Electromagnetic Wave Absorption Characteristics Research Articles

Effects of Heat Treatment on the Electromagnetic Wave Absorption Characteristics of Resorcinol Formaldehyde Silicon Dioxide Ceramic Particles

In light of the pressing environmental and health issues stemming from electromagnetic pollution, advanced electromagnetic wave absorbing materials are urgently sought to solve these problems. The present study delved into the fabrication of the resorcinol formaldehyde (RF)/SiO2 ceramic particles using the sol–gel route. From SEM images and XRD and XPS analysis, it can be seen that the RF/SiO2 ceramic particles are successfully generated after heat treatment at 1500 °C. At room temperature, the sample treated at 1500 °C exhibited a minimum reflection loss of −47.6 dB in the range of 2–18 GHz when the matching thickness was 5.5 mm, showcasing strong attenuation capabilities. Moreover, these particles demonstrated a considerable effective electromagnetic wave absorption bandwidth of 3.14 GHz, evidencing their potential for wideband electromagnetic wave absorption. The temperature adjustment played a pivotal role in achieving optimal impedance matching. When the heat treatment temperature is increased from 800 °C to 1500 °C, the dielectric properties of the material are improved, thus achieving the best impedance matching, thereby optimizing the material’s absorption properties for specific frequency ranges, which makes it possible to customize the electromagnetic wave-absorbing characteristics to meet specific requirements across a range of applications.

Co/C Nanocomposites with Tunable Condensed States Induced by Conformation-Mediated Strategy for Electromagnetic Wave Absorption.

The strategic regulation of condensed state structures in multicomponent nanomaterials has emerged as an effective approach for achieving controllable electromagnetic (EM) properties. Herein, a novel conformation-mediated strategy is proposed to manipulate the condensed states of Co and C, as well as their interaction. The conformation of polyvinylpyrrolidone molecules is adjusted using a gradient methanol/water ratio, whereby the coordination dynamic equilibrium effectively governs the deposition of metal-organic framework precursors. This process ultimately influences the combined impact of derived Co and C in the resulting Co/C nanocomposites post-pyrolysis. The experimental results show that the condensed state structure of Co/C nanocomposites transitions from agglomerate state → to biphasic compact state → to loose packing state. Benefiting from the tunable collaboration between interfacial polarization and defects polarization, and the appropriate electrical conductivity, the diphasic compact state of Co/C nanocomposites achieves an effective absorbing bandwidth of 7.12GHz (2.1mm) and minimum reflection loss of -32.8dB. This study highlights the significance of condensed state manipulation in comprehensively regulating the EM wave absorption characteristics of carbon-based magnetic metal nanocomposites, encompassing factors such as conductivity loss, magnetic loss, defect polarization, and interface polarization.

Hierarchical heterostructure Ni2P hollow carbon spheres derived from MOFs for efficient electromagnetic wave absorption

In this study, a hierarchical heterogeneous structure of Ni2P hollow carbon spheres (Ni2P-HCS) was synthesized through a two-step process involving carbonization and phosphorization of Ni-metal organic framework (Ni-MOF) precursors. During the construction of the Ni2P/C nanostructure, heterointerface recombination and secondary graphitization were observed, which contribute to the modulation of interface polarization. Structural analysis revealed that the Ni2P/C nanoparticles are uniformly dispersed, forming stable porous structured microspheres, thereby leveraging dielectric and magnetic losses. The combination of Ni2P with metal-organic frameworks (MOFs) can optimize impedance matching, enhance effective absorption bandwidth, and consequently improve electromagnetic wave absorption performance. The results show that Ni2P-HCS (Ni2P-HCS700) exhibited superior electromagnetic wave (EMW) absorption characteristics when the carbonization temperature is 700 ℃. It achieves a maximum reflection loss (RL) of −46.7 dB at a thickness of 2.9 mm and an effective absorption bandwidth (EAB) of 4.8 GHz at 1.71 mm thickness, almost covering the Ku-band (13.3 GHz−18 GHz). Radar cross-section (RCS) simulations utilizing CST indicated an optimal RCS reduction value of 41 dB m² at theta=0° for Ni2P-HCS700. This work introduces a universal approach to designing high-performance lightweight absorbers derived from MOFs, incorporating transition metal phosphides to form composites for impedance matching control.

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.

Mn–Zn ferrite foam concrete: Enhanced electromagnetic wave absorption and pore structure by incorporating carbon fibers

In this study, an absorbent composite of carbon-fibre-reinforced Mn–Zn ferrite foam concrete was fabricated. The influence of carbon fibre (CF) concentration on the mechanical and electromagnetic wave (EMW) absorption characteristics of Mn–Zn ferrite foam concrete within the 0.2–5GHz were investigated. Key performance indicators, such as compressive and flexural strengths, electromagnetic parameters, reflection loss, and absorption bandwidth were thoroughly analysed. The pore size and distribution were examined by X-ray computed tomography (CT) to reveal the EMW absorption mechanism. The findings indicate that CF effectively mitigates agglomeration in Mn–Zn ferrites, enhancing dielectric and magnetic losses synergistically, which improves not only the mechanical properties but also the EMW absorption capacity of Mn–Zn ferrite foam concrete. The optimal wave absorption performance was observed at a CF content of 0.3 wt%, yielding an impressive absorption bandwidth of 1.46 GHz and a minimum reflection loss (RLmin) of −28.75 dB. A noteworthy observation was the inverse correlation between the CF doping level and resistivity. The attenuation constant peaked at 108.13. When the CF content reached 1.2 wt %, the composite attained its percolation threshold, manifesting a resistivity of 145.4 Ω·m.

Enhanced electromagnetic wave absorption in YAG-modified SiC foam

Electromagnetic technology applications are escalating, leading to increased human exposure to electromagnetic radiation. In addressing the challenges posed by this radiation, electromagnetic wave absorbing materials stand out due to their distinguished properties. This study focused on developing porous fibrous SiC three-dimensional (3D) foams. These were synthesized by freeze-drying SiC nanofiber dispersions followed by high-temperature sintering. Measurements demonstrated that the resulting SiC foams possess a relatively low density, approximating 0.1 g cm−3. Upon microscopic analysis, it became evident that the foam's porous structure is predominantly made up of SiC fibers intermixed with yttrium aluminum garnet granules. These tailored SiC foams delivered outstanding electromagnetic wave absorption characteristics, recording a minimum reflection loss value of −63 dB. Furthermore, an expansive effective absorption bandwidth of 6.9 GHz (spanning from 9.3 to 16.2 GHz) was noted for a sample thickness of 3.15 mm. Several factors contribute to this high absorption efficacy, including multiple reflections and both interface and dipole polarizations. It is also worth noting that the SiC foam displayed commendable oxidation resistance when exposed to elevated temperatures. Cumulatively, these findings underscore the promising potential of porous fibrous SiC 3D foams in electromagnetic wave absorption applications, especially in extreme conditions.

Synergy of micron graphite and fly ash for alkali-activated cementitious material: Electromagnetic absorption characteristics and mechanism

To attain a balance between compressive strength and electromagnetic wave absorption performance, this paper combined two electromagnetic wave loss mechanisms (magnetic loss and electrical loss), and prepared an environmentally friendly alkali-activated slag/fly cementitious material (ASFC) using micron graphite (MG) as the absorber and ground granulated blast furnace slag (GGBS) and fly ash (FA) as the precursors. The conductivity, electromagnetic wave absorption characteristics and compressive strength of ASFC with different ratios of GGBS and FA, MG size (800 mesh, 320 mesh, and 100 mesh), and content were investigated. The results indicated that when the ratio of GGBS and FA was 7:3, natural resonance and eddy current loss contributed to electromagnetic waves absorption at 8.2–11.0 GHz and 11.0–15.5 GHz range respectively. Additionally, the conductivity of MG/ASFC showed typical percolation characteristics, with the percolation threshold reached at a dosage of 3 wt%. In the 8.2–18.0 GHz, the incorporation of MG significantly augmented the conductive loss and polarization loss of ASFC. Furthermore, smaller-size MG was more beneficial for facilitating conductive loss of MG/ASFC among three different sizes. By adding 2 wt% of MG with 800 mesh, MG/ASFC can achieve a minimum reflection loss of −27.8 dB with a bandwidth of 3.0 GHz (Reflection loss ˂-7 dB). However, when compared to other cement-based absorbing materials reported, the MG/ASFC prepared in this experiment demonstrated better compressive strength and wave absorption properties. This finding contributing to a better understanding of green building materials with electromagnetic radiation protection capabilities.

Synthesis of Cobalt Particles and Investigation of Their Electromagnetic Wave Absorption Characteristics.

As the integration technology for integrated circuit (IC) packaging continues to advance, the issue of electromagnetic interference in IC packaging becomes increasingly prominent. Magnetic materials, acknowledged for their superior electromagnetic absorption capabilities, play a pivotal role in mitigating electromagnetic interference problems. In this study, we employed a liquid-phase reduction method. We prepared three types of cobalt (Co) particles with distinct morphologies. Through variations in the synthesis process conditions, we were able to control the aspect ratio of protrusions on the surface of the Co particles. It was found that the sword-like Co particles exhibit superior electromagnetic wave absorption capabilities, showing a reflection loss value of up to -50.96 dB. Notably, when the coating thickness is only 1.6 mm, the effective absorption bandwidth is extended up to 7.6 GHz. The spatially expansive sword-like Co particles, with their unique structure featuring dipole polarization and interfacial polarization, demonstrated enhanced dielectric and magnetic loss capabilities, concurrently showcasing superior impedance-matching performance.

Electromagnetic wave absorption properties of Ni0.5Zn0.5Fe2O4–BaTiO3–epoxy composites

Composites consisting of ferrimagnetic spinel ferrite Ni0.5Zn0.5Fe2O4 (ZNF) and ferroelectric BaTiO3 (BT) powders embedded in epoxy (10 wt%) were synthesized and analyzed for their electromagnetic (EM) wave absorption properties. The ZNF and BT powders were combined in weight ratios of 1-x: x, where x = 0, 0.1, 0.2, 0.3, 0.4, and 1.0. With increasing x, the height of the complex permittivity (ε′ and ε″) spectra increased, while the height of the complex permeability (μ′ and μ″) spectra gradually decreased. The reflection loss (RL) value, indicative of EM absorption efficiency, was calculated using measured ε′, ε″, μ′, and μ″ data. Apart from the BT–epoxy sample (x = 1.0), which exhibited no magnetic loss mechanisms, the EM wave absorption characteristics in the NZF-BT-epoxy composites were predominantly influenced by magnetic loss mechanisms, as reflected in the μ″ values. The incorporation of BT modified the impedance matching conditions, causing the frequency at which maximum EM wave absorption indicated by the minimum RL (RLmin) occurs to shift to lower frequencies. The most remarkable EM wave absorption performance was observed for the sample with x = 0.4, where RLmin reached −70 dB. Notably, the samples with x values ranging from 0 to 0.4 demonstrated outstanding EM wave absorption capabilities within the radar frequency range of L and S-bands (1–4 GHz). Furthermore, the EM wave absorption bandwidth (Δf), representing the frequency range where RL < -10 dB, was 8.3 GHz (4.5–12.8 GHz) for the x = 0 sample. However, this bandwidth decreased to 2.6 GHz (5.0–7.6 GHz) for the x = 0.4 sample. Although the addition of BT led to a reduction in the EM wave absorption bandwidth compared to the NZF–epoxy composite (x = 0), it enabled the tuning of the absorption band towards lower frequencies, particularly emphasizing excellent EM wave absorption in the L-band.

Effect of Mn content on the structure, electromagnetic properties, and electromagnetic wave absorption characteristics in La0.7Sr0.3Mn1+xO3

The perovskite manganese oxide, La0.7Sr0.3Mn1+xO3 (x = −0.4, −0.2, 0, 0.2, 0.4, 0.6, 0.8, 1.0), was synthesized using the solid-state reaction method. A single-phase perovskite structure was obtained at the stoichiometric composition (x = 0). However, with an increase in Mn excess (x > 0), secondary phases of Mn2O3 and Mn3O4 formed and increased, while La2O3 and Sr-rich phases emerged when Mn is deficient (x < 0). The electrical conductivity, permittivity, and permeability of the samples showed significant variations with x, as both charge transport and magnetism originate from the presence of Mn. Complex permittivity (ε', ε") and permeability (μ', μ") spectra were utilized to calculate RL maps based on a transmission line theory. For samples with x ≥ 0, which exhibited relatively high values of ε' and ε", there was no significant absorption of electromagnetic (EM) waves within the measured frequency range (0.1 ≤ f ≤ 18 GHz) due to high EM wave reflection. Conversely, the Mn-deficient samples (x = −0.2, −0.4) demonstrated excellent EM wave absorption properties in the GHz range. This can be attributed to their favorable impedance matching characteristics, resulting from significantly reduced ε' and ε" values in the Mn-deficient samples. Notably, the sample with x = −0.2 exhibited the most outstanding EM wave absorption characteristics, with an RL value of −56 dB at a frequency of 2.33 GHz and a thickness of 7.59 mm. Additionally, it achieved an RL value of −50 dB at 9.8 GHz and 2.90 mm thickness.

Ultra-broadband terahertz metamaterial absorber based on flexible wave-absorbing material

Metamaterial absorbers (MA) in terahertz (THz) based bands are receiving much attention for its potential applications. However, the limited bandwidth greatly reduces the further development and wide application of terahertz absorbers. To solve this problem, achieving ultra-broadband and efficient absorption characteristics in the terahertz band, we propose a nickel-based microstructure ultra-broadband MA that operates in the THz band. The proposed MA's electromagnetic wave absorption characteristics and physical absorption mechanism are modeled and numerically simulated. The research demonstrates that MA can achieve ultra-wideband efficient absorption covering the whole THz spectrum (0.1 THz-16 THz) with an overall absorption rate of over 95%. The proposed absorber has polarization-insensitive characteristics and achieves a broad-angle incidence with a range of almost 80°.allows a range of incidence angles up to 80°. The MA consists of only three classical metal-dielectric layer-metal structures, which greatly reduces the application cost. The proposed ultra-thin geometry super-surface scheme uses a flexible absorbing material (ECCOSORB AN-72), and the results show that the overall absorption efficiency are significantly improved after the application of the flexible absorbing material. This design presents a unique and innovative idea for the development and use of ultrawideband terahertz absorbers across various industries including terahertz stealth, sensor technology, imaging, and communication, as well as optoelectronics. The potential applications of this technology are vast and can greatly benefit these industries.

Preparation and electromagnetic wave absorption characteristics of multifunctional light-weight high titanium slag-based foam geopolymer

In this work, a novel multifunctional light-weight high titanium slag (HTS)-based foam geopolymer was fabricated. The physical properties such as compressive strength, thermal conductivity, electrical conductivity, and electromagnetic wave absorption characteristics of HTS-based foam geopolymer composites with different matrix densities and pore structures were investigated. Furthermore, the electromagnetic wave absorbing mechanism and the carbon footprints were elaborated. The results indicated that microwave radiation assistance has greatly shortened the curing time of the foam geopolymer. The HTS-based foam geopolymer incorporated with carbon fibers exhibited favorable electromagnetic waves absorption performance with the lowest reflection loss (RLmin) value of −17.2 dB and a broad effective absorption bandwidth (EAB) of 8.40 GHz within 8–18 GHz frequency, and the CO2 emissions of this geopolymer were significantly reduced than ordinary Portland cement composites.

Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt;

Perovskite manganese La&lt;sub&gt;0.7&lt;/sub&gt;Sr&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (&lt;i&gt;T&lt;/i&gt;) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at &lt;i&gt;T&lt;/i&gt; ≥ 600 &lt;sup&gt;o&lt;/sup&gt;C. The average grain size was ~15 nm at the calcination temperature (T&lt;sub&gt;cal&lt;/sub&gt;) = 600 &lt;sup&gt;o&lt;/sup&gt;C and it increased to ~1 μm when T cal increased up to 1200 &lt;sup&gt;o&lt;/sup&gt;C. &lt;i&gt;M&lt;/i&gt;-&lt;i&gt;H&lt;/i&gt; curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;cal&lt;/sub&gt;. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ &lt;i&gt;f&lt;/i&gt; ≤ 18GHz. The complex permittivities (ε', ε") increased significantly in samples calcined above 800 &lt;sup&gt;o&lt;/sup&gt;C because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the &lt;i&gt;M&lt;/i&gt;&lt;sub&gt;S&lt;/sub&gt; value increased significantly. As the &lt;i&gt;T&lt;/i&gt;&lt;sub&gt;cal&lt;/sub&gt; increased, the height of the μ' and μ" spectra also gradually increased. The large values of ε', ε" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.

Performance Simulation and Fused Filament Fabrication Modeling of the Wave-Absorbing Structure of Conductive Multi-Walled Carbon Nanotube/Polyamide 12 Composite.

Fused filament fabrication (FFF) is a reliable method for fabricating structured electromagnetic wave (EMW) absorbers from absorbing materials. In this study, polymer-matrix composites were prepared using polyamide 12 (PA12) which was recovered from selective laser sintering (SLS) as the substrate and multi-walled carbon nanotubes (MWCNT) as the filler. The CST software is used for simulation calculation and study of electromagnetic wave absorption characteristics of composite materials. After that, based on the obtained parameters and results, modeling was carried out, and finally, EMW absorbers with various microstructures were fabricated by FFF. For the honeycomb structure sample, when the side length is 5 mm and the height is 2 mm, the minimum return loss (RL) of the composite at 15.81 GHz is -14.69 dB, and the maximum effective absorption bandwidth is 1.93 GHz. These values are consistent with the simulation results. The pyramid structure has better absorbing performance than plate structure and honeycomb structure. According to simulation calculations, the pyramid structure shows the best performance at an angle of 28°. The absorption performance of the printed pyramid structure sections exceeded the simulated values, with effective absorption bandwidth (EAB) reaching all frequencies from 2 to 18 GHz, with a minimum return loss of -47.22 dB at 8.24 GHz.

Microcellular foamed polyamide 6/carbon nanotube composites with superior electromagnetic wave absorption

Electromagnetic (EM) wave pollution causing damage to precision equipment and threatening the health of living organisms has attracted considerable attention. Herein, promising microcellular foamed polyamide 6 (PA6)/carbon nanotube (CNT) composites for highly efficient EM wave absorption were successfully fabricated using supercritical CO2 foaming. Nanocomposites foams with a void fraction ranging from 38.7% to 85.1% were achieved, providing a platform to assess the correlation of the electrical conductivity, the dielectric permittivity and the EM wave absorption properties with porosity. Notably, the Foam-257.5C sample with a void fraction of 38.7% exhibited outstanding EM wave absorption characteristics at a thickness of only 1.59 mm and an ultra-low reflection loss value of -55.3 dB (99.9997% wave absorption). Most importantly, the effective absorption bandwidth (EAB) of the Foam-257.5C sample could cover the entire Ku band (12.4–18 GHz) by slightly adjusting the thickness from 1.20 to 1.60 mm. The superior EM wave absorption performance of the Foam-257.5C sample was attributed to multiple reflections and scattering at the solid-gas interfaces, favorable impedance matching due to the existence of a large polymer-air interface area, conductive loss near the interfaces and interfacial polarization. Thus, this study offers an eco-friendly, simple and versatile methodology to develop high-efficiency, flexible polymer-based EM wave absorbents.

Anti-bacterial and arsenic remediation insights in aqueous systems onto heterogeneous metal oxide (Cu0.52Al0.1Fe0.47O4)/rGO hybrid: an approach towards airborne microbial degradation.

Copper-based ternary metal oxide (i.e., Cu0.52Al0.01Fe0.47O4) impregnated reduced graphene oxide nanohybrid is verified for microbial and arsenic treatment. Growth inhibition of colonies are observed around 99.99% (E. coli), and 99.83% (S. aureus) at 10-20μg/mL of hybrid dosage, respectively. The inhibition rates for both the colonies are increased to 99.9998% at 80μg/mL. TEM images have shown insight of cell-content/lipid leakage behavior after inoculating with the hybrid. The efficient hindrance towards microbial colony growth is attributed to better charge transfer, reactive oxygen species generation, and metal-ion release. Maximum arsenic sorption capacities are observed around 248 and 314mg/g for As(III), and As(V), respectively (Ci ~ 500ppm). Surface morphology studies onto arsenic adsorption are reported with atomic force microscope, and FT-IR/Raman analysis. A detailed discussion onto individual spectra of As 3d spectra confirmed the occurrence of redox transformation in arsenic species [As(III)]. The variation in the quantity (at. %) of oxygen functional groups in O1s spectra (i.e., M-O, M-OH, and -OH2) onto the hybrid supported the ligand-exchange behavior. Cyclic voltammetry study in arsenic electrolytes (10µM - 1mM) provides the occurrence of various in-situ electrochemical reactions supporting the redox activity. A significant electromagnetic wave absorption characteristics of the present hybrid is proposed with plausible airborne antimicrobial-agent abilities.

Effects of the absorber, thickness and surface roughness on the electromagnetic wave absorption characteristics of magnesium phosphate cement

Magnesium phosphate cement (MPC) functionalized with excellent electromagnetic wave absorption performance, bonding capacity, fast hardening and early strength can meet the requirements for rapid electromagnetic radiation protection of military and civil building structures. Hollow glass microsphere (HGM) is added uniformly to improve the impedance matching of MPC to free space, so that the electromagnetic wave is able to be maximally introduced into MPC and effectively absorbed by carbon nanotubes (CNT) through high dielectric loss effect. Influences of HGM contents, thickness and surface roughness of specimens on the electromagnetic wave absorption performance of MPC are systematically investigated. Test results demonstrate that the electromagnetic absorption performance of MPC is significantly enhanced by the additions of HGM and CNT. The peak reflection loss and the bandwidth below −10 dB first increase and then decrease with increasing HGM content. Increasing the thickness of the MPC improves the electromagnetic reflection loss. The electromagnetic absorption properties of MPC are improved further by cutting notches. MPC blended with 50 vol% HGM and 1 wt% CNT (by MgO) with 5 mm deep notches spaced 18 mm apart has excellent electromagnetic absorption capacity as featured by a peak reflection loss of –33.5 dB and a bandwidth of 7.03 GHz below −10 dB. In the perspective of structural strengths, the modified MPC is able to repair damaged concrete of pre-fractured concrete. It achieves the dual features of absorbing electromagnetic waves and repairing existing concrete structures.

Construction of Si3N4/SiO2/SiC–Y2Si2O7 composite ceramics with gradual impedance matching structure for high-temperature electromagnetic wave absorption

Good impedance matching is vital in upgrading the performance of electromagnetic (EM) wave-absorbing materials. In this study, Si3N4/SiO2/SiC–Y2Si2O7 composite ceramics were synthesized by sintering and chemical vapor infiltration (CVI) technology with gradual impedance matching. The relationship between the microstructure of the as-prepared composite ceramics and EM wave absorption characteristics was thoroughly explored. It was found that the amorphous Si3N4, SiO2, and SiC layers were constructed with a gradual impedance matching structure, which not only improved impedance matching but also increased the number of nano interfaces. More importantly, SiC nanocrystals effectively increased the conduction loss, and the presence of defects and nanoscale heterogeneous interfaces further increased the polarization loss. Consequently, the as-prepared composite ceramics displayed enhanced EM wave absorption properties, with a minimum reflection coefficient (RCmin) value of less than −20 dB over a temperature range of 25 °C (RT)-300 °C, and an effective absorption bandwidth (EAB) maintained at 4.2 GHz with the thickness range of 3.75–4.75 mm. These results demonstrated the practical significance of high-performance EM wave absorption materials that can be applied in high-temperature and water vapor environments.

Comparative study of microwave absorption properties of Ni–Zn ferrites obtained from different synthesis technologies

Spinel ferrites are widely used for electromagnetic wave (EMW) absorption applications. In this study, spinel Ni–Zn ferrites with excellent microwave absorption properties were synthesized. Their EMW absorption characteristics and interaction mechanisms were studied to lay the foundation for the study of the role of Ni–Zn ferrite as a magnetic substrate for composites. Herein, Ni0·5Zn0·5Fe2O4 was prepared by the hydrothermal method (H-NZFO) and the sol–gel auto-combustion method (S-NZFO); both samples exhibited distinct microwave absorption properties. The S-NZFO absorber (thickness = 3.72 mm) demonstrated the best dual-zone microwave absorption with two strong reflection loss peaks at 5.1 and 10.5 GHz. The corresponding effective absorption bandwidth (EAB) reached 9.0 GHz, which covered part of the S-band and all of the C- and X-bands. These results were attributed to the high saturation magnetization, outstanding complex permeability, and multiple magnetic loss channels of S-NZFO. The H-NZFO sample exhibited excellent absorption capability and matching thickness. At a thickness as low as 1.71 mm, the minimum reflection loss (RLmin) of the H-NZFO absorber reached -60.2 dB at 13.1 GHz. The maximum bandwidth corresponding to RL below -10 dB was 4.6 GHz. These results can be attributed to small particle size, high complex permittivity, and multiple dielectric loss channels of H-NZFO. The observed wide effective absorption bandwidth of S-NZFO and strong microwave absorption capability of H-NZFO suggest the potential of both materials as substrates for efficient microwave absorbers in military as well as civilian absorption applications.

Microwave absorption properties of Ni0.6Zn0.4Fe2O4 composites with nonmagnetic nanoferrite percentages

Microwave absorption materials need to be thin and lightweight and possess strong wave absorption ability and a wide absorption frequency band. To satisfy these conditions, we changed the microstructure of the composite by mixing ferrite material with different particle sizes. Specifically, we mixed nanosized nonmagnetic ZnFe2O4 powder into Ni0.6Zn0.4Fe2O4 powder, investigated the microwave absorption properties depending on the packing fraction. The crystal structure of the synthesized ferrite powders was analyzed through XRD, and the particle size was analyzed using a PSA and SEM. The density of the powders, which is required to measure the packing fraction, was determined via the gas disposition method, and the magnetic properties of the composites were analyzed using a VSM. The reflection loss represents the electromagnetic wave absorption characteristics, and it was calculated by substituting the measured permittivity and permeability values, into the equation based on the transmission line theory. The Ni0.6Zn0.4Fe2O4/ZnFe2O4 composite showed 99.9% absorption with a high packing fraction, and the absorption peak shifted to high frequencies. These characteristics suggest that the absorption ability and frequency range of the electromagnetic-wave-shielding composite can be easily controlled. Because of the high-absorption characteristic, absorption frequency control, and cost effectiveness, this composite can be applied to products such as thin electromagnetic-wave-shielding sheets.