Microwave Absorption Applications Research Articles

Investigation of Magnetic and Microwave Absorption Properties of Ba(1−2x)LaxNaxFe10CoTiO19 Hexaferrites in 18.0–26.5 GHz Band

A series of Ba(1−2x)LaxNaxFe10CoTiO19 hexaferrite samples with x = 0.00–0.25 (step size 0.05) were prepared by using conventional solid-state reaction technique. The magnetic properties of the hexaferrites have been investigated at room temperature by employing a vibrating sample magnetometer. There is an overall decrease in saturation magnetization from 70.64 to 57.83 emu/g with an increase in doping concentration from x = 0.00–0.25. The microwave measurements were done utilizing vector network analyzer in the k-band (18.0–26.5 GHz) frequency range. The electromagnetic measurements revealed that the gross tangent loss is maximum for x = 0.10 sample. The microwave absorption measurements show that sample x = 0.10 with 1.4 mm thickness exhibits a reflection loss of − 26.59 dB (99.78% signal absorption) and 7.65 GHz bandwidth. Thus, it is considered for thin single-layer broadband microwave absorber applications in 18.0–26.5 GHz frequency range.

Synthesis and high-performance microwave absorption of reduced graphene oxide/Co-doped ZnNi ferrite/polyaniline composites

The rise of modern communication devices has seriously imperiled human health due to electromagnetic (EM) pollution. In this context, the aim of this work is to develop novel reduced graphene oxide/Co-doped ZnNi ferrite/polyaniline ternary composites that exhibit enhanced microwave absorption properties. It is observed that the ternary composite prepared by in-situ polymerization show best EM absorption. The maximum reflection loss (RL) reaches −24.2 dB and the efficient bandwidth (RL < −10 dB) is more than 3 GHz with an absorbed thickness of 1.7 mm. The in-depth analysis based on complex permittivity and permeability reveals that the improved microwave absorption ability is related to the uniform sandwich-like multilayer structure and impedance compatibility of the ternary composites. The results and analysis show that these ternary composites with small thickness and wide absorption band are the potential candidates for microwave absorption applications.

Synthesis of popcorn-like α-Fe2O3/3D graphene sponge composites for excellent microwave absorption properties by a facile method

Popcorn-like α-Fe2O3/3D graphene sponge (α-F/3DGS) composites have been successfully fabricated by a novel and facile two-step synthetic route combining template-assisted preparation and co-precipitation method for microwave absorption application. The results show that the popcorn-like α-Fe2O3 nanoparticles with an average diameter about 150–200 nm are uniformly encapsulated into the 3DGS exhibiting a porous microstructure with plenty of wrinkles. The composite displays the optimum microwave absorption properties with the minimum reflection loss (RLmin) of − 55.7 dB and the maximum effective microwave absorption bandwidth up to 4.42 GHz (12.30–16.72 GHz) when the thicknesses are merely 1.4 and 1.7 mm, respectively, exhibiting greatly enhanced microwave absorption properties compared to those of some 2D graphene-based microwave absorbing materials. The excellent microwave absorption properties are attributed to the synergistic effect between dielectric loss and magnetic loss mechanism and improvement for the impedance matching behavior. This study paves a way for designing and fabricating lightweight and high performance microwave absorption materials based on 3D graphene composites.

A novel microwave absorber of FeCoNiCuAl high-entropy alloy powders: Adjusting electromagnetic performance by ball milling time and annealing

The FeCoNiCuAl high-entropy alloy powders are prepared in equimolar ratio by mechanical alloying in different milling time and then annealing at 773 K. The microstructure, morphology, particle size, magnetic and electromagnetic performance of powders were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), laser scattering particle size distribution analyzer, vibrating sample magnetometer (VSM) and vector network analyzer. The results indicate that flaky particles, which formed in the process of ball milling, show a soft magnetic character, as well as, the ranges of coercivity (Hc) are 67.6–105.1 Oe and the values of saturation magnetization (Ms) range from 69.1 emu/g to 94.2 emu/g. As the increasing of the milling time, the real parts of complex permittivity (ε′) increase firstly and then decrease, however, the imaginary parts of complex permittivity (ε″) close to zero for all the samples. Meanwhile, the real parts of complex permeability (μ′) are 1.26–1.56 and the imaginary parts of complex permeability (μ″) are 0.28–0.36 with change of milling time. The reflection loss (RL) of powders can reach −10 dB or less and 30 h-milling sample shows the maximum RL is −19.17 dB at 7.84 GHz with the thickness of 2 mm. After annealing, there appear two new phases, CoFe2O4 and AlFe3, that improve the values of Ms. The increased particles sizes and the enhanced values of Ms of powders all can promote complex permittivity and complex permeability. In addition, the RL also can get increased. These encouraging findings provide the potential advantages of high-entropy alloys for microwave absorption application.

Nano Bimetallic@Carbon Layer on Porous Carbon Nanofibers with Multiple Interfaces for Microwave Absorption Applications

Porous carbon fibers (FeCo@C-PCFs) hybrids are fabricated by a two-step process involving the electrospinning followed by heat treatment, in which several steps are involved including the reduction of polyvalent metal ions, the produced alloy nanoparticles are encapsulated into porous carbon substrate, yielding the FeCo-polyacrylonitrile networks (FeCo-PAN) that are formed in situ and function as the building blocks. After altering feeding proportion of Co2+ and Fe3+, the formation of FeCo@C-PCF compounds could be controlled. More importantly, FeCo alloys seem to have higher chemical stability. With different graphitization degrees, FeCo@C-PCF compounds were proven to be outstanding microwave (MW) absorbent including thickness, effective bandwidth, and reflection loss (RL). The maximum RL values reached −56 dB at 1.85 mm and broadest bandwidth was 8.3 GHz.

Design and microwave absorption properties of thistle-like CoNi enveloped in dielectric Ag decorated graphene composites

A novel hierarchical composites for coupling thistle-like CoNi with dielectric Ag decorated graphene in paraffin wax as high performance microwave absorber has been synthesized by a facile two-step strategy. The components, particle size, microstructure and morphology of the resulting composites are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, scanning electron microscope, transmission electron microscopy and energy dispersive X-ray spectroscopy, etc. Due to the unique flower structure and good synergistic effect of dielectric loss and magnetic loss, thistle-like CoNi@dielectric Ag decorated graphene composites have showed glorious microwave absorption intensity and frequency width. The maximum reflection loss of −61.9 dB can be gained at 6.96 GHz, which has rarely been reported yet. In addition, the corresponding effective bandwidth with reflection loss less than −10 dB is 5.6 GHz ranging from 12.4 to 18 GHz at only 1.67 mm thickness. This highly efficient and broad band features endow thistle-like CoNi@dielectric Ag decorated graphene composites with promising applications in microwave absorption, electromagnetic shielding, information safety, direct broadcast satellite and military radar fields.

Preparation of Cr3+-Substituted NiFe2O4 Nanoparticles and Its Microwave Absorption Properties

In the present work, spinel Ni(1−X)CrXFe2O4 (X = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 M) nanoparticles were synthesized by co-precipitation method followed by calcination at 400 °C for 2 h. The structural and morphological properties of the synthesized nanoparticles were studied using powder XRD,micro-Raman measurements, FE-SEM, TEM and EDS. The results revealed that the synthesized nanoparticles were single-crystal, cubic-phase structure with spherical shape. Energy-dispersive X-ray spectroscopy confirmed the elements present in the synthesized nanoparticles. Moreover, microwave absorption properties were measured using vector network analyser (VNA). The minimum reflection loss − 14.44 dB at 9.49 GHz was observed for Ni(1−X)CrXFe2O4 (X = 0.5 M) nanoparticles at 3 mm thickness. These results suggest that Ni(1−X)CrXFe2O4 (X = 0.5 M) nanoparticles would be applicable for microwave absorption application.

Cubic MnFe2O4 particles decorated reduced graphene oxide with excellent microwave absorption properties

Herein, we have fabricated the reduced graphene oxide/manganese ferrite (RGO/MnFe2O4) hybrid composites by a facile one-pot hydrothermal method. The obtained MnFe2O4 particles exhibited the uniquely cubic morphology with an average particle size of 100.6 nm, which were uniformly attached to the surface of RGO sheets. Results demonstrated that both the ratio of RGO to MnFe2O4 and filling ratio had notable effects on the microwave absorption performance of the as-prepared hybrid composites. Moreover, the hybrid composites showed the characteristics of thin thickness, broad bandwidth and strong absorption. Significantly, the hybrid composite with a filling ratio of 70 wt% (S2) exhibited the best microwave absorption performance, i.e. the minimum reflection loss reached −47.5 dB and effective absorption bandwidth (less than −10 dB) was 5.2 GHz for a thickness of only 1.7 mm. Therefore, the RGO/MnFe2O4 hybrid composites could be potential candidates for application in microwave absorption.

Graphitized nitrogen-doped porous carbon composites derived from ZIF-8 as efficient microwave absorption materials

Rational construction of profitable microstructure in carbon-based electromagnetic composites is becoming a promising strategy to reinforce their microwave absorption performance. Herein, a N-doped highly porous carbon composite derived from thermal decomposition of Zn-based MOF (ZIF-8) has been synthesized for microwave absorption applications. The maximum reflection loss (RL) of −39.7 dB could be achieved with a thickness of 4 mm and the effective absorption bandwidth was from 7.9 GHz to 12.2 GHz covered X band (8–12 GHz). By comparing the porous carbon composites derived from conventional ZIF-8, it can be validated that porous structure, degree of graphitization and graphitic-N level is the key factors to improve the microwave absorption performance by increasing dielectric loss ability. The results demonstrated that the ZIF-8 derived graphitized nitrogen-doped porous carbon composites had great potential for microwave absorption performance, which may open up a new avenue to promote the electromagnetic applications of MOF-derived carbon composites.

Highly-efficient electromagnetic interference shielding and microwave dielectric behavior of a (Bi2O3 + B2O3)-doped MWCNT/BaTiO3 ceramic nanocomposite

Microwave dielectric properties along with electromagnetic interference shielding effectiveness (EMI SE) of a multi-walled carbon nanotube (MWCNT)/barium titanate (BaTiO3) nanocomposite are investigated in this paper. Appropriate amount of sintering additive (Bi2O3 + B2O3) was doped into some nanocomposites to reduce the sintering temperatures. The dielectric properties of the nanocomposites with various MWCNT and sintering additive contents were evaluated at different microwave frequency ranges. It was found that the incorporation of optimized amount of (Bi2O3 + B2O3) can give rise to significantly good dielectric properties. Results also indicated that incorporation of 6 wt% (Bi2O3 + B2O3) into 1.5 mm-thick nanocomposite containing 8 wt% MWCNT led to an EMI SE greater than 28 dB, suggesting this novel nanocomposite as a promising candidate for microwave absorption and electromagnetic interference applications.

One-step fabrication of N-doped CNTs encapsulating M nanoparticles (M = Fe, Co, Ni) for efficient microwave absorption

By using a modified non-toxic pyrolysis method, M@NCNTs comprising in-situ formed M nanoparticles encapsulated in nitrogen-doped carbon nanotubes (NCNTs) have been synthesized. Compared to traditional preparation process of M@CNTs (eg: acid-aid treatment to CNTs then decorating M particles onto), this method holds the advantage of free of complicated treatment processes. The M@NCNTs exhibit tightly connected interfaces of M/NCNTs and contain abundant N dopants, which could contribute interfacial polarization and defect-dipole polarization to improving the microwave absorption performance. An intense dielectric relaxation is observed in Fe@NCNTs samples, which further enhances the dielectric loss. As expected, the as-synthesized M@NCNTs composites demonstrate promising candidates in microwave absorption (MWA) application. The minimum reflection loss (RL) of Fe@NCNTs (with 10 wt% loading) is up to −30.43 dB at 3.2 mm, and the effective absorption bandwidth (RL < −10 dB) is as wide as 5.7 GHz which benefits from the neighboring dual absorption peaks induced by the intense dielectric relaxation. Co@NCNTs and Ni@NCNTs also have satisfactory effective absorption bandwidth ∼4.08 and ∼4.72 GHz, respectively. The modified pyrolysis method is low-cost and non-toxic, which could become an industrial technique to synthesize carbonaceous composites for microwave absorption.

Effect of rare earth doping on the structural and magnetic features of nanocrystalline spinel ferrites prepared via sol gel route

Rare earth Ce doped NiZn with composition of Ni0.8Zn0.2CexFe2−xO4 at x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10 were synthesized via sol-gel route. Rare earth Ce was doped to tune the structural and magnetic properties of the spinel ferrites. Therefore, the systematic effect of Ce on the structural, morphological and magnetic studies was carried out. FTIR, XRD, FESEM and VSM were carried out to investigate the metal stretching vibrations, structure, phase, morphology and magnetic characteristics of Ni0.8Zn0.2CexFe2−xO4 nanoferrites respectively. The size of the crystallites, cell volume and lattice parameters (theoretical and experimental) were decreased with Ce3+ doping. The size of the crystallites was in the range of 41–9 nm. The physical characteristics such as X-ray density, bulk density and porosity were also decreased with Ce3+ substitution. However, the lattice strain was increased with Ce3+substitution in the NiZn ferrite lattice. The cations distributions study was determined using Bertaut method. Force constants at tetrahedral and octahedral sites were calculated from the FTIR studies. Saturation magnetization, remanent magnetization, coercivity, anisotropy constant (K) and Bohr magneton were evaluated from the magnetic hysteresis loops. Saturation, remanence, initial permeability and Bohr magneton were decreased whereas the coercivity was increased with Ce3+ doping. Yafet and Kittle (Y-K) angles were increased with Ce doped NiZn nanoferrites from x = 0 to x = 0.04 respectively. Switching field distribution (SFD) evaluations for Ce doped NiZn nanoferrites were determined by taking first derivative of the demagnetization data respectively. In conclusion, Single phase Ce doped NiZn nanoferrites have large magnetic saturation, remanence whereas other samples have higher coercivity accordingly. Ce-doped NiZn nanoferrites with varying structural and magnetic properties have potential applications in various fields such as switching, security, core, microwave absorption applications, nanofabrication and nanodevices.

Influence of La3+ ion doping on physical properties of magnesium nanoferrites for microwave absorption application

Lanthanum (La3+ ions) doped magnesium ferrite nanoparticles i.e. MgLaxFe2−xO4 (x = 0, 0.05, 0.075, 0.1, 0.125) have been prepared using sol-gel technique. These as-prepared nanomagnetic particles were characterized by using X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), High resolution field emission scanning electron microscopy (HRFESEM) with energy dispersive spectroscopy (EDS), Transmission electron microscopy (TEM) and Vibrating sample magnetometer (VSM) techniques. X-ray diffraction analysis reveal that the samples are single phase cubic spinel crystals with size 12–15 nm. Lattice parameter increases with the increase in La3+ ion concentration. The induced strain calculated from Williamson-Hall plots shows that strain decreases from x = 0.0 to x = 0.075 and then increases from x = 0.1 to x = 0.125. FTIR spectra show that FeO stretching vibration peaks of octahedral (FeO6) and tetrahedral (FeO4) group broadness increases with lanthanum content due to gradual decrease in the grain size. These variations are attributed to lattice deformation induced by interparticle interactions, cation distribution, and La3+ ions concentration in the spinel structured samples. SEM micrographs revealed the existence of superfine particles and agglomerated patterns for higher La3+ ion content. The average particle size obtained from TEM images are in close agreement with the crystallite size calculated from the XRD patterns. The magnetic studies exhibited the saturation magnetization, retentivity, anisotropy constant and magnetic moment of the particles decrease with increasing La3+ ions concentration indicating the superparamagnetic nature of lanthanum doped magnesium ferrite samples.

Porous Co-C Core-Shell Nanocomposites Derived from Co-MOF-74 with Enhanced Electromagnetic Wave Absorption Performance.

The combination of carbon materials and ferrite materials has recently attracted increased interest in microwave absorption applications. Herein, a novel composite with cobalt cores encapsulated in a porous carbon shell was synthesized via a facile sintering process with a cobaltic metal-organic framework (Co-MOF-74) as the precursor. Because of the magnetic loss caused by the Co cores and dielectric loss caused by the carbon shell with a unique porous structure, together with the interfacial polarization between two components, the ferromagnetic composite exhibited enhanced electromagnetic wave absorption performance compared to traditional ferrite materials. With the thermal decomposition temperature of 800 °C, the optimal reflection loss value achieved -62.12 dB at 11.85 GHz with thin thickness (2.4 mm), and the bandwidth ranged from 4.1 to 18 GHz with more than 90% of the microwave that could be absorbed. The achieved performance illustrates that the as-prepared porous Co-C core-shell composite shows considerable potential as an effective microwave absorber.

Effect of untreated fiber loading on the thermal, mechanical, dielectric, and microwave absorption properties of polycaprolactone reinforced with oil palm empty fruit bunch biocomposites

Basic research on recyclable, renewable and biodegradable polymer composite materials reinforced with natural fibers is increasingly growing. In this article, we characterize agricultural waste by determining its dielectric properties for microwave absorber application. Recently, polymer composites reinforced with natural fibers are increasingly used in dielectric and aircraft applications. We used a Thermal Hake blending machine to blend oil palm empty fruit bunch with polycaprolactone grain to make a homogeneous powder. The functional groups of the resulting composites were then analyzed through Fourier transform infrared spectrometry. Thermogravimetric and differential thermogravimetric analyses were performed to determine the thermal degradation behaviors of the composites. The tensile strength, tensile modulus and elongation at break of the composites were measured in an Instron universal testing machine. A rectangular waveguide and open‐ended coaxial probe connected to a microwave network analyzer (PNA) Agilent N5230A PNA‐L was used to measure the reflection coefficient S11 and transmission coefficient S21 values and the dielectric properties of the composite materials. Results showed that the thermal stability and dielectric properties of the polymer composites decreased as the fiber content increased. The composites exhibited potential as microwave absorbers at microwave frequencies. POLYM. COMPOS., 39:E1778–E1787, 2018. © 2018 Society of Plastics Engineers

Synthesis of hollow Fe3O4 particles via one-step solvothermal approach for microwave absorption materials: effect of reactant concentration, reaction temperature and reaction time

Hollow Fe3O4 particles with variable crystal sizes were synthesized by one-step solvothermal method for lightweight and efficient microwave absorber applications. The reactant concentration, reaction temperature and reaction time are three key factors for morphology control of the products and can further influence the microwave absorption properties. The diameters of as-prepared hollow magnetite particles ranged from 200 to 1000 nm, while the shell thickness differed from 35 to 280 nm. It is found that the microwave absorption properties are improved along with the increasing of the hollow structure size which depend on the reaction conditions. The sample prepared at 200 °C for 36 h exhibited an optimal reflection loss of − 55.14 dB at 11.76 GHz with the thickness of 2.07 mm, while possessing the broadest effective bandwidth reaching 4.72 GHz (5.6–10.32 GHz) at 2.49 mm. The excellent microwave absorbing properties of such materials can be attributed to the high magnetic loss and favorable impedance matching property.

Rational Construction of Uniform CoNi-Based Core-Shell Microspheres with Tunable Electromagnetic Wave Absorption Properties

Core-shell particles with integration of ferromagnetic core and dielectric shell are attracting extensive attention for promising microwave absorption applications. In this work, CoNi microspheres with conical bulges were synthesized by a simple and scalable liquid-phase reduction method. Subsequent coating of dielectric materials was conducted to acquire core-shell structured CoNi@TiO2 composite particles, in which the thickness of TiO2 is about 40 nm. The coating of TiO2 enables the absorption band of CoNi to effectively shift from Ku to S band, and endows CoNi@TiO2 microspheres with outstanding electromagnetic wave absorption performance along with a maximum reflection loss of 76.6 dB at 3.3 GHz, much better than that of bare CoNi microspheres (54.4 dB at 17.8 GHz). The enhanced EMA performance is attributed to the unique core-shell structures, which can induce dipole polarization and interfacial polarization, and tune the dielectric properties to achieve good impedance matching. Impressively, TiO2 coating endows the composites with better microwave absorption capability than CoNi@SiO2 microspheres. Compared with SiO2, TiO2 dielectric shells could protect CoNi microspheres from merger and agglomeration during annealed. These results indicate that CoNi@TiO2 core-shell microspheres can serve as high-performance absorbers for electromagnetic wave absorbing application.

Template‐Free Formation of Uniform Fe3O4 Hollow Nanoflowers Supported on Reduced Graphene Oxide and Their Excellent Microwave Absorption Performances

Iron oxides (Fe2O3, Fe3O4) are highly desirable for electromagnetic (EM) microwave absorption applications because of their high magnetization, low toxicity and good magnetic loss. Herein, we repot an effective strategy to improve the reflection loss (RL) of iron oxides‐based materials via a delicate design of distinctive hybrid nanostructures, where uniform magnetite (Fe3O4) hollow nanoflowers organized from ultrathin nanosheets are supported on the reduced graphene oxide (rGO) matrix (MHF‐rGO). The designed MHF‐rGO exhibits excellent microwave absorption performance with a low RL of −53.3 dB at 4.96 GHz and a wide bandwidth of 5.68 GHz (&lt; − 10 dB). The top level microwave absorption properties are associated with the high surface areas, ultrathin nanosheets and hollow structures of magnetic Fe3O4 nanoflowers, which present a good synergetic role with lightweight rGO. Furthermore, the controllable permittivity in MHF‐rGO is developed by adjusting the rGO content, which can balance the permeability to obtain a good impedance matching. This study paves an effective way to improve and extend the microwave absorption performances of iron oxides‐based materials through a delicate hybrid nanostructures design strategy.

Aluminum and chromium substituted Y and Z-type hexaferrites for electromagnetic shielding interference and microwave absorber applications

Aluminum and chromium substituted Y and Z-type hexaferrites for electromagnetic shielding interference and microwave absorber applications

Ni/graphitic carbon core–shell nanostructure-based light weight elastomeric composites for Ku-band microwave absorption applications

Graphitic carbon-coated Ni metal core nanoparticles with respective reflection loss for different thickness of Ni/C and rubber composites.