Novel optimization method of single square FSS impinged and cascaded radar absorbing composites

It is well known that radar absorbing potentiality of existing magneto-dielectric composites can be significantly enhanced by the application of frequency selective surface (FSS) and cascaded electromagnetic (EM) structures. But the optimization of such complex EM structures and validation of the adopted optimization strategy is still a very challenging task for the researchers. Therefore, in this study, an effective effort has been made for the optimization and the corresponding validation for Single Square FSS (SS-FSS) impinged and cascaded radar wave absorbers using advanced computational EM software’s like FEldberechnung fur Korper mit beliebiger Oberflache – a German acronym (FEKO) and high frequency structure simulator (HFSS). In addition, a critical analysis of dielectric constant (ε′) has been carried out to select the best combination of composites for the development of efficient radar wave absorbers. A comparison between optimized and simulated results have been carried out to examine the effect of advanced EM approaches over reflection loss (RL) characteristics of composite radar absorbing materials (CRAMs). A rapid change in radar absorption properties of composites has been observed after the application of SSFSS and cascading. A SS-FSS impinged composite has been found to provide a wide absorption bandwidth of 3.6 GHz at X-band. A cascaded absorber having layer thickness 1.8 mm provides a peak RL of ?42.6 dB at 10.6 GHz with an absorption bandwidth of 2.5 GHz. The strong agreement between mathematical model, HFSS and FEKO results clearly reflects the efficiency of adopted approach for distinct practical EM applications.     

Double-layer type microwave absorber made of magnetic-dielectric composite material

Changing the combination of 2^nd layer in a double-layer type microwave absorber, the matching frequency (8.10–10.88 GHz), maximum reflection loss and matching thickness at the matching frequency could be systematically controlled and compared with those of single-layer type microwave absorber. Received: 2 December 2001 / Accepted: 20 January 2002     

含Minkowski活性碳毡电路屏复合材料的吸波性能研究

研究了含Minkowski活性碳毡电路屏复合材料的微波吸收特性,并对电路屏的吸波机理进行了初步的探讨。结果表明,含Minkowski活性碳毡电路屏复合材料的吸波性能与电路屏阵列单元的尺寸密切相关,经合理设计,复合材料在5.3～18GHz频率范围内有-10dB以下的吸收,有效带宽达12.7GHz。复合材料对电磁波的主要吸收机制是电磁波在电路屏和反射板之间的多次反射、衰减。     

氧化铟锡(ITO)薄膜的透明吸波特性研究

利用直流磁控溅射技术室温下在柔性聚酯薄膜衬底上制备了ITO薄膜,将ITO薄膜与有机玻璃和空白聚酯薄膜等介质材料组合成复合结构,最终得到吸波能力较强的透明吸波体.该吸波体在Ku带(12～18GHz)范围波段衰减低于-10dB,峰值超过-20dB,且在可见光区透光率达到68%.     

聚苯胺与Si/C/N复合粉体的制备及其微波介电特性

用原位合成法在Si/C/N纳米粉表面包覆聚苯胺,制备出聚苯胺与Si/C/N复合材料,复合粉体近似球形,粒径为1～3μm.研究了聚苯胺与Si/C/N复合粉在8.2～12.4GHz的微波介电特性,与纳米Si/C/N相比,聚苯胺与Si/C/N复合粉体的ε′、ε"和tanδ有所增加,ε′在5.16～5.88范围内波动,ε"的变化范围为1.96～2.53,介电损耗角正切值达到了0.43,具有较好的微波介电特性.在8～12.4GHz范围内随频率的增加,聚苯胺与Si/C/N复合粉体的ε′、ε"和tanδ值均出现频响效应,是较为理想的微波吸收材料.     

钩针工艺之于活性碳纤维/环氧树脂电路屏吸波复合材料的设计

通过钩针工艺将活性碳纤维(ACF)和玻璃纤维(GF)混编,提高了频率选择性表面(FSS)的可设计性和复杂性,制备了ACF钩针结构单元电路屏碳纤维/环氧树脂(ACF/EP)复合材料。研究了不同编织结构和ACF质量分数对复合材料吸波性能的影响。结果表明:ACF质量分数为100%的4针枣形FSS的ACF/EP复合材料和质量分数为50%的16针枣形FSS复合材料的最大反射损耗(RL)可以达到-50dB以上,有效吸收带宽(RL-10dB)达10GHz以上。复杂的钩针设计使ACF/EP复合材料的多孔结构增多,有效吸收带宽变宽,4针枣形结构具有较多不规整孔径使吸波效果显著。适量的ACF质量分数结合编织结构有利于获得理想的CF/EP吸波复合材料。     

玻璃包覆磁性合金微丝复合媒质的微波介电性能

利用熔融拉微丝法制备了玻璃包覆非晶态磁性合金微丝，采用微波矢量网络分析仪及同轴线法测试了不同含量和排布的玻璃包覆磁性合金微丝-石蜡复合媒质的微波复介电常数，并和铁镍合金微丝-石蜡复合媒质的介电性能进行了比较。结果表明玻璃包覆磁性合金微丝复合媒质具有比相同含量的铁镍合金微丝复合媒质具有更低的复介电常数。圆周排列的玻璃包覆磁性合金微丝复合媒质在所测试的微波频率范围内具有电偶极子共振特征，一定含量的短玻璃包覆磁性合金微丝复合媒质具有电禁带结构。讨论了含量和排列方式影响玻璃包覆非晶磁性合金微丝复合媒质微波介电性能的原因。     

Design of a polarization-independent,wide-angle,broadband visible absorber

Many optical systems benefit from elements that can absorb a broad range of wavelengths over a wide range of angles, independent of polarization. In this paper, we present a polarization-independent, wide-angle, broadband absorber in the visible regime that exploits strong symmetric and asymmetric resonance modes of electromagnetic dipoles. It makes use of a bilayer cross-pattern structure which is simple, having five layers that include two stacks of metal ribbon in cross-patterns, two dielectric spacers and a metal reflecting layer. Simulations show that the design exhibits a significantly enhanced absorption property when compared to a device with a bilayer metal film structure or any other complex structure of cross-patterns that have no intersection angle. The maximum absorption efficiency of the device is 100% at resonances, and its absorption characteristics can be maintained over a wide range of angles of incidence – up to ± 60° – regardless of the incident polarization. This strategy can, in principle, be applied to other material systems and could be useful in diverse applications, including thermal emitters, photovoltaics and photodetectors.     

碳毡电路模拟吸波复合材料的研究

分别研究了含矩形碳毡电路屏和“十”字形碳毡电路屏吸波复合材料的微波吸收特性，并对碳毡电路屏的吸波机理做了初步的探讨。结果表明，碳毡电路模拟吸波材料的吸波性能与电路屏阵列单元的结构和尺寸密切相关。矩形电路屏阵列单元中矩形缝隙的长或宽增大，材料的吸波性能提高；矩形缝隙之间的距离增加，材料的吸波性能降低。本实验条件下当矩形缝隙的长、宽和间距分别为24、12和6mm时，材料可获得8．56GHz的有效带宽和-25dB的最大反射衰减。“十”字形电路屏阵列单元中“十”字形缝隙的臂长或臂宽增大，材料的吸波性能提高；“十”字形缝隙之间的距离增加，材料的吸波性能降低。“十”字形缝隙的臂长、臂宽和“十”字形缝隙之间的距离分别为16、8和6mm时，材料的有效带宽7．2GHz，最大反射衰减-26．2dB。     

单壁碳纳米管/六角钡铁氧体复合材料的微波吸收性能

用电弧法制备含铁的单壁碳纳米管(SWCNTs), 并将其提纯之后掺杂到用溶胶-凝胶自燃法制备的M型六角钡铁氧体(BaFe₁₂O₁₉)纳米晶粉体中, 得到了具有网状结构的复合材料。利用同轴法测试了样品的电磁参数, 研究了不同混合比SWCNTs/BaFe₁₂O₁₉ 复合材料的吸波性能。结果表明: 复合粉体SWCNTs/BaFe₁₂O₁₉的磁损耗主要是由于自然共振和交换共振引起的; 当掺杂2%(质量分数)SWCNTs时, 微波反射衰减最大值可以达到 24.85 dB, 高于10 dB的频带宽度可以达到6.30 GHz, 具有较宽的吸波频段。      

Magnetic and microwave absorption properties of polymer composites with amorphous Fe-B/Ni-Zn ferrite nanoparticles

In this study, polymer composites containing amorphous Fe-B submicrometer particles and Ni-Zn ferrite nanoparticles were fabricated. A polymer composite of mixed particles showed high permeability of μ^′r=13.7 at 0.5 GHz and μ^″r=8.3 at 1.2 GHz. In addition, this composite exhibited good microwave absorption properties (R.L. < −20 dB) in the frequency range of 0.65-1.12 GHz for absorber thickness of 2.38-4.06 mm. It is concluded that this polymer composite can be used for fabricating microwave absorbers in the UHF range, and would result in thinner microwave absorbers than any other microwave absorbers reported thus far.     

羰基铁室温硫化硅橡胶复合材料的吸波性能EI北大核心CSCD

为制备兼具力学性能和电磁吸收性能的高带宽吸波材料,采用纳米粒子改性及物理共混法设计制备一种以聚二甲基硅氧烷为基体的羰基铁室温硫化硅橡胶复合材料,系统地分析了该复合材料的力学性能与吸波性能。结果表明:当白炭黑质量分数为3%时,复合材料的综合力学性能最佳,便于材料加工;该复合材料为磁损耗型吸波材料,材料的衰减常数随羰基铁含量和频率呈正相关。根据仿真计算得出,在2~18 GHz下,随着复合材料厚度和羰基铁含量增加,电磁波的吸收峰都逐渐向低频移动,当复合材料的厚度为1.5 mm且羰基铁质量分数为75%时,吸波材料有效吸收带宽可以达到9.07 GHz,占目标带宽56.68%。在实际应用中可根据应用场景需求来优化配方和控制材料厚度,达到最佳的吸波效果。     

掺杂态聚苯胺/三元乙丙橡胶共混物(PAn-DBSA/EPDM)的宽频微波吸收性能研究

采用乳液聚合制备的掺杂态聚苯胺(PAn-DBSA)与三元乙丙共聚物(EPDM)进行熔融混炼,热压成不同厚度的共混物(PAn-DBSA/EPDM)吸波贴片。在雷达波频段(S、C、X、Ku,2—18GHz)测试结果表明,不同掺杂态聚苯胺(PAn-DBSA)含量(wt%)、贴片厚度(mm)与加工工艺条件(混练时间、混炼温度)和聚苯胺形貌特征对共混物(PAn-DBSA/EPDM)的吸波性能有明显影响,并呈现宽频吸波效应(X频段,8-12GHz)。     

吸波材料与FSS复合的隐身技术研究进展

吸波材料通过把电磁波转化为其它形式的能量来降低目标的雷达散射截面,从而实现目标隐身的目的.频率选择表面(FSS)是一种具有二维周期性结构的滤波结构,主要在滤波器上使用.在总结了吸波材料作用原理和FSS结构分析方法的基础上,介绍了FSS结构和吸波材料复合构成的隐身技术的研究进展.     

聚苯乙烯-磁性吸收剂复合材料微波吸收特性研究

采用铁氧体和铁合金纳米晶材料组成的磁性吸收剂对回收的聚苯乙烯泡沫塑料进行复合电磁改性处理,得到聚苯乙烯-磁性吸收剂复合材料;使用微波矢量网络分析仪系统测量复合材料试样的复磁导率、复介电常数频谱特性及材料标样的电磁波吸收性能。结果表明,随磁性吸收剂含量增加,复合材料磁性和介电性增强,当磁性吸收剂质量含量达15%(质量分数)时,复合材料具有明显的吸波材料特性,在2～18GHz频段呈现多个共振型电磁能吸收峰,2GHz附近的损耗吸收峰值达-12dB;电磁改性的聚苯乙烯复合材料在原有的隔热、隔音特性基础上可兼具吸波性能,成为一种颇具应用价值的多功能材料。     

Microwave generation with photonic frequency octupling using a DPMZM in a Sagnac loop

A photonic microwave signal generation scheme with frequency octupling is proposed and experimentally demonstrated. The scheme is based on bi-directional use of a dual-parallel Mach–Zehnder modulator (DPMZM) in a Sagnac loop. The two sub-modulators in the DPMZM are driven by two low-frequency signals with a π/2 phase difference, and the dc biases of the modulator are all set at the maximum transmission points. Due to the velocity mismatch of the modulator, only the light wave along the clockwise direction is effectively modulated by the drive signals to generate an optical signal with a carrier and ±4th order sidebands, while the modulation of the light wave along the counterclockwise direction is far less effective and can be ignored. By properly adjusting the polarization of the light wave output from the Sagnac loop, the optical carrier can be significantly suppressed at a polarizer, and then an optical signal with only ±4th order sidebands is generated. In the experiment, a pure 24-GHz microwave signal without additional phase noise from the optical system is generated using a 3-GHz local oscillator signal. As no electrical or optical filter is used, the photonic frequency octupler is of good frequency tunability.     

Fe基玻璃包覆微丝的吸波性能研究

实验分析了微丝的组织结构，表明微丝是非晶态的，内部芯丝表面光滑，在长度方向上厚度均匀。用矢量网络分析仪测定了微丝的电磁参数，并进行了不同填充率不同厚度的单层吸波涂层设计，结果显示微丝在微波波段10～18GHz频段范围内具有较好的衰减特性，反射率最小值为--32dB，吸波效果好。     

Microwave absorption properties of carbon nanotubes dispersed in alumina ceramic

Ceramic nanocomposites of alumina and carbon nanotubes (CNTs) are experimentally studied for use as microwave absorbers in particle accelerators. The weight percentage of multi-walled CNTs in SPS sintered nanocomposite samples is varied from 0.5 to 10% and the complex permittivity is measured. The RF absorption is strong and relatively flat in the frequency band 1-40 GHz for a CNT weight percentage in the range 1-2.5%, which is just above the percolation threshold. The permittivity is observed to increase dramatically with increasing CNT weight percentage above the percolation threshold as observed elsewhere, and in accordance with theoretical treatments. The electromagnetic properties of the nanocomposites are little changed in going from 294 K to 77 K. The DC conductivity of the alumina-CNT nanocomposite is also sufficient to drain static charge in particle accelerator beamline environments, even at cryogenic temperatures. Fabrication of the nanocomposites using an industrial RF sintering process compatible with large sizes shows that the microwave absorption properties of small samples are similar to those of the SPS sintered samples.     

新型宽带动力吸振器优化设计*

基于导纳功率流理论建立了变截面阻尼复合梁式新型宽带吸振器吸振分析理论模型,以输入被控制结构净功率峰值最小为目标函数,运用混沌粒子群算法对吸振器参数进行了优化,并给出了吸振效果较好的参数分布范围。结合实验结果表明：通过混沌粒子群算法优化后的得到的变截面阻尼复合梁式新型宽带吸振器具有好的吸振效果。     

卡西尼卵形贴片的电磁微波吸收研究

简单介绍了卡西尼卵形线的形成和卵形线族，提出了基于卡西尼卵形线的新型贴片电磁结构，并采用商业软件HFSS对雷达散射截面（RCS）随入射频率与随视角的变化进行了仿真计算。得到：在频率4-8GHz范围内，卡西尼贴片的RCS小于-8dBm，明显优于矩形贴片，约小2．2dBm。在频率6GHz，Φ=90°时，RCS随视角口的变化也优于矩形贴片。通过与相同面积的矩形贴片RCS的结果对比与简单分析，得出卡西尼卵形线贴片结构用于电磁隐身将优于相同面积的矩形贴片的结论。最后指出了卡西尼卵形线新型贴片结构在电磁隐身、天线设计等方面可能具有潜在的应用前景。