Designing Electronic Structures of Multiscale Helical Converters for Tailored Ultrabroad Electromagnetic Absorption

Atomic-scale doping strategies and structure design play pivotal roles in tailoring the electronic structure and physicochemical property of electromagnetic wave absorption(EMWA)materials.However,the relationship between configuration and electromagnetic(EM)loss mechanism has remained elusive.Herein,drawing inspiration from the DNA transcription process,we report the successful synthesis of novel in situ Mn/N co-doped helical carbon nanotubes with ultrabroad EMWA capability.Theoretical calculation and EM simulation confirm that the orbital coupling and spin polarization of the Mn–N4–C configuration,along with cross polarization generated by the helical structure,endow the helical converters with enhanced EM loss.As a result,HMC-8 demonstrates outstanding EMWA performance,achieving a minimum reflection loss of−63.13 dB at an ultralow thickness of 1.29 mm.Through precise tuning of the graphite domain size,HMC-7 achieves an effective absorption bandwidth(EAB)of 6.08 GHz at 2.02 mm thickness.Furthermore,constructing macroscale gradient metamaterials enables an ultrabroadband EAB of 12.16 GHz at a thickness of only 5.00 mm,with the maximum radar cross section reduction value reaching 36.4 dB m2.This innovative approach not only advances the understanding of metal–nonmetal co-doping but also realizes broadband EMWA,thus contributing to the development of EMWA mechanisms and applications.

Achieving Ultra-Wideband and Elevated Temperature Electromagnetic Wave Absorption via Constructing Lightweight Porous Rigid Structure

Realizing ultra-wideband absorption,desirable attenuation capability at high temperature and mechanical requirements for real-life applications remains a great challenge for microwave absorbing materials.Herein,we have constructed a porous carbon fiber/polymethacrylimide(CP)structure for acquiring promising microwave absorption performance and withstanding both elevated temperature and high strength in a low density.Given the ability of porous structure to induce desirable impedance matching and multiple reflection,the absorption bandwidth of CP composite can reach ultra-wideband absorption of 14 GHz at room temperature and even cover the whole X-band at 473 K.Additionally,the presence of imide ring group in polymethacrylimide and hard bubble wall endows the composite with excellent heat and compressive behaviors.Besides,the lightweight of the CP composite with a density of only 110 mg cm^(−3) coupled with high compressive strength of 1.05 MPa even at 453 K also satisfies the requirements in engineering applica-tions.Compared with soft and compressible aerogel materials,we envision that the rigid porous foam absorbing material is particularly suitable for environmental extremes.

Numerical and Experimental Investigation on the Attenuation of Electromagnetic Waves in Unmagnetized Plasmas Using Inductively Coupled Plasma Actuator

The attenuation of electromagnetic （EM） waves in unmagnetized plasma generated by an inductively coupled plasma （ICP） actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square fiat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.

A classical relativistic hydrodynamical model for strong EM wave-spin plasma interaction

Based on the covariant Lagrangian function and Euler-Lagrange equation,a set of classical fluid equations for strong EM wave-spin plasma interaction is derived.Analysis shows that the relativistic effects may affect the interaction processes by three factors:the relativistic factor,the time component of four-spin,and the velocity-field coupling.This set of equations can be used to discuss the collective spin effects of relativistic electrons in classical regime,such as astrophysics,high-energy laser-plasma systems and so on.As an example,the spin induced ponderomotive force in the interaction of strong EM wave and magnetized plasma is investigated.Results show that the time component of four-spin,which approaches to zero in nonrelativistic situations,can increase the spin-ponderomotive force obviously in relativistic situation.

Application of geophysical methods in fine detection of urban concealed karst:A case study of Wuhan City,China

The construction of modern livable cities faces challenges in karst areas,including ground collapse and engineering problems.Wuhan,with a population of 13.74×10^(6) and approximately 1161 km^(2)of soluble rocks in the urban area of 8569.15 km^(2),predominantly consists of concealed karst areas where occasional ground collapse events occur,posing significant threats to underground engineering projects.To address these challenges,a comprehensive geological survey was conducted in Wuhan,focusing on major karstrelated issues.Geophysical methods offer advantages over drilling in detecting concealed karst areas due to their efficiency,non-destructiveness,and flexibility.This paper reviewed the karst geological characteristics in Wuhan and the geophysical exploration methods for karst,selected eight effective geophysical methods for field experimentation,evaluated their suitability,and proposed method combinations for different karst scenarios.The results show that different geophysical methods have varying applicability for karst detection in Wuhan,and combining multiple methods enhances detection effectiveness.The specific recommendations for method combinations provided in this study serve as a valuable reference for karst detection in Wuhan.

Threshold of parametric instability in the ionospheric heating experiments

Many observations in the ionospheric heating experiment, by a powerful high frequency electromagnetic wave with ordinary polarization launched from a ground-based facility, is attributed to parametric instability （PI）. In this paper, the general dispersion relation and the threshold of the PI excitation in the heating experiment are derived by considering the inhomogeneous spatial distribution of pump wave field. It is shown that the threshold of PI is influenced by the effective electron and ion collision frequencies and the pump wave frequency. Both collision and Landau damping should be considered in the PI calculation. The derived threshold expression has been used to calculate the required threshold for excitation of PI for several ionospheric conditions during heating experiments conducted employing EISCAT high frequency transmitter in TromsФ, Norway, on 2nd October 1998, 8th November 2001, 19th October 2012 and 7th July 2014. The results indicate that the calculated threshold is in good agreement with the experimental observations.

Single source precursor derived SiBCNHf ceramic with enhanced high-temperature microwave absorption and antioxidation

Electromagnetic(EM)wave-absorbing materials with high-temperature-resistance are urgently desirable to eliminate EM interference in extreme conditions.Precursor derived ceramics(PDC)route is being evolved as an effective strategy to solve the puzzle.Herein,a single source hyperbranched polyborosi-lazane precursor containing hafnium(hb-PBSZ-Hf)is introduced and the SiBCNHf ceramic is obtained by further pyrolysis.The micro-sized tissues including HfC,SiC,HfB 2 nanocrystals and segregated carbons are in situ generated during annealing which not only increase EM wave absorption ability(minimum re-flection coefficient(RC_(min))is-56.71 dB with a thickness of 2.5 mm,effective absorption bandwidth(EAB)is 3.4 GHz),but also improve antioxidation property(less than 2 wt.%mass fluctuation at 1400℃in air).Theoretical simulation of complex permittivity suggests that SiBCNHf ceramic has an RC_(min)of less than-5 dB for the whole X-band even at 1100℃.Such SiBCNHf ceramic with superior high-temperature-resistance and antioxidation performance derived from single source precursors possesses great potential for EM wave absorbing coatings in high-temperature and harsh environments.

Stacking MoS_(2) flower-like microspheres on pomelo peels-derived porous carbon nanosheets for high-efficient X-band electromagnetic wave absorption

The key to solve increasingly severe electromagnetic(EM)pollution is to explore sustainable,easily prepared,and cost-effective EM wave absorption materials with exceptional absorption capability.Herein,instead of anchoring on carbon materials in single layer,MoS_(2) flower-like microspheres were stacked on the surface of pomelo peels-derived porous carbon nanosheets(C)to fabricate MoS_(2)@C nanocomposites by a facile solvothermal process.EM wave absorption performances of MoS_(2)@C nanocomposites in X-band were systematically investigated,indicating the minimum reflection loss(RLmin)of-62.3 dB(thickness of 2.88 mm)and effective absorption bandwidth(EAB)almost covering the whole X-band(thickness of 2.63 mm)with the filler loading of only 20 wt.%.Superior EM wave absorption performances of MoS_(2)@C nanocomposites could be attributed to the excellent impedance matching characteristic and dielectric loss capacity(conduction loss and polarization loss).This study revealed that the as-prepared MoS_(2)@C nanocomposites would be a novel prospective candidate for the sustainable EM absorbents with superior EM wave absorption performances.

Synthesis of covalently bonded reduced graphene oxide-Fe_(3)O_(4) nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic(EM)wave absorbers,covalently bonded reduced graphene oxideFe_(3)O_(4) nanocomposites(rGO-Fe_(3)O_(4)),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe_(3)O_(4) nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe_(3)O_(4) nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe_(3)O_(4) is 2:1(sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss(RL)reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth(RL<-10 dB)is 6.32 GHz(11.68-18.0 GHz)with a matching thickness of 2.1 mm.Furthermore,radar cross section(RCS)simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption perfo rmance.This work provides a possible method for preparing efficient EM wave absorbers.

Construction of multiple interfaces and dielectric/magnetic heterostructures in electromagnetic wave absorbers with enhanced absorption performance:A review

The construction of structures with multiple interfaces and dielectric/magnetic heterostructures enables the design of materials with unique physical and chemical properties,which has aroused intensive interest in scientific and technological fields.Especially,for electromagnetic(EM)wave absorption,enhanced interface polarization and improved impedence match with high Snoek's limitation could be achieved by multiple interfaces and dielectric/magnetic heterostructures,respectively,which are benificial to high-efficiency electromagnetic wave absorption(EWA).However,by far,the principles in the design or construction of structures with multiple interfaces and dielectric/magnetic heterostructures,and the relationships between those structures or heterostructures and their EWA performance have not been fully summarized and reviewed.This article aims to provide a timely review on the research progresses of high-efficency EM wave absorbers with multiple interfaces and dielectric/magnetic heterostructures,focusing on various promising EWA materials.Particularly,EM attenuation mechanisms in those structures with multiple interfaces and dielectric/magnetic heterostructures are discussed and generalized.Furthermore,the changllenges and future developments of EM wave absorbers based on those structures are proposed.

3D flower-like hollow CuS@PANI microspheres with superb X-band electromagnetic wave absorption

Superior electromagnetic(EM)wave absorption properties in 8.2-12.4 GHz(X-band)can be obtained via the effective combination of polyaniline(PANI)and CuS.Herein,novel 3D flower-like hollow CuS@PANI microspheres were fabricated by a solvothermal process followed by in-situ polymerization.EM wave absorption properties of 3D flower-like hollow CuS@PANI microspheres in X-band were systematically studied,indicating the minimum reflection loss(RL_(min))of-71.1 dB and effective absorption bandwidth(EAB)covering 81%of test frequency range were achieved with a thickness of 2.75 mm.Excellent EM wave absorption properties of 3D flower-like hollow CuS@PANI microspheres were mainly ascribed to outstanding impedance matching characteristic and dielectric loss capability(conduction loss,interfacial polarization loss and dipole polarization loss).Moreover,due to the distinctive flower-like hollow struc-ture of CuS@PANI microspheres,an additional wave-absorbing mechanism was provided by increasing the transmission paths of EM waves.

Achieving ultra-broadband electromagnetic wave absorption in high-entropy transition metal carbides (HE TMCs)

Electronic devices pervade everyday life,which has triggered severe electromagnetic(EM)wave pollution.To face this challenge,developing EM wave absorbers with ultra-broadband absorption capacity is critically required.Currently,nano-composite construction has been widely utilized to realize impedance match and broadband absorption.However,complex experimental procedures,limited thermal stability,and interior oxidation resistance are still unneglectable issues.Therefore,it is appealing to realize ultra-broadband EM wave absorption in single-phase materials with good stability.Aiming at this target,two high-entropy transition metal carbides(HE TMCs)including(Zr,Hf,Nb,Ta)C(HE TMC-2)and(Cr,Zr,Hf,Nb,Ta)C(HE TMC-3)are designed and synthesized,of which the microwave absorption performance is investigated in comparison with previously reported(Ti,Zr,Hf,Nb,Ta)C(HE TMC-1).Due to the synergistic effects of dielectric and magnetic losses,HE TMC-2 and HE TMC-3 exhibit better impedance match and wider effective absorption bandwidth(EAB).In specific,the exclusion of Ti element in HE TMC-2 endows it optimal minimum reflection loss(RL_(min))and EAB of−41.7 dB(2.11 mm,10.52 GHz)and 3.5 GHz(at 3.0 mm),respectively.Remarkably,the incorporation of Cr element in HE TMC-3 significantly improves the impedance match,thus realizing EAB of 10.5,9.2,and 13.9 GHz at 2,3,and 4 mm,respectively.The significance of this study lays on realizing ultra-broadband capacity in HE TMC-3(Cr,Zr,Hf,Nb,Ta),demonstrating the effectiveness of high-entropy component design in tailoring the impedance match.

High-entropy spinel ferrites MFe_(2)O_(4)(M=Mg,Mn,Fe,Co,Ni,Cu,Zn)with tunable electromagnetic properties and strong microwave absorption

Ferrites are the most widely used microwave absorbing materials to deal with the threat of electromagnetic(EM)pollution.However,the lack of sufficient dielectric loss capacity is the main challenge that limits their applications.To cope with this challenge,three high-entropy(HE)spineltype ferrite ceramics including(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4),(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Cu_(0.2))Fe_(2)O_(4),and(Mg_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2)Zn_(0.2))Fe_(2)O_(4)were designed and successfully prepared through solid state synthesis.The results show that all three HE MFe_(2)O_(4) samples exhibit synergetic dielectric loss and magnetic loss.The good magnetic loss ability is due to the presence of magnetic components;while the enhanced dielectric properties are attributed to nano-domain,hopping mechanism of resonance effect and HE effect.Among three HE spinels,(Mg_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))Fe_(2)O_(4)shows the best EM wave absorption performance,e.g.,its minimum reflection loss(RL_(min))reaches-35.10 dB at 6.78 GHz with a thickness of 3.5 mm,and the optimized effective absorption bandwidth(EAB)is 7.48 GHz from 8.48 to 15.96 GHz at the thickness of 2.4 mm.Due to the easy preparation and strong EM dissipation ability,HE MFe_(2)O_(4) are promising as a new type of EM absorption materials.

Lightweight,self-cleaning and refractory FeCo@MoS_(2)PVA aerogels:from electromagnetic wave-assisted synthesis to flexible electromagnetic wave absorption

The emergence of wearable and foldable electronic devices urges advanced electromagnetic(EM)wave absorbers with maintained performance under deformation.Here FeCo@MoS_(2)poly vinyl alcohol(PVA)aerogels have been fabricated with the assistance of EM waves for simultaneous splitting of the MoS_(2)flakes and dispersive growth of FeCo nanoparticles.The resultants in-return have been used for EM wave absorption with excellent performance,providing minimum reflection loss(RL_(min))of-40.7 dB and a broad effective absorption bandwidth(EAB)of 6.4 GHz at a thickness of 2.5 mm.Real-time compression has been introduced to reveal the evolution of EM parameters.The aerogels maintain satisfactory performance even under 50%compression due to the balance of impedance matching and attenuation.Despite the deterioration of impedance matching,the attenuation is significantly enhanced due to both strengthened conductive loss and magnetic loss.In addition,features such as lightweight,self-cleaning and refractory can be achieved for the aerogels for applications in complex environments.As such this work not only provides a versatile synthetic route assisted by EM wave energy,but also insights on the evolution of absorption performance under deformation together with the design strategy of multifunctional flexible wave absorbers.

Bifunctional SiC/Si_(3)N_(4) aerogel for highly efficient electromagnetic wave absorption and thermal insulation

SiC ceramics are attractive electromagnetic(EM)absorption materials for the application in harsh environment because of their low density,good dielectric tunable performance,and chemical stability.However,the performance of current SiC-based materials to absorb EM wave is generally unsatisfactory due to poor impedance matching.Herein,we report ultralight SiC/Si3N4 composite aerogels(~15 mg·cm^(−3))consisting of numerous interweaving SiC nanowires and Si3N4 nanoribbons.Aerogels were prepared via siloxane pyrolysis and chemical vapor reaction through the template method.The optimal aerogel exhibits excellent EM wave absorption properties with a strong reflection loss(RL,−48.6 dB)and a wide effective absorption band(EAB,7.4 GHz)at a thickness of 2 mm,attributed to good impedance matching and multi attenuation mechanisms of waves within the unique network structure.In addition,the aerogel exhibits high thermal stability in air until 1000℃and excellent thermal insulation performance(0.030 W·m^(−1)·K^(−1)).These superior performances make the SiC/Si_(3)N_(4) composite aerogel promising to become a new generation of absorption material served under extreme conditions.

Multispectral ErBO_(3)@ATO porous composite microspheres with laser and electromagnetic wave compatible absorption

The high-speed advances in electromagnetic(EM)wave and laser detection technology have accelerated the innovation of absorbing materials toward specific multi-band compatibility.It is difficult to achieve dual absorption of EM waves and near-infrared lasers by absorbing materials in a single frequency band;the design of high-performance laser-EM wave multi-band compatible absorbing materials is imminent.Herein,ErBO_(3)@ATO(erbium borate/antimony-doped tin oxide)porous composite microspheres with an average size of 15-20μm are produced solvothermal method and self-assembly,which exhibit excellent laser-EM wave compatible absorption.The porous structure on the surface of ErBO_(3)microspheres provides heterogeneous nucleation sites for ATO particle deposition.The minimum reflectivity of the composite for1.06 and 1.54μm lasers is 9.59%and 4.79%,which is0.57%and 3.78%lower than those of pure ATO particles,respectively.The composites containing 70 wt%porous ErBO_(3)@ATO reveal the minimum reflection loss(RL)value of-31.6 dB,and an effective absorption band width reaches 2.08 GHz at 2.5 mm thickness.The mechanism of near-infrared laser and EM wave compatible absorption is the synergistic effect of the energy level transition of ErBO_(3)and the dielectric loss of ATO,coupled with the large surface area and porous structure of the micro spheres.Therefore,the designed porous ErBO_(3)@ATO composite microspheres can be an attractive choice for lasers and EM wave high-quality compatible absorption.

Interference of human's ankle to the channel characteristics of near surface WUSN

Because of its potential applications in agriculture, environment monitoring and so on, wireless underground sensor network（WUSN） has been researched more and more extensively in recent years. The main and most important difference of WUSN to terrestrial wireless sensor network（WSN） is the channel characteristics, which determines the design methodology of it. In this paper, the propagation character of electromagnetic（EM） wave in the near surface WUSN is analyzed, as well as the path loss model of it is given. In addition, the influence of human＇s ankle to the channel characteristics of near surface WUSN is investigated by electromagnetic theory analysis, simulation and experiment. A novel path loss model of near surface WUSN which takes the interference of human＇s ankle into consideration is proposed. It is verified that the existing of human above the WUSN system may cause additional attenuation to the signal of near surface WUSN which propagates as lateral wave along the ground. Moreover, the relation of the attenuation and operating frequency is deduced, which gives a reference to extend the frequency band applied in WUSN.

Electromagnetic wave manipulation based on few-layer metasurfaces and polyatomic metasurfaces

Metasurfaces,whose electromagnetic(EM)responses can be artificially designed,are two-dimensional arrays composed of subwavelength nanostructures.Accompanied by various fascinating developments in the past decade,metasurfaces have been proved as a powerful platform for the implementation of EM wave manipula-tion.However,the planar monoatomic metasurfaces widely used in previous works have limited design freedoms,resulting in some disadvantages for the realization of high-performance and new functional EM wave control.The latest developments show that few-layer metasurfaces and polyatomic metasurfaces are good alternatives to overcome the drawbacks of planar monoatomic metasurfaces and realize high-efficient,multi-band and broad-band EM functionalities.They provide additional degrees of design freedom via introducing multilayer layouts or combining multiple meta-atoms into a unit cell respectively.Here,recent advances of few-layer and polyatomic metasurfaces are reviewed.The design strategies,EM properties and main advantages of few-layer metasurfaces and polyatomic metasurfaces are overviewed firstly.Then,few-layer metasurfaces and polyatomic metasurfaces in recent progress for EM wave manipulation are classified and discussed from the viewpoint of their design strategy.At last,an outlook on future development trends and potential applications in these fast-developing research areas is presented.