Broadband Electromagnetic Wave Research Articles

Synthesis of nitrogen-doped graphene-based binary composite aerogels for ultralightweight and broadband electromagnetic absorption

The development of ultralightweight and broadband electromagnetic wave (EMW) absorbing materials remains a big challenge. In this work, porous magnesium ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/MgFe2O4) composite aerogels were prepared by a two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that NRGO/MgFe2O4 composite aerogels had a unique hierarchical porous structure. Moreover, the influence of additive amounts of graphene oxide on the electromagnetic parameters and EMW absorption properties of NRGO/MgFe2O4 composite aerogels was explored. Remarkably, the attained binary composite aerogel with the content of NRGO of 70.21 wt% exhibited the best EMW absorption performance. The minimum reflection loss reached up to −55.7 dB, and the corresponding effective absorption bandwidth was as large as 5.36 GHz at a thin matching thickness of 1.98 mm. Furthermore, when the matching thickness was slightly increased to 2.29 mm, the widest effective absorption bandwidth was enlarged to 7.1 GHz, covering the entire Ku-band. The magnetodielectric synergy and unique hierarchical porous structure in NRGO/MgFe2O4 composite aerogels not only improved the impedance matching, but also greatly enhanced the EMW absorption capacity. It was believed that the results of this work could be helpful for the preparation of graphene-based magnetic composites as broadband and efficient EMW absorbers.

Dual-induced SiC/SME multifunction composite for high - Efficiency broadband electromagnetic wave absorption

Uniformly sized silicon carbide nanoparticles (SiC NPs) were prepared using the carbothermal reduction method, and subsequently dispersed into an epoxy resin matrix to create the SiC- shape memory epoxy resin (SSME) composites. The absorption and thermo-mechanical properties of these composites can be tailored by varying the ratio of SiC nanoparticles. When the proportion of SiC nanoparticles is 20wt%, the minimum reflection loss (RLmin) is −62.02dB and the effective absorption bandwidth (EAB) is 7.7 GHz at the optimum thickness of 4.25 mm. While the thickness is 4.50 mm, the widest EAB is 8.1 GHz, which almost achieves 99% absorption of the whole X-band and Ku-band. The distance between SiC nanoparticles and the interfacial interaction between the particles and epoxy resin matrix enhances the electromagnetic wave absorption performance of the composites. At the same time, the SSME-3 sample with 20 wt% SiC nanoparticles has better thermal and mechanical properties than other proportions. Compared with the sample without nano-filler, the elastic modulus of SSME-3 increased by 18.48%, the shape recovery rate (Rr) increased by 17.84%, and the MW-induced shape memory recovery speed increased by 125%. Furthermore, a MW-induced shape memory test was conducted to demonstrate that the absorbent material is capable of converting electromagnetic energy into heat energy, thereby enabling it to function as a thermal and microwave dual-induced shape memory material. The findings of this study hold great significance for the development of multifunctional, deformable wide-band electromagnetic absorption composites.

Tunable and broad-band electromagnetic wave absorption using W-type Hexaferrites in 1–40 GHz range

W-type Sr-hexaferrites, Sr0.75Ca0.25Zn2-xCoxFe16O27 (0.0 ≤ x ≤ 2.0), were synthesized, and their magnetic and electromagnetic (EM) wave absorption properties were investigated. As x increased from 0.0 to 2.0, the saturation magnetization value increased and reached a maximum at x = 1.25, followed by a decrease, while the magnetic anisotropic field (Hani) decreased and showed a minimum at x = 1.0, then increased again. The variation in Hani could be controlled by adjusting the value of x, which also changed the ferromagnetic resonance (FMR) frequency and enabled control over the frequency band of EM wave absorption. It is demonstrated that the EM wave absorption is primarily controlled by imaginary part of permeability (μ") induced by FMR. Composite of the W-type hexaferrite-epoxy (10 wt%) with x = 0.75–2.0 showed a broad-band EM wave absorption in the 1–18 GHz range, while the composites with x = 0–0.4 showed it in the 26.5–40 GHz. The x = 1.25 sample satisfied RL < − 10 dB in the 7–17 GHz range with a thickness of 2.1 mm, while x = 0.3 sample satisfied RL < − 10 dB in the 27–39 GHz with a thickness of 0.8 mm. Sr0.75Ca0.25Zn2-xCoxW is a very promising material for tunable wideband EM wave absorbers in 1–40 GHz range.

Effective broadband electromagnetic wave absorption performance of nano-Fe3O4 magnetic fluid-modified resin geopolymer by metamaterial with a novel patterned structure

It is challenging to achieve high-strength absorption and effectively broaden the absorbing bandwidth when using conventional flat microwave-absorbing cementitious materials. To address this challenge and achieve excellent microwave-absorptive performance, this study proposes a novel two-layered periodic stepped absorbing structure (PSAS) composed of a mixture of nano-Fe3O4 magnetic fluid and a resin geopolymer. Additionally, the incident angle-dependent absorption performance, the impact of geometrical parameters, and the shape of the unit cell were investigated. The results demonstrate that the absorption of the designed metamaterial absorber exceeds 90% in the total frequency range of 2–18 GHz. A mean reflection value of −18.3 dB was obtained in this study. The outstanding absorption performance of PSAS results from the cooperative effect of multiple λ/4 resonances and edge diffraction effects, which improve the impedance matching to the level of the free space in a broad frequency domain. Combining the effect of electromagnetic field regulation with metamaterial structure, the ultra-broadband absorption can be significantly enhanced by adjusting the geometrical parameters of the unit cell for absorption resonance.

Research and simulation of three-layered lightweight cement-based electromagnetic wave absorbing composite containing expanded polystyrene and carbon black

Based on impedance gradient principle, a three-layered lightweight and broadband electromagnetic wave (EMW) absorbing cement-based composite is designed and prepared using expanded polystyrene (EPS) and carbon black (CB) as wave-transparent and absorbent medium, respectively. The three-layer absorber indicates excellent EMW absorbing properties in 1.1–18 GHz frequency range due to the good impedance matching and attenuation capacity. The minimum value of reflection loss (RL) is –49.6 dB with a 7 cm thickness and an effective absorbent bandwidth (RL < –20 dB) of 14.32 GHz can be achieved at a thickness of 8 cm. Furthermore, the idealized EPS-cement/CB structure model is established and simulated by finite element method in X-band. The propagation process of EMW is visual and greatly affected by EPS, and the electric field distribution presents a circular loop. Here the Smith chart can be used to analyze the impedance source of each circular loop at different frequencies. What’s more, the density of three-layered composites is between 170–250 kg/m3, meeting the requirements of lightweight, and the compressive strength of single-layer composite reaches about 0.65 MPa when the density is 350 kg/m3. Thus, the three-layer lightweight EPS-cement/CB composite is a promising EMW absorber with broadband absorption performance, which could be used for protecting buildings from electromagnetic interference.

Preparation and properties of zirconium-doped copper calcium titanate ceramics for broadband electromagnetic spectrum conversion

In this paper, zirconium-doped CaCu3Ti4-xZrxO12 (0 ≤ x ≤ 0.3, CCTZO) ceramics were prepared by traditional solid-state reaction. The prepared CaCu3Ti4-xZrxO12 display cubic phase structure, as shown by the XRD analysis, and interplanar spacing increase, as obtained by TEM. The surface morphologies, electrical conductivity, optical properties, solar and microwave thermal conversion characteristics of the synthesized samples were investigated in detail. The experimental results indicate that both the solar absorbance and thermal emittance of the samples could be tailored by Zr ions doping. In general, the CaCu3Ti4-xZrxO12 system displays relatively high thermal radiation properties, with an optimal composition of CaCu3Ti3.9Zr0.1O12 exhibiting a solar absorbance of 0.85 and a thermal emittance of 0.75. The incorporated Zr ions enhanced the solar–thermal conversion while weakened the microwave–thermal conversion. Under simulated solar irradiation (3 W/cm2), the equilibrium temperature of CaCu3Ti3.9Zr0.1O12 could reach above 260 °C. The equilibrium temperature of CaCu3Ti4O12 could reach up to 493 °C at a frequency of 2.45 GHz over 140 s. The results demonstrate that the CCTZO ceramics have the potential to emerge as the broadband electromagnetic wave–thermal conversion materials.

Dielectric loss enhancement induced by the microstructure of CoFe2O4 foam to realize broadband electromagnetic wave absorption

Dielectric loss enhancement induced by the microstructure of CoFe2O4 foam to realize broadband electromagnetic wave absorption

Construction of core-shell structured SiO2@MoS2 nanospheres for broadband electromagnetic wave absorption

Herein, core-shell structured SiO2@MoS2 nanospheres were made via hydrothermal method, with MoS2 nanosheets growing irregularly on the outside surface of SiO2. The microstructure and EM wave absorption properties of the prepared SiO2@MoS2 nanospheres were explored. SiO2@MoS2 achieved a minimum reflection loss (RLmin) value of − 49.35 dB with a thickness of 2.8 mm, and an effective absorption bandwidth (EAB) of 7.44 GHz. The remarkable EM wave absorption performance of SiO2@MoS2 nanospheres could be attributed to interfacial polarization originating from the designed core-shell structure and the multiple reflections on MoS2 ultrathin nanosheets. Meanwhile, impedance matching was regulated effectively by combination of SiO2 and MoS2, which provided a synergistic effect and enhanced EM wave dissipation. Therefore, the core-shell structured SiO2@MoS2 could be a great potential candidate material in the application of high-performance EM wave absorbing area.

Molecularly Resonant Metamaterials for Broad-Band Electromagnetic Stealth.

Electromagnetic (EM) metamaterial is a composite material with EMstealth properties, which is constructed by artificially reverse engineering metal split resonance rings (SRR). However, the greatest limitation of EM metamaterials is that they can only stealth at a fixed and lower frequency of EM waves, and modern processing techniques still cannot meet the accuracy requirements to fabric nano-size structural unit. Nano-sized and even ultra-small SRR at molecular level are promising arrays to realize the ability of EM stealth function at a higher frequency, although it has proven challenging to synthesize long, straight, connected molecular SRR, and also difficult to arrange those molecular SRR into a strict array. Here, the study overcomes this challenge and demonstrates that the fabric of polypyrrolemolecular SRR achieves an ultra-small inner diameter of 2.49 Å and realizes the arrays arrangement at molecular level. Furthermore, the study exploits the EM stealth function and verifies that such arrays of molecular SRR with 2.49 Å have the ability to reach high-performance EM stealth in the range of 106 -1016 Hz. This design concept opens a pathway for developing new metamaterials with broadband EM wave stealth and also serves the wider range of new applications.

Two Birds with One Stone: Broadband Electromagnetic Wave Absorption and Anticorrosion Performance in 2-18GHz for Prussian Blue Analog Derivatives Aimed for Practical Applications.

Nowadays, the exploration of electromagnetic (EM) wave absorbers with anticorrosion to improve the survivability and environmental adaptability of military targets in the harsh environments is becoming an attractive and unavoidable challenge. Herein, through modulation of the metal composition in the precursors, the core@shell structure Prussian blue analog-derived NiCo@C, CoFe@C, NiFe@C, and NiCoFe@C are obtained with excellent EM wave absorption performance. As for NiCoFe@C, ascribed to the coupling effect of the dual magnetic alloy, a minimum reflection loss (RL) of -47.6dB and an effective absorption bandwidthof 5.83GHz are realized, which cover the whole Ku-band. Meanwhile, four absorbers display the lower corrosion current density (10-4 -10-6 A cm-2 ) and larger polarization resistance (104 -106 Ω) under acid, neutral, and alkaline corrosion conditions over uninterrupted 30 days. Furthermore, due to the spatial barrier effect and the passivation effect of the graphitic carbon shell , the continuous salt spray test has little effect on RL performance and inconspicuously changes the surface morphologies of coating, demonstrating its excellent bifunctional performance. This work lays the foundation for the development of metal-organic frameworks-derived materials with both anticorrosion and EM wave absorption performance.

Porous, magnetic carbon derived from bamboo for microwave absorption

Designing lightweight, environmentally friendly and broadband electromagnetic wave (EMW) absorbers to solve the increasingly EM pollution problem has become a research hotspot. Carbon material, especially the graphitized carbon derived from the biomass which possessing highly porosity on the framework, has considered the extremely potential in electromagnetic absorption since the ultralow density, abundant dipoles and moderate dielectric value, however, lacking of magnetic property restricts the efficient and broad absorption. Herein, a biomass-derived porous graphite-like carbon (g-C) matrix with controllable magnetic component (α-Fe and Fe3O4) decoration are realized via one-step pyrolysis reaction The development absorber exhibits an excellent EMW absorption performance with largest |RLmin| value of 47.06 dB and widest effective absorption frequency width of 5.52 GHz at a fixed coating thickness as thin as 1.80 mm, which is attributed to the good conductive loss and dielectric loss capacities permitted by the synergistic effect of equivalent circuit conductive network, the optimized impedance matching, the dipoles polarization, defect polarization and interfacial polarization. This work provides a theoretical and experimental basis for developing a green and sustainable method for preparing bamboo-derived carbon-based composites, and applying such materials to the field of EM protection and EM pollution control.

Facile synthesis of CoxFey@C nanocomposite fibers derived from pyrolysis of cobalt/iron chelate nanowires for strong broadband electromagnetic wave absorption

Nowadays, constructing electromagnetic wave (EMW) absorbing materials with high absorption strength and wide response frequency is an urgent demand and also a challenge. In this work, the bimetallic organic precursors of cobalt/iron nitrilotriacetic acid chelate nanowires (Co/Fe-NTAC) were prepared by one-step hydrothermal self-polymerization strategy. Then, the CoxFey@C nanocomposite fibers with different Co/Fe atomic ratios were synthesized by directly calcining the Co/Fe-NTAC precursors. Notably, when the atomic ratio of Co/Fe is 1:1, the sample exhibits high-efficient microwave absorption performance with the minimum reflection loss (RL) of −117.8 dB, whose effective absorption bandwidth (EAB, RL ≤ −10 dB) reaches up to 12.6 GHz (5.4–18 GHz) at the same thickness. The outstanding EMW attenuation properties are attributed to the strong magnetic loss, multiple heterogeneous interface polarizations, synergistic effects between magnetic cores and dielectric shells, as well as optimal impedance matching. Especially, the heterointerfaces polarization behavior and ferromagnetic coupling effect were verified by High-Frequency Structure Simulator (HFSS). The Radar Cross-Sectional (RCS) values of the optimized sample are all lower than −10 dBm2 in the range of −60° < θ < 60°, which can achieve almost full-angle coverage in the practical environment. This work provides inspiration and strategy for the facile construction of high-intensity and ultra-wideband EMW absorbers.

In situ modification of MXene nanosheets with polyaniline nanorods for lightweight and broadband electromagnetic wave absorption

MXene exhibits excellent electromagnetic (EM) wave attenuation ability, but its high dielectric constant is prone to impedance mismatch. Usually, the introduction of other components can adjust EM parameters and improve the impedance matching of MXene. In this paper, MXene/polyaniline (PANI) composites with lots of heterogeneous interfaces were designed and prepared by electrostatic self-assembly process, and PANI was used as impedance matching modifier of MXene to adjust the impedance matching of the composites and achieve greater reflection loss. The effect of the content of PANI nanorods loaded on MXene nanosheets on the EM properties of the material was discussed in this work. The maximum reflection loss (RLmax) of −60.6 dB corresponds to an effective absorption bandwidth (EAB) of 6.0 GHz for the composite with only 10% PANI loading, while the EAB reaches 8.64 GHz when the sample thickness is 2.3 mm. Moreover, the introduction of PANI balances the impedance matching of MXene while bridging individual MXene nanosheets to form a three-dimensional structure that increases the EM wave propagation path. The rich loss mechanisms such as interfacial polarization and dipole polarization provide effective attenuation of EM waves. This work provides a simple way to develop lightweight and broadband EM wave absorption materials.

Carbon nanotubes decorated FeNi/nitrogen-doped carbon composites for lightweight and broadband electromagnetic wave absorption

Magnetic-dielectric component modulation and heterogeneous interface engineering were considered as an effective strategy for designing lightweight and broadband electromagnetic wave (EMW) absorbors. Herein, a series of carbon nanotubes (CNTs) decorated core-shell nitrogen-doped carbon (CNTs/FeNi/NC) composites were successfully fabricated via the carbonization of CNTs/NiFe2O4/PDA precursors obtained by hydrothermal and polymerization method. The EMW absorption (EMWA) properties of CNTs/FeNi/NC composites were explored by varying the CNTs content. When the CNTs content was 15%, the minimum reflection loss (RLmin) value was -51.13 dB at 9.52 GHz and the corresponding effective absorption bandwidth (EAB) value was 2.96 GHz (8.96–11.12 GHz) at 2.5 mm. Particularly, the maximum EAB value can reach up to 4.64 GHz (12.80–17.44 GHz) at 1.7 mm. The excellent EMW attenuation capability resulted from the enhanced conductive loss, polarization loss, magnetic loss, and improved impedance matching. This work offers a novel reference for designing lightweight and broadband EMWA materials.

Ti3C2Tx/Co-MOF derived TiO2/Co/C composites for broadband and high absorption of electromagnetic wave

With the dramatic development of electronic and radar detection technologies, electromagnetic (EM) wave absorbing and shielding materials with superior microwave absorption (MWA) performance, light weight and wide bandwidth are widely concerned. Herein, novel Ti3C2Tx/Co-MOF derived TiO2/Co/C composite architectures with rutile-TiO2 decorated carbon flakes originated from Ti3C2Tx and Co/C composites with wrapped Co in the tips of carbon nanotubes (CNTs) are fabricated by in-situ solvothermal growth and pyrolysis. The multi-component synergistic effect and appropriate combination with adjustable amount of Ti3C2Tx loading and Co-MOF size optimize the impedance matching and exhibit satisfactory broadband EM wave absorption. The nanocomposites achieve effective absorption bandwidth (EAB) of 5.48 GHz at only 1.7 mm, and the minimum reflection loss (RLmin) value of −50.45 dB at 7.32 GHz with a 3.0 mm thickness. The outstanding broadband MWA properties cover nearly the whole frequency bands of C, X, and Ku with the corresponding RLmin values almost below −30 dB. This work highlights a promising strategy to design and synthesize various MOF-derived carbon composites with excellent MWA capacities.

Effect of neodymium doping on structure, magnetic properties and microwave absorption performance of SrMnO3

A simple composite Sr1–xNdxMnO3 (x = 0, 0.05, 0.1, 0.15, 0.2) nano powders were successfully prepared by the sol–gel method as a light-weight broadband electromagnetic wave absorber. The effect of Nd3+ doping on the structure, microstructure and properties of SrMnO3 was investigated. It is found that with the doping of Nd3+, the space group of the SrMnO3 changes from p63/mmc to pm3m, and the crystalline shape starts to change from hexagonal to cubic crystalline. Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) tests confirm that the particle sizes of the sample decrease and the specific surface area increases, which are attributed to the inhibition of grain growth after Nd3+ is doped. X-ray photoelectron spectroscopy (XPS) shows that after Nd3+ doping, the content of oxygen vacancy increases, and Mn4+ converts to Mn3+. Due to the defects of the materials, the polarization effect is enhanced, thus, the dielectric and magnetic properties of the doped samples are improved. The maximum reflection loss of the Sr0.85Nd0.15MnO3 is −33.41 dB at 7.84 GHz for a thickness of 2.4 mm, while Sr0.9Nd0.1MnO3 has the best bandwidth performance at 2.32 GHz with a reflection loss below −10 dB.

A novel approach on design of a fractal inspired logarithmic spiral antenna-based absorber for polarization and incident angle insensitive broadband electromagnetic energy harvesting

Design analysis employing numerical analysis has become one of the most significant components in realizing broadband spiral absorbers in the infrared (IR) region. To date, there have been very few research studies on broadband electromagnetic (EM) wave absorptions by such absorbers in that frequency band. Therefore, in this research, we have proposed a new type of absorber based on gradient log-spiral to enhance the absorption bandwidth in the IR region. The absorbers are designed by considering arrangements of different log-spiral arms in a fractal-like pattern. Investigation was carried out in both unit cell and array configuration. Strong average absorption reaching 88.5% in the unit cell and 83.6% in the array configuration was observed over the bandwidth from 4.5 to 100 THz for a wide range of incident angles. The absorption of the unit cell absorber remains almost stable up to 45° for transverse electric and 75° for transverse magnetic mode polarizations. This unique approach opens a new direction of imaging, EM stealth, camouflaging, and wireless EM energy harvesting applications.

A novel lightweight metamaterial with ultra broadband electromagnetic wave absorption induced by three-dimensional CNTs conductive-coated arrays

A novel lightweight metamaterial with ultra broadband electromagnetic wave absorption induced by three-dimensional CNTs conductive-coated arrays

Broadband electromagnetic dissipation superiority of hierarchical ZnO flakes co-decorated with CoFe/CoFe2O4 and rGO

Currently, in order to solve the increasing issues caused by the electromagnetic radiation pollution and broadened radar detection bandwidth, electromagnetic wave dissipating materials with high performance of broadband absorption are desired urgently. Herein, the CoFe/CoFe2O4/ZnO/rGO composites composed of hierarchical ZnO flakes with anchored CoFe/CoFe2O4 and rGO-doping were synthesized via a facile aging approach and subsequent calcination process under vacuum atmosphere. The constituents and electromagnetic parameters of absorbers could be efficiently modulated through tuning the additive amount of raw GO. Notably, the composite with GO additive amount of 0.025 g exhibits a prominent broadband electromagnetic wave absorbing capacity. In detail, the widest effective absorption bandwidth reaches 7.66 GHz with thin thickness of just 2.5 mm. This superior broadband microwave absorption property is owing to the synergistic effect of hierarchical nanostructure and well-matched impedance, as well as enhanced interfacial polarization, conduction loss, eddy current, natural and exchange magnetic resonances. The investigation demonstrates the specific CoFe/CoFe2O4/ZnO/rGO composite is a potential candidate to be applied for broadband military radar stealth and serious electromagnetic radiation contamination.

A hierarchical CoNi @ nitrogen doped C/macroporous C composite derived from a new bimetallic MOF and Juncus effusus as a broadband electromagnetic wave absorber

Biomass-derived carbon has attracted extensive attention because of its unique form, wide range of sources and low cost. However, the construction of efficient biomass-based microwave absorbers with hierarchical structures and multicomponent magnetic/dielectric structures remains a great challenge. Therefore, CoNi-MOF was self-assembled in situ on the plant Juncus effusus by the microwave method, and CoNi/NC/C composites were prepared by in situ pyrolysis in a nitrogen atmosphere. The morphology, electromagnetic parameters, specific surface area and porous structure of the composites were adjusted by controlling the pyrolysis temperature. For a pyrolysis temperature of 600 ℃ and filling of 16 wt%, the composite was found to show an RLmin value of − 64.3 dB at 12.88 GHz at a thickness of 2.5 mm, and the effective absorption bandwidth (EAB)reached 7.36 GHz. The excellent microwave absorption performance was attributed to conduction loss, dipole polarization, interface polarization, magnetic loss and balanced impedance matching.