Absorption Bandwidth Research Articles

Efficient Nanofibrous Electromagnetic Wave Absorber Inspired by Spider Silk Hunting.

With the rapid advancements in wireless communication and radar detection technologies, there has been a significant uptick in the utilization frequency of electromagnetic waves across both civilian and military sectors, consequently generating substantial electromagnetic radiation and interference. These electromagnetic pollutants present a considerable threat to public health and information security. Consequently, materials capable of absorbing and mitigating electromagnetic pollution have garnered significant attention.The nanomaterials with multiple components and various heterogeneous interfaces have been considered as preferred efficient electromagnetic wave (EMW) absorbers. In this work, carbon nanofibers doped with magnetic metal oxide particles (Co/Ni-CNFs) are prepared by electrospinning and heat treatment. In these samples, the minimum reflection loss can reach -40.13dB at 4.6mm, and the widest effective absorption bandwidth is 4.4GHz. The excellent microwave absorption is attributed to the appropriate impedance matching. The electromagnetic parameters of Co/Ni-CNFs are balanced by adjusting the concentration of magnetic metal-organic framework material (MOFs) in the precursor solution. It is believed that this work can provide a reference for developing lightweight, flexible, and robust electromagnetic wave-absorbing materials.

High anisotropy 2D large-size iron-based coral for C-band ultra-wide microwave absorption

Lightweight microwave-absorbing (MA) materials with broadband absorption in the C-band remain challenging to date. Recent studies have shown that promoting anisotropy in materials is expected to break the Snoek limit and enhance the absorption performance of magnetic materials in the C-band. In this paper, two-dimensional (2D) large-size coral-like iron-based composites (LCIC) were prepared using an NH4NO3-assisted blow molding separation strategy. The special structure with large shape anisotropy realizes a wide and strong natural magnetic resonance, leading to strong magnetic loss. The enhanced natural resonance effectively broadens the effective absorption bandwidth (EAB) of the LCIC in the C-band. The minimum reflection loss (RLmin) of LCIC is −41.64 dB, and the EAB is 5.42 GHz (3.83–9.25 GHz), covering the entire C-band. Strong natural resonance is necessary to improve the dissipation of magnetic losses in low-frequency electromagnetic waves. This work explores the important role of size effect in enhancing the C-band absorption properties of magnetic materials. It provides a feasible reference for the preparation of C-band broadband, strongly absorbing MA materials.

Functional Carbon Springs Enabled Dynamic Tunable Microwave Absorption and Thermal Insulation.

Electromagnetic (EM) wave pollution and thermal damage pose serious hazards to delicate instruments. Functional aerogels offer a promising solution by mitigating EM interference and isolating heat. However, most of these materials struggle to balance thermal protection with microwave absorption (MA) efficiency due to a previously unidentified conflict between the optimizing strategies of the two properties. Herein, this study reports a solution involving the design of a carbon-based aerogel called functional carbon spring (FCS). Its unique long-range lamellar multi-arch microstructure enables tunable MA performance and excellent thermal insulation capability. Adjusting compression strain from 0% to 50%, the adjustable effective absorption bandwidth (EAB) spans up to 13.4GHz, covering 84% of the measured frequency spectrum. Notably, at 75% strain, the EAB drops to 0GHz, demonstrating a novel "on-off" switchability for MA performance. Its ultralow vertical thermal conductivity (12.7mW m-1 K-1) and unique anisotropic heat transfer mechanism endow FCS with superior thermal protection effectiveness. Numerical simulations demonstrate that FCS outperforms common honeycomb structures and isotropic porous aerogels in thermal management. Furthermore, an "electromagnetic-thermal" dual-protection material database is established, which intuitively demonstrates the superiority of the solution. This work contributes to the advancement of multifunctional MA materials with significant potential for practical applications.

Study on the electromagnetic wave absorption performance of dual-loss type composite MWCNT/CIP/GF/EP

Abstract The electromagnetic properties of single-loss glass fiber (GF) absorbing composites with the addition of multi-walled carbon nanotube (MWCNT) particles and single-loss glass fiber (GF) absorbing composites with the addition of carbonyl iron powder (CIP) particles in the X-band were studied. Using CST electromagnetic simulation combined with experiments, dual-loss multi-walled carbon nanotube/carbonyl iron powder/glass fiber/epoxy (MWCNT/CIP/GF/EP) resin absorbing composites were designed and prepared. The effects of thickness ratio and periodic layering on the absorbing properties of dual-loss glass fiber absorbing composites were investigated. The results show that by changing the thickness ratio and periodic layering, the impedance matching and attenuation characteristics of the dual-loss glass fiber absorbing composites can be altered, thereby affecting the overall absorbing performance. The optimal group exhibited a maximum reflection loss of -55.3 dB at 8.5 GHz, with an effective absorption bandwidth of 3.0 GHz, covering 71.4% of the X-band.

Enhanced SiC/NFG/Ni ternary composite microwave absorbing materials with micro-network structures produced by selective laser sintering

In this paper, a ternary composite wave-absorbing material consisting of silicon carbide (SiC), natural flake graphite (NFG) and nickel (Ni) has been successfully fabricated through a combined process of selective laser sintering (SLS) and vacuum pressure impregnation. The study investigated how the content of SiC powder affected the absorption capacity and mechanical performances of the composites. The findings indicate that as the proportion of SiC powder rises, the porosity of the composites diminishes, while the bending strength increases. As the content of SiC is 40 wt%, the porosity is 52.14 % and the flexure strength is 9.58 MPa, approximately five times greater than that of graphite-type ceramic preforms. The composite’s electromagnetic wave-absorbing capability initially improves and then declines with the increase of SiC content. When the SiC content is 10 wt% and the thickness is 1.5 mm, the composite absorbing material exhibits optimal electromagnetic absorption performance, with a minimum reflection loss (RLmin)of −44.04 dB and an effective absorption bandwidth (EAB) of 5.42 GHz (8.24–13.66 GHz). The composite material, characterized by its lightweight, high strength, and broad frequency range, shows promise for applications in microwave absorption technology.

Exploration of physical aspects of Li2AgAsZ6 (Z = F, Cl, Br, I) double perovskites for energy harvesting perspectives

Using density functional theory, the current investigation investigates the physical attributes of the halide double perovskites Li2AgAsZ6 (Z = F, Cl, Br, I). The cubic layout and values of the octahedral and tolerance factors have been evaluated to confirm phase stability. The formation energy of each perovskite has been calculated to ensure thermodynamic stability. The electronic properties have been elaborated, which indicates the semiconductor behavior of Li2AgAsZ6. The calculations exhibited that the energy band gaps of Li2AgAsF6, Li2AgAsCl6, Li2AgAsBr6, and Li2AgAsI6 are 2.35 eV, 2.08 eV, 1.57 eV, and 1.05 eV, respectively. We also computed and comprehensively studied the optical characteristics of these materials in the energy range of 0–8 eV. These materials demonstrate absorption bandwidth in the visible range and are viable contenders for optoelectronic applications. To determine the transport and thermodynamic aspects, we used the BoltzTraP and Gibbs2 codes, respectively. The figures of merit values are observed as 0.79, 0.77, 0.76, and 0.71, respectively. Thermodynamic properties confirm the high-temperature stability of studied materials. Finally, these perovskites can benefit photovoltaic and thermoelectric devices, further requiring experimental validation.

Fabrication of ultra-high strength MWCNTs/CI /PI rigid composite foam with excellent microwave absorption performance by pressure foaming method

Polyimide (PI) foam exhibits excellent high-temperature resistance and outstanding physical and chemical stability, making it an ideal matrix for absorbing materials. However, the growing demand for absorbing materials that can serve as load-bearing components has revealed that existing polyimide composite foams often fall short of practical application requirements due to their low mechanical properties. The study employed a simple foaming method using isocyanate-based polyimide as the foam base under a 0.2 MPa atm. Multi-walled carbon nanotubes (MWCNTs) and carbonyl iron (CI) powder were added sequentially to the precursor solution. Under the filling parameters of 2.0 % MWCNTs and 10 % CI powder, the compressive strength of polyimide composite foam reaches 16.2 MPa and exhibits excellent microwave absorption properties, with a minimum reflection loss (RLmin) of −62.51 dB and an effective absorption bandwidth (EAB) of 7.86 GHz. Additionally, the prepared composite foam has potential infrared stealth capability. This work offers new insights for rapid and low-cost manufacturing of high-strength absorbing foam.

Integration of Electrical Properties and Polarization Loss Modulation on Atomic Fe–N-RGO for Boosting Electromagnetic Wave Absorption

HighlightsSingle-atom Fe–N4 sites embedded into graphene were successfully synthesized to exert the dielectric properties of graphene.The absorption mechanisms of metal-nitrogen doping reduced graphene oxide mainly include enhanced dipole polarization, interface polarization, conduction loss and defect-induced polarization.Excellent reflection loss of − 74.05 dB (2.0 mm) and broad effective absorption bandwidth of 7.05 GHz (1.89 mm, with filler loading only 1 wt%) were obtained.

Engineered Core-Shell SiC@SiO2 Nanofibers for Enhanced Electromagnetic Wave Absorption Performance.

To enable SiC material to achieve high electromagnetic wave (EMW) absorption performance, solving its impedance mismatch with EMW is necessary. Therefore, a novel approach is proposed for the precise control of impedance matching by adjusting the shell thickness of SiO2 nanolayers on the surface of SiC nanofibers (NFs). High-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) reveals the atomic scale oxidation process of SiC, providing fresh insights into the oxidation mechanism. By oxidizing to construct a heterogeneous core-shell structure nanofiber (NF) can effectively lock the incident EMW inside the NF through the generated charges gathered at the interface, forming an electronic barrier that prevents the outward propagation of EMWs. The produced SiC@SiO2 NFs-3 exhibits exceptional EMW absorption properties, including an impressive minimum reflection loss (RLmin) of -53.09dB and a broad maximum effective absorption bandwidth (EABmax) of 8.85GHz. These findings not only deepen understanding of the oxidation mechanism of SiC but also offer valuable insights for further enhancing the EMW absorption capabilities of SiC materials, paving the way for their application in advanced EMW technologies.

Growth of YAG:Nd laser crystals by Horizontal Directional Crystallization in Protective Carbon‐Containing Atmosphere

AbstractLaser‐quality yttrium‐aluminum garnet single crystals doped with neodymium (YAG:Nd) of a concentration up to 1 at. % is grown by the method of horizontal directional crystallization from a molybdenum crucible in the protective reducing atmosphere based on argon, СО, and hydrogen. It is found that the content of carbon impurity in the grown crystals does not exceed 5·10−3 wt %, the content of molybdenum being on the level of 1.5·10−3 wt %. The optical quality of the crystals depends on the composition of the growth atmosphere and annealing. It is shown that, besides the bands of neodymium ion absorption, the crystals are characterized by the intense absorption in the UV edge of the spectrum at 370 nm wavelength, and by the wide absorption band with a maximum at 580 nm caused by formation of F and F+‐centers. The absorption at 370 and 580 nm can be eliminated by annealing. The structure perfection of the crystals is characterized by the rocking curve half‐width (β) which value varies within the limits of 10–14 arc. sec for (001) plane. Laser testing demonstrates the parameters comparable with those of YAG:Nd crystals grown by the Czochralski method from iridium crucible.

Hollow core-shell structured Fe3O4@Polypyrrole composites for enhanced electromagnetic wave absorption

Due to the rapid development of electronic devices, the electromagnetic pollution has become increasingly serious. Developing electromagnetic wave absorption (EWA) materials with lightweight, strong absorption capacity and wide effective absorption bandwidth (EAB) becomes a research hotspot. In this work, the hollow-Fe3O4@polypyrrole (HFO@PPy) composites with core-shell structure were successfully synthesized by in situ polymerization method. The electromagnetic parameters could be adjusted by controlling the content of HFO in HFO@PPy. In addition, HFO@PPy composites show both dielectric and magnetic losses. The synergistic effect of both two losses contributes to an enhanced electromagnetic attenuation. The enhanced impedance matching is achieved by the composition (HFO and PPy) and designed unique structure (core-shell and hollow structure). The maximum reflection loss (RL) and EAB are −52.01 dB and 2.72 GHz at 3.1 mm for 60.0 wt% HFO@PPy composites. Therefore, by reasonably regulating the component content and optimizing the structural design, the EWA performance of HFO@PPy composites could be effectively improved, providing a significant inspiration for fabrication of microwave absorbers.

Interface-driven microwave absorption enhancement in Mn-optimized Co2FeAl1-xMnx Heusler alloys

To address the urgent need for efficient and stable electromagnetic wave absorbing materials for electromagnetic interference (EMI) protection, we synthesized Co2FeAl1−xMnx Heusler soft magnetic alloys using a high-energy planetary ball milling method. We comprehensively analyzed their structural characteristics, surface morphology, magnetic properties, and electromagnetic parameters to explore their potential in electromagnetic wave absorption. The results show that incorporating manganese (Mn) significantly changes the alloys' crystal structure, surface morphology, and magnetic properties, greatly enhancing their wave absorption performance. The Mn doping specifically alters the surface morphology, which plays a crucial role in influencing the wave absorption characteristics of the Heusler alloys. When the Mn content increased to 25 %, the sample exhibits superior wave absorption, achieving the maximum reflection loss of −44.83 dB at 13.68 GHz with a thickness of 1.5 mm and an effective absorption bandwidth of 5.52 GHz. With a significant increase in the aspect ratio and noticeable changes in surface morphology, the sample with 75 % Mn content shows exceptional performance with an effective absorption bandwidth of 5.68 GHz, representing the highest effective absorption bandwidth in single-phase Heusler alloys. The Mn doping strategy effectively improves the material's impedance matching by adjusting its permittivity and permeability, facilitating multiple polarization relaxation mechanisms and significantly enhancing the alloys' electromagnetic wave absorption efficiency. Our study provides detailed experimental data for optimizing the electromagnetic wave absorption characteristics of Heusler alloys, verifies their practical application potential, and paves the way for developing new high-performance electromagnetic wave absorbing materials.

Generating Immunological Memory Against Cancer by Camouflaging Gold-Based Photothermal Nanoparticles in NIR-II Biowindow for Mimicking T-Cells.

Photothermal therapy (PTT) against cancer not only directly ablates tumors but also induces tumor immunogenic cell death (ICD). However, the antitumor immune response elicited by ICD is insufficient to prevent relapse and metastasis because of the immunosuppressive tumor microenvironment (TME). A biomimetic nanoplatform (bmNP) mimicking cytotoxic lymphocytes (CTLs) for combinational photothermal-immunotherapy to effectively regulate the immunosuppressive TME is reported here. The bmNP is constructed by wrapping the T-cell membrane onto a new type of photothermal agents, spherical Au-based PNCs (sAuPNCs). Similar to T-cells, the bmNP enhanced accumulation at the tumor site by targeting the tumor via adhesion proteins on T-cell membrane. The obtained sAuPNCs have a wide absorption band in the second near-infrared (NIR-II) region with a high photothermal conversion efficiency (PCE) up to about 75% and excellent photostability. The bmNP with a smaller size is more superior compete with T-cells to bond with tumor cells via PD-1/PD-L1 interaction to effectively block the PD-1 checkpoint of T-cells for preventing T-cell exhaustion. Furthermore, in vivo studies reveal the immunological memory effect is significantly elicited in mice received bmNPs therapy. Collectively, bmNPs show great potential in photothermal-enhanced immunotherapy.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

CNTs/lamellar VSe2/Fe3O4 self-assembled a variety of unique three-dimensional multilayer interface structures and microwave absorption properties

Fabrication of microwave absorption (MA) materials of matched small thickness, low density, broad effective absorption bandwidth (EAB), as well as high absorption performance remains a technical challenge to be solved today. In this paper, three-dimensional (3D) VSe2/CNTs/Fe3O4 ternary composites with a variety of self-assembled structures were fabricated by a two-step hydrothermal and one-step carbothermal reduction method. Via varying the content of Fe3O4 in the composites, different 3D multilayer interfacial structures, such as star fruit-, bitter melon-, goldfish-, starfish-, peony- and chrysanthemum-shaped structures were self-assembled, and excellent MA absorption characteristics were obtained. The best reflection loss (RLmin) was −50.96 dB at 1.8 mm thickness. The maximum EAB was 4.93 GHz at 2.0 mm thickness. Carbon nanotubes mainly contributed to conduction and polarization losses. In situ generated VSe2 nanosheets and Fe3O4 nanoparticles promoted the assembly of multilevel interfacial structures, thus contributing to interfacial polarization loss and dipole polarization loss. Fe3O4 also created magnetic losses. This study lays the foundation for fabricating highly efficient MA materials in special self-assembled heterostructures with ternary synergistic effects at the nanoscale.

Mesoporous carbon spheres modified with atomically dispersed iron sites for efficient electromagnetic wave absorption

Carbon materials have obtained some achievements in electromagnetic wave (EMW) absorption owing to their excellent electrical conductivity and low density. However, poor impedance matching and high electrical conductivity limit their EMW absorption properties. Metal single atoms absorbers have garnered considerable attention in EMW absorption, largely due to the high metal availability and special coordination structure, but the modulation of the EMW absorption properties still needs to be improved. Herein, atomically dispersed Fe sites embedded into the N-doped mesoporous carbon spheres (Fe–SAs/NC) were synthesized through a facile coordination-assisted polymerization assembly strategy without acid leaching treatment. Benefitting from abundant mesoporous structure, the Fe–SAs/NC displays large specific surface area (339 m2 g−1) and optimized impedance matching, which results in an effective reduction of the absorber density. The homogeneously dispersed Fe single atoms (Fe–SAs) on the carbon skeleton lead to the improvement in conduction and dipole polarization losses of Fe–SAs/NC, which endows Fe–SAs/NC with exceptional EMW absorption properties. Experimental results indicate that Fe–SAs/NC displays desirable EMW absorption properties with the minimal reflection loss of −52.5 dB at 2.8 mm and the effective absorption bandwidth of 4.8 GHz. The study provides valuable insights for the development of carbon materials modified with atomically dispersed metal sites to achieve high-efficient EMW absorbers.

Metamaterial-inspired infrared electrochromic devices with wideband microwave absorption for multispectral camouflage

Infrared (IR) electrochromic devices, capable of dynamically controlling thermal radiation, hold promising applications in adaptive camouflage. However, the strong microwave reflective properties inherent in the device’s electrodes present a significant challenge, rendering them susceptible to radar detection and weakening their camouflage effect. Inspired by the remarkable electromagnetic control capabilities of metamaterials, the integration of frequency selective surfaces into IR electrochromic devices is proposed to address this multispectral compatibility challenge. The designed integrated metadevices simultaneously exhibit large and reversible IR emissivity tunability (Δε≥0.55 at 3–5 μm, Δε≥0.5 at 7.5–13 μm) and wideband microwave absorption (reflection loss ≤−10 dB at 8.5–18 GHz). Furthermore, the monolithic integrated design of the shared barium fluoride substrate offers a simple device architecture, while careful design considerations mitigate coupling between IR electrochromism and microwave wideband absorption. This work introduces opportunities for the development of multispectral adaptive camouflage systems, offering potential advancements in concealment technology.

Excellent Low-Frequency Microwave Absorption and High Thermal Conductivity in Polydimethylsiloxane Composites Endowed by Hydrangea-Like CoNi@BN Heterostructure Fillers.

The advancement of thin, lightweight, and high-power electronic devices has increasingly exacerbated issues related to electromagnetic interference and heat accumulation. To address these challenges, a spray-drying-sintering process is employed to assemble chain-like CoNi and flake boron nitride (BN) into hydrangea-like CoNi@BN heterostructure fillers. These fillers are then composited with polydimethylsiloxane (PDMS) to develop CoNi@BN/PDMS composites, which integrate low-frequency microwave absorption and thermal conductivity. When the volume fraction of CoNi@BN is 44 vol% and the mass ratio of CoNi to BN is 3:1, the CoNi@BN/PDMS composites exhibit optimal performance in both low-frequency microwave absorption and thermal conductivity. These composites achieve a minimum reflection loss of -49.9dB and a low-frequency effective absorption bandwidth of 2.40GHz (3.92-6.32GHz) at a thickness of 4.4mm, fully covering the n79 band (4.4-5.0GHz) for 5G communications. Meanwhile, the in-plane thermal conductivity (λ∥) of the CoNi@BN/PDMS composites is 7.31W m-1 K-1, which is ≈11.4 times of the λ∥ (0.64W m-1 K-1) for pure PDMS, and 32% higher than that of the (CoNi/BN)/PDMS composites (5.52W m-1 K-1) with the same volume fraction of CoNi and BN obtained through direct mixing.

Architectural Design of a Multichannel Porous Carbon Fiber for Efficient Electromagnetic Microwave Absorption.

An ingenious microstructure of electromagnetic microwave absorption materials is crucial to achieve strong absorption and a broad bandwidth. Herein, one-dimensional (1D) carbon fibers with implantation of zero-dimensional (0D) ZIF-8-derived carbon frameworks and construction of a three-dimensional (3D) microcosmic multichannel porous structure are fabricated by electro-blown spinning, solvent-thermal reaction, and high-temperature pyrolysis techniques. The 1D carbon fiber skeleton with a multichannel structure provides a direct axial conductive pathway for charge transport, which plays an important role in dielectric loss. The 0D surface carbon frameworks offer plenty of heterogeneous interfaces to trigger intensive interfacial polarization loss and act as dihedral angles for microwave scattering. The 3D microcosmic multichannel pores can not only generate multiple reflections as much as possible to dissipate electromagnetic microwave energy but also supply huge interior cavities to improve impedance matching. Thanks to the synergistic effect of a strong electrically conductive pathway for enhancing the conductive loss, a plenteous heterogeneous interface for triggering intensive interfacial polarization loss, microcosmic multichannel pores for generating multiple reflections and improving impedance matching, and N and O atom doping for inducing dipole polarization, the optimal sample with an ingenious microstructure delivers an excellent absorption performance of a minimum reflection loss of -35.5 dB at a thickness of 5.0 mm and an effective absorption bandwidth of 6.72 GHz (10.96-17.68 GHz) at a thickness of 2.0 mm. Such a well-designed multichannel porous carbon fiber may pave the way for the exploitation of high-performance microwave absorbing materials.

Genome engineering of materials based on Ce doping, high-performance electromagnetic wave absorber for marine environment

Traditional microwave absorbing materials (MAM) are difficult to meet the current increasingly complex electromagnetic environment, MAM began to functionally integrated development to meet the needs of diversified applications. For the high humidity and high salt spray environment of the ocean, the development of electromagnetic absorber integrating microwave absorption (MA) and corrosion protection functions is imminent. In this work, high-quality genes were screened through materials genome engineering, and in-situ doping strategies of Ce gene were designed to synergistically enhance MA properties using composition modulation and structure modulation, the effective absorption bandwidth (EAB) of composite material WC@FCC1 can reach 5.62 GHz at an ultra-thin thickness of 1.66 mm. Thanks to the unique 4f orbital mechanism of Ce element, CeO2 is endowed with excellent redox property, forming an oxide protective film on the surface, which prevents the entry of external corrosive media. The excellent corrosion protection performance of the composite material has been verified through electrochemical testing and molecular dynamics simulation. This work provides new design ideas for high-performance MAM, as well as new strategies and insights for functionally integrated electromagnetic absorber.