ = 4.1 at 8.2 GHz) were obtained for x = 0.06. Monolayer absorbent containing 75 wt% LiCo_0.94Mg_0.06O₂ had the peak microwave absorption properties in a thickness of 2.1 mm. The available bandwidth (<−10 dB) was obtained in 8.4-10.2 GHz and the minimum reflection loss was −50.4 dB, which indicated that LiCo_1−xMg_xO₂ powders would be potential materials as microwave absorption.     

Synthesis and electromagnetic characterization of frequency selective radar absorbing materials using carbon nanopowders

A new method for the synthesis of multilayered radar absorbing materials is analyzed by using carbon nanomaterials. With respect to the literature, a desired profile of reflection coefficient is a priori established as a function of the frequency. The goal of the synthesis is to follow this target profile by computing thickness and type of the material of each layer until the reflection coefficient of the electromagnetic-wave absorber best approximates the wanted reflection coefficient. The material available for each layer is epoxy-resin reinforced by different kind of carbon-based nano/micro powders: graphene nanoplatelets, carbon nanofibers, multi-walled carbon nanotubes and polyaniline. The dielectric characterization of the composite materials is performed in the frequency range 2–18 GHz. The synthesis uses evolutionary computation by drawing on the electric permittivity of composite materials. Three square layered electromagnetic wave absorbers of 25 cm side are manufactured. The comparison between the target, the simulated and the measured reflection coefficients shows a good agreement thus confirming the scientific validity of the dielectric characterization and the proposed design method. Finally, a finite element analysis has been carried out to explain the mechanism of electromagnetic wave absorption by a multilayer and to simulate a low radar observable naval military gun.     

缠绕式变频电磁水处理器电磁频率对抑垢效果的影响

针对缠绕式变频电磁水处理系统,利用ANSYS仿真软件对处理腔内水溶液的磁感应强度和感生电流进行分析,探究水体内磁感应强度以及感生电流做功与激励信号频率的内在关系,并利用电磁抑垢效果在线评价实验台,通过改变缠绕式处理腔中电磁场的频率大小分析其对特定硬水循环换热实验管道抑垢效果的影响规律,进而寻求理想的抑垢频率。实验结果表明,电磁频率在分界频率附近时水处理系统能到达较长的污垢诱导期以及较好的抑垢率,抑垢效果最佳。     

全热换热膜的制备及性能研究

首先通过将溶解有LiCl的壳聚糖溶液与8%(质量分数,下同)的聚乙烯醇胶液进行混合得到涂料,涂覆到多孔的聚乙烯膜上制备换热膜,对壳聚糖溶液添加量进行研究,当壳聚糖溶液含量为80%时,所制备的换热膜透湿率高达2 600 g/(m²·24 h),且具有较好的耐水洗性能;其次将该换热膜经过裁切组装成换热芯,该换热芯在风量为100 m³/h时的送风净新风率高达95%,制热状态下的焓效高达77.8%,具有较好的节能效果;最后将换热芯的新风机里运行3个月后再次测试,与放入新风机运行前的数据进行对比,性能并未衰减。     

Microstructure and electromagnetic properties of flake-like Nd-Fe-B nanocomposite powders with different milling times

The microstructure and electromagnetic properties of melt-spun Nd-Fe-B nanocomposites, which have been dealt with by the ball milling process with different milling times, are studied specifically in this paper. The powder size ranges from 20 μm to 5 μm after different milling times. Moreover the powder particles even remain flake-like shape after 11 h milling time. X-ray diffraction spectra strongly suggest that all samples only have the single α-Fe phase. By using the complex permeability (μ = μ′ − μ″) and permittivity (ε = ε′ − ε″) within 2 to 18 GHz frequency range, determined by vector network analysis, the experiment shows that the permeability of flake-like Nd₃Fe₆₈Co₁₈B₁₁ can be increased while its permittivity is decreased by increasing the milling time. For the sample with 11 h milling time, its imaginary permeability μ″ can be increased to an abnormal state below the frequency of 6 GHz. Based on transmission line theory, it is calculated that the Nd₃Fe₆₈Co₁₈B₁₁ composites can achieve their optimal reflection loss (RL = − 8 dB) at 3.7 GHz with a matching thickness of 1.5 mm. This paper shows the possibility to obtain good microwave absorbing properties at a proper milling time for melt spun Nd-Fe-B nanocomposites.