Microwave Attenuation Research Articles

Микроволновая диагностика разрядов в искусственном облаке заряженных водяных капель

The microwave diagnostics of discharges occurring in an artificial cloud of charged water droplets created in an open air simulating the environment of thunderclouds is implemented. An artificial cloud with a droplet size of about 1 microns is opaque in the visible range, so intra-cloud discharges are not available for investigation by traditional methods in the spark discharge physics based on the registration of visible discharge radiation. Microwaves pass through such a cloud without noticeable attenuation, they interact only with the plasma of discharges occurring in the cloud. The probing microwave radiation had a wavelength of 8 mm. The attenuation of microwaves passed through the cloud was measured with temporary resolution of about 10 ns. The temporal characteristics of intra-cloud discharges were investigated.

Construction of one-dimensional MoO2/NC heteronanowires for microwave absorption.

A combination of a special micro–nanostructure and multiple components has been proven as an effective strategy to strengthen the microwave attenuation capacity. In this work, one-dimensional MoO2/N-doped carbon (NC) nanowires with a heterostructure have been successfully prepared by utilizing mild in situ chemical oxidative polymerization and pyrolysis treatment. After compounding them with a thermoplastic polyurethane (TPU) matrix, the flexible composites exhibit tunable wave absorbing performance by modulating the filler loading of MoO2/NC heteronanowires. Experimental results demonstrate that the minimum reflection loss value of the MoO2/NC–TPU hybrid is up to −35.0 dB at 8.37 GHz under a thickness of only 2.3 mm with 40 wt% filler amounts. Moreover, the effective absorption bandwidth enables 3.26 GHz to be achieved (8.49–11.75 GHz) when the thickness changes to 2.0 mm, covering almost the whole X-band. Meanwhile, when the filler loading becomes 30 wt%, dual-absorption peaks appear. The relevant absorption mechanism is mainly attributed to the dielectric loss including strong dipolar/interfacial polarizations, Debye relaxation loss and multiple reflection and scattering.

Polyimide-derived porous carbon/Co particle-based composites for high-performance microwave absorption.

A simple method that combines liquid-liquid phase separation and high-temperature pyrolysis has been developed for the synthesis of polyimide-derived porous carbon/Co particle-based composite absorbers (PIC/Co-800 and PIC/Co-1000). The excellent heat resistance of polyimide allows the composite precursor to maintain its porous structure during pyrolysis. According to the results, PIC/Co-800 and PIC/Co-1000 have a coral-like porous structure, which can enhance the impedance matching property and microwave attenuation ability of the synthesized materials. The impedance matching condition and dissipation ability of PIC/Co-800 and PIC/Co-1000 have been enhanced due to the synergistic effect between the carbon-induced dielectric loss and Co nanoparticle-induced magnetic loss. PIC/Co-1000 shows the highest absorption performance with a minimum reflection loss (RL) of -40.22 dB at a thickness of 5.3 mm and an effective absorption bandwidth (EABW, RL ≤ -10 dB) of 4.10 GHz at a thickness of 1.4 mm. With thicknesses in the range of 1.4 mm to 5.3 mm, the minimum RL value of each thickness is lower than -15 dB. Therefore, this work provides a new strategy for the synthesis of promising absorbing materials with outstanding EMW absorption performance.

Fabrication of bimetallic metal-organic frameworks derived Fe3O4/C decorated graphene composites as high-efficiency and broadband microwave absorbers

Developing strong absorption and broadband microwave absorbers derived from metal-organic frameworks (MOFs) still remains a big challenge in the field of microwave absorption. Herein, iron zinc bimetallic metal-organic frameworks/reduced graphene oxide (FeZn-MOFs/RGO) precursors derived ferroferric oxide/carbon (Fe 3 O 4 /C) decorated graphene composites were fabricated via a solvothermal and carbonization two-step strategy. It was found that the morphology of carbon frameworks could be regulated from the traditional regular octahedron to the pomegranate shape by simply adjusting the molar ratios of Fe 3+ to Zn 2+ in the precursors. Moreover, results revealed that the molar ratios of Fe 3+ to Zn 2+ had notable effects on the electromagnetic parameters and microwave attenuation capacity of attained composites. Significantly, the obtained composites with the molar ratio of Fe 3+ to Zn 2+ of 1:2 presented the optimal electromagnetic attenuation performance, i.e. the minimum reflection loss achieved −79.0 dB with a matching thickness of 2.76 mm and effective absorption bandwidth was as high as 5.8 GHz under a thin thickness of 1.8 mm and low filling ratio of 20.0 wt%. Additionally, the potential microwave dissipation mechanisms were illuminated. Therefore, our results would shed light on the development of high-efficiency and broadband microwave absorbing composites derived MOFs. • Fe 3 O 4 /C decorated graphene composites derived from bimetallic MOFs were prepared. • Morphology of carbon frameworks evolved from octahedron to pomegranate shape. • Microwave absorption was regulated by adjusting the molar ratios of Fe 3+ to Zn 2+ . • Strong absorption, broad bandwidth, thin thickness and low loading were achieved. • The potential microwave dissipation mechanism of attained composites was proposed.

Heterogeneous Junctions of Magnetic Cip and Binary Dielectric Carbon-Based Material Toward High-Efficiency Microwave Attenuation

Heterogeneous Junctions of Magnetic Cip and Binary Dielectric Carbon-Based Material Toward High-Efficiency Microwave Attenuation

Improvement of multiple attenuation characteristics of two-dimensional lamellar ferrocobalt@carbon nanocomposites as excellent electromagnetic wave absorbers.

The lightweight carbon skeleton compounded with magnetic nanoparticles as excellent electromagnetic wave absorbers has attracted much attention considering their strong dielectric loss and magnetic loss, as well as the optimized impedance matching. However, the conventional method of compounding magnetic metals with carbon materials usually leads to the inevitable aggregation of magnetic nanoparticles, resulting in poor microwave attenuation characteristics. In this study, two-dimensional (2D) lamellar carbon matrix ferrocobalt (CoxFe1-x/C) nanocomposites are prepared using sodium chloride (NaCl) as a hard-template. By regulating the relative contents of Co and Fe in the nanocomposites, the 2D lamellar carbon skeleton with uniformly dispersed magnetic nanoparticles can be obtained successfully. Furthermore, the existence of a variety of metal and alloy phases promotes the generation of multiple attenuation characteristics. As a result, the Co0.9Fe0.1/C exhibits a broad effective absorption bandwidth of about 5.4 GHz at a thin thickness of only 1.65 mm. The excellent electromagnetic wave absorption can be attributed to the formation of a 2D lamellar structure and the uniform distribution of magnetic nanoparticles being conducive to the enhancement of polarization loss including dipole polarization loss and interfacial polarization loss. Considering that, the 2D lamellar Co0.9Fe0.1/C nanocomposite is promising to be a candidate for excellent electromagnetic wave absorbers.

Improved Microwave Absorption Performance with Sustainable Porous Carbon/Carbon Nanotube Composites

The great technological advancement in wireless communication systems and devices generated the problem of electromagnetic pollution. Developing lightweight, sustainable, and low-cost materials is necessary to minimize electromagnetic pollution. A sustainable porous carbon (PC) absorber material was obtained from the crude black liquor by a simple and low-cost synthesis, and combined with carbon nanotube (CNT), presenting excellent microwave attenuation results. The PC absorber at 20 wt.% filling ratio exhibited an intense reflection loss of ‑35.7 dB at 15.5 GHz, and bandwidth of 1.15 GHz for a thickness of 5.90 mm. By adding 0.2 wt.% of CNT, the reflection loss was -34.6 dB at 17.9 GHz, and a bandwidth of 1.54 GHz for 4.90 mm. The study reveals that the combination of PC and CNT improves the attenuation capacity, allows adjustment in the frequency range of the attenuation peak, and promotes thickness reduction. The results obtained allow us to advance studies in developing high-performance, sustainable, and low-cost microwave-absorbing materials.

0D/1D/2D Architectural Co@C@MXene Composite for Boosting Microwave Attenuation Performance in 2-18 GHz

0D/1D/2D Architectural Co@C@MXene Composite for Boosting Microwave Attenuation Performance in 2-18 GHz

Hierarchical Core-Shell Fes2/Fe7s8@C Microspheres Embedded into Interconnected Graphene Framework for High-Efficiency Microwave Attenuation

Hierarchical Core-Shell Fes2/Fe7s8@C Microspheres Embedded into Interconnected Graphene Framework for High-Efficiency Microwave Attenuation

A Two‐Dimensional Semiconductive Metal‐Organic Framework for Highly Efficient Microwave Absorption

Comprehensive SummaryAdvanced microwave absorbing materials (MAMs) are urgently required to eliminate and attenuate microwaves to address the ubiquitous microwave radiations and interference. In this contribution, we report the microwave absorption application of a two‐dimensional (2D) semiconductive metal‐organic framework (MOF), i.e., CuHT (HT = 4‐hydroxythiophenol), without any pyrolysis at high temperature. Owing to the suitable electrical conductivity (2.69 × 10–4 S·cm–1), CuHT renders remarkable microwave absorption performance, with the minimum reflection loss (RLmin) of –50.9 dB and the effective absorption bandwidth of 4.2 GHz (7.7—10.9 GHz) at a thickness of 1.74 mm. Based on DFT calculation, microwave attenuation is mainly originated from resistance loss due to the conducting planes of honeycomb‐like Cu2S layers. Thanks to the facile kilogram‐scale synthesis, CuHT holds great potential for future microwave absorption applications.

Construction of flower-like core-shell Fe3O4@2H-MoS2 heterostructures: Boosting the interfacial polarization for high-performance microwave absorption

Optimizing impedance matching and boosting interfacial polarization by constructing hierarchical magnetic/dielectric heterostructures is a promising strategy to acquire high-performance microwave absorption. Herein, 3D flower-like core-shell Fe3O4@2H-MoS2 architectures were constructed, in which magnetic Fe3O4 submicrospheres are uniformly coated by 2H-MoS2 nanosheets. Compared to bare Fe3O4 and 2H-MoS2, the hierarchical Fe3O4@2H-MoS2 heterostructures show boosting microwave absorption, which is related to the content of Fe3O4 submicrospheres. When the thickness is only 1.9 mm, the Fe3O4@2H-MoS2 heterostructures display an optimal reflection loss (RL) of −50 dB at 13.2 GHz and effective absorption bandwidth (EAB, RL ≤ −10 dB) of 4.2 GHz (11.4–15.6 GHz). Besides, an EAB can be achieved in 14.6–18.0 GHz with an ultrathin thickness of 1.5 mm. The superior microwave absorption of Fe3O4@2H-MoS2 heterostructures is mainly originated from two aspects. First, the combination of magnetic Fe3O4 and semi-conducting 2H-MoS2 can induce better impedance matching in comparison with the bare Fe3O4 and 2H-MoS2. Second, the embedded Fe3O4 core can greatly boost the complex permittivity and dielectric loss of 2H-MoS2, leading to improved microwave attenuation capacity. The boosting dielectric loss is primarily due to the unique interfacial polarization, induced by the special core-shell hierarchical architectures. This work suggests that optimizing impedance matching and boosting interfacial polarization are effective strategies to improve the microwave absorption of 2H-MoS2, which can be realized by loading magnetic nanostructures and designing 3D hierarchical heterostructures.

Influence of synergistic effect of Mn valence state and oxygen vacancy concentration on microwave absorbing properties of CaMnO3

The research of microwave absorption material has great significance for solving electromagnetic pollution and military security. Manganite perovskite has huge potential for developing into a fine microwave absorption material due to its adjustable electromagnetic property, while the mechanisms are still being explored. Therefore, we aim to explain the microwave loss mechanism of manganite perovskite with the double exchange interaction of Mn ion. Orthorhombic structure CaMnO3 was effectively synthesized, and the Mn valence state and oxygen vacancy concentration were changed by doping at Ca-site, while the total number of Mn ions remained intact. Ba, Sr, La, Sm, and Ce were the doping ions employed. Analyses revealed that the microwave absorption performance of CMO was linked to the Mn valence state and oxygen vacancy concentration. The Sr-CMO with the optimal microwave attenuation capability had the most Mn3+ ions and its dielectric loss is primarily due to polarization relaxation loss. In the microwave attenuation mechanism of La-CMO, which had the least oxygen vacancy content, conductive loss played a larger role. Through the double exchange interaction of Mn, the synergistic impact altered the microwave absorption performance. Hence, we can manipulate Mn valence state and oxygen vacancy concentration to improve the microwave absorption performance of CaMnO3, and the technique might be applied to other Mn-based absorbents.

Lightweight and broadband 2D MoS2 nanosheets/3D carbon nanofibers hybrid aerogel for high-efficiency microwave absorption

Three-dimensional (3D) porous molybdenum disulfide nanosheets/carbon nanofibers (MoS2/CNF) hybrid aerogels were synthesized by using solvothermal method and following carbonization, where two-dimensional (2D) MoS2 nanosheets were homogenously in-situ grown on the interconnected CNF skeleton derived from bacterial cellulose, forming a hierarchical porous structure. This unique heterogeneous structure of the MoS2/CNF hybrid aerogels were conducive to electromagnetic loss, including conduction, polarization, multi-scatterings, and reflections, thus resulting in a balanced impedance matching and microwave attenuation capacity. It was found that the resulted MoS2/CNF hybrid aerogels demonstrate excellent microwave absorbing performance when the only 5.0 wt% fillers were loaded in paraffin. Particularly, MoS2/CNF-2–900 hybrid aerogel displayed an effective absorption bandwidth of 5.68 GHz and minimum reflection loss (RLmin) value of −36.19 dB at a thickness of 2.0 mm. As the thickness increases to 4.4 mm, the RLmin value of MoS2/CNF-2–900 hybrid aerogel reaches −48.53 dB. Electromagnetic loss mechanism analysis indicates that such improved microwave attenuation is attributed to proper component, multiple heterogenous interface and hierarchical porous structures. All the results in this work pave the avenue for the development of ultralight microwave absorber with high absorption capacity as well as broad effective absorption bandwidth.

Self-supported construction of three-dimensional NiCo2O4 hierarchical nanoneedles for high-performance microwave absorption

Grafting one-dimensional (1D) structure onto three-dimensional (3D) carbon foam is a practical and novel protocol to improve its microwave attenuation capability. Herein, a unique microwave absorber with NiCo2O4 nanoneedle grew on carbon foam (NCOCF) has been built via a combined approach of carbonization and hydrothermal treatment. The obtained NCOCF exhibit good impedance matching and excellent attenuation capability, which means that the microwave energy can be dissipated through conductive loss, interfacial polarization and multiple-scattering. These advantages result in the effective transformation of microwave energy to heat, thus yielding a remarkable microwave adsorption (with a thickness of 2.8 mm, the maximum reflection loss (RLmax) is −63.6 dB, and the effective absorption bandwidth (EAB) is as wide as 4.72 GHz with a thickness of 1.3 mm). The study would offer a strategy for development of the high-performance microwave absorber.

The controllable porous structure and s-doping of hollow carbon sphere synergistically act on the microwave attenuation

Currently, the development of high-efficiency electromagnetic wave (EMW) absorbing materials has received close attention. Due to unique composition and structure, porous hollow carbon spheres (PHCSs) have been extensively studied in the EMW absorption field. In order to obtain the regulated EMW absorber, in the present study, sulfur was successfully doped into the PHCS by hydrogen peroxide etching and high temperature vulcanization. By fixing the amount of sulfur doped and the etching time, the micro-structure of the product could be effectively controlled, and the corresponding electromagnetic parameters would also change accordingly. The optimized sulfur-doped porous hollow carbon sphere (SPCHS) had the minimum reflection loss (RL) value of −27.2 dB, and the effective bandwidth of 4.76 GHz. More importantly, the best effective bandwidth (EAB, RL < −10 dB) could reach 6.72 GHz (11.28–18 GHz) at the thickness of 2.25 mm. It should be pointed out that the sample filling ratio was only 5 wt% in the paraffin matrix. In addition, when the incidence θ reached −60°, the maximum reduction of radar cross section (RCS) was −21.9 dB m2. The convenient and efficient RCS simulation provided reliable support for the practical application of SPHCS materials in the field of EMW absorption.

Electromagnetic performance, optical and physiochemical features of CaTiO3/NiO and SrFe12O19/NiO nanocomposites based bilayer absorber

Herein, two distinct nanocomposites of CaTiO3 micro-cubes and polygonal SrFe12O19, both decorated with NiO nanoparticles, were successfully synthesized using hydrothermal method. The physico-chemical features of as-prepared samples were evaluated via XRD, FTIR, UV–vis, BET, XPS, FESEM and EDS analysis. Microwave attenuation features of as-prepared single layer absorbers were determined by VNA analysis in 2–18 GHz. Simulation confirmation was checked by preparing a bi-layer samples and evaluating it using VNA analysis after finding the appropriate thickness of each layer. The reflection loss from each single layer samples containing 20 wt% of each CaTiO3/NiO and SrFe12O19/NiO nanocomposites were −16 dB and −35 dB at 6.3 GHz with 2.5 mm matching thickness respectively. However, the RL was −34 dB at 10 GHz frequency with 2 mm thickness in a bilayer absorber with SrFe12O19/NiO nanocomposite layer put as absorbing layer with 1 mm thickness and CaTiO3/NiO positioned as matching layer with 1 mm thickness. Furthermore, at the X-band frequency, approximately entire band absorption is obtained. The findings demonstrate that adjusting the order and thickness of the layers in a bilayer absorber may readily improve microwave absorption performance. By comparing the results of simulation with real prepared bilayer absorbers, we found that with a 2 mm overall thickness, the bi-layer absorbers display accurate RL values, but not the matching frequency monitored in the simulation process. In reality, this discrepancy was unavoidable.

Absorption-dominant microwave shielding properties of Sn0.2Fe2.8O4-graphite-PVDF ternary nanocomposite films

Absorption-dominant microwave shields are in high demand for mitigating the effect of electromagnetic interference (EMI) on devices and the environment. In this paper, we describe the development of absorption enhanced ternary nanocomposites and their EMI shielding capability. Polymer based shields have been fabricated by dispersing conducting graphite and magnetic spinel ferrite Sn0.2Fe2.8O4 nanoparticles in electroactive polymer polyvinylidene fluoride. Shielding effectiveness (SE) values in the expected range of 10–30 dB in the X-band region, were achieved with as low as 30–50 wt% of pristine graphite and 1–10 wt% of Sn0.2Fe2.8O4. The industrial standard of 99% shielding (SE ⩾ 20 dB) was obtained with 50 wt% of graphite. The composites exhibit absorption as the dominant mechanism of shielding. The percentage SE due to absorption is about 70% and is tuned upwards by the increase in ferrite concentration. The composites were characterized by x-ray diffraction and vibrating sample magnetometry; thermal analysis confirms their stability. The thin, flexible films fabricated by the simple and cost-efficient technique of solution casting will be extremely valuable as wrap-on shields for X-band microwave attenuation.

Controllable heterogeneous interfaces of cobalt/carbon nanosheets/ rGO composite derived from metal-organic frameworks for high-efficiency microwave attenuation

Structural design and composition control are crucial in determining the EM wave attenuation of an absorber; however, the balancing of the EM parameters has always been a formidable challenge. Here, we successfully designed a 3D hierarchical Co/carbon nanosheets (CNS)/rGO magnetic-dielectric composite with controllable composition and microstructure as a high-efficiency absorber by using a three-step route. Benefiting from the synergetic effect and heterogeneous interfaces, the hierarchical Co/CNS/rGO composite displayed strong microwave attenuation and broad absorption frequency band. Furthermore, the nanocomposite with porous structure promoted multiple reflection and scattering, thereby improving the attenuation capacity. The hierarchical Co/CNS/rGO composite exhibited strong microwave absorption capabilities when the filler loading was 20 wt%. Specifically, the maximum reflection loss (RL) was up to −65.5 dB at 12.4 GHz with a matched thickness of 2.5 mm and the corresponding absorption bandwidth was 8 GHz. Such excellent results not only serve as an inspiration for the enhancement of interfacial polarization of an absorber, but they also provide a novel avenue to synthesize high-efficiency microwave absorber with controllable structural design and composition regulation.

Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers

Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe2O4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9–13.5 mg·cm−3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached −40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites.

Synthesis of trimanganese tetroxide nanoparticles decorated nitrogen-doped reduced graphene oxide composite aerogels with excellent microwave absorption performance

In this work, trimanganese tetroxide nanoparticles decorated nitrogen-doped reduced graphene oxide (NRGO/Mn3O4) composite aerogels were synthesized via a hydrothermal route and subsequent lyophilization treatment. The obtained composite aerogels possessed low bulk density (12.5–14.1 mg·cm−3) and particular three-dimensional (3D) porous netlike structure formed through stacking of neighboring NRGO flakes. Moreover, the microwave attenuation properties of as-synthesized composite aerogels could be modulated by regulating the contents of Mn3O4 and matching thicknesses. Significantly, the attained composite aerogel with the content of Mn3O4 of 20.2 wt% presented the integrated excellent electromagnetic attenuation performance, i.e. the optimal minimum reflection loss achieved −52.9 dB (larger than 99.999% absorption) at a thin matching thickness of 1.6 mm and broadest effective absorption bandwidth was as high as 5.4 GHz (from 12.3 GHz to 17.7 GHz, covering 90% of Ku-band) under a very thin thickness of only 1.5 mm. Additionally, the potential microwave dissipation mechanisms of as-fabricated composite aerogels were illuminated, which primarily originated from the optimized impedance matching, strengthened interfacial polarization and dipole polarization loss, and notable conduction loss. Our results would shed light on the development of lightweight and high-performance graphene-based 3D microwave absorption composites.