Electromagnetic Wave Absorption Applications Research Articles

Emerging fabrication of ceramic nanofiber aerogel with the application in high-temperature thermal insulation, environment, and electromagnetic wave absorption

Emerging fabrication of ceramic nanofiber aerogel with the application in high-temperature thermal insulation, environment, and electromagnetic wave absorption

Facile design and permittivity regulation of porous carbon and magnetic particles based composite nanofibers towards highly efficient electromagnetic wave absorption

Two kinds of porous carbon and magnetic particles-based composite nanofibers (PCNTF-CoFe and PCNTF-NiFe) were synthesized for electromagnetic wave (EMW) absorption. Magnetic particles were used as the catalyst to increase the crystallinity of carbon and the corresponding dielectric loss ability, while porous structure was designed to improve the impedance matching. According to the results, the dielectric loss abilities of PCNTF-CoFe and PCNTF-NiFe are enhanced without significant degradation in their impedance matching condition. Therefore, through the polarization and conduction-induced dielectric loss together with the natural and exchange resonance-induced magnetic loss, the incident EMW can be attenuated rapidly inside PCNTF-CoFe and PCNTF-NiFe. PCNTF-CoFe shows a minimum reflection loss (RLmin) of −54.6 dB and effective band width (RL≤-10 dB, EABW) of 6.0 GHz at 2.0 mm, while PCNTF-NiFe shows RLmin of −33.4 dB and EABW of 5.7 GHz at 1.7 mm. Consequently, PCNTF-CoFe and PCNTF-NiFe can be promising candidates for application in EMW absorption.

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.

A Liquid‐Metal‐Assisted Competitive Galvanic Reaction Strategy Toward Indium/Oxide Core−Shell Nanoparticles with Enhanced Microwave Absorption

AbstractThe preparation of core–shell structured nanoparticles using the galvanic replacement reaction of liquid metals is a simple and efficient method. However, precise modulation of the core and shell components to regulate the microwave absorption performance still needs to be further explored. In this study, various types of indium/oxide core–shell nanoparticles are prepared based on a competitive galvanic reaction of gallium‐indium liquid metals. The prepared indium/oxide core–shell structured nanoparticles exhibit superior electromagnetic (EM) wave absorption properties with a minimum reflection loss (RL) of −40.25 dB at 1.7 mm and the widest effective absorption band of 6.12 GHz at 2.1 mm. The superior wave‐absorbing properties originate from the dielectric losses of the interfacial and dipole polarizations. In addition, an externally applied magnetic field improves the polarization loss and microwave dissipation to achieve a minimum RL of −45.65 dB at 2.4 mm. The liquid‐metal‐assisted competitive galvanic reaction strategies extend the variety of core–shell structured nanoparticles for electromagnetic wave absorption applications.

Fabrication of Multiwalled Carbon Nanotubes (MWCNT) and Reduced Graphene Oxide (rGO)‐based thermoplastic polyurethane and polypyrrole nanocomposites for electromagnetic wave absorption application with a low reflection

AbstractElectromagnetic radiation (EMR) pollution is a serious concern in today's environment, causing problems not just for electronic gadgets but also for living society. The goal of this research is to fabricate thermoplastic polyurethane (TPU) and polypyrrole (PPy)‐based 95:5 blend nanocomposites using a simple solvent casting method at such a low concentration of rGO and MWCNT (0.3, 0.4, 0.5 php) (parts per hundred polymers), for electromagnetic wave (EMW) absorption applications. The chemical interaction between the different phases and morphology of the nanocomposites is characterized by Raman spectroscopy, X‐ray diffraction (XRD), and field emission scanning electron microscopy (FESEM) techniques. The material properties, such as dielectric and magnetic properties, are analyzed in X‐band frequency (8.2–12.4 GHz). The total shielding effectiveness of (SETot) 0.5 rGO system is found to be 27 dB, whereas, for corresponding MWCNT nanocomposites, it is 26 dB. Interestingly, in 0.5 rGO nanocomposites, absorption shielding effectiveness (SEAbs) is approximately 25 dB, and reflection shielding effectiveness (SERef) is less than 2 dB, which indicates the absorption of 70% of the electromagnetic wave, and the rest gets reflected. Apart from that, the rGO‐based nanocomposites possess a greater extent of thermal stability than the corresponding MWCNT‐based nanocomposites.Highlights Fabrication of TPU‐PPy‐rGO and TPU‐PPy‐MWCNT nanocomposites by solvent casting. Low reflection of TPU‐PPy‐rGO nanocomposites with a 70% absorption rate. FESEM confirms the multilayer interface structures. Tunable Dielectric and magnetic properties of nanocomposites in X‐band. Excellent absorption dominant properties of the fabricated nanocomposites.

Enhanced electromagnetic wave absorption via optical fiber-like PMMA@Ti3C2Tx@SiO2 composites with improved impedance matching

Ti3C2Tx nanosheets have attracted significant attention for their potential in electromagnetic wave absorption (EWA). However, their inherent self-stacking and exorbitant electrical conductivity inevitably lead to serious impedance mismatch, restricting their EWA application. Therefore, the optimization of impedance matching becomes crucial. In this work, we developed polymethyl methacrylate (PMMA)@Ti3C2Tx@SiO2 composites with a sandwich-like core-shell structure by coating SiO2 on PMMA@Ti3C2Tx. The results demonstrate that the superiority of the SiO2 layer in combination with PMMA@Ti3C2Tx, outperforming other relative graded distribution structures and meeting the requirements of EWA equipment. The resulting PMMA@Ti3C2Tx@SiO2 composites achieved a minimum reflection loss of −58.08 dB with a thickness of 1.9 mm, and an effective absorption bandwidth of 2.88 GHz. Mechanism analysis revealed that the structural design of SiO2 layer not only optimized impedance matching, but also synergistically enhanced multiple loss mechanisms such as interfacial polarization and dipolar polarization. Therefore, this work provides valuable insights for the future preparation of high-performance electromagnetic wave absorbing Ti3C2Tx-based composites.

Carbonization of Ni@SiC@C nanoparticles reinforced PAN nanofibers for adjustable impedance matching

Achieving a broad bandwidth and efficient absorption of electromagnetic wave absorption materials remains a significant challenge, especially when considering electromagnetic pollution protection. One-dimensional carbon nanofibers with a three-dimensional network structure have been extensively studied to address this need. However, the high permittivity of carbon nanofibers results in a strong impedance mismatch with free space. In this work, we successfully dispersed double-shell Ni@SiC@C nanoparticles into one-dimensional carbon nanofibers (Ni@SiC@C CNFs) using electrospinning and heat treatment. We extensively explored the effect of carbonization temperature on the impedance matching and magnetic-dielectric loss for electromagnetic wave. The presence of rich interfaces from the double-shell nanoparticles and defects from N-doping optimizes the impedance matching of the composites. The exceptional electromagnetic wave absorption properties of the Ni@SiC@C CNFs are attributed to the synergistic effect between the three-dimensional conductive network, the interface electronic engineering induced by the sensibly loaded double-shell nanoparticles, and the multiple reflections, especially at a carbonization temperature of 600 ℃. The achieved minimum reflection loss value has been measured at an outstanding −53.27 dB, coupled with a remarkable absorption bandwidth that spans from 2.53 GHz to 18.00 GHz (15.47 GHz) across various thicknesses. These findings underscore the potential of the meticulously engineered Ni@SiC@C CNFs as highly promising candidates for efficient and broadband electromagnetic wave absorption applications.

SYNTHESIS OF Fe3O4 NANOPARTICLES GROWN ON RICE HUSK WASTE-DERIVED POROUS CARBON FOR HIGH-EFFICIENCY MICROWAVE ABSORPTION

In this study, a straightforward process was employed to synthesize Fe3O4 nanoparticles-decorated porous carbon derived from rice husk waste (Fe3O4/C). The composite material was made by using pyrolysis and then coprecipitation. Fe3O4 nanoparticles were dispersed evenly across the surface of a porous carbon structure made from rice husks (PC) in three dimensions (3D). The highly graphitized porous carbon framework makes the tracks for electromagnetic waves that propagate longer and increases the loss of conductivity. With its unique structure and the effects of great attenuation and good impedance matching, Fe3O4/C is much better at absorbing microwaves than pure porous carbon. Most samples have a minimum reflection loss (RL) of less than -10 dB (90% reduction) over a wide range of electromagnetic frequencies (3.6 - 18.0 GHz) when the thickness of the absorber varies from 1.5 - 4.0 mm. With a thickness of 3.0 mm, the best RL is -70.8 dB, and with a thin thickness of 1.5 mm, the effective absorption bandwidth (EAB) is 14.4 GHz. According to the findings of this study, the use of Fe3O4/C material for electromagnetic wave absorption applications holds great promise due to the low cost and extensive benefits of the preparation process, as well as its excellent electromagnetic absorption performance.

Natural green raw-based Biochar@Co/C composites: Simple water bath synthesis and excellent electromagnetic wave absorption properties

Over the last few years, wave absorbing materials synthesized based on green and eco-friendly natural materials were less studied. Carbon materials derived from natural materials, for example, have a limited absorption performance due to impedance mismatch in electromagnetic wave absorption applications. In this work, composites of MOF derivatives and biochar with strong wave absorbing capability were prepared by biochar and MOF. Biochar was green raw material originated from kapok trees in the school. Then it was compounded with MOF derivatives by pretreatment and water bath to form Biochar@Co/C composites. The effect of annealing temperature on the absorption properties was investigated by varying the annealing temperature. According to the results of the transmission line theory analysis, Biochar@Co/C-700 have RLmin value of −55.22 dB at 5.43 GHz and 3.69 mm. Also, the effective absorption bandwidth EAB can reach 6.37 GHz at 1.94 mm. And the above absorption properties were measured when the filling ratio was only 15 %. Electromagnetic parameter analyses showed that the combination between biochar and MOF derivatives greatly improves the impedance matching of the carbon-based materials, which is a vital factor that enables Biochar@Co/C-700 to have excellent wave-absorbing properties. In addition, the loss mechanism of the complexes to electromagnetic waves was also analyzed and summarized. These results provide a reference path for the preparation of high-performance electromagnetic wave absorption composites from green materials.

Microwave-absorbing performance of FeCoNi magnetic nanopowders synthesized by electrical explosion of wires

This study demonstrates fabrication of FeCoNi magnetic nanoparticles by joint electrical explosion of wires for electromagnetic wave absorption applications. An increase in the energy storage capacity of the capacitors can increase the maximum reflection loss of the nanoparticles and shift the corresponding frequency in the low-frequency direction, but has no significant effects on the maximum bandwidth. The minimum reflection loss of the magnetic nanoparticles reaches − 50.2 dB at 6.8 GHz when the thickness is 2.5 mm, while the maximum effective absorption bandwidth reaches 8.1 GHz at a thickness of 1.5 mm. The wire explosion method, as an instantaneous synthesis method with a low cost, environmental friendliness, and high-output characteristics, provides a new approach to industrial batch preparation of microwave-absorbing materials.

Enhancing electromagnetic absorption performance of Molybdate@Carbon by metal ion substitution

Transition metal molybdate (RMoO4) has been extensively studied in optics, electricity and catalysis due to its low cost and multivalent Mo atoms, while its poor electrical conductivity limits its application in electromagnetic wave absorption (EMA). Compounding molybdate with conductive materials is an effective way to improve its electrical conductivity. In this work, a homogeneous coating on the molybdate surface was achieved by utilizing a pyrrole oxidation polymerization mechanism, and then stabilized composites of Molybdate@Carbon (RMoO4@C) were obtained by high-temperature pyrolysis. The EMA properties of the nanocomposites were tuned by substituting the species of transition metal elements (RMoO4@C, R=Fe, Co, Cu). Among them, Fe2(MoO4)3@C has a minimum reflection loss of −60.62 dB at an ultra-low thickness of 1.7 mm, and the effective absorption bandwidth (EAB) can reach 4.75 GHz at 3.00 mm. This work expands the range of applications for molybdate and provides a new material basis for building high-performance EMA materials.

Lightweight cementite/Fe anchored in nitrogen-doped carbon with tunable dielectric/magnetic loss and low filler loading achieving high-efficiency microwave absorption

Magnetoelectric composites have promising application in electromagnetic wave absorption for their regulatory structures and interfacial interactions. In this research, a facile one-step pyrolyzing procedure was applied to achieve cementite/Fe nanoparticles anchored on nitrogen-doped carbon nanotubes (Fe3C/Fe/N-CNTs) composites. Fe3C/Fe encapsulated in nitrogen-doped carbon was generated through in-situ Fe-catalyzed carbothermal reactions.The obtained magnetoelectric composites displayed excellent microwave absorption properties with a minimum reflection loss of −54.4 dB at 10.4 GHz, a matching thickness of 2.3 mm, and low filler loading (15%). Moreover, even at a low matching thickness of 1.55 mm, the reflection loss was less than −10 dB in the range of 13.7–18.0 GHz, and an effective absorption bandwidth of 4.3 GHz was achieved. The outstanding microwave absorption performance can be summarized as follows. 1) The CNT network enriches the transmission path, enhancing the dielectric loss capability. 2) The hollow one-diameter CNT structure helps strengthen interfacial polarization, optimizing the impedance matching while promoting multiple reflections and scattering. 3) Magnetic Fe3C/Fe provides a strong magnetic dissipation ability and eddy current losses. 4) The heterogeneous magnetoelectric Fe3C/Fe/N-CNTs possess multiple interfaces, increasing the interfacial polarization and electromagnetic synergistic losses. This study provides a potential strategy for the large-scale synthesis of low filler loading magnetic–dielectric microwave absorbers.

Microstructures, Mechanical Properties and Electromagnetic Wave Absorption Performance of Porous SiC Ceramics by Direct Foaming Combined with Direct-Ink-Writing-Based 3D Printing.

Direct-ink-writing (DIW)-based 3D-printing technology combined with the direct-foaming method provides a new strategy for the fabrication of porous materials. We herein report a novel method of preparing porous SiC ceramics using the DIW process and investigate their mechanical and wave absorption properties. We investigated the effects of nozzle diameter on the macroscopic shape and microstructure of the DIW SiC green bodies. Subsequently, the influences of the sintering temperature on the mechanical properties and electromagnetic (EM) wave absorption performance of the final porous SiC-sintered ceramics were also studied. The results showed that the nozzle diameter played an important role in maintaining the structure of the SiC green part. The printed products contained large amounts of closed pores with diameters of approximately 100-200 μm. As the sintering temperature increased, the porosity of porous SiC-sintered ceramics decreased while the compressive strength increased. The maximum open porosity and compressive strength were 65.4% and 7.9 MPa, respectively. The minimum reflection loss (RL) was -48.9 dB, and the maximum effective absorption bandwidth (EAB) value was 3.7 GHz. Notably, porous SiC ceramics after sintering at 1650 °C could meet the application requirements with a compressive strength of 7.9 MPa, a minimum RL of -27.1 dB, and an EAB value of 3.4 GHz. This study demonstrated the potential of direct foaming combined with DIW-based 3D printing to prepare porous SiC ceramics for high strength and excellent EM wave absorption applications.

A facile salt-templating synthesis route of bamboo-derived hierarchical porous carbon for supercapacitor applications

Porous carbon materials have been widely used as electrodes for various energy storage and conversion devices, particularly for supercapacitors. Herein, a bamboo-derived hierarchical porous carbon (BHPC) is directly prepared under air atmosphere via an eco-friendly, one-step, and easily-scalable salt-templating strategy using ZnCl2/KCl salt mixture as a pore-directing solvent. The obtained BHPC material exhibits large specific surface area (1296 m2 g−1) and large total pore volume (1.26 cm3 g−1) which make the BHPC material applicable for supercapacitor as an electrode material. Electrochemical performance evaluated in a 6 M KOH electrolyte in a three-electrode system indicates a high specific capacitance of 394 F g−1 at 1 A g−1 and a good rate capacity with 76.14% capacitance retention at 20 A g−1. The as-prepared symmetric supercapacitor delivers a high energy density of 11 Wh kg−1 at a powder density of 126 W kg−1, and an outstanding lifespan with 81% capacitance retention over 10,000 cycles. These results further open new possibilities for tailoring the surface properties (i.e., heteroatom doping, surface modification, metal oxides incorporation, etc.) towards energy storage and conversion applications such as electrocatalysts for oxygen reduction reaction/hydrogen evolution reaction, lithium-ion batteries, and supercapacitors, as well as wastewater treatment, and electromagnetic wave absorption applications.

MXene/PEO aerogels with two-hierarchically porous architecture for electromagnetic wave absorption

MXene aerogels have drawn much attention for electromagnetic wave (EMW) absorption application and the internal microstructure of aerogels has a prominent influence on EMW response behaviors. However, as far as we know, it is still a challenge to modulate the microstructure of MXene aerogels. Herein, MXene/PEO aerogels with two-hierarchically porous structure have been successfully constructed where the 3D porous network of MXene/PEO aerogels is assembled by MXene layers featuring with secondary pore structure, which hasn't been reported in other work. It has been demonstrated that the amount of added PEO is responsible for the microstructure of MXene/PEO aerogels, thus having a direct effect on their complex permittivity and impedance matching. The resultant MXene/PEO aerogels deliver excellent EMW absorption performance that a broad effective absorption bandwidth of 5.20 GHz and a minimum reflection loss value of −50.8 dB can be achieved. The attractive EMW absorption properties depend on the comprehensive contributions of multiple dissipation modes and better impedance matching. Overall, this work fabricated MXene aerogel with two-hierarchically porous structure to satisfy the strong absorption capability and lightweight requirements of future EMW absorbers.

Synchronously enhanced electromagnetic wave absorption and heat conductance capabilities of flower-like porous γ-Al2O3@Ni@C composites

Efficient multifunction materials with strong electromagnetic wave (EMW) absorption and high thermal conductance play a pivotal role in addressing the heat accumulation and EM interference problems in miniaturized and integrated electronics. However, incompatibility between EMW absorption and heat conductance makes their simultaneous improvement a major challenging issue. In this work, flower-like porous γ-Al2O3@Ni@C composites are successfully formulated via a hydrothermal-soaking-calcining route. The original findings of the concerted improvement in EMW absorption and heat conductance are reported. By controlling [Ni2+] and sintering temperature (Ts), the interfaces, components, and defects are modified to achieve synergistic enhancement in the performance of the target composites. Results show that the γ-Al2O3@Ni@C composites formed at [Ni2+] = 2.0 M and Ts = 700 °C present an optimal thermal conductance of 2.84 W/(m⋅K) at a low filling ratio of 30 % due to the phonon/electron relay transmiss on in the 3D network of unique flower-like porous structures, clearly superior to γ-Al2O3 and most of the other γ-Al2O3-based composites. Meanwhile, the composites synchronously present a broad absorption band (4.24 GHz, beyond 90 % damping over 15.75 ∼ 18.00 GHz) and strong absorption (-42.43 dB) relative to a 1.7 mm-thick specimen owing to the enhanced damping coefficient and EM parameters. The outstanding properties exhibited by the flower-like porous γ-Al2O3@Ni@C composites suggest that they have promising prospects for application in EMW absorption and thermal management.

Ni–Co Prussian blue analogue/graphene aerogel: a green synthesis approach for high-performance electromagnetic wave absorption and radar stealth applications

A superlight Ni–Co Prussian blue analogue microcube/graphene aerogel is synthesized through a sustainable and ecofriendly route for highly efficient electromagnetic wave absorption.

Two-dimensional (PEA)2PbBr4 perovskite modified with conductive network for high-performance electromagnetic wave absorber

Two-dimensional (2D) hybrid halide perovskites have shown great potential for application in the field of electromagnetic wave (EMW) absorption thanks to their inherent high-equilibrium electron hole and electron mobility as well as enhanced water-resistance and photo-stability. However, research on the application in EMW absorption has never been reported. Here, we first design the (PEA)2PbBr4/CNTs wave-absorption system. By adjusting the component ratio, the 2D perovskite-based composite shows an excellent wave absorbing performance. The maximum effective absorption bandwidth reaches 5.12 GHz at 1.74 mm (12.28–17.40 GHz) and a minimum reflection loss of −56.88 dB at 1.90 mm, respectively, as the component mass ratio is 12:1. This outstanding performance is attributed to the combined action of multiple loss mechanisms and provide a great potential of 2D perovskite for application in EMW absorption.

Self-Limited ultraviolet laser sintering of liquid metal particles for μm-Thick flexible electronics devices

Lightweight, deformable and highly conductive conductors are rather appealing in flexible electronics devices such as electromagnetic interference (EMI) shielding films; however, the most commonly used metallic foils or carbon nanomaterials suffer from critical limitation of either film thickness or electrical conductivity. Herein, we present a facile approach to rapidly fabricate sintered liquid metal submicron particles (LMSPs) films in combination spray-coating with direct nanosecond ultraviolet (UV) laser sintering. High conductive, μm-thick sintered LMSPs films were prepared owing to the self-limited penetration depth of UV laser, and their sheet resistances are easily tuned at least seven orders of magnitude by the laser processing parameters. A calculated parametric map upon particle diameter and laser fluence whether or not a liquid metal particle is ruptured has been obtained and it is quite well in accordance to the experiment results. Such laser-sintered LMSPs films are finally utilized to fabricate shielding films with superior EMI shielding effectiveness (SE) of ∼33 dB and specific EMI SE over thickness (SSE/t) of ∼27500 dB•cm2•g−1, and flexible electromagnetic metamaterials with a high absorption above 99.9 % at resonance frequency of 12.9 GHz and 14.3 GHz, showing their high potential for flexible EMI shielding and electromagnetic wave absorption applications.

Facile synthesis of core-shell structured C/Fe3O4 composite fiber electromagnetic wave absorbing materials with multiple loss mechanisms.

The use of heterostructures in electromagnetic wave absorption applications has been limited by the problem of homogeneous dispersion in composites. In this study, three-dimensional (3D) cross-linked electromagnetic wave absorbing composites with the carbon nanofiber/Fe3O4 (CNF/Fe3O4) core-shell structure were synthesized by expanding the interface of the heterogeneous structure with Fe3O4 nanocrystals uniformly modified on the surface of the carbon nanofiber. The 3D cross-linked structure of the composites contributes to the generation of conductive loss and macroscopic eddy current loss. The heterogeneous interface formed by graphite nanocrystals and amorphous carbon in the carbon nanofiber is identified by high-resolution transmission electron microscopy and Raman spectroscopy as having a strong electromagnetic wave absorption capacity for boundary-type defects. The Fe3O4 nanocrystal particles on the surface of the carbon nanofiber not only have the strong magnetic loss capability of magnetic materials but also form a new heterogeneous interface with the carbon nanofiber surface, which further enhances the interfacial polarization of the composite and improves the electromagnetic wave absorption properties. With the synergistic effects of interfacial polarization, macroscopic and microscopic eddy current losses, conductive losses, and magnetic losses, the electromagnetic wave absorption performance of the composites is further enhanced based on the carbon nanofiber. The reflection loss reaches -51.11, -42.99, and -55.98 dB at 9, 12 (X-band), and 17GHz (Ku-band), respectively, corresponding to the thicknesses of 2.0, 1.5, and 1.0mm. In addition, the widest effective absorption bandwidth is 3.3GHz at 14.7-18GHz (only 1.09mm).