EM Wave Attenuation Research Articles

MXene-derived titanate heterojunctions with lightweight and heat-resistant properties for electromagnetic wave absorption

The development of high-efficiency titanate-based electromagnetic wave (EMW) absorbers presents a significant challenge, primarily due to the limited number of loss mechanisms available in such materials. Herein, an innovative approach has been employed, utilizing g-C3N4 as a connecting bridge linking KTi8O16.5 nanorods with Fe2O3 nanoparticles, thereby crafting a KTO/Fe2O3–CN absorber with a dual heterojunction architecture. This sophisticated structure is realized through a detailed freeze-drying process followed by heat treatment. In this structure, g-C3N4 and KTi8O16.5 originate from melamine and MXene precursors, respectively, while Fe2O3 component is derived from the thermal decomposition of FeSO4. The integrated KTO/Fe2O3–CN system fosters enhanced interfacial and dipole polarization, as well as conduction and magnetic loss, all collaboratively aiding in the attenuation of EM waves. In addition, the specially designed EMW absorber is notable for its lightweight nature, along with impressive heat dissipation and resistant performance. It demonstrates exceptional thermal stability, capable of withstanding temperatures as high as 500 °C and sustaining repeated thermal cycles at 400 °C. This strategy not only elevates the efficacy of titanate-based EMW absorbers but also paves the way for the conceptualization of high-performance, multifunctional EMW absorption materials. Such advancements hold the promise of transforming a wide range of applications that necessitate effective EM wave attenuation, marking a significant leap forward in the field.

All-Around Electromagnetic Wave Absorber Based on Ni-Zn Ferrite.

Exploring a convenient, scalable, yet effective broadband electromagnetic wave absorber (EMA) in the gigahertz (GHz) region is of high interest today to quench its expanding demand. Ni-Zn ferrite is considered as a potential EMA; however, their performance study as a scalable effective millimeter-length absorber is still limited. Herein, we investigated EM wave attenuation properties of Ni0.5Zn0.5Fe2O4 (NZF) samples substituting Mn ion in place of Fe3+ as well as Zn2+ within a widely used frequency range of 0.1-9 GHz. Through composition optimization, Ni0.5Zn0.4Mn0.1Fe2O4 (NZM0.1F) EMA demonstrates excellent microwave absorption performance accompanied by simultaneous maximum reflection loss (RL) of -50.2 dB and wide BW of 6.8 GHz (with RL < -10 dB, i.e., attenuation >90%) at an optimum thickness of 6 mm. Moreover, the attenuation constant significantly increases from ∼217 to 301 Np/m with Mn doping. The key contribution arises from magnetic-dielectric properties synergy along with enhanced dielectric and magnetic losses owing to cation chemistry and site occupation in spinel NZF. In addition, porosity is induced in the system by a controlled two-step heat treatment process that promotes total loss with multiple internal reflections of the EM wave. Furthermore, RL is simulated by varying incident EM wave angles for the NZM0.1F sample displaying its angle insensitivity up to 50°. Our results reveal NZM0.1F as a futuristic environment-friendly microwave absorber material that is suitable for practical high-frequency applications.

Effect of carbon allotropes and thickness variation on the EMI shielding properties of PANI/NFO@CNTs and PANI/NFO@RGO ternary composite systems.

The innovative design of thin, multiphase flexible composite systems with good mechanical properties, low density and improved EMI shielding properties at low filler content has become a key area of research. In this work, we report the low temperature synthesis of three-dimensional ternary composites (PANI/NFO@CNTs and PANI/NFO@RGO) by oxidative chemical polymerization of aniline in the presence of two different binary composites, viz. NFO@CNTs and NFO@RGO. Enhanced impedance matching is achieved by varying the ratio of the carbon allotropes (CNTs and RGO) to the ferrite component. The synthesis of NFO, PANI/NFO@CNTs and PANI/NFO@RGO is validated by XRD and FTIR spectroscopy. Field emission scanning electron microscopy (FE-SEM) confirmed the synthesis of core-shell structures of PANI/NFO@CNTs and PANI/NFO@RGO, where the binary composites (NFO@CNTs and NFO@RGO) serve as a core onto which a tubular PANI layer was coated. Shielding effectiveness of 22.36 dB (99.41% attenuation) is exhibited by the ternary composite PANI/NFO@CNTs (8 : 1), while for PANI/NFO@RGO (20 : 1) a total shielding effectiveness of 31 dB equivalent to 99.92% attenuation was observed at a thickness of 2 mm. The ternary composite PANI/NFO@RGO (20 : 1) 4 mm showed a maximum SET of 43 dB corresponding to 99.996% attenuation of incident EM waves. The enhanced EMI shielding properties of the synthesized ternary composite systems are accredited to good impedance matching, effective dielectric and magnetic loss mechanisms and good conductivity, which facilitate multiple reflections and scattering of incident radiation.

Broadband microwave absorption effects in 2D nitrogen capacitively coupled plasma under different operating conditions

In recent years, the interaction of electromagnetic waves (EM) with plasma sources under argon and helium discharges has been extensively studied due to its potential applications in plasma stealth. However, nitrogen, as a more economical discharge gas, has been ignored in terms of its absorption of EM waves and stealth effect. In this work, a numerical calculation model combining two-dimensional capacitively coupled plasma (CCP) fluid model and EM wave model was developed to investigate the plasma uniformity degree and broadband microwave absorption effects in helium and nitrogen CCP. It is concluded that the two-dimensional model in this paper has more accurate and reasonable through comparison with the one-dimensional and experimental results in helium CCP. Nitrogen CCP shows better broadband absorption effects than that of helium, and helium plasma has better uniformity than nitrogen under the same discharge parameters. But the uniformity degree of nitrogen plasma is not much different from that of helium under the same electron density, which means that nitrogen can significantly improve its broadband wave absorption properties to some extent without loss of uniformity degree. Based on the above conclusions, the absorption characteristics of nitrogen CCP under different radio frequency (RF) power and pressure are analyzed. The attenuation effect of nitrogen CCP increases with the increasing RF power, and it is interesting that the influence of pressure on the attenuation of EM waves is not monotonically increasing, and the related mechanism is discussed. Finally, discussion of skin depth under different RF power and pressure validates the above conclusions. The absorption band of nitrogen CCP under the best parameters in this work can reach the X-band, which shows great application potential in plasma stealth.

Freestanding Foils of NbSe2 and Carbon Nanotubes for Efficient Electromagnetic Shielding

The presence of electromagnetic radiation is becoming an ongoing topic due to possible interference issues as well as potential health risks. Therefore, the development of electromagnetic interference (EMI) shielding materials is of utmost importance. Herein, a composite material for EMI shielding based on metallic niobium diselenide (NbSe2) and single-walled carbon nanotubes (CNTs) with a low loading of 3 wt % is reported. The NbSe2 + 3CNTs composite was prepared using a high shear-force homogenizer followed by vacuum filtration to obtain a freestanding foil with a thickness of 219 ± 22 μm. The EMI shielding effectiveness (SE) of the NbSe2 + 3CNTs composite was also compared with its building blocks. The EMI SEs at 12.4 GHz were 31.4, 48.5, and 62.7 dB for pure NbSe2, pure CNTs, and the NbSe2 + 3CNTs composite, respectively. Such excellent performance of our composite material is attributed to a synergistic effect between the NbSe2 and CNTs, where the CNTs not only increase the conductivity of the composite but also form an interconnecting network between the NbSe2 sheets, thus forming a 3D network with abundant sites for EM wave attenuation. It is the first study on the EMI shielding performance of a TMD other than MoS2-based material.

In-situ preparation of CoFe2O4 nanoparticles on eggshell membrane-activated carbon for microwave absorption

This study explores the potential of using cobalt ferrite (CF) nanoparticles grown in situ on eggshell membranes (ESM) to mitigate the increasing problem of electromagnetic interference (EMI). A simple carbonization process was adopted to synthesize CF nanoparticles on ESM. The study further examines the composites' surface morphology and chemical composition and evaluates their microwave absorption performance (MAP) at X-band frequency. Results showed that the composite of CF and ESM - CESM@CF, exhibited a strong RL peak value of −39.03 mm with an optimal thickness of 1.5 mm. The combination of CF and ESM demonstrates excellent impedance matching and EM wave attenuation. The presence of numerous interfaces, conduction loss from the morphology, interfacial polarisation, and dual influence from both CF and ESM contribute to the high MAP of the composite. CESM@CF composite is projected as an excellent biomass-based nano-composite for EM wave absorption applications.

Absorption-dominant EMI shielding polymer composite foams: Microstructure and geometry optimization

Absorption-dominant electromagnetic interference (EMI) shielding materials have garnered considerable attention to mitigate secondary EM pollution. The generation of a microcellular structure offers great promise in the development of absorption-dominant shielding materials. However, the underlying mechanisms governing the structure-EMI shielding properties relationship of microcellular shielding materials have rarely been studied. In this work, an input impedance model was applied to explore the thickness dependency of reflectivity (R) in microcellular conductive polymer composite (CPC) foams and then decouple the effect of thickness on the R-value from other structural variables, such as the void fraction (VF) and cellular morphology. As suggested by a theoretical model, PVDF/carbon nanotube (CNT)/SiC nanowire (SiCnw) composite foams having a 65% VF were fabricated. Absorption-dominant EMI shielding effectiveness was achieved by changing the foam thickness from 1.4 to 2.4 mm, with a decreased R-value from 0.63 to 0.48 and a correspondingly increased absorptivity/reflectivity (A/R) ratio from 0.53 to 1.07 (102%). Also, by increasing the VF from 0% to 85% while maintaining a constant cell size of around 10 μm, the optimal A/R ratio for each VF increased from 0.35 to 1.61. Furthermore, it was demonstrated that increased cell density in the cellular morphology with a fixed VF can create additional solid/air heterogeneous interfaces, promoting the EM wave attenuation capability via internal scattering and reflection of the incident EM waves. Consequently, this work allows for theoretically driven fabrication of absorption-dominant EMI shielding CPC foam with a tailored A/R ratio.

Attenuation of EM Waves Emitted From Inset Feed Type Microstrip Rectangular Patch Antenna by Wet Snow

Microstrip patch antennas stand out because of their low cost, smaller size and easy fabrication. The study presents the design of a microstrip rectangular patch antenna operating at 2.6 GHz frequency and the effect of different weather conditions on the antenna. During the antenna design on CST program and manufacturing in the laboratory, it is aimed to perform the measurement at the desired frequency and decibel level. The study includes experiments and results made on different types of snow, apart from the normal measurement with the VNA. A good S11 scattering value was obtained at the desired frequency in the designed microstrip patch antenna as -18.48 dB. This value decreased to around -5 dB when there was wet snow on the antenna due to attenuation and thermal effects. If the snow was removed from the antenna, the old S11 value could not be returned because of the wetness left by the snow, and it remained at approximately -14 dB. Consequently, the attenuation of the electromagnetic waves have been confirmed by the literature under different conditions as wet snow with nano VNA for the first time. Attenuation by wet snow and water is greater than dry snow with voids.

Superhydrophobic and thermally conductive carbon black/hexagonal boron nitride@Fe3O4/cellulose composite paper for electromagnetic interference shielding

Herein, a series of superhydrophobic thin polyacrylic resin-coated carbon black (CB)/hexagonal boron nitride (h-BN)@Fe3O4/cellulose composite papers with good flexibility, low density (~0.67 g/cm3), high electrical conductivity (~0.065 S/cm), good thermal conductivity (0.462 W.m−1. K−1), and with water contact angle (WCA) of 153° were successfully fabricated by a facile dip-coating/spraying method. The CB-BN@Fe3O4 distribution in cellulose matrix provided high electrical conductivity in the in-plane and thickness directions. The electrical conductivity in both in-plane and thickness directions increased by increasing the number of vacuum-assisted dip-coating cycles. Moreover, these composites exhibited excellent electromagnetic interference shielding effectiveness (EMI SE) in the frequency range of 8.2–12.4 GHz. The absorption was the main mechanism for attenuation of EM waves for this composite paper. A multilayer of this composite with 12 wt% filler exhibited a higher EMI SE of 68.2 dB compared to its monolayer composite. The composites showed good thermal stability and excellent stability against washing and 150 times bending tests. Overall, this study proposes that polyacrylic resin-coated CB/BN@Fe3O4/cellulose papers can be used as wallpaper in buildings such as hospitals and antenna rooms that are exposed to electromagnetic waves.

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.

Effect of non-ionizing reaction rate (assumed to be controllable) on the plasma generation mechanism and communication around RAMC vehicle during atmospheric reentry

Radio frequency (RF) blackout occurs during radio attenuation measurement C (RAMC) vehicle reentry due to the attenuation effect of the plasma sheath on the communication signal. In recent years, the mitigation mechanism of chemical reaction for RF blackout problem has gradually been studied numerically and experimentally. However, the effect of non-ionization reaction rate has been ignored because it does not directly involve the generation of electrons. In the present study, the influence of non-ionizing reaction rate on the plasma generation mechanism and EM wave attenuation was numerically solved by the plasma flow and multilayer transmission model. According to the simulation results, only the reaction rate of NO rightleftharpoons N + O has a significant effect on the electron number density in all non-ionizing reactions, and the degree of influence is less than the ionization reaction rate. The EM wave attenuation decreases with the decrease of the reaction rate of NO rightleftharpoons N + O. When the reaction rate is reduced by 25 times, the maximum attenuation of electromagnetic wave can be reduced by 12 dB. Finally, a potential scheme by reducing the reaction rate of NO rightleftharpoons N + O was proposed to mitigate the RF blackout problem.

NiO nanosheets on pine pollen-derived porous carbon: construction of interface to enhance microwave absorption

Efficient microwave absorbing materials have been drawn extensive attention. Herein, biomass porous carbon (BPC) from pine pollen has been obtained through KOH carbonization. In order to tune the microwave absorption, NiO has been composited with the as-prepared BPC with different contents. Despite the high specific surface area for the BPC activated at 600 °C, it exhibits poor microwave absorption properties as pure NiO. In contrast, the BPC/NiO composite with proper nickel precursor (0.1:1.0) has the maximum reflection loss (RL) of − 52.6 dB at 10.0 GHz and the effective absorption bandwidth (RL < − 10 dB) reaches up to 4.9 GHz (from 7.8 to 12.7 GHz) when the absorber thickness is 3 mm. Three-dimensional porous architecture, interfacial polarization and their related relaxation from defects and interfaces cooperatively favor the impedance matching and strong EM wave attenuation capacities, which brings about multiple absorption mechanisms of the microwave. The present study not only provides a facile route to prepare porous carbon, but also sheds light on a new strategy in constructing BPC/NiO composites for excellent microwave absorption.

Effect of Temperature and Frequency on Microwave Shielding Behaviour of Functionalized Kenaf Fibre-Reinforced MWCNTs/Iron(III) Oxide Modified Epoxy Hybrid Composite

A strong conductive and magnetically strengthened microwave shielding hybrid epoxy composite was prepared and analyzed. The principal aim of this research work was to prepare a high stable microwave shielding hybrid epoxy composite with surface modified MWCNTs and iron(III) oxide nano particles. The surface-modification on these reinforcements favour the composites been retained their magnetic and electrical conductivity even in elevated temperatures 100 °C and 200 °C and frequency up to 50 GHz. The kenaf fibre, MWCNTs and iron(III) oxide particles were surface-modified by APTMS for effective protection of reinforcements. The composites were prepared using hand layup method. The additions of silane-treated kenaf fibre and MWCNTs with iron(III) oxide into epoxy resin improved the mechanical properties, the same has been discussed in the previous article by the author. The silane surface-modified composites gave unaltered dielectric constant and microwave shielding behaviour in elevated temperatures. The acquisition of residual magnetism remains same as room temperature and 200 °C. The maximum relative magnetic permeability of 1.2 and dielectric constant of 4.0 was observed for composite designation ‘E’ in room temperature. Similarly maximum EM wave attenuation of 44 dB was achieved in J band frequency at 200 °C. These high stable microwave shielding composite materials are capable of serving as shielding materials in electronic communication gadgets, radar and microwave shielding helmets.

Study on Electromagnetic Wave Absorption performance of Dendritic-like Co

Dendritic-like Co particles consisting of leaf-shaped nano-units were successfully synthesized by chemical reduction method. The absorbing particles have abundant multi-stage branches. Since the crystal structure, size and special morphology have an important influence on the microwave absorption performance, the X-ray diffractometer, scanning electron microscope, vibration sample magnetic measurement and vector network analysis are used to characterize the dendritic Co. Absorbing mechanism was analyzed systematically. The nano-sized, multi-stage branches, porous structures and rough surfaces of the prepared particles all contribute to the penetration, scattering and attenuation of EM waves. Hence the composite, in the test band, especially in the S-band (2-4 GHz), presents excellent microwave absorption properties.

Sodium citrate assisted hydrothermal synthesis of nickel cobaltate absorbers with tunable morphology and complex dielectric parameters toward efficient electromagnetic wave absorption

NiCo2O4 was synthesized by sodium citrate assisted hydrothermal method. Four NiCo2O4 samples were fabricated by changing the ratio between sodium citrate and metal ions (0.5, 1, 1.5 and 2). Morphology evolution from 3-dimensional flower-like structure to 2-dimensional nanosheet structure is observed as the ratio between sodium citrate and metal ions increased from 0.5 to 2. In addition to the morphology, the complex permittivity of NiCo2O4 can also be simply adjusted by regulating the addition amount of sodium citrate. The decent complex permittivity was obtained when the ratios between sodium citrate and metal ions were 0.5, 1 and 1.5. The optimal absorber (sodium citrate: metal ions = 1.5: 1) displays high absorption capacity of −47.9 dB and wide effective absorption bandwidth (EABs) of 4.28 GHz (from 13.72 GHz to 18 GHz) at ultrathin thickness of 1.39 mm. This NiCo2O4 absorber, possessing high absorption capacity as well as wide adsorption bandwidth, is the thinnest pristine NiCo2O4 absorbers currently reported. The high EM wave attenuation performance is ascribed to the well matched impedance originated from the rational design of complex permittivity values, and other dissipation mechanism, including dipole polarization, interfacial polarization and conduction loss, etc. This work may provide us a novel strategy for regulating the effective absorption band of other Co-based spinel structure EM wave absorption materials.

Stretchable microwave absorbing and electromagnetic interference shielding foam with hierarchical buckling induced by solvent swelling

Abstract Wearable devices and morphing aircrafts require stretchable microwave absorbing (MA) and electromagnetic interference (EMI) shielding materials, which could work as EMI shielding clothes and battleplane coatings. Although conductive foams could work well in both microwave absorption and EMI shielding, their performances under stretching have not been studied thus far, which is possibly due to the difficulty in maintaining the electrical conductance under stretching. Herein, a carbon nanotube/polyurethane (PU) foam with hierarchical buckling structure is prepared as a stretchable MA and EMI shielding material. The foam is fabricated by dip-coating PU foam in carbon nanotube/organic solvent solution. The PU foam swells in organic solvents and forms hierarchical buckling structures upon drying. After reinforcement with Ecoflex, the composite shows a suitable degree of stability in its resistance during stretching. Hierarchical buckling can maintain the conductance during stretching and enhance the attenuation of EM waves. A minimum microwave absorption reflection loss of −35.6 dB at a 10% strain level in 2–18 GHz and an average EMI shielding effectiveness of 20.2 dB at a 30% strain level in X-band are achieved. These results represent a new step towards the application of elastic and stretchable electronic materials for electromagnetic wave protection.

Electrospinning of lightweight TiN fibers with superior microwave absorption

In this work, the titanium nitride (TiN) ceramic fibers with average diameter of ~ 1 μm and length of tens of micrometer range were synthesized by electrospinning followed by thermal nitridation reaction. And their dielectric property and EM wave absorption performance were investigated in the GHz range. Due to the strong high-frequency polarization effect resulted from the large surface contact area of the obtained TiN fibers, satisfactory EM wave attenuation was achieved with a low absorbent content of only 14.5 wt%. Specifically, the composite TiN fibers displayed an ultrawide effective absorption bandwidth of 4.1 GHz with > 90% EM attenuation and an optimal reflection loss as high as − 47.2 dB at the thickness of 2 mm. The combined excellent EM absorption property with high-temperature and corrosion resistance, simple production procedure and low cost endow TiN fibers as a promising candidate for lightweight microwave absorption materials suitable for harsh application conditions.

Underwater Localization using Received Signal Strength of Electromagnetic Wave with Obstacle Penetration Effects

In this paper, we discuss a range sensor model using EM wave attenuation for localizing in an underwater environment with obstacles. Because an acoustic sensor is unsuitable for environment with obstacles due to the multi-path effect and diffraction, we propose a alternative range estimation method using EM wave attenuation. By considering the penetration distortion effect with underwater distance-signal attenuation model, we defined a robust EM wave attenuation function in the environment with obstacles. We performed the several experiments in order to determine the calibration factors according to the material, and the obstacle model is developed. Also, we obtained a robust localization results using the obtained sensor model with obstacle penetration effects.

Porous magnetic carbon nanofibers (P-CNF/Fe) for low-frequency electromagnetic wave absorption synthesized by electrospinning

The recent criteria to evaluate electromagnetic wave absorber include low density, strong absorbency, wide absorption bandwidth and thin absorber thickness, but its performance at low frequencies is always ignored. In this paper, the porous magnetic carbon nanofibers (P-CNF/Fe) for high-efficient electromagnetic wave absorption at low frequencies were fabricated by electrospinning followed by stabilization and carbonization. With the introduction of porous nanostructure, the permittivity of carbon nanofibers was decreased at low frequency and the impedance matching of permittivity and permeability was realized. The electromagnetic absorbing properties were investigated in detail. The minimum reflection coefficient reaches −44.86 dB at 4.42 GHz, and the widest effective absorption bandwidth (EAB) in the frequency was 3.28 range from 12.96 to 16.24 GHz. Consequently, considering the EM wave absorption performance, P-CNF/Fe synthesized in this work can be a promising candidate in the field of EM wave attenuation.

Relationship between the velocity of hypersonic vehicles and the transmission efficiency of radio waves

ABSTRACTAnalyzing the flow field distributions around a near-space blunt-cone vehicle at different flight speeds, we observe that, when the flight speed exceeds a certain threshold, the relationship between the flow field density and the vehicle speed presents a characteristic opposite to that at the flight condition of the speed lower than the threshold. On this basis, the Runge–Kutta method is applied to solve the ray equations in non-uniform plasma, in which the electron density at any computing point is obtained by the Lagrange interpolation based on the discrete data of the flow field. Then the EM wave attenuation in the sheath is determined by the subsection integral method combining with the electromagnetic theory. The numerical results also show that when the flight velocity is lower than the threshold, the energy transfer efficiency of the EM waves decreases with the increase of the vehicle velocity. However, when the flight speed is greater than the threshold, the energy transfer efficiency increases as the vehicle speed increases. This conclusion will be helpful to further understand the EM wave propagation characteristics for hypersonic vehicles, and to provide a reference for the channel selection of antennas.