Maximum Effective Bandwidth Research Articles

Ingeniously construction of industrial carbon fiber/nickel-iron layered double hydroxide heterostructure composite for high-efficient microwave absorption in aircraft

To enhance the survivability of military aircraft in electromagnetic warfare, carbon fiber/nickel-iron layered double hydroxide (CF/NiFe-LDH) composites with heterogeneous structure were constructed starting from the raw industrial carbon fiber (CF) by electrostatic self-assembly. By reasonably adjusting the mass ratio of CF and NiFe-LDH, the voids formed by LDH arrays stacked on the fiber surface are utilized to promote reflection and scattering of electromagnetic wave (EMW), optimizing impedance matching, as well as synergize dielectric-magnetic dual loss mechanism. Moreover, interfacial polarization effect induced by the abundant heterogeneous interfaces significantly enhance the ability of EMW dissipation. The optimized CF/NiFe-LDH heterostructure composite exhibits the minimum reflection loss (RLmin) value of −52.48 dB at mere 1.77 mm thickness and an expansive maximum effective bandwidth (EABmax) of 7.29 GHz at 2.14 mm. In addition, the computer simulation technology (CST) revealed that the radar scattering cross section (RCS) reduction of composites reaches up to 26.92 dBm2 at an incidence angle of 90°, demonstrating their excellent radar attenuation capability. Tremendously, the heterogeneous composites achieve an SRL1 value of 524.8, which is appreciably better than most of the EMW absorbing materials. The wondrous characteristics including lightweight, ultra-thin, high-efficient microwave absorbing ability of CF/NiFe-LDH heterostructure composites display potential application in fighter aircraft.

The effect of conduction loss on microwave absorption performance of Fe-doped NiCo2O4 spinel oxide

Strong absorption and large bandwidth are two contributors to material’s electromagnetic wave absorbing performance. While spinel ferrite materials have garnered extensive attention in the realm of microwave absorption, their relatively low conductivity remains a practical challenge.In this work, NiCo2-xFexO4 (x = 0, 0.04, 0.06 and 0.08) precursor was prepared by hydrothermal and after-sintered method. It was found that Fe doping exhibit excellent EM absorption properties. Specially, when the Fe content is 0.08, the maximum reflection loss −48.90 dB at 15.40 GHz and the maximum effective bandwidth 4.20 GHz are achieved. More importantly, the absorption frequency can be broadened from Ku to C band even to S band with proper adjusting Fe content. Doping with Fe enhances conduction loss and make a significant contribution to dielectric loss, as a result, the impedance matching degree of the Fe-NiCo2O4 composite is influenced by the synergistic effect of its dielectric and magnetic properties. This work provides a simple way for enhancing the microwave absorption capabilities of ferrite materials and provides insight into understanding conduction loss in microwave absorption.

Design, modeling and experiments of bistable piezoelectric energy harvester with self-decreasing potential energy barrier effect

It is difficult for conventional bistable energy harvesters to undergo interwell motion in weak excitation environment. In this study, a bistable energy harvester with self-decreasing potential energy barrier effect is proposed, which innovatively turns a fixed end of S-shaped generator beam into the movable end with a spring oscillator, which effectively decreases the potential energy barrier and makes the harvester susceptible to interwell motion. Furthermore, a theoretical analysis of the nonlinear driving magnetic force and the system governing equations is carried out, then a numerical simulation of potential energy surface of harvester is performed to demonstrate the effect of the self-decreasing potential energy barrier in detail. The effect of spring pre-compression and stiffness of the moveable end on the system potential energy is analyzed by numerical simulation. Finally, the key parameters affecting the output performance, such as spring pre-compression, magnets distance, and external load resistance, are analyzed. The harvester has a maximum effective bandwidth of 6.62Hz (4.61–11.23Hz), a maximum peak-to-peak voltage of 10.2V, an RMS voltage of 1.3V, and a maximum output power of 2.91 μW. The proposed harvester achieves efficient broadband energy harvesting in low frequency environments.

Sustainable chitosan derived 3D hierarchically porous carbon aerogel toward advanced infrared-radar compatibility

Simultaneously achieving infrared-radar compatibility in one material is an important challenge for multi-spectral compatible stealth technology. Chitosan-derived three-dimensional (3D) hierarchically porous carbon aerogel can effectively solve the problem. Inspired by floors-pillars concept, this work elaborately designed and successfully fabricated 3D skeletons consisted of two-dimensional (2D) sheets and one-dimensional (1D) struts. Benefiting from esterification and directional freeze drying method, the entire network could provide sufficient space for reducing thermal conductivity and motivating dipole polarization sites. Thanks to the facile calcination process, conductive components could be obtained, which guarantee low infrared (IR) emissivity and high conduction loss performance. In this work, the as-prepared carbon aerogel with ultra-low density of 0.005 g cm−3 exhibits superb infrared stealth property. It shows a low thermal conductivity coefficient of only 0.0933 W m−1 K−1. In addition, the heating rate of the upper surface is slow when placed on a heating platform of 60 °C. The relevant IR emissivity value is as low as 0.563 in 3–5 μm band and 0.432 in 8–14 μm band. Under relatively thin thicknesses, the prominent radar stealth performance including the optimum reflection loss value of −75.90 dB, the maximum effective bandwidth of 3.93 GHz, and the simulated radar cross section reduction value of 27.66 dB m2, can be obtained. This study not only introduces innovative design ideas but also offers technical approaches, facilitating further development in the realm of infrared-radar compatible stealth.

Design and optimization of double-layer structure for improved electromagnetic wave absorbing characteristic of single-layer foam cement-based materials containing carbon black

Electromagnetic wave (EMW) absorbing properties are increasingly needed in cement-based materials; however, lightweight and broadband absorption properties are challenging to realize. This study aims to create lightweight, broadband, and highly efficient EMW-absorbing materials by investigating a foam cement-based material with single- and double-layer structures containing carbon black (CB). The results revealed that CB significantly affects the mechanical properties and electrical conductivity of foam cement-based materials. The compressive strength of the foam cement-based material containing 1.5 wt% CB with a density of 0.9 g cm−3 can reach 7.0 MPa and has satisfactory workability and conductivity. The dielectric properties of the foam cement-based material can be synergistically controlled by its density and CB content, and obtain favorable electric loss ability. For a single-layer structure, the optimal reflection loss (RL) value of a specimen with 10 mm-thick can reach −29.67 dB with an efficient bandwidth of 0.99 GHz. In contrast, the double-layer structure exhibited remarkable broadband characteristics. When the total thickness of double-layer structure is 10 mm, the optimal two specimens can achieve a minimum RL value of −28.62 and −25.52 dB with a maximum effective bandwidth of 1.49 and 1.87 GHz, respectively. This study proposes single- and double-layer foam cement-based structures with excellent impedance matching and loss attenuation ability, and constructs an effective design method for cement-based materials to achieve lightweight and broadband absorption. In addition, these cement-based materials can be regarded as a new generation of EMW-absorbing materials in the field of construction engineering.

Microwave Absorption Performance of One-dimensional Mixed Metal Oxide Nanocomposite

Abstract: Microwave-absorbing materials have received numerous attentions in terms of their key roles in the fields of stealth technology and controlling electromagnetic radiation pollution. In this paper, we aim to develop one-dimensional CoFe2O4-TiO2 mixed metal oxide nanocomposite via combination of sol-gel method and electrospinning technique. and investigate its microwave absorbing capability. The phase evolution from precursor fiber to final product and corresponding micromorphology are characterized, and microwave absorption performance for different CoFe2O4-TiO2 composite fibers are investigated with a vector network analyzer in 2-18 GHz. The prepared CoFe2O4-TiO2 mixed metal oxide composite fibers exhibit excellent microwave absorbing ability. The low reflection loss can reach -32.8 dB, and the maximum effective bandwidth is up to 6 GHz (12-18 GHz) at the thickness of 4 mm. The results further reveal that the lightweight mixed metal oxide composite fiber is promising for applications in electromagnetic attenuation and other related research fields.

Synthesis of ZSM-5/FexOy@C/Ni microspheres for enhanced electromagnetic wave absorption

Reasonable microstructure design and composition of absorbing materials are essential to improve absorbing properties. In this paper, ZSM-5/FexOy@C/Ni composite absorbing material with double core-shell structure was prepared by hydrothermal method and sol-gel method. The composite's structure, morphology, chemical composition, and magnetic properties were studied. The surface and C layer of ZSM-5 were densely covered with FexOy and Ni nanoparticles, respectively. At the same time, the uniform distribution of magnetic units can effectively improve the spatial distribution of magnetism. It was worth noting that the optimized composites had excellent microwave absorption properties. When the sample thickness was 2.5 mm, the minimum reflection loss of the sample could reach −21.4 dB, and the maximum effective bandwidth could reach 5.4 GHz. It was found that by changing the carbon layer's thickness, the prepared sample's absorption property could be adjusted to achieve the best impedance matching. The superior electromagnetic absorption performance of ZSM-5/FexOy@C/Ni composite microspheres was due to the synergistic effect of dielectric loss and magnetic loss and the enhanced porous core-shell interface effect. These results indicated that the composite could be used as a promising new type of high-performance absorbing material.

Synthesis of Fe3O4@SiO2@C/Ni microspheres for enhanced electromagnetic wave absorption

With the rapid development of electromagnetic and radar technology, military stealth technology has become an essential measure of a country's military strength. In this paper, hydrothermal and improved Stober methods prepared the composite absorbing material Fe3O4@SiO2@C/Ni with a double core-shell structure. The minimum reflection loss of the sample is −38.9 dB, and the maximum effective bandwidth is 10.1 GHz. By changing the thickness of the carbon layer and the thickness of the SiO2 layer, the absorption performance of the prepared sample can be adjusted to achieve the best impedance matching. The synergistic effect of the composite's dielectric loss and magnetic loss improves its microwave absorption capacity, making it a promising choice for absorptive material applications.

Toward high performance microwave absorber by implanting La0.8CoO3 nanoparticles on rGO

The advent of “intelligent era” brings our life more convenience, but the electromagnetic radiation surrounding us not only greatly threatens human health, also makes information leakage and hidden trouble to national defense security. Hence, it is very urgent to develop novel electromagnetic wave absorption materials with lightweight, strong absorption, tunable absorption frequency and broad band absorption. Herein, a novel electromagnetic wave absorber is obtained by constructing La0.8CoO3-rGO nanocomposite, where La0.8CoO3 nanoparticles are anchored on graphene nanosheets by the electrostatic interaction between GO and La0.8CoO3. The effect of hybridization ratio of La0.8CoO3 and rGO on microwave absorption properties is carefully studied. The optimal reflection loss of La0.8CoO3-rGO nanocomposite can reach -62.34 dB with the maximum effective bandwidth of 6.08 GHz, presenting 48.78% and 245.45% increment compared to bare La0.8CoO3 nanoparticles, respectively. The effective absorption bandwidth covers a broad electromagnetic wave absorption band from Ku band to the C band by tailoring thickness of the absorbers from 2.4 mm to 4.4 mm. The fascinating electromagnetic wave absorption performance is attributed to the synergy effect of La0.8CoO3 and rGO, which integrates magnetic and dielectric loss caused by resonance, conductance, relaxation, and scattering loss. This result confirms that La0.8CoO3-rGO nanocomposite is potential candidates toward high-efficiency microwave absorbers and provides a valuable pathway for designing high-performance microwave attenuation materials in the future.

Carbon–ceramic nanofiber embedded with LDHs-derived composites for enhanced electromagnetic wave absorption

Hydrotalcite-like layered double hydroxides (LDHs) exhibit distinct microstructures and atomic compositions, and thus, they are expected to be superior microwave absorbing materials. However, preparation of excellent absorbers from LDHs is still a challenging task. Herein, NiCo-LDHs@SiC/C heterostructure composites were designed and then heat-treated to obtain NiCo@SiC/C nanofibers. Finally, with a synergistic effect of dielectric and magnetic losses, the minimum reflection loss value of the sample could reach −56.3 dB with a thickness of 2.7 mm, and the maximum effective bandwidth absorption reached 6.8 GHz at 2.3 mm. Moreover, the simulated radar cross-section indicates that the NiCo@SiC/C nanofibers well suppress the electromagnetic scattering from metal trench structure. This result further indicates the outstanding microwave absorption properties of the nanofibers. This study contributes to the development of LDH materials in the field of wave-absorbing materials, and is an important guideline for exploring efficient microwave absorbers with fibrous structure.

In‐Situ Fabrication of Sustainable‐N‐Doped‐Carbon‐Nanotube‐Encapsulated CoNi Heterogenous Nanocomposites for High‐Efficiency Electromagnetic Wave Absorption

Developing carbon encapsulated magnetic composites with rational design of microstructure for achieving high-performance electromagnetic wave (EMW) absorption in a facile, sustainable, and energy-efficiency approach is highly demanded yet remains challenging. Here, a type of N-doped carbon nanotube (CNT) encapsulated CoNi alloy nanocomposites with diverse heterostructures are synthesized via the facile, sustainable autocatalytic pyrolysis of porous CoNi-layered double hydroxide/melamine. Specifically, the formation mechanism of the encapsulated structure and the effects of heterogenous microstructure and composition on the EMW absorption performance are ascertained. With the presence of melamine, CoNi alloy emerges its autocatalysis effect to generate N-doped CNTs, leading to unique heterostructure and high oxidation stability. The abundant heterogeneous interfaces induce strong interfacial polarization to EMWs and optimize impedance matching characteristic. Combined with the inherent high conductive and magnetic loss capabilities, the nanocomposites accomplish a high-efficiency EMW absorption performance even at a low filling ratio. The minimum reflection loss of -84.0dB at the thickness of 3.2mm and a maximum effective bandwidth of 4.3GHz are obtained, comparable to the best EMW absorbers. Integrated with the facile, controllable, and sustainable preparation approach of the heterogenous nanocomposites, the work shows a great promise of the nanocarbon encapsulation protocol for achieving lightweight, high-performance EMW absorption materials.

Microwave absorbing properties of electrodeposited mixed flake-like and dendritic-like FexNi1−x alloy particles

Electrodeposition as a simple and effective method is widely used in the production of metallic materials. In this paper, we prepared mixed flake-like and dendritic-like FexNi1−x (x = 0.5, 0.33, 0.25, 0.2) alloy particles by electrodeposition in constant current mode using fluorocarbon surfactant (FS) and emulsifier OP-10 (OP-10) as the surfactants. The crystal structure, morphology and electromagnetic properties of FexNi1−x were characterized by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, and vector network analysis. The effects of different values of x on the morphologies and structures of the FexNi1−x particles were investigated. The growth mechanism of FexNi1−x from hemispherical to a mixture of dendritic and flaky structures was discovered. The electromagnetic parameters and microwave absorbing properties of the composites of the FexNi1−x were studied in 2–18 GHz. All FexNi1−x alloy particles have good absorbing properties, among which the prepared Fe0.25Ni0.75 exhibits the best microwave absorption properties, whose minimum reflection loss (RLmin) reaches − 68.64 dB at 5.76 GHz when the thickness is 3.4 mm, and the maximum effective bandwidth (RL<−10 dB) is 4.56 GHz when the thickness is 1.5 mm. The excellent microwave absorbing property of Fe0.25Ni0.75 is from its excellent impedance matching characteristics.

Core-shell CuCo2S4 based microspheres composited with carbon black nanoparticles for effective microwave absorption

CuCo2S4 with core-shell structure was prepared by ion exchange self-template method, and the microwave absorption property of CuCo2S4 with this morphology was studied. At 30% filling, the maximum effective bandwidth is 4.88 GHz (13.12–18 GHz, 2 mm), and the strongest absorption peak is − 25.52 dB (18 GHz, 1.7 mm). In order to optimize the absorption performance of core-shell CuCo2S4, conductive carbon black nanoparticles were blended with core-shell CuCo2S4 to obtain CuCo2S4/C composite. Compared with single-phase CuCo2S4 absorber, the maximum effective bandwidth of the composite increased to 6.00 GHz (12.00–18 GHz, 2 mm), and the strongest absorption peak increased to − 52.60 dB (15.42 GHz, 1.9 mm). These results demonstrated that the introduction of small amount of conductive carbon black nanoparticles not only optimize the impedance matching, but also enhance the polarization loss of the composite, therefore, comprehensively improve the microwave absorption performance of the samples.

Boosting microwave absorption performance of bio-carbon flakes via magneto-alignment

Besides composition, macrostructure of a material is also crucial to its microwave absorption performance. In this work, we demonstrate a magneto-alignment effect on the microwave absorption property of the bio-carbon flakes synthesized from phoenix tree leaves. When a magnetic field is applied, the prepared bio-carbon flakes tended to be aligned into a desired direction due to their diamagnetic feature. Moreover, a rotating magnetic field has a better magneto-alignment effect than a static one, which significantly boosts microwave absorption efficiency. By adjusting parameters, conditions have been optimized, i.e., 10 wt% mass concentration, 760 Gs magnetic field intensity, and 15 rpm rotating speed. At optimized conditions, the maximum reflection loss of −49.7 dB at 6.6 GHz and the maximum effective bandwidth of 4.9 GHz (10.66–15.56 GHz) are achieved. It is discovered that the maximum reflection loss of the sample treated in a rotating magnetic field is 4.6 and 5.85 times higher than that of the sample treated in static and non-magnetic field conditions, respectively. This work provides a simple and environmentally friendly physical route to modify the macroscopical order degree and enhance the microwave absorption performance of carbon materials.

Microwave absorption performance of porous heterogeneous SiC/SiO2 microspheres

It is confirmed that the composites with multiple components and plentiful heterogeneous interfaces have been considered as preferred efficient electromagnetic (EM) wave absorbers. The special structure for hollow, porous, and core-shell has good adjustable dielectric properties. Herein, porous heterogeneous SiC/SiO2 microspheres are prepared based on the self-assembly technology and carbothermal reduction strategy. The structural evolution and composition control of porous heterogeneous SiC/SiO2 microspheres can be achieved by adjusting the carbothermal reduction temperature. The results indicate that structure and composition have a significant effect on the absorption performance. Especially, when the temperature is 1400 °C, the porous heterogeneous SiC/SiO2 microspheres exhibit the most excellent EM wave absorption properties; the minimal reflection loss (RLmin) value is −54.68 dB at 8.99 GHz. The maximum effective bandwidth (EABmax) for RLmin < −10 dB reaches 8.49 GHz, exhibiting absorption capacity in almost all bands (S, C, X, and Ku bands). It can well satisfy the comprehensive requirements of efficient EM wave absorption absorbers for lightweight and broad EAB characteristics. The excellent performance is due to the strong interfacial polarization caused by plentiful heterogeneous interfaces between different phases. Meanwhile, a highly porous structure and SiO2 phase can regulate complex dielectric constant, leading to better impedance matching. This work provides useful thinking for the design of efficient EM wave absorption absorbers.

Synthesis of nitrogen-doped polyaniline-derived carbon/Ni3Fe nanocomposites as high-performance microwave absorbers

Polyaniline-derived carbon (PDC) and Ni3Fe composites for electromagnetic wave (EMW) absorption were prepared through in-situ polymerization and carbonization. Using polyaniline as carbon source not only realized the doping of carbon with nitrogen, but also allowed homogeneous dispersion of Ni3Fe nanoparticles to achieve multiple reflection interfaces. The content of Ni3Fe can be used to control the impedance matching of the composites, while the dual loss mechanism of dielectric loss and magnetic loss was realized to promote EMW absorption performance. The polyaniline-derived carbon/Ni3Fe (PDC/Ni3Fe) nanocomposite with optimized composition had a minimum reflection loss (RL) of − 80.91 dB. A maximum effective bandwidth of 6.10 GHz (11.90 −18.00 GHz) was achieved, while the thickness is 2.12 mm.

Outstanding microwave absorption behavior and classical magnetism of Y1-K FeO3 honeycomb-like nano powders

Yttrium perovskite ferrite has a stable and symmetrical crystal structure and a simple preparation route. However, it exhibits poor absorption performance at 17–18 GHz. Several studies in the past have reported on the formation of mixed-valence states induced by the addition of monovalent K ions. In this study, YFeO3 was synthesized by doping with monovalent K via the sol-gel auto combustion method. This greatly optimized the wave-absorbing properties and effective bandwidth of YFeO3. The influence of different K additions on the absorption properties of the materials was also studied. All the hybrid composites showed excellent absorbing properties, with Y0.8K0.2FeO3 having an effective bandwidth of 4.88 GHz at a simulated thickness of 2.0 mm, Furthermore, the reflection loss (RL) value of Y0.7K0.3FeO3 reached − 30.56 dB at 15.44 GHz (effective bandwidth up to 4.72 GHz) corresponding to the thickness of only 1.6 mm. This demonstrates that this broadband effect is greater than other similar materials. Moreover, the as-prepared samples completely covered the X and Ku band at only 2.2 mm, and the maximum effective bandwidth reached 5.28 GHz at 2.0 mm. The excellent wave absorption and frequency broadening effects were due to the various loss mechanisms and improved impedance matching characteristics caused by doping.

Anisotropic electromagnetic absorption of the aligned Ti3C2Tx MXene/RGO nanocomposite foam

Transition metal carbides/nitrides (MXenes) with superb electrical properties have excellent applications for electromagnetic wave absorption (EMA). Whereas, the three-dimensional (3D) MXene's fabrication assemblies with anisotropic EMA performance are still a challenge as MXene nanosheets have weak gelation capabilities. In this study, graphene oxide was introduced to assist in fabricating the 3D MXene/RGO porous foam through the method of unidirectional freeze casting followed by hydrazine hydrate chemical reduction. Combined with the excellent electrical properties of MXene and RGO, the resultant lightweight (∼6 mg/cm3) MXene/RGO composite foam (MGF) with a free-standing configuration exhibits anisotropic microwave absorption performance. At the sample thickness of 5 mm, MGF-1/2 shows −26.79 dB minimum reflection loss at 4.39 GHz along the perpendicular direction that relates to the unidirectional freeze casting direction. While along the parallel direction, materials with 3 mm thickness reach the maximum effective bandwidth of 8.34 GHz. The lightweight MXene/RGO nanocomposite foam with anisotropic performance may significantly extend the feasibility of MXenes in EMA.

Bio-Inspired Microwave Modulator for High-Temperature Electromagnetic Protection, Infrared Stealth and Operating Temperature Monitoring

HighlightsA multifunctional microwave modulator is developed for electromagnetic protection, infrared stealth and operating temperature monitoring over wide temperature ranges for the first time.Microwave modulator achieves the integration of two electromagnetic protection mechanisms, microwave absorption and radiation deflection.Microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz with a thickness of only 1.5 mm in the temperature range 298–673 K.

High electromagnetic wave absorption and thermal management performance in 3D CNF@C-Ni/epoxy resin composites

Electronic packaging materials with efficient heat dissipation and anti-electromagnetic-interference performance are highly desirable to realize the long-term stable operation of highly integrated electronic devices. Such combined functions of heat dissipation and anti-electromagnetic-interference are achieved here by filling 3D CNF@C-Ni network skeleton in epoxy resins (EP). The CNF@C-Ni is a carbon nanofibers network skeleton embedded with micron flower-like C-Ni particles and has been obtained by carbonizing nickel metal–organic frameworks (Ni-MOF) embellished bacterial cellulose. The 3D CNF@C-Ni network skeleton provides a highly efficient heat transfer channel for EP, rendering a high thermal conductivity of 0.5 W·m−1K−1 at room temperature for the 5 wt% CNF@C-Ni filled EP, ~2.8 times higher than that of pristine EP. In addition, the flower-like C-Ni particles realize an optimization in the impedance matching of CNF@C-Ni/EP, enabling a high electromagnetic wave absorption performance in the wave-transparent epoxy resins. In particular, a lowest reflection loss value of −49.77 dB at 13.44 GHz with a maximum effective bandwidth of 5.44 GHz (from 12.08 to 17.52 GHz) has been achieved in the 5 wt% CNF@C-Ni filled epoxy resins with a thickness of 2.2 mm. Such a new dual-functionated epoxy resin with combined high electromagnetic wave absorption and thermal management performance shows great potential in manufacturing of highly integrated electronic devices.