A Novel Ultra-Wideband Electromagnetic-Wave-Absorbing Metastructure Inspired by Bionic Gyroid Structures

Atomic spin engineering of Fe-N-C by axial chlorine-ligand modulation for lightweight and efficient electromagnetic wave absorption

Introducing atomic magnetic factors to regulate the electromagnetic parameters of graphene is essential to achieving new-generation electromagnetic wave (EMW) absorbing materials. Herein, a new strategy of endowing graphene with atomic magnetic moments was developed by implanting high-spin FeN4 moieties with axial Cl ligands into 3D N-doped graphene (Cl-Fe-NG). The design facilitates the multi-reflection loss, dielectric loss and magnetic loss of EMW at ultra-low filling. Its minimum reflective loss (RL) is up to -65.9 dB with the biggest effective absorption bandwidth (EAB) of up to 5.5 GHz in the thin thickness of 1.9 mm and a low filler loading of 5 wt%. Meanwhile, a waterborne polyurethane wave-absorbing coating filled with 5 wt% Cl-Fe-NG demonstrates its high absorption performance with a dominant absorption loss of 90 %. Additionally, theory calculations reveal that introducing axial Cl-ligand FeN4 moiety with high-spin Fe into graphene not only generates additional electric dipoles but also induces an atomic magnetic moment, effectively enhancing the dielectric and magnetic loss of graphene for EMW absorption. This work provides a new approach to designing graphene with atomic magnetic moments for developing EMW absorbing materials with "thin, wide, light, and strong" characteristics instead of the conventional route of graphene with magnetic nanoparticles.

Activating Basal Plane Inert Sites of Iron Telluride for Motivational Electromagnetic Microwave Absorption

The basal plane inert sites and inadequate intrinsic dielectric relaxation are the major bottlenecks limiting the electromagnetic microwave (EMW) absorption performance of transition metal tellurides (TMTs). Here, an effective dual defect model based on electron polarization relaxation is established on iron telluride (FeTe) flakes via one-step O2 plasma treatment. Therefore, the basal plane inert sites of FeTe are activated by Te vacancies and O incorporation, which form abundant polarization centers, resulting in charge redistribution and increased dipole site density, thereby effectively optimizing dielectric relaxation loss. Consequently, the optimal EMW attenuation performance achieves a minimum reflection loss exceeding -69.6 dB at a thickness of 2.2 mm, with an absorption bandwidth of up to 4.9 GHz at a thickness of 1.3 mm. Besides, FeTe with dual defect exhibits a prominent radar cross-section reduction of 42 dBsm, indicating excellent radar wave attenuation capability. This study illustrates an innovative model system for elucidating dielectric relaxation loss mechanisms and provides a feasible approach to developing high-loss TMTs-based absorbers.

From Magnetoelectric Core-Shell Structure to Compound Eye-Inspired Metamaterials: Multiscale Design of Ultra-Wideband Electromagnetic Wave Absorber Device

The integration of macroscopic and microscopic structural designs plays a crucial role in developing high-performance electromagnetic wave (EMW) absorber devices. In this work, an innovative metamaterial based on a multi-scale design is introduced to address the challenge of narrowband absorption. Specifically, at the microscopic scale, a highly efficient absorbing material (FCIP@SiO2@Ppy) is synthesized through an integrated optimization strategy, in which functional layers are uniquely combined to maximize performance. By leveraging heterogeneous interfaces, this design establishes a magneto-electric coupling network, ensuring excellent impedance matching and significantly enhancing the EMW absorption capacity of the material. Notably, the material achieves a record low reflection loss (RL) of -66.66 dB at 9.95 GHz with a broad absorption bandwidth of 5.92 GHz (RL ≤ -10 dB), which is subsequently used to fabricate metamaterial absorber device. Building upon this, at the macroscopic scale, inspired by the compound eye structure of arthropods, a groundbreaking metamaterial structure is proposed. Simulations reveal the achievement of ultra-wideband absorption (2.75-18 GHz) with a remarkably thin thickness of just 12 mm. These pioneering results present effective strategies for the development of next-generation high-performance EMW absorber devices.

Nucleus-Spike 3D Hierarchical Superstructures via a Lecithin-Mediated Biomineralization Approach

3D hierarchical superstructures (3DHSs) are key products of nature's evolution and have raised wide interest. However, the preparation of 3DHSs composed of building blocks with different structures is rarely reported, and regulating their structural parameters is challenging. Herein, a simple lecithin-mediated biomineralization approach is reported for the first time to prepare gold 3DHSs composed of 0D nucleus and 1D protruding dendritic spikes. It is demonstrated that a hydrophobic complex by coordination of disulfiram (DSF) with a share of chloroauric acid is the key to forming the 3DHSs. Under the lecithin mediation, chloroauric acid is first reduced to form the 0D nucleus, followed by the spike growth through the reduction of the hydrophobic complex. The prepared 3DHSs possess well-defined morphology with a spike length of ≈95 nm. Notably, the hierarchical spike density is systematically manipulated from 38.9% to 74.3% by controlling DSF concentrations. Moreover, the spike diameter is regulated from 9.2 to 12.9 nm by selecting different lecithin concentrations to tune the biomineralization process. Finite-difference time-domain (FDTD) simulations reveal that the spikes form "hot spots". The dense spike structure endows the 3DHSs with sound performance in surface-enhanced Raman scattering (SERS) applications.

Biomimetic Multi-Interface Design of Raspberry-like Absorbent: Gd-doped FeNi3@Covalent Organic Framework Derivatives for Efficient Electromagnetic Attenuation

Structural design and interface regulation are useful strategies for achieving strong electromagnetic wave absorption (EMWA) and broad effective absorption bandwidth (EAB). Herein, a monomer-mediated strategy is employed to control the growth of covalent organic framework (COF) wrapping flower-shaped Gd-doped FeNi3 (GFN), and a novel raspberry-like absorbent based on biomimetic design is fabricated by thermal catalysis. Further, a unique dielectric-magnetic synergistic system is constructed by utilizing the COF-derived nitrogen-doped porous carbon (NPC) as the shell and anisotropic GFN as the core. The electromagnetic parameters of the GFN@NPC composites can be tuned by adjusting the proportions of GFN and NPC. Off-axis electron holography results further clarify the interface polarization and microscale magnetic interactions affecting the EMW loss mechanism. As a result, the GFN@NPC samples exhibit broad EMWA performance. The EAB values of all GFN@NPC composites reach up to 6.0 GHz, with the GFN@NPC-2 sample showing a minimum reflection loss (RLmin) of -69.6 dB at 1.68 mm. In addition, GFN@NPC-2 achieves a maximum radar cross-section (RCS) reduction of 29.75 dB·m2. A multi-layer gradient structure is also constructed using metamaterial simulation to achieve an ultra-wide EAB of 12.24 GHz. Overall, this work provides a novel bio-inspired design strategy to develop high-performance EMWA materials.

Bacterial cellulose nanofibers-assisted construction of core-shell structured polyaniline aerogel for superior electromagnetic wave absorption

Due to the increasing pollution of electromagnetic waves and the vigorous development of intelligent electronic devices, there is great interest in finding high-quality electromagnetic wave absorbing materials for integrated control boxes (ICBs) that integrate various electronic components. Polyaniline (PANI) is a new type of absorbing material with great potential due to its designable structure, simple preparation process, low density and adjustable conductivity. Herein, we prepared BCNF/PANI nanoscale conductive fibers with core-shell structure by in-situ growth of PANI on the surface of bacterial cellulose nanofibers (BCNF) by oxidative polymerization and further prepared cellulose/polyaniline/polyvinyl alcohol (BCNF/PANI/PVA) composite aerogel absorbing material by a freeze-drying process. The results show that the prepared BCNF/PANI/PVA aerogel has excellent absorption performance: the minimum reflection loss is -53.19 dB at 4.16 GHz with 6.11 mm thickness, and the effective absorption bandwidth is 2.20 GHz. The influence of the macrostructure of the BCNF/PANI/PVA absorbing unit on the absorption performance was further explored through numerical simulation, and the efficient electromagnetic protection of the small ICB was finally realized with the help of the macro-optimization strategy. This achievement provides an important reference and guidance for further developing and applying high-performance electromagnetic wave absorbing materials.

Ultra-Broadband Perfect Absorbers Based on Biomimetic Metamaterials with Dual Coupling Gradient Resonators

Ultra-broadband metamaterial absorbers can achieve near-perfect absorption of omnidirectional electromagnetic waves, crucial for light utilization and manipulation. Traditional ultra-broadband metamaterials rely on the superposition of different resonator units either in the plane or in perpendicular directions to broaden absorption peaks. However, this approach is subject to quantity restrictions and complicates the fabrication process. This study introduces a novel concept for broadband absorption metamaterial design-Metal-Insulator-Metal metamaterials with gradient resonators (GR-MIMs) to surpass limitations in quantity and fabrication. The GR-MIMs absorber features gradient resonant cavities in both nanoscale and microscale dimensions, each with continuous resonance points. By converting "resonance points" into "resonance bands" and perfectly coupling the two gradient resonators, the GR-MIMs absorber with a thickness of only 200 nm demonstrates 93% ultra-broadband high absorption across the UV, visible, near-infrared, and mid-infrared spectra (0.2-5 µm). Moreover, the solar spectrum absorption rate of the GR-MIMs absorber can reach 94.5%, offering broad prospects for applications in solar energy utilization. The design of gradient resonators provides a new approach for the development of ultra-broadband metamaterials and photothermal conversion metamaterials.

High-Performance Flexible Microwave Absorption Films with Dynamic Adjustable Macrostructures and Alterable Electromagnetic Field Polarizations

Electromagnetic wave absorption materials that can be utilized for freewill adhering or peeling from the target substrate remain a challenge to be solved. Compared to powder-based slurry and coatings, microwave absorption films possess clear advantages for their good flexibility and machinability. However, the matching thickness and effective bandwidth of 2D microwave absorption films cannot satisfy the current application requirements. As a result, it is necessary to complete a rational structural design based on flat films. In view of the fact that common film-forming methods based on blocks or hard bases cannot be changed or replaced easily once the structural construction is done, here solvent evaporation molding combined with phase change material filling was proposed for the first time to accomplish continuous structural transformation for flexible films. Unlike the original reflection loss (RL) peaks of flat films at around 17.0 GHz, a new absorption peak near 12.25 GHz was generated thanks to the design of coherent structures, resulting in the peaks' boundary merging and effective bandwidth extension. Specifically, 4.56 GHz of absorption bandwidth (RL < -5 dB) at 1.0 mm and 4.27 GHz (RL < -10 dB) of absorption bandwidth at 2.3 mm could be obtained by arch testing under electrical field polarization. Importantly, correlations between EM field polarizations and coherent structures as well as the rules of the absorption peak generation and frequency shift related to the structural variation have all been figured out. The presented laws of EM pattern evolutions for structural films in this work lay the foundation for the applications of high-efficiency microwave absorption materials in complex surfaces and switchable scenes.

Enhanced dielectric losses in α-MnO2via protonation modulation

MnO6 octahedra without distortions in α-MnO2 have a low dipole content, which limits their dielectric loss capabilities. Herein, we develop protonated MnO2 with distorted MnO6 octahedra for increased dipole numbers via a two-step hydrothermal method. In comparison with α-MnO2, this protonated MnO2 provides greatly improved dipole polarization loss capabilities, resulting in a reflection loss value of -19.1 dB with an effective absorption bandwidth of 3.3 GHz at a low thickness of 2 mm.

Electromagnetic Functions Modulation of Recycled By-Products by Heterodimensional Structure

One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic (EM) wave jamming and the recycling of defensive shields. The synergistic effect of heterodimensional materials can effectively enable the manipulation of EM waves by altering the nanostructure. Here we propose a novel approach for upcycling by-products of silver nanowires that can fabricate shape-tunable aerogels which enable the modulation of its interaction with microwaves by heterodimensional structure of by-products. By-product heterodimensionality was used to design EM-wave-jamming-dissipation structures and therefore two typical tunable aerogel forms were studied. The first tunable form was aerogel film, which shielded EM interference (EMI shielding effectiveness (EMI SE) > 89 dB) and the second tunable form was foam, which performed dual EM functions (SE > 30 dB& reflective loss (RL) < -35 dB, effective absorption bandwidth (EAB) > 6.7 GHz). We show that secondary recycled aerogels retain nearly all of their EM protection properties, making this type of closed-loop cycle an appealing option. Our findings pave the way for the development of adaptive EM functions with nanoscale regulation in a green and closed-loop cycle, and they shed light on the fundamental understanding of microwave interactions with heterodimensional structures.

Multi-Physical Lattice Metamaterials Enabled by Additive Manufacturing: Design Principles, Interaction Mechanisms, and Multifunctional Applications

Lattice metamaterials emerge as advanced architected materials with superior physical properties and significant potential for lightweight applications. Recent developments in additive manufacturing (AM) techniques facilitate the manufacturing of lattice metamaterials with intricate microarchitectures and promote their applications in multi-physical scenarios. Previous reviews on lattice metamaterials have largely focused on a specific/single physical field, with limited discussion on their multi-physical properties, interaction mechanisms, and multifunctional applications. Accordingly, this article critically reviews the design principles, structure-mechanism-property relationships, interaction mechanisms, and multifunctional applications of multi-physical lattice metamaterials enabled by AM techniques. First, lattice metamaterials are categorized into homogeneous lattices, inhomogeneous lattices, and other forms, whose design principles and AM processes are critically discussed, including the benefits and drawbacks of different AM techniques for fabricating different types of lattices. Subsequently, the structure-mechanism-property relationships and interaction mechanisms of lattice metamaterials in a range of physical fields, including mechanical, acoustic, electromagnetic/optical, and thermal disciplines, are summarized to reveal critical design principles. Moreover, the multifunctional applications of lattice metamaterials, such as sound absorbers, insulators, and manipulators, sensors, actuators, and soft robots, thermal management, invisible cloaks, and biomedical implants, are enumerated. These design principles and structure-mechanism-property relationships provide effective design guidelines for lattice metamaterials in multifunctional applications.

Localized Morphological Modulation of Ultrathin Magnetic Nanosheets via a Strategically Designed Reduction Approach

2D inorganic nanomaterials have attracted considerable research interest owing to their exceptional physical and chemical properties. Nonetheless, achieving precise control over the morphology of 2D nanomaterials presents a significant challenge, primarily due to their elevated surface energy and the stringent requirements for growth control. In this study, a designed reduction technique is employed to finely tune the morphology of 2D nanosheets, with iron salts serving as morphology-directing agents. Al-doped α-Fe2O3 nanosheets are synthesized through a solvothermal process and subsequently reduced to Al-doped Fe3O4 nanosheets, characterized by distinctive sawtooth-like edges. The incorporation of iron salts facilitates atomic rearrangement within the iron oxide lattice, wherein rapid atomic migration induces defects along the crystal facets, resulting in unique morphologies. Furthermore, the doping of aluminum elements and the resultant Fe3O4 significantly enhance the electromagnetic properties of the nanosheets, yielding exceptional electromagnetic wave absorption performance. Notably, a remarkable minimum reflection loss (RLmin) of -66.1 dB is achieved at a thickness of 4.0 mm, with an effective absorption bandwidth (RL ≤ -10 dB) extending up to 3.9 GHz. This controlled reduction strategy presents a promising pathway for tailoring the morphology of 2D nanomaterials and optimizing their performance in electromagnetic wave absorption applications.

A Rapidly Assembled and Camouflage-Monitoring-protection Integrated Modular Unit

Optical-electromagnetic compatible devices are urgently required in intelligent building monitors and cross-band protection. Meanwhile, the insufficient systematicness and semi-empirical attempts significantly limit the prosperity of cross-band materials, causing enormous challenges for deviceization and material database construction. Herein, the systematical component-deviceization-machine learning prediction-array construction strategy is attempted to solve the bottleneck issues. A luminance-triggered camouflage-monitoring-protection triune integrated modular unit (IMU) is hierarchically encapsulated to simultaneously achieve efficient anti-electromagnetic interference (EMI), light-absorbing, quick gradient-colorization response. Moreover, an illumination intensity dataset and a surrogate model based on fully connected neural network fitting (FCNN-fitting) are constructed, which accurately predicts the light-absorbing property of IMUs and can be instructional for material selection. The IMUs are specifically assembled into a 4*4 array, aiming at multi-scenario application of programmable display, camouflage pattern, surface conformality, and rapid replaceability. This work paves the path and provides a promising strategy for optical-electromagnetic compatibility and material genetics-deviceization-array systematization.

A tunable metamaterial microwave absorber inspired by chameleon's color-changing mechanism

A metamaterial absorber capable of swiftly altering its electromagnetic response in the microwave range offers adaptability to changing environments, such as tunable stealth capabilities. Inspired by the chameleon's ability to change color through the structural transformation of photonic lattice crystals, which shift the bandgaps of reflection and transmission of visible light, we designed a crisscross structure that transforms from an expanded to a collapsed form. This transformation enables a switch between broadband absorption and peak transmission in the microwave range (4 to 18 gigahertz). The structure, optimized through data-driven design, is mechanically actuated by the rotation of interlinked trusses. This mechanism changes the entire array's response, allowing it to remain undetected by an external radar or to transmit an internal radar signal to a near-field receiver when needed. The mechanical actuation and the shifting electromagnetic response of the arrayed structure are demonstrated.

Lessons from Nature: Advances and Perspectives in Bionic Microwave Absorption Materials

Inspired by the remarkable electromagnetic response capabilities of the complex morphologies and subtle microstructures evolved by natural organisms, this paper delves into the research advancements and future application potential of bionic microwave-absorbing materials (BMAMs). It outlines the significance of achieving high-performance microwave-absorbing materials through ingenious microstructural design and judicious composition selection, while emphasizing the innovative strategies offered by bionic manufacturing. Furthermore, this work meticulously analyzes how inspiration can be drawn from the intricate structures of marine organisms, plants, animals, and non-metallic minerals in nature to devise and develop BMAMs with superior electromagnetic wave absorption properties. Additionally, the paper provides an in-depth exploration of the theoretical underpinnings of BMAMs, particularly the latest breakthroughs in broadband absorption. By incorporating advanced methodologies such as simulation modeling and bionic gradient design, we unravel the scientific principles governing the microwave absorption mechanisms of BMAMs, thereby furnishing a solid theoretical foundation for understanding and optimizing their performance. Ultimately, this review aims to offer valuable insights and inspiration to researchers in related fields, fostering the collective advancement of research on BMAMs.

Broadband Sound Absorption and High Damage Resistance in a Turtle Shell-Inspired Multifunctional Lattice: Neural Network-Driven Design and Optimization

Incorporating acoustic and mechanical properties into a single multifunctional structure has attracted considerable attention in engineering. However, effectively integrating these sound absorption properties and damage resistance to achieve multifunctional structural designs remains a great challenge due to imperfect design methods. In this study, the inherent mechanical properties of turtle shells by introducing dissipative pores are leveraged to present a lattice structure that possesses both excellent sound-absorbing and high damage-resistant characteristics. To achieve acoustic optimization design, a universal high-fidelity neural network correction model is proposed to address the impedance calculation challenge in complex structures. Building upon this foundation, a multi-cell combination design enables to achieve high absorption through optimization with a low thickness of 50 mm, resulting in average sound absorption coefficients reaching 0.88 and 0.93 within the frequency ranges of 300-600 Hz and 500-1000 Hz, respectively. It is also found that the optimized structures exhibit exceptional damage resistance under varying relative densities via the coupling effect of the shell thickness on the acoustic and mechanical properties. Overall, this work introduces a novel paradigm for designing intricate multifunctional structures with acoustic and mechanical properties while providing valuable inspiration for future research on multifunctional structure design.

Multi-Frequency Asymmetric Absorption-Transmission Metastructures-Photonic Crystals and Their Application as a Refractive Index Sensor

In this paper, a kind of metastructure-photonic crystal (MPC) with multi-frequency asymmetric absorption-transmission properties is proposed. It is composed of various dielectric layers arranged in a periodically tilting pattern. When electromagnetic waves (EMWs) enter from the opposite direction, MPC shows an obvious asymmetry. EMWs are absorbed at 13.71 GHz, 14.37 GHz, and 17.10 GHz in forward incidence, with maximum absorptions of 0.919, 0.917, and 0.956, respectively. In the case of backward incidence, transmission above 0.877 is achieved. Additionally, the MPC is utilized for refractive index (RI) sensing, allowing for wide RI range detection. The refractive index unit is denoted as RIU. The RI detection range is 1.4~3.0, with the corresponding absorption peak variation range being 17.054~17.194 GHz, and a sensitivity of 86 MHz/RIU. By adjusting the number of MPC cycles and tilt angle, the sensing performance and operating frequency band can be tailored to meet various operational requirements. This MPC-based RI sensor is simple to fabricate and has the potential to be used in the development of high-performance and compact sensing devices.

Fixed-Point Atomic Regulation Engineered Low-Thickness Wideband Microwave Absorption

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.

Hetero-Interface Engineering on 9.0 wt% CoOx-Doped CeO2 Nanorods as Electromagnetic Wave Absorber and Integrated into Multifunctional Aerogel

Ceria (CeO2) becomes a promising candidate as electromagnetic wave absorbing materials (EWAMs) for their abundant natural source, rich oxygen vacancy, charge conversion, and electron transfer abilities. However, it remains challenging to regulate its nanoscale and atom-scale composition to optimize the absorbing performance and develop high-performance commercial devices. Herein, a facile method to large-scale synthesis CeO2@Co-x% (x = 5, 7, 9, 11, 13) series EWAMs with diverse amounts of decorated CoOx is presented. By modulating the ratio of doped CoOx, a rational hetero-interface is created in CeO2@Co-9% to enhance natural and exchange resonances, improving magnetic loss capability and optimizing impedance matching. Doped CoOx promotes the charge accumulation, interfacial polarization, and multiple scattering of the CeO2 for strengthening the EW absorption and attenuation, which display superb minimum reflective loss (RLmin) of -74.4 dB with a wide effective absorbing bandwidth (EAB) of 5.26 GHz. Furthermore, a dual crosslinking strategy is employed to fabricate CeO2@Co-9% into an aerogel device with integrated lightweight, heat insulation, compression resistance, and fame-retardant functions. This work presents an excellent example of large-scale fast synthesis of high-performance CeO2-based EWAMs and multiplication 3D devices.

Superior Strength, Toughness, and Damage-Tolerance Observed in Microlattices of Aperiodic Unit Cells

Characterized by periodic cellular unit cells, microlattices offer exceptional potential as lightweight and robust materials. However, their inherent periodicity poses the risk of catastrophic global failure. To address this limitation, a novel approach, that is to introduce microlattices composed of aperiodic unit cells inspired by Einstein's tile, where the orientation of cells never repeats in the same orientation is proposed. Experiments and simulations are conducted to validate the concept by comparing compressive responses of the aperiodic microlattices with those of common periodic microlattices. Indeed, the microlattices exhibit stable and progressive compressive deformation, contrasting with catastrophic fracture of periodic structures. At the same relative density, the microlattices outperform the periodic ones, exhibiting fracture strain, energy absorption, crushing stress efficiency, and smoothness coefficients at least 830%, 300%, 130%, and 160% higher, respectively. These improvements can be attributed to aperiodicity, where diverse failure thresholds exist locally due to varying strut angles and contact modes during compression. This effectively prevents both global fracture and abrupt stress drops. Furthermore, the aperiodic microlattice exhibits good damage tolerance with excellent deformation recoverability, retaining 76% ultimate stress post-recovery at 30% compressive strain. Overall, a novel concept of adopting aperiodic cell arrangements to achieve damage-tolerant microlattice metamaterials is presented.

Mechanical metamaterials as broadband electromagnetic wave absorbers: investigating relationships between geometrical parameters and electromagnetic response

The utilization of low-density and robust mechanical metamaterials rises as a promising solution for multifunctional electromagnetic wave absorbers due to their structured porous structures, which facilitates impedance matching and structural absorption. However, the various geometrical parameters involved in constructing these metamaterials affect their electromagnetic response, necessitating a comprehensive understanding of underlying absorbing mechanisms. Through experimentally validated numerical analysis, this study delves into the influence of geometrical factors on the electromagnetic response of representative low-density, high strength mechanical metamaterials, namely octet-truss and octet-foam. By juxtaposing electromagnetic response under varying volume fractions, cell lengths, and multilayer configurations of octet-truss and octet-foam, distinct absorption mechanisms emerge as geometrical parameters evolve. These mechanisms encompass diminished reflection owing to porous structures, effective medium approximations within subwavelength limits, and transmission-driven or reflection-driven phenomena originating from the interplay of open- and closed-cell structures. Through analyses on these mechanical metamaterials, we demonstrate the viability of employing them as tunable yet scalable structures that are lightweight, robust, and broadband electromagnetic wave absorption.

Structural Engineering of Hierarchical Magnetic/Carbon Nanocomposites via In Situ Growth for High-Efficient Electromagnetic Wave Absorption

Materials exhibiting high-performance electromagnetic wave absorption have garnered considerable scientific and technological attention, yet encounter significant challenges. Developing new materials and innovative structural design concepts is crucial for expanding the application field of electromagnetic wave absorption. Particularly, hierarchical structure engineering has emerged as a promising approach to enhance the physical and chemical properties of materials, providing immense potential for creating versatile electromagnetic wave absorption materials. Herein, an exceptional multi-dimensional hierarchical structure was meticulously devised, unleashing the full microwave attenuation capabilities through in situ growth, self-reduction, and multi-heterogeneous interface integration. The hierarchical structure features a three-dimensional carbon framework, where magnetic nanoparticles grow in situ on the carbon skeleton, creating a necklace-like structure. Furthermore, magnetic nanosheets assemble within this framework. Enhanced impedance matching was achieved by precisely adjusting component proportions, and intelligent integration of diverse interfaces bolstered dielectric polarization. The obtain Fe3O4-Fe nanoparticles/carbon nanofibers/Al-Fe3O4-Fe nanosheets composites demonstrated outstanding performance with a minimum reflection loss (RLmin) value of - 59.3 dB and an effective absorption bandwidth (RL ≤  - 10 dB) extending up to 5.6 GHz at 2.2 mm. These notable accomplishments offer fresh insights into the precision design of high-efficient electromagnetic wave absorption materials.

Bioinspired Hollow/Hollow Architecture with Flourishing Dielectric Properties for Efficient Electromagnetic Energy Reclamation Device

The exploitation of advanced electromagnetic functional devices is perceived as the effective prescription to deal with environmental contamination and energy deficiency. From the perspective of observing and imitating nature, pine branch-like zirconium dioxide/cobalt nanotubes@nitrogen-doped carbon nanotubes are synthesized victoriously through maneuverable electrospinning process and follow-up thermal treatments. In particular, introducing carbon nanotubes on the surface of hollow nanofibers to construct hierarchical architecture vastly promoted the material's dielectric properties by significantly augmenting specific surface area, generating abundant heterogeneous interfaces, and inducing the formation of defects. Supplemented by the synergistic effect between each constituent, ultra-strong attenuation capacity and perfect impedance matching characteristics are implemented simultaneously, and jointly made contributions to the splendid microwave absorption performance with a minimum reflection loss of -67.9 dB at 1.5 mm. Moreover, this fibrous absorber also exhibited promising potential to be utilized as a green and efficient electromagnetic interference shielding material when the filler loading is enhanced. Therefore, this design philosophy is destined to inspire the future development of energy conversion and storage devices, and provide theoretical direction for the creation of sophisticated electromagnetic functional materials.

Linkage Effect Induced by Hierarchical Architecture in Magnetic MXene-based Microwave Absorber

Hierarchical architecture engineering is desirable in integrating the physical-chemical behaviors and macroscopic properties of materials, which present great potential for developing multifunctional microwave absorption materials. However, the intrinsic mechanisms and correlation conditions among cellular units have not been revealed, which are insufficient to maximize the fusion of superior microwave absorption (MA) and derived multifunctionality. Herein, based on three models (disordered structure, porous structure, lamellar structure) of structural units, a range of MXene-aerogels with variable constructions are fabricated by a top-down ice template method. The aerogel with lamellar structure with a density of only 0.015 g cm-3 exhibits the best MA performance (minimum reflection loss: -53.87 dB, effective absorption bandwidth:6.84 GHz) at a 6 wt.% filling ratio, which is preferred over alternative aerogels with variable configurations. This work elucidates the relationship between the hierarchical architecture and the superior MA performance. Further, the MXene/CoNi Composite aerogel with lamellar structure exhibits >90% compression stretch after 1000 cycles, excellent compressive properties, and elasticity, as well as high hydrophobicity and thermal insulation properties, broadening the versatility of MXene-based aerogel applications. In short, through precise microstructure design, this work provides a conceptually novel strategy to realize the integration of electromagnetic stealth, thermal insulation, and load-bearing capability simultaneously.

The Electron Migration Polarization Boosting Electromagnetic Wave Absorption Based on Ce Atoms Modulated yolk@shell Fex N@NGC

The electron migration polarization is considered as a promising approach to optimize electromagnetic waves (EMW) dissipation. However, it is still difficult to realize well-controlled electron migration and elucidate the related EMW loss mechanisms for current researches. Herein, a novel Fex N@NGC/Ce system to construct an effective electron migration model based on the electron leaps among the 4f/5d/6s orbitals of Ce ions is explored. In Fe4 N@NGC/CeSA+Cs+NPs , Ce single-atoms (SA) mainly represent a +3 valence state, which can feed the electrons to Ce4+ of clusters (Cs) and CeO2 nanoparticles (NPs) through a conductive network under EMW, leading to the electron migration polarization. Such electron migration loss combined with excellent magnetic loss provided by Fe4 N core, results in the optimal EMW attenuation performance with a minimum reflection loss exceeds -85.1 dB and a broadened absorption bandwidth up to 7.5 GHz at 1.5 mm. This study clarifies the in-depth relationship between electron migration polarization and EMW dissipation, providing profound insights into developing well-coordinated magnetic-dielectric nanocomposites for EMW absorption engineering.

Physiochemical Coupled Dynamic Nanosphere Lithography Enabling Multiple Metastructures from Single Mask

Metastructures are widely used in photonic devices, energy conversion, and biomedical applications. However, to fabricate multiple patterns continuously in single etching protocol with highly tunable photonic properties is challenging. Here, a simple and robust dynamic nanosphere lithography is proposed by inserting a spacer between the nanosphere assembly and the wafer. The nanosphere diameter decrease and uneven penetration of the spacer during etching lead to a dynamic masking process. Coupled anisotropic physical ion sputtering and ricocheting with isotropic chemical radical etching achieve highly tunable structures with various 3D patterns continuously forming through a single etching process. Specifically, the nanosphere diameters define the periodicity, the etched spacer forms the upper parts, and the wafer forms the lower parts. Each part of the structure is highly tunable through changing nanosphere diameter, spacer thickness, and etch conditions. Using this protocol, numerous structures of varying sizes including nanomushrooms, nanocones, nanopencils, and nanoneedles with diverse shapes are realized as proof of concepts. The broadband antireflection ability of the nanostructures and their use in surface-enhanced Raman spectroscopy are also demonstrated for practical application. This method substantially simplifies the fabrication procedure of various metastructures, paving the way for its application in multiple disciplines especially in photonic devices.

Biomimetic Bouligand chiral fibers array enables strong and superelastic ceramic aerogels

Ceramic aerogels are often used when thermal insulation materials are desired; however, they are still plagued by poor mechanical stability under thermal shock. Here, inspired by the dactyl clubs of mantis shrimp found in nature, which form by directed assembly into hierarchical, chiral and Bouligand (twisted plywood) structure exhibiting superior mechanical properties, we present a compositional and structural engineering strategy to develop strong, superelastic and fatigue resistance ceramic aerogels with chiral fibers array resembling Bouligand architecture. Benefiting from the stress dissipation, crack torsion and mechanical reinforcement of micro-/nano-scale Bouligand array, the tensile strength of these aerogels (170.38 MPa) is between one and two orders of magnitude greater than that of state-of-the-art nanofibrous aerogels. In addition, the developed aerogels feature low density and thermal conductivity, good compressive properties with rapid recovery from 80 % strain, and thermal stability up to 1200 °C, making them ideal for thermal insulation applications.