Wide Effective Absorption Bandwidth Research Articles

Hierarchical Magnetic Carbon Nanoflowers for Ultra-Efficient Electromagnetic Wave Absorption.

Porous carbon nanomaterials are widely applied in the electromagnetic wave absorption (EMWA) field. Among them, an emerging flower-like carbon nanomaterial, termed carbon nanoflowers (CNFs), has attracted tremendous research attention due to their unique hierarchical flower-like structure. However, the design of flower-like carbon nanomaterials with different magnetic cores for EMWA has rarely been reported. Herein, a general template method is proposed to achieve a set of high-quality magnetic CNFs, namely Co@Void@CNFs, CoNi@CNFs, and Ni@CNFs. The prepared magnetic CNFs have highly accessible surface area and internal space, rich heteroatom content, multi-scale pore system, and uniform and highly dispersed magnetic nanoparticles, as a result, deliver superior EMWA performance. Specifically, when the thickness is 2.6mm, the Co@Void@CNFs exhibit a maximum refection loss (RLmax) of -56.6dB and an effective absorption bandwidth (EAB) from 8.0 to 12.1GHz covering the whole X band. The CoNi@CNFs have an RLmax of up to -57.6dB and a wide EAB of 5.6GHz at just 1.9mm. For the Ni@CNFs, possess an ultra-broad EAB of 6.1GHz, covering the entire Ku band at 2.0mm. Overall, the hierarchical magnetic carbon nanoflowers proposed here offer new insights toward realizing multifunctional integrated carbon nanomaterials for EMWA.

V-Based MXene/MAX Heterostructure Composites with Enhancing Dielectric Loss for Broadband Microwave Absorption.

Electromagnetic wave absorption performance is strictly dependent on attenuation and impedance matching, which are directly influenced by the ratio of MXene/MAX in the multilayer structured MXene/MAX composites. However, there is still a challenge to achieve collaborative optimization of dielectric loss and impedance matching by precisely regulating the proportional relationship of MXene/MAX. Herein, V-based MXene/MAX heterostructure composites with different V2C/V2AlC ratios were successfully synthesized by rationally controlling the temperature and time of the hydrothermal reaction. Experimental results indicated that V2C-100 °C-1 harvested the balance between reduced impedance matching and enhanced dielectric losses, which was attributed to the mildly enhanced conduction loss and polarization loss. The first principles indicated that abundant electrons migrate from the V atoms of the MXene to the C atoms of the MAX phase. The charge redistributed and accumulated at the interface, exciting the increase in the dielectric loss of V2C-100 °C-1. As a result, the V2C-100 °C-1 heterostructure composite had an excellent electromagnetic absorption effect with a minimum reflection loss of -50.06 dB and a wide effective absorption bandwidth of 4.0 GHz (12.72-16.72 GHz). This work provides a valuable experience for the development of efficient MXene-based microwave absorbing materials.

N-doped CNTs/CoNi nanochains-carbon hollow microspheres multi-level multi-scale heterogeneous interface structures and microwave absorption properties

Constructing multi-level multi-scale heterogeneous interfaces in magnetic carbon-based composites remains a formidable challenge, requiring rational material combinations to effectively balance dielectric and magnetic losses for achieving high strength and wide frequency wave absorption. Electromagnetic wave (EMW) absorbing materials consisted of cobalt-nickel (CoNi) magnetic nanochain, nitrogen-doped carbon nanotubes (NCNTs) and hollow carbon microspheres were prepared by hydrothermal method without external magnetic field. These composites possessed a unique multi-level multi-scale heterogeneous interface structure that is highly advantageous for efficient absorption of EMWs. The CoNi nanoparticles were self-assembled into uniformly distributed and randomly oriented magnetic nanochains, which were further reassembled with NCNTs and hollow carbon microspheres to form heterogeneous interface structures resembling a rose, chrysanthemum, hedgehog ball, and bauhinia tree. Due to the high-density interface enhancing the loss ability of interface polarization, as well as the higher saturation magnetization, coercivity, and wave absorption ability of the magnetic nanochains compared to the magnetic nanoparticles themselves, the minimum reflection loss achieved is −66.86 dB, and the effective absorption bandwidth achieved is 5.01 GHz, at a content as low as 11 wt%. This study provides a new idea for generating nanochains without magnetic fields and constructing multi-level and multi-scale heterogeneous interface structures to achieve strong absorption and wide effective absorption bandwidth (EAB).

Preparation of cellulose derived carbon/reduced graphene oxide composite aerogels for broadband and efficient microwave dissipation

The development of cellulose derived carbon-based composite aerogels with light weight, broad bandwidth and strong absorption remains a challenging task. In this work, the cellulose derived carbon/reduced graphene oxide composite aerogels were prepared by a two-stage process of chemical crosslinking and high-temperature carbonization. The results revealed that the as-fabricated binary composite aerogels had a unique lightweight characteristic and three-dimensional porous network structure, which was chemically crosslinked by epichlorohydrin. Furthermore, the weight concentration of graphene oxide (GO) had a notable influence on the electromagnetic parameters and microwave absorption properties of the composite aerogels. The obtained binary composite aerogel possessed the optimal microwave dissipation capability when the concentration of GO was 1.5 mg/mL. Remarkably, the minimum reflection loss reached −50.42 dB at a thickness of 2.47 mm and a filling ratio of 17.5 wt%. Concurrently, the composite aerogel with a comparable thickness of 2.73 mm showed a wide effective absorption bandwidth of 7.28 GHz, spanning the total Ku-band and extending into a portion of the X-band. The radar cross section contribution of binary composite aerogels in the far-field was also simulated by computer simulation technique. In addition, the potential microwave attenuation mechanism was proposed. It was believed that the results of this paper would offer a reference for the preparation of cellulose derived carbon-based composite aerogels as efficient and broadband microwave absorbers.

Designing Symmetric Gradient Honeycomb Structures with Carbon-Coated Iron-Based Composites for High-Efficiency Microwave Absorption

HighlightsMIL-88C (Fe) with varying aspect ratios as a precursor was synthesized by regulating oil bath conditions, followed by one-step thermal decomposition to obtain carbon-coated iron-based composites.High-efficiency microwave absorption properties were achieved with RLmin value of -67.4 dB (2.13 mm) and wide effective absorption bandwidth (EAB) of 5.52 GHz (1.90 mm) under the low filler loading.A symmetric gradient honeycomb structure was constructed utilizing the high-frequency structure simulator, achieving an EAB of 14.6 GHz and a RLmin of -59.0 dB.

The tune of shell numbers of multi-shell hollow mesoporous carbon microspheres for enhanced microwave absorption

The morphology of carbon nanomaterials plays significant effect on the complex permittivity and microwave absorption (MA) capability. Elaborate morphology design would bring about efficient MA performance. In this work, we develop a hollow mesoporous carbon microspheres with different shells (from single to quadruple shells) through a facile template method and layer-by-layer etching process. This multi-shell hollow mesoporous carbon microspheres (MS-HMCMs) can be regarded as a complex composite morphology consisting of hollow, mesoporous and yolk-shell structure, which presents the tunable number of shells for optimal impedance matching, multiple interfacial polarization and the extended microwave transmission path from internal spaces. Thus, the MS-HMCMs demonstrates wide effective absorption bandwidth (EAB) of 6.4 GHz and 5.96 GHz at the thicknesses of 2.5 mm and 3.0 mm. Besides, the complex permittivity and MA properties can be effectively tuned via regulating the shell numbers. This MS-HMCMs with controllable shells may be a promising wideband and lightweight microwave absorber.

Dual-Step Redox Engineering of 2D CoNi-Alloy Embedded B, N-Doped Carbon Layers Toward Tunable Electromagnetic Wave Absorption and Light-Weight Infrared Stealth Heat Insulation Devices.

2D layered metallic graphite composites are promising electromagnetic wave absorption materials (EWAMs) for their combined properties of abundant interlayer free spaces, rich metallic polarized sites, and high conductivity, but the controllable synthesis remains rather challenging. Herein, a dual-step redox engineering strategy is developed by employing cobalt boron imidazolate framework (Co-BIF) to construct 2D CoNi-alloy embedded B, N-doped carbon layers (2D-CNC) as a promising EWAM. In the first step, a chemical etching oxidation process on Co-BIF is used to obtain an optimized 2D-CoNi-layered double hydroxide (2D-CoNi-LDH) intermediate and in the second, high-temperature calcination reduction is implemented to modify graphitization of the degree of the 2D-CNC. The obtained sample delivers superior reflection loss (RLmin) of -60.1dB and wide effective absorption bandwidth (EAB) of 6.24GHz. The synergy mechanisms of interfacial/dipole polarization and magnetic coupling are in-depth evidenced by the hologram and Lorentz electron microscopy, revealing its significant contribution on multireflection and impedance matching. Further theoretical evaluation by COMSOL simulation in different fields based on the dynamic loss process toward the test ring reveals the in situ EW attenuation process. This work presents a strategy to develop multifunctional light-weight infrared stealthy aerogel with superior pressure-resistant, anti-corrosion, and heat-insulating properties for future applications.

Screw dislocation growth defects enhancing electromagnetic wave absorption performance of GdB6

In this study, a purity of up to 98.36 wt. % GdB6 with screw dislocation growth morphology were successfully fabricated using an in-situ reaction approach. The terraced-like structure of the GdB6 enhanced the interfacial polarization and multiple interface scattering of the electromagnetic waves. As a result, the as-obtained high purity GdB6 powder presented superior electromagnetic wave absorption performance. The minimum reflection loss value can be −49.24 dB at the frequency of 13.12 GHz with a thin matching thickness of 1.44 mm. In addition, the widest effective absorption bandwidth can be up to ∼4 GHz (14–18 GHz) with a thin matching thickness of 1.25 mm. The remarkable electromagnetic wave absorption performance of GdB6 ceramics could be attributed to conductance loss and polarization loss enhanced by the screw dislocation growth defects, as well as synergistic effects with magnetic loss. The as-obtained GdB6 with synergistic dielectric loss and magnetic loss is to be a novel single-phase with excellent electromagnetic wave absorbing material, which will pave the way on the investigation of rare earth hexaborides for the ultra-high temperature environment applications.

Hollow Fe3O4/Fe@C nanocubes for broadband microwave absorption spanning low- and high-frequency bands

Rationally constructing hollow structures with heterogeneous interface is usually an effective strategy to regulate the electromagnetic response behavior for lightweight and strong absorption, but achieving low-frequency and broadband absorption is a major challenge. This work adopts a novel Fe(II)/Fe(III) ions regulation strategy to design and synthesize hollow Fe(OH)X (x = 2, 3) nanocubes, which addresses the disadvantages of time-consuming or using etchant. Subsequently, a unique hollow Fe3O4/Fe@C nanoboxes with adjustable magnetic composition and uniformly coated shell have been successfully synthesized by in-situ carbonization with the assistance of phenolic resin and hydrogen thermal reduction. Notably, the different magnetic components induce the magnetic coupling assembly and play a crucial role in determining its electromagnetic parameters, whereas Fe3O4 contributes to more dipole polarization and stronger low-frequency response characteristics. For Fe3O4@C hollow nanoboxes, the minimum reflection loss (RLmin) is as low as –119.9 dB at 2.3 mm, and extremely wide effective absorption bandwidth (EAB) of 11.4 GHz is achieved spanning low-frequency band of 2.8 ∼ 7.2 GHz and high-frequency band of 11.0 ∼ 18 GHz at 5.0 mm. Surprisingly, the Fe3O4@C also has satisfactory EAB20 (RL＜ –20 dB) reaching 7.1 GHz (14.9 ∼ 18 GHz) at a thin thickness of 1.8 mm. The RLmin of other hollow nanoboxes is also below –30 dB, and the EAB is greater than 9 GHz. This study provides a competitive candidate for efficient microwave absorption in complex frequency bands, especially low-frequency bands.

Construction of multilayer carbon magnetic heterostructures on the surface of carbon fibers to improve the absorption performance

AbstractThis study utilizes the strong complexation effect of polydopamine on metal ions and constructs multilayer carbon magnetic heterostructures on the surface of carbon fibers through the in situ reduction method, thereby obtaining a new type of multilayer carbon‐based composite absorbing material. The absorption properties at different layers were analyzed and compared through various characterization methods. Finally, the double‐layer structure demonstrated outstanding electromagnetic wave absorption characteristics, exhibiting a wide effective absorption bandwidth of 7.24 GHz and robust absorption of −44.48 dB, all within a mere thickness of 3.5 mm. Therefore, excellent market prospects for this material are anticipated.Highlights A multilayer carbon magnetic heterostructure absorbing material was constructed on micrometer‐scale carbon fibers. The test results show that a wide effective absorbing bandwidth of 7.24 GHz and a minimum reflection loss of −44.48 dB are obtained when the composite thickness is 3.5 mm. The prepared multilayer absorbing composites can adapt to a variety of application scenarios and have excellent application prospects in the industry. The self‐polymerization of dopamine and complexation of metal ions were used to construct multilayer absorbing materials, and the dielectric loss and magnetic loss capacity of the carbon fibers improved.

Enhancing the microwave absorption performance of graphite/Al2O3 composites through manipulating sheet resistance

AbstractThe graphite/Al2O3 composite was prepared using plasma spray technology, the material design, experimental methods, and process flow are introduced. The microstructure, chemical composition, and complex permittivity of the composite are investigated, and its performance to absorb electromagnetic waves is studied. The mechanism of interaction between chemical composition, microstructure, complex permittivity, and absorption performance is analyzed. Furthermore, a microwave absorber composed of graphite/Al2O3 and sheet resistance, and performance is discussed. The reflectivity of the composite coating with different periods and sizes and resistances is analyzed. The impedance and reflectivity of the designed absorber that contains sheet resistance are discussed, and its absorption mechanism is explained in detail. The results demonstrate that the microwave absorption performance of graphite/Al2O3 coating is enhanced by electromagnetic resonance of the sheet resistance. The designed absorber exhibits good wave‐absorbing performance and stability at the frequency of the 8.2–18 GHz range. When the sample thickness is 2.3 mm, the absorber achieves a reflection loss (RL) value of −16.8 dB at 9.8 GHz and a wide effective absorption bandwidth (EAB) of 9.8 GHz. It means that the RL below −10 dB can be obtained in the whole X band and Ku bands. These results proved that the EAB can be tuned and enhanced by manipulating sheet resistance.

Synthesis of Air@Co@Co7Fe3@Fe3O4 composite with enhanced electromagnetic wave absorption performance

Electromagnetic pollution prevention and military stealth technology requirements for wave absorbing materials gradually increased, therefore, the research and development of absorbing materials with the merits of low reflection loss, wide effective absorption bandwidth, and lightweight is of great significance. In this work, Air@Co@Co7Fe3@Fe3O4 hollow spherical particles have been successfully synthesized via a simple chemical plating method combined with a post heat treatment. It reveals that the Air@Co@Co7Fe3@Fe3O4 particles with a loading of 50 wt % exhibits an optimum reflection loss (RL) value of −20.77 dB at 15.52 GHz and broad effective absorption bandwidth (EAB, RL ≤ −10 dB) of 4.56 GHz with a thickness of 1.4 mm. Compared to Air@Co hollow spherical particles, Air@Co@Co7Fe3@Fe3O4 particles with natural resonance and eddy current loss, as well as the interlayer interfacial polarization mechanism of the multilayer structure, exhibit superior electromagnetic wave(EMW) absorption capabilities. The Air@Co@Co7Fe3@Fe3O4 hollow spherical particles could be a new highly efficient absorbing material for electromagnetic waves.

Effect of metal doping on the microwave absorption performance of multi-element (metal, N, and Cl) doped carbon composites

Multi-element-doped carbons are actively being pursued as efficient lightweight microwave absorbers. In this work, metal, nitrogen and chlorine codoped carbons (metal,N,Cl–C, where metals = Ni, Co, Mn, or Zn) were synthesized through the high-temperature carbonization of polypyrrole doped with hydrochloric acid (PPy-HCl) and prepared in the presence of certain metal chloride salts (NiCl2, CoCl2, MnCl2, or ZnCl2). The dielectric parameters and microwave absorption properties of the metal,N,Cl–C composites could be regulated by simply altering the type of metal salt. Compared with N,Cl–C, it was discovered that Co,N,Cl–C and Ni,N,Cl–C possessed higher graphitization degrees, smaller particle sizes and more surface chemical functional groups (metal−N), which significantly improved the conduction loss and polarization loss effects including interfacial polarization and dipole polarization. At a filler ratio of 9.0 wt%, Ni,N,Cl–C displayed a wide effective absorption bandwidth (EAB, RL ≤ −10 dB) of 7.1 GHz at a thickness of 2.5 mm and a minimum reflection loss (RLmin) of −29.7 dB at 9.7 GHz and 3.5 mm thickness. Similarly, Co,N,Cl–C offered an RLmin value of −48.2 dB at 11.3 GHz and a thickness of 3.0 mm and an EAB of 6.0 GHz at a thickness of 2.5 mm. These results showcase the advantages of metal,N,Cl–C composites as microwave absorbers.

Heterointerface engineering in porous microspheres for magnetic-dielectric balance to boost electromagnetic wave absorption

Heterointerface engineering originated from structure design is a promising approach to develop high-performance electromagnetic (EM) absorption materials but remains challenges in revealing the EM modulation mechanism. In this work, a diffusion-driven self-assemble strategy was proposed to construct porous NiFe2O4 microspheres with rich confined cavities. Followed by an in-situ vapor phase polymerization, conductive polypyrrole (PPy) layers were tightly coated on NiFe2O4 surface, building numerous ferrite-polymer heterointerfaces. Systematic investigation demonstrated that the controllable coating thickness and porous structure were crucial to regulate the component dependency EM properties and the dielectric-magnetic balance. Accordingly, these activated heterointerfaces and lattice defects inevitably produced polarization response to enhance the dielectric loss, and the confined magnetic coupling among hierarchical cavities strengthened the magnetic loss, jointly contributing to the boosted dissipation of incident EM energy. Owing to the synergy merits, optimum core–shell NiFe2O4@PPy microspheres exhibited an impressive broadband EM absorption performance with a wide effective absorption bandwidth covered 6.8 GHz at 2.62 mm. This study provides methodological guidance to design magnetic-dielectric EM absorption materials, and deciphers the mechanism of structure-interface modulated EM properties.

Band gap, ferromagnetic resonance and strong microwave absorption of BaFe12-2xZnxSnxO19 compounds and enhanced dielectric loss in BaFe12-2xZnxSnxO19/carbon nano tube composites

The forbidden bandgap energy, magnetic properties, natural ferromagnetic resonance and microwave absorption are studied on the Zn2+ and Sn4+ doped BaFe12-2xZnxSnxO19. The forbidden band gap of BaFe12-2xZnxSnxO19 increases with the increasing doping content x from 1.80 eV up to 1.97 eV. The coercive field, the anisotropy field and the magnetocrystalline constant of BaFe12-2xZnxSnxO19 decreases with the increasing doping. The natural ferromagnetic resonance is observed. The high permeability, accompanied with the ferromagnetic resonance, enables strong microwave absorption. BaFe10.4Zn0.8Sn0.8O19 has a wide effective microwave absorption bandwidth (RL≤-10dB) of 6 GHz with the material thickness below 2.5 mm in 11.4–17.4 GHz. The dielectric loss has little contribution to the excellent microwave absorption of BaFe12-2xZnxSnxO19. The BaFe12-2xZnxSnxO19/carbon nanotube (CNT) composites significantly increase the permittivity. The high dielectric loss and the high magnetic loss further improve the microwave absorption. With a very thin thickness of 1.8 mm, BaFe10.4Zn0.8Sn0.8O19/CNT has a bandwidth of 7.1 + GHz of 10.9–––18 + GHz. With the material thickness thinner than 3 mm, BaFe12-2xZnxSnxO19/CNT composites have very broad effective microwave absorption bandwidth of 11.4+, 10.7 and 10.7 GHz, with x = 0.6, 0.8 and 1.0, respectively. It illustrates that both BaFe10.4Zn0.8Sn0.8O19 and BaFe12-2xZnxSnxO19/CNT composites are very promising microwave absorbers.

Cation Bimetallic MOF Anchored Carbon Fiber for Highly Efficient Microwave Absorption.

Carbon fiber (CF) is a potential microwave absorption (MA) material due to the strong dielectric loss. Nevertheless, owing to the high conductivity, poor impedance matching of carbon-based materials results in limited MA performance. How to solve this problem and achieve excellent MA performance remains a principal challenge. Herein, taking full advantage of CF and excellent impedance matching of bimetallic metal-organic frameworks (MOF)derivatives layer, an excellent microwave absorber based on micron-scale 1D CF and NiCoMOF (CF@NiCoMOF-800)is developed. After adjusting the oxygen vacancies of the bimetallic MOF, the resultant microwave absorber presented excellent MA properties including the minimum reflection loss (RLmin ) of -80.63dB and wide effective absorption bandwidth (EAB) of 8.01GHz when its mass percent is only 5wt.% and the thickness is 2.59mm. Simultaneously, the mechanical properties of the epoxy resin (EP)-based coating with this microwave absorber are effectively improved. The hardness (H), elastic modulus (E), bending strength, and compressive strength of CF@NiCoMOF-800/EP coating are 334MPa, 5.56GPa, 82.2MPa, and 135.8MPa, which is 38%, 15%, 106% and 53% higher than EP coating. This work provides a promising solution for carbon materials achieving excellent MA properties and mechanical properties.

Constructing mixed-dimensional lightweight magnetic cobalt-based composites heterostructures: An effective strategy to achieve boosted microwave absorption and self-anticorrosion

Subtle microstructure design and an appropriate multicomponent strategy are essential for advanced electromagnetic absorbing (EMA) materials with a wide effective absorption bandwidth (EAB) and intense absorption. However, sophisticated environments restrict the range of applications for EMA materials. Herein, three hollow spherical bifunctional CoSx/MnS/C nanocomposites with different crystal structures were constructed via cation exchange and subsequent vulcanization. The manganese sulfide and carbon generated during vulcanization exhibit a narrow band gap and enhanced conductivity, thereby facilitating conductive loss. The presence of cobalt sulfide facilitates the improvement of magnetic loss. More importantly, there is a potential difference between different phases at the heterogeneous interface, resulting in a region of space charge, which is conducive to interfacial polarization. The 3D hollow structure and heterogeneous dielectric/magnetic interfaces benefit the predominant EMA performance by forming perfect impedance matching, interface polarization, conduction loss, and magnetic loss effects. Specifically, an optimal reflection loss (RL) of –51.31 dB at 10.72 GHz and an effective EAB of 5.92 GHz at 2.1 mm can be achieved for Co1–xS/MnS/C nanocomposite. Moreover, the nanocomposites maintained promising self-anticorrosion properties in simulated seawater environments. Transition metal sulfides with superior self-anticorrosion properties provide a pathway to efficient wave-absorbing materials in complicated environments.

Effect of Ce doping on electromagnetic characteristics and absorbing properties of M-type barium ferrite

In this study, Ce3+-doped M-type barium ferrite BaCexFe12-xO19 (x = 0 ∼ 1.2) was prepared by sol-gel method. The effects of Ce3+ doping on the crystal structure, microstructure, electromagnetic properties and absorption properties of M-type barium ferrites were investigated. The results indicate that the crystal structure remains unchanged with the increase of Ce3+ doping. The crystal size of Ce3+ doped barium ferrite is in the micro-meter range, and the grain size remains almost constant with increasing doping. The addition of Ce3+ to the BaFe12O19 samples resulted in significant improvements in their electromagnetic and microwave absorption properties. These improvements were mainly due to the synergistic effect of magnetic and dielectric losses. Among the samples doped with different concentrations of Ce3+, BaCe0.2Fe11.8O19 exhibited the best absorption performance, which has a minimum reflection loss of −58 dB and an effective absorption bandwidth of 9.44 GHz at a matched thickness of 2.3 mm. This study proposes an efficient electromagnetic wave absorber with a wider effective absorption bandwidth.

Synergistic effect of nickel selenide‑carbon composites for efficient broadband electromagnetic wave absorption

Novel NiSe2-based composites loaded with carbon nanotubes (CNTs) and graphene (GNs), respectively, were successfully synthesized via a facile hydrothermal reaction, aiming to enhance the electromagnetic wave (EMW) absorption performance. Microstructure, morphology, dielectric properties and EMW absorption performance of as-prepared NiSe2/CNTs and NiSe2/GNs composites were explored. Results showed that both NiSe2/CNTs and NiSe2/GNs composites exhibited improvement in EMW absorption compared to pure NiSe2, especially NiSe2/GNs showed the best EMW absorption performance. NiSe2/GNs composites demonstrated an exceptional minimum reflection loss (RLmin) of −52.10 dB at a thin thickness of merely 1.71 mm, accompanied by a wide effective absorption bandwidth (EAB) of 4.1 GHz. However, the EMW absorbing performance of NiSe2/CNTs composites was slightly lower than that of NiSe2/GNs composites, showing an RLmin of −45.10 dB and an EAB of 3.76 GHz at a thin thickness of 1.60 mm. Such significantly enhanced absorption capability of NiSe2/GNs composites can be attributed to the synergistic interplay of desirable impedance matching and efficient attenuation ability. These findings highlight the potential of NiSe2-based composites loading with carbon conductive fillers as highly promising contenders for high-performance EMW absorption materials.

All-in-one: Multi-parameter engineering on γ-Fe2O3 for ultra-broadband microwave absorption

The functionality and property of materials are normally controlled by changing their composition, defects, morphology, lattice, crystallinity, etc. However, achieving a wide effective absorption bandwidth through multiple-parameter optimization is less reported. Simultaneously adjusting these parameters can serve as an effective control knob to increase dielectric loss, including conduction and polarization, thereby providing a broadband absorption toward radiated microwave for potential applications. Herein, magnetic γ-Fe2O3 in a two-dimensional configuration was synthesized through a molten salt process, which was further modified by Co and Al heteroatoms to facilitate more polarization processes. The reinforcement of conduction loss is achieved by increasing the crystallinity of the absorber, which facilitates the rapid transfer of free electrons and reduces scattering. Controlled alkaline etching was employed to extract a portion of the intercalated Al atoms. Henceforth, appropriate lattice distortion and numerous O vacancies are constructed, which can not only generate new polarization centers on the absorber matrix but also maintain a high crystalline structure with good conduction loss feature. In addition, the magnetic loss and impedance matching characters are optimized. As a result, the composition, structure, defects, and crystallinity of magnetic γ-Fe2O3 nanosheets have all been optimized, which enable an impressive microwave absorption performance with an effective absorption bandwidth of 7.82 GHz and a minimum reflection loss of −54.9 dB. This work explores improving the electromagnetic parameters of absorbers through collaborative regulation of multiple parameters and provides guidance for a novel and facile strategy for controlling microwave absorbers.