Spherical Carbonyl Iron Research Articles

Absorption-diffusion integrated stacked metamaterials by multi-compound strategy for broadband electromagnetic attenuation

The meta-structural design of flat absorbers demonstrates significant potential for improving microwave attenuation performance. However, the single mechanism of amplitude attenuation through resonance-enhanced effect necessitates considerable material thickness, restricting its application in electromagnetic (EM) defense. Utilizing the synergistic effect of multiple mechanisms is expected to break through the performance limits of microwave stealth metamaterials at the sub-wavelength scale. Herein, absorption-diffusion integration stacked metamaterials (ADISM) were designed using a multi-compound strategy, which comprises bionic porous spherical carbonyl iron powder (SCIP) coatings and stacked vortex metasurfaces (VMs). Such a metamaterial integrates EM scattering modulation with microwave absorption, enabling the creation of a broadband, high-efficiency, low-reflection design, providing an effective absorption bandwidth (EAB) reaching 10.42 GHz (7.58–18 GHz) at a thickness of 2.48 mm. Manipulating the orbital angular momentum (OAM) to effect wavefront transformation, the dissipation of EM wave energy is achieved. The absorption peak frequency modulation and absorption bandwidth broadening are achieved by the intrinsic loss capability of the porous coating, and corresponding mechanisms are demonstrated by simulation models. In short, the synergistic effects of microwave absorption and scattering modulation significantly enhance the return loss capability and facilitate broadband microwave attenuation. This research offers new insights into the multifunctional integration of EM stealth metamaterials.

Influence of normal force on magnetic-field-induced shear modulus of isotropic and anisotropic magnetorheological elastomers having spherical and non-spherical shape iron particles

ABSTRACT Isotropic and anisotropic magnetorheological elastomers (MRE) were prepared using spherical carbonyl iron (CI) particles and electrolyte non-spherical iron (EI) particles having a 60% weight fraction in silicon rubber. The pre-structured MREs were prepared under a constant magnetic field of 0.3 Tesla. A parallel-plate MR rheometer with a magneto-rheological cell was used to conduct dynamic measurements under different normal forces. All the data were recorded under 1 Hz frequency and strain amplitude of 0.1% (in the linear viscoelastic region), and normal force was varied from 1N to 10 N. Results show that the magnetic-induced shear modulus increases in both MREs with normal force for isotropic as well as anisotropic samples. However, in CIP-based MRE, the MR effect increases with a pre-structured sample, whereas for EIP-based pre-structured MRE, the MR effect decreases compared to isotropic samples. Nevertheless, the relative MR (RMR) effect decreases with normal force in both cases. The rate of decrease is different in CIP- and EIP-based MREs. A possible mechanism for the same is discussed in the paper.

Effect of the shape and content for added iron powder on properties of nanocrystalline soft magnetic composites

The objective of this work is to investigate the difference of the shape and content for iron powders on properties of nanocrystalline SMCs prepared under the low baking temperature and molding pressure. The results show that both irregular reduced iron powders (RIP) and spherical carbonyl iron powders (CIP) can effectively improve the relative density (ρr), saturation magnetization and effective permeability (μe) of nanocrystalline SMCs, but the optimization effect of RIP on the ρr and μe is higher when the content is less than 50 wt%. Because RIP is more easily filled between nanocrystalline particles and coupled and agglomerated to form new magnetic path. The SMCs prepared by adding CIP has higher DC-bias characteristics (> 94% at 100 Oe), frequency stability and lower total losses (Pcv). When the content of CIP is 30 wt%, the Pcv is 748.4 mW/cm3 (20 mT, 1 MHz), which is 6.5% lower than nanocrystalline SMCs and 18.6% lower than RIP mixed SMCs. This is due to the fact that CIP has a slight deformation during the molding process, which has low damage to the insulation coating layers. The present work provides reference for the application of nanocrystalline powders in the field of molding inductors.

Mechanical and Electromagnetic Wave Absorption Performance of Carbonyl Iron Powder-Modified Nonwoven Materials

In order to develop carbonyl iron-enhanced electromagnetic wave-absorbing composites, this paper utilizes two different morphologies of carbonyl iron powder (CIP), spherical and flake-like, which are blended with aqueous polyurethane (PU) in three different ratios to prepare impregnating solutions. Polyester (PET) needle-punched nonwoven materials are impregnated with these solutions to produce electromagnetic wave-absorbing composites. First, electromagnetic parameters of the two CIP particle types, spherical carbonyl iron (SCIP) and flake-like carbonyl iron (FCIP), are tested with the coaxial method, followed by calculation of the results of their electromagnetic wave absorption performance. Next, the composites are subjected to microscopic morphology observation, tensile testing, and arched frame method electromagnetic wave absorption performance testing. The results indicate that the microwave absorption performance of FCIP is significantly better than that of SCIP. The minimum reflection loss value for F3, a kind of FCIP-modified nonwoven fabric, at the thickness of 1 mm, at 18 GHz is −17 dB. This value is even better than the calculated RL value of CIP at the thickness of 1 mm. The anisotropic shape of flake-like magnetic materials is further strengthened when adhering to the surface of PET fiber material. Additionally, the modified composites with carbonyl iron exhibit higher tensile strength compared with pure PET. The addition of fibrous skeletal materials is expected to enhance the impedance matching of flake-like magnetic particles, forming a wearable and microwave-absorbing composite.

Direct ink writing printed flexible double-layer staggered woodpile structure for multi-band compatible absorption of gigahertz and terahertz waves

Soft multi-band compatible electromagnetic wave absorbers have wide applications in 6G communication, radar stealth, detection instruments, and radio astronomy. In this context, a kind of double-layer staggered woodpile absorber is designed and manufactured by the direct ink writing (DIW) technology with a composite ink system composed of reduced graphene oxide (RGO)/spherical carbonyl iron (SCI) and polydimethylsiloxane (PDMS). The as-prepared absorber shows compatible absorption in both microwave and terahertz frequency bands. The effective absorption bandwidth (EAB) and minimum reflection loss (RLmin) reach 8.24 GHz and −52.2 dB at a thickness of 3.2 mm, respectively. In the terahertz band (0.5–3.5 THz), it shows effective absorption (absorption rate greater than 99 %) and achieves RL < -20 dB throughout the entire tested band. In addition, the double-layer staggered woodpile absorber has good flexibility and can be conveniently used for curved substrates. This work enables the potential for rapid manufacturing of flexible and compatible absorbing devices through DIW 3D printing for applications in 5/6G communication, military stealth and flexible wearable intelligent devices.

Self-assembled bio-inspired cauliflower-like MnFe2O4 nanospheres as dispersed materials for high-stability magnetorheological fluid

In this research, novel hierarchically structured cauliflower-shaped MnFe2O4 nanospheres were synthesized via a simple solvothermal method and their potential application for high performance magnetorheological fluids was investigated. The samples were comprehensively characterized using FE-SEM, TEM, FTIR, XRD, BET, TGA, XPS and VSM. It was revealed that the prepared MnFe2O4 nanospheres exhibited hierarchical cauliflower-like morphology and the average particle size was found to be 182 nm. More importantly, the MnFe2O4 nanospheres demonstrated typical mesoporous structure, high specific surface area of 30.3 m2/g and moderate saturation magnetization of 29.3 emu/g, which were suitable for preparation of a uniform and stable MR suspension. The rheological performances comprising shear stress, viscosity, storage modulus and loss modulus of MR fluid under different external magnetic fields were measured using a dynamic rotational rheometer. The results indicated that the MR fluid possessed enhanced MR responses as the magnetic field intensity increased, which were attributed to the rapid formation of robust chain-like structures composed of MnFe2O4 nanospheres inside the MR suspension. In addition, it was observed that the sedimentation stability of MR fluid containing MnFe2O4 nanospheres was much more prominent than that of the suspension based on spherical carbonyl iron particles in the same testing period.

Multicomponent induced localized coupling in Penrose tiling for electromagnetic wave absorption and multiband compatibility

• Design quasiperiodic absorbers with long-range order but no periodicity. • Explored the relationship between electromagnetic parameters and frequency by structural design and component selection in depth. • The effective absorption bandwidth of Penrose absorber can realize 9.32 GHz in 2 mm thickness. • The multilayer metamaterials perfectly unify radar-infrared compatible capability. In the electronic information and intelligent era, microwave absorption materials have been focused on the issue of electromagnetic (EM) pollution, but high-performance absorbers with thin thickness are highly desirable. The positive action between structural design and component selection can be regarded as a function to optimize the microwave loss capacity, which contributes to understanding the response mechanisms from the micro and macro. Therefore, we designed the absorber with quasiperiodic structures of Penrose tiling that has finely engineered the location of maximum absorption peak, the spherical carbonyl iron in thin rhombus, and flakey carbonyl iron in fat rhombus, the effective absorption bandwidth (Reflection Loss ≤ –10 dB) was realized from 6.46 GHz to 15.78 GHz in the 2 mm thickness. The unique arrangement of Penrose tiling can respond alternatingly to EM waves at large scales, and multicomponent coupling is distinctly in the neighboring unit cells. In addition, spraying aluminum pigment as the upper layer, the infrared emissivity is less than 0.35 to meet the complex application environment. This work opens up novel ideas on quasiperiodic structure combined multicomponent and injects infinite vitality to provide prospects for broadband responsive and high-efficiency EM absorbers.

Enhanced Electromagnetic Absorption of Flake Carbonyl Iron/Reduced Graphene Oxide Composites

Carbonyl iron is an excellent microwave absorption material. However, the high density limits its application in lightweight microwave absorbing. In this study, flake carbonyl iron (FCI) was prepared by high-energy ball milling, and mixed with TPU to prepare the TPU/FCI composites. The large shape anisotropy of FCI makes the TPU/FCI samples exhibit higher permittivity and permeability, and consequently better microwave absorption performance than TPU/SCI (spherical carbonyl iron). Then, rGO was added into the TPU/FCI composites. The permittivity of the TPU/FCI/rGO composites is significantly enhanced by a few amount of rGO (less than 0.5 wt.%). As a result, the TPU/FCI/rGO sample with mFCI: mTPU = 3:10 and 0.5 wt.% rGO consumes only half of FCI that the TPU/FCI sample with mFCI: mTPU = 6:10 uses, and shows much better microwave absorbing performance than this TPU/FCI sample, that the minimum reflection loss reaches-68.3 dB (at 3.4 mm) and the effective absorption bandwidth is up to 5.9 GHz (at 1.5 mm). The TPU/FCI/rGO materials demonstrate promising application in light-weight high-efficient microwave attenuation.

Effect of Magnetorheological Grease's Viscosity to the Torque Performance in Magnetorheological Brake.

Recently, magnetorheological grease (MRG) has been utilized in magnetorheological (MR) brakes to generate a braking torque based on the current applied. However, the high initial viscosity of MRG has increased the off-state torque that led to the viscous drag of the brake. Therefore, in this study, the off-state viscosity of MRG can be reduced by the introduction of dilution oil as an additive. Three samples consist of pure MRG (MRG 1) and MRG with different types of dilution oil; hydraulic (MRG 2) and kerosene (MRG 3) were prepared by mixing grease and spherical carbonyl iron particles (CIP) using a mechanical stirrer. The rheological properties in the rotational mode were examined using a rheometer and the torque performances in MR brake were evaluated by changing the current of 0 A, 0.4 A, 0.8 A, and 1.2 A with fixed angular speed. The result shows that MRG 3 has the lowest viscosity which is almost 93% reduction while the viscosity of MRG 2 has lowered to 25%. However, the torque performances generated by MRG 3 were highest, 1.44 Nm, when 1.2 A of current was applied and followed by MRG 2 and MRG 1. This phenomenon indicated that the improvement of torque performances was dependent on the viscosity of MRG. By reducing the viscosity of MRG, the restriction on CIP to form chain formation has also decreased and strengthen the torque of MRG brake. Consequently, the utilization of dilution oil in MRG could be considered in MR brake in near future.

Polarization insensitive hierarchical metamaterial for broadband microwave absorption with multi-scale optimization and integrated design

The structural destructive resonance caused by the single resonant thickness of flat microwave absorbers results in narrow absorption, hindering the progress of stealth materials. Multi-scale optimization and metastructure design are effective in the improvement of multiple resonance thickness as well as wavefront transmission, allowing for greater freedom in the realization of broadband. Herein, hierarchical metamaterials constructed from pyramid metastructure composites and Huygens' metasurface on the basis of Fibonacci spiral element are reported here, with effective absorption bandwidth (reflection loss ≤ −10 dB) ranging from 4.8 to 18 GHz in terms of subwavelength thickness. The hybrid absorber also exhibits robustness with incident angle across 0°–50° for transverse magnetic polarization. The gradient impedance model based on pyramid composites comprising spherical carbonyl iron particles and graphene sheets will serve as a driver for the enhancement of the electromagnetic wave transmission and the booster of impedance matching. Huygens’ resonance of HMS induces the magnetic field convergence effect due to the simultaneous balance of effective surface current and magnetic current, which facilitates the absorption of lossy composites for further broadening absorption bandwidth. This integrated design could be widely applied to other absorbent materials of choice.

Pressure sensing properties for the dielectric layer of graphene/silicone rubber‐based magnetorheological elastomer

AbstractIn order to expand the application of magnetorheological elastomers (MREs) in the field of sensor technology and improve their dielectric properties, a type of MRE with modified graphene, graphene/silicone rubber‐based magnetorheological elastomer (GR/RTV‐MRE), is proposed and its dielectric sensing properties were investigated. A model for calculating the relative permittivity of MRE was developed and combined with VASP software simulation to obtain the relative permittivity of GR/RTV‐MRE with different graphene contents. Combining the silicone rubber matrix with 30 vol% micro‐sized (ca 3.5 μm) spherical carbonyl iron particles, GR/RTV‐MRE samples with different graphene contents were prepared and tested for their relative permittivity. There is an error of approximate 7% between the test results and the simulation results, and the relative permittivity of GR/RTV‐MRE with a graphene content of 3 vol% reaches a maximum value of 35.400. An experimental platform for compressive properties was constructed and the compressive modulus of GR/RTV‐MRE with a graphene content of 3 vol% was tested under a magnetic field of 0–1 T. The results show that the modulus of compressibility is positively correlated with the magnetic field intensity in the range 0–0.9 T, up to 3.98 MPa, and is almost constant in the range 0.9–1 T. GR/RTV‐MRE with a graphene content of 3 vol% was used as the dielectric of a capacitive type transducer. The sensitivity of the capacitive sensor was measured to be 0.07 kPa−1 with a linear fitting of 99.6%. It is shown that GR/RTV‐MRE with 3 vol% graphene has good dielectric sensing capability. © 2022 Society of Industrial Chemistry.

Achieving in-situ alloy-hardening core-shell structured carbonyl iron powders for magnetic abrasive finishing

The finishing accuracy and efficiency of magnetic abrasive finishing (MAF) are mainly depending on magnetic abrasive powders (MAPs). A new kind of core–shell structured carbonyl iron powders (CI-MAPs) with a hard Fe/Al intermetallic shell for magnetic abrasive finishing is successfully synthesized by in-situ alloy-hardening the surface of spherical carbonyl iron powders in this study. The feasibility of such an in-situ alloy-hardening strategy is theoretically designed according to the Fe/Al intermetallic compound formation chemical reaction using the Gibbs free energy principle and the TG-DSC testing, and thus the experimental thermodynamics temperature and time ranges of such chemical reactions are proposed. Experimental results shown that a densely zigzag-like uniform alloy-hardening layer with a thickness of about 11 μm, which are composed of Fe3Al, FeAl, and Fe2Al5 intermetallic compounds, was in-situ chemically synthesized on the surface of the spherical carbonyl Fe powders. The achieved core–shell structured powder is performed to finishing a Zirconium tube experimentally, and the roughness (Ra) of the Zirconium tube is greatly improved from 0.361 μm to 0.085 μm by 3 MAF passes.

Magnetorheological Characterization of PTFE-Based Grease With MoS2 Additive at Different Temperatures

Thermorheological characterizations of magnetorheological (MR) grease thickened with polytetrafluoroethylene (PTFE) and molybdenum disulphide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) used as an additive for two different greases prepared with 50% (MRG50) and 70% (MRG70) weight fractions of spherical carbonyl iron (CI) particles, respectively, are presented. The magnetic properties and glass transition temperature of prepared MR greases (MRGs) have been measured using vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC), respectively. The MR properties are investigated at different temperatures ranging from 25 °C to 65 °C at magnetic fields ranging from 0 to 0.75 T under rotational and oscillatory sweep tests using a magnetorheometer. It is observed that for MRG70, the shear stress and apparent viscosity increase with increasing temperature. This is explained based on the formation of monolayers of MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as it interacts with MRG and the effect of thermal conductivity on magnetorheology. Yield stress of PTFE-based MRG has been shown to increase with temperature and magnetic field. Formation of PTFE particle clusters decreasing the localized heat dissipation has been explained to be the reason for this. With increasing magnetic field strength, the flow properties show an increasing trend. ON-state storage and loss modulus are studied to understand the effect of temperature and magnetic field on the viscoelasticity of PTFE-based MRG.

FeSiCr Alloy Powder to Carbonyl Iron Powder Mixing Ratio Effects on the Magnetic Properties of the Iron-Based Alloy Powder Cores Prepared Using Screen Printing.

A screen printing process was used to substitute dry molding to solve the uneven compaction problem in the coil center column during molding in this study. FeSiCr alloy powders (FSC) with a large particle size were mixed with fine spherical carbonyl iron powder to increase the compaction density. FSC to carbonyl iron powder (CIP) mixing ratio effects on magnetic paste rheological behaviors and magnetic properties of the molding coil prepared using screen printing were investigated. A magnetic paste with the lowest viscosity can be obtained using 3C7F (30% CIP + 70% FSC) due to the small-sized CIP adsorbed onto the FSC surface. This process reduces the interlocked network formation resulting from the CIP. The toroidal core with 3C7F exhibited the highest relative density and highest inductance. The coils with pure CIP and higher CIP content exhibited the better DC superposition characteristic. The toroidal core loss increased rapidly as the FSC content was increased. A proper trade-off between the inductance, DC-bias superposition characteristic, and magnetic core loss can be reached by choosing a suitable powder mixing ratio.

Preparation and characterization of carbonyl iron soft magnetic composites with magnesioferrite insulating coating layer

Abstract Spherical carbonyl iron (Fe) powders were coated with magnesioferrite (MgFe2O4) insulating coating layer and then mixed with epoxy-modified silicone resin (ESR). Soft magnetic composites (SMCs) were fabricated by compaction of the coated powders and annealing treatment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the MgFe2O4 layer was coated on the surface of the iron powders. The magnetic properties of SMCs were determined using a vibrating sample magnetometer and an auto testing system for magnetic materials. The results showed that the SMCs prepared at 800 MPa and 550 °C exhibited a significant core loss of 167.5 W/kg at 100 kHz and 50 mT.

High-frequency magnetic properties and core loss of carbonyl iron composites with easy plane-like structures* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11574122 and 51731001) and Joint Fund of Equipment Pre-Research and Ministry of Education, China (Grant No. 6141A02033242).

To fully release the potential of wide bandgap (WBG) semiconductors and achieve high energy density and efficiency, a carbonyl iron soft magnetic composite (SMC) with an easy plane-like structure is prepared. Due to this structure, the permeability of the composite increases by 3 times (from 7.5 to 21.5) at 100 MHz compared with to the spherical carbonyl iron SMC, and the permeability changes little at frequencies below 100 MHz. In addition, the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz. The total core losses of the composites at 10, 20, and 30 mT are 80.0, 355.3, and 810.7 mW/cm3, respectively, at 500 kHz. Compared with the spherical carbonyl iron SMC, the core loss at 500 kHz is reduced by more than 60%. Therefore, this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics.

Wide-angle microwave absorption properties of multilayer metamaterial fabricated by 3D printing

Conventional absorbing materials have always been challenged by the technical difficulty of effectively absorbing (<−10 dB) oblique incident electromagnetic waves in a wide frequency domain. In this study, 3D printing technology was used to combine metamaterials with multilevel gradient absorbing materials. To provide good impedance matching, the multilayer structure absorber was designed with a gradient index of characteristic impedanceby adjusting the geometric parameters of the unit cell and the distribution of spherical carbonyl iron powderenhancedpolyether ether ketone (CI-PEEK). The results show that the prepared 3D-printed multilayer metamaterial effectively absorbed electromagnetic waves across a wide range of incident angles (0°–50°) in the bandwidth of 8–18 GHz. Compared with the current technology on wave absorbing materials, this work showed a considerable improvement in the effective absorption of wide-angle electromagnetic waves and the integrated manufacturing of absorption composite materials with the desired characteristics. Thus, this study has important research significance and engineering value.

Preparation and Characterization of High Magnetic Loss Microwave Absorber for Splitter Load

Microwave absorbing material was prepared using epoxy resin as matrix and spherical carbonyl iron powder (s-CIP), flaky carbonyl iron powder (f-CIP) as absorbing agent. Microwave absorbing, mechanical properties and structure of the composites containing different kinds of carbonyl iron powder (CIP) were investigated. The results show that the microwave absorber with flaky CIP have better electromagnetic properties than composites with spherical CIP. With concentration of spherical CIP increasing the electromagnetic properties of composites becomes better, except for the mechanical performance. The flaky CIP/epoxy resins composites with a loading of 79 wt% plate-like CIP has attenuation constant of 25.443 dB/cm in 3 GHz. The absorber prepared using flaky CIP has homogenous, dense structure and has excellent mechanical properties.

Wideband square spiral metamaterial absorbers based on flaky carbonyl iron/epoxy composites

A broadband and thin microwave absorber composed of metal-base planar metamaterials (MMs) sandwiched between two layers of flaked-shaped carbonyl iron (FCI) composites is presented. FCI powder was prepared by ball milling spherical carbonyl iron powder and then added to epoxy resin to prepare FCI composite (FCIC) samples with different weight fractions. With these electromagnetic characteristics, a broadband, polarization-insensitive and thin metamaterial absorber comprising of arrays of square spirals embedded between two different layers of FCIC is optimally designed through a genetic algorithm. The reflection loss of the measured square spiral MM absorber with a thickness of 3.4 mm can reach –26 dB at matching frequency 4.4 GHz and the absorbing bandwidth below –9.3 dB is covered from 3.6 to 18.0 GHz which almost 4 fourfold bandwidth compared to that of the FCIC without the incorporation of MM layers.

Electromagnetic and microwave absorption properties of coatings based on spherical and flaky carbonyl iron

Single-layer and double-layer polyurethane (PU) matrix coatings containing spherical carbonyl iron (SCI) and flaky carbonyl iron (FCI) were designed and prepared by using a simple and effective manufacturing method, and the thickness of the coatings was kept at 1.5 mm. The complex permittivity, complex permeability and absorption properties of the coatings were investigated in the frequency range of 2–18 GHz. The results indicate that all the single-layer and double-layer coatings exhibit excellent absorption properties and wide absorption bands. By optimizing the filler radio and coating structure, the optimal reflection loss (RL) value can reach − 35 dB at 8.6 GHz and make the widest absorption band reach 15.5 GHz (2.5–18.0 GHz) and 4.9 GHz (10.7–15.6 GHz) for RL < − 5 dB and RL < − 10 dB, respectively. The coatings of SCI/FCI/PU exhibit a broad effective absorption bandwidth, which can be effectively applied to radar signature reduction and electromagnetic interference suppression in military and civil fields.