Microwave Absorption Applications Research Articles

The synergistic effects on the magnetic CoNi and Fe3O4 nanoparticles co-embedded porous carbon toward enhanced microwave absorbing performance

Abstract Lightweight and environmentally friendly three-dimensional biomass-derived porous carbon (3D BPC) holds great potential as a highly effective material for microwave absorption (MA) applications. However, the high complex permittivity and lack of magnetic loss in a single 3D BPC lead to impedance mismatching and a limited absorption bandwidth. Developing 3D BPC–based absorbers with multiple loss mechanisms and excellent impedance matching remains a notable yet challenging task. In this study, inspired by a synergistic composition and microstructure design, 3D BPC co-embedded with magnetic cobalt–nickel (CoNi) and iron(III) oxide (Fe3O4) nanoparticles (3D BPC@CoNi@Fe3O4) was developed. 3D BPC@CoNi@Fe3O4 exhibited consistently low complex permittivity, primarily due to the suppression of conductive loss, whereas the introduction of magnetic phases (CoNi and Fe3O4) enhanced the magnetic loss. Optimised impedance matching, achieved through the synergistic regulation of the electromagnetic parameters, emerged as the key mechanism for improving the MA properties. The as-synthesised 3D BPC@CoNi@Fe3O4 composite, with only 20 wt.% loading demonstrated a wide effective absorption bandwidth (reflection loss [RL] < −10 dB) of 6.08 GHz and an impressive minimum RL value of −40.08 dB. These findings offer valuable insights into the development of high-performance 3D BPC–based microwave absorbers through composition and microstructure optimisation.

Collective effect of reduced graphene oxide and Zn2U hexaferrite filler based epoxy composites on microwave absorption with improved mechanical properties

Herein, we have synthesized Ba4Zn2Fe36O60 (Zn2U) and have produced reduced graphene oxide (rGO) wrapped filler material for the preparation of epoxy composites of different weight percentages (40, 50 and 60 wt %). These rGO wrapped Zn2U hexaferrite filler was analyzed by XRD and SEM to examine the crystal structure and distribution of Zn2U hexaferrite in between/on the surface of rGO respectively. The magnetic and mechanical properties of prepared rGO@Zn2U@epoxy composites were evaluated by employing vibrating sample magnetometer and universal testing machine respectively. The investigation involved analyzing the complex permittivity and permeability, and based on this information, an assessment of the reflection loss was conducted. The results obtained indicate that epoxy composites with a filler content of 60 % rGO@Zn2U have significant promise as an advantageous choice for EMI shielding and microwave absorption applications.

Influence of Dy3+ doping on Mössbauer, magnetic and microwave absorption properties of M-type Ba0.5Ca0.5DyxFe12-xO19 hexaferrites

The present research paper reports a systematic study of the magnetic, and structural properties of Ba0.5Ca0.5DyxFe12-xO19 M-type hexaferrite. The dysprosium was doped @ x = 0 − 0.2, keeping Δx = 0.05, in BCDF by the sol–gel self-ignition technique. The sintering of the synthesized samples was performed for 4 h at 1050°C. The crystallographic analysis of the samples was made from the X-ray diffractograms (XRD), while the morphological and elemental analysis was made from field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDAX) profiles. The structural results revealed the formation of the M-type hexaferrite having P63/mmc as a space group along with the co-existence of a secondary Fe2O3 phase. FESEM micrographs exhibit the hexagonal platelets randomly arranged with agglomerations at some places giving rise to the random variations in particle size with varying ’x’. Magnetic measurements (VSM) show that the saturation magnetization (MS) and coercivity (HC) increase with the increasing Dy3+ doping pointing towards the fact that the Dy doping in Ba-Ca ferrite can be used to fabricate the hard ferrites with good saturation magnetization. The Mössbauer spectrum recorded at room temperature reveals five superimposed sextets representing the five Fe3+ ion sites. Investigating the Microwave absorption (MWA) characteristics in the frequency range 8 − 12 GHz (X-band), reveals that the sample with x = 0.1 having 3 mm thickness possesses good MWA power. Its minimum RL value for matching frequency 10.06 GHz is approximately −26.96 dB, indicating that more than 90 % of microwaves are absorbed. The current work offers the Dysprosium-doped BCDF hexaferrites, as promising candidatesfor microwave absorption applications.

MOF-derived metal oxides with hollow porous nanocube structure realize ultra-wideband, lightweight, and anticorrosion microwave absorber

High density, skin effect, and environmental instability are significant limitations that restrict the application of metal-based microwave absorbers in achieving lightweight, high performance, and long service life. This study broke from traditional methods for preparing a microwave absorber Mn2O3-Fe3O4@PPy (polypyrrole) by employing an innovative annealing process to convert metal into metal oxide by the introduction of metal organic framework (MOF), which effectively achieving a more lightweight absorber material with hollow porous nanocube structure. Subsequently, PPy was coated onto the metal oxide surface to form a core-shell structure by a situ chemical oxidation synthesis method. The combination of metal oxide of the hollow porous nanocube structure and the core-shell structure formed by highly conductive PPy shell significantly enhanced heterogeneous interfaces and electromagnetic (EM) wave reflection. Excellent dielectric loss and impedance matching contributed evidently to the ultra-wideband EM wave absorption performance. It was demonstrated that, with a filling amount of only 20 wt%, the prepared Mn2O3-Fe3O4@PPy achieved an effective bandwidth (EAB) of 10.0 GHz at a thickness of 3.08 mm, with EABmax reaching 13 GHz. At a filling amount of only 10 wt%, the reflection loss (RL) was −62.13 dB, achieving an EAB of 7.4 GHz at 2.98 mm thickness, with EABmax reaching 11.4 GHz. Furthermore, the proposed strategy incorporating metal oxide and PPy enhanced corrosion resistance with higher charge transfer resistance.

MOF-derived ZnCo2O4 @ Ti3C2TX nanosheet with high microwave absorption

Abstract Electromagnetic wave absorbing (EWA) materials have a wide application in military technology, so it is necessary to develop EWA materials with lightweight, and wide absorption bandwidth and strong absorption. Novel two-dimensional material (MXene) with high dielectric constant property and unique structure has attracted extensive focus in microwave absorption. However, the high conductivity of MXene limits its application in microwave absorption. In this work, ZnCO2O4 nanoparticles were obtained via a hydrothermal method and subsequent heat treatment. Then it was anchored on MXene nanosheets. The effective absorption bandwidth (EAB) of the ZnCO2O4@Ti3C2Tx is 4.77GHz at 1.5mm thickness. Composites show great potential in the field of designing a new generation of efficient and lightweight microwave absorbers, which are expected to be used in various EWA applications.

Enhanced microwave absorption in Fe3O4@PS/MWCNT multicomponent composites: Fabrication, characterization, and performance analysis

Multiple-component materials with advanced microstructure are increasingly utilized in the development of microwave absorption materials. In this paper, a magnetic hollow sphere composed of Fe3O4@PS was fabricated by simply depositing Fe3O4 nanoparticles onto the surface-modified PS hollow spheres through electrostatic interactions. The microwave absorption properties of Fe3O4 @PS hollow spheres were studied by varying the loading capacity of Fe3O4. The results show that when the Fe3O4 content is 28.59 wt%, the optimal minimum reflection loss is −26.9 dB with effective absorption bandwidths (RL ≤ −10 dB) exceeding 0.3 GHz. Furthermore, the straightforward combination of the Fe3O4@PS with MWCNTs enables the enhancement of the microwave absorption up to −41.4 dB at 14.5 GHz, with an effective absorption bandwidth exceeding 5.9 GHz (12.1–18 GHz) at a thickness of 2 mm. This study is expected to provide valuable insights into the design of nanocomposites for microwave absorption applications.

Dimensional Self‐Assembled Magnetic Coupling via Embedding Ferromagnetic Nanoparticles in Multi‐Channel Fibers for Microwave Absorption

Abstract1D magnetic fibers with significant morphological diversity and magnetic anisotropy are highly desirable for optimizing magnetic properties and electromagnetic responsiveness. However, it remains challenging for the precise control over internal magnetic interactions within each fiber. Herein, a strategy for self‐assembled magnetic coupling is taken to achieve the controllable reconstruction of continuous multiple coupling networks within a single fiber. High‐density ultrafine cobalt nanoparticles are uniformly embedded inside a carbon framework with a 1D multi‐channel structure (Co@MCF). This structure establishes a complex magnetic response system characterized by inherent inter‐fiber interactions and refined intra‐fiber self‐assembling coupling. The distinctive distribution of magnetic flux lines demonstrates enhanced magnetic sensitivity. This results in a minimum reflection loss of −57.65 dB and a broadband absorption frequency range of 7.28 GHz at 1.9 mm, effectively covers the entire Ku band and a substantial portion of the X band. The multi‐channel structure enhances the understanding of the relationship between microstructure and performance in magnetic fibers. Additionally, it positions Co@MCF as a highly competitive candidate for microwave absorption applications.

Zn-Al Ferrite/Polypyrrole Nanocomposites: Structure and Dielectric and Magnetic Properties for Microwave Applications.

In this study, Zn-Al ferrite/polypyrrole (PPy) nanocomposites were synthesized and thoroughly characterized to explore their potential for microwave applications. X-ray diffraction analysis confirmed the presence of ZnO, AlFeO3, and Fe2O3 phases, with the crystal size decreasing from 31 nm to 19.6 nm as aluminum content increased. High-resolution transmission electron microscopy (HR-TEM) revealed a distinctive core-shell morphology, where the polypyrrole encapsulates the ZnAlxFe2-xO4 particles. Magnetic measurements showed that decreasing aluminum concentration led to a reduction in both saturation magnetization (Ms) from 75 emu/g to 36 emu/g and remanent magnetization (Mr) from 2.26 emu/g to 2.00 emu/g. Dielectric analysis indicated that both the real (ε') and imaginary (ε″) components of dielectric permittivity decreased with increasing frequency, particularly between 10 and 14 GHz. Furthermore, electrical modulus analysis highlighted the significant impact of aluminum doping on relaxation time (τIP), indicating the presence of interface polarization. Impedance spectroscopy results underscored the dominance of interface polarization at lower frequencies and the presence of strong conduction paths at higher frequencies. These combined magnetic and dielectric loss mechanisms suggest that the Zn-Al ferrite/polypyrrole nanocomposite is a promising candidate for advanced microwave absorption applications.

3D MXene architectures for electromagnetic protection

Electromagnetic (EM) pollution is becoming increasingly severe due to the explosive growth of various communication devices. EM protection materials are the key to solving EM pollution. MXenes, by virtue of larger specific surface area, numerous surface functional groups and excellent conductivity, are attracting increasing attention and showing competitive performance in EM protection. By constructing 3D MXene architectures, not only can the EM protection performance be significantly improved, but it can also meet the development needs of lightweight, miniaturization, and portability in the future. In this review, we summarized the methods for preparing 3D MXene architectures applied in the field of EM protection. Then, we comprehensively elaborate on the structure-property relationships of 3D MXene architectures and their applications in microwave absorption (MA) and electromagnetic interference (EMI) shielding. Finally, we discuss the challenges and opportunities in the development of 3D MXene architectures for EM protection.

Correction: The study of structural, magnetic and dielectric properties of spinel ferrites for microwave absorption applications

Correction: The study of structural, magnetic and dielectric properties of spinel ferrites for microwave absorption applications

Tunable interlayer spacings Ti3C2Tx MXene/Ni/C for enhanced electromagnetic microwave absorption

While two-dimensional lamellar materials, specifically Ti3C2Tx MXenes, have shown great promise as wave-absorbing materials, the precise design of interlayer spacing poses a persistent challenge. In this study, Ti3C2Tx MXene layers with adjustable interlayer spacings were crafted using a straightforward molecular welding technique. Through the incorporation of Ni nanoparticles onto the Ti3C2Tx MXene layers using a combination of simple mechanical stirring and carbonation reactions, we successfully developed Ti3C2Tx MXene/Ni/C composites featuring a distinct lamellar structure. A uniform dispersion of Ni nanoparticles on the surface of the Ti3C2Tx MXene nanosheets was found with some of the nanoparticles intercalated into the layers. The Ti3C2Tx MXene/Ni/C composites exhibited a maximum reflection loss (RL) value of −42.3 dB at 12.3 GHz, accompanied by an impressive effective absorption bandwidth (EAB) of 5.6 GHz. This outstanding absorption performance could be attributed to various factors, including the dielectric loss of the Ti3C2Tx MXene lamellae, reflections and scattering of multiphase heterostructures, the magnetic loss of the Ni nanoparticles, and their synergistic attenuation. Furthermore, Ni nanoparticles with high electrical conductivity induced vortex currents under the alternating influence of electromagnetic waves (EMWs), resulting in a substantial depletion. This study introduces an innovative approach for synthesizing Ti3C2Tx MXene/Ni/C composites with tunable interlayer spacing, showing their potential for applications in microwave absorption (MA).

High-performance electromagnetic wave absorption in VS2@multi-walled carbon nanotube composites

In this work, composites comprising VS2 and multi-walled carbon nanotubes (MWCNTs) were prepared using a simple hydrothermal method. The MWCNTs were dispersed among the VS2 nanosheets, which produced dipole polarization and interfacial polarization, thus enhancing the dielectric loss. Meanwhile, the electrical conductivity of the composites gradually increased with the rising content of the MWCNTs, which improved the electromagnetic wave absorption performance. By adjusting the mass ratio of VS2 to MWCNTs to 5:1, a minimum reflection loss value (RL) of −24.7 dB was achieved with a thickness of only 1.3 mm at a frequency of 14.4 GHz. Besides, when the thickness was reduced to 1.2 mm, the effective absorption bandwidth extended to 3.75 GHz. The results suggest that impedance matching and the synergistic effect of multiple loss mechanisms contribute to the excellent electromagnetic wave absorption performance of the materials. Consequently, the VS2/MWCNTs composites exhibit simple synthesis, wide absorption bandwidth, thin thickness, and high absorption capacity, rendering them a promising material for practical microwave absorption applications.

The lightweight titanium dioxide/reduced graphene oxide composites prepared by hydrothermal method for microwave absorption

To solve electromagnetic pollution, microwave absorption materials with high performance have gained attention. Manipulating the impedance matching is an effective strategy to obtain the outstanding electromagnetic wave absorption material. In this work, a series of titanium dioxide/reduced graphene oxide (TiO2/RGO) composites were prepared by the hydrothermal method for microwave absorption. The relationship between the microstructure and microwave absorption performance of the composite was analyzed in detail. The impedance matching and attenuation ability of TiO2/RGO composites could be precisely manipulated by regulating the titanium dioxide content. The reflection loss and effective absorption bandwidth of the TiO2/RGO composite could reach −46 dB and 3.36 GHz (1.9 mm), respectively. Thus, the lightweight TiO2/RGO composite has the potential application in microwave absorption.

Magnetic resonance behavior modulation of Ba3Co1.6−xZnxCu0.4Fe24O41 hexaferrites for microwave absorption and surface wave suppression

The intrinsic high magnetocrystalline anisotropy equivalent field can help the hexaferrites break through Snoek's limit and increase the resonance frequency. This is advantageous for microwave absorption applications in the mid to low-frequency range of gigahertz. In this study, we prepared Z-type Ba3Co1.6−xZnxCu0.4Fe24O41 hexaferrites using the sol-gel auto-combustion method. By changing the ratio of Co and Zn ions, the magnetocrystalline anisotropy of ferrite is further manipulated, resulting in significant changes in their magnetic resonance frequency and intensity. Ba3Zn1.6Cu0.4Fe24O41 with high-frequency resonance achieved the lowest reflectivity of −72.18 dB at 15.56 GHz, while Ba3Co1.5Zn0.1Cu0.4Fe24O41 with stronger loss obtained the widest bandwidth of 4.93 GHz (6.14–11.07). Additionally, we investigated surface wave suppression properties previously overlooked. Ba3Co1.5Zn0.1Cu0.4Fe24O41 can achieve a larger attenuation at low frequency under low thickness, which has an excellent effect on reducing backscattering. This work provides a useful reference for the preparation and application of high-performance magnetic-loss materials.

Joule heat induced ultrafine ZrO2/C composites for enhanced microwave absorption

Lightweight absorbers with effective broad absorption and high thermal stability are highly desirable in the field of electromagnetic wave absorption. In this work, we introduce a facile carbon thermal shock method to prepare ZrO2/C composites using UIO 66 (Zr) as the precursor. The instant heating and cooling process ensures the uniform deposition of nano-sized ZrO2 (ca. 5–15 nm) on graphene, exhibiting an ultrahigh interfacial number density of ca. 1015 m−2 that favors polarization loss. Due to the synergetic effect of dielectric loss and impedance matching, the prepared ZrO2/graphene composites show tunable wide-microwave absorption performance by adjusting the heat temperature, and possess a wide absorption band covering the entire X and Ku band. Notably, the ZrO2/graphene composites show high thermal stability up to 1000 °C, which presents great potential for microwave absorption applications.

Synthesis, Characterisation, and Applications of TiO and Other Black Titania Nanostructures Species (Review)

Black titania, a conductive ceramic material class, has garnered significant interest due to its unique optical and electrochemical properties. However, synthesising and properly characterising these structures pose a considerable challenge. This diverse material family comprises various titanium oxide phases, many of them non-stoichiometric. The term “black TiO2” was first introduced in 2011 by Xiaobo Chen, but Arne Magneli’s groundbreaking discovery and in-depth investigation of black titania in 1957 laid the foundation for our understanding of this material. The non-stoichiometric black titanium oxides were then called the Magneli phases. Since then, the science of black titania has advanced, leading to numerous applications in photocatalysis, electrocatalysis, supercapacitor electrodes, batteries, gas sensors, fuel cells, and microwave absorption. Yet, the literature is rife with conflicting reports, primarily due to the inadequate analysis of black titania materials. This review aims to provide an overview of black titania nanostructures synthesis and the proper characterisation of the most common and applicable black titania phases.

Broadband microwave absorption and antibiosis effect of Cu@C@Fe3O4 nanocomposites

Metal Cu nanoparticles have been recognized as the long-standing presence in the fields of antibacterial and low-induced bacterial resistance, however, the uncontrollable Cu ion concentration from Cu nanoparticle leads to the unstable release of copper ions, limiting their controllable antibacterial application. Based on stable release of copper ions from Cu@C nanocapsules, herein, we report a novel A/B/C structure Cu@C@Fe3O4 nanocomposite to present integrated functionalities of highly controllable antibiosis and electromagnetic wave (EMW) absorption to realize a bifunctional EMW absorption system. With stable concentration, the Cu@C@Fe3O4 nanocomposite can slowly release Cu ions to experience an efficient reactive oxygen species process to realize extreme stable antibiosis behavior and long-term antibacterial effect that is 100 % bactericidal effect. With the sustained antibacterial conditions, the Cu@C@Fe3O4 with magnetic component simultaneously exhibits a good impedance matching to lead a broad microwave absorption with a bandwidth of 5.87 GHz. Considering above two functions, the multifunctional Cu@C@Fe3O4 provides a pathway for multifunctional EMW absorption materials exploration in antibacterial and microwave absorption applications. This strategy also indicates the possibility to functionalize magnetic nanocapsules towards even broader applications.

Polypyrrole modified MIL-101-Fe-derived Fe/Fe3O4@C composites for high-performance microwave absorber

Carbon-based microwave absorbing composites with magnetic-dielectric properties and multiple loss mechanism are considered to be an effective choice for solving electromagnetic pollution. In this paper, the PPy/Fe/Fe3O4@C composite was synthesized from MIL-101-Fe derivatives and subsequently coated polypyrrole (PPy) by combining hydrothermal, high-temperature pyrolysis and oxidative polymerization. The effects of pyrolysis temperature and PPy loading on components, microstructures and electromagnetic parameters were investigated. The results showed that the PPy/Fe/Fe3O4@C composite consisted of two-dimensional carbon flakes modified by magnetic particles and laminated conductive polymers. When the PPy loading is moderate, the composite reaches a minimum reflection loss (RLmin) of −61.38 dB at a 3.1 mm thickness and effective absorption bandwidth (EAB) of 5.81 GHz at the thickness of 2.2 mm. After pyrolysis, the unique three-dimensional structure of carbon sheet stacking, as well as the heterogeneous interface and conductive networks generated by the modification of magnetic particles Fe and Fe3O4 and conductive PPy, are beneficial to improve the dielectric and magnetic losses to optimize the impedance matching. These conductive polymer-modified magnetic-dielectric composites have potential for development and application in microwave absorption.

Enhancement of microwave absorption performance of cobalt ferrite by adding MXene (Ti3C2Tx) nanosheets

In this work, CoFe2O4 powders were combined with various amounts of MXene (Ti3C2Tx) through the solution combustion method for microwave absorption applications. Despite the absence of MXene reflections in X-ray diffraction patterns, the MXene sheets were observed in electron microscopy images. The CoFe2O4 nanoparticles were uniformly dispersed on the MXene nanosheets. The specific surface area increased from 57 to 83 m2 g−1 by adding 20 wt% MXene. The saturation magnetization and coercivity decreased from 44 to 35 emu g−1 and from 834 to 775 Oe, respectively. By adding the MXene, the minimum reflection loss and effective absorption bandwidth increased up to −38 dB and 5.6 GHz at a matching thickness of 1.8 mm, respectively, which was attributed to the enhancement of impedance matching by the decrease of permittivity.

Influence of particle size on the magnetic and microwave absorption properties of magnetite via mechano-mechanical methods for micro-nano-spheres

The demand for innovative electromagnetic wave absorbers stems from the pressing need to mitigate electromagnetic interference and pollution emanating from electronic devices and communication technologies, which pose risks to human health and disrupt the functionality of electronic equipment. This study investigates how particle size influences the magnetic and microwave absorption properties of magnetite micron-nano-spheres. Utilizing ball milling (BM) and mechanochemical alloying (MA), particle sizes were controlled by varying the milling times, resulting in a reduction of magnetite's average particle size from 3 µm to 43 nm. The research uncovers the unique effects of blending micron and nano-sized particles, a phenomenon previously undocumented. It was observed that saturation magnetization and coercivity increase with larger particle sizes due to the small size effect. The complex permittivity, dielectric loss and attenuation constant of the magnetite nanocomposites were influenced by the larger interface area and increased defects in smaller-sized nano-filler composites. Decreasing the magnetite particle size leads to a lower frequency shift and a broader bandwidth of the reflection loss (RL) peak in the fixed absorber, with maximum RL achieved for thinner absorber layers. Notably, the mixed micron-nano magnetite composite exhibits promising microwave absorption capabilities, achieving a maximum RL of −35.36 dB at 16.8 GHz with a 1 mm thickness, making it suitable for lightweight microwave absorption. Resonance frequencies corresponding to RL below −20 dB extend to 3.63 GHz, meeting the 99 % wave absorption requirement due to the high loss tangent of antiferromagnetic resonance and significant magnetic relaxation peak over the 8–18 GHz frequency range. This study underscores the significant impact of adjusting the particle size on microwave absorption properties, where decreasing the size broadens the absorption bandwidth, shifts the RL peak to lower frequencies and maximizes RL with thinner thicknesses. Increasing the nano-filler content enhances the absorption bandwidth and microwave absorber performance by augmenting the dielectric loss, attenuation constant and impedance matching. Overall, controlling the particle size proves effective in tailoring microwave absorption, highlighting the potential of magnetite composites as ultra-thin, lightweight materials capable of absorbing a wide range of microwave frequencies. These composites find applications in microwave absorption, stealth technology and managing electromagnetic interference, leveraging the magnetic properties of ferrites and exploiting super-exchange interactions in microparticles-sized materials. Moreover, they benefit from the amplified dielectric or/magnetic losses resulting from the characteristics of nanoparticle-sized materials, including high surface area, greater surface atoms and multiple reflections, resulting in exceptional microwave absorption performance exceeding 99 % across an exceptionally broad bandwidth.