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Water is considered an effective microwave absorber due to its high transmittance and frequency-dispersive dielectric constant, yet it is challenging to form it into a stable state as an absorber. Herein, we developed a water-containing microwave absorber using chemical vapor deposition (CVD), namely, the bifunctional carbon/NaCl multi-interfaces hybrid with excellent water harvesting and microwave absorption performance. Carbon/NaCl exhibits remarkable water harvesting abilities from air, exceeding 210 % of its weight in 12 h. The development of the hydrophilic/hydrophobic heterojunction interface is responsible for this outstanding performance. Additionally, the interfacial polarization provided by carbon/NaCl, along with the dipole polarization induced by the internally captured water and defects, enhances its microwave absorption. The carbon/NaCl hybrid achieved a minimum reflection loss (RLmin) of -69.62 dB at 17.1 GHz with a thickness of 2.13 mm, and a maximum effective absorption bandwidth (EABmax) of 6.74 GHz at a thickness of 2.5 mm. Compared with raw NaCl (RLmin of -24.5 dB, EABmax of 3.88 GHz), the RLmin and EABmax values of the absorber increased by approximately 2.85 and 1.74 times. These results highlight the potential for bifunctional carbon/NaCl hybrid in applications within extreme environments, presenting a promising avenue for further research and development.

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The optimization of electromagnetic microwave absorbing (EMA) materials for radar stealth has been a continuous endeavor. However, meeting the defense requirements across multiple-frequency bands in increasingly complex and variable environments remains challenging. Drawing inspiration from the cytoskeleton-organelle structure, we designed and prepared a hierarchical MXene/NiFe2O4/calcined melamine foam (MNC) composite. The composite exhibits efficient and adjustable microwave absorption, infrared stealth, and solar absorption performance through the synergistic interaction of the components and the spatial effect of its novel microstructure. The composite achieves a minimum reflection loss of -58.57 dB and an effective absorption bandwidth (EAB) of 7.00 GHz, both of which can vary with the thickness. MNC also offers stable infrared stealth performance for heat sources ranging from 37 to 300 °C and high solar absorptivity up to 96.2%, promoting ambient-temperature-adaptive infrared stealth through electricity-sunlight cooperative regulation. With exceptional environmental adaptability characteristics such as photothermal conversion, lightness, elasticity, and hydrophobicity, the MNC composite holds promise as a multispectrum defense material for radar, infrared, and visible light for various forms of equipment, clothing, and wearables in harsh conditions.

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In this study, Zn-Al ferrite/polypyrrole (PPy) nanocomposites were synthesized and thoroughly characterized to explore their potential for microwave applications. X-ray diffraction analysis confirmed the presence of ZnO, AlFeO3, and Fe2O3 phases, with the crystal size decreasing from 31 nm to 19.6 nm as aluminum content increased. High-resolution transmission electron microscopy (HR-TEM) revealed a distinctive core-shell morphology, where the polypyrrole encapsulates the ZnAlxFe2-xO4 particles. Magnetic measurements showed that decreasing aluminum concentration led to a reduction in both saturation magnetization (Ms) from 75 emu/g to 36 emu/g and remanent magnetization (Mr) from 2.26 emu/g to 2.00 emu/g. Dielectric analysis indicated that both the real (ε') and imaginary (ε″) components of dielectric permittivity decreased with increasing frequency, particularly between 10 and 14 GHz. Furthermore, electrical modulus analysis highlighted the significant impact of aluminum doping on relaxation time (τIP), indicating the presence of interface polarization. Impedance spectroscopy results underscored the dominance of interface polarization at lower frequencies and the presence of strong conduction paths at higher frequencies. These combined magnetic and dielectric loss mechanisms suggest that the Zn-Al ferrite/polypyrrole nanocomposite is a promising candidate for advanced microwave absorption applications.

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Highly efficient electromagnetic wave (EMW)-absorbing multicomposites can be fabricated by constructing particular structures using suitable components. Expanded graphite (EG) has a 3D, low-density porous structure; however, it suffers from poor impedance matching and EMW absorption properties. Based on this information, in the present study, NiCo2S4 components with different morphologies are successfully loaded onto a 3D EG surface using a facile microwave solvothermal method to achieve a synergistic effect between the different components. The NiCo2S4 content is adjusted to alter the compositional morphology and electromagnetic parameters of the composites to achieve impedance-matching and obtain excellent EMW absorption properties. The heterogeneous interface between EG and NiCo2S4 induces an inhomogeneous spatial charge distribution and enhances interfacial polarization. The defects in the material and oxygen-containing groups induce dipole polarization, which enhances the polarization-relaxation process of the composites. The 3D porous heterostructure of the "Fibonacci cauliflower"-shaped NiCo2S4/EG composites results in an optimal reflection loss of -64.93 dB at a filler rate of only 14 wt.%. Analysis of the synergistic conduction loss and polarization loss mechanisms in carbon-based materials with heterogeneous interfaces has led to the development of excellent EMW absorption materials.

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Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

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The constantly evolving environment imposes increasingly stringent demands on the mechanical qualities of materials employed for absorbing electromagnetic waves (EMWs). Therefore, there is an urgent need for advanced materials capable of efficiently absorbing EMWs and withstanding harsh electromagnetic conditions. In this study, the electrodeposition method was effectively used to synthesize nickel-cobalt layered double hydroxides (NiCo-LDHs) in a controlled manner on a composite structure of carbon nanotubes and carbon foam, creating an exquisite construction. The manipulation of the electrodeposition time facilitated the regulation of the density of the layered structure within the composite material, thereby significantly enhancing its polarization relaxation performance. Increased defect sites and interface polarization enhance impedance matching and the attenuation constant, resulting in greatly improved absorption performance. The optimized sample demonstrated exceptional wave-absorbing performance in comparative experimental analysis, attaining a maximum reflection loss of -58.18 dB. It also has an effective absorption bandwidth of 5.36 GHz at a wavelength of 2.28 mm. The exceptional isolation effect of LDH, coupled with the outstanding insulation ability of the porous carbon skeleton, confers remarkable corrosion resistance and thermal insulation performance on the composite material. Hence, this discovery offers novel insights into designing environmentally tolerant absorbent materials.

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The construction of heterogeneous microstructure and the selection of multicomponents have turned into a research hotspot in developing ultralight, multifunctional, high-efficiency electromagnetic wave absorbing (EMA) materials. Although aerogels are promising materials to fulfill the above requirements, the increase in functional fillers inevitably leads to the deterioration of intrinsic properties. Tuning the electromagnetic properties from the structural design point of view remains a difficult challenge. Herein, we design customized pore creation strategies via introducing sacrificial templates to optimize the conductive path and construct the discontinuous dielectric medium, increasing dielectric loss and achieving efficient microwave absorption properties. A 3D porous composite (MEM) was crafted, which encapsulated an EVA/FeCoNi (EVA/MNPs) framework with Ti3C2Tx MXene coating by employing a direct heated cross-linking and immersion method. Controllable adjustment of the conductive network inside the porous structure and regulation of the dielectric character are achieved by porosity variation. Eventually, the MEM-5 with a porosity of 66.67% realizes RLmin of -39.2 dB (2.2 mm) and can cover the entire X band. Moreover, through off-axis electronic holography and the calculation of conduction loss and polarization loss, the dielectric property is deeply investigated, and the inner mechanism of optimization is pointed out. Thanks to the inherent characteristic of EVA and the porous structure, MEM-5 showed excellent thermal insulating and superior compressibility, which can maintain 60 °C on a 90-100 °C continuous heating stage and reached a maximum compressive strength of 60.12 kPa at 50% strain. Conceivably, this work provides a facile method for the fabrication of highly efficient microwave absorbers applied under complex conditions.

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For materials with coexisting phases, the transition from a random to an ordered distribution of materials often generates new mechanisms. Although the magnetic confinement effect has improved the electromagnetic (EM) performance, the transition from random to ordered magnetic confinement positions remains a synthetic challenge, and the underlying mechanisms are still unclear. Herein, precise control of magnetic nanoparticles is achieved through a spatial confinement growth strategy, preparing five different modalities of magnetic confined carbon fiber materials, effectively inhibiting magnetic agglomeration. Systematic studies have shown that the magnetic confinement network can refine CoNi NPs size and enhance strong magnetic coupling interactions. Compared to CoNi@HCNFs on the hollow carbon fibers (HCNFs) outer surface, HCNFs@CoNi constructed on the inner surface induce stronger spatial charge polarization relaxation at the interface and exhibit stronger magnetic coupling interactions at the inner surface due to the high-density magnetic coupling units at the micro/nanoscale, thereby respectively enhancing dielectric and magnetic losses. Remarkably, they achieve a minimum reflection loss (RLmin) of -64.54 dB and an absorption bandwidth of 5.60 GHz at a thickness of 1.77 mm. This work reveals the microscale mechanism of magnetic confinement-induced different polarization relaxation and magnetic response, providing a new strategy for designing magnetic materials.

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In this work, N-doped and oxygen vacancy-rich NiCo2O4/NiO/Co3O4composites are synthesized by the direct calcination method. Noticeably, by changing the additive concentrations of urea dissolved in DMF (N-N dimethylformamide), the electromagnetic wave (EMW) absorption abilities of NiCo2O4/NiO/Co3O4composite effectively. A maximum reflection loss (RLmax) value at 12.94 GHz for a 2.8 mm thick sheet is -29.76 dB, while its effective absorption bandwidth (RL < -10 dB) reaches 4.21 GHz. In-depth research of possible mechanisms of EMW absorption enhancement. Owing to its simple preparation method and superb EMW absorption properties, the NiCo2O4/NiO/Co3O4composites have a chance to be suitable candidates for high-property EMW absorbers.

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To address the challenges of slow curing speed and suboptimal microwave absorption during the paving of cold-mixed and cold-laid asphalt mixtures, this study introduces SiC-Fe3O4 composite material (SF) into emulsified asphalt mixtures to enhance microwave absorption and accelerate curing via microwave heating. Initially, based on the maximum density curve theory, an appropriate mineral aggregate gradation was designed, and the optimal ratio of emulsified asphalt mixture was determined through mixing tests, cohesion tests, wet wheel wear tests, and load wheel sand adhesion tests. Subsequently, the influence of SF content on the mixing performance of emulsified asphalt mixtures was analyzed through mixing and consistency tests. Finally, the microwave absorption performance of the mixture was evaluated by designing microwave heating tests under different conditions, using temperature indicators and quality indicators. The experimental results indicate that when SF content ranges from 0% to 4%, the mixing performance of the emulsified asphalt mixture meets specification requirements. The dosage of SF, SF composite ratio, and microwave power significantly impact microwave absorption performance, whereas environmental temperature has a relatively minor effect. The optimal mix ratio for the emulsified asphalt mixture is mineral aggregate:modified emulsified asphalt:water:cement = 100:12.8:6:1. The ideal SF dosage is 4%, with an optimal SiC to Fe3O4 composite ratio of 1:1, and a suitable microwave power range of 600-1000 W.

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Interface design has enormous potential for the enhancement of interfacial polarization and microwave absorption properties. However, the construction of interfaces is always limited in components of a single dimension. Developing systematic strategies to customize multidimensional interfaces and fully utilize advantages of low-dimensional materials remains challenging. Two-dimensional transition metal dichalcogenides (TMDCs) have garnered significant attention owing to their distinctive electrical conductivity and exceptional interfacial effects. In this study, a series of hollow TMDCs@C fibers are synthesized via sacrificial template of CdS and confined growth of TMDCs embedded in the fibers. The complex permittivity of the hollow TMDCs@C fibers can be adjusted by tuning the content of CdS templates. Importantly, the multidimensional interfaces of the fibers contribute to elevating the microwave absorption performance. Among the hollow TMDCs@C fibers, the minimum reflection loss (RLmin) of the hollow MoS2@C fibers can reach -52.0 dB at the thickness of 2.5 mm, with a broad effective absorption bandwidth of 4.56 GHz at 2.0 mm. This work establishes an alternative approach for constructing multidimensional coupling interfaces and optimizing TMDCs as microwave absorption materials.

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Composite plates comprising a blend of rare earth neodymium-(Nd) doped M-type barium ferrite (BaM) with CNTs (carbon nanotubes) and polyethylene WERE synthesized through a self-propagating reaction and hot-pressing treatment. The plates' microscopic characteristics were analyzed utilizing X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), thermo-gravimetric analysis (TGA), Raman, and scanning electron microscopy (SEM) analytical techniques. Their microwave absorption performance within the frequency range of 8.2 to 18 GHz was assessed using a vector network analyzer. It showed that CNTs formed a conductive network on the surface of the Nd-BaM absorber, significantly enhancing absorption performance and widening the absorption bandwidth. Furthermore, dielectric polarization relaxation was investigated using the Debye theory, analyzing the Cole-Cole semicircle. It was observed that the sample exhibiting the best absorbing performance displayed the most semicircles, indicating that the dielectric polarization relaxation phenomenon can increase the dielectric relaxation loss of the sample. These findings provide valuable data support for the lightweight preparation of BaM-based absorbing materials.

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A flexible phase-change film with thermal management and microwave absorption capabilities was developed for use in wearable devices. The film was created using a solution casting method based on a porous carbon-loaded eicosane (LP33/EI) material. LP33 served as the porous encapsulation medium, while Eicosane (EI) acted as the phase change component. The flexible substrate was a blend of polyvinyl alcohol (PVA) and bacterial cellulose nanocellulose (BC). The ultrathin film had a thickness of 0.262 mm, and LP33/EI-4 exhibited exceptional mechanical strength of 188 MPa. Testing revealed that the phase transition process had melting and crystallization enthalpies of 134.71 J/g and 126.11 J/g, respectively. The encapsulation structure effectively prevented any leakage during the phase transition process. Under simulated solar irradiation of 200 mW/cm2, LP33/EI-4 achieved a photothermal conversion efficiency (η) of 89.46 %. Additionally, the porous LP33 structure and high dielectric loss contributed to remarkable microwave absorption capabilities of -42 dB in the X-band and - 52 dB in the Ku-band. Overall, LP33/EI films demonstrated exceptional performance in thermal management, energy storage, and microwave absorption, making them an ideal choice for a variety of applications in wearable devices.

Asunto(s)

RESUMEN

Carbon based materials are widely used in the preparation of microwave absorption materials due to their low density, high attenuation loss and large specific surface area. However, their high conductivity usually leads to high reflection loss. In this study, multi-layer heterogeneous interfaces were constructed in liquid metal graphite hybrid powder to reduce reflection loss and enhance microwave absorption performance. Gallium oxide (Ga2O3) layer was formed in Ga coated graphite powder to improve impedance matching and attenuation constant via an annealing treatment. Specifically, the hybrid particles with 50 wt% Ga and being annealed at 120 °C for 2 h have a minimum reflection loss (RLmin) value of -42.68 dB and a maximum effective absorption bandwidth (EAB) of 4.11 GHz at a thickness of 3.3 mm. The hybrid particles not only have multi-layer structures with different electrical conductivity, but also form heterojunctions between different interfaces, which can further enhance dipole and interfacial polarization.

RESUMEN

Reconfigurable metamaterial absorbers (MAs), consisting of tunable elements or deformable structures, are able to transform their absorbing bandwidth and amplitude in response to environmental changes. Among the options for building reconfigurable MAs, origami/kirigami structures show great potential because of their ability to combine excellent mechanical and electromagnetic (EM) properties. However, neither the trial-and-error-based design method nor the complex fabrication process can meet the requirement of developing high-performance MAs. Accordingly, this work introduces a deep-learning-based algorithm to realize the fast inverse design of origami MAs. Then, an accordion-origami coding MA is generated with reconfigurable EM responses that can be smoothly transformed between ultrabroadband absorption (5.5-20 GHz, folding angle α = 82°) and high reflection (2-20 GHz, RL > -1.5 dB, α = 0°) under y-polarized waves. However, the asymmetric coding pattern and accordion-origami deformation lead to typical polarization-sensitive absorbing performance (2-20 GHz, RL > -4 dB, α < 90°) under x-polarized waves. For the first time, a kirigami polarization rotation surface with switchable operation band is adapted to balance the absorbing performance of accordion-origami MA under orthogonal polarized waves. As a result, the stacked origami-kirigami MA maintains polarization-insensitive ultrabroadband absorption (4.4-20 GHz) at ß = 0° and could be transformed into a narrowband absorber through deformation. Besides, the adapted origami/kirigami structures possess excellent mechanical properties such as low relative density, negative Poisson's ratio, and tunable specific energy absorption. Moreover, by modulating the PEDOT:PSS conductive bridges among MXene nanosheets, a series of low-concentration MXene-PEDOT:PSS inks (∼46 mg·mL-1) with adjustable square resistance (5-32.5 Ω/sq) are developed to fabricate the metamaterials via screen printing. Owing to the universal design scheme, this work supplies a promising paradigm for developing low-cost and high-performance reconfigurable EM absorbers.

RESUMEN

Currently, facing electromagnetic protection requirement under complex aqueous environments, the bacterial reproduction and organic dye corrosion may affect the composition and micro-structures of absorbers to weaken their electromagnetic properties. To address such problems, herein, a series of CoFe2O4@BCNPs (cobalt ferrite @ bio-carbon nanoparticles) composites are synthesized via co-hydrothermal and calcining process. The coupling of magnetic cobalt ferrite and dielectric bio-carbon derived from Apium can endow the composite multiple absorption mechanisms and matched impedance for effective microwave absorption, attaining a bandwidth of 8.12 GHz at 2.36 mm and an intensity of -49.85 dB at 3.0 mm. Due to the ROS (reactive oxygen species) stimulation ability and heavy metal ions of cobalt ferrite, the composite realizes an excellent antibacterial efficiency of 99% against Gram negative bacteria of Escherichia coli. Moreover, the loose porous layer of surface stacked bio-carbon can promote the adsorption of methylene blue for subsequent eliminating, a high removal rate of 90.37% for organic dye can be also achieved. This paper offers a new insight for rational design of composite's component and micro-structure to construct multi-functional microwave absorber for satisfying the electromagnetic protection demand in complicated environments.

RESUMEN

The development of new electromagnetic absorbing materials is the main strategy to address electromagnetic radiation. Once traditional electromagnetic wave-absorbing materials are prepared, it is difficult to dynamically change their electromagnetic wave-absorbing performance. Facing the complexity of the information age and the rapid development of modern radar, it is significant to develop intelligent modulation of electromagnetic wave-absorbing materials. Here, CNTs/VO2/ANF composite aerogels with dynamic frequency tunability and switchable absorption on/off were synthesized. Based on the phase change behavior of VO2, the degree of polarization and interfacial effects of multiple heterogeneous interfaces between VO2 and CNTs and aramid nanofibers (ANFs) were modulated at different temperatures. With the increase in temperature (from 25 to 200 °C), the maximum absorption frequency of the frequency tunable aerogel is modulated from 12.24 to 8.56 GHz in the X-band, and the absorption intensity remains stable. The maximum effective switching bandwidth (ΔEAB) of the wave-absorbing switchable aerogel is 3.70 GHz. This study provides insights into intelligent electromagnetic wave absorption performance and paves the way for temperature-driven application of intelligent modulation of electromagnetic absorbers.

RESUMEN

A novel low-density composite for the absorption of microwaves was prepared by loading La-doped spinel cobalt ferrite (La-CFO) onto biomass carbon (BC) derived from corn stalks using a hydrothermal method. This composite (La-CFO@BC) not only maintained the advantageous properties of low density and abundant porosity, but also exhibited a unique morphology, with La-CFO displaying a carpet-like structure interspersed with dandelion-shaped particles. The incorporation of La-CFO effectively tuned the electromagnetic parameters of the composite, thereby improving its impedance-matching attributes and its ability to absorb microwave radiation. At a frequency of 12.8 GHz for electromagnetic waves and with a thickness of 2.5 mm, La-CFO@BC demonstrated remarkable performance in microwave absorption, attaining a noteworthy minimum reflection (RLmin) of -53.2 dB and an effective absorption bandwidth (EAB) of 6.4 GHz. Furthermore, by varying the thickness of the La-CFO@BC within the range of 1.0 to 5.5 mm, the EAB could be broadened to 13.8 GHz, covering the entire X-band, the entire Ku-band, and a substantial portion of the C-band. This study demonstrated that La-CFO@BC was a promising alternative for electromagnetic wave attenuation, which offered superior performance in microwave absorption.

RESUMEN

Two-dimensional carbon-based materials have shown promising electromagnetic wave absorption capabilities in mid- and high-frequency ranges, but face challenges in low-frequency absorption due to limited control over polarization response mechanisms and ambiguous resonance behavior. In this study, we propose a novel approach to enhance absorption efficiency in aligned three-dimensional (3D) MXene/CNF (cellulose nanofibers) cavities by modifying polarization properties and manipulating resonance response in the 3D MXene architecture. This controlled polarization mechanism results in a significant shift of the main absorption region from the X-band to the S-band, leading to a remarkable reflection loss value of - 47.9 dB in the low-frequency range. Furthermore, our findings revealed the importance of the oriented electromagnetic coupling in influencing electromagnetic response and microwave absorption properties. The present study inspired us to develop a generic strategy for low-frequency tuned absorption in the absence of magnetic element participation, while orientation-induced polarization and the derived magnetic resonance coupling are the key controlling factors of the method.

RESUMEN

Atomic doping is widely employed to fine-tune crystal structures, energy band structures, and the corresponding electrical properties. However, due to the difficulty in precisely regulating doping sites and concentrations, establishing a relationship between electricity properties and doping becomes a huge challenge. In this work, a modulation strategy on A-site cation dopant into spinel-phase metal sulfide Co9S8 lattice via Fe and Ni elements is developed to improve the microwave absorption (MA) properties. At the atomic scale, accurately controlling doped sites can introduce local lattice distortions and strain concentration. Tunned electron energy redistribution of the doped Co9S8 strengthens electron interactions, ultimately enhancing the high-frequency dielectric polarization (ɛ' from 10.5 to 12.5 at 12 GHz). For the Fe-doped Co9S8, the effective absorption bandwidth (EAB) at 1.7 mm increases by 5%, and the minimum reflection loss (RLmin) improves by 26% (EAB = 5.8 GHz, RLmin = -46 dB). The methodology of atomic-scale fixed-point doping presents a promising avenue for customizing the dielectric properties of nanomaterials, imparting invaluable insights for the design of cutting-edge high-performance microwave absorption materials.