High Microwave Absorption Research Articles

The Co/CoNi sequential configurations based on transparent basalt substrates toward excellent microwave absorption

The typical design for electromagnetic wave absorbing materials is the composites made of high dielectric components and magnetic materials, which is a single type. This article presents a unique paradigm for high microwave absorption (MA), whereby the transparent basalt substrates are evenly covered by the sequential configurations formed by the entangled Co/CoNi nano-units. The sequential nanostructure consistently displays a net-like morphology at a 5/10 min reaction for the higher Co content in CoNi, exhibiting the regular variety for complex permittivity. On the other hand, it is constructed by the spherical nano-units with a higher Ni ratio in CoNi. After 5 min of reaction, the nanospheres are arranged with the nanogaps, or they are continuously arranged on basalt after 10 min. Correspondingly, the basalt/CoNi composites exhibit unfavorable ‘mutation’ characteristics with the too-small or too-large complex permittivity, detrimental for optimized MA. As expected, with the specific Co/Ni ratio, the net-like basalt/CoNi obtained at 5 min displays outstanding MA due to appropriate dielectric loss and strong magnetic coupling (−61.98 dB at 2.03 mm, 4.665 GHz at only 1.47 mm). Especially, the nano-scale magnetic coupling is confirmed by micromagnetic simulation. This work breaks the limitations of traditional absorbers and provides new design ideas about magnetic-dielectric components.

Causal optimal and optically transparent ultra-wideband microwave metamaterials absorber with high angular stability.

Wideband microwave absorbers, especially those with high optical transparency, are significantly used in civil and military fields. This paper proposes an ultra-wideband optically transparent metamaterial absorber (MMA) with causal optimal thickness and high angular stability. Based on the equivalent circuits model of the MMA, a genetic algorithm is adopted to identify the best circuit parameters that can realize broadband microwave absorption. High transparent indium tin oxide and poly-methyl methacrylate are utilized to realize the absorber. Optimization and simulation results show that the designed MMA presents a high microwave absorption above 90%, covering a wide frequency of 2.05-15.5 GHz with an impressive FBW of 153.3%. The proposed MMA exhibits extraordinary angular stability. For TM polarization, it can still maintain a fractional bandwidth (FBW) over 114.5% at an incidence angle of 70° and over 142% at an incidence angle of 60°, while the FBW of both TE polarization and TM polarization exceeds 150% when the incidence angle is below 45°. Furthermore, the proposed absorber has the advantages of high transparency and polarization insensitiveness. A prototype of the proposed MMA is fabricated and experimentally tested. The measured results are in excellent agreement with the optimized design and the full-wave simulation results, demonstrating its excellent performance. Most significantly, the overall thickness of the absorber is 0.102 λ at the lowest working frequency and only 1.08 times the causality-dictated minimum sample thickness. The MMA proposed herein provides methods to achieve high compatibility with wideband microwave absorption, optical transparency, and wide-angle incidence, thus enabling a wide range of applications in stealth, electromagnetic pollution reduction, and electromagnetic compatible facilities.

MP/tubular-CF composite carbon foam of high microwave absorption and electromagnetic interference shielding properties

The MWA material hopes to achieve sufficiently low reflection loss, while the EMI shielding pursues sufficiently high electromagnetic shielding efficiency. At present, EMI shielding materials pursue sufficiently low reflection losses to avoid secondary pollution of electromagnetic waves. Therefore, it is the goal pursued by researchers of developing a material with enough high absorption loss and sufficiently low reflection loss. For this purpose, mesophase pitch/hollow carbon fiber composite carbon foam (MP/tubular-CF) was prepared by high-pressure pyrolysis. It was found that tubular-CF could effectively regulate the pore cell structure of the MP/tubular-CF. Meanwhile, tubular-CFs distributed randomly form a complete conductive network in composites, thereby improving the dielectric loss performance of composites. In addition, tubular-CF distributed randomly in composites result in more defects and heterogeneous interfaces which enhancing the electromagnetic wave loss performance. Of the prepared samples, MP/tubular-CF-9 exhibits the minimum reflection loss (RLmin) of −37.84 dB, as high as 32.47 dB of average total shielding efficiency, and 15.06 MPa of compressive strength simultaneously. This work proved a strategy that the synergistic regulation of pore cell structure, conductivity and defects are achieved in the process of composites preparation, which enables the composites to obtain simultaneously excellent MWA performance, EMI shielding performance and compressive strength.

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.

Multifunctional MnFe2O4/TiO2/Ti3C2Tx composites based on in-situ grown TiO2 for efficient microwave absorption, high hydrophobicity, and heat dissipation properties

Despite the fact that the 2D structure Ti3C2Tx with abundant defects and functional groups contributes to the high microwave absorption (MA) performance, it is difficulty to improve the strength and bandwidth by pursuing higher conductivity or loading more groups due to the limitation of intrinsic properties. Therefore, it is important to ingeniously design efficient Ti3C2Tx based MA composites assembling the features of abundant surface groups, good dispersibility, multiple composition, and precise structure. Inspired by the fact that Ti3C2Tx contains thermodynamically metastable marginal Ti atoms, TiO2 nanoparticles can be grown in-situ on Ti3C2Tx nanosheets uniformly and increase the spacing of Ti3C2Tx layers, and then MnFe2O4 nanoparticles are introduced into the layers of Ti3C2Tx by electrostatic self-assembly method for optimized impedance matching. This designed hierarchical MnFe2O4/TiO2/Ti3C2Tx composites shows excellent MA performance, and the minimum reflection loss (RLmin) reaches −46.91 dB with a thickness of 2.5 mm at frequency of 10.4 GHz. The high MA performance mainly comes from the enhanced interfacial polarization induced by edges location and interface region among TiO2, MnFe2O4, and Ti3C2Tx. In addition, the conduction loss existed in the interior untreated Ti3C2Tx, the dielectric loss generated by multiple composition, the multiple scattering from improved large surface specific area all contribute to the excellent MA performance. Meanwhile, the simple preparation process and good stability storage at room temperature under air atmosphere of the MnFe2O4/TiO2/Ti3C2Tx composites promote its exploration on practical use, and the lab-gown cloth coated with MnFe2O4/TiO2/Ti3C2Tx composites shows better electromagnetic shielding properties, hydrophobicity, and heat transfer ability than pure fabric, showing the potential for practical application.

Molybdenum substituted M‐type hexagonal barium ferrite for high microwave absorption performance

AbstractWith the advancement of electrical and electronic devices, overcoming electromagnetic pollution turns into an urgent problem. In this work, high‐valence molybdenum (Mo6+) was doped into M‐type hexagonal barium ferrite (BaFe12‐xMoxO19) to improve its electromagnetic performance. The relationship between the Mo6+ doping concentration and the crystallographic structure, morphology and electromagnetic properties was studied in detail. Structural characterizations authenticate that the Mo6+ ions prefer the 2b site, increasing the lattice values and grain size, and boosting more Fe3+ conversion into Fe2+. The magnetic hysteresis loops demonstrate a reduction of saturation magnetization and coercivity values with the increase of Mo6+ concentration. While the microwave absorption properties were obviously improved by the doping Mo6+, and obtained the highest RLmin value of ‐56.12 dB@16.1 GHz and effective absorption bandwidth of 4.2 GHz at x = 0.1, displaying a potential role in absorbing material.

Enhanced electromagnetic interference shielding in nickel oxide and graphene composite nanostructures loaded polyvinylidene difluoride thin films

Polyvinylidene difluoride nanocomposites having high dielectric, microwave absorption and electromagnetic interference (EMI) shielding properties has been prepared by loading Nickel oxide (NiO) and NiO embedded graphene hybrid nanostructures into PVDF matrix, and characterized. NiO nanoparticle and NiO/graphene were synthesized from hydrothermal reactions at 80 °C. The nanocomposites are prepared by the solvent casting method of NiO and NiO/graphene hybrid nanomaterials embedded PVDF are evaluated for their thermal, morphological, dielectric, microwave absorption and electromagnetic interference shielding behavior. The TGA results revealed that the thermal permanence of the nanocomposites was improved proportional to the NiO and NiO/graphene content in the PVDF matrix. The SEM analysis revealed the dissemination of the NiO nanoparticles (3%) indicating homogeneous distribution unvaryingly throughout the PVDF matrix. The 10 wt% of NiO/Graphene/PVDF composites showed highest conductivity of 6.8 × 10-14 at 1000 Hz and a dielectric constant of 90. The reinforcement of 3% NiO in PVDF matrix leads to a tremendous enrichment in the EMI shielding value with a highest shielding effectiveness of 39 dB at 10.3 GHZ which is considerably higher than the Pristine PVDF and other samples prepared.

Facile synthesis of hollow SiC/C nanospheres for high-performance electromagnetic wave absorption

Hollow silicon carbide/carbon (SiC/C) nanospheres have found wide applications owing to their excellent dielectric properties, high surface area, thermal insulation, and low effective density at high temperatures. However, their hollow structure is typically obtained by removing the templates using strong acids, which can lead to massive waste and severe pollution. Herein, a three-layer nanospheres containing resorcinol-formaldehyde (RF) and SiO2 (RF@SiO2@RF) were first prepared by a simple one-step method and used as precursors. Subsequently, monodispersed hollow SiC/C nanospheres (90 ± 5 nm in diameter) prepared in-situ through carbon thermal reduction. The hollow structure was formed by pyrolysis, eliminating the extra procedure to remove templates. The structure, size, and composition of the nanospheres were precisely controlled via synthesis temperatures (1400, 1450, 1500 °C) and using different raw material ratios. The obtained hollow SiC/C nanospheres demonstrated remarkable resistance to high temperature resistance. The specific surface area of the optimised hollow SiC/C nanospheres reached 301.9 m2 g−1. Their reflection loss (RL) value achieved −41.34 dB at 14.58 GHz, and the effective absorption bandwidth(EAB)was 4.0 GHz (12.77–16.78 GHz) with a thickness of 1.70 mm. The results of this study confirm that the proposed method allows for an in-situ synthesis of hollow SiC/C nanospheres for high temperature microwave absorption with low matching thickness.

Barium and Yttrium Co-doping in Bismuth Ferrite Nanoparticles to Enhance Microwave Properties

The microwave properties of multiferroic Bismuth Ferrite have been widely studied and focus has been placed on the improvement of microwave absorption, impedance matching, effective bandwidth through doping with suitable elements, and formation of nanostructures. In this work, Barium and Yttrium co-doping at the Bi site of BiFeO3 nanoparticles (BayBi1-x-yYxFeO3) were observed to be effective in enhancing the dielectric and magnetic properties of the sample with x = 0.03 and y = 0.1. A minimum reflection loss of −61.7 dB was achieved in the sample for a composite absorber length of 7.5 mm attributed to the best balance observed between dielectric loss (tanδ ε ) and magnetic loss (tanδ μ ) based on the match equation, tanδ ε = tanδ μ . The best impedance matching observed in this sample also supports the observed high microwave absorption required for practical application as microwave absorption material.

Sandwich structure electromagnetic interference shielding composites based on Fe3O4 nanoparticles/PANI/laser-induced graphene with near-zero electromagnetic waves transmission

High-performance electromagnetic interference (EMI) shielding materials with flexible and lightweight characteristics are still a hot research direction, which will be highly promising in many application fields. In this work, laser-induced graphene (LIG) as the top and bottom layer, and binary composites of co-precipitated Fe3O4 NPs and in-situ chemical polymerized PANI (FePA) functioned as the intermediate layer is assembled to prepare a sandwich structure shielding material (FePA/LIG composite). 3D porous LIG with excellent conductivity is conducive to promote reflection and multiple reflections of incident electromagnetic waves (EMWs), while the transmitted EMWs will be further absorbed and attenuated via FePA composite due to its high impedance matching and microwave absorption (MA) properties. Near-zero EMWs transmission can be achieved and the average EMI shielding effectiveness (SE) of FePA/LIG composite (with thickness less than 2 mm) over the entire X-band and Ku-band is 50 dB and 63 dB, respectively. The admirable EMI shielding performance and flexibility of FePA/LIG composite endows enormous potential in portable electronic devices.

Unraveling the role of counter anions on optical and microwave absorption characteristics of flexible copolymers

Engineering the structural architecture of materials is critical for the transmittance of visible light and absorb microwave radiation in various stealth and electronic applications. Transparent copolymers comprising of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were synthesized at different compositions using reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers exhibited a high percentage of light transmittance (>90%) within the visible range owing to the majority fraction of MMA units. The amine functionalities in the synthesized copolymers were ionized at room temperature by treating with dilute acids such as hydrochloric acid (HCl), trifluoroacetic acid (TFA), nitric acid (HNO3), tetrafluoroboric acid (HBF4), and hexafluorophosphoric acid (HPF6). The quaternization of the side-chain amine groups have resulted in a series of copolymer salts with an ion-pair complex. The investigation of the counter anion effect on the conductivity of the materials has been carried out to produce the highly transparent and conductive MMA-based copolymers. The presence of partially mobile Cl⁻ counter anions in the copolymers can result in conductance as high as 0.939 mS cm−1. Moreover, the optically transparent MMA-based copolymer salts have witnessed a high microwave absorption due to multiple reflections from structural and physical anisotropies.

Lightweight Co3O4/CC Composites with High Microwave Absorption Performance.

With the rapid development of electronic and communication technology for military radars, the demand for microwave-absorbing materials in the low-frequency range with thin layers is growing. In this study, flexible Co3O4/CC (carbon cloth) composites derived from Co-MOFs (metal-organic frameworks) and CC are prepared using hydrothermal and thermal treatment processes. The flexible precursors of the Co-MOFs/CC samples are calcined with different calcination temperatures, for which the material structure, dielectric properties, and microwave absorption performance are changed. With the increases in calcination temperature, the minimum reflection loss of the corresponding Co3O4/CC composites gradually moves to the lower frequency with a thinner thickness. In addition, the Co3O4/CC composites with the 25 wt% filler loading ratio exhibit the minimum reflection loss (RL) of -46.59 dB at 6.24 GHz with a 4.2 mm thickness. When the thickness is 3.70 mm, the effective absorption bandwidth is 3.04 GHz from 5.84 to 8.88 GHz. This study not only proves that the Co3O4/CC composite is an outstanding microwave-absorbing material with better flexibility but also provides useful inspiration for research on wideband microwave absorption materials below 10 GHz.

Effect of fluorine doping on the performance of multi−heteroatom doped carbons (F,N,B−C or F,N,S−C) for microwave absorption

Heteroatom-doped porous carbon materials offer great promise as microwave absorbers. However, template−free methods for synthesizing porous carbon materials rich in heteroatoms (N,F,B and S), necessary for tuning impedance matching and optimizing attenuation losses, need to be dicovered. In this article, we report the successful preparation of porous fluorine−doped multi−heteroatom carbons (F,N,B−C and F,N,S−C) by the high−temperature pyrolysis of polypyrrole-based precursors. The introduction of the heteroatoms created defective carbon structures with high microwave absorption ability. In particular, the F,N,S−C absorber offered an excellent loss capacity, including the RLmin of − 38.0 dB at 13.2 GHz (2.5 mm thickness) and the EAB of 6.3 GHz from 11.7 − 18 GHz (2.0 mm thickness) using a filler amount of only 9.0 wt%. The outstanding microwave absorption properties are the result of the interactions between incoming microwaves and carbon defects/pores, which together provide a moderate conductive loss, good polarization relaxation (interfacial polarization and defect/dipole polarization) as well as scattering of microwaves via reflection.

High mechanical properties and microwave absorption performances of SiCw/Si3N4 ceramic composites

High mechanical properties and microwave absorption performances of SiCw/Si3N4 ceramic composites

Iron carbide interface modulating for synergies of 3D-graphene-like and iron-coated Fe3O4 particles for high microwave absorption performance

Iron carbide interface modulating for synergies of 3D-graphene-like and iron-coated Fe3O4 particles for high microwave absorption performance

Large aspect ratio makes high low-frequency microwave absorption performance via a unique roll grinding method for flake FeSiAl

Increasing aspect ratio for flake magnetic alloy to facilitate microwave absorption capability in low-frequency is highly desired but remains changes by conventional methods. Here we report a unique roll grinding method to fabricate flake FeSiAl alloys with large aspect ratio of 40–100, which is beyond the limit of traditional ball milling method (< 40). As a result, such roll ground flake FeSiAl obtains a 3 times larger low frequency reflection loss (RL= −56.2 dB at 3.47 GHz) than that of ball milled one. Furthermore, the fabricated microwave absorber shows an ultra-wide effective absorption band of 14 GHz (RL < −20 dB, 2.3–16.3 GHz) with the thin coating thickness of 1.6–6.0 mm. Further analysis showed its exceptional properties stem from large aspect ratio induced satisfied impedance matching, enhanced magnetic loss, and intense dielectric loss. Our findings provide an easy industrial preparation method for making flake magnetic alloys that possess unconventional and technologically important electromagnetic properties.

Multi-heterostructure composites of Fe3O4 coated Janus nanoparticles and MWCNTs with high microwave absorption

Microwave-absorbing materials with heterostructure represent a major challenge and opportunity in enabling strong microwave absorption over a wide bandwidth. Here, novel hydrophilic multi-heterostructure composites (Mag@J/MWCNT) were fabricated by combining nanostructured Fe3O4 covered snowman-like Janus nanoparticles (Mag@J) with MWCNTs for enhanced microwave absorption. The good hydrophilicity and low reflection loss (RL) demonstrated the potential application of Mag@J as an effective microwave absorbent with environmentally friendly processibility. Further, the multi-heterostructure composites constructed by Mag@J (with 77.73 wt% Fe3O4) and MWCNTs exhibited strong absorption intensity (RL = −38.98 dB), wide bandwidth (6.04–8.23 GHz), and low thickness (3.5 mm). The excellent microwave absorption properties were attributed to the strong dielectric loss, magnetic loss, and good impedance matching of different components in multi-heterostructure composites, as well as multiple reflection absorption of microwave in the hollow sphere of Janus particle. Therefore, this work provides important inspiration for multi-heterostructure composites to achieve potential applications as electromagnetic wave absorbing materials.

Optimization design of broadband absorber for high optical transparency

A broadband absorber with high optical transparency is proposed and realized using an optimization-designed method. The absorber’s reflection, lossy, and dielectric layers are considered for obtaining high optical transparency. First, to maintain microwave absorption, the artificial structures of the reflection layer are designed on the micron scale. Low square resistance and high optical transparency are achieved simultaneously. Then, considering the artificial structure fabrication process [fabricated on polyethylene terephthalate (PET)], high light transmittance polymethyl methacrylate (PMMA) was selected as the material of the dielectric layer. The permittivity of PMMA is similar to that of PET. The light reflection of layer-to-layer is reduced, and the light transmittance is improved. Finally, under the same microwave absorption band and absorption efficiency, the topology structures of the lossy layer are optimized to increase the duty ratio and the light transmittance. Through the above-mentioned design, high optical transparency and broadband microwave absorption are achieved simultaneously. The simulated and measured results prove that more than 90% of the absorption rate is obtained from 4.4 to 11.5 GHz (89.3%) and the average light transmittance reached 80%. The results verify the optimization-designed method’s effectiveness and provide technical support for transparent absorbers to be better applied to optical windows.

High-temperature multispectral stealth metastructure from the microwave-infrared compatible design

Microwave and infrared stealth technology plays an important role in the development of military equipment and national defense. However, with the development of high Mach number weapons, it is urgent to develop the new materials with high temperature multispectral compatible stealth. In this paper, a new multispectral stealth metastructure is proposed, which can achieve high temperature microwave absorption and infrared stealth simultaneously. The metastructure is optimized based on Large-Mutation Genetic Algorithm (LMGA), and the high temperature resistant patterned resistive film (PRF) is reasonably distributed to dissipate the incident microwave energy. The high temperature infrared stealth is realized by the dual regulation of high-strength thermal insulation skeleton and low emissivity infrared metasurface to reduce target infrared radiation. Effective bandwidth (≤−10 dB) at 1000 °C is 2–3.5 GHz and 5.4–18 GHz. Low thermal insulation (∼0.104 W/(m·k)) and low infrared emissivity (∼0.39 at 800 °C) can reduce the target infrared radiation energy by 91.7%. This research provides an effective way to design microwave infrared compatible stealthy materials with huge multifunction.

Sequential Architecture Induced Strange Dielectric‐Magnetic Behaviors in Ferromagnetic Microwave Absorber

AbstractThe high filler loading (FL) is a bottleneck in developing lightweight ferromagnetic microwave absorbers (MAs) for the actual applications. Sequential architecture design of MAs can induce strange physical behaviors due to the unique coupling‐enhancement effect between functional units, providing a vast potential for achieving high microwave absorption performance. However, the FLs of current sequential MAs fail to be designed on demand because the strange dielectric‐magnetic behaviors cannot be fulfilled. The influence of sequential architecture engineering on the macroscopic properties or microscopic loss mechanism still needs more exploration. Herein, based on four mesoscopic models (particles, chains, bundles, and fibers) of ferromagnetic functional units, a series of ferromagnetic MAs with different sequential architectures are prepared via a bottom‐up self‐assembly method. The fibrous samples exhibit the best microwave absorption performance (−51.3 dB, 4.12 GHz) at a breakthrough FL of 2 wt%, which is one order of magnitude less than other ferromagnetic MAs. Strange dielectric‐magnetic behaviors, including negative permittivity and heterodromous chiral vortex, occur due to functional units with lateral and fibrous configurations. Further, four special models are established to reveal the microwave attenuation evolutionary mechanism. This study clarifies the relationship between sequential architecture and strange dielectric‐magnetic behaviors, which provides new sight to understand microscopic electromagnetic loss mechanism.