Microwave absorption properties of FSS-impacted composites as a broadband microwave absorber

The development of a cost-effective microwave absorber with wide bandwidth corresponding to reflection loss (RL)?≤??10 dB is still a very challenging task. A sugarcane bagasse-based agricultural waste composite has been analyzed for its elemental contents. The combination of elements is suitable for its possible usage as a cost-effective microwave absorbing material. Therefore, this composite has been subjected to morphological and electromagnetic studies to analyze its microwave absorbing behavior. The frequency dependent complex dielectric permittivity and complex magnetic permeability values were obtained using a transmission/reflection waveguide approach in the X-band. Furthermore, the effect of the Minkowski loop frequency selective surface (FSS) was studied over the absorption capability of the composite. It was found that the application of FSS leads to a reduction in thickness up to 2.9 mm and an enhancement in absorption bandwidth up to 3.6 GHz. The FSS patterned composite shows a remarkable performance with peak RL of ?28.4 dB at 10.7 GHz and absorption bandwidth of 3.6 GHz.     

Critical analysis of frequency selective surfaces embedded composite microwave absorber for frequency range 2–8 GHz

Radar wave absorbers are important for the reduction of radar cross section of the target for stealth applications. Earlier the radars were available in the frequency range 8–12 GHz (X-band) and 12–18 GHz (Ku-Band). Due to recent advancement in radar technology, radars are now available from 2 to 18 GHz frequency range. So there is an urgent need to develop such a material that can work as radar wave absorber in the lower frequency band of the microwave spectrum i.e., 2–8 GHz. For this purpose the selection of material is an important criterion as the radar wave absorption depends primarily upon the material characteristics i.e., complex permittivity and complex permeability. For lower frequency radar wave absorption, the material must also possess the conducting property along with dielectric and magnetic properties. Therefore, an attempt has been made to develop a radar wave absorbing nano-composite material by selecting constituent materials with such inherent properties that can work for the absorption of radar wave in the lower frequency range. It is observed that the developed composite give good absorption in the lower frequency range but with narrow radar wave absorption bandwidth (4–7 GHz). So we have explored the possibility of the efficient use of an advanced electromagnetic technique like frequency selective surface to enhance the radar wave absorption bandwidth in the lower frequency region of the microwave frequency spectrum and precaution has been taken such that complexity due to FSS can be avoided. It has been observed that the synthesised single layer absorber with single square loop, cross dipole and Jerusalem cross FSSs provides radar wave absorption bandwidth in the frequency range 2–8 GHz.     

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。     

Synthesis of covalently bonded reduced graphene oxide-Fe3O4 nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic (EM) wave absorbers,covalently bonded reduced graphene oxide-Fe3O4 nanocomposites (rGO-Fe3O4),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe3O4 nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe3O4 nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe3O4 is 2∶1 (sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss (RL) reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth (RL＜-10 dB) is 6.32 GHz (11.68-18.0 GHz) with a matching thickness of 2.1 mm.Furthermore,radar cross section (RCS) simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption performance.This work provides a possible method for preparing efficient EM wave absorbers.     

Synthesis of core–shell FeCo@SiO<Subscript>2</Subscript> particles coated with the reduced graphene oxide as an efficient broadband electromagnetic wave absorber

The FeCo@SiO₂@RGO composites were prepared by combining liquid-phase reduction reaction in Argon atmosphere with hydrothermal reaction. The crystal structure, chemical composition and morphology of the as-prepared composites have been investigated in detail. SEM and TEM results illustrate that the FeCo@SiO₂ composites are of core–shell structure with a diameter of about 150–200 nm. Compared with FeCo@SiO₂ and FeCo@RGO composites, the as-prepared FeCo@SiO₂@RGO composites exhibit excellent electromagnetic (EM) wave absorption properties. As an EM wave absorber, the maximum R_L reaches ?52.9 dB at 9.12 GHz with a thickness of 3.0 mm, and the absorption bandwidth with the reflection loss below ?10 dB was up to 5.36 GHz (from 8.8 to 14.16 GHz) with a thickness of 2.5 mm. It is believed that the FeCo@SiO₂@RGO composites can serve as an excellent microwave absorbent and can be widely used in the microwave absorbing area.     

Microwave absorption properties of double-layer absorbers based on spindle magnetite nanoparticles and flower-like copper sulfide microspheres

In this work, the spindle magnetite nanoparticles (SMNPs) and flower-like copper sulfide microspheres (FCSMSs) were synthesized via hydrothermal method. The structures, chemical composition and morphologies of samples were analyzed and characterized in detail. The microwave absorption properties of single-layer and double-layer absorbers were investigated based on the electromagnetic transmission line theory in the frequency range from 2 to 18 GHz. The results show that the double-layer absorbers consisting of FCSMSs as matching layer and SMNPs as absorbing layer display superior microwave absorbing performance compared to the single-layer ones due to the proper combination of magnetic loss of SMNPs and dielectric loss of FCSMSs, and the improved impedance matching characteristics. When the thicknesses of the absorbing layer and the matching layer are 1.6 and 0.4 mm, respectively, the minimum reflection loss reaches ??74.3 dB at 10.9 GHz, and the efficient absorption bandwidth is up to 5.34 GHz (8.46–13.8 GHz). The optimal SMNPs/FCSMSs double-layer absorbers can become a novel microwave absorption material with strong-absorption and broad-band.     

Effects of Multi-walled Carbon Nanotubes on the Electromagnetic Absorbing Characteristics of Composites Filled with Carbonyl Iron Particles

The electromagnetic(EM) wave absorbing property of silicone rubber filled with carbonyl iron particles(CIPs) and multi-walled carbon nanotubes(MWCNTs) was examined.Absorbents including MWCNTs and spherical/flaky CIPs were added to silicone rubber using a two-roll mixer.The complex permittivity and complex permeability were measured over the frequency range of 1-18 GHz.The two EM parameters were verified and the uniform dispersion of MWCNTs and CIPs was confirmed by comparing the measured reflection loss(RL) with the calculated one.As the MWCNT weight percent increased,the RL of the spherical CIPs/silicone rubber composites changed insignificantly.It was attributed to the random distribution of spherical CIPs and less content of MWCNTs.On the contrary,for composites filled with flaky CIPs the absorption bandwidth increased at thickness 0.5 mm(RL value lower than-5 dB in 8-18 GHz) and the absorption ratio increased at lower frequency(minimum-35 dB at 3.5 GHz).This effect was attributed to the oriented distribution of flaky CIPs caused by interactions between the two absorbents.Therefore,mixing MWCNTs and flaky CIPs could achieve wider-band and higher-absorption ratio absorbing materials.     

Synthesis and characterization of MoS2/Fe@Fe3O4 nanocomposites exhibiting enhanced microwave absorption performance at normal and oblique incidences

Herein, we attempted to prepare MoS₂/Fe@Fe₃O₄ nanocomposites capable of strongly absorbing broadband incident electromagnetic (EM) radiation and probed the effects of their composition on complex permittivity and permeability at 2–18 GHz. Calculations of normal-incidence reflection losses (RLs) based on EM parameters revealed that the Fe@Fe₃O₄ to MoS₂ mass ratio strongly influenced the absorption peak intensity and bandwidth. Specifically, an RL peak of −31.8 dB@15.3 GHz and a bandwidth (RL < − 10 dB) of 4.8 GHz (13.2–18 GHz) were achieved at a thickness of 1.52 mm and a Fe@Fe₃O₄ to MoS₂ mass ratio of 60:40. Further, RL and bandwidth were investigated for oblique incidence, in which case two kinds of EM waves (TE – electric field perpendicular to plane of incidence; TM – electric field in the plane of incidence) were considered. The absorption peaks of TE and TM waves did not exceed −20 dB when the incidence angle increased to 30°, and the bandwidth (RL < − 10 dB) reached 4.2 GHz (TE wave) and 4.0 GHz (TM wave) when this angle was further increased to 40.0° and 50.4°, respectively. Finally, the mechanism of microwave absorption was discussed in detail.     

Preparation and electromagnetic wave absorption properties of CoNi@SiO<Subscript>2</Subscript> microspheres decorated graphene–polyaniline nanosheets

In this work, we successfully parepared the quaternary composites of CoNi@SiO₂@graphene@PANI via a four-step method. The structures, chemical composition and morphologies of obtained composites are analyzed in detail. The electron microscopy results show spherical CoNi@SiO₂ particles evenly dispersed into the surface of graphene@polyaniline nanosheets. The electromagnetic parameters indicate that CoNi@SiO₂@graphene@PANI exhibits enhanced electromagnetic absorption properties compared to CoNi@SiO₂, which can be mainly attributed to the improved impedance matching and multi-interfacial polarization. The maximum reflection loss of CoNi@SiO₂@graphene@PANI can reach ??43 dB at 15.4 GHz and the absorption bandwidth with the reflection loss exceeding ??10 dB is 5.7 GHz (from 12.3 to 18 GHz) with the thickness of 2 mm. Our results demonstrate the quaternary composites composed of CoNi@SiO₂ microparticles and rGO–PANI nanocomposites can serve as light weight and high-performance EM absorbing material.     

Development of thin broad band radar absorbing materials using nanostructured spinel ferrites

Stealth applications now emphasise on development of efficient Radar Absorbing Materials of light weight, less coating thickness, broad bandwidth of absorption along with cost effective raw materials and manufacturing techniques. Therefore, in this paper an attempt has been made to develop such an efficient cost effective radar absorbing material which possesses broad band absorption with less coating thickness. Unconventionality of acquiring impedance match for a double layer absorber of nanostructured nickel ferrite (NF) with reasonably good dielectric properties and its cation substituted counterpart, nickel zinc ferrite (NZF) with enhanced magnetic properties has been thoroughly investigated for radar wave absorption for very low coating thickness. Complex permittivity and permeability of NF and NZF with crystallite sizes of 10.0 and 16.0 nm, respectively, are measured and used as the data bases. The microwave absorption properties of the ferrites are correlated with their size, morphology, permittivity, permeability, thickness and bandwidth of absorption. Multilayering has been performed using the optimization through Genetic Algorithm in order to attain suitable impedance matching layer for minimum reflection loss (RL) at lower thickness. The results indicate an enhancement in the absorption with RL value of ?45.0 dB for a moderately low coating thickness of 1.72 mm. Single layers NF, NZF and multilayer NF–NZF are fabricated over the aluminium sheets and the results are experimentally verified.     

Ordered mesoporous inter-filled SiC/SiO<Subscript>2</Subscript> composites with high-performance microwave absorption by adding ethylenediamine

In this study, ordered mesoporous inter-filled silicon carbide/silica composites containing ethylenediamine (EDA-SiC/SiO₂) were fabricated by nanocasting and cold-pressing. The as-prepared composites exhibited enhanced microwave absorption. By multi-technique approach utilization, it was demonstrated that EDA acted as a carbon source during pyrolysis progress. The EDA-SiC/SiO₂ fabricated at 1300 °C exhibited a minimum reflection loss (RL) of ?53.0 dB at 10.1 GHz, and effective absorption bandwidth (RL < ?10 dB) covered the entire X-band. It was also illustrated that the enhanced dielectric loss originated from the high electrical conductivity induced by the ordered inter-filled network and crystalline carbon. Furthermore, the optimal absorbing thickness was also determined by the impedance match and quarter-wavelength law.     

Microwave absorption response of nickel/graphene nanocomposites prepared by electrodeposition

In this study, nanostructures of nickel have been successfully deposited on graphene nanosheet by direct electrochemical deposition. The morphology, nickel content, and magnetic properties of the graphene as well as composites were examined by scanning electron microscopy, transmission electron microscopic, elemental analysis, and vibrating sample magnetometer, respectively. Their relative complex permeability and permittivity were also measured, and reflection loss values were calculated at given thickness layer according to transmit line theory in the range 2–18 GHz. The results reveal that with the increasing of the thickness of the samples, the matching frequency tends to shift to the lower frequency region, and theoretical reflection loss becomes less at the matching frequency. When the absorbing thickness is 1 mm, the maximum absorption value of graphene is ?6.5 dB at about 7 GHz. After decorating graphene sheet with magnetic nickel nanoparticles, the composites were shown to efficiently promote microwave absorbability. When the thickness is 1.5 mm, the absorption value of the composites exceeds ?10 dB in the 5 GHz absorbing bandwidth and the maximum absorption value is ?16.0 dB at 9.15 GHz.     

Broad bandwidth of thin composite radar absorbing structures embedded with frequency selective surfaces

The three-layer ultrathin radar absorbing structure (RAS) involving a frequency selective surface (FSS) exhibiting excellent broad bandwidth properties is designed and fabricated. The EW and flaky carbonyl iron powders were used to produce two kinds of silicone rubber matrix magnetic composites for the top and the bottom layer, respectively. The electromagnetic parameters of the composites were measured in the frequency range of 2–18 GHz. The middle layer is an FSS in the form of double-square loops with four micro-split gaps in the middle of the outer loop. The results show that the proposed RAS can provide a 10 dB absorbing bandwidth of 13.2 GHz from 4.8 to 18 GHz (1.7 mm thickness) and a 10 dB absorbing bandwidth of 14.1 GHz from 3.9 to 18 GHz, covering C-band, X-band and Ku-band (2.0 mm thickness). A good match between simulation and measurement results demonstrates the validity of our design.     

Investigation of adjacent spacing dependent microwave absorption properties of lamellar structural Ti3C2Tx MXenes

Ti₃C₂Tx MXenes and their composites play a vital role in the research on microwave absorbing materials. Herein, the different interlamellar spaces of Ti₃C₂Tx MXene materials were prepared by an etching process. The dependence of the microwave absorbing properties of the Ti₃C₂Tx MXene nanosheets on different interlamellar spaces was studied. The complex permittivity, dielectric loss, impedance matching characteristic and the minimum reflection loss (RL) value with the variation in interlamellar space were systematically investigated. Results showed that 40% ratio paraffin-bonded composites (S3) have a strong electromagnetic wave absorption performance and large effective absorbing bandwidth. The maximum RL reaches −36.3 dB at 4.67 GHz with the thickness of 4.5 mm, ascribed to its a high dielectric loss and good impedance matching characteristics. The RL value of Ti₃C₂Tx MXenes is strongly dependent on the inter-lamellar space. The enhanced microwave absorption originates from the unique 2-D structure, good impedance matching characteristics, and enhanced space-charge polarization effects. This work provides a new avenue for exploring high-performance microwave absorbers based on MXene materials.     

短切中空多孔碳纤维复合材料的吸波性能

以中空多孔聚丙烯腈(PAN)原丝为原料, 通过预氧化处理和碳化处理工艺制备了中空多孔碳纤维, 采用SEM和XRD对其微观结构和晶体结构进行了表征, 并对其吸波性能进行了分析. 研究结果表明, 中空多孔碳纤维是一种非石墨结构的电损耗型雷达波吸收剂; 随着短切中空多孔碳纤维体积分数的提高, 随机分布的纤维/石蜡复合吸波材料的介电常数随之增大; 用所得的电磁参数结果计算了不同厚度材料的反射率, 在2～18GHz频率范围内, 当体积分数为33.30%, 厚度为2mm时, 最低反射率为-21.36dB, 其中<-5dB的反射率带宽为5.17GHz, <-10dB的反射率带宽为2.88GHz.     

The microwave absorbing properties of CoFe<Subscript>2</Subscript> attached single walled carbon nanotube/BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> nanocomposites

The CoFe₂ attached single-walled carbon nanotubes (CoFe₂@SWCNTs) and BaFe₁₂O₁₉ ferrite nanocomposites with different CoFe₂@SWCNTs weight ratios (1, 3, 5, 7 wt%) were synthesized by a simple combination process. Then, the electromagnetic and microwave absorption properties were systematically investigated by a vector network analyzer in the frequency range of 2–18 GHz. High-quality CoFe₂@SWCNTs were prepared by a direct current arc discharge method in one-step. BaFe₁₂O₁₉ nanocrystals were synthesized by a nitrate citric acid sol–gel auto-ignition method. The CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposites exhibited an efficient reflection loss (RL) and a wide absorption bandwidth. The minimum RL of ?54.13 dB was observed at 11.84 GHz for the nanocomposite (5 wt% CoFe₂@SWCNTs) with a thickness of 2.8 mm, 3.4 times greater than those without CoFe₂@SWCNTs, and a broad absorption bandwidth of 4.64 GHz (<?10 dB) was achieved. In addition, the nanocomposite (1 wt% CoFe₂@SWCNTs) shows a broader effective microwave absorption bandwidth of 7.12 GHz with a thickness of 1.9 mm. The experimental results reveal that the absorbing properties of the nanocomposites are greatly improved by controlling the CoFe₂@SWCNTs weight ratio and the matching thickness of the absorber. This CoFe₂@SWCNT/BaFe₁₂O₁₉ nanocomposite is anticipated to be applied in advanced microwave absorbers.     

EM characteristics of the RAS composed of E-glass/epoxy composite and single dipole FSS element

From the methods to reduce radar cross section (RCS) such as shaping of the target, radar absorbing material (RAM), and radar absorbing structure (RAS), the RAS composed of frequency selective surface (FSS) screens and low-loss composite materials is used widely because the FSS screen transmits or reflects electromagnetic (EM) waves selectively and the composite material withstands external loads. In this study, the RAS composed of the E-glass/epoxy composite and single dipole FSS element was fabricated by printed circuit board (PCB) manufacturing process, and their EM transmission characteristics, such as a resonant frequency, a minimum transmission loss, and a transmission bandwidth, were measured in the X-band frequency range by the free space method with respect to the size of dipole element and its periodicity of array.     

Facile synthesis and novel microwave electromagnetic properties of flower-like Ni structures by a solvothermal method

Flower-like Ni structures composed of leaf-like flakes were synthesized through a facile solvothermal approach independent of surfactants or magnetic force. The evolution of the morphology was closely related to the variation of NaOH and volume ratios of ethylene glycol to water. The microwave absorbing properties of the flower-like Ni wax-composite were evaluated based on the complex permittivity (ε_r = ε′ ? jε″) and permeability (µ_r = µ′ ? jµ″). The Ni wax-composite exhibited excellent microwave absorption performances with a minimum reflection loss of ?46.1 dB at 13.3 GHz, corresponding to a matching thickness of 2.0 mm. In particular, the absorption bandwidth of RL below ?10 dB was 3.6 GHz (11.7–15.3 GHz). The attenuation of microwave could be attributed to the dielectric loss and unique flower-like structure.     

一种三层雷达吸波涂层的制备和性能

在磁性金属微粉的雷达吸波涂层中引入导电纤维层具有减轻质量和展宽吸收频带作用,本文采用磁性金属微粉和短导电纤维制备了一种三层雷达吸波材料.研究表明,三层的相对顺序对吸波涂层的带宽与峰值具有明显影响,在面密度为2.50 kg/m2的条件下,当导电纤维层位于表层时带宽最大,在8～18 GHz频段范围内反射率小于-10 dB的带宽达7 GHz.     

Development of the composite RAS (radar absorbing structure) for the X-band frequency range

Since the EM properties of fiber reinforced polymeric composites can be tailored effectively by adjusting its composition, they are plausible materials for fabricating the radar absorbing structure (RAS) of desired performance. In this study, the composite RAS which has superior load bearing capacity and EM absorption characteristics has been developed by blending the conductive carbon black with the binder matrix of the E-glass/polyester composite, and its EM absorption characteristics has been measured by the free space method in the X-band frequency range (8.2–12.4 GHz). The composite RAS was designed so as to have the optimal performance for the X-band centered at 10 GHz. From the investigation, it was found that the composite RAS of 2.93 mm thickness with the conductive carbon black absorbed more than 90% of incident EM wave throughout the entire X-band frequency range.