Improved Microwave Absorption Research Articles

Manganese oxides/graphene aerogels as lightweight microwave absorbers for extreme environment application

The development of microwave absorbing materials (MAMs) with photothermal and electrothermal properties can satisfy special requirements for MAMs used in extreme environment. Herein, manganese oxide/graphene aerogel (MnOx/GA) composites were successfully fabricated by uniformly growing MnOx on GA through combining the hydrothermal and freeze-drying methods. The MnOx/GA composite exhibits a distinctive three-dimensional network structure with heterogeneous interfaces and lattice defects that can optimize the impedance matching and enhance the interfacial polarization, resulting in improved microwave absorption (MA) performance, including absorption intensity and bandwidth. The MnOx/GA sample prepared in this study exhibits an outstanding MA intensity of −54.70 dB at a frequency of 9.92 GHz, accompanied by an effective absorption bandwidth (EAB) of 5.60 GHz with a sample thickness of 2.60 mm and a filling content of 8.0 wt%. Meanwhile, the simulation of the radar cross section (RCS) further confirms the excellent MA performance and practical application potential of the MnOx/GA material. Additionally, MnOx/GA possesses outstanding electrothermal and photothermal properties, rendering it suitable for application in extreme environments. This work provides an economical, environmentally friendly, and efficient method for preparing lightweight and broadband multi-functional MAMs.

Microwave absorption and electromagnetic properties of ultra-high-strength cementitious materials: Influence of basalt powder and underlying mechanism

The utilization of basalt powder in ultra-high-strength cementitious materials (UHSCMs) holds significant potential for application in mitigating CO2 emissions and reducing electromagnetic pollution. This study investigated the microwave absorption and electromagnetic properties of UHSCMs incorporating basalt powder, with the silica-fume-based mix as a comparison. A comprehensive multi-scale investigation was conducted to gain an in-depth understanding of the electromagnetic properties of UHSCMs. From the results, the UHSCM with basalt powder was demonstrated to possess improved microwave absorption performance, characterized by a mean reflection loss of −8.22 dB and effective bandwidths of 58.3% (<-7.0 dB) and 26.6% (<-10.0 dB). The enhanced performance of this mixture was attributed to its superior impedance-matching capability and microwave attenuation ability. The dielectric loss peaks within frequency ranges of 7.0–8.5 GHz and 10.0–11.5 GHz were caused by the interfacial polarization of macro pores and gel pores, respectively. The natural resonance, exchange resonance, and eddy current effect were the primary mechanisms of the magnetic loss. CaFeSi2O6 particles from basalt powder contributed to the enhanced natural resonance. In addition, basalt powder had the better market potentials and lower environmental impact as a supplementary cementitious material than silica fume for enhancing microwave absorption of UHSCMs. The finding of this study demonstrated the suitability of adopting basalt powder in UHSCM production with improved greenness and electromagnetic properties.

A three-dimensional BaFe11.6(ZrSm)0.2O19/rGO composite aerogel with superior microwave absorption properties

The combination of dielectric and magnetic materials can significantly improve microwave absorption properties. In this work, we introduce a novel Zr–Sm doped barium ferrite BaFe11.6(ZrSm)0.2O19, which is compounded with rGO aerogel and presents superior microwave absorption properties. The results show that the BaFe11.6(ZrSm)0.2O19/rGO composite aerogel exhibits a unique three-dimensional porous network structure which enhances the reflection and scattering of electromagnetic waves. Meanwhile, the addition of BaFe11.6(ZrSm)0.2O19 abounds the folds and defects on the surface of rGO sheet layer, generating a large amount of polarisation and relaxation. In addition, with the increase of BaFe11.6(ZrSm)0.2O19 content, the permeability gradually increases, while the dielectric constant gradually decreases. At a certain content, both of them can be well balanced to obtain high attenuation constants and great impedance matching, which regulates the wave-absorbing properties of the material. The minimum reflection loss (RLmin) of BaFe11.6(ZrSm)0.2O19/rGO composite aerogel can reach −53.17 dB at a matching thickness of 2.9 mm, and the absorption bandwidth reaches 7.04 GHz, which has been improved by 40% than pure BaFe11.6(ZrSm)0.2O19. Therefore, it is expected to be a candidate for lightweight, thin, high loss, large bandwidth microwave absorbing materials.

Synergistic impact of nickel ferrite and titanium dioxide composites for improving microwave absorption in X-band

The present study focuses on the synthesis of composites with varying loading percentages of nickel ferrite and titanium dioxide using a mechanical alloy method. The developed composites underwent a comprehensive evaluation of various parameters, which yielded valuable insights. Among the developed composites, nickel ferrite and titanium composite with 50:50 wt% (NT-C) have emerged as a potential candidate for microwave absorbing material. Notably, NT-C exhibits excellent electromagnetic characteristics, with a minimum reflection loss (RL) of –33.34 dB at 9.6 GHz and −27.98 dB at 11.06 GHz, both achieved with a pallet thickness of 2.2 mm. The exceptional microwave absorption properties of this developed composite are a result of the synergistic interplay between impedance matching and strong electromagnetic energy attenuation capabilities. This finding, resulting from the synergistic incorporation of nickel ferrite and titanium dioxide phases, offers an effective pathway for developing a material capable of exceptional electromagnetic capabilities.

Metal Valence State Modulation Strategy to Design Core@shell Hollow Carbon Microspheres@MoSe2/MoOx Multicomponent Composites for Anti-Corrosion and Microwave Absorption.

The exploitation of multicomponent composites (MCCs) has become the main pathway for obtaining advanced microwave absorption materials (MAMs). Herein, a metal valence state modulation strategy is proposed to tune the electromagnetic (EM) parameters and improve microwave absorption performances. Core@shell hollow carbon microspheres@MoSe2 and hollow carbon microspheres@MoSe2/MoOx MCCs with various mixed-valence states content are well-designed and produced by a simple hydrothermal reaction or/and heat treatment process. The results reveal that the thermal treatment of hollow carbon microspheres@MoSe2 in Ar and Ar/H2 leads to the in situ formation of MoOx and multivalence state, respectively, and the enhanced content of Mo4+ in the designed MCCs greatly boosts their impedance matching characteristics, polarization, and conduction loss capacities, which lead to their evidently improved EM wave absorption properties. Amongst, the as-prepared hollow carbon microspheres@MoSe2/MoOx MCCs achieve an effective absorption bandwidth of 5.80 GHz under a matching thickness of 1.97 mm and minimum reflection loss of -21.49 dB. Therefore, this work offers a simple and universal method to fabricate core@shell hollow carbon microspheres@MoSe2/MoOx MCCs, and a novel and feasible metal valence state modulation strategy is proposed to develop high-efficiency MAMs.

Synthesis of Fe3Al@Al2O3 flakes showing improved microwave absorption performance after servicing at high temperatures

Most magnetic loss-type absorbers exhibit very poor microwave absorption performance at high temperatures. Herein, we developed a thermal treatment and controlled oxygen partial pressure process to design a Fe3Al@Al2O3 core-shell structure by inducing the in situ oxidation of Al elements in the Fe3Al particles. Owing to the in situ growth of the dense and thin Al2O3 layer on the Fe3Al surface, the oxidation issue at high temeratures can be effectively alleviated. Compared to the Fe3Al counterpart without a Al2O3 shell that tends to be oxidized at high temperatures, the Fe3Al@Al2O3 absorber keeps good microwave attenuation properties and impedance matching ratios even at a temperature of 400 ℃, with the minimum reflection loss of −52.4 dB at 5.8 GHz. Moreover, the effective absorption bandwidth is 4.9 GHz. The new findings demonstrated in this work provides a possible approach for the exploration of efficient microwave absorption materials used at high temperatures.

Controllable synthesis of CeFeO3/Fe+2Fe2+3O4/C composites with improved microwave absorption performances

Magnetic-dielectric component modulation and heterogeneous interface engineering have been acknowledged as a highly potent strategy for the effective development of lightweight and broad-spectrum electromagnetic wave (EMW) absorbers. In this investigation, a series of carbon-based Ce/Fe-MOF derivatives were successfully synthesized via the carbonization process of Ce/Fe-MOF precursors. The EMW absorption characteristics of these derivatives were investigated by manipulating the metal ion ratio and the pyrolysis temperature. Notably, the Ce/Fe-MOF-700 composite, derived from the calcination of Ce/Fe-MOF with a molar ratio of Ce/Fe of 1:2 at 700 °C, demonstrated an impressive minimum reflection loss value of −44.6 dB at 1.38 mm. Furthermore, it exhibited an efficient absorbing bandwidth (EAB) of 6.88 GHz at a thinner coating thickness ranging from 1.38 to 1.8 mm. This remarkable ability of these materials to attenuate EMW can be ascribed to the heightened conductivity dissipation, polarization dissipation, magnetic dissipation, and enhanced impedance matching achieved by these materials. The findings of this study provide a novel point of reference for the design of lightweight and broad-spectrum EMW absorbing materials.

Bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles for improved microwave absorption properties

High reflection loss and wide absorption bandwidth materials are in great demand to prevent electromagnetic pollution and military applications. The composites prepared by combining different components with good dielectric and magnetic losses are expected to achieve ideal absorbing performance. In this study, a composite of cobalt nanoparticles enveloped in nitrogen-doped bamboo-like carbon nanotubes (Co@N-CNTs) was prepared by one-step annealing the mixture of melamine and cobalt nitrate at 800 °C in a mixed atmosphere of hydrogen and argon. Co nanoparticles derived from the reaction between H2 and cobalt nitrate during the sintering process were used as catalysts to prompt the carbonization of melamine and the formation of the bamboo-shaped N-doped carbon nanotubes, thus forming the composite structure of bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles. This Co@N-CNTs composite not only had an excellent dielectric loss and magnetic loss but also greatly improved its impedance matching, thus having good electromagnetic wave absorption performance. The coating made from the Co@N-CNTs composite had a maximum reflection loss (RL) of −35.89 dB at only 1.8 mm thickness at 14.1 GHz and possessed an effective absorption bandwidth of up to 4.91 GHz (12.35–17.26 GHz), suggesting it a high-performance and wide-absorption bandwidth composite material.

Correction: Study of SrLa0.04Fe1.96O4/polyaniline composites for improving microwave absorption

Correction: Study of SrLa0.04Fe1.96O4/polyaniline composites for improving microwave absorption

MOFs-derived Co/C nanoparticle embedded in N, S co-doped graphene for superior electromagnetic wave absorption capacity

Due to their physicochemical properties, the three-dimensional Metal-organic frameworks (MOFs) derived composites show great potential as electromagnetic wave (EMW) absorbers. However, poor impedance matching limits their actual EMW absorption performance. Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this work, a novel N,S-GS/Co/C composite was fabricated via a solvothermal method and a subsequent pyrolysis process to introducing nitrogen and sulfur co-doped graphene (N,S-GS) into Co-MOF. By co-doping nitrogen and sulfur, abundant defects and disordered sites were introduced on graphene, which stimulate interfacial polarization and dipole polarization. The minimum reflection loss (RL) of the sample obtained by pyrolysis at 600 °C is −68.8 dB at 9.7 GHz. Simultaneously, the thickness is 2.51 mm, and the effective absorption bandwidth (EAB) can reach 3.04 GHz. Its excellent EMW absorption performance is mainly attributed to interfacial polarization, multiple reflections, dipole polarization, magnetic resonance and eddy current loss. Accordingly, the N,S-GS/Co/C composite is convinced to be a competent candidate among EMW absorbers with high absorption intensity.

Strategies toward processing high-efficient MWCNTs/AgBr/PTs -co-PQ nanocomposite coupling for X-band stealth application

There is a pressing desire for the development of ideal microwave absorption materials to tackle the escalating issue of electromagnetic interference (EMI) in electronic gadgets. So, EMI absorption material is an urgent requirement at the present time. Herein, a novel composite, MWCNTs enwrapped with AgBr and Poly(Thiophene-co-Quinoxaline), has been successfully synthesized to study absorption properties in X-bnad frequency range. The primary objective of this study is to increase the microwave absorption performance of composites by regulating their attenuation constant and impedance matching. The improved microwave absorption efficiency of MWCNTs/AgBr/Poly(Thiophene-co-Quinoxaline) has been achieved by using various filler contents. The optimal sample achieves RLmini of −54 dB with EAB of 2.2 GHz. As a result, the developed nanocomposites could be used in the field of microwave absorption.

Tunable microstructure and microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbent prepared via a reduction diffusion method

Magnetic materials with highly efficient microwave absorption properties, crucial for dealing with the advanced wireless communications and radar detections, have been garnering significant attentions. Rare-earth transition-metal compounds were researched as the potential candidates but still suffer from the disadvantages of complex powder metallurgy process and low serving frequencies. In this work, the novel magnetic composites consisting of SmCo5 and Sm2Co17 are developed by a reduction diffusion method. The micromorphology and the binary phase ratios of the SmCo5/Sm2Co17 could be easily modulated by simply altering the reactant concentrations. Consequently, an optimum reflection loss of − 50.2 dB and broad absorption bandwidth of 4.95 GHz at a thickness of only 2.0 mm are achieved. The improved microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbents can be attributed to their adjustable magnetic phases and the distinctive flaky particle shape, which greatly enhance microwave absorption capabilities. This work demonstrated a feasible reduction diffusion method and proposed a new strategy of designing binary-phase magnetic materials to achieve high microwave absorption properties.

P-doped in the shell of Ni@WO3-δ nanocomposites induced electronic structure change for improving microwave absorption performance

In this work, we reported P-doped WO3-δ coated Ni (Ni@P-WO3-δ) nanocomposites prepared by the arc discharge method with a subsequent phosphorylation treatment, where the Ni@P-WO3-δ nanocomposites exhibited a tunable electromagnetic wave absorption (EMA) performances by the doping P into the surface shell WO3-δ compared with the Ni@WO3-δ. The experimental evidence combined with the theory calculation results based on First-principles revealed that the doping P into the WO3-δ endowed improvable electrical conductivity, resulting in higher conduction loss for the Ni@P-WO3-δ nanocomposites. Meanwhile, P doping causes more defects and distorted lattice for the WO3-δ shell, which enhances defect-induced polarization loss. As a result, enhanced conduction loss and polarization relaxation loss of the Ni@P-WO3-δ nanocomposites are dominant for improving EMA performance. Further, the study found that the EMA properties of the Ni@P-WO3-δ nanocomposites are related to P doping content and can be tailored efficiently by controlling the amount of P dopant source. Thus, the Ni@P-WO3-δ nanocomposites with appropriate P doping can optimize their balance between impedance matching and dielectric loss, achieving excellent microwave absorption performance. The minimum reflection loss (RL) value of the Ni@P-WO3-δ nanocomposites was − 55.62 dB, and the efficient absorption bandwidth achieved in 12.58 GHz, with a thickness rang of 1.61–5.00 mm. Therefore, this work confirms that doping engineering has a significant application for the design and synthesis of dielectric-typed microwave absorbers.

The Improved Microwave Absorption Performance of the 3D Porous (Ni@NO-C)n/NO-C Composite Absorber.

Microwave absorbers that are lightweight and have good stability and high efficiency have attracted much attention for their applications in many contemporary fields. In this work, a 3D porous (Ni@NO-C)n/NO-C composite absorber was prepared using a wet chemistry method with Ni chains and melamine as precursors, in which NO-C (N,O-doped carbon)-encapsulated Ni particles are homogenously dispersed in the 3D porous networks of NO-C in the form of (Ni@NO-C)n chains. The special microstructure of the as-prepared material is proven to be beneficial for the improvement of its microwave absorption performance. The as-synthesized (Ni@NO-C)n/NO-C composite absorber exhibited an effective absorption bandwidth of 4.1 GHz and an extremely large reflection loss of -72.3 dB. The excellent microwave-absorbing performances can be ascribed to the cooperative consequences of dielectric loss and magnetic loss, along with the balance between attenuation capability and impedance matching.

Construction of one-dimensional hierarchical MoS2/Ni3S2 composites with enhanced interfacial polarization and improved wideband microwave absorption

The construction of one-dimensional (1D) sulfides has attracted extensive attention for improving microwave absorption (MA) performance owing to the anisotropic conductive networks. However, the synthesis of conductive 1D hierarchical materials with unique interfacial polarization and excellent MA properties remains challenging. In this study, cable-like MoS2/Ni3S2 was synthesized by a one-step hydrothermal strategy. The complex permittivity of the binary composites could be improved by tuning the thickness of the MoS2 coating. Importantly, the construction of heterogeneous contacts by MoS2 and Ni3S2 contributed to enhanced polarization loss, and the charge distribution was validated by electron holography. The wide efficient absorption bandwidth can reach above 4.8 GHz at a thin thickness. These new discoveries shed light on novel structures for 1D sulfide materials and the design of functional core-shell composites for microwave absorption.

Exploration on the multi-structural morphology regulation and microwave absorption performance of LDHs

In this paper, the microstructure of MgAl-layered-double-hydroxides (MgAlLDHs) was adjusted by one-step hydrothermal method, and the MgAlLDHs with various stacking structures were prepared successfully. It is found that the different stacking structures have significant effects on the microwave absorption performance of LDHs. The minimum reflection loss (RL) of the solid microsphere LDHs is 63% higher than that of the layered LDHs, and the effective absorption bandwidth (EAB) is also increased from 1 GHz to 2.50 GHz. The results show that adjusting the microstructure and morphology of the material is an effective way to improve microwave absorption performance.

Microwave All-Dielectric Metamaterial Design of FeSiAl/MWCNT Composite for Low-Frequency Broadband-Absorbing Properties

FeSiAl flakes were fabricated by vibrating ball milling the FeSiAl ribbons. And the microwave absorption properties of FeSiAl flakes were improved by doping the multi-wall carbon nanotubes (MWCNTs) with different mass concentrations. The results show that the FeSiAl/MWCNT composites exhibit significantly improved microwave absorption performance with advantages of strong and broadband absorption in the L-band and S-band. In particular, the reflection loss (RL) of the FeSiAl/MWCNT2 composite reaches −7.4 dB at 1.0 GHz, whereupon, through the electromagnetic simulation software CST Microwave Studio, FeSiAl/MWCNT2 all-dielectric metamaterial absorbers (ADMMAs) were macroscopically designed, achieving an ultra-wideband absorption (RL ≤ −10 dB) of 14.4 GHz (3.6~18.0 GHz). It is recognized that the standing wavelength resonance and diffraction effect are responsible for absorbing electromagnetic waves, and the broadband absorption is improved via dielectric dispersion; their synergistic effect makes the ADMMAs exhibit good microwave absorption performance. This work provides a useful method for designing microwave absorption materials with broadband absorption.

Fabrication of cobalt-zinc bimetallic oxides@polypyrrole composites for high-performance electromagnetic wave absorption

Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co3O4/ZnCo2O4 and ZnCo2O4/ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal–organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core–shell structures known as Co3O4/ZnCo2O4@PPy (CZCP) and ZnCo2O4/ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RLmin) of −71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials.

Soft matter with magnetically oriented macro - micro structure for improving microwave absorption efficiency

The key challenge for the most widely used magnetic absorbers is how to simultaneously combine low filling with efficient electromagnetic absorption performance. This paper exploited carbonyl iron particles (CIPs) to develop some soft material that possessed orderly orientated structure via applying an external excitation signal, so as to reduce hyperosmotic threshold of conductive loss network, improve impedance matching pattern and thus modulate absorption efficiency. The arch test results showed that effective absorption band (EAB, RL<−10 dB) and reflection loss (RL) efficiency of oriented structure (40 wt%−300mT sample) was much higher than that of unoriented structure (60 wt%−0mT sample), and the reflection loss intensity was reduced to − 15.2 dB, especially EAB was expanded by 8.1 GHz, which significantly alleviated the critical conflict between low filling and electromagnetic loss performance. Also, it was attempted to reveal surface topography changes caused by multiple magnetized particles interaction, and how excitation signal intensity, magnetic particles filling concentration and structural parameters affect microwave absorption efficiency and bi-directional frequency conversion. Thus, a magnetic-manipulated absorbing material proposed laid a theoretical foundation for improving loss efficiency of magnetic materials at low filling concentration.

The microwave absorption properties variation with temperature of RF/SiO2 and improved microwave absorption by periodic structure

With the widespread application of radar detection systems in the military field, the development of radar stealth technology can effectively reduce the characteristic signals of targets, which was of great significance for the protection of important military targets. In this paper, the resorcinol/formaldehyde (RF) reinforced silica aerogel (RF/SiO2) was synthesized successfully. The RF was introduced into the sol/gel technology to build a porous skeleton, and the SiO2 aerogel was prepared by atmospheric pressure drying. The RF/SiO2 aerogel was then heat treated, and the microstructure and physical properties of the RF/SiO2 aerogel before and after heat treatment were characterized to study the influence of the heat treatment temperatures on the RF/SiO2 aerogel. With the increase of the heat treatment temperature, its electromagnetic wave absorption performance had been significantly improved. When the heat treatment temperature reached 1500 ℃, the RF/SiO2 aerogel possessed a minimum reflection loss of − 36.42 dB at 1.95 mm and an effective bandwidth of 2.94 GHz at 2.00 mm within the radar band of 8.00–12.00 GHz. In addition, this paper used CST software to optimize and design the periodic structure of metamaterial based on the RF/SiO2 aerogel. The optimization design of the patch size and substrate thickness on the substrate surface provided a reference for the future application of this material in specific radar stealth fields.