Relaxation Of Dipole Polarization Research Articles

Controllable surface functionalization of rice husk-derived porous carbon by atomic layer deposition for highly-efficient microwave absorption

Multilayer absorbers, characterized by their distinctive structures and numerous heterogeneous interfaces, possess the potential to become exceptionally efficient and stable electromagnetic wave absorbers. Herein, we have ingeniously engineered multilayer ZnO/NiCo/C (ZNC) composite absorbers, utilizing a combination of an annealing procedure and atomic layer deposition (ALD) process. From the SEM images, the ZnO layers composed of ZnO nanoparticles (NPs) fabricated via ALD almost completely cover the surface of rice husk-derived carbon and the NiCo NPs residing on the surface. Benefiting from the specific multilayer structure, the well-designed ternary dielectric/magnetic components, and the synergistic interplay between dipole polarization relaxation and interfacial polarization relaxation, coupled with good impedance matching, the ZNC150 and ZNC200 composites exhibit best microwave absorption capacities. Through the precise control of the electromagnetic parameters by the deposition circle modifications, the minimum reflection loss reaches −52.5 dB and the effective bandwidth extends to 4.96 GHz with thin thickness of 1.52 mm.

MOF derived α-Fe2O3/Ti3C2Tx magnetic-dielectric composites for microwave absorption

The design and development of microwave-absorbing materials with excellent performance hold significant importance in both civil and military fields. The combination of magnetic loss materials and dielectric loss materials can achieve complementary performance effects and regulate impedance matching. In this paper, spindle-like α-Fe2O3 was synthesized using MIL-88A as a template, which was then composited with Ti3C2Tx phase possessing excellent electrical conductivity to obtain Fe2O3/Ti3C2Tx composites. Ti3C2Tx can provide good conductance loss and dipole polarization relaxation, while the incorporation of Fe2O3 between the layers of Ti3C2Tx not only triggers the interfacial polarization effect but also increases layer spacing, thereby enhancing multiple reflection effects. Furthermore, the magnetic-dielectric synergies further optimize the impedance matching. Through the combined action of multiple mechanisms, the Fe2O3/Ti3C2Tx composites (with a mass ratio of 1:3 for Fe2O3 and Ti3C2Tx) exhibit a minimum reflection loss of −34 dB and an effective absorption bandwidth of 1.53 GHz at a thickness of 3 mm, as well as an effective absorption bandwidth of 2.805 GHz at a thickness of 1.5 mm. This paper presents a reference strategy for constructing highly efficient microwave absorbers derived from Metal-organic frameworks (MOFs) and MXene based on their outstanding properties.

CNTs-improved electromagnetic wave absorption performance of Sr-doped Fe3O4/CNTs nanocomposites and physical mechanism

Electromagnetic wave pollution is a serious environmental problem, and it is urgent to develop high-efficiency electromagnetic wave absorption (EMA) materials. In this paper, carbon nanotubes (CNTs) were combined with Sr-doped Fe3O4 nanoparticles to form Sr-doped Fe3O4/CNTs nanocomposites with by hydrothermal method. After the characterization of microstructure and magnetic properties, EMA properties of Sr-doped Fe3O4/CNTs nanocomposites are investigated in detail. The well-dispersed CNTs lead to the uneven average grain size of Sr-doped Fe3O4 nanoparticles and a little decrease of saturation magnetization. While CNTs greatly improve EMA performance, and SFC1 sample exhibits the minimum reflection loss value of −65.64 dB at 6.32 GHz with the thickness of 3 mm. CNTs reduces the natural resonance of magnetic loss while increasing the permittivity, conductivity, and heterogeneous interfaces. As the result, Sr-doped Fe3O4/CNTs nanocomposites exhibit not only better impedance matching but also higher electric dipole polarization relaxation loss, interfacial relaxation loss, conductivity loss, and eddy current loss. In this way, the excellent EMA performance is attributed to the good impedance matching, intense dielectric loss and enhanced eddy current loss for Sr-doped Fe3O4/CNTs nanocomposites.

Broadband electromagnetic wave absorption performance of CuS-biomass carbon composites derived from moss

The absorption performance of broadband electromagnetic waves is of utmost importance in safeguarding diverse electronic equipment against electromagnetic wave pollution, necessitating materials with low density, thin thickness, and cost-effectiveness to be employed. This study presents the successful synthesis of biomass-derived carbon (BC) composites via the hydrothermal method, utilizing moss coated with flower-like CuS. The CuS was uniformly dispersed on BC matrix, contribute to dipole polarization relaxation. The formation of heterogeneous interfaces between CuS and the BC phase resulted in significant polarization loss. Additionally, the wrinkled BC and flower like CuS constructed by nanosheets boosted scattering of electromagnetic wave due to its large specific surface area, which can provide additional channels for charge transfer and avail dissipation of electromagnetic wave energy. With an efficient absorption bandwidth (EAB) that encompasses the whole X band, the electromagnetic waves absorption (EMA) performance of CuS/BC composites was able to reach a minimum reflection loss of − 28.8 dB.

Effective dielectric attenuation for excellent microwave absorption with broadband response of carbon hollow microspheres derived from resin

Carbon hollow microspheres as microwave absorption materials (MAMs) are of great significance in the research focuses owing to their lightweight, good impedance matching, and modifiable dielectric properties. However, it is still a huge challenge to distinguish the contribution of dielectric attenuation between carbon intrinsic feature and hollow structure due to the lack of appropriate model materials. Then, the inadequate analysis of effective dielectric attenuation resulted in the construction of carbon hollow microspheres semiempirical and often lacked precise modification of microstructure. Herein, a series of carbon hollow microspheres with controllable graphitization and thickness of shell derived from phenolic resin coated on polystyrene microspheres that fully decomposed were synthesized, which is free of the impact of template residue. The carbon fragments ground from hollow microspheres exhibit the same broadband response as hollow microspheres, with effective bandwidth (RL ≤ –10 dB) of 7.6 GHz, while their electromagnetic wave loss mechanisms are distinct. The high dielectric loss of carbon fragments with the same intrinsic characteristics as carbon hollow microspheres is mainly caused by dipole polarization relaxation and enhancement of electrical conductivity ascribed to overlapping between carbon sheets. For the hollow structure, in addition to dipole polarization relaxation attributed to carbon intrinsic feature, the effective dielectric loss is also comprised of the interfacial polarization in advantage due to the effective heterogeneous interface between air and carbon shell. This work provides a simplified model to clarify the effect of carbon intrinsic feature and microstructure on the dielectric loss of carbon hollow microspheres.

NiCo2 O4 /Hollow Mesoporous Carbon Nanosphere Hybrids Enabling Super-Hydrophobicity, Thermal Insulation, and Highly Efficient Microwave Absorption.

The combination of 2D magnetic nanosheets and mesoporous carbon with unique interfaces shows considerable prospects for microwave absorption (MA). However, traditional assembly procedures make it impossible to accurately manage the assembly of magnetic nanosheets in carbon matrices. Herein, a reverse strategy for preparing complex magnetic nanosheet cores inside carbon-based yolk-shell structures is developed. This innovative approach focuses on controlling the initial crystallite formation sites in a hydrothermal reaction as well as the inflow and in situ growth behavior of 2D NiCo-layered double hydroxide precursors based on the capillary force induced by hollow mesoporous carbon nanospheres. Accordingly, the as-prepared YS-CNC-2 absorber exhibits remarkable MA performances, with an optimal reflection loss as low as -60.30dB at 2.5mm and an effective absorption bandwidth of 5.20GHz at 2.0mm. The loss of electromagnetic waves (EMW) depends on natural resonance loss, dipole polarization relaxation, and multiple scattering behavior. Ontopof that, the functionalized super-hydrophobic MA coating is produced in spraying and curing processes utilizing YS-CNC-2 nanoparticles and fumed silica additives in the polydimethylsiloxane matrix. The excellent thermal insulation, self-cleaning capability, and durability in diverse solutions of the coating promise potential applications for military equipment in moist situations.

Study on electromagnetic wave absorbing properties of nanocrystalline Fe81.5Si3B9P3C1Cu1Ti1.5/Graphene oxide composite

To prevent and control electromagnetic pollution problems, there is an urgent need to develop better wave-absorbing materials. In this study, nanocrystalline alloy/graphene oxide(GO) composite modified powder was obtained on the basis of Fe81.5Si3B9P3C1Cu1Ti1.5 nanocrystalline alloy powder with different weight percentages of GO, which was mechanically mixed by high-energy ball milling treatment, and the microstructure and morphology of the materials and the electromagnetic wave absorption properties were characterized. The results show that the Fe81.5Si3B9P3C1Cu1Ti1.5/GO composite powder has excellent wave absorption performance, and the loss mechanism is magnetic loss including eddy current loss and natural resonance. Defects and groups in GO not only improve the impedance matching characteristics, but also introduce defect polarization relaxation and electron dipole polarization relaxation of the groups, which are beneficial to the penetration and absorption of electromagnetic waves. The minimum reflection loss (RLmin) of the nanocrystalline alloy powder can reach −37.55 dB and the maximum effective absorption bandwidth (ΔfRL<-10dB) can reach 5.95 GHz; the RLmin of the composite powder is as high as −52.55 dB when the GO content is 1.5 wt%, and the widest bandwidth can reach 6.12 GHz at 2.00 mm when the GO content is 0.5 wt%. With the addition of GO, its RLmin increased by 40%. This indicates that the composite material have superior absorption performance compared to a single absorber.

Three-dimensional porous manganese oxide/nickel/carbon microspheres as high-performance electromagnetic wave absorbers with superb photothermal property

Regulating electromagnetic parameters and thus improving impedance matching characteristics by multi-component design is regarded as a prospective approach to obtain highly efficient electromagnetic wave absorption materials. Whereas, it is still challenging to fabricate microwave absorbers with strong absorption capacity and durability in harsh conditions. Based on the above considerations, three-dimensional porous multi-functional manganese oxide/nickel/carbon microspheres had been designed and prepared through a combined approach of facile solvothermal reactions and subsequent carbonization processes. The textural characteristic examinations demonstrated that, numerous manganese oxide and Ni nanoparticles of 15–20 nm in diameter were well dispersed in the carbon-based microspheres of approximately 0.8–1 μm in size. Microwave absorption property evaluation indicated that the minimum reflection loss reached up to −53.6 dB at 9.5 GHz, and effective absorption bandwidth of 3.7 GHz was achieved at matching thickness of merely 2.0 mm. The electromagnetic wave attenuation mechanisms analysis displayed that excellent impedance matching and various dissipation pathways, including magnetic loss, interfacial and dipole polarization relaxation synergistically contributed to the high microwave absorption performances of the porous composites. Radar cross-sectional simulation and photothermal measurements verified that the materials were supposed to have promising foregrounds in complicated circumstances.

Ruthenium-doping-induced strong electromagnetic loss in FeCo nanoparticles by orbital hybridization and electron transmission

Ferromagnetic metal/alloy particles are widely used in the field of electromagnetic wave absorption. Doping is an effective means of modulating the electromagnetic properties of magnetic metals and alloys. In this study, (Fe3Co7)1−xRux nanoparticles with different Ru doping contents are prepared using a polyvinylpyrrolidone (PVP)-assisted liquid-phase reduction process. First-principles calculations reveal that strong electron-orbit hybridization occurs between Ru-4d and Fe/Co-3d owing to the strong spin-orbit coupling effect of Ru-4d orbital electrons. This generates a space charge distribution and carries a magnetic moment of 1.80 hbar/2. The use of Ru doping results in a reduction in FeCo alloy particle size from 1.5 µm to 200 nm, slight decrease in the saturation magnetization from 179 to 152 emu/g, and increase in the electrical conductivity from 2.79 × 10-4 to 6.62 × 10-4 S·cm-1. The dielectric and magnetic loss values vary from 0.22 to 0.95 and 0.06–0.37, respectively, in the 2–18 GHz frequency range. Ru doping-induced dipole polarization relaxation, exchange resonance, and increased conductivity loss are the primary reasons for the enhanced electromagnetic loss of the material. When the level of Ru doping x reaches 0.10, the minimum reflection loss (RLmin) increases from − 21.5 to − 41.9 dB. Thus, (Fe3Co7)1−xRux is a promising material for electromagnetic loss due to its tunable composition, size, conductivity, magnetic properties, and excellent electromagnetic loss capability.

A 3D multifunctional nitrogen-doped RGO-based aerogel with silver nanowires assisted self-supporting networks for enhanced electromagnetic wave absorption

We designed a promising three-dimensional (3D) nitrogen-doped reduced graphene oxide-based aerogel (NGA) with silver nanowires (Ag NWs) assisted self-supporting networks for enhanced electromagnetic wave (EMW) absorption. 3D AgNWs@NGAs (8–12 mg/mL) were synthesized by a three-step strategy of sonication, reduction, and lyophilization. The results show that introduced sp3 defects and disordered sites in nitrogen doping from a rarely-reported liquid nitrogen source of acetonitrile remarkably improved electronic dipole polarization relaxation and EMW absorption ability. Besides, electronic band structure and density of states of the NGA were investigated by first-principles calculations to indicate that the carrier mobility became smaller during nitrogen doping. The Ag NWs were distributed on an NGA as the 3D network structure of an elastic support and a conductive and compatible unit, which limited the aggregation of NGA flakes, and further strengthened conductive loss. Significantly, the synthesized ultralight AgNWs@NGA exhibits excellent performance at 9.52 GHz, with a strong minimal reflection loss of –79.99 dB, a small thickness of 2.660 mm, a wide effective absorption bandwidth of 3.5 GHz, and an ultra-low filler content of 5 wt%. Furthermore, a large specific surface of 331.5 cm3/g, a good conductivity of approximately 50 S/cm, a high resilience, and an excellent heat insulation capability, guarantee the durable stability in EMW absorption of AgNWs@NGAs to resist distortion and heat attacks.

Hydrothermal synthesis of NixCo10-x nanoalloys with an enhanced microwave absorption performance

By using a facile hydrothermal synthesis, NiCo alloys with a particle size of 50–300 nm were prepared. The effects of the Ni:Co molar ratios on the microwave absorption properties in NiCo alloys were studied. The results showed that for Ni:Co molar ratios from 4:6 to 6:4, the morphology of the alloys changed from flower-like to nanoball-shaped. Specifically, the average size of Ni6Co4 was 84 nm, which showed a large specific surface area and produced increased interfacial polarization and multiple scattering. Ni6Co4 alloys exhibited excellent dielectric and magnetic properties, which enhanced microwave absorption properties. The optimum reflection loss in Ni6Co4 alloys was −53.29 dB at 9.44 GHz, and its thickness was 3.29 mm. The effective absorption bandwidth reached 6.64 GHz when the Ni6Co4 alloy thickness was 2.84 mm, which covered the C, Ku, and whole X bands. Additionally, the potential microwave dissipation mechanisms of as-fabricated NiCo alloys were illuminated, which were primarily derived from the optimized impedance matching, strengthened interfacial polarization, dipole polarization relaxation, and magnetic loss. These designs supply an effective way of obtaining promising candidate materials as high-efficient microwave absorbers.

A Flexible Sandwich Structure Carbon Fiber Cloth with Resin Coating Composite Improves Electromagnetic Wave Absorption Performance at Low Frequency.

In order to improve the electromagnetic wave absorbing performance of carbon fiber cloth at low frequency and reduce the secondary pollution caused by the shielding mechanism, a flexible sandwich composite was designed by a physical mixing coating process. This was composed of a graphene layer that absorbed waves, a carbon fiber cloth layer that reflected waves, and a graphite layer that absorbed transmitted waves. The influence of the content of graphene was studied by a control variable method on the electromatic and mechanical properties. The structures of defect polarization relaxation and dipole polarization relaxation of graphene, the interfacial polarization and electron polarization of graphite, the conductive network formed in the carbon fiber cloth, and the interfacial polarization of each part, combined together to improve the impedance matching and wave multiple reflections of the material. The study found that the sample with 40% graphene had the most outstanding absorbing performance. The minimum reflection loss value was −18.62 dB, while the frequency was 2.15 GHz and the minimum reflection loss value compared to the sample with no graphene increased 76%. The composites can be mainly applied in the field of flexible electromagnetic protection, such as the preparation of stealth tent, protective covers of electronic boxes, helmet materials for high-speed train drivers, etc.

Synthesis of three-dimensional porous netlike nitrogen-doped reduced graphene oxide/cerium oxide composite aerogels towards high-efficiency microwave absorption

Three-dimensional (3D) graphene aerogels with porous structure and lightweight feature have been regarded as promising candidates for microwave attenuation. Herein, nitrogen-doped reduced graphene oxide/cerium oxide (NRGO/CeO2) composite aerogels were fabricated via a hydrothermal route. The obtained composite aerogels possessed low bulk density and unique 3D porous netlike structure constructed by the stacking of lamellar NRGO. Moreover, it was found that the microwave dissipation performance of NRGO aerogel could be notably improved through complexing with CeO2 nanoparticles and carefully regulating the contents of CeO2 in the composite aerogels. Remarkably, the attained NRGO/CeO2 composite aerogel with the content of CeO2 of 44.11 wt% presented the comprehensively excellent microwave attenuation capacity, i.e. the optimal reflection loss reached −50.0 dB (larger than 99.999% absorption) at a thickness of 4.0 mm and wide bandwidth achieved 5.7 GHz (from 12.3 GHz to 18.0 GHz, covering 95.0% of Ku-band) under an ultrathin thickness of only 1.9 mm. Furthermore, the probable microwave dissipation mechanisms of as-synthesized composite aerogels were clarified, which included the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, notable oxygen vacancy effect and enhanced conduction loss. This work could shed light on developing graphene-based 3D broadband microwave absorption composites.

Preparation of FeNi/C composite derived from metal-organic frameworks as high-efficiency microwave absorbers at ultrathin thickness

Developing metal–organic frameworks (MOFs) derived microwave absorbers with the merits of thin matching thickness, broad bandwidth and strong absorption still remains a big challenge in the electromagnetic absorption field. Herein, FeNi-MOFs derived magnetic-carbon composites were fabricated via a solvothermal and pyrolytic two-step strategy. It was found that the micromorphology of carbon frameworks could be regulated from the regular octahedron to spherical shape through facilely adjusting the molar ratios of Fe3+ to Ni2+ in the precursors. Furthermore, results revealed that the molar ratios of Fe3+ to Ni2+ had notable effects on the electromagnetic parameters and microwave attenuation capacity of attained composites. Significantly, the obtained FeNi/C composite with the molar ratio of Fe3+ to Ni2+ of 1:0.5 showed the comprehensively optimal electromagnetic attenuation performance, i.e. the reflection loss achieved −40.2 dB (larger than 99.99% absorption) and absorption frequency band was as high as 5.8 GHz (from 11.9 to 17.7 GHz, covering 96.7% of Ku-band) under an ultrathin thickness of 1.65 mm. Besides, the probable microwave dissipation mechanisms were clarified, which mainly derived from the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, enhanced conduction loss and natural resonance effect. Therefore, our results would be helpful for designing and developing high-performance microwave absorbing composites derived from MOFs.

Dielectric Relaxation of Nanocomposites Based on Poly(phenylene oxide) and Endometallofullerene

The molecular mobility of poly(phenylene oxide) nanocomposites with endometallofullerene at a concentration of 0.1, 0.5, and 1.0 wt % is studied by dielectric spectroscopy. Two processes of dipole polarization relaxation in the glassy state (β-process) and in the rubbery state (α-process) are found. It is shown that the molecular mobility of the β-process related to the presence of a nanoadditive does not change with concentration. Molecular mobility in the region of the α-process, which is associated with segmental mobility, shows a downward trend.

Comparative study of deoxygenation behavior for graphene oxide with different oxidation degree and mildly reduced graphene oxide via solid-state microwave irradiation

The influence of the oxidation degree of graphene oxide (GO) on its deoxygenation efficiency via hybrid microwave heating (HWH) method by using graphite powder as the external susceptor was investigated, and the response behavior was compared with the situation when GO is directly submitted to microwave irradiation. In addition, the deoxygenation behavior of mildly reduced GO (VRGO) that was obtained via chemical reduction by Vitamin C was compared with that of GO during above two microwave heating processes. No response of GO to microwave irradiation when GO samples are exposed directly to microwave, no matter how the oxidation degree is. However, the VRGO sample can be heated when it is solely submitted to microwave irradiation. The partial reduction of GO leads to enhancement of the dielectric parameters, and the residual defects and oxygen-containing functional groups not only can improve the impedance matching characteristics, but also produce defects polarization relaxation and dipole polarization relaxation, which are all beneficial to the microwave penetration and absorption. The deoxygenation efficiency of VRGO is lower in comparison with GO under the HWH condition, which should be attributed to higher amount of epoxides in GO samples that can be easily reduced in a mixed heating mode.

Dielectric spectroscopy of thermoplastic polyimide R-SOD in the region of medium and high temperatures

Molecular mobility and charge transport in R-SOD aromatic thermoplastic polyimide were studied by dielectric method. Dielectric spectra of all samples in the examined temperature and frequency range revealed two regions of dipole polarization relaxation. The β- process is determined by local motion of the phenyl rings in the diamine and dianhydride moieties of the macromolecule with the adjacent groups. The α-process can be associated with crossing the glass transition temperature, i.e., with the segmental large-scale mobility of the main chains. The introduction of nano-additives (R-SOD 3%) does not change the relaxation times in the regions of β and α process, but leads to an increase in intensity compared to pure polyimide R-SOD.

One-pot solvothermal synthesis of Fe/Fe3O4 composites with broadband microwave absorption

In the present work, we have developed a simple and low-cost solvothermal method for the one-pot construction of the Fe/Fe3O4 composites with the Fe3O4 nanoparticles depositing on the surface of Fe polyhedrons. The Fe3O4 content in the Fe/Fe3O4 composites can be easily improved by the decrease of volume ratio of ethanol (95 vol%)/distilled water (Vethanol/Vwater). The electromagnetic parameters of the Fe/Fe3O4 composites (70 wt%)-paraffin mixtures are deeply depended upon the Fe3O4 content. The complex permittivity is gradually decreased and the complex permeability maintain the modest value with the increase of the Fe3O4 content. When the Fe3O4 content is 56 wt%, the minimum reflection loss (RL) value can reach −33 dB at a matching thickness of 1.5 mm. The optimal RL is −24.6 dB at 2 mm with the absorption bandwidth of 5 GHz and the integrated bandwidth with RL below −10 dB is 14.4 GHz in the frequency range of 3.6–18 GHz with a changeable thickness of 1.4–5 mm. Due to the double-loss characteristics of the Fe3O4 nanoparticles, the wide-frequency microwave absorption properties of the Fe/Fe3O4 composites at high frequency can be attributed to dipole polarization relaxation loss of the Fe3O4 nanoparticles, interfacial polarization relaxation loss between Fe and Fe3O4 and preferable impedance matching. This result indicates that the Fe/Fe3O4 composites could be a candidate for microwave absorption field.

Molecular mobility of thermoplastic aromatic polyimides studied by dielectric spectroscopy

The dielectric behavior of five aromatic thermoplastic polyimides with a sequentially changing chemical structure of the diamine and dianhydride parts of the macromolecule is studied. The dielectric spectra have shown three ranges of dipole polarization relaxation: γ, β (in the glassy state) and α (in the highly elastic state). The γ process takes place due to local mobility of phenylene rings in the diamine moiety of the macromolecule. The β process is related with local mobility of phenylene rings in the diamine and dianhydride parts of the macromolecule with adjacent polar groups. For γ and β processes, the chemical structure of polyimides has virtually no effect on molecular mobility. The source of the α process is large-scale segmental mobility. Its molecular mobility is more caused by the structure of the dianhydride part rather than that of the diamine one. It is shown that there is a linear correlation between free volume and glass transition temperature, which is determined by the dielectric method.

Dielectric properties of thermoplastic polyimide R-SOD at low temperatures

Molecular mobility and charge transport in R-SOD aromatic thermoplastic polyimide was studied by dielectric method. Dielectric spectra of all PI samples in the examined temperature and frequency range revealed one region of dipole polarization relaxation. The γ-process can be linked to the local mobility of phenylene rings in the diamine part of a macromolecule. The dependence of the σ'∼ωs type was observed in the studied temperature range (s<1.0), which indicates the existence of hopping mechanism of charge transport.