Maximum Reflection Loss Value Research Articles

Electromagnetic properties of Ce substituted barium hexaferrite in X band frequencies

Ce3+ substituted barium hexaferrite Ba1−xCeXFe12O19 (x = 0.25, 0.5, 0.75) ferrite samples were synthesized by ceramic technique. Besides the simple hexaferrite phase structure, the all three of the as-prepared barium hexaferrites have small amount of CeO2 phases. The phase composition is studied using X-ray diffractometer. The structure morphology is carried out using scanning electron microscopy. The magnetic properties of these ferrites were characterized by employing vibrating sample magnetometer. The complex intrinsic parameters and the electromagnetic properties such as reflection loss (RL), absorption loss (AL), shielding effectiveness (SE) were measured by using transmission/reflection coaxial airline method in the range of 4–16 GHz. The doping of Ce3+ ions has to lead to changes in the phase of the crystal structure to dual phase including barium hexaferrite and cerium oxide. The results present that the obtained composition has a maximum RL value of − 25.7 dB and maximum SE value of 42.3 dB at 10.7 GHz. From these results it was concluded that the synthesized samples had good potential as absorbers in the gigahertz frequency range.

Magnetic and microwave absorption properties of barium hexaferrite doped with La3+ and Gd3+

In this paper, BaLa‌xGdxFe12-2xO19 (x=0.2, 0.4, 0.6 and 0.8) were synthesized via sol-gel auto-combustion method. Fourier transform infrared spectroscopy (FTIR) of samples was represented that the bands at 400 and 500 cm-1 were related to the formation of hexaferrite phase. The (x-ray diffraction) XRD patterns were matched exactly with the structure of barium hexaferrite. (Field emission scanning electron microscopy) FESEM were represented the hexagonal shapes of all products. Magnetic analysis of barium hexaferrite were investigated by (vibrating sample magnetometer) VSM. The saturation magnetization of all samples decreased by increasing dopant’s substitution due to the different occupation sites of dopants instead of Fe3+ (64 to 36.56 emu/g) in the hexaferrite structure. The coercivity increased because of its reverse relation with saturation magnetization (5010 to 5500 Oe). Microwave absorption properties of samples was investigated by (vector network analyzer) VNA. The maximum value of reflection loss was -7.8 db at 10.4 GHz frequency in 3mm thickness for x=0.4 sample.

MAGNETIC AND MICROWAVE ABSORPTION PROPERTIES OF NEODYMIUM DOPED NICKEL FERRITE USING MILLING TECHNIQUE

Nickel ferrite doped by neodymium in the form of (Ni(1-x)NdxFe2O4) with (x = 0.0 ; 0.2 and 0.4) have been synthesized using solid state reaction method with milling technique from NiO, Nd2O3 and Fe2O3 powder. The mixture of those compound materials was milled using High Energy Milling (HEM) machine for 10 hours and then sintered at 1000 °C for 5 h. X-ray diffraction patterns showed that a single phase of spinel ferrite has been formed in all of the compositions. The result of morphological observation using Scanning Electron Microscope (SEM) exhibited a homogeneous structure has been formed with particle size about 200 nm. The magnetic measurement using vibrating sample magnetometer (VSM) showed that the sample exhibited a ferromagnetic behavior, where the Ms value decrease (around of 58.4 to 39.40 emu/g) and value of Hc increased (around of 116-170 Oe) along with the addition of the Nd3+ ion (x values) content. While the ability of microwaves absorption measured by using Vector Network Analyzer (VNA) indicates that the maximum value of Reflection Loss (RL) obtained at the composition of x = 0.4 up to -29 dB at a frequency of 10.81 GHz. It means the Ni0,6Nd0,4Fe2O4 sample can absorb microwave up to ~ 96.5% at a frequency of 10.81 GHz.

Synthesis and characterization of carbonyl iron@epoxy core–shell microspheres for enhanced microwave absorption performance

Carbonyl iron powder (CIP) coated with a layer of epoxy (EP) shell, denoted as core–shell CIP@EP composites, were designed and prepared via in situ polymerization. The CIP@EP composites containing 4.5–6.8 wt% EP were systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, scanning and transmission electron microscopy, and vector network analyzer. The results indicated that CIP@EP composites with 9–254 nm EP shell thickness were successfully prepared through an efficient in situ polymerization method. The particle diameter of core CIP particles was 0.49–4.24 µm. The microwave absorption properties of the microspheres were then experimentally measured, and the CIP@EP composites exhibited a maximum reflection loss value of − 66.2 dB at 7.1 GHz at 2.0 mm absorber thickness. The effective absorbing bandwidth below − 10 dB was 8.0 GHz (from 10.0 to 18.0 GHz). The presence of the EP shell not only enhanced the microwave absorption performance of CIP@EP composites but also improved the overall chemical stability of CIP particles. The as-prepared CIP@EP composites may be a promising candidate for electromagnetic wave absorption applications, and the core–shell structure design can be extended to other microwave absorption materials.

Rational Design of Hierarchical SiO2@TiO2 Composite with Large Internal Void Space for High-Performance Microwave Absorption

The design and development of excellent microwave absorption (MA) material is significant for healthcare, electronic, and security industries. Herein, a sophisticated composite with the advantages of large interlayer space, nanoparticles with small size, and hierarchical nanostructure (core@shell@void@shell configuration) simultaneously is demonstrated for the first time. Such unique SiO2@TiO2 nanoparticle was fabricated via a multi-step process. Associating maximum reflection loss value can reach –35.2 dB in certain frequency of 11 GHz and thickness of 3.0 mm. Small-sized TiO2 nanoparticles (about 6 nm) in first coating and large gap between TiO2 coating layers are significantly critical for the superior MA performance. Our work points a new direction to rationally construct high-performance microwave absorber.

Enhanced microwave absorption properties in C band of Ni/C porous nanofibers prepared by electrospinning

Ni/C porous nanofibers (NiCPNFs) have been fabricated by electrospinning and a series of subsequent heat treatment cycles. Transmission electron microscope (TEM) and brunauer-emmett-teller measurement (BET) results exhibit that NiCPNFs with a diameter of 300 nm have numerous different size pores. In the meanwhile, nickel nanoparticles (NiNPs) are evenly embedded in porous carbon nanofibers. Moreover, Raman and vibrating sample magnetometer (VSM) results indicate that NiCPNFs possess lower graphitization, lower magnetization (MS) and higher coercivity (HC). The electromagnetic properties of samples show that NiCPNFs have excellent microwave absorbing performance. An absorbing frequency bandwidth with reflection loss (RL) value exceeding −10 dB can reach 12.8 GHz (3.7–12.3 GHz and 13.8–18.0 GHz) when the matching thicknesses are only 2.5–5.5 mm. In addition, the more excellent effective absorbing bandwidth (RL ≤ − 20 dB) reaches 5.4 GHz in the range of 4.2–9.6 GHz. Particularly, the maximum reflection loss (RL) value can reach - 69.5 dB at 7.8 GHz with a thickness of 3.2 mm. Investigations reveal that the participation of porous carbon material in NiCPNFs could obviously improve the microwave absorbing ability of this novel composite material, especially in the C band frequency range (4–8 GHz).

Porous flower-like Ni/C composites derived from MOFs toward high-performance electromagnetic wave absorption

Abstract The porous flower-like Ni/C composites were simply prepared through the pyrolysis of Zn-doped metal organic frameworks (MOFs) under a N2 atmosphere. The method is facile, controllable and without surface active agents. The microstructure, composition, and electromagnetic parameters can be easily controlled by varying thermal decomposition temperature to achieve the high electromagnetic loss. Interestingly, the Ni/C composites calcined at 800 °C have strong electromagnetic absorption with the maximum reflection loss (RL) value of −52.4 dB. In addition, the effective absorption band width (

PVP-encapsulated CoFe2O4/rGO composites with controllable electromagnetic wave absorption performance

Nowadays, developing electromagnetic wave (EMW) absorbers with lightweight, broad bandwidth and strong absorbing capacity is of great importance in electromagnetic radiation issue. In this work, a novel PVP encapsulated CoFe2O4/rGO composite is designed and synthesized by a facile hydrothermal technique. Noticeably, by altering the additive amount of PVP, the microstructure and morphology of CoFe2O4/rGO@PVP ternary composites can be effectively tuned. A typical capsule structure with a length of about 140 nm and a diameter of about 90 nm is obtained, where CoFe2O4/rGO binary composite is covered by PVP. Further, the electromagnetic parameters of as-synthesized CoFe2O4/rGO@PVP samples can be adjusted well by changing the weight fraction of PVP. Particularly, when the mass ratio of PVP to Fe(NO3)3·9H2O is 2, a maximum reflection loss (RL) value at 15.7 GHz with a thin thickness of 1.96 mm is −56.8 dB, Meanwhile, its effective absorption bandwidth (RL < −10 dB) is 6.8 GHz (from 10.64 to 17.44 GHz) with a thickness of 2.2 mm. Considering the specific CoFe2O4/rGO@PVP capsule structure, the possible mechanism of the enhanced EMW absorption is deeply investigated. Herein, a new route to improve the microwave absorbing performance of rGO-based composites is presented. Owing to its excellent EMW absorption performance, the obtained CoFe2O4/rGO@PVP composite can be considered as a promising and suitable candidate for high-performance EMW absorbers.

Fabrication of Fe3O4-modified lignocellulose composite for microwave absorption via a sol–gel-assisted hot-pressing process

An Fe3O4-modified lignocellulose (FeLC) composite was fabricated via a sol–gel-assisted hot-pressing process and used for microwave-absorbing and structural materials. The Fe3O4 nanoparticles could be formed in situ at the interface of the lignocellulose (LC) during sol–gel and hot-pressing processing. The obtained FeLC composites exhibited good mechanical and microwave absorption properties. The maximum reflection loss values of the FeLC composite reached − 10.97 dB at 17.04 GHz, and the effective electromagnetic wave absorption reached 90%. Compared with the modulus of rupture (MOR) and modulus of elasticity (MOE) of the LC composite, the maximum MOR and MOE values of the FeLC composite were 26.50 ± 1.16 MPa and 3.015 ± 0.25 GPa, respectively, increasing by 30.2% and 62.1%, respectively. Therefore, the properties of the FeLC could be enhanced via sol–gel assisted hot-pressing.

Preparation and Characterization of Magnetite Nanoparticles Combined with Polyaniline and Activated Carbon

In this paper, we report the preparation of magnetite nanoparticles combined with polyaniline and activated carbon. The results of the X-Ray diffraction data analysis showed that the samples had a magnetite crystal phase without other phases. The existence of polyaniline and activated carbon was confirmed using Fourier transform infrared spectroscopy characterization shown by the presence of S=O, C-N, and C-C. The sample of synthesis results in this work had the band gap of 3.23 eV. Moreover, the results of data analysis using vector network analyzer revealed the maximum reflection loss value of -14 with the absorbance of 50%. Thereby, the synthesis optimization needs to be done to increase the sample absorbance to the radar wave.

Combination of various grain sizes from nano to micron in polycrystalline holmium manganite (HoMnO3) as potential microwave absorbing application

The combinations of various grain sizes from nano to micron in polycrystalline holmium manganite (HoMnO3) as potential microwave absorber were investigated. HoMnO3 was prepared via high energy ball milling pursued by sintering process. The phase analysis confirmed that the formation of hexagonal holmium manganite, HoMnO3 along with small amount of orthorhombic holmium dimanganese pentaoxide, HoMn2O5. SEM micrographs indicated larger grain size as the sintering temperature increased. Explicitly, HoMnO3 provides an electromagnetic (EM) wave absorption characteristics and it was found that HoMnO3 sample have a potential as an efficient microwave absorber which exhibited the maximum reflection loss value of—23.4 dB at 8.5 GHz. This study advocates that by combining different grain size (nano and micron size) would contributed an enhancement value of microwave absorption.

3D hierarchical Co3O4/Reduced graphene oxide/melamine derived carbon foam as a comprehensive microwave absorbing material

In this work, a simple and cost-effective method was developed to prepare a novel structure with Co3O4 nanoparticles dispersed on 3D graphene-wrapped carbon foam with melamine foam as initial skeleton. This Co3O4/Reduced graphene oxide/Melamine derived carbon foam (Co3O4/RGO/MDCF) hybrid with a continuous conductive network and low bulk density of 10.6 mg/cm3 exhibits high specific microwave absorption performance. The maximum Reflection Loss (RL) value of −31.88 dB at 11.54 GHz and a qualified bandwidth of 3.4 GHz (RL ≤ −10dB) with the coating layer thickness of only 2.0 mm under 10 wt% loading was achieved by Co3O4/RGO/MDCF composite. Notably our work provides a general and low-cost method to fabricate comprehensive microwave absorption materials with high RL value, low density, thin thickness and low loading content, which can be applied on scale and meet the requirement for the new type of electromagnetic wave absorptive material.

Flower-like MoS2@Bi2Fe4O9 microspheres with hierarchical structure as electromagnetic wave absorber

Uniform MoS2 nanosheets were tightly installed on the smooth surface of Bi2Fe4O9 microplatelets (MPLs) via a facile two-step hydrothermal process. MoS2, as a typical two-dimensional transition metal sulfide, combining with multiferroic material Bi2Fe4O9, was shown to exhibit high dielectric activity for electromagnetic wave absorption while exhibiting hierarchical structure to achieve an effective multiple reflection. In accordance with transmit-line theory, a maximum reflection loss value of MoS2@Bi2Fe4O9 microspheres (MPs) was calculated as −52.3 dB at 12.4 GHz with a sample thickness of 2.8 mm as well as an effective absorption bandwidth (reflection loss below −10 dB) reached 5.0 GHz (10.4–15.4). In the light of electromagnetic parameters, it can be found that flower-like MoS2@Bi2Fe4O9 MPs can utilize the merits of both multi-interfaces constructed by multi-polarization and reflection, as well as synergistic effect between MoS2 nanosheets and Bi2Fe4O9 MPLs. Construction of such hierarchical structure composed of flower-like dielectric shell and multiferroic core paves an advisable way for gaining a new candidate for lightweight electromagnetic wave absorbers.

The effect of Ce–Co substitution on the structural and the electromagnetic properties of barium hexaferrite

Ce–Co substituted, barium hexaferrite with the chemical composition of Ba0.5Ce0.5Fe11CoO19 was prepared by using the ceramic technique. The structural properties of the Ce–Co substituted, barium hexaferrite was investigated using X-ray diffractometer. The magnetic hysteresis loop of the sample was characterized by vibrating sample magnetometry. In order to identify the surface morphology of the sample, field emission scanning electron microscopy was used. Using the transmission/reflection coaxial line method in the range of 2–18 GHz, the complex permeability and complex permittivity, the reflection loss (RL) properties, absorption loss and shielding effectiveness of the prepared composition were determined. The maximum RL value of − 31.4 dB at 11.4 GHz with a 3 mm thickness sample was obtained and the maximum shielding effectiveness value was observed around 59.2 dB.

Electron Holography of Yolk–Shell Fe3O4@mSiO2 Microspheres for Use in Microwave Absorption

Yolk–shell nanostructures are very promising alternatives as next-generation microwave absorption materials. However, it still remains a great challenge to understand structure–property relationships and develop highly efficient yolk–shell structured microwave absorbers. Herein, a series of dielectric-magnetic yolk–shell Fe3O4@mesoporous SiO2 microspheres (denoted as Fe3O4@mSiO2) were synthesized by combining a modified Stober method and hydrothermal etching process. The microwave absorption performance of the Fe3O4@mSiO2 yolk–shell microspheres could be optimized by tuning the void space and shell number easily. By increasing the average diameter of the void space from 380 to 490 nm, the maximum reflection loss (RL) value of −38.7 dB at 8 GHz was achieved with a composite thickness of 2 mm, and the effective bandwidth (RL < −10 dB) was beyond 4 GHz. Compared with the single-shelled counterparts, the double-shelled Fe3O4@mSiO2 microspheres exhibited significantly enhanced absorption properties. Importantl...

Novel nanocomposites of cobalt ferrite covalently-grafted on graphene by amide bond as superior electromagnetic wave absorber

Unique covalently bonded cobalt ferrite (CoFe2O4)/graphene nanocomposites are successfully fabricated via an amino-ester-amide reaction process. The morphology, component, functional groups and electromagnetic properties are detected by Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectra (FTIR), Vibrating Sample Magnetometer (VSM) and Vector Network Analyzer (VNA). Compared to non-covalently bonded nanocomposites, the covalently bonded CoFe2O4/graphene nanocomposites have outstanding electromagnetic wave absorption properties. We found that the maximum reflection loss value reached at −55.2 dB and the absorption bandwidth with reflection loss below −10 dB was about 5.4 GHz at 1.7 mm of thickness. The efficiency is attributed to the introduction of amide bonds in the nanocomposites. As a stable carrier channel, amide bonds can promote the migration rate of electrons and binding degree between CoFe2O4 and graphene nanosheets, which provide a crucial impact on electromagnetic parameters and polarization modes of materials, thus improving the absorption capacity of electromagnetic waves. It can be inferred that the nanocomposites have a broad application prospect in the field of electronic instruments, aerospace, military radars and national defense security fields.

Fabrication, characterization and electromagnetic wave absorption properties of covalently modified reduced graphene oxide based on dinuclear cobalt complex

We are reporting on well-designed single-layered and gradient concentration triple-layered microwave-absorbing composites based on functionalized reduced graphene oxide (FRGO). The RGO-[Co2L2Cl3]Cl, called FRGO, was fabricated through systematic experimental efforts by the covalent attachment of the 2,6-diamino-3-[(2-carboxylicacid) phenylazo]-pyridine (L)/Cobalt (Co) complex with graphene oxide (GO) functionalities. The formation of FRGO was proven by a series of characterization techniques, such as XPS, FTIR, XRD, Raman spectroscopy, FESEM, and TEM. The consideration of RGO-[Co2L2Cl3]Cl as a highly efficient microwave-absorbing material is a result of its magnetoelectric synergistic effect, impedance match, and multiple scattering. The maximum reflection loss (RL) of single-layered an RGO-[Co2L2Cl3]Cl/epoxy resin composite can reach −16.32 dB at 8.69 GHz, which corresponds to a composite with 30 wt % absorber loading and a thickness of 4.5 mm. For the triple-layered composite with increasing mass percentage (10–20–30 wt %) of RGO-[Co2L2Cl3]Cl in the direction of microwave propagation, the maximum reflection loss value of −34.9 dB can be achieved at 10.69 GHz, with a coating layer thickness of 4.5 mm. The result demonstrates that the RGO-[Co2L2Cl3]Cl/epoxy resin composites of both models can be ideal microwave-absorbing candidates for application in the X-band.

Constructing excellent electromagnetic wave absorber with dielectric-dielectric media based on 3D reduced graphene and Ag(I)-Schiff base coordination compounds

The dielectric-dielectric composite (SRGA) for electromagnetic absorber was fabricated via integrating Ag(I)-Schiff base coordination compounds (SSBCC) with three-dimensional reduced graphene aerogel (3D-rGA) powders. SRGA showed excellent electromagnetic wave absorption properties in terms of reflection loss, absorption band width and absorber thickness. Specially, when the mass ratio of SSBC to 3D-rGA powders was 1:3 (SRGA-25), the maximum value of reflection loss at 2 mm was up to −63.82 dB and the effective frequency bandwidth of 6.28 GHz (10.16–16.44 GHz) at 2.5 mm can be obtained. The mechanism investigation of electromagnetic wave absorption for SRGA showed that the enhanced electromagnetic wave absorption was ascribed to enhanced polarization loss derived from good 3D-conductive-network units of 3D-rGA, abundant interfaces caused by the media heterostructure due to the introduction of SSBCC and the good impedance matching condition. And 3D-rGA based materials might be put into practical application only in powder state due to the very low strength of the buck state. Therefore, the investigation on SRGA in our contribution is considered to be an actual performance evaluation of the materials based on three-dimensional graphene for microwave attenuation. This work also provided a method for fabricating excellent graphene-based electromagnetic wave absorbers by simply mixing a suitable dielectric lossy material, e.g. SSBCC.

Microwave absorption enhancement of porous C@CoFe2O4 nanocomposites derived from eggshell membrane

As the rapid development of electronic devices and wireless communication tools, it is urgent to design and fabricate low-cost, lightweight and effective electromagnetic absorption materials to solve electromagnetic interference of electromagnetic wave. Herein, a feasible and low-cost method has been developed to synthesize an effective carbon-based microwave absorber. The hierarchically porous structures derived from eggshell membrane (ESM) and the anchored CoFe2O4 nanoparticles (NPs) helped the C/CoFe2O4 nanocomposites perform a favor for strengthening electromagnetic absorption capability. The porous C@CoFe2O4 nanocomposites achieves the maximum reflection loss value of −49.6 dB at 9.2 GHz with 30% loading in the paraffin matrix. Detailed investigation reveals that the porous structure as well as strong synergetic effect between porous carbon matrix and magnetic nanoparticles can effectively improve the impedance matching condition and attenuation ability of the nanocomposites, leading to a high microwave absorption performance. In addition, the simulation results indicate that the radar cross section (RCS) of a strong metal scattering sources at different degrees can be significantly reduced after coating with C@CoFe2O4 nanocomposites. These achievements light the way to prepare low-cost and sustainable microwave absorbents with excellent electromagnetic wave absorbing performances, utilizing the wasted eggshell membrane biomasses as precursors.

Microwave absorption enhancement and loss mechanism of lamellar MnO2 nanosheets decorated reduced graphene oxide hybrid

Manganese oxide/reduced graphene oxide (MnO2/rGO) hybrid with layered MnO2 nanosheets grow on rGO surfaces have been prepared for microwave absorbing. The hybrid exhibits significantly enhanced microwave absorption properties compared with rGO and MnO2. A maximum reflection loss value can reach − 26.7 dB at 11.04 GHz with the matching thickness of 2.6 mm, and the effective absorption bandwidths exceeding − 10 dB and − 20 dB are 3.6 GHz and 1.06 GHz, respectively. The enhancement in microwave absorption efficiency of MnO2/rGO hybrid is arose from the synergistic effects between lamellar MnO2 and rGO in its unique three-dimensional (3D) architecture, which leads to strong conduction loss and multiple reflections, and further in favour of appropriate impedance matching ratio and good attenuation ability. These fundamental understandings on the property–structure relationship of as-synthesized MnO2/rGO hybrid will prove an efficient approach to the designing and construction of MnO2-based 3D nanostructures for advanced electromagnetic wave absorbing applications.