Characteristics of surface waves in anisotropic left-handed materials

We report the coexistence of TE and TM surface modes in certain same frequency domain at the interface between one isotropic regular medium and another biaxially anistotropic left-handed medium. The conditions for the existence of TE and TM polarized surface waves in biaxially anisotropic left-handed materials are identified, respectively. The Poynting vector and the energy density associated with surface modes are calculated. Depending on the system parameters, either TE or TM surface modes can have the time averaged Poynting vector directed to or opposite to the mode phase velocity. It is seen that the characteristics of surface waves in biaxially anisotropic left-handed media are significantly different from that in isotropic left-handed media.

Enhanced microwave absorption property of silver decorated biomass ordered porous carbon composite materials with frequency selective surface incorporation

Porous carbon(PC)is a promising electromagnetic(EM)wave absorbing material thanks to its light weight,large specific surface area as well as good dissipating capacity.To further improve its microwave absorbing performance,silver coated porous carbon(Ag@PC)is synthesized by one-step hydro-thermal synthesis process making use of fir as a biomass formwork.Phase compositions,morphological structure,and microwave absorption capability of the Ag@PC has been explored.Research results show that the metallic Ag was successfully reduced and the particles are evenly distributed inward the pores of the carbon formwork,which accelerates graphitization process of the amorphous carbon.The Ag@PC composite without adding polyvinyl pyrrolidone(PVP)exhibits higher dielectric constant and better EM wave dissipating capability.This is because the larger particles of Ag give rise to higher electric conductivity.After combing with frequency selective surface(FSS),the EM wave absorbing performance is further improved and the frequency region below-10 d B is located in8.20-11.75 GHz,and the minimal reflection loss value is-22.5 dB.This work indicates that incorporating metallic Ag particles and FSS provides a valid way to strengthen EM wave absorbing capacity of PC material.

Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate

An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface（FSS） absorber by using a magnetic substrate,showing that it is possible to widen the wave absorbing bandwidth.Three pieces of magnetic substrates are prepared.According to the complex permittivity and permeability,the reflectivity of the corresponding absorber is calculated by the finite difference time-domain（FDTD） method,and the bandwidth of the reflectivity below 10 dB is optimized by genetic algorithm.The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate;the reflectivity bandwidth below 10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm,which is wider than that with a dielectric substrate.The density of the FSS absorber is only 0.92 g/cm 3.Additionally,the absorption band can be further widened by inserting a second lossy FSS.Finally,a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result.The experimental result is consistent with the design one.

Electromagnetic Waves Absorbing Characteristics of Composite Material Containing Carbonyl Iron Particles

Results of measurements of permeability, permittivity and radar absorption properties of composites on basis of carbonyl iron particles R-10 brand are presented in this paper. The calculations and experimental studies have shown that in the super high frequency (SHF) and extremely high frequency (EHF) ranges on the basis of two-layer structures with different content of carbonyl iron particles can create a radar absorbing coatings with a reflectivity of less than -10 dB over a wide bandwidth from 3.1 to 17.1 GHz and from 27 to 37 GHz. Absorbing properties of composites are saved in terahertz frequency range from 250 to 525 GHz.

Millimeter-Wave Absorption Properties of Thin Wave Absorber in Free Space with New Porous Carbon Material

In this paper, we focus on PHYTOPOROUS, a porous carbon material made entirely from plant-based ingredients, as a new broadband-wave absorber material that acts in the millimeter wave band. We created prototypes of thin rubber-sheet wave absorbers that contain porous carbon (PHYTOPOROUS) made from rice chaff and soybean hulls, which are both agricultural residue products that are generated in large quantities. We investigated the permittivity and reflectance characteristics of this material using the free-space time-domain method. The thin rubber-sheet wave absorber that contained PHYTOPOROUS made from soybean hulls exhibited a frequency band that was approximately 18 GHz wide and centered at 90 GHz. The return loss for this material was greater than −20 dB. This demonstrates that the material provides nearly constant reflection absorption over a wide frequency band.

A Wide-Spaced Dual-Band Metamaterial Absorber Based on 2.5D Frequency Selective Surfaces and Magnetic Material

By applying meander-line for electrical loss and magnetic material for magnetic loss,we present a metamaterial absorber which is wide-spaced and dual-band(1.35—2.24 GHz and 10.37—12.37 GHz).The novelty of this study mainly lies in a combination of two kinds of losses to consume electromagnetic energy,which can get better dual-band absorption.In the electrical loss layer,meander-line structures are printed on both surfaces of the substrate and the structure series with resistors.Considering the need for miniaturization,we connect eight metallic vias with these meander-line areas to form a compact 2.5-dimensional(2.5D)structure.The dimension of the unit cell is miniaturized to be 5.94 mm×5.94 mm,about 0.035λat the center frequency of the lower absorption band.In the magnetic loss layer,the 0.4 mm thick magnetic material is employed on a metallic ground plane.In addition,the complex permittivity and complex permeability of the magnetic material are given.Finally,we fabricate a prototype of the proposed absorber and obtain a measurement result which is in good agreement with the full-wave simulation result.

TE Modal Dispersion in Dielectric Slab Waveguide with Lossy Left-Handed Metamaterial

In this work, we derived the modal dispersion relation for TEm modes for a symmetric slab waveguide constructed from SiO2 dielectric guiding core material with lossy left-handed material (LHM) as cladding and substrate, and the power confinement factor. The dispersion relations and the power confinement factor were numerically solved for a given set of parameters: allowed frequency range;core’s thicknesses;and TEm mode order. We found that the real part of the effective refractive index decreased with thickness and frequency increase. Moreover, the imaginary part (extinction coefficient) of the effective refractive index has very small values for all thickness in the frequency ranges, which means the waveguide structure is transparent for the used frequencies. The waveguide structure offers good guiding power for all thickness in the frequency range with low power attenuation. The real part of the effective refractive index increases with the increase of mode order, and the power confinement factor decreases with the increase of mode order.

A low-profile metamaterial absorber with ultrawideband reflectionless and wide-angular stability

An ultrawideband reflectionless metamaterial absorber(MA)is proposed by replacing the metallic ground with the complementary split-ring resonator(CSRR)structure.The proposed MA exhibits-10 d B reflectivity spectrum from 1 GHz to 20 GHz,which maintains more than 90%absorption from 1.5 GHz to20 GHz.Furthermore,it achieves angle stability for TE and TM polarization at oblique incident angles up to 40°and 65°,respectively.To achieve broadband absorption spectrum,we have adopted a single-layer high-impedance surface(HIS)loaded with a double-layer magnetic material(MM)structure.To further realize the RCS reduction into a lower frequency range,we have employed the scattering cancellation technology into the traditional metallic ground.Finally,we have fabricated a sample exhibiting the 10 d B RCS reduction from 1 GHz to 20 GHz with a thickness of 10 mm.Measurement and simulation results confirm that the proposed MA exhibits excellent comprehensive performance,making it suitable for many practical applications.

Preparation and radar-absorbing properties of Al2O3/TiO2/Fe2O3/Yb2O3 composite powder

Al2O3/TiOe/FeeO3/Yb2O3 composite powder was synthesized via the sol-gel method. The structure, morphology, and ra- dar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes （100-200 rim） and the other is spherical A1203 particles （smaller than 80 rim）. Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 （at 15.68 GHz） in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increas- ing matching thickness. The effective absorption hand covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.

Giant Magnetostrictive Material Loudspeaker System Acoustic Radiation Simulation

An infinite panel model of giant magnetostrictive material loudspeaker system （GMMLS） is proposed by making use of finite element method（FEM）. Bending wave eigenfunction is introduced to describe the acoustic radiation condition of the panel. Far-field response in different conditions is calculated by changing the mass surface density. Conclusion is obtained by analyzing the curves simulated, that panel which has larger mass surface density can hardly generate far-field acoustic radiation for lower frequency, while the panel has smaller mass surface density generates far-field acoustic radiation for lower frequency evenly and stronger.

Adaptive Lagrange finite element methods for high precision vibrations and piezoelectric acoustic wave computations in SMT structures and plates with nano interfaces

This paper discusses the validity of (adaptive) Lagrange generalized plain finite element method (FEM) and plate element method for accurate analysis of acoustic waves in multi-layered piezoelectric structures with tiny interfaces between metal electrodes and surface mounted piezoelectric substrates. We have come to conclusion that the quantitative relationships between the acoustic and electric fields in a piezoelectric structure can be accurately determined through the proposed finite element methods. The higher-order Lagrange FEM proposed for dynamic piezoelectric computation is proved to be very accurate (prescribed relative error 0.02% - 0.04% ) and a great improvement in convergence accuracy over the higher order Mindlin plate element method for piezoelectric structural analysis due to the assumptions and corrections in the plate theories.The converged lagrange finite element methods are compared with the plate element methods and the computedresults are in good agreement with available exact and experimental data. The adaptive Lagrange finite elementmethods and a new FEA computer program developed for macro- and micro-scale analyses are reviewed, and recently extended with great potential to high-precision nano-scale analysis in this paper and the similarities between piezoelectric and seismic wave propagations in layered structures and plates are stressed.

FeCoNiAl@C/CCB/NR吸波贴片的制备及微波吸收性能

近年来,橡胶吸波贴片由于具有优异的力学性能和吸波性能被广泛应用于各种电子设备,确保设备免受电磁波干扰而正常运行。采用机械搅拌法、碳热还原法以及密炼和硫化等工艺制备了具有优异力学性能和吸波性能的FeCoNiAl@C/导电炭黑(CCB)/天然橡胶(NR)吸波贴片,并调节FeCoNiAl@C的添加量,以调控贴片的力学性能和吸波性能。对FeCoNiAl@C复合材料的物相组成和微观形貌进行表征,并研究了吸波贴片微波吸收性能和吸波机理。结果表明,当FeCoNiAl@C添加量为5.0 g时,FeCoNiAl@C/CCB/NR吸波贴片在4.40 GHz、厚度5.0 mm处最小反射损耗(RL)可达-24.45 dB,有效吸收带宽(EAB)达到1.60 GHz;当厚度为1.5 mm时,EAB可达到3.04 GHz。吸波贴片良好的吸波性能源于吸波剂优异的阻抗匹配和多重损耗的协同作用。此研究为天然橡胶基吸波贴片的结构设计和实际应用提供了新的思路。

石墨粉吸波剂对抹灰石膏性能的影响

【目的】为了低成本制备民用建筑吸波材料,研究不同种类石墨粉对抹灰石膏性能的影响。【方法】以新型墙体抹灰砂浆抹灰石膏作为研究对象,掺入包括自制的膨胀破碎石墨在内的不同种类的低成本石墨粉作为吸波剂,制备石墨-抹灰石膏复合材料;使用X射线衍射仪、扫描电子显微镜、网络分析仪等设备对复合材料的结构、物性、强度和吸波性能进行测试和表征。【结果】在抹灰石膏中掺入石墨粉,导致标准扩散度用水量增加,凝结时间缩短,体积密度减小,力学性能降低,吸波性能提高;相比于天然鳞片石墨和石墨微片,抹灰石膏中掺入质量分数为8%的膨胀破碎石墨粉可获得最好的吸波性能,在频率为2~18 GHz时,反射损耗(reflection loss,R_(L))小于-5 dB的带宽可达10.8 GHz,至少有68.38%的电磁波被吸收,且凝结时间、体积密度和力学性能均可达到国标中对轻质底层抹灰石膏的要求。【结论】膨胀破碎石墨粉是几种石墨粉中最适合用于民用建筑的低成本吸波剂。

Co^(2+)掺杂W型铁氧体的制备和吸波性能研究

为解决单一铁氧体吸波材料吸波频带窄的问题,采用固相法制备了Co^(2+)掺杂的W型钡铁氧体Ba(Zn_(1-x)Co_(x))_(2)Fe_(16)O_(27)(x=0、0.2、0.4、0.6、0.8、1.0)铁氧体,研究了Co^(2+)掺杂对W型钡铁氧体晶体结构、微观形貌、电磁性能和吸收性能的影响。结果表明,随着Co^(2+)掺杂量的增加,铁氧体晶体结构保持不变,掺杂Co^(2+)的W型钡铁氧体具有六角片状结构。随着金属离子的加入,粒径有不同程度减小。当Co^(2+)掺杂的摩尔分数x为0.4时,铁氧体的磁损耗最高。含量为70%的Ba(Zn_(0.6)Co_(0.4))2Fe_(16)O_(27)铁氧体吸收涂层的最大反射损耗为-22 dB,峰值位置在12.5 GHz,反射损耗RL<-10 dB的带宽约为8 GHz(8~16 GHz),实现了宽频带强吸收。

某型接收机中放大器自激机理分析与预防措施

对某型接收机中频噪底升高故障进行了分析处理,分析结果表明射频模块腔体内存在个体差异,导致本振放大器在脉冲工作条件下产生自激,通过对放大器自激机理的分析给出了相应的预防措施,在射频小盒侧壁中粘贴吸波材料,可以有效消除自激。论文对今后腔体自激问题的处理分析具有参考价值。

激光声表面波技术在材料加工表面损伤检测中的应用

激光声表面波技术是一种新兴的无损检测方法,在材料加工表面损伤评估中展现出独特优势。本文重点探讨了该技术在表面裂纹、粗糙度和热损伤定量表征方面的应用。通过激光激发表面波并分析其传播特性,实现了高灵敏度、强定量化能力的损伤检测。优化激励-接收方案和信号处理算法,可进一步提升检测性能。实验研究表明,表面波的时频域特征参数与损伤量纲间存在确定性关联,为工程应用奠定了基础。

损耗型吸波材料与水泥基复合吸波材料的制备及性能调控研究现状

针对目前日益恶化的电磁污染问题,吸波功能材料得到广泛应用。如何经济、高效、宏量制备高性能吸波材料,对功能建筑材料行业的发展具有重要意义。从损耗型吸波材料的吸波机理出发,在广泛总结对比磁损耗型、电阻损耗型、介电损耗型吸波材料制备的基础上,分析了水泥基复合吸波材料的制备技术及性能调控研究现状,并指出结构设计和材料复合石水泥基吸波材料的重要发展方向。

银/碳纳米管涂层织物的制备及其性能表征

碳纳米管(CNTs)因其优异的电学性能和力学性能,近年来被广泛运用在电磁波吸收织物的开发和研究中。本研究先通过化学还原法制得银纳米颗粒,后将其沉积于酸化的多壁碳纳米管(MWCNTs)上,再将银/碳纳米管(Ag/MWCNTs)采用三浸三轧法涂层于棉织物制备吸波织物。分别对Ag/MWCNTs复合材料形貌组成和电磁参数进行测试分析,并采用弓形法测试了吸波织物在X、Ku频段的吸波性能。研究结果表明,化学处理后的Ag纳米颗粒在MWCNTs上附着均匀,更利于阻抗匹配,且具有稳定的介电损耗和磁损耗;涂层织物的吸波性能随Ag/MWCNTs质量分数的增加而增强。5 wt%涂层织物可实现在9~15 GHz频段内的吸收均优于-10 dB,7 wt%的涂层织物可实现在8~17 GHz频段内的吸收均优于-10 dB,反射率最低可达到-24 dB。

面内传播方向对SAW滤波器性能的影响研究

为了满足窄带声表面波滤波器对品质因数Q值和带外抑制日益增长的需求,提出了一种窄带滤波器设计方法。在基于新型POI结构谐振器的基础上,通过旋转谐振器达到改变波传播角度的目的,并利用二维全模型得到准确的实验数据,与原结构谐振器分别代入滤波器设计中进行比较。实验结果表明,该方法在一定程度上能够有效地增加带外抑制,对过渡带抑制能力有2~4 dB的提升,且具有设计简便,占用空间小等优点。

羰基铁吸收剂耐腐蚀、抗氧化表面改性技术研究进展

随着通讯技术和武器装备的不断更新换代,吸波材料扮演的角色越来越重要,近些年对吸波材料的研究迎来迅速发展。羰基铁具有高饱和磁化强度和低生产成本等特点,因此被广泛用于制备吸波材料,但由于羰基铁吸收剂的表面活性较高,在海洋环境或高温环境下容易发生腐蚀或高温氧化,严重影响其吸波性能,随着装备对吸波材料的要求不断提高,羰基铁吸收剂的耐腐蚀、耐氧化改性技术逐渐成为研究热点。重点介绍了羰基铁吸收剂表面改性技术的研究进展,研究表明表面包覆改性可以提高羰基铁吸收剂的耐腐蚀、抗氧化性能,部分改性方法还可以改善材料的吸波性能。在兼顾耐高温氧化和耐腐蚀性能的基础上,发展厚度薄、吸收频段宽的吸波材料是未来发展的主要方向。