Microwave Absorption Characteristics Research Articles

Metamaterial-Based Radar-Infrared Camouflage Material for Building Insulation: Design and Performance Analysis

This study introduces a metamaterial microwave absorber (MMA)-lightweight envelope (LE), which is an innovative solution for integrating electromagnetic and infrared-compatible camouflage technologies into building structures. Specifically, MMA-LE incorporates a MMA into building designs for microwave/infrared-compatible camouflage. This study evaluated the microwave absorption performance, infrared camouflage capabilities, and energy-saving effects of MMA-LEs by analyzing the microwave absorption characteristics using the impedance matching theory and simulation software. A coupled heat and moisture transfer model was used to assess isothermal moisture absorption, heat transfer coefficients, and annual heating/cooling loads. Furthermore, infrared imaging tests verified the effectiveness of the camouflage. Two MMA-LE designs (single and double absorber layers) achieve over 90% microwave absorption in the 3.2–11.2 GHz and 1.85–12.67 GHz frequency ranges with relative bandwidths of 111.1% and 149%, respectively, and with polarization insensitivity. Moreover, the MMA-LE enhanced the wall heat and moisture transfer performance, reduced the relative humidity, and reduced the thermal load under Guangzhou's climate conditions. However, despite the improved moisture resistance, the double-layer MMA-LE increased the envelope moisture content, thus reducing thermal insulation. In addition, the limited absorbency of the substrate material results in a modest increase in the dielectric constant, consequently decreasing the resonant frequency of the hybrid structure compared to dry samples. Nevertheless, the thermal insulation properties of MMA-LEs effectively insulate the internal heat sources, achieving optimal infrared camouflage. In conclusion, this study provides a novel solution for microwave-infrared-compatible camouflage in building applications, offering significant theoretical and practical value.

Influence of Dy3+ doping on Mössbauer, magnetic and microwave absorption properties of M-type Ba0.5Ca0.5DyxFe12-xO19 hexaferrites

The present research paper reports a systematic study of the magnetic, and structural properties of Ba0.5Ca0.5DyxFe12-xO19 M-type hexaferrite. The dysprosium was doped @ x = 0 − 0.2, keeping Δx = 0.05, in BCDF by the sol–gel self-ignition technique. The sintering of the synthesized samples was performed for 4 h at 1050°C. The crystallographic analysis of the samples was made from the X-ray diffractograms (XRD), while the morphological and elemental analysis was made from field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDAX) profiles. The structural results revealed the formation of the M-type hexaferrite having P63/mmc as a space group along with the co-existence of a secondary Fe2O3 phase. FESEM micrographs exhibit the hexagonal platelets randomly arranged with agglomerations at some places giving rise to the random variations in particle size with varying ’x’. Magnetic measurements (VSM) show that the saturation magnetization (MS) and coercivity (HC) increase with the increasing Dy3+ doping pointing towards the fact that the Dy doping in Ba-Ca ferrite can be used to fabricate the hard ferrites with good saturation magnetization. The Mössbauer spectrum recorded at room temperature reveals five superimposed sextets representing the five Fe3+ ion sites. Investigating the Microwave absorption (MWA) characteristics in the frequency range 8 − 12 GHz (X-band), reveals that the sample with x = 0.1 having 3 mm thickness possesses good MWA power. Its minimum RL value for matching frequency 10.06 GHz is approximately −26.96 dB, indicating that more than 90 % of microwaves are absorbed. The current work offers the Dysprosium-doped BCDF hexaferrites, as promising candidatesfor microwave absorption applications.

THE X-BAND MICROWAVE ABSORPTION CHARACTERISTICS OF POROUS ACTIVATED CARBON FROM NATURAL RESOURCES

Porous activated carbon (PAC) from bamboo, sisal, and coconut coir fibres with two carbonization steps were prepared and the microwave absorbing characteristics in the frequency range of 8 GHz to 12 GHz were investigated. The PAC based on bamboo, sisal and coconut coir had BET surface areas of 354.79, 141.91, and 25.70 m2/g, respectively. The return loss of -27.3, -25.6 and -16.4 dB was achieved for PAC from bamboo, sisal, and coconut fiber at 10.46, 11.08 and 11.00 GHz, respectively. The microwave absorption of more than 99% for porous activated carbon of bamboo and sisal, and more than 90% for porous activated carbon of coconut coir fiber, is indicated by these return loss values. It is shown by these results that biomass resources can be considered a promising lightweight, cost-effective, and eco-friendly microwave absorber material.

Conjugated Matrix Nanocomposites with Nanodiamond Nanoadditives—Fundamentals and Forefronts

Nanodiamonds have been researched as sphere-shaped carbon nano-entities having countless surface/structural properties, facile fabrication and mammoth technological value. An important utilization of nanodiamonds has been observed as nano-reinforcing agents for nanocompositing purposes. Semiconducting polymers (conjugated polymers) having π electron delocalization have been documented for worthy electrochemical/optical/thermal/mechanical features, in addition to the electron transfer through their backbone. Doping of carbonaceous nanoparticles, like nanodiamonds, with conjugated polymers have been found to further improve the valuable physical characteristics in their final nanocomposite form. Correspondingly, this overview describes the impact of nanodiamond nano-reinforcement on the specialized aspects of polyaniline/nanodiamond, polypyrrole/nanodiamond and polythiophene/nanodiamond nanocomposites. According to literature reports, these groupings of conjugated polymer/nanodiamond hybrids revealed noteworthy microstructural, conductive, optical, electrochemical, microwave absorption, specific capacitance, photovoltaic and actuation characteristics. Subsequently, several significant applications of polymer/nanodiamond nanomaterials have been explored including the solar cells, supercapacitors and actuators.

Two birds with one stone: Bimetallic ZnCo2S4 polyhedral nanoparticles decorated porous N-doped carbon nanofiber membranes for free-standing flexible anodes and microwave absorption

Cost-efficient material with an ingenious design is important in the engineering applications of flexible energy storage and electromagnetic (EM) protection. In this study, bimetallic ZnCo2S4 (ZCS) polyhedral nanoparticles homogenously embedded in the surface of porous N-doped carbon nanofiber membranes (ZCS@PCNFM) have been fabricated by electrospinning technique combined with carbonization and hydrothermal processes. As a self-assembled electrode for lithium-ion batteries (LIBs), the bimetallic ZCS nanoparticles possess rich redox reactions, good electrical conductivity, and pseudocapacitive properties, while the three-dimensional (3D) multiaperture architecture of the nanofiber film not only shortens the transfer spacing of lithium ions and electrons but also effectively tolerates the volume variation during lithiation and delithiation cycles. Benefiting from the above merits, the ZCS@PCNFM electrode exhibits good cycle performance (662.3 mA h/g at 100 mA/g after 100 cycles), superior rate capacity (401.3 mA h/g at 1 A/g) and an extremely high initial specific capacity of 1152.2 mAh/g at 100 mA/g. Meanwhile, depending on the hierarchical nanostructure and multi-component heterogeneous interface effects constructed by 3D inlaid architecture, the ZCS@PCNFM nanocomposite exhibits fascinating microwave absorption (MA) characteristics with a superhigh reflection loss (RL) of –49.7 dB at a filling content of only 20 wt% and corresponding effective absorption bandwidth (EAB, RL<–10 dB) of 5.2 GHz ranging from 12.8 to 18.0 GHz at 2.2 mm.

Co-pyrolysis characteristics and pyrolysis oil analysis of Chlorella vulgaris and marine waste plastics with multi-metal MOFs-derived additive

In this study, MOFs-derived additives with microwave absorption and catalytic characteristics were employed in the microwave co-pyrolysis of Chlorella vulgaris (CV) and marine waste plastics (MW) to produce high-quality pyrolysis oil. The effects of additives (Ni-Cu@C, Ni-Co@C, Cu-Co@C and Ni-Cu-Co@C) under different addition amounts (10%, 20%, 30%) on co-pyrolysis characteristics, product yield and pyrolysis oil composition were investigated. Furthermore, the pyrolysis mechanism was analyzed. The results showed that the MOFs-derived additives improved the co-pyrolysis characteristics, especially at 30% addition amount. The maximum average weight loss rate (0.0273 wt.%/s) and pyrolysis oil yield (14.33%) obtained at 30% Ni-Cu-Co@C group. Moreover, the aromatic content (30.07%), deoxygenation efficiency (27.70%) and denitrogenation efficiency (80.03%) in pyrolysis oil were maximum at adding 30% Ni-Cu-Co@C. Ni-Cu-Co@C promoted the nitrogen transformation into gaseous products, while reduced the nitrogen contents in char and pyrolysis oil. Meanwhile, the nitrogen in char was dominated by pyridine-N and quaternary-N. Importantly, the activity of the Ni-Cu-Co@C remained 0.66 times of the initial activity after 5 cycles, demonstrating the excellent regenerative usability.

Microwave Absorption Characteristics of M2+, 3+ (M = Mn3+, Zn2+, Ni2+)-substituted Sr3Co2Fe24O41 Hexaferrite Composites

Microwave Absorption Characteristics of M2+, 3+ (M = Mn3+, Zn2+, Ni2+)-substituted Sr3Co2Fe24O41 Hexaferrite Composites

Study on the microwave absorption properties of FeCoNiCrMn/PLA 3D printed composites

The work in this paper is dedicated to the study of wave-absorbing materials for applications in extremely harsh environmental conditions such as seawater and oil. In this paper, FeNiCrMn high-entropy alloy material with corrosion resistance and polylactic acid (PLA) material with high strength and high modulus were used to prepare more environmentally adaptable FeNiCrMn/PLA electromagnetic(EM) microwave-absorbing materials by two-step method of ball milling and melt extrusion.The physical phases, microscopic morphology, EM parameters and mechanical performance of FeCoNiCrMn/PLA composites were characterized using XRD, SEM, Vector Network Analyzer and Universal Testing Machine respectively. The microwave-absorbing properties of FeCoNiCrMn/PLA composites were investigated, and the effects of their components and micro-morphology on the microwave-absorbing and mechanical performance were discussed. The results show that when the FeCoNiCrMn content reaches 25 wt% and the thickness is 4.5 mm, the minimum reflection loss of FeCoNiCrMn/PLA composites reaches −24.58 dB, and the effective microwave-absorbing bandwidth is 2.51 Ghz. The maximum tensile strength and elongation at break of the composites could reach 23.83 MPa and 7.12 %, respectively. The microwave-absorbing ability of FeCoNiCrMn composites is mainly due to their rich EM loss mechanisms, including dielectric losses such as dipole polarization, interface polarization, defect-induced polarization, etc., as well as magnetic losses such as natural resonance, exchange resonance, and eddy current losses. Finally, the wide-angle microwave-absorbing characteristics of FeCoNiCrMn/PLA 3D-printed composites were investigated, the results showed that the composites with FeCoNiCrMn content of 25 wt% had Radar Cross Section (RCS) values lower than −10 dBm² within the microwave incidence angle of −90° < θ < −6° and 6° < θ < 90°, which indicated that the composites had wide-angle microwave-absorbing capability. The materials have microwave-absorbing properties along with a certain degree of mechanical strength, and at the same time have good environmental adaptability. The FeCoNiCrMn/PLA composite wire can be used in FDM technology to prepare structural microwave absorbers, realizing the integration of “material-design-manufacturing”, which has a broad application prospect in the field of EM microwave absorption and 3D printing.

BST@Copper Nanowire/Epoxy composites with excellent microwave absorption in the X-band

In this work, hybrid epoxy nanocomposites containing varying loading of copper nanowires (CuNW), Ba0.7Sr0.3TiO3 (BST), and BST@CuNW hybrid nanoparticles were prepared and analyzed for their microwave absorption characteristics. The nanoparticles used in this study were prepared using a facile co-precipitation and hydrothermal methodology. The synthesized nanoparticles were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their morphology and phase determination. While the XRD results confirmed the presence of BST and CuNW, the SEM micrographs obtained on the hybrid BST@CuNW nanoparticles show BST anchored on the CuNW surfaces. A series of epoxy composites containing varying loading of synthesized nanoparticles were prepared and characterized for their microwave properties, such as complex permittivity, shielding effectiveness, and power coefficients. The results indicate that nanocomposites containing BST@CuNW hybrids exhibited enhanced dielectric loss and more significant microwave power absorption compared to samples with equivalent CuNW and/or BST loading. The best composite sample, i.e., a one-millimeter-thick epoxy containing 10:15 (wt/wt) CuNW: BST hybrid nanoparticles with an estimated density of 1.49 g/cc attenuated 99.1 % of incident microwave power and exhibited a shielding effectiveness value of 21.2 dB in the X-band (8–12 GHz) of the microwave frequency spectrum. These lightweight polymer composites with high microwave absorption in the X-band are useful for military and civilian applications.

Enhancing X-band microwave absorption properties with nickel ferrite and carbon-based composites

The present study focuses on synthesizing a composite material comprising of nickel ferrite and carbon derived from cotton, to exhibit exceptional microwave absorption capabilities over a wide frequency range. By adopting a mechanical alloy method, the microwave-absorbing composite is developed. The microwave absorption characteristics of the developed composites are further unearthly in terms of their permittivity and permeability. Combining magnetic and dielectric phases produces better eddy current loss and polarization, which are primarily responsible for absorption characteristics. The developed composites are cast into rectangular pallets to evaluate microwave absorption characteristics and examined using a vector network analyzer within the 8.2–12.4 GHz frequency range. With a pallet thickness of 2.55 mm, the entire X-band frequency is effectively covered, yielding a remarkable minimum reflection loss of −20.46 dB at 10.01 GHz. The current work's findings, owing to the synergistic combination of nickel ferrite and carbonized carbon provide a practical approach for developing a hybrid material with remarkable electromagnetic performance.

Microwave Absorption Properties of Hexagonal Ba3(VO4)2 through Zn Doping: A Comprehensive Analysis of Ba3–xZnx(VO4)2

The current study explores the influence of Zinc (Zn) doping on the crystallography, optical behavior, dielectric properties, and microwave absorption characteristics of hexagonal Barium Vanadate (Ba3(VO4)2). Samples were systematically synthesized with Zn doping concentrations of x = 0, 0.05, 0.1, 0.15, and 0.2 mol%, resulting in Ba3–xZnx(VO4)2. Employing various characterization techniques, the alterations in structural, optical, and electrical responses due to incremental Zn incorporation are reported. The UV–VIS DRS absorption spectra reveal a decrease in energy bandgap with increasing concentration of Zn. The lowest optical energy band gap observed was 3.65 eV for x = 0.2 mol% Zn. Notably, at a thickness of 6.5 mm, the material achieved a high reflection loss of −82.37 dB at 12.47 GHz for x = 0.05 mol% of Zn. Similarly, the same material configuration exhibited a maximum effective absorption bandwidth (EAB) of 5.01 GHz, spanning a frequency range from 12.24 to 17.25 GHz when the thickness was set to 5.5 mm. Furthermore, as the Zn concentration increased from x = 0.05 to 0.2 mol%, a decreasing trend in reflection loss was observed, correlating well with the dielectric parameters of samples with different Zn concentrations. The work provides insightful correlations between Zn doping levels and the material’s performance in potential applications ranging from optoelectronics to electromagnetic wave absorption.

Unveiling ball size heterogeneity effect on microwave absorption properties of cobalt

Recent advances in material science have led to impressive microwave absorbing materials, yet their practical applications are hindered by complex synthesis processes. This study explores a cost-effective alternative, emphasizing modifying material morphology using ball size heterogeneity. Unlike using same-sized balls, employing different-sized balls maximizes collision energy, yielding finer particles. In this study, the effect of ball size heterogeneity on microwave absorption performance has been investigated for the first time. An attempt has been made to explore how using ball size heterogeneity changes structural, magnetic, and dielectric properties of cobalt (Co) and how these modifications affect material's absorption properties. Results show that by using ball size heterogeneity, the particle size distribution in 0.1–1 μm range has been increased, yielding much finer particles. The relative permittivity value also increases due to changes in average particle size and surface area. Microwave absorption characteristics of Co milled with different-sized balls showed a significant change. A 15 h milled Co sample using different-sized balls achieved an effective bandwidth of 9.65 GHz (4.75–14.4), contrasting with no absorption bandwidth when using same-sized balls, with a 2 mm coating thickness. This work provides new insights into preparing materials for microwave absorption applications using ball milling method.

Optimizing the electromagnetic wave absorption properties of core-shell Fe/FeN/Fe3C@GN nanoparticles by low-temperature NH3 plasma

Surface modification via low-temperature plasma has an extensive application prospect in different engineering fields due to its comprehensive merits in facilitating the introduction of functional groups and creating more heterogeneous interfaces. Herein, a simple high-temperature plasma method is developed to get novel multiple-phase nanocomposites of core-shell Fe/FeN/Fe3C@GN nanoparticles with bifunctional characteristics of microwave absorption (MA) and anti-corrosion. And then, we further investigate the MA properties of Fe/FeN/Fe3C@GN nanoparticles after low-temperature NH3 plasma etching. It is found that surface modification of Fe/FeN/Fe3C@GN nanoparticles can generate remarkable changes in specific surface areas, Raman features and MA properties of these nanocomposites. The Fe/FeN/Fe3C@GN nanoparticles after NH3 plasma etching possess excellent MA properties with an optimal reflection loss (RL) of −51.0 dB at an ultra-thin thickness of 1.9 mm with a low filling content of 30 wt% and the corresponding effective absorption bandwidth (EAB < −10 dB) up to 4.7 GHz (13.3–18.0 GHz). The fascinating MA properties of etched Fe/FeN/Fe3C@GN nanoparticles may be attributed to the cooperative effect of several points: (i) The NH3 plasma etch introduces a large number of polar functional groups, which can be regarded as the polarization center to produce more polarization loss; (ii) The appropriate dielectric loss and impedance matching achieve a good balance, and the abundant heterogeneous interface significantly enhances the polarization relaxation loss; (iii) The existence of hetero-nanostructure further improves the multiple reflections and scattering of the propagating microwaves. In addition, this work provides a new strategy for the design and fabrication of core-shell MA materials.

Facile and rapid synthesis method of dielectric nanocomposite for simultaneous enhancement of electromagnetic wave absorbing/shielding characteristics

The present study involves the fabrication of poly[4-(2-thiophene)aniline] (PTA) nanocomposite for absorption-dependent shielding applications, demonstrating enhanced absorption and small reflection properties. The Microwave absorption characteristics of the fabricated polymer were studied at different loading ratios, resulting in a minimum reflection loss (RLmini) of − 44 dB for the 8 wt % loading ratio. The macromolecular architecture of the PTA material offers higher dielectric loss resulting from higher conduction and interfacial loss. Additionally, the shielding performance is also evaluated, and the sample containing 8 wt % filler demonstrates an impressive − 36.5 dB shielding efficacy. The performance of polymers is significantly impacted by their unit periodic order arrangement. Conducting polymers with linear structure and special π-orbitals angles possess unique characteristics in comparison to their branched and the random copolymer, making them highly sought after as efficient organic conductors, magnetic substances, electrochromic materials, and high dielectric agents. Monomer units contained two periodical cyclic structures and the creation of the inductive effects of heteroatoms elongates the conjugation and reduces the energy bandgap difference between the HOMO and LUMO levels, enabling smoother electron flow and enhancing absorption capacity. The findings indicate that PTA nanocomposite is a promising radar-absorbing coating material due to its superior absorption ability and outstanding shielding performance.

Achieving high-efficiency electromagnetic wave absorption performance in a 3-layer hierarchical porous magneto-dielectric nanocomposite

Hierarchical porous structures along with micro- and nanoparticles of magneto-dielectric components in sandwich structure design have superior potential applications in the field of electromagnetic wave absorption, due to high active dissipation phenomena such as multiple scatterings and reflections between components, 3D network pores and layers, coupling interactions between each layer, promotion of interfacial polarization, and so on. The Sandwich-Structure absorber composed of hierarchical porous Bi2MoO6, Cu microparticles, and FeNi nanoparticles was effectively constructed with optimization in layer thickness and low filler loading percentage. The microwave absorption characteristics of absorber samples varied in thickness but all less than 1.6 mm in total thickness were thoroughly examined. The as-prepared sandwich structure displayed a unique microwave absorbing behavior due to the multiple-layer structure, the dielectric dissipation property of both Bi2MoO6, Cu microparticles and the magnetic dissipation feature of FeNi nanoparticles, as well as the complementary effect between particles and layers. Minimum reflection loss (RLmini) of −45.5 dB at 5.5 GHz is obtained with proper optimization of layer order and thickness in a resin base 3-layer absorber sample with Bi2MoO6 placed as a top layer with 0.4 mm thickness, FeNi placed as a middle layer with 0.5 mm thickness, and finally Cu placed as a bottom layer with 0.7 mm thickness. The results show that the as-prepared 3-layer nanocomposite sample has a high potential for usage in microwave absorption in the low-frequency band.

Vat photopolymerization 3D printing SiBCN ceramic metamaterials with strong electromagnetic wave absorption

Starting from the simulation prediction, SiBCN polymer-derived-ceramic metamaterials, integrating both structure and function in a single component, were obtained using vat photopolymerization technology starting from a preceramic polymer. The low-density gyroid triply periodic minimal surface (TPMS) structures used in this study increases the multiple reflection loss of electromagnetic wave (EMW) in the macro-interpenetrating channel structure, generates surface characteristics (stair-stepping effect) structure interface polarization, and improves microwave absorption characteristics. The possible multiple reflection effects of a gyroid structure on electromagnetic waves are discussed by Computer Simulation Technology simulation. At the same time, the precipitated phases in polymer derived ceramics (PDCs) were adjusted by controlling the pyrolysis temperature. The results show that the crystal phases (such as β-SiC and C) precipitated in the gyroid structure sample pyrolyzed at 1200°C enrich the heterogeneous interface polarization in the material. In addition, C forms a (semi-)conductive network, which increases the conductivity loss. The effective absorption bandwidth (EAB, RL<-10 dB) of the samples pyrolyzed at 1200°C was 3.09 GHz (thickness of 2.21 mm) and the minimum reflection loss (RLmin) was −70.6 dB (thickness of 2.31 mm), indicating that the samples have favorable EMW absorption properties and great potential for applications, providing a foundation for the preparation of high-performance lightweight structural ceramics.

Highly electrically conductive MOF/conducting polymer nanocomposites toward tunable electromagnetic wave absorption

Metal-organic frameworks (MOFs) have attracted significant interest as self-templates and precursors for the synthesis of carbon-based composites aimed at electromagnetic wave (EMW) absorption. However, the utilization of high-temperature treatments has introduced uncertainties regarding the compositions and microstructures of resulting derivatives. Additionally, complete carbonization has led to diminished yields of the produced carbon composites, significantly limiting their practical applications. Consequently, the exploration of pristine MOF-based EMW absorbers presents an intriguing yet challenging endeavor, primarily due to inherently low electrical conductivity. In this study, we showcase the utilization of structurally robust Zr-MOFs as scaffolds to build highly conductive Zr-MOF/PPy composites via an inner-outer dual-modification approach, which involves the production of conducting polypyrrole (PPy) both within the confined nanoporous channels and the external surface of Zr-MOFs via post-synthetic modification. The interconnection of confined PPy and surface-lined PPy together leads to a consecutive and extensive conducting network to the maximum extent. This therefore entails outstanding conductivity up to ∼14.3 S cm−1 in Zr-MOF/PPy composites, which is approximately 1–2 orders of magnitude higher than that for conductive MOF nanocomposites constructed from either inner or outer modification. Benefiting from the strong and tunable conduction loss, as well as the induced dielectric polarization originated from the porous structures and MOF-polymer interfaces, Zr-MOF/PPy exhibits excellent microwave attenuation capabilities and a tunable absorption frequency range. Specifically, with only 15 wt.% loading, the minimum reflection loss (RLmin) can reach up to –67.4 dB, accompanied by an effective absorption bandwidth (EAB) extending to 6.74 GHz. Furthermore, the microwave absorption characteristics can be tailored from the C-band to the Ku-band by adjusting the loading of PPy. This work provides valuable insights into the fabrication of conductive MOF composites by presenting a straightforward pathway to enhance and regulate electrical conduction in MOF-based nanocomposites, thus paving a way to facilely fabricate pristine MOF-based microwave absorbers.

Preparation of a double-layer bionic bamboo structure absorber based on CB/PLA-TPU composites and its broadband microwave absorption characteristics

The study of the mechanical characteristics and microwave absorption capabilities of multifunctional composite materials in complex environments has attracted considerable interest in recent years. Inspired by the structure of bamboo in nature, a novel double-layer microwave absorber structure, a CB/PLA-TPU composite bionic bamboo joint’s structure, was conceived and manufactured for this investigation. This structure ingeniously integrates the load-bearing attributes of bamboo joints with the microwave absorption qualities of CB composites. At the material level, enhancing the CB particle content enhances the matrix's folds and defects, thereby improving its dielectric polarization loss capacity. An effective absorption bandwidth of 3.84 GHz was achieved, with a minimum reflection loss of −60.24 dB at a 2.58 mm thickness and a 9.2 GHz frequency. The bionic bamboo absorber's unit structure is meticulously engineered, with experimental simulations validating its performance. According to the findings, the structure attains a 10.03 GHz broadband absorption and a yield strength of 11.6 MPa. It maintains broadband absorption capabilities above 9 GHz even at oblique incidence angles for TM polar wave (0–60°) and TE polar wave (0–30°). The biomimetic design based on bamboo offers significant potential for engineering applications in stealth technology under adverse conditions.

Non-iridescent magnetite photonic crystal films and pigments with enhanced magnetic coupling effect

Non-iridescent structural color films and pigments with novel enhanced microwave absorption characteristics are successfully fabricated at room temperature for the first time. The quasi-uniform magnetite nanoparticles (CV = 0.10 ∼ 0.20) with high refractive index (n = 2.42) and broad light absorption provide evident low-angle-independent property for the structural color pigments. More importantly, a universal technical protocol is developed for preparation of photonic crystals with inorganic nanoparticles, i.e., through designing of the binding strength between nanoparticles and mediated molecules, the slurry modulus is increased to 105 Pa, which effectively drives the nanoparticles to rapidly assemble into closely packed ordered arrays by our-designed powerful assembly technique. Additionally, the structural color materials are subjected as photonic crystal pigments (∼20 wt%) embedding in a transparent polymer matrix to form color coatings. Remarkably, the photonic crystal pigments exhibit strong magnetic coupling effect and enhanced microwave absorption performance due to the regular arrangement, with superior reflection loss (RLmin) values of −14.97 dB (increase by 65.8 % compared with randomized magnetic nanoparticles), and the effective absorption bandwidth (EAB) of 2.15 GHz. This new kind of photonic crystal pigment, combining visual color and radar wave absorption, provides a novel idea for developing of multi-wave-band high-performance stealth materials.

Aspects of annealing and particle morphology on the microwave absorption characteristics of carbonyl iron powders

Aspects of annealing and particle morphology on the microwave absorption characteristics of carbonyl iron powders