Multiple Loss Mechanisms Research Articles

Heterodimensional structure porous nanofibers embedded confining magnetic nanocrystals for electromagnetic functional material and device

The development of electronic devices and communication technology has put forward higher requirements for electromagnetic (EM) materials, and the exploration of multifunctional EM materials has become a new trend. Herein, heterodimensional structured porous nanofibers are constructed by zero-dimensional Fe nanocrystals and one-dimensional carbon nanofibers, which show excellent microwave absorption and electromagnetic interference (EMI) shielding performance. The balance between impedance matching and EM energy attenuation ability can be tailored through the tunable conductive network. The maximum reflection loss (RL) value of −56.8 dB can be achieved at a lower loading ratio, and the efficient EMI shielding effectiveness of 29.3 dB can be obtained at a higher loading ratio. In addition, the green EMI shielding with absorption as the main microwave attenuation mechanism can be observed in the higher frequency range. An EM energy conversion device is designed to effectively recover wasted EM energy. The EM energy is converted into valuable electrical energy through multiple loss mechanisms caused by heterodimensional structures. This work provides new guidance for the realization of multifunctional EM materials and devices.

Polymer‐derived Co2Si(Co)/SiCN composite ceramics with tunable microwave absorption properties

AbstractIn this paper, Co2Si(Co)/SiCN composite ceramics were synthesized by simple precursor‐derived ceramics method. The phase composition, morphology, and microwave absorption properties of Co2Si(Co)/SiCN composite ceramics at different pyrolysis temperatures (1000–1400°C) were studied. When pyrolysis temperature was 1300°C, carbon nanowires (CNWs), Co2Si, Si2N2O, SiC and Si3N4 were in situ generated and the best electromagnetic wave (EMW) absorption performance was obtained. The minimum reflection loss reached−50.04 dB at 4.81 mm, and the effective absorption bandwidth broadened to 3.48 GHz (14.52–18 GHz) at 1.31 mm. The excellent EMW absorption performance mainly comes from the coexistence of multiple loss mechanisms, including the magnetic loss of Co2Si, the conduction loss of CNWs, and the heterogeneous interfaces polarization between varieties of nanocrystals and amorphous ceramic matrix. By adjusting the sample thickness from 1 to 5 mm, the effective absorption of S1300 can cover the entire X and Ku bands, from 3.36 to 18 GHz. This study provides a simple way to synthesize high performance ceramic‐based microwave absorbing materials.

Optimized impedance matching and enhanced attenuation by heteroatoms doping of yolk-shell CoFe2O4@HCN as highly efficient microwave absorbers

Microwave absorbing (MA) materials with yolk-shell structures have been extensively studied in impedance matching. However, the impedance matching achieved by the complementary effect of the core and the shell does not determine the reflection of the microwaves upon the occurrence at the first incidence. The interaction between the outer layer of materials and the electromagnetic waves significantly impacts the MA properties of materials. In this study, the impedance matching improvement method of the shell structure was further explored by preparing CoFe2O4@HCN (honeycomb carbon with N-doping) through the hydrothermal method followed by hydrolysis, polymerization, etching, and annealing. The resulting structure with heteroatoms doping provided the novel CoFe2O4@HCN with excellent impedance matching and multiple loss mechanisms contributing to MA process. The absorber with a filler loading of 40% exhibited an RLmin of −68.03 dB with a matching thickness of 2.5 mm. The efficient absorbing bandwidth reached 5.92 GHz (a change from 11.92 to 17.84 GHz) at 1.99 mm thickness. Interestingly, these findings look promising for future synthesis and application of yolk-shell structure microwave absorbers.

Enhanced microwave absorption performance originated from interface and unrivaled impedance matching of SiO2/carbon fiber

Carbon fiber (CF) is a research focus due to its high performance in aviation, aerospace, and defense. However, its inherent high electrical conductivity makes it impedance mismatched. Herein, a material was prepared by grafting and coating SiO2 on short-cut carbon fiber (SCCF). The structure of SiO2 layer coated on the surface of SCCF brings about a stronger synergy of multiple loss mechanisms such as interface polarization and dipole polarization. It is shown that with the increase of SiO2 content, it has a significant optimizing effect on the impedance matching of SiO2/SCCF composites, and the SiO2 layer structure increases the loss mechanisms of interface and dipole polarization. At 2 vol% filling ratio and 6.35 GHz frequency, corresponding reflection loss (RL) value was −29.3 dB. Meanwhile, the SiO2/SCCF composite achieves an ultra-broadband electromagnetic wave absorption performance with an effective absorption bandwidth (EAB) of 12.3 GH. Therefore, this work provides a strategy for designing efficient and lightweight CF-based composites with electromagnetic wave absorption performance.

Multifunctional flower-like Ni particles/silicon carbide nanowires for infrared radar compatible stealth performance

Alongside the rapid development of detection systems and improved detection accuracy, infrared/radar-compatible stealth materials have become the emphasis of current stealth technology research. Versatile flower-like Ni particles/silicon carbide nanowires (SiC NWs) composites for infrared radar stealth compatibility have been successfully prepared. Due to its special microstructure in combination with the multiple loss mechanisms of dielectric and magnetic, the minimum reflection loss (RLmin) achievable with the paraffin matrix mixture is −49.26 dB at a composite content of 50 wt%, which has a thickness of 1.9 mm and an effective absorption bandwidth (EAB) of 4.85 GHz. By increasing the absorbent content to 60 wt%, the EAB in the Ku band can attain 5.0 GHz at 1.8 mm thickness. Petal-shaped Ni particles are introduced to improve the impedance matching characteristics, increase interfacial polarisation and multiple scattering of electromagnetic (EM) wave, and enhance the microwave absorption properties. Simultaneously, the pure SiC NWs material can protect against infrared radiation emitted from the hand for more than 15 min, and the infrared (IR) reflectivity is improved in all three bands after the composite metal Ni particles. A novel formulation guide for the design of versatile and high-performance EM wave absorbing and infrared stealth materials is provided by this work.

Fabrication of an Ultralight Ni-MOF-rGO Aerogel with Both Dielectric and Magnetic Performances for Enhanced Microwave Absorption: Microspheres with Hollow Structure Grow onto the GO Nanosheets.

An ultralight Ni-MOF-rGO aerogel which possess the merits of not only broad bandwidth and strong absorption but also lightweight and thin matching thickness is fabricated through a hydrothermal treatment, freeze-drying, and annealing procedure. The Ni@C microspheres are dispersed randomly and evenly on the graphene oxide (GO) nanosheets, which can be proved through SEM and TEM results. The electromagnetic parameters of the composite can be adjusted by changing the mass ratio of the MOF and GO to endow the material with both good impedance matching and superior electromagnetic wave absorption performances. Consequently, the resulting composite shows outstanding microwave absorption performance, which achieves strong absorption (-51.19 dB) and broad effective absorption bandwidth (6.32 GHz) with a thickness of 1.9 mm while the filling content is only 2 wt %. In addition, the multiple loss mechanisms of the Ni-MOF-rGO aerogel are illustrated, including conduction loss, dipolar polarization, interfacial polarization, magnetic resonance, and eddy current loss. In a word, the extraordinary microwave absorption performance is ascribed to the synergistic effects of the unique multiple layered structure of GO and the hollow core-shell structure of the Ni@C microsphere. This work demonstrates that the ultralight aerogel with excellent electromagnetic wave absorption performance is a promising strategy for microwave absorption application.

Expanded graphite/Co@C composites with dual functions of corrosion resistance and microwave absorption

The development of microwave absorption materials with good environmental adaptability is a hot topic in the electromagnetic protection field. In this research, Expanded graphite (EG)/ZIF-67 nanocubes-derived (Co@C) composites were successfully fabricated by electrostatic assembly and subsequent heat treatment. The results show that the involvement of an appropriate content of Co@C not only overcomes the problem of single EG impedance mismatch but also introduces additional magnetic loss for the absorber. At the thicknesses of 1.6 mm and 1.5 mm, an effective absorption bandwidth (EAB) of 4.52 GHz and a minimum reflection loss (RLmin) of −48.4 dB were achieved for the Z2-700 sample with a low filling ratio (20 wt%). The enhancement of EMW-absorption performance is attributed to the optimization of impedance matching and the synergistic action between multiple loss mechanisms. Electrochemical corrosion test showed that graphite nanoflakes of EG enhanced the transfer resistance during corrosion, and the corrosion resistance of pure Co@C was enhanced with the protection of EG. This work provides a reasonable attempt to design and fabricate efficient microwave absorption materials suitable for harsh environments.

Synthesis of RGO/Cu@ FeAl2O4 Composites and Its Applications in Electromagnetic Microwave Absorption Coatings.

In order to satisfy the requirements of wide frequency bands, the lightweight and strong absorption for the electromagnetic wave absorbing materials, a uniform mixture of FeAl2O4 with RGO/Cu (reduction graphene oxide, RGO) was obtained by the mechanical mixing method, and composite coating was obtained by plasma spraying. The addition of RGO/Cu into FeAl2O4 is conducive to improve the dielectric properties and the impedance matching performance of spinel. When the RGO/Cu composite powders are doped by 10 wt.%, the reflection loss at 15 GHz is -16 dB and the absorption bandwidth is 2 GHz, indicating that the composite material has potential application value in the field of high-frequency wave absorption. The research on the electromagnetic wave absorption mechanism shows that its superior wave absorption performance is determined by the synergistic effect of multiple loss mechanisms such as interfacial polarization, dipole relaxation, natural resonance, exchange resonance, and eddy current loss.

Enhanced microwave absorbing performance of epoxy composites filled with solvent-free and liquid-like Fe3O4 organic hybrid material

Owing to the large surface energy and easy agglomeration, ferroferric oxide (Fe3O4) nanoparticle usually is difficult to be widely application in microwave absorbing coatings. In this paper, a new synthesis process was used to prepare solvent-free fluid Fe3O4 (S-Fe3O4) by surface modification of solid Fe3O4 with a long chain of organic bimolecular layer, which showed excellent dispersion in resin materials. Moreover, S-Fe3O4 was compounded with CNT@Fe3O4 to prepare S-Fe3O4/CNT@Fe3O4/EP composites, which realized the multiple loss mechanism of electromagnetic wave (EMW) absorption. The results showed that the minimum reflection loss of composite was −52.57 dB with a matching thickness of 3.3 mm; the maximum effective absorption bandwidth at 1.4 mm thickness was 5.2 GHz (12.08–17.28 GHz). This surface molecular engineering composite based on inorganic particles enhanced the attenuation ability of EMW by improving the dispersion of inorganic particles and providing multiple loss mechanisms, which was a novel medium regulation strategy to provide a new insight for nanoparticles in the field of EMW absorbing coatings.

Rational manipulation of composition and construction toward Zn/Co bimetal hybrids for electromagnetic wave absorption

• Zn@Co and Co@Zn Zn/Co bimetal hybrids were fabricated by bi-orientation etching strategy. • The components and constructions are regarded as major factors determining electromagnetic properties. • The RL min and f E of Zn@Co-C-2h reached -34.99 dB and 5.52 GHz (2.00 mm), respectively. Rational manipulation of multi-metal hybrids with controllable compositions and constructions is evolving as an efficacious strategy for tunable electromagnetic (EM) characteristics and EM wave (EMW) absorption. Herein, a novel bi-orientation etching approach is proposed to regulate the chemical compositions and hybridization construction of Zn/Co hybrids, thence meeting the synergistic interaction among diverse compositions for ultra-high EMW absorption. Attributing to the stepwise heterometallic modification by Zn in Co-ZIFs (Zn@Co-ZIF) and Co in Zn-ZIFs (Co@Zn-ZIF), corresponding pyrolysis products with variable Zn/Co atomic concentration and hybridization states (Zn@Co-C, Co@Zn-C) can be obtained. The Co species was confirmed to have a positive impact on both the dielectric and magnetic response, while an appropriate amount of Zn hybridization in Co substance further enhanced the synergistic effect between multiple loss mechanisms, promoting the minimum reflection loss and effective absorption bandwidth of Zn@Co-C reached -34.99 dB and 5.52 GHz (2.00 mm), respectively. Finally, this work reveals the composition and construction dependency of bimetal hybrids on EMW absorption, which can be a strong reference for developing EMAs with diverse hybridization structures.

Ultralight Ti3C2Tx-derivative chrysanthemum-like Na2Ti3O7/Ti3C2Tx MXene quantum dots 3D/0D heterostructure with advanced microwave absorption performance

As an outstanding representative of two-dimensional materials, newly emerged Ti3C2Tx MXene has aroused widespread attention in the field of microwave absorption (MA). However, the high conductivity of Ti3C2Tx MXene is prone to lead to impedance mismatch, and the attenuation performance of incident electromagnetic waves in the Ti3C2Tx matrix needs to be further improved. To address these issues, Ti3C2Tx MXene quantum dots (MQDs) were applied in the field of MA for the first time, and combined with Ti3C2Tx derivative chrysanthemum-like Na2Ti3O7 to prepare Na2Ti3O7/MQDs composites with 3D/0D heterostructure. Compared with Ti3C2Tx MXene bulks and nanosheets, Ti3C2Tx MQDs possess larger specific surface area and richer surface-active groups and defects, which are more favorable for interfacial polarization and dipole polarization, while the moderate conductivity of Ti3C2Tx MQDs is conducive to impedance matching. The unique chrysanthemum-like Na2Ti3O7/MQDs with 3D/0D heterostructure generates abundant heterointerfaces to promote the increase of interfacial polarization, achieves a rational combination of different conductive materials to optimize impedance matching, and facilitates multiple reflections of electromagnetic waves among numerous nanowires in the chrysanthemum-like structure. Benefiting from the good impedance matching and the synergistic effect of multiple loss mechanisms, Na2Ti3O7/MQDs composites show excellent MA performance with a minimum reflection loss of −48.28 dB at a thickness of 2.6 mm. Simultaneously, the effective absorption bandwidth comes up to 6.38 GHz at 2.5 mm thickness. This study demonstrates the potential of MQDs as efficient microwave absorbers and points out the direction for a wide application of various MQDs in the field of MA.

Graphene/carbonyl iron powder composite microspheres enhance electromagnetic absorption of 3D printing composites

The RGO-CIP composite microspheres were prepared by solvent evaporation method using ethyl cellulose as the backbone and epoxy resin as the adhesive. The composite microspheres effectively combined graphene (RGO) with carbonyl iron powder (CIP) to achieve the synergy of multiple loss mechanisms and obtain good electromagnetic absorption capability. 3D printed wire was prepared by using RGO-CIP composite microspheres and polylactic acid (PLA), and coaxial rings were printed by fused deposition molding (FDM) to test electromagnetic properties. In this study, many heterogeneous interfaces triggering polarization loss are formed on the surface and inside of the composite microspheres. These heterogeneous interfaces produce abundant folds and pores, which enhance the multiple reflections and scattering of microwaves. The added RGO and CIP forms a conductive network, forming a conductance loss. When the RGO content is 5.1 wt%, RGO-CIP/PLA −4 composite exhibits excellent microwave absorption performance. At the material thickness of 2.2 mm, the maximum reflection loss is −50.1 dB and the absorption bandwidth is 6.0 GHz. At the material thickness of 2.2 mm, the effective absorption bandwidth is 6.24 GHz and the maximum reflection loss is −29.08 dB. The RGO-CIP composite microspheres improve the microwave absorption performance of 3D printed composites and provide an effective way to prepare structural wave absorbing plates and devices by 3D printing technology.

Electrically aligned Ti3C2Tx MXene composite with multilayered gradient structure for broadband microwave absorption

High-performance electromagnetic microwave (EM) absorbers demand not only wide effective absorption bandwidth (EAB) and strong absorption capability, but also lightweight and small thickness. In this work, a new strategy was developed to simultaneously strengthen the lossy capacity and reduce the inclusion loading by designing the orientation of inclusions and constructing multilayered gradient structures. Accordingly, Ti3C2Tx MXene fillers were aligned in the same chains by the electric field-assisted alignment technique, forming a parallel-plate structure, throughout epoxy matrix resulting in strong lossy capacity. The widest EAB of aligned 16 wt% MXene/epoxy composite reached 5.08 GHz with a thickness of 1.34 mm. By comparison, the random 16 wt% MXene/epoxy composite exhibited an EAB of only 0.96 GHz with a thickness of 1.96 mm. Further, the impedance matching was optimized by designing multilayered gradient structures based on aligned MXene/epoxy composites. The trilayered gradient structure with an equivalent filler content of 10.97 wt% illustrated the best EAB of 6.01 GHz at only 1.53 mm thickness. In addition, the synergistic effect of the multiple loss mechanisms was also discussed. Overall, the proposed method demonstrates the effectiveness of coupling the alignment of inclusions with gradient structural design to prepare lightweight, thin, and high-performance EM absorbing materials.

Construction of SiCnws/carbon foam composites with multiple loss mechanisms for excellent electromagnetic wave absorption

Composition optimization and delicate microstructure construction are considered to be critical factors to achieve outstanding electromagnetic (EM) wave absorption performance. SiC nanowires/carbon foam (SiCnws/CF) composites were prepared by the in-situ growth of SiCnws inside carbon foam pores using an internal growth method. After self-foaming of the silicon powder and mesophase pitch mixture, a carbonizing process was adopted subsequently to synthesis SiCnws/CF composites with excellent EM wave absorption performance. With increasing silicon content, the amount of SiCnws generated increases, the distribution of SiCnws becomes uniform, and the diameter decreases continuously. The prepared SiCnws were composed of β-SiC coated with an amorphous Si layer on the surface, which were conducive to the reception of EM wave and impedance matching to free space. Multiple loss mechanisms involving the dipole polarization generated by SiCnws, the interface polarization generated by multi heterogeneous interfaces and the conductive loss provided by CF, which caused high effective energy loss of incident EM wave, hence, improved the EM wave absorption performance significantly. After the addition of silicon, the SiCnws/CF composites obtained excellent impedance matching. When the silicon content was 15 wt %, the prepared SiCnws/CF composite showed the best wave absorption performance, the minimum reflection loss value of the 3.11 mm thick sample was − 55.27 dB, and the effective absorption bandwidth was 2.08 GHz, which provides a new method toward the high-performance EM wave absorbing materials with multiple loss mechanisms.

Bi-semiconductor heterojunction Cu9S5@VO2 microspheres with morphology regulation as broadband high-performance electromagnetic wave absorber

The development of heterojunction composite materials with excellent electromagnetic wave absorption performance is emerging as an effective means to address the hazardous electromagnetic waves. Here, two types of Cu9S5@VO2 microspheres with different morphologies were designed. The Cu9S5@VO2 microspheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and vector network analyzer. Results show that the minimum reflection loss (RLmin) of unique lamellar-flower Cu9S5@VO2 sphere reaches −56.98 dB, and the wide effective absorption bandwidth (EAB) is 6.88 GHz at only 2.5 mm thickness due to the synergistic effect of multiple loss mechanisms. Radar simulated radar cross section (RCS) results show a reduction of 16.56 dBm2. The design engineering of the phase interface on the material surface can functionalize the material surface properties, introduce lattice defects and polarization behavior, and improve the microwave absorption performance of the material. This work enriches the use of copper sulfide-based functional composites in microwave absorption with high-performance microwave absorbers by designing microscopically controllable, simple processes and heterojunction design.

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.

In situ growth of 3D multi-interface Ni@carbon nanotube networks towards highly-efficient microwave absorption

In this paper, 3D multi-interface carbon nanotube networks were in-situ constructed from carbon nitride (g-C 3 N 4 ) and nickel chloride as precursors. With the temperature increase, g-C 3 N 4 was continuously decomposed to the components containing C and N element, and these produced compounds reduced Ni 2+ into Ni nanoparticles at the same time. After that, these compounds were enriched and precipitated on the surface of Ni nanoparticles, resulting in formation of bamboo-like carbon nanotubes with Ni particles embedded on the top (Ni@CNTs). The obtained Ni@CNTs exhibited high electromagnetic absorption performance with the filler loading content of 3 wt% in paraffin. The minimum reflection loss of 0.2Ni@CNTs was dramatically enhanced to − 31.7 dB and the effective absorption bandwidth was 6 GHz. The excellent microwave absorption performance was attributed to multi-interface reflections, good impedance matching and synergistic effects of multiple loss mechanisms from the Ni@CNTs. This work provides a new method to prepare multi-interface bamboo-like CNTs, which exhibited potential applications in microwave absorption. • Multi-interface carbon nanotube networks were constructed from g-C 3 N 4. • Excellent absorption resulted from multiple reflections and polarization losses. • Reflection loss reached − 31.7 dB with the EAB of 6 GHz under 3 wt% loading.

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).

Microwave absorption performance and multiple loss mechanisms of three-dimensional porous Fe4N@Fe3O4@Fe/carbon composite

Microwave absorption performance and multiple loss mechanisms of three-dimensional porous Fe4N@Fe3O4@Fe/carbon composite

Design of polyaniline encapsulated greigite(Fe3S4) microparticles for excellent microwave absorption performance with broad bandwidth and ultrahigh reflection loss

Exploring microwave absorption materials with the advantages of wide effective absorption bandwidth, thin thickness, strong absorption capacity and light weight is significant to solving the problems of electromagnetic (EM) irradiation in both military and civil areas. Herein, to make up for the weaknesses of single component Fe3S4 or polyaniline in microwave absorption performance, the composites with extraordinary microwave absorption performance composed of Fe3S4 encapsulated in polyaniline was elaborately designed. The successful synthesis and the microwave absorption mechanisms of Fe3S4@PANI composites were demonstrated by several characterizations. The results indicated that the dielectric constant of the composites can easily be adjusted by the content of PANI in favor of the impedance matching within the frequency range. Therefore, the sample F–P-2 presented the optimum performance, the minimum reflection loss (RLmin) value and broadest effective absorption bandwidth (EAB) respectively reach −63.8 dB at 7.68 GHz and 5.04 GHz (ranging from 12.88 to 17.92 GHz) under 40 wt% loading. Such good performance could be dependent on multiple loss mechanisms, such as the interface and dipole polarization, conduction loss as well as the multiple reflection and scattering. Based on the excellent properties and simple preparation methods, the Fe3S4@PANI composites can be a potential candidate in military and civil microwave absorption field.