Electromagnetic Wave Absorption Properties Research Articles

Effective electromagnetic wave absorption strategy: Unlocking the potential of NiCo2O4 as an absorber

This study addresses a scientific challenge by elucidating the influence of calcination temperature on the properties and electromagnetic wave absorption capabilities of NiCo2O4, a material whose performance is inherently tied to its preparation process. Specifically, we systematically investigate how varying calcination temperatures not only diversify the material’s composition and morphology but also enhance its electromagnetic wave absorption properties. By controlling the calcination temperature, we not only achieve the successful synthesis of NiCo2O4 but also unravel intricate correlations among calcination conditions, material composition, and wave absorption performance. Notably, NiCo2O4 sample calcined at 400 °C exhibits remarkable electromagnetic wave absorption, marked by an exceptional maximum reflection loss of −53.93 dB and a broad absorption bandwidth spanning 6.24 GHz. These insights contribute to advancing the frontiers of NiCo2O4 utilization, particularly in the realm of electromagnetic wave absorption and beyond, underscoring the novelty and impact of our research.

A novel biomass-derived carbon@ZnO@ZnSe composites for efficient electromagnetic wave absorption

A novel biomass carbon-based ternary composite coated with ZnO and ZnSe was synthesized by activated carbonization and hydrothermal method. The composition, microstructure and electromagnetic wave (EMW) absorption performance and related mechanism of the composites were investigated in detail. The unique coating structure of lamellar ZnO and spherical ZnSe facilitates multiple reflection and scattering of EMWs, thereby enhancing the dissipation of EMW energy. Moreover, the incorporation of highly conductive ZnO and ZnSe not only enhances the polarization loss and conductivity loss of CBP@ZnO@ZnSe composites, but also improves the impedance matching, further optimizing the EMW absorption property greatly. The CBP@ZnO@ZnSe composites exhibited enhanced EMW absorption performance, characterized by a minimum reflection loss of −24.57 dB and an effective absorption bandwidth of 3.43 GHz at 2.89 mm, owing to the synergistic interplay of favorable impedance matching and attenuation ability. In addition, radar cross section simulation results further demonstrated that CBP@ZnO@ZnSe composites have good electromagnetic energy dissipation effect in practical applications. This study not only offers a simple and feasible method for preparing CBP@ZnO@ZnSe composites with excellent EMW absorption properties, but also serves as a reference for the research of ternary composites based on bio-derived carbon.

A novel oxide ceramic matrix composite with integrated high-temperature EMW absorption and mechanical performance

Oxide ceramic matrix composites (OCMC) are extensively used as thermal structural materials due to good high-temperature resistance, mechanical properties, and oxidation resistance, but they are rarely regarded as electromagnetic wave absorbing materials due to the high resistivity of oxide ceramics/fibers. However, high-performance Al2O3 fiber can be used to design and fabricate OCMC with integrated high-temperature microwave absorbing and mechanical properties by introducing dielectric material into Si-based ceramic matrix. The N610/Si3N4-SiOC composites have the prior mechanical performance because the uniformly distributed Si3N4 matrix made the fiber bear effectively. After that, the Sc2O3 modified SiOC matrix was filled into inter- and intra-fascicular pores forming interfacial polarization, dipole polarization, multiple reflection and scattering to attenuate the incident electromagnetic wave (EMW). The effective absorption bandwidth (EAB) and the minimum reflection coefficient (RCmin) of N610/Si3N4-SiOC(Sc) composites at the thickness of 2.75 mm reach 3.0 GHz and −42 dB in the X band, respectively. In addition, the EMW absorption performance of the composite is relatively stable with EABmax and RCmin of 3.5 GHz and −41 dB in 4–18 GHz at high temperatures. This work provides a strategy for designing and fabricating OCMC with excellent mechanical properties and EMW absorption properties.

Constructing MXene-based mixed-dimensional structure with multiple interfaces to optimize dielectric-magnetic synergistic effect for effective electromagnetic wave absorption

Exploring efficient microwave absorbing materials (MAMs) which could convert electromagnetic (EM) energy into thermal energy represents an approbatory vision to reducing EM radiation and interference. Designing of mixed-dimensional structure with multiple interfaces represents the available target to investigate an ideal MAMs, which maximizes the superiority of mixed-dimensional structure in electromagnetic wave absorption (EMWA). Herein, we take full advantage of multiple interfaces engineering of MXene for optimizing the impedance matching to improve EMWA, MXene-based mixed-dimensional structure was designed by incorporating three-dimensional Fe3C@Carbon layers coated zero-dimensional Fe3O4 nanoparticles (NPs) supported two-dimensional MXene nanosheets (MXene/Fe3O4@Fe3C@Carbon, MFC). The Fe3O4@Fe3C@C with Core@shell structure arrests the essentially self-restacked of MXene and provides various attenuation mechanisms for the incident electromagnetic waves (EMWs). By regulating the carbonization temperature, the MFC exhibits enhanced EMWA property which is attributed to the characteristic structure and optimized dielectric-magnetic synergy effect. The minimum reflection loss (RLmin) value of MFC can reach to −64.3 dB with a matching thickness of 1.73 mm. Otherwise, the maximum effective absorption bandwidth (EAB) (RLmin < -10 dB) reaches 6.42 GHz at only 1.5 mm. Thus, our study refers a novel-fire enlighten to develop excellent mixed-dimensional microwave absorbent based on MXene.

Construction of periodic hollow SiC microtube ceramic for synergistic broadband absorption performance at elevated temperatures

Silicon carbide (SiC) has been utilized as a semiconductor material and has been shaped into various structural forms to obtain outstanding electromagnetic wave (EMW) absorption properties, characterized by low weight and excellent absorption capabilities even at high temperatures. A chemical vapor infiltration (CVI) approach was used to synthesis a periodic structured SiC microtube ceramic on a carbon fiber plain preform, taking inspiration from the porous structure found in SiC materials. Afterwards, the carbon fibers were removed by oxidation at a temperature of 900 °C. The periodic structural SiC microtube ceramic exhibited a porosity above 68 %, rendering it a lightweight material possessing a density of 0.8 g/cm3. The SiC microtube ceramic displays a periodic structure and exhibits anisotropy at 0° and 45°, respectively, as a result of the braided structure of the fiber fabric. When evaluated at a 0° angle of incidence, the SiC microtube ceramic, with a thickness ranging from 2.4 to 2.6 mm, showed excellent absorption of EMW energy in the Ku-band frequency range, attenuating more than 90 % of the energy, with a minimum reflection loss of −56.36 dB at 15.65 GHz. SiC microtube ceramics have demonstrated an effective absorption bandwidth exceeding 8.2 GHz throughout a temperature range of ambient temperature to 600 °C, with a thickness of 2.8 mm. Furthermore, the SiC microtube ceramic exhibited stable EMW absorption properties and thermal conductivity even at temperatures as high as 600 °C.

A novel mullite anti-gyroid/SiC gyroid ceramic metastructure based on digital light processing 3D printing with enhanced electromagnetic wave absorption and mechanical properties

A novel mullite anti-gyroid/SiC gyroid ceramic metastructure based on digital light processing 3D printing with enhanced electromagnetic wave absorption and mechanical properties

Investigation of the impact of non-magnetic Si element addition and heat treatment on the electromagnetic wave absorption properties of medium entropy FeCoNiSi alloy particles

Based on chemical liquid phase reduction and high temperature annealing, the effects of non-magnetic Si element addition and heat treatment regime on the microstructure, magnetic properties, and electromagnetic wave absorption properties of medium entropy alloy particles FeCoNiSi were studied. The results show that the prepared Fe1Co0.8Ni1Six alloy particles have a spherical structure, and with the increase of Si content, the particle size continuously decreases, with the average particle size decreasing from 150 to 200 nm to 20-50 nm. After high temperature annealing, the alloy particles undergo some agglomeration and growth. The as-prepared Fe1Co0.8Ni1Six alloy particles exhibit an amorphous state, and crystallization occurs during high temperature annealing, but the increase in Si element content has a certain inhibitory effect on the crystallization of the alloy particles. With the increase of Si element content and annealing temperature, the specific saturation magnetization intensity of the material shows a decreasing trend, while the residual magnetism and coercivity show an increasing trend. With the increase of Si element content, the real and imaginary parts of the permeability change alternately in different frequency ranges. The magnetic loss mechanism for the three alloy particles was eddy current loss in the frequency ranges of 10-14GHz and 16.5-18GHz. With the increase of Si element content, the magnetic loss shows an increasing trend, and the impedance matching shows a decreasing trend. The Fe1Co0.8Ni1Si0.5 alloy particle sample has the maximum reflection loss |RLmax| of 28.2 dB at thickness of 2.3 mm, and the Fe1Co0.8Ni1Si0.7 alloy particle sample has an effective absorption bandwidth of 1.7GHz at thickness of 1.9 mm. Eddy current loss was the main magnetic loss mechanism for Fe1Co0.8Ni1Si0.6 alloy particles under 400 °C and 600 °C annealing conditions, and for Fe1Co0.8Ni1Si0.7 alloy particles under 600 °C annealing conditions. With the increase of annealing temperature, the fluctuation of dielectric loss with frequency decreases in the low frequency range, and increases in the high frequency range, while annealing reduces the fluctuation of magnetic loss with frequency. Under 400 °C annealing conditions, the attenuation constant of the three alloy particles was lower than that of the unannealed alloy particles, and under 600 °C annealing conditions, the attenuation constant of Fe1Co0.8Ni1Si0.5 alloy particles in the frequency range of 6-15GHz was higher than that of unannealed and 400 °C annealed alloy particles, and that of Fe1Co0.8Ni1Si0.6 alloy particles in the frequency range of 7-14GHz was higher than that of unannealed and 400 °C annealed alloy particles. High temperature annealing was not able to effectively improve the impedance matching performance of Fe1Co0.8Ni1Six alloy particles. The maximum reflection loss |RLmax| of Fe1Co0.8Ni1Si0.6 alloy particles under 600 °C annealing conditions was 37.8 dB.

A Semi-amorphous Ti-BDC-derived Ti/C nanocomposite for efficient electromagnetic wave absorption

Electromagnetic (EM) interference presents a crippling risk to both human health and the dependability of technological devices. Due to their diverse advantages, metal-organic framework (MOF) derivatives have received much attention in developing novel EM wave-absorbing materials. Nevertheless, achieving desirable EM wave absorption capabilities in magnetic carbon-based absorbers through deliberate adjustment of MOFs remains a difficult task. In this study, a novel nanoporous carbon material (TiO2/C) has been successfully synthesized by a semi-amorphous material (Ti-BDC), which has excellent EM wave absorption properties. In detail, the minimum reflection loss (RL) of −49.7 dB and broad effective absorbing bandwidth (EAB) of 4.16 GHz can be reached with an absorbent thickness of 2.2 mm. The improved performance is mostly due to the dipole polarization of the functional groups and the even distribution of the nanoparticles, which form a seamless network. This promotes the dissipation of polarization and dielectric energy at the interface. In addition, the TiO2 nanoparticles on the carbon material improve the impedance matching, further enhancing the material's absorption performance.

One‐Pot Synthesis of Conductive Metal–Organic Framework@polypyrrole Hybrids with Enhanced Electromagnetic Wave Absorption Performance

Rational heterostructure design can bring interfacial polarization relaxation to significantly enhance the electromagnetic wave (EMW) absorption performance. However, intelligently building a homogeneous heterostructure with superior EMW absorption properties remains a great challenge. Herein, a typical conductive metal–organic framework Cu3(HHTP)2 (hexahydroxytriphenylene, HHTP) is delicately packed onto a polypyrrole (PPy) conductive polymer surface via a one‐step in situ polymerization approach. Results show that Cu3(HHTP)2 is well packed on the PPy surface to form an elegant Cu3(HHTP)2@PPy hybrids interfacial microstructure with a unique superiority regarding EMW absorption compared with single components of PPy and Cu3(HHTP)2. Interestingly, the interfacial microstructure of Cu3(HHTP)2@PPy hybrids can be tuned by adjusting the composition of the PPy and Cu3(HHTP)2, resulting in the improvement of impedance matching, conductive loss, and enhancement of interfacial polarization relaxation, endowing the optimization of the EM wave absorption properties of the Cu3(HHTP)2@PPy. The broad effective absorption bandwidth covers a range as broad as 6.68 GHz (11.00–17.68 GHz), which is higher than most reported metal‐organic frameworks (MOFs) and conductive polymer‐based EM absorbing materials. Herein, new insight for developing highly efficient EMW absorption materials through hybridized interfacial microstructure engineering is provided.

Modifying the CNTs with high dielectric loss NiCo2O4 to enhance the electromagnetic wave absorption properties

Decorating the CNTs with dielectric loss material is an effective means of enhancing electromagnetic wave absorption properties. In this work, we synthesized high dielectric loss NiCo2O4 nanoparticles on CNTs through hydrothermal method. By adjusting hydrothermal time, the NiCo2O4/CNTs with different NiCo2O4 content were obtained. The nucleation and growth of NiCo2O4 nanoparticles would cause a lot of defects and heterogeneous interfaces on CNTs, which influences the conduction loss and polarization loss of CNTs. Therefore, adjusting the content of NiCo2O4 in CNTs is an efficient path to enhance its absorbing performance. When the content of NiCo2O4 is 45.05 wt%, the reflection loss of NiCo2O4/CNTs reaches −43.2 dB, and the effective absorption bandwidth can be up to 3.3 GHz. It proves that NiCo2O4/CNTs has potential to be a high quality absorbing agent.

Porous carbon composite nanosheets loaded with magnetic FeNi/NiFe2O4 and dielectric SiO2 nanoparticles for adjustable microwave absorption

According to the escalating concern regarding the health hazards associated with electromagnetic radiation, the significance of absorbing materials underscores which could mitigate the healthy risks. While magnetic materials offer excellent absorption performance, their high density poses challenges to achieving optimal absorption efficiency. Conversely, carbon-based materials are known for their lightweight and versatile but face impedance matching issues. To address these obstacles, carbon/magnetic composite materials have been explored. However, their absorption performance has not fully met requirements due to weaker magnetic properties and increased density. Herein, we synthesized a porous carbon material embedded with magnetic FeNi/NiFe2O4 and dielectric SiO2 nanoparticles (FeNi-NiFe2O4-SiO2@PC) using carbonthermal method. By adjusting the ratio of polyvinylpyrrolidone to nitrates, the electromagnetic wave (EMW) absorption performance is adjusted. The FeNi-NiFe2O4-SiO2@PC composites display remarkable EMW absorption properties, achieving a minimum reflection loss of −69.9 dB at a thin thickness of 1.495 mm and a maximum effective absorption bandwidth of 5.68 GHz, covering the range from 12.32 to 18.0 GHz at a thickness of 1.92 mm. This outstanding performance can be attributed to the favorable impedance matching and the three-dimensional porous structure, which facilitates a 3D transmission network for multiple reflections. Additionally, the presence of FeNi, NiFe2O4, and SiO2 nanoparticles enhances magnetic loss, conductive loss, interface polarization, and dipolar polarization, leading to excellent ab. Hence, this work offers insights into the composition design of high-performance absorbing materials.

Multi-interface spatial star-like MoC/Co/C composites toward enhanced electromagnetic wave absorption properties

Interfacial engineering and morphology design are two popular strategies to strengthen the performance of carbon-based composites as electromagnetic wave absorbing materials (EWAMs). Herein, we integrate their advantages simultaneously in ternary MoC/Co/C composites (SMCCs). On one hand, highly dispersed MoC and Co nanoparticles create abundant heterogeneous interfaces, and on the other hand, the spatial star-like carbon skeletons derived from ZnCo-MOF also bring significant structure contribution to EM energy consumption. EM measurement reveals that the pyrolysis temperature greatly impacts EM properties of SMCCs. After blending with paraffin (organic binder), the mixture that involves SMCC-800 (pyrolyzed at 800 °C) may have both good impedance matching degree and powerful EM attenuation ability. As a result, SMCC-800/paraffin displays excellent EM absorption performance, including strong reflection loss intensity down to −67.3 dB at 16.2 GHz (thickness: 1.8 mm) and broad response bandwidth of 6.0 GHz (12.0–18.0 GHz, thickness: 2.0 mm) less than −10.0 dB, which outdo the performance of many composites with similar chemical composition ever reported. The EM absorption mechanism of SMCC-800/paraffin is comprehensively illustrated through the investigation on EM properties of the mixtures with various control samples.

Preparation and electromagnetic wave absorption properties of CAU-Al MOF and graphene oxide aerogel composites

The application of microwave technology has penetrated all aspects of life, but also lead to the electromagnetic pollution, therefore the research of high efficiency microwave absorption materials has been widely concerned. In this work, a new type of Al based CAU-10-H MOF was prepared by hydrothermal method. The particles were polyhedral in size of 2 [Formula: see text]m. After high temperature annealing, the interplanar spacing increased with the annealing temperature, and the lattice structure was destroyed at 400°C. CAU-Al/rGO aerogels were prepared by freeze-drying of hydrogels. With the increase of CAU-Al content and the annealing temperature, the carbon crystallinity decreases, and the pores of the aerogels became larger and fluffier. The real parts of permittivity of CAU-Al/rGO aerogels were between 5 and 30, which can be tuned by the annealing temperature and CAU-Al content. For the microwave absorption performance, the CAU-Al/rGO aerogel with a ratio of 3:1 achieved the minimum reflection loss of −37.8 dB at 3 mm. Moreover, the CAU-Al/rGO aerogels showed a wide effective bandwidth, which reached 5.1 GHz under the thickness of 2.5 mm. Therefore, the CAU-Al/rGO aerogels could be used as a kind of broadband microwave absorber with excellent microwave absorption performance.

Enhanced EM shielding: Synergetic effect of zirconium ferrite, MWCNT, and graphene in LDPE polymer composite to counteract electromagnetic radiation in the X-band range

In this work, we present a study on the evaluation of electromagnetic (EM) shielding performance using low-density polyethylene (LDPE) polymer composite as an EM wave-absorbing material in the X-band range. Using magnetic and conducting fillers is proven to enhance the shielding performance of the composite polymer. In this study, we show that the use of zirconium ferrite (ZrFe2O4) as magnetic filler and multiwall carbon nanotube (MWCNT)/ graphene nanoplatelet (GNP) as conductive fillers exhibit excellent electromagnetic wave-absorbing properties in the X-band range. Fillers and the polymer matrix are characterized by various techniques such as XRD, SEM, color mapping, EDAX, etc. Systematic optimization of the composition of LDPE polymer composite with varying ZrFe2O4 and conducting fillers are carried. The results showed that a composite with 5 wt% displayed enhanced EMI shielding in X-band (8.2–12.4 GHz) within the concentrations studied. For the optimized composite highest shielding effectiveness being 58.57 dB (99.9936 %) at 10.3 GHz is recorded. The shielding mechanism and dominate shielding phenomena are evaluated by calculating coefficients of absorption, reflection and transmittance. The findings of this study show that the use of ZrFe2O4 has excellent potential as a magnetic filler in polymer-based composites for EMI shielding applications.

Bimetallic MOFs-derived CoFe/Fe/C particles prepared by explosion and pyrolysis methods for electromagnetic wave absorption

In this study, {[CoFe3O(tza)6(H2O)3]·(NO3)3·5 H2O}n was applied as a precursor for fabricating CoFe/Fe/C composite materials via explosive and high-temperature calcination techniques. The explosive method was identified as a straightforward approach for achieving remarkable electromagnetic wave absorption properties. At a thickness of 2.03 mm, the CoFe/Fe/C (CoFe-700) composite material exhibited a minimum reflection loss of −77.84 dB. Similarly, it demonstrated the widest effective absorption (≦ −10 dB) bandwidth (4.06 GHz) with a thickness of 2.00 mm. Encompassing frequencies from 2.90 GHz to 18 GHz, the total effective absorption bandwidth extended throughout the thickness range of 1.00−5.50 mm. Under the same mixing ratio of powder and paraffin (1:1), the effective absorption bandwidth value of CoFe/Fe/C (CoFe-600) sample at a thickness of 1.40 mm is 4.95 GHz. The CoFe/Fe/C carbon composite materials emerged as optimal electromagnetic wave absorbers due to their exceptional conductivities, abundant dielectric losses, and magnetic loss mechanisms.

Mechanical properties and electromagnetic wave absorption characteristics of solid waste low-carbon cementitious materials

A low-carbon multi-functional cement substitute material has been developed to reduce electromagnetic pollution in building spaces and protect human health. The solid waste electromagnetic absorption cementitious material (SWEACM) is produced by combining steel slag (SS), blast furnace slag (BFS), and phosphogypsum (PG). In this study, the properties of SWEACM were analyzed, including flow, electromagnetic wave absorption, strength, and environmental properties. Additionally, the hydration and electromagnetic wave absorption mechanisms were examined. The results indicate that SS, BFS, and PG content significantly affect the strength and electromagnetic wave absorption properties of SWEACM. S-6 exhibits the best overall performance (SS: BFS: PG = 3:6:1), with the highest strength (28 days compressive strength = 33.5 MPa) and fluidity (19.1 cm). Furthermore, it has excellent electromagnetic absorption performance (RLmin = −45.4 dB), with an adequate absorption bandwidth of up to 10 GHz in the 2–18 GHz range. The excellent electromagnetic wave absorption capability of SWEACM is mainly due to the resonance, polarization relaxation loss, and conduction loss of the magnetic and conductive components in the material. The results show that SWEACM can be used as a multi-functional construction engineering material for electromagnetic protection, combining high levels of high electromagnetic wave absorption, strength performance, and environmental benefits.

Lan+1NinO3n+1 (n = 1, 2, 3) RP-phases for EMI shielding and ESD applications

Advancements in electronics and digitization have led to concerns about electromagnetic interference (EMI), necessitating effective EMI shielding measures. This study investigates the electromagnetic wave absorption properties of Lan+1NinO3n+1 (n = 1, 2, 3) Ruddlesden-popper (RP) phases. While a single phase, La2NiO4, was obtained for n = 1, mixed phases of La3N2O7-δ/La4Ni3O10-δ were observed for n = 2 and 3. Electron paramagnetic resonance spectroscopy revealed superparamagnetic behavior for La2NiO4 and multi-resonance peaks for La3Ni2O7-δ, suggesting increased surface defects. La3Ni2O7-δ exhibited enhanced absorption properties, with a minimum reflection loss of −19.4 dB and a broader (less than −10 dB) bandwidth covering 4.2 GHz (X-band) at a thickness of 1.4 mm, attributed to optimal conductivity, magnetic resonance, eddy current losses, and synergistic dielectric loss. The sample with n = 2 demonstrates potential for EMI absorption and electrostatic discharge (ESD) applications.

Synergistic enhancing effect for electromagnetic wave absorption via melamine resin-based magnetic core-shell microspheres/multi-walled carbon nanotubes

Rational design of corrosion-resistant electromagnetic wave (EMW) absorbing materials with wide bandwidth, strong absorption, and low filling ratio remains a significant challenge. In this work, the melamine resin-based magnetic core-shell microspheres (MF@Fe3O4@SiO2) were synthesized via dispersion polymerization and in-situ growth method. Experimental and simulation results indicated that the content and magnetism of the magnetic shell coordinated with the MF-core could be tactfully regulated with a small amount of incorporated Ni content. Moreover, the dispersion and corrosion resistance of MF@Fe3O4 core-shell microspheres were obviously enhanced by coating SiO2. It is worth noting that after the composite of MF@Fe3O4@SiO2 with MWCNTs-20, the presence of numerous heterogeneous interfaces, the tactfully improved conductive loss, and the optimized impedance matching synergistically result in superior EMW absorption properties. When the filling amount was 30 wt%, F9N1-S/MWCNTs-20 with a matching thickness of 1.76 mm, exhibited the maximum effective absorption bandwidth (EABmax) of 6.55 GHz, while maintaining a reflection loss (RL) of −62.94 dB at 1.53 mm. When the thickness of F9N1-S/MWCNTs-30 was increased to 3.24 mm, the RLmin at low frequencies was achieved at −67.14 dB. Besides, the simulation of radar cross section values ascertains the enormous potential of F9N1-S/MWCNTs to achieve stealth under radar detection. This study introduces a novel method for producing lightweight and efficient EMW absorbers with corrosion resistance.

Nitrogen-doped bean-like SiC-based nanofibers for thermal insulation and electromagnetic wave absorption

SiC nanofibers that can be used to absorb electromagnetic wave (EMW) radiation and as thermal insulators simultaneously are highly desirable. In this work, nitrogen-doped bean-like SiC-based nanofibers were prepared by a simple electrospinning and high-temperature pyrolysis in a nitrogen atmosphere, focusing on studying the effects of nitrogen atom doping on the microstructure, EMW absorption, and thermal insulation properties of the fibers. The results showed that nitrogen doping promoted the formation of the SiOxCyNz phase in the fibers, which improved their interfacial thermal resistance and endowed the fibers with extremely low thermal conductivities (∼0.024 W·m−1·K−1 at 25 ℃, 0.092 W·m−1·K−1 at 1000 ℃). Furthermore, the density of carbon defects in the fibers was improved by nitrogen doping, which created numerous new polarization centers and effectively improved the dielectric loss. With a 4 mm thickness, a minimum reflection loss of −51.8 dB was exhibited at 6.3 GHz, indicating that these fibers are highly promising as an absorption material in harsh environments.

Poorly-/well-dispersed Fe3O4: Abnormal influence on electromagnetic wave absorption behavior of high-mechanical performance polyurea

In this work, novel core–shell Fe3O4 nanoparticles were prepared by self- assembly technology using phytate-melamine aggregates (PM) or phytate-melamine-Fe3+ aggregates (PM-Fe) as building block. A polyurea (PUA) matrix was filled with magnetic nanoparticle. The influence of Fe3O4, Fe3O4@PM or Fe3O4@PM-Fe content and dispersion on the mechanical and electromagnetic wave (EMW) absorption properties of PUA composite were investigated. Good dispersion of modified Fe3O4 in PUA matrix was obtained. Loading well-dispersed Fe3O4 significantly enhanced the mechanical properties of their PUA nanocomposite under quasi-static tensile, nanoindentation, and dynamic compression tests. Excellent EMW absorption performance of PUA/Fe3O4@PM nanocomposite was desired. Although well-dispersed Fe3O4@PM could effectively enhance the mechanical properties, nonetheless it surprisingly plays a negative role in the EMW absorption performance. The Fe3O4@PM with high dispersion and interfacial compatibility in the PUA matrix was detrimental to EMW absorption performance, which contradicts the well accepted EMW absorption mechanisms. A novel mechanism and model were suggested, along with a fresh understanding of the role of Fe3O4 in the EMW absorption of PUA composite. Furthermore, the Fe3O4@PM-Fe, obtained by constructing a conductive network on the surface of Fe3O4@PM, was used to investigate this assumption. The radar cross section simulation also demonstrated the superior EMW attenuation capability of PUA nanocomposites in the service condition. This work is beneficial to the development of EMW absorber, not limited to Fe3O4 magnetic nanoparticles.