Electromagnetic Microwave Research Articles

Light-weight 1D heteroatoms-doped Fe3C@C nanofibers for microwave absorption with a thinner matching thickness

Emergency situation of electromagnetic microwave pollution generated by daily electronic devices urgently requires light-weight and efficient microwave absorption materials with thin thickness and low filling ratio. Herein, the heteroatoms-doped Fe3C@C nanofibers are fabricated from a mixture solution of Iron (III) 2, 4-pentanedionate (Fe(acac)3) and nitrogen-containing polymer poly (phthalazinone ether nitrile ketone) (PPENK) by electrospinning and the following thermal treatment. The morphologies and compositions of nanofibers can be controlled by annealing temperature. The 1-Dimensional (1D) heteroatoms-doped Fe3C@C nanofibers display outstanding microwave absorption performance. When the filling ratio is 30 wt% in paraffin for nanofibers heat-treated in 700 ℃, the optimal reflection loss value is − 35.5 dB at 8.3 GHz with a thickness of 2.8 mm. Additionally, the maximal efficient absorption bandwidth reaches as wide as 4.9 GHz ranging from 13.1 to 18.0 GHz with a rather thin thickness of 1.6 mm. The Fe3C@C nanofibers have adjustable electromagnetic parameters and thus, balance impedance matching and microwave attenuation performance at the same time. This work investigates the relationship between microwave absorption performance and the chemical states of nitrogen atoms, revealing a facile strategy to prepare a multi-interface microwave absorber and presenting a candidate application for microwave absorption materials with low matching thickness.

Ni@Carbon nanocomposites with hierarchical three-dimensional network for electromagnetic waves absorption

The design of a novel magnetic carbon nanocomposite with unique structure and element doping plays an important role in the development of electromagnetic microwave absorption (EMA) materials and the improvement of its performance. In this work, the EMA properties and mechanism of N-doped Ni@carbon network (Ni@CN) nanocomposite via polydopamine-assisted pyrolysis were systematically investigated. The networked microstructure can increase the multiple scattering of electromagnetic microwaves and thus reduce the intensity of incident microwave. The surface electronic structure of carbon is effectively regulated by Ni particles, which improve the impedance matching and increase ability of eddy current loss. The doping of N atoms provides dipole polarization. These causes the Ni@CN to display remarkable EMA performance, in which the maximal absorption reaches −45 dB and the maximum effective absorption bandwidth is from 10.9 to 16 GHz (5.1 GHz). This research indicates that strategy of Ni composite carbon network provides a new way for the rational design of lightweight carbon-based EMA material.

Enhanced electromagnetic microwave absorption of SiOC ceramics targeting the integration of structure and function

The electromagnetic waves (EMW) absorption properties of SiOC ceramics synthesized by polymer-derived method were investigated, and additive manufacturing was employed to obtain the integration of structure and functions. The presence of free carbon and β-SiC nanocrystallites increased the internal relaxation interfacial polarization, which improved the EMW absorption properties significantly. In particular for the sample pyrolyzed at 1200 °C, the effective absorption bandwidth (EAB, RL<-10 dB) and minimum reflection loss (RL)were 4.9 GHz (at a thickness of 1.58 mm) and -23.5 dB, respectively, indicating the excellent EMW absorption properties of this SiOC material. In addition, we 3D printed two typical porous structures (a log-pile grid and a gyroid) in which the thickness of solid element corresponded to the one providing optimal absorption. Additive Manufacturing of designed structures will enable to improve and further optimize the selection and control of the absorbing material in practical applications.

Roll-to-roll layer-by-layer assembly bark-shaped carbon nanotube/Ti3C2Tx MXene textiles for wearable electronics

Smart wearable electronics have drawn increasing attention for their potential applications in personal thermal management, human health monitoring, portable energy conversion/storage, electronic skin and so on. However, it is still a critical challenge to fabricate the multifunctional textiles with tunable morphology and performance while performing well in flexibility, air permeability, wearing comfortability. Herein, we develop a novel roll-to-roll layer-by-layer assembly strategy to construct bark-shaped carbon nanotube (CNT)/Ti3C2Tx MXene composite film on the fiber surface. The fabricated bark-shaped CNT/MXene decorated fabrics (CMFs) exhibit good flexibility, air permeability and electrical conductivity (sheet resistance, 6.6 Ω/□). In addition, the CMFs demonstrate good electrothermal performance (70.9 °C, 5 V), electromagnetic interference (EMI) shielding performance (EMI shielding effectiveness, 30.0 dB under X-Brand), and high sensitivity as the flexible piezoresistive sensors for monitoring the human motions. Importantly, our CMFs show distinctive EMI shielding mechanism, where a great proportion of incident electromagnetic microwaves are reflected by the bark-shaped CNT/MXene films owing to the multi-interface scattering effects. This work may provide a new strategy for the fabrication of multifunctional textile-based electronics and pave the way for smart wearable electronics.

Study on the electromagnetic properties and microwave absorbing mechanism of flaky FeSiAl alloy based on annealing and phosphate coating

A low-frequency composite absorbing material with high permeability and low permittivity in low frequency was prepared after the flaky FeSiAl alloy powder was annealed in N2 atmosphere and modified with zinc-based phosphate solution. The effects of annealing temperature and phosphating time on the phase composition, morphology and static magnetic properties of the flaky FeSiAl alloy were investigated with x-ray diffraction (XRD), scanning electron microscope (SEM) and vibrating sample magnetometer (VSM). With the aid of vector network analyzer (VNA), the electromagnetic properties and absorbing performance of the powder treated in two ways were studied. The results showed that after annealing in N2 atmosphere, the crystallization degree of FeSiAl powder increased, the crystal type underwent a phase transition of A2-A2/B2-A2/B2/D03, the permittivity decreased, and the permeability was greatly improved. After phosphating, the phosphating reaction products were deposited on the surface of FeSiAl particles, the permittivity was significantly reduced, the low-frequency impedance matching and low-frequency absorption performance were improved. The causes and frequency changes of electromagnetic wave absorption peaks were analyzed with the λ/4 interference cancellation theory, the interface reflection model and the impedance matching principle.

Magnetically tuning microwave propagation parameters in ferrofluids.

The paper reports on the frequency (f) and static magnetic field (H) dependencies of the microwave propagation parameters, in the ranges 0.1-6 GHz and 0-90.7 kA/m, of a kerosene-based ferrofluid with magnetite particles, filtered in magnetic field gradient. In the investigated range, the sample exhibits ferromagnetic resonance phenomenon and Maxwell-Wagner dielectric relaxation. Unlike the usual way of studying the propagation of microwaves through different media, in this paper we have defined an overall reflection coefficient, Rw(f, H), of a material with thickness, w, deposited on a total reflective support, which takes into account both the attenuation of wave within the material and the reflection at the air-material interface. Based on the measured relative magnetic permeability, [Formula: see text], and relative dielectric permittivity, [Formula: see text], a comprehensive and meaningful set of microwave propagation parameters are determined. Apart from Rw(f, H), this set of parameters of ferrofluid includes the attenuation constant of the electromagnetic wave, [Formula: see text](f, H), the phase constant [Formula: see text](f, H), the real, n'(f, H), and imaginary, n"(f, H), components of the refractive index, the reflection coefficient at the interface air-material, R(f, H), and the quarter wavelength in material, [Formula: see text](f, H). Based on the theoretical considerations and characteristics of ferrofluid, simplified and practical formulas of the propagation parameters are given and also possible applications of the results are suggested (such as electromagnetic absorber, phase shifter, microwave lenses and vibration sensor). This connection between theory and experimental results offers an example for the preliminary design of microwave applications of ferrofluids and, by extension, for any material consisting of magnetic nanoparticles dispersed in a dielectric matrix.

Design and Simulation of Extended Interaction Cavities for a Ka band Multi beam Klystron

This article reports about the design approach, electromagnetic simulation and analysis results of high-frequency ladder-type input, output, and intermediate RF cavaties for Ka-band multi-beam extended interaction klystron. Several parameters of the cavity, such as quality factor, shunt impedance, etc., have been investigated by the assistance of electromagnetic software CST microwave studio.

Electromagnetic absorbers with Schottky contacts derived from interfacial ligand exchanging metal-organic frameworks

Various types of polycrystals have been regarded as excellent electromagnetic (EM) microwave absorbents, while differentiated heterointerfaces among grains usually manipulate conductive loss and polarization relaxation, especially interfacial polarization. Herein, polar facets that dominated the optimization of EM attenuation were clarified by carefully designing polycrystalline Schottky junctions with metal–semiconductor contacts for the first time. An ingenious ligand exchange technique was utilized to construct Zn-MOF (ZIF-L) precursors for Fe-ZnO polycrystals, in which Fe-containing Fe(CN)63− etching ligand acted as metallic source in Schottky junctions. By adjusting the Schottky contacts in polycrystals, the enhanced grain boundaries mainly induced stronger interfacial polarization and affected the microcurrent lightly. This is because Schottky barriers can cause local charge accumulation on heterointerfaces for polarization relaxation. Additionally, the coexistence of Zn and O vacancies brought a lot of lattice defects and distortions for dipole polarization. Thus, optimal EM wave absorbability was obtained by polycrystals with 8 h ligand exchange and an effective absorption band reaching 4.88 GHz. This work can provide guidance for designing advanced polycrystalline EM absorption materials and also highlight the mechanism and requirement of Schottky junctions dominating polarization.

Hierarchical structure of in-situ Fe2O3 nanoparticles decorated on crumpled Ti3C2Tx nanosheets with enhanced cycle performance as anode for lithium ion battery

This paper presents a simple wet-chemical method for preparing hierarchical Fe2O3@Ti3C2Tx nanocomposites with 50–70 wt% Fe2O3 based on hydrothermal synthesis followed by freeze-drying. In this method, positively charged Fe2O3 nanoparticles homogeneously nucleate in-situ, grow, and are electrostatically anchored on the surface of negatively charged and crumpled Ti3C2Tx nanosheets. The synergy between the Fe2O3 and Ti3C2Tx inhibits the agglomeration and grain growth of the Fe2O3 nanoparticles, prevents the restacking and oxidation of the Ti3C2Tx nanosheets, and provides abundant voids, thus significantly improving the charge transport kinetics of the composite and absorbing the expansion of the Fe2O3 nanoparticles. In this study, a 60 wt% Fe2O3@Ti3C2Tx composite showed excellent electrochemical performance as an anode for a lithium ion battery, with a capacity of 701.86 mAh g-1 after 200 cycles at 0.2 A g-1 and a capacity of 609.9 mAh g-1 after 600 cycles at 0.5 A g-1. The proposed strategy is scalable, universal applicable for constructing MXene-based hybrids, and can be potentially viable in fields such as energy storage, electromagnetic interference shielding, microwave absorbance, and catalysis.

The ordered mesoporous carbon coated graphene as a high-performance broadband microwave absorbent

There has been a great challenge in developing highly efficient electromagnetic microwave absorbers with strong absorbility, wide effective absorbing bandwidth and lightweight to solve the increasingly severe electromagnetic pollution. Here, we unveil the great potential of highly ordered mesoporous carbon coated graphene composites in the application of microwave absorption. The ordered mesoporous carbon composites possess well-defined spherical mesopores that are uniformly distributed on graphene surfaces and with uniform diameters of ∼20 nm (graphene@mesoporous carbon, abbreviated as G/MC). This renders the nanocomposites with high BET surface areas of up to 316 m2 g−1. Impressively, the G/MC nanosheets carbonized at 900 °C (G/MC-900) exhibit an outstanding microwave absorbility, with a maximum reflection loss (RL) of −66.1 dB and an exceptionally broad effective absorbing bandwidth (EAB) of 8.2 GHz (RL < −10 dB) at ultralow filler loading of only 5 wt%. This microwave absorbility is superior to that of most microwave absorbing materials that have been reported, making the 2D mesoporous carbon nanocomposites a strong candidate for microwave attenuating materials.

Lightweight PVDF/γ-Fe2O3/PANI foam for efficient broadband microwave absorption in the K and Ka bands

Lightweight magnetic polyvinylidene fluoride/ferric oxide/polyaniline nanofiber (PVDF/γ-Fe2O3/PANI) foams with excellent microwave absorption performance in the K (18–26.5 GHz) and Ka (26.5–40 GHz) bands were successfully fabricated using heat shaping and a sacrificial templating method. By varying the diameter of the PANI nanofibers (50, 100 or 500 nm), the electromagnetic microwave absorption (EMWA) properties of the composite foams could be precisely tuned. PVDF/γ-Fe2O3/PANI-50 foams with a PANI nanofiber diameter ~50 nm delivered the best all-round EMWA performance, demonstrated by minimum reflection loss (RLmin) values of −38.7 dB at 26.33 GHz and −38.4 dB at 28.9 GHz at an absorber thickness of 2.5 mm. Further, the effective absorption bandwidth (EAB) of the composite could be adjusted to cover the entire 18–40 GHz frequency region simply by changing the absorber thickness (from 1.5 to 3.5 mm). This work introduces a simple low cost strategy for designing high performance microwave absorbers.

Electromagnetic microwave generation by acoustic vibrations gives rise to nanoradiophotonics

The development of new methods for generating pulsed electromagnetic microwave radiation is currently an actively developing area of research. Schemes for microwave radiation generation with optical pumping are of great interest. In this paper we propose and experimentally demonstrate principally new method for photonic generation of microwave electromagnetic radiation. This method is based on the use of radiation of charged submicron particles oscillating at their own acoustic frequency. Laser radiation of the optical range implements an effective buildup of acoustic vibrations of submicron particles forming the system under study, according to the Raman mechanism.

Transbronchial microwave ablation of lung nodules with electromagnetic navigation bronchoscopy guidance-a novel technique and initial experience with 30 cases.

BackgroundMicrowave ablation of lung nodules may provide a faster, larger and more predictable ablation zone than other energy sources, while bronchoscopic transbronchial ablation has theoretical advantage of fewer pleural-based complications than percutaneous approach. Our study aims to determine whether the novel combination of bronchoscopic approach and microwave ablation in management of lung nodules is technically feasible, safe and effective.MethodsThis is a retrospective analysis of a single center experience in electromagnetic navigation bronchoscopy microwave ablation in hybrid operating room. Patients had high surgical risks while lung nodules were either proven malignant or radiologically suspicious. Primary endpoints include technical feasibility and safety.ResultsTotal of 30 lung nodules from 25 patients were treated. Mean nodule size was 15.1 mm, and bronchus directly leads to the nodules (bronchus sign positive) in only half of them. Technical success rate was 100%, although some nodules required double ablation for adequate coverage. Mean minimal ablation margin was 5.51 mm. The mean actual ablation zone volume was −21.4% compared to predicted, likely due to significant tissue contraction ranging from 0–43%. There was no significant heat sink effect. Mean hospital stay was 1.73 days, and only 1 patient stayed for more than 3 days. Complications included pain (13.3%), pneumothorax requiring drainage (6.67%), post-ablation reaction (6.67%), pleural effusion (3.33%) and hemoptysis (3.33%). After median follow up of 12 months, none of the nodules had evidence of progression.ConclusionsBronchoscopic transbronchial microwave ablation is safe and feasible for treatment of malignant lung nodules. Prospective study on clinical application of this novel technique is warranted.

Research on electromagnetic properties and microwave deicing performance of carbon fiber modified concrete

The electromagnetic properties of concrete have an important effect on the microwave deicing performance of concrete road. In this paper, the carbon fiber was added into the concrete matrix to prepare carbon fiber modified concrete (CMFC), aiming to improve the concrete’s microwave absorbing performance and enhance the efficiency of road microwave deicing. Moreover, a rectangular waveguide transmission/reflection method was used to test the electromagnetic properties of concrete, and a self-developed microwave deicing test system was employed to test the microwave deicing performance. The electromagnetic characteristics tests show that with the increase of carbon fiber content, the microwave energy storage performance of CFMC is firstly increased and then decreased, its performance of microwave energy loss increases gradually, and its reflection of microwave enhances gradually as well. When the microwave frequency is in the vicinity of 2.45 GHz, the real part of complex permittivity of CFMC with a carbon fiber content of 1‰ (CFMC-1), 3‰ (CFMC-2) and 5‰ (CFMC-3) are 1.59 times, 1.69 times and 0.94 times of that of plain concrete (PC), respectively. As for the imaginary part of complex permittivity, the ratios are 4.42 times, 36.38 times and 37.74 times, respectively. As for the reflection properties, CFMC-1 has the lowest reflectivity, which is −6.21 dB. In addition, the microwave deicing tests show that CFMC-3 has the fastest heating rate, which is 1.680 ℃/s, 4.46 times that of PC. However, considering the mechanical properties, deicing effect and economic cost, CFMC-1 has the best application prospects, whose heating rate is 1.289 ℃/s, 3.42 times that of PC. Above all, it can be concluded that the efficiency of concrete road microwave deicing can be effectively improved by adding carbon fiber, and the research in this paper can provide theoretical guidance for the road microwave deicing operations in some sense.

Differential Effects of Decimetric Electromagnetic Microwaves on Pyruvate Kinase Activity in the Rat Brain during Ontogenesis

Differential Effects of Decimetric Electromagnetic Microwaves on Pyruvate Kinase Activity in the Rat Brain during Ontogenesis

Hydrothermal synthesis of micro-flower like morphology aluminum-doped MoS2/rGO nanohybrids for high efficient electromagnetic wave shielding materials

In this study, a three-dimensional (3D) micro-flower like morphology aluminum-doped molybdenum disulfide/reduced graphene oxide (Al@MoS2/rGO) nanohybrids have been developed using a simple and sensitive hydrothermal approach. Their electromagnetic (EM) parameters (permittivity, permeability) and microwave shielding parameters (S11, S12) have been analyzed and reported for the first time in the microwave frequency range of 8.0–12.0 GHz. It is interesting to note that the electrical conductivity of the nanohybrids increases with the doping concentration of Al-ions, whereas skin-depth has a reverse trend. The 12% Al@MoS2/rGO nanohybrid shows a higher total electromagnetic interference shielding effectiveness (EMI SE) value about SET ~33.38 dB, whereas undoped MoS2/rGO nanohybrid exhibits a lower value around ~17.07 dB at the same thin thickness. The higher doping concentration of Al-ion creates lattice distortion and crystal defects with high charge carrier mobility between multiple interfaces and at defective sites. Hence, the Al-doping into MoS2 lattice supported on the rGO surface can greatly enhance EM wave absorption and EMI SE value. The present work suggests that the 12% Al@MoS2/rGO nanohybrid can be treated as a good microwave absorbing and shielding material and useful in various techno-commercial devices.

Graphitic carbon nitride (g-C3N4) in situ polymerization to synthesize MOF-Co@CNTs as efficient electromagnetic microwave absorption materials

Metal-organic framework (MOF) derivatives show potential as electromagnetic microwave (EMW) absorbers. In this study, a series of MOF-Co@CNTs were prepared by pyrolyzing a ZIF-67/g-C3N4 precursor. ZIF-67 catalyzed the polymerization of g-C3N4 into CNTs on the surface of ZIF-67. The effect of the carbonization temperature and ratio of g-C3N4 to ZIF-67 on the EMW absorption capacity of MOF-Co@CNTs is discussed. The complex permittivity increased upon increasing the temperature, but the complex permeability changed only subtly. The optimal process used a carbonization temperature of 700 °C and a mass ratio of g-C3N4 and Co(NO3)2‧6H2O of 1. The RLmin was −59.5 dB at a thickness of 1.6 mm, and the effective bandwidth (RL < −10dB) reached 5.27 GHz at a thickness of 1.8 mm with only 8 wt% filled. Meanwhile, the 99% energy absorption bandwidth (RL < −20dB) reached 13.52 GHz (4.48–18 GHz) at thicknesses from 1.5 to 5.0 mm. Our research provides a new method for introducing CNTs into MOFs by utilizing g-C3N4 as the carbon source, and we believe MOF-Co@CNTs will make excellent EMW absorbers.

Generation of a Periodic Sequence of Ultrashort Electromagnetic Pulses in a Scheme with Two Parallel Radiating and Absorbing Electron Beams

We demonstrate the possibility of generating a periodic sequence of ultrashort electromagnetic microwave pulses in a scheme with two parallel coaxial electron beams formed by a common cathode and transported via common vacuum channel. The external cylindrical tubular beam ensures the amplification of radiation during rectilinear propagation along periodic slow-wave system, while the internal (paraxial) beam accounts for the nonlinear cyclotron-resonance absorption.

Flexible and Conformal Metamaterial based Microwave Absorber for WLAN, Wi-MAX and ISM Band Applications

ABSTRACT In this work, a flexible electromagnetic microwave absorber working in tri-band and dual band (i.e.) WLAN, Wi-Max and ISM applications are designed, fabricated, and characterised experimentally. The absorber consists of 9 × 9 array of rectangle and circular metamaterial structures with absorption rate above 90 and 80% respectively. The absorption response value varying with incident angle up to 60° in both TM and TE polarisation. The absorbers are designed and fabricated, and analyzed in both planar and conformal cases and observed that the rectangular metamaterial absorber having high absorption value when compared with circular metamaterial absorber. Prior to metamaterial characteristics of the absorber, the E-Field distributions, H-field distributions surface current distribution and return loss of both rectangular and circular metamaterial absorbers also evaluated. The proposed metamaterial absorber is tested using ANRITSU-MS2037C combinational analyser. The work demonstrates absorbers application to radar cross section reduction for WLAN, Wi-Max, and ISM applications.

Enhancement of magnetic field intensity with a left-handed metamaterial tunnel resonator for obstacle sensing

A narrow metal strip inspired by the left-handed metamaterial and sensitive LC resonator structure has been released in this work where the narrow metal strip is presented as a tunnel structure which can enhance electric and magnetic properties. A commercially available electromagnetic simulator CST Microwave Studio is utilized to design and investigate the eSRR (electric split-ring resonator) and tunnelled LC resonator structures. Furthermore, ADS (Advance Design software) is used to determine the scattering parameters of the equivalent circuit. The proposed metamaterial structure is employed as a sensor operating in the C-band (6.88 GHz) of the microwave region, and its sensing properties are tested using glossy paper as an obstacle. The designed metamaterial tunnelling structure exhibits very high sensitivity toward dielectric obstacles at different rotational angles and thus can be potentially used in various sensing applications. The field enhancement effects on sensing application are verified by measured obtained results for eSRR and tunnelled LC resonator structures.