基于铁氧体制备的泡沫吸波材料性能

为了研究铁氧体的电磁性能以及铁氧体引入量的质量分数和样块厚度对材料性能的影响,以玻璃和陶瓷造粒料为基料,炭黑为发泡剂,引入铁氧体,经过球磨、烧结、发泡、退火工艺后制备出泡沫吸波材料.结果表明:900℃处理对铁氧体的电磁性能无明显影响.铁氧体引入量的质量分数为5%和10%的吸波性能优于铁氧体为15%和20%引入量的吸波性能;研究初步显示,该结果是由于铁氧体的引入影响多孔材料的泡孔结构.铁氧体引入量的质量分数为10%时,材料的吸波性能随着样块厚度的增加而增大;样块厚度为50 mm时,材料的有效吸收带宽(反射率小于-10 d B)达18 GHz,反射率低至-23.4 d B.     

泡沫吸波材料结构对吸波性能的影响

为了研究吸波材料结构与吸波性能的关系,以无机泡沫吸波材料作为基体,采用多层复合研究阻抗匹配特性对吸波性能的影响,当材料为"透波层/吸收层"的2层复合结构时,在2.0~18.0 GHz频段反射率均小于-10.0dB,且于12.7 GHz处出现最大衰减峰为-21.5 dB.采用角锥和锥台处理研究材料表面构造对吸波性能的影响,结果表明:表面处理可以明显提高材料吸波性能,且角锥处理优于锥台处理.5×5阵列角锥的有效吸收带宽(反射率小于-10.0 dB)为15.3 GHz,反射率在9.4 GHz处到达最小值为-43.4 dB;8×8阵列角锥的有效吸收带宽(反射率小于-10.0 dB)为18.0 GHz,平均反射率达-34.5 dB.     

Electromagnetic shielding and absorption properties of fiber reinforced cementitious composites

In order to investigate the electromagnetic shielding effectiveness (SE) and absorbing properties of fiber reinforced concrete, steel fiber, carbon fiber and synthetic polyvinyl alcohol (PVA) fiber reinforced concrete were researched. The results show that with the increase of fiber volume fraction, the SE and trend of frequency change of corresponding fiber reinforced concrete are enhanced. When the volume content of steel fiber is 3%, the SE of concrete is above 50 dB and its frequency is above 1.8 GHz. Moreover, in the range of 8-18 GHz, steel fiber, carbon fiber and PVA fiber all can improve the microwave absorption properties of concrete. The concrete with 0.5% carbon fiber can achieve the best absorbing property, the minimum reflectivity is about -7 dB; while steel fiber optimal volume fraction is 2%. The reflectivity curve of PVA fiber reinforced concrete fluctuates with the frequency, and the minimum value of the reflectivity is below -10 dB. The results show that fiber reinforced concrete could be used as EMI(electromagnetic interference) prevention buildings by attenuating and reflecting electromagnetic wave energy.     

Microwave Absorption Properties of the Carbonyl Iron/EPDM Radar Absorbing Materials

Employing carbonyl iron powder and Ethylene-Propylene-Diene Monomer(EPDM)as the absorbent and matrix,rubber radar absorbing materials(RAM)were prepared.Effects of the carbonyl iron volume fraction and the thickness of the RAM on the microwave absorption properties in the frequency range of 2.6-18GHz were studied,and a mathematical analysis was made using the electromagnetic theory. The experimental results indicate that the minimum reflectivity of the radar absorbing materials continuously decreases with the increase of the carbonyl iron volume fraction,and the absorption peak also moves towards the low frequency for the same thickness of the RAM.The minimum reflectivity of the 3.0 mm RAM is -21.7dB at 3.5 GHz when the volume fraction of carbonyl iron is 45%.The reflectivity of the RAM is not in direct proportional to the thickness of the RAM,when the RAM has the same volume fraction of the carbonyl iron.The reflectivity of the RAM presents a regular trend at a given carbonyl iron volume fraction in the frequency range of 2.6-18 GHz.With the increase of the thickness,the maximum absorption peak moves towards low frequency band,the minimum reflectivity firstly decreases and then increases,and the absorption bandwidth for reflectivity<-10 dB firstly increases and then decreases.The microwave absorption properties of the RAM are determined by the thickness and the composition of the radar absorbing materials. Theoretical analysis indicates that the reflectivity of the RAM is determined by the matching degree of the air’s characteristic impedance and the input impedance.     

铁氧体/铁粉混合材料的电磁吸波性能

以铁氧体、铁粉作为吸收剂制备多种电磁吸波涂料,测试与分析所得电磁吸波涂料的电导率、电磁参数及吸波性能。结果表明随着铁粉掺量的增加,所得电磁吸波涂料的电导率增加,在中高频区介电损耗和磁损耗均有所提高;铁粉与铁氧体的质量比为2：8时吸波涂层的吸波性能最好;反射率损耗〈-10.0 dB时的有效吸收频段在中低频区,有效带宽达4.5 GHz,最大吸收率为-16.63 dB。     

纳米Fe3O4及其复合体系的微波吸收特性研究

研究了纳米Fe3O4及其复合体系的微波吸收特性,并分析了吸收机制以及复合组分对吸波性能的影响。结果表明,在Fe3O4/BaTiO3复合体系中,通过调节材料组分可调节吸收峰的位置,复合体系的有效吸收频带较单一材料拓宽。当样品的厚度为2 mm,Fe3O4与BaTiO3的质量比为3:2时,反射率为-10 dB的有效频宽达2.7 GHz,Fe3O4与BaTiO3的质量比为2:3时,反射率为-10 dB的有效频宽可达4 GHz。在Fe3O4/PANI复合体系中,当Fe3O4在复合体系中的质量比为35%左右时,微波吸收率最高,吸收峰值为-21 dB,-10 dB频宽大于4GHz。     

Regulation mechanism of EM parameters in natural ferrite and its application in microwave absorbing materials

1 Introduction Microwave absorbing materials (MAM) refer to a kind of materials that can be used to absorb the emitted electromagnetic (EM) energy and to minimize the wave reflected in the direction of an energy radar receiver. When the EM wave incidents into MAM, it is readily absorbed, attenuated, and changed into heat or other energy. MAM are functional materials that possess special performance for absorbing EM wave. Along with the advancement in radar and microwave technologies, MA…     

双层混杂纤维／炭黑改性环氧树脂复合材料的制备及其吸波性能

通过采用整体压制的方法制备了双层混杂纤维／炭黑改性环氧树脂复合材料,对其吸波性能进行了研究。结果表明：随着炭黑含量的增加,材料的反射衰减峰向低频移动,当炭黑含量较高时,吸收主要作用在低频波段,且存在明显的双反射衰减峰。当炭黑含量为6％时,在13．6GHz处反射衰减峰值可达-20．6dB,≤-10dB的有效带宽为3．6GHz。当炭黑含量为8％时,双反射衰减峰分别在10．6GHz和7．8GHz,峰值分别为-17．0dB和-14．9dB,≤-10dB的有效带宽为6．7GHz。     

钡铁氧体表面化学镀Ni-P合金的制备及性能

为提高钡铁氧体的吸波性能,以钡铁氧体为芯材,采用化学镀的方法制备表面包覆Ni-P镀层的钡铁氧体复合粒子.并利用XRD、SEM、EDS及矢量网络分析仪对其晶体结构、表面形貌、成分、电磁吸收性能进行分析.结果表明:钡铁氧体表面包覆完整的Ni-P合金镀层,化学镀工艺显著改善材料的电磁性能,并提高材料对电磁波的吸收能力,镀后复合粒子在2～18GHz频段内,最大反射率为-24.3dB,大于-10dB的吸收频带宽约2.8GHz.     

电磁污染控制用S带吸波粉煤灰板材的制备

报道了根据λ/4型电磁波吸收原理,通过理论设计和模拟分析,以电厂废渣粉煤灰为介电材料,通过电阻膜复合,成功制备出新型粉煤灰吸波板材.实验表明,电阻膜的电阻为356Ω/□(方块电阻),厚度1.5 cm的粉煤灰板试样在S带(2~4 GHz),-10 dB吸收带宽达到60%以上,在2.9 GHz,最大吸收为-25 dB,新材料可用于室内电磁环境的改善和污染控制,并为粉煤灰的利用提供了新的高附加值途径.     

双频窄带超材料吸波体的设计

为了降低吸波体的雷达散射截面,实现完美吸波,利用超材料的电磁谐振特性,设计了一款开缝双环型结构吸波体。得益于超材料的LC谐振,该结构在1.59和4.06GHz具有超强吸波特性,在谐振频点处,超材料吸波体的某些区域相当于一个电磁波收集器,将能量限制在吸波体内,再转化成热能。经计算验证,该吸波体结构在1.59、4.06GHz的雷达散射截面(RCS)分别为-24、-23dB,远低于传统金属表面结构,能实现理想吸波。     

平板抗电磁辐射材料反射性能的研究及设计

给出了抗电磁辐射平板吸收材料的反射系数公式,并利用MATLAB软件进行了优化设计.设计结果表明,只要选取μ和ε较小值的电磁损耗平板材料就可以使频率在2-18GHz的电磁波的后向反射率达到5dB的工程要求.同时本文的研究和设计方法也为工程上材料的选择与设计具有很好的指导性.     

Effect of chemical vapor infiltration treatment on the wave-absorbing performance of carbon fiber/cement composites

Short carbon fibers were treated at high temperatures around 1100℃ through chemical vapor infiltration technology. A thinner layer ofpyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a cement matrix and the mechanical properties of carbon fiber/cement composites were investigated by scanning electron microscopy （SEM） and other tests. The reflec- tivity of electromagnetic waves by the composites was measured in the frequency range of 8.0-18 GHz for different carbon fiber contents of 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt%. The results show that the reflectivity tends to increase with the increase of fiber content above 0.4wt%. The minimum reflectivity is -19.3 dB and the composites exhibit wave-absorbing performances. After pyrocarbon is deposited on the fiber, all the refiectivity data are far greater. They are all above -10 dB and display mainly wave-reflecting performances.     

铁尾矿粉对碱矿渣泡沫混凝土力学性能的影响

为了研究铁尾矿粉对碱矿渣泡沫混凝土力学性能的影响,用掺入了铁尾矿粉的碱矿渣泡沫混凝土制成100 mm×100 mm×100 mm的立方体试块,分别将混凝土试块养护3、7、28 d后,测试其抗压强度。结果表明：随着铁尾矿粉碱矿渣泡沫混凝土表观密度的增加,其抗压强度不断增大;当铁尾矿粉的掺量从10%增加到30%时,碱矿渣泡沫混凝土的抗压强度逐渐增大;当铁尾矿粉的掺量从30%增加到50%时,碱矿渣泡沫混凝土的抗压强度逐渐减小,且强度损失较明显,随着铁尾矿粉细度的提高,碱矿渣泡沫混凝土的强度逐渐增大。     

新型宽带行波管线性化器设计

现代卫星通讯利用非恒包络数字调制技术,需要高效宽带线性功率放大器。由于行波管高效率和宽带特性广泛应用于卫星通讯中,但是其强非线性造成带外失真和带内干扰影响通讯质量。模拟预失真由于其电路简单易于实现、低功耗、小体积、高可靠性等优点适用于卫星通讯。该文介绍一种宽带行波管线性化器设计,扩展带宽达到1.2 GHz,频率范围19.8~21.0 GHz。测试结果显示该线性化器在带宽1.2 GHz内,非线性可以在幅度扩张2~5 dB,相位扩张20~50°内调整,双音测试时,输入双音信号功率回退6 dB时与行波管级联测试后三阶交调改善17.8 dB,取得很好的改善效果。     

W波段宽带电调信号源

依据电调基频、提取谐波的构想,建立了串联型宽带变容管电调谐波振荡器的电路模型。在3mm频段上完成了电路设计,获得了15%的相对电调带宽,带内最小功率5mW,最大功率超过17mW;输出功率大于5mW的电调带宽达到13GHz。以宽带电调谐波振荡器为核心,完成了3mm电调信号源的系统设计,该信号源工作带宽10GHz,频率显示误差小于100MHz,频率稳定度(2~9)×10-4/h,可以连续波和方波两种方式工作。     

带有方形切角和正交槽线的带通滤波器设计

设计了一种带有两个方形切角和相互正交槽线的平面双模带通滤波器,并进行了仿真研究和分析.该滤波器在中心频率2.04 GHz处,最小插入损耗达到0.09 dB,通带内在2.01～2.14 GHz之间回波损耗大于10 dB,在2.00～2.14 CHz之间插入损耗小于1 dB,3 dB相对带宽为9.31%.通带两侧在1.82...     

Wave-absorbing Properties of a Cement-based Coating with MnO_2/Activated Carbon Composite

MnO_2/activated carbon composite(Mn-ACC) wave absorber was prepared by the reaction between Mn(CH_3COO)_2 and KMnO_4 on activated carbon. Then, a novel cement based composite absorbing coating(CB-CAC) was prepared by adding the Mn-ACC, manganese zinc ferrite and rubber particles into cement. XRD method was used to analyze the reaction products of the Mn-ACC. The tensile bond strength and the wave absorbing properties of the CB-CACs were also tested. The results showed that the crystallinity of MnO_2 formed in the Mn-ACC was poor. Adding Mn-ACC into the CB-CAC led to first increase and then decrease of the tensile bond strength. The tensile bond strength reached 1.89 MPa with 8.51% of the Mn-ACC. The CB-CACs obtained the optimal absorbing properties with the cement, manganese zinc ferrite, Mn-ACC, rubber particles and H_2O mass ratio of 7.5?7.5?1?1?5.5, respectively. The band width of the reflection below-10 dB was up to 8.8 GHz, which accounted for 57.14% of the test band.     

关于45GHz毫米波对矩形阻挡物的绕射研究

基于45 GHz毫米波室内通信测量对木板、镜子以及白铁板的阻挡绕射特性进行了研究.根据阻挡物材料的不同,分别提出三射线和四射线阻挡绕射模型.对12 mm厚的木板、6 mm厚的镜子以及0.35 mm厚的白铁板进行了矩形阻挡绕射测量实验.实验结果表明,在矩形木板阻挡下45 GHz毫米波的平均传输衰减系数约为-4.28 dB,其衰减测量结果与提出的四射线模型仿真结果平均误差为-0.02 dB.在0.35 mm厚的矩形白铁板阻挡下,45 GHz毫米波的平均传输衰减系数约为-18.2 dB.在镜子远离天线的情况下,面对发射天线时的平均传输衰减比背对发射天线时大1 ～2 dB,而在镜子靠近天线的情况下,其面对发射天线时测量的结果与白铁板阻挡下的衰减类似.     

一种电磁耦合馈电双极化毫米波微带天线设计

为拓展双极化毫米波天线的带宽,提出一种基于电磁耦合馈电的微带贴片实现方案.采用共面寄生贴片和空间平行寄生贴片将天线单元的阻抗带宽展宽,采用成对反相馈电技术设计2×2的子阵天线,在中心频点37.5 GHz,驻波2的标准下,天线阵列的相对带宽为6.13%,隔离度30 d B,交叉极化达到-23.6 d B,增益为11.5 d Bi.提出的双极化微带天线,具有频带宽、端口隔离度大、交叉极化低、增益高的特点,天线性能符合毫米波双极化天线的一般工程要求.