Attenuation Of Microwave Energy Research Articles

Lightweight composites derived from carbonized taro stems for microwave energy attenuation and thermal energy storage

Lightweight composites derived from carbonized taro stems for microwave energy attenuation and thermal energy storage

Constructing multiple heterogeneous interfaces in one-dimensional carbon fiber materials for superior electromagnetic wave absorption

Due to impedance mismatch and a single loss mechanism, carbon fiber fails to meet the requirements for efficient absorbers in terms of lightweight construction and broad absorption band. In this study, we have successfully prepared one-dimensional beaded SiO2@SiC@C nanofiber (SSCF) composites with multiple heterogeneous interfaces by employing the electrospinning-carbothermal reduction method. The beaded SSCF composites effectively address the impedance mismatch issue by controlling silicon dioxide and silicon carbide through carbothermal reduction. This optimization enriches the defects and interfaces of carbon fibers composites, consequently enhancing the electromagnetic wave absorption performance. The SSCF composites demonstrate remarkable performance, with a minimum reflection loss of −59.53 dB at a matched thickness of 2.21 mm and a maximum absorption bandwidth of 6 GHz. This outstanding performance is attributed to the synergistic effects of the multi-phase composition, bead structure, and one-dimensional network structure. These features not only optimize impedance matching but also enhance defect loss, interface polarization loss (SiC/SiO2, C/SiO2, SiC/C, C/Air), conduction loss, and relaxation loss of the SSCF composites. Furthermore, radar cross-section analysis utilizing computer simulation technology confirms the excellent attenuation of microwave energy by the SSCF composites under realistic far-field conditions. This study provides valuable insights for designing efficient one-dimensional carbon-based electromagnetic wave absorbers.

Regulating N-doping strategies to construct 3D interconnected abundant porous N-doped carbon for polarization loss-enhanced microwave absorbers: Theory, design, and experiments

The widespread proliferation of modern portable electronic devices has necessitated the development of functional materials with high-efficiency microwave absorption properties. In this study, we utilized biomass-derived jujube shells as a carbon source and employed a nitrogen-doping process to modify carbon materials, resulting in the fabrication of outstanding microwave-absorbing biomass-based nitrogen-doped porous carbon. Additionally, we discussed the influence of different nitrogen sources on material structure and microwave absorption performance. These N-doped porous carbon materials exhibited excellent specific surface areas, particularly Org-N, which facilitated the formation of conductive networks and the multi-stage reflection and scattering of microwave. Moreover, N-doping created numerous defect sites and heterogeneous structures, improving impedance matching, thus promoting dipole polarization and interface polarization effects, which accelerated electron migration and interlayer hopping, contributing to the attenuation of microwave energy. The lowest reflection loss for Org-N, Inorg-N, and Mixed-N reached −27.3 dB, −40.9 dB, and −45.6 dB, respectively. Mixed-N exhibited optimal microwave absorption performance at 9.9 GHz with d = 2.4 mm and achieved an effective absorption bandwidth (EAB10) of 3.0 GHz (11.0 GHz–14.0 GHz) at d = 2.0 mm. Additionally, the enhancement of polarization relaxation effects was elucidated by examining the charge density distribution in molecular models featuring various N-doping forms. Consequently, biomass-derived N-doped porous carbon materials emerge as lightweight and highly efficient functional materials for microwave absorption purposes.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation.

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96dB and 5.25GHz, respectively, while the absorbing thickness is only 2mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

Cellular-like sericin-derived carbon decorated reduced graphene oxide for tunable microwave absorption

Sodium hydroxide (NaOH) activation on biomass-derived carbon materials has been a developed strategy to construct the porous and lightweight microwave absorber. However, the resulting random porous structures still remain a formidable challenge to optimize the impedance matching and microwave absorption performance. Here, a sericin-guided NaOH activation and subsequent carbonization process were proposed to synthesize uniform cellular-like sericin-derived carbon decorated reduced graphene oxide (SC/rGO) nanohybrids. The NaOH was used as a bi-functional activator to regulate the self-assembly of sericin protein between graphene oxide lamellas, while the sericin-guided NaOH further in situ activates the nanohybrids to produce uniform cellular nanostructures by carbonization. The abundant natural doped nitrogen and oxygen atoms derived from the industry wastes sericin are in-situ maintained after carbonization, which act as polarization centers to promote the attenuation of microwave energy. Benefiting from these merits, the synthesized cellular-like SC/rGO nanohybrids exhibit excellent impedance matching performance, promoted multiple electromagnetic transmission, excellent relaxation polarization phenomenon and microwave absorption properties. The optimized microwave absorption of SC/rGO40-500 reached −53.68 dB at 15.30 GHz, and the effective absorption bandwidth achieved 4.4 GHz (13.35–17.75 GHz) at the thickness of 1.51 mm with a low surface density of 0.035 g/cm2. Our work demonstrates a novel porous structure design strategy on biomass-derived carbon materials as high-efficiency microwave absorbers.

Polypyrrole coated 3D flower MoS2 composites with tunable impedance for excellent microwave absorption performance

Conductive materials have been widely studied as the dielectric loss type microwave absorption absorbers due to their specific properties. In this work, Molybdenum disulfide @polypyrrole (MoS2@Ppy) composites were prepared through microwave-assisted hydrothermal method followed by in-situ polymerization. The MoS2 nanoparticles showed three-dimensional flower-like structures. The Ppy nanoparticles were uniformly coated on the surface of MoS2, and some of small Ppy particles were embed in the folds of flower-like MoS2. The complex permittivity of composites was greatly enhanced because of the high conductivity of Ppy. The microwave absorption performances of MoS2@Ppy composites were investigated systematically. For the MoS2@100py composite, the minimum RL of −61.1 dB was obtained at 11.2 GHz under the thickness of 2.28 mm. Compared with the related materials, the MoS2@Ppy composite showed strong microwave energy attenuation, thin thickness and broad absorption bandwidth. The MoS2@Ppy composites have great potential application values as the high-efficiency microwave absorber.

Excellent electromagnetic wave absorption by complex systems through hybrid polymerized material

Management of magnetic properties of polymer without changing its chemical formation is the main challenge in polymer engineering and science. In the current study, the innovative three-dimensional hybrid polymerized material was prepared through an atom transfer radical polymerization (ATRP) procedure. A structure with extraordinary properties in electromagnetic absorption has been effectively characterized and polymerized. Also, the polymerized structure and morphology of the composites have been successively verified by XRD, FTIR, and FE-SEM tests. Moreover, these structures were uniformly embedded into the paraffin as a matrix, which is extremely beneficial for microwave energy attenuation. The exceptional architecture provided a 3D structure with impressive absorption of microwave energy. Particularly, reflection loss (RL) of a specimen of 2 mm thickness was −18.54 dB at 10,600 MHz as the maximum absorption, while the maximum RL of another specimen of 1 mm thickness was about −13 dB at 11,600 MHz. The absorption mechanism of the hybrid polymerized material is related to multiple reflections and electric conductive loss. The high absorption with low thickness and low-cost hybrid polymerized material has an excessive perspective for the application of electromagnetic absorption.

Novel, hierarchical SiC nanowire-reinforced SiC/carbon foam composites: Lightweight, ultrathin, and highly efficient microwave absorbers

The novel hierarchical SiC nanowire-reinforced SiC/carbon foam composites (SnwSCF) were prepared for the first time by carbonization, CVD, and CVI processes. Morphological results demonstrated that the hierarchical structure, composed of carbon foam with a SiC coating and SiC nanowires, was fabricated successfully. The hierarchical structure significantly improved the microwave-absorbing performance of the carbon foam. The optimal reflection loss value of SnwSCF achieved −31.216 dB at 15.76 GHz with a 1.5 mm absorber thickness. The corresponding effective absorption bandwidth was 4.1 GHz. Furthermore, the microwave-absorption mechanism of SnwSCF is discussed in depth. The incident EM waves were trapped in the hierarchical structure and experienced multiple microwave energy attenuation processes including multiple reflections, interface polarization, and dipole polarization. As a result, SnwSCF is believed to be a superior candidate to its competitors as an ultralight, ultrathin, and highly efficient microwave absorber.

Urchin-like Amorphous Nitrogen-Doped Carbon Nanotubes Encapsulated with Transition-Metal-Alloy@Graphene Core@Shell Nanoparticles for Microwave Energy Attenuation.

Herein, we report three-dimensional (3D) urchin-like amorphous nitrogen-doped CNT (NCNT) arrays with embedded cobalt-nickel@graphene core@shell nanoparticles (NPs) in the inner parts of NCNTs (CoNi@G@NCNTs) for highly efficient absorption toward microwave (MW). The CoNi NPs are covered with about seven layers of graphene shell, resulting in the formation of CoNi@G core-shell structures. In the meanwhile, the CoNi@G core-shell NPs are further encapsulated within NCNTs. Benefitting from the multiple scattering of the unique 3D structure toward MW, cooperative effect between magnetic loss and dielectric loss, and additional interfacial polarizations, the 3D urchin-like CoNi@G@NCNTs exhibit excellent MW energy attenuation ability with a broad absorption bandwidth of 5.2 GHz with a matching thickness of merely 1.7 mm, outperforming most reported absorbers. Furthermore, the chemical stability of the 3D urchin-like CoNi@G@NCNTs is improved greatly due to the presence of the graphene coating layers and outmost NCNTs, facilitating their practical applications. Our results highlight a novel strategy for fabrication of 3D nanostructures as high-performance MW-absorbing materials.

Synthesis of fish skin-derived 3D carbon foams with broadened bandwidth and excellent electromagnetic wave absorption performance

The novel three-dimensional (3D) co-doped carbon foam was fabricated via a facile hydrothermal and subsequent pyrolysis process using fish skin as carbon precursor. The fish-derived carbon foam (CFs) obtained at 650 °C (CFs-650) possesses large specific surface area of 1369.3 m2/g with natural inherited micropore-dominate porosity. Moreover, the heteroatoms O and N in the fish skin are uniformly planted into the carbon frameworks, which is highly advantageous for the attenuation of microwave energy. The unique architecture endows the 3D carbon foam with impressive microwave absorbing property. Especially, the broadest bandwidth (RL < −10 dB) of CFs-650 can be up to 8.6 GHz (9.4–18 GHz) at 3 mm with the minimum reflection loss (RL) of −33.5 dB. The optimal RL of CFs-650 is −52.6 dB at 15.8 GHz with the matching thickness of 2.6 mm. The mechanism of the microwave absorption of the carbon foam is attributed to electric conductive loss, interfacial polarization relaxation, multiple reflections and scattering. The low-cost and eco-friendly carbon foam has great potential for application of microwave absorption.

High efficiency microwave absorption nanocomposites of multiple-phase core-shell CoNi alloy@C loaded on rGO conducting network

A novel multiple-phase nanocomposites of core-shell CoNi alloy@C nanoparticles uniformly implanted on graphene conducting network are prepared via combining liquid phase reduction and hydrothermal reaction. The core-shell CoNi alloy@C nanoparticles are uniformly dispersed over graphene nanosheets. The abundant conductive network of reduced graphene oxide is favorable for CoNi alloy@C nanoparticles insertion. Compared to single CoNi alloy and CoNi alloy@C, the ternary CoNi alloy@C/rGO nanocomposites reveal a remarkable increase in microwave absorption. The maximum reflection loss achieves −62.4 dB at 7.84 GHz, and the effective bandwidth of reflection loss below −10 dB (90% attenuation of microwave energy) is up to 14.4 GHz. Meanwhile, through calculation of absorption efficiency, it can be obtained that the nanocomposites have a best absorption performance at 3.3 mm and the efficiency value is 24.88 dB GHz/mm. So this study provides an excellent candidate for military radars, aerospace, electronic instruments and other fields.

Studies of the ceramic material produced by pressureless sintering from the AlN-Y2O3-(Si-C) powder composition using electron microscopy, Raman spectroscopy and measurements of the thermal conductivity and microwave radiation

Samples of composite with ceramic matrix of aluminum nitride have been produced by pressureless sintering of the AlN-Y2O3 powder compositions with addition of SiC-C particles of size 50 nm (agglomerates of 200 nm). The presence of a SiC solid solution in AlN has been revealed by Raman and X-ray diffraction microanalyses and measurements of microwave energy attenuation and of thermal conductivity. The basic physico-mechanical properties of the resultant AlN-(SiC-C) composites: hardness, thermal conductivity, attenuation of the microwave energy in the frequencies range from 9.5 to 10.8 GHz have been defined.

Investigation of some dielectric properties of phosphate glasses doped with iron oxides, by a microwave technique

The effects of iron ions on dielectric properties of lithium sodium phosphate glasses were studied by non-usual, fast and non-destructive microwave techniques. The dielectric constant ( ε′), insertion loss ( L) and microwave absorption spectra (microwave response) of the selected glass system xFe 2O 3·(1 − x)(50P 2O 5·25Li 2O·25Na 2O), being x = 0, 3, 6, … , 15 expressed in mol.%, were investigated. The dielectric constant of the samples was investigated at 9.00 GHz using the shorted-line method (SLM) giving the minimum value of ε′ = 2.10 ± 0.02 at room temperature, and increasing further with x, following a given law. It was observed a gradual increasing slope of ε′ in the temperature range of 25 ⩽ t ⩽ 330 °C, at the frequency of 9.00 GHz. Insertion loss (measured at 9.00 GHz) and measurements of microwave energy attenuation, at frequencies ranging from 8.00 to 12.00 GHz were also studied as a function of iron content in the glass samples.

Structure, mechanical and functional properties of aluminum nitride-silicon carbide ceramic material

Two-phase ceramic composites of the dielectric-semiconductor type having different semiconducting phase content (aluminum nitride ceramics with uniformly distributed inclusions of silicon carbide of a certain size) have been produced by pressureless sintering. These composites are characterized by Vickers hardness HV (150 N) 9.5–15.8 GPa, Palmqvist fracture toughness 3.0–4.2 MPa m0.5, bending strength 132–209 MPa, thermal conductivity 37–82 W/(m K), and by a coefficient of the microwave electromagnetic energy attenuation to 36.3 dB/cm. It has been found that as the size of silicon carbide grains in aluminum nitride-based ceramics increases, the thermal conductivity increases and microwave energy attenuation decreases, which is indicative of the decisive role of grain boundaries in scattering both phonons and microwave radiation.

A Review and Assessment of Microwave Energy for Soil Treatment to Control Pests

Reports of experimental work on controlling pests such as insects, nematodes, weed seeds, and fungi in soil with microwave energy are reviewed. The assessment of the practicability of microwave radiation for soil treatment to control pests involves estimation of energy costs for heating soil to lethal levels for devitalization of weed seeds and consideration of parameters affecting microwave energy attenuation in the soil, conditions for selectively heating organisms in soil, and other factors that need to be taken into account for practical use. It is concluded that little probability exists for practical application of microwave energy for field control of these pests without major new discoveries of lethal mechanisms other than heating. Reasons include the severe attenuation of microwave energy in soils, the improbability of effective, selective heating of organisms, and the extremely high costs of energy and equipment for such applications.

The Dielectric Properties of Ice and Snow at 3.2 Centimeters

A knowledge of the permittivity and loss tangent of snow and ice is essential in studying both radar echoes from snow-covered terrain and the attenuation of microwave energy through snowstorms. To provide this information, a program was carried out at the National Research Council of Canada to measure the permittivity and loss tangent of ice and snow, and also to determine the reflection coefficients of snow-covered surfaces, at a wavelength of 3.2 centimeters. As a result of these investigations values have been obtained for the permittivity and loss tangent of snow of varying density, temperature, and water content. Theoretical values of the reflection coefficients of snow-covered surfaces, calculated from these data, are compared with the values obtained from the direct measurement of reflections from natural snow surfaces.