Dielectric Loss Ability Research Articles

Mixed-Dimensional Assembly Strategy to Construct Reduced Graphene Oxide/Carbon Foams Heterostructures for Microwave Absorption, Anti-Corrosion and Thermal Insulation

HighlightsReduced graphene oxide/carbon foams (RGO/CFs) vdWs heterostructures are efficiently fabricated via a simple mixed-dimensional assembly strategy.Linkage effect of optimized impedance matching and enhanced dielectric loss abilities endows the excellent microwave absorption performances of RGO/CFs vdWs heterostructures.Multiple functions such as good corrosion resistance performances and outstanding thermal insulation capabilities can be integrated into RGO/CFs vdWs heterostructures.

Glucose derived carbon encapsulated boron nitride core-shell composites for efficient electromagnetic microwave absorption

Hexagonal boron nitride (h-BN) has the advantages of outstanding insulation, high thermal conductivity and excellent chemical stability, which promote the wide application of h-BN in thermal interface electronic packaging and other related fields. However, due to the poor dielectric loss ability of h-BN, which leads to its weak absorption capacity of electromagnetic waves (EMW), so it limits its practical application in related advantageous fields. In this paper, glucose-derived carbon-encapsulated BN core-shell composites (C@BN) were prepared by a simple hydrothermal reaction followed by high-temperature pyrolysis. The dielectric loss capacity of the C@BN was investigated by manipulating the concentration of glucose solution and pyrolysis temperature. Specifically, by adjusting the glucose derived carbon defect to induce polarization loss and impedance matching performance, so that more EMW entering the interior of the composite is absorbed and dissipated. The results show that C@BN obtained at 800 °C shows the best EMW absorption performance when the concentration of glucose solution is 3.6 wt%. The minimum reflection loss value (RLmin) is −43.5 dB and the maximum width effective absorption bandwidth (EABmax) of 6.72 GHz. Therefore, this study provides a reliable reference for the preparation of h-BN based EMW absorbing materials.

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.

Interface Engineering of Titanium Nitride Nanotube Composites for Excellent Microwave Absorption at Elevated Temperature

HighlightsThe boosted heterogeneous interfaces in titanium nitride (TiN) nanotube/polydimethylsiloxane (PDMS) composite contributed to strong polarization loss relaxation ability.The TiN nanotubes/PDMS composite possessed both good impedance matching behavior and strong dielectric loss ability in wide temperature spectrum.The TiN nanotubes/PDMS composite exhibited excellent EMWA performances (effective absorption bandwidth value of 3.23 GHz and minimum reflection loss value of − 44.15 dB) at the varied temperature from 298 to 573 K.

Facile preparation of ZIF-8/ZIF-67-derived biomass carbon composites for highly efficient electromagnetic wave absorption

Biomass absorbing materials have received increasing attention for electromagnetic wave (EMW) absorption field absorbing materials due to its low density and high dielectric loss. However, the biomass EMW absorbing materials often suffer from the insufficient magnetic loss and impedance matching. In this work, a facile ZIF-8/ZIF-67-derived biomass composites (CoZnO@BPC) was prepared for high-performance EMW absorption based on multi-component micro, nano structures metal particles and xanthoce sorbifolia bunge shells-derived biomass porous carbon (BPC). The dielectric loss and/or magnetic loss abilities of CoZnO@BPC composites were adjusted by changing the mass ratio of Zn2+ to Co2+ ions. Under the filled amount of 20 wt%, CoZnO@BPC exhibited excellent EMW absorption with the minimum reflection loss (RL) at 15.84 GHz is -50.2 dB, and the matching thickness is only 1.7 mm. By adjusting the ZIFs mass ratio, the effective absorption bandwidth (EAB) can be up to 5.92 GHz (from 12.08 GHz to 18 GHz), and the matching thickness is only 1.9 mm. The results provide a new insight for the economical and efficient preparation of lightweight and advanced microwave absorbing materials.

A combined engineering of hollow and core-shell structures for C@MoS2 microcapsules toward high-efficiency electromagnetic absorption

Rational design of profitable structure is widely considered as an effective strategy for electromagnetic wave absorbing materials (EWAMs) to improve their performance. Herein, we conduct a combined engineering of hollow and core-shell structures, in which surface shell is formed by a number of MoS2 nanosheets crossing each other and internal core is hollow carbon microcapsule (HC). HC has strong dielectric loss ability, and its hollow structure facilitates the multiple reflection of incident EM wave. The construction of MoS2 shells not only improves impedance matching but also introduces heterogeneous interfaces that result in interfacial polarization loss. It is found that the synergistic effect of intrinsic loss mechanisms and structural advantages endow C@MoS2 composites (HCM-x) with excellent EM wave absorption performance, and especially for HCM-2, whose minimum reflection loss (RL) intensity and effective absorption bandwidth (EAB) are −63.8 dB and 6.0 GHz, respectively. It is believed that this work is valuable for the enhancement of performance for EWAMs through the upgrade of microstructure and regulation of chemical composition.

Electrostatically self-assembled Fe3O4@SiO2/MXene 3D interlayered structure improves Ku-band microwave absorption efficiency of epoxy-based nanocomposites

It is challenging to develop lightweight and efficient frequency-selective microwave absorption materials due to the trade-off between impedance matching and microwave attenuation ability. This study proposes a multiple heterointerfaces engineering strategy via electrostatically assembling to construct Fe3O4@SiO2/MXene 3D interlayer structure, which fully exerted the synergistic effect of dielectric-magnetic components. The 3D interlayer heterostructure achieves good impedance matching due to electromagnetic coupling and extended microwave propagation path. Simultaneously, massive charge transfer and redistribution at multiple heterointerfaces embedded in this structure boost the polarization relaxation and dielectric loss ability. Consequently, the prepared nanocomposites exhibit remarkable Ku-band microwave absorption efficiency (−60.9 dB at a thickness of 1.0 mm), and have demonstrated valid practicality via Tesla wireless transmission shielding experiments. This study opens exciting possibilities for progress in the structural design, facile preparation and practical application of high-performance Ku-band microwave absorption materials.

Flexible SiO2/rGO aerogel for wide-angle broadband microwave absorption

Graphene aerogel has been a promising microwave absorber due to ultralow density and strong dielectric loss ability. However, its intrinsic brittleness, and poor absorbing properties because of impedance mismatch severely hinders practical engineering applications. Herein, flexible silica fibers with excellent impedance matching properties were introduced into graphene honeycomb structures to co-construct a dual-structure aerogel (GS) by eco-friendly and low-cost technology. The unique dual-structure significantly enhances its resilience, enabling it to rebound after 1000 cycles of 75% compression. In addition, it can withstand 450 times of 180° folding and 360° rotation without damage, featuring remarkable flexibility and reliability. Furthermore, the simulation and experimental results indicate that GS has excellent wave absorbing performance. When the thickness is 6 mm, the effective absorption bandwidth is 32.55 GHz; when the thickness increases to 10 mm, the reflection loss is less than −8 dB in the range of 2.79–40 GHz. Moreover, the reflection loss remains almost constant when the oblique incidence angle ranges from 5° to 45°, which further demonstrates the critical role of impedance matching in enhancing the microwave absorption performance. These superior characteristics make GS an ideal candidate for many microwave absorption applications such as flexible electronics and aerospace.

Promotion of bio-oil production from the microwave pyrolysis of cow dung using pretreated red mud as a bifunctional additive: Parameter optimization, energy efficiency evaluation, and mechanism analysis

To address the issues of high oxygen content and energy consumption in the microwave-assisted pyrolysis of biomass for biofuel production, this study used high-temperature pretreated red mud (RM) as an additive. The pretreated RM exhibited dual functionalities, namely microwave absorption and catalytic properties, during the microwave-assisted pyrolysis of cow dung (CD). This study also evaluated the optimization potential of energy recovery efficiency. The results showed that the addition of pretreated RM significantly increased the oil yield during the microwave-assisted pyrolysis of CD. The highest oil yield (59.63%) was obtained via the microwave-assisted pyrolysis of CD over catalysis with RM pretreated at 750 °C (RM750). Through the optimization of the RM750-to-CD mixing ratio, optimal oil quality and energy recovery efficiency were achieved. At a mixing ratio of 1:1, the pyrolysis oil featured the highest aromatic hydrocarbon content and lowest acid content. The high-temperature pretreatment of RM increased the Fe2O3 content, which enhanced the dielectric properties and magnetic loss ability of the reactants. This resulted in localized high temperatures and the formation of “hot spots,” which can promote the deoxygenation and hydrogenation reactions of oil. Consequently, the lower heating rate of oil increased from 35.12 to 40.11 MJ kg−1. The released oxygen escaped in the form of CO. In addition, pyrolytic char was used as an in situ microwave absorbing material owing to its increased Fe2O3 content and graphitization degree, leading to an increase in energy recovery efficiency from 4.71% to 9.98%. This study provides valuable guidance for the efficient utilization of diversified solid wastes and demonstrates the potential application of microwave-assisted pyrolysis technology in the resource utilization of solid wastes.

N-doped magnetic carbon nanosheets for broad, strong, stable and thin microwave absorption properties

The novel magnetic carbon nanocomposite, in which N-doped onion-like carbon encapsulated FeNi nanoparticles are embedded into N-doped carbon nanosheets, are prepared for realizing “broad, strong, stable and thin” microwave absorption behaviors. Good impedance match between magnetic FeNi nanoparticles and dielectric carbon and the large attenuation capability accompanied with strong dielectric loss ability induced by interfacial polarization loss, defect dipole polarization loss, Debye relaxation loss, conductive loss and magnetic loss originating from natural/exchange resonance and eddy current loss ensure the good microwave absorption ability. This nanocomposite exhibits the minimal reflection loss value of –27.62 dB at 4.72 GHz and the effective absorbing bandwidth of 5.76 GHz (covering 12.24–––18 GHz) at 1.9 mm and the peak of reflection loss basically locates at −21.62 dB- −27.62 dB from 1.7 mm to 5.0 mm.

Graphene Implanted Shape Memory Polymers with Dielectric Gene Dominated Highly Efficient Microwave Drive

AbstractMicrowave‐driven strategy shows many advantages including selective energization, uniform heating, and high penetration depth, which is a hot topic in wireless actuators. Understanding microwave stimulus‐response mechanisms is the key to developing universal construction strategies for advanced microwave‐driven actuators. Herein, reduced graphene oxide (rGO) with specified dielectric genes and thermal properties is implanted into the shape memory polymer, liquid crystal elastomer (LCE) as an example, to construct soft, reversible, and sensitive microwave actuators. Based on the analysis of microstructure and dielectric properties, LCE‐rGO composites exhibit excellent polarization relaxation‐dominated dielectric loss and electromagnetic (EM) energy conversion ability. The maximum dielectric loss factor (ε″) and loss tangent (tan δe) of LCE‐rGO are dramatically increased by 216% and 87.5% compared to pure LCE, respectively, and the optimum apparent energy harvest efficiency is 19.4 times higher than that of LCE. In addition, the implantation of rGO significantly lowers the microwave actuation threshold of LCE‐rGO composites and reinforces their stimulus‐response capacity. Response time under 750 W microwave irradiation of LCE‐rGO is shortened to <10s. These findings can provide a solid basis for the design and fabrication of highly efficient microwave stimuli‐responsive polymers and enlighten a new approach to wireless actuated smart devices.

Controllable synthesis of porous carbon@Fe20Ni80 composites with improved microwave absorption performance

The two-component composites with porous carbon and magnetic metals exhibit a promising application prospect in microwave absorption due to their superior impedance matching and excellent loss ability. Herein, a novel process combined sol-gel and in-situ pyrolysis methods was proposed to prepare a series of porous carbon@Fe20Ni80 composites. The structure and composition of composites were controlled by adjusting pyrolysis temperature and doping amount of Fe20Ni80 for achieving an improvement on microwave absorption performance. Under the optimal Fe20Ni80 doping amount of 2 mmol, the composite pyrolyzed at 800 °C shows the highest performance. With 15 wt% filler loading, the composite achieves the minimum reflection loss value (RLmin) of −39.5 dB at 6.7 GHz with a thickness of 3 mm. Moreover, under the optimal matching thickness of 2.2 mm, the maximum effective absorption bandwidth (EABmax) reaches 5.4 GHz (8.0–13.4 GHz), covering the whole X-band. The porous structure is maintained at appropriate pyrolysis temperature, which optimizes the impedance matching of materials. The porous carbon matrix with partial graphitization exhibits the dielectric loss ability to electromagnetic waves. In addition, the introduction of Fe20Ni80 endows the composite with magnetic loss ability. This study develops an avenue for the preparation of two-component composites with porous carbon and magnetic metals and has potential application in microwave absorption.

Design of double-layer absorbers based on Co2Y@C core-shell nanofibers and carbon nanofibers for high-efficient and tunable microwave absorption

A novel double-layer microwave absorber based on Ba2Co2Fe12O22@C core-shell nanofibers (Co2Y@C NFs) and carbon nanofibers (CNFs) was designed, and their microwave absorption properties were systematically investigated in the frequency range of 2–18 GHz. Benefiting from the better impedance matching characteristic of the matching layer (50 wt% Co2Y@C NFs/paraffin composite) and the stronger dielectric loss ability of the absorbing layer (5 wt% CNFs/paraffin composite), the optimized double-layer absorbers exhibit stronger absorption and wider effective absorption bandwidth compared to the corresponding single-layer absorbers. When the thicknesses of the absorbing and matching layer are respectively 0.62 mm and 1.38 mm (total thickness of 2 mm), the optimal reflection loss (RL) reaches −46.9 dB at 16.8 GHz, and the effective absorption bandwidth (EAB) is 4.1 GHz (from 13.9 to 18 GHz). Meanwhile, when the thicknesses of the absorbing and matching layer are 1.03 and 1.98 mm (total thickness of 3.01 mm), respectively, the optimal RL is up to −63.7 dB at 10.0 GHz with an EAB of 9.5 GHz ranging from 8.5 to 18 GHz. The absorption intensity and range of the double-layer absorber can be easily adjusted by regulating the thickness of the absorber, which shows good potential for practical applications.

Engineering polarization surface of hierarchical ZnO microspheres via spray-annealing strategy for wide-frequency electromagnetic wave absorption

• Hierarchical ZnO microspheres were successfully synthesized via spray-annealing strategy. • Pure dielectric loss ZnO materials were assembled by nanorods and nanoparticles with adjusting different aspect ratios, defects and polar faces. • Hierarchical ZnO-1 materials shown the widest efficient absorption region from 9.9 to 18.0 GHz at 2.4 mm. Regulating orientation growth plays a dominant role in enhancing dielectric properties for the electromagnetic (EM) functional materials, which faces a huge challenge in the synthesis method. By spray-annealing strategy, hierarchical ZnO microspheres assembled by ZnO nanorods and nanoparticles were successfully fabricated. With confined microsphere space and controlling crystal growth, oriented ZnO nanorods possess rich defects, Zn-polar, O-polar faces, and high permittivity. Meanwhile, temperature-dependency of exposed polarization surfaces is discovered in the semiconductor ZnO nanoparticles with evolved aspect ratios. As pure dielectric EM wave absorption material, the hierarchical ZnO microsphere exhibits adjustable complex permittivity and polarization behaviors. When the thickness is 2.4 mm, the hierarchical ZnO-1 absorber shows the widest efficient absorption (RL ≤ –10 dB) region from 9.9 to 18.0 GHz (8.1 GHz, ∼50.6% testing frequency). The minimum reflection loss (RL) of ZnO-1 can reach –31.5 dB at only 2.0 mm. Because of the outstanding dielectric loss ability and wide absorption frequency, large-scale hierarchical ZnO microspheres can be a potential EM absorption candidate.

Morphology modulation induced enhancement of microwave absorption performance in Fe20Ni80 particles

Exploring the influence of material morphology on microwave absorption performance is of significance for designing high performance absorbers. A feasible coprecipitation strategy was proposed for preparing three kinds of Fe20Ni80 particles with different morphologies (ball-like, worm-like and flower-like). The morphology, structure and performance of the particles were contrastively studied. The results showed that the morphology had a remarkable effect on microwave absorption performance. Under the same structure and composition, the performance of worm-like particles was obviously better than that of other particles. Particularly, under the filler loading of 20 wt%, the minimum reflection loss (RLmin) value reached − 48.5 dB at 7.9 GHz, and the maximum effective absorption bandwidth (EABmax) was 4.3 GHz (8.3–12.6 GHz) with a matching thickness of 2.5 mm. The arrangement of worm-like particle resembles a chaotic porous nest, which optimizes impedance matching. In addition, the worm-like particle has a large aspect ratio, exhibiting stronger dielectric loss ability. The loss mechanisms to incident waves mainly include conductive loss, interfacial polarization loss, natural resonance and exchange resonance.

Interface engineering to regulate hollow one-dimensional N-doped Carbon@ZnO nanocomposite for boosting electromagnetic wave absorption

Hollow composite structure has attracted much attention due to its great design space for adjusting impedance matching and enhancing interfacial polarization. Heterogeneous interface as well as improve the polarization relaxation and enhance the dielectric loss ability of material. However, the precise control of heterogeneous interface and hollow structure is a complex issue, which hiders the development of hollow composite structure for practical application. Herein, a mild sacrificial template method is proposed to construct a hollow nanocomposite comprised of N-doped carbon and ZnO (ZnO@HNCR), where self-assembled nanostructure (9,10-dibromoanthracene, DBA), polydopamine (PDA) and ZIF-8 were used as a sacrificial template, conductive scaffold and the ZnO precursor, respectively. During the calcination treatment, ZIF-8 and PDA were in situ converted into ZnO and N-doped carbon. In addition, self-assembled nanostructure sublimated away, leaving hollow structure behind, which overcomes the shortcoming of using corrosive agents. The large specific surface area and unique hollow structure optimize the impedance matching, and the abundant heterogeneous interfaces between HNCR and ZnO improve interfacial polarization. By virtue of joint efforts of conduction loss, multiple scattering and polarization relaxation, ZnO@HNCR exhibits outstanding performance, including minimum reflection loss value (RLmin) of − 57.4 dB at 2.6 mm and effective absorption bandwidth (EAB) of 6.04 GHz at 2.2 mm. This work proposes a feasible method to synthesize hollow heterogeneous electromagnetic absorbent.

2D Ti3C2Tx MXene/MOFs composites derived CoNi bimetallic nanoparticles for enhanced microwave absorption

The emerging two-dimensional (2D) transition metal carbide (MXene) has been a hot topic due to its special structure and high dielectric loss. However, the inevitable stacking phenomenon and lack of magnetic loss of the related MXene materials seriously restrict their application in electromagnetic (EM) absorption. Herein, Ti3C2Tx (a typical material of MXene family) modified with metal–organic frameworks (MOFs) is prepared via simple electrostatic self-assembly and consequent heat treatment. The lamellar MXene provided the substrate for anchoring the MOFs, and the Ni nanoparticles catalytically derived carbon nanofibers (CNFs) served as bridges to construct the cross-linked network. Based on this network structure, the extensive heterogeneous interfaces effectively facilitate the dielectric loss ability, and the addition of magnetic CoNi nanoparticles can enhance the additional magnetic loss capacity. It is worth noting that when the matching thickness is only 1.76 mm, the minimum reflection loss (RLmin) value of the sample (Ti3C2Tx/CNFs/TiO2/CoNi) reaches –54.6 dB, and the corresponding effective absorption bandwidth (EAB, RL < –10 dB) is 4.0 GHz (11.9–15.9 GHz). These results show that magnetic-dielectric synergistic, interfacial polarization, and multilayer structure, were conducive to the improvement of microwave absorption (MA) properties. This study envisions a novel strategy for constructing efficient MXene-based microwave absorbers.

Surface modification engineering of iron-silicon-aluminum alloys: Microstructure evolution investigation and microwave absorption enhancement

Developing highly efficient electromagnetic (EM) absorbers with a broad bandwidth remains a major challenge for reducing EM pollution originating from the ever-rising electronic and telecommunication devices. Designing core-shell structures containing a magnetic core and dielectric shell could be an effective strategy to tackle this problem. Herein, we report a surface modification strategy to synthesize the FeSiAl/phosphate core-shell materials with unique rodlike structure through a facile surface passivation process. Multilevel phosphate shells are in situ introduced for significantly facilitating the EM absorbing performance by inducing multiple interfacial polarizations and obtain ideal impedance matching. Direct evidence of the morphology and microstructure evolution of resultant FeSiAl/phosphate composites correlated to the EM properties has been systematically investigated. Due to intense synergistic effects between magnetic and dielectric loss, exceptional microwave dissipation capacity can be achieved over an ultra-wide absorption bandwidth of 9.8 GHz at 2.5 mm. • The microstructure evolution at high temperatures has been elaborated at different scales by the focused ion beam technology. • Core-shell structure enhanced the dielectric loss ability by inducing multiple interfacial polarizations and achieved ideal impedance matching. • Superb dissipation capacity has been achieved over an ultra-wide range of 9.8 GHz attributed to the magnetic-dielectric synergistic effects.

Rational construction of yolk-shell structured Co3Fe7/FeO@carbon composite and optimization of its microwave absorption

The construction of yolk-shell composites with dielectric/magnetic multiple loss mechanisms has become a promising strategy to obtain high-efficiency microwave absorbing materials. An ideal microwave absorber should possess dielectric and magnetic loss abilities, thereby leading to the attenuation and absorption of incident electromagnetic radiation. Herein, the yolk-shell structured CoFe2O4@carbon (YS-CoFe2O4@C) and Co3Fe7/FeO@carbon (YS-Co3Fe7/FeO@C) composites were designed and synthesized through a series of processes, which include in-situ coating, heat-treating, etching and subsequent carbonization reduction reaction. The composite materials with specific structure, composition, and electromagnetic parameters could be effectively obtained by controlling the reaction conditions. The combination of alloy with high magnetic loss and carbon with advanced dielectric loss as well as the unique yolk-shell structure endow YS-Co3Fe7/FeO@C improved impendence matching and large attenuation constant. The YS-Co3Fe7/FeO@C composites show optimized microwave absorption behaviors, the minimum reflection loss is up to −57.6 dB at 12.30 GHz with the of 2.5 mm and the corresponding effective absorption bandwidth is 5.27 GHz (10.10–15.37 GHz). Moreover, the widest effective bandwidth could reach 7.0 GHz (11–18 GHz) with the thickness of 2.3 m. This design provides a novel concept for tuning microwave absorption efficiency of magnetic/dielectric composites to prepare high-performance microwave absorbers.

Single crystal to polycrystal: Enhanced dielectric loss and electromagnetic wave absorption of MoO2 ceramic at Gigahertz

In this work, the dielectric loss behavior and electromagnetic wave absorption (EMA) property of MoO2 ceramic from single crystal to polycrystal have been in-depth investigated. It is found that polycrystal MoO2 shows better dielectric loss ability than single crystal MoO2, leading to greatly enhanced EMA performance. It is determined that polarization loss occupies the dominant position in the dielectric loss of MoO2 ceramic. This research provides new insights in understanding of dielectric loss behavior and EMA mechanism for dielectric MoO2 crystals.