A Novel Strategy in Electromagnetic Wave Absorbing and Shielding Materials Design: Multi‐Responsive Field Effect

Thermo-Chemo-Mechanically Robust, Multifunctional MXene/PVA/PAA-Hanji Textile with Energy Harvesting, EMI Shielding, Flame-Retardant, and Joule Heating Capabilities

The rapid development of wearable electronics, personal mobile equipment, and Internet of Things systems demands smart textiles that integrate multiple functions with enhanced durability. Herein, the study reports robust and multifunctional textiles with energy harvesting, electromagnetic interference (EMI) shielding, flame resistance, and Joule heating capabilities, fabricated by a facile yet effective integration method using the deposition of cross-linked MXene (Ti3C2Tx), poly(vinyl alcohol) (PVA), and poly(acrylic acid) (PAA) onto traditional Korean paper, Hanji via vacuum filtration. Comprehensive analyses confirm robust cross-linking, structural integrity, and interface stability in the MXene/PVA/PAA-Hanji (MPP-H) textiles, which synergistically boost their multifunctional performance. The MPP-H textiles exhibit remarkable power generation lasting over 60 min with a power density of 102.2 µW cm-3 and an energy density of 31.0 mWh cm-3 upon the application of 20 µL of NaCl solution. The EMI shielding effectiveness (SE) per unit thickness in the X-band (8.2-12.4 GHz) is up to 437.6 dB mm-1, with the ratio of absorption to reflection reaching 4.5, outperforming existing EMI shielding materials. Superior thermo-chemo-mechanical properties (flame resistance, rapid Joule heating, durability, and washability) further demonstrate their versatile usability. The MPP-H enables diverse functionalities within a single, robust textile through a scalable fabrication method, offering transformative potential for wearable and mobility platforms.

Broadband multi‐layered stepped cone shaped metamaterial absorber for energy harvesting and stealth applications

In this study, a broadband polarization and angle‐independent metamaterial absorber (MA) is investigated in the microwave range. It is made up of a periodic array of multi‐layered metal‐dielectric stepped cones. Since the dimensions of the layers forming the unit cell are different, each layer resonates at different frequencies with overlapping bands. The overall response of the structure, with its extremely wide bandwidth, can be obtained by summing all the overlapping frequency responses corresponding to each layer. In numerical simulation, it is observed that the absorption at normal incidence is above 90% in the frequency range between 9.68 and 17.45 GHz and 95% in the frequency range between 9.91 and 14.86 GHz. The energy harvesting ratios of the structure are also evaluated in a wide spectral band. A power ratio of around 90% is obtained in the same frequency range in accordance with absorption response. A noticeable harvesting efficiency of up to 82% is observed, which represents the energy level converted into electrical energy on resistors.

Efficient Synthesis of Fe3O4/PPy Double-Carbonized Core-Shell-like Composites for Broadband Electromagnetic Wave Absorption

Ever-increasing electromagnetic pollution largely affects human health, sensitive electronic equipment, and even military security, but current strategies used for developing functional attenuation materials cannot be achieved in a facile and cost-effective way. Here, a unique core-shell-like composite was successfully synthesized by a simple chemical approach and a rapid microwave-assisted carbonization process. The obtained composites show exceptional electromagnetic wave absorption (EMWA) properties, including a wide effective absorption band (EAB) of 4.64 GHz and a minimum reflection loss (RLmin) of -26 dB at 1.6 mm. The excellent performance can be attributed to the synergistic effects of conductive loss, dielectric loss, magnetic loss, and multiple reflection loss within the graphene-based core-shell-like composite. This work demonstrates a convenient, rapid, eco-friendly, and cost-effective method for synthesizing high-performance microwave absorption materials (MAMs).

Succulent-Inspired Implicit Structural Change for Smart "ON/OFF" Switchable and Flexible EMI Shielding Coating

Modern miniaturized intelligent electronics call for smart switchable and flexible electromagnetic interference (EMI) shielding material for highly precise applications. However, most switchable EMI shielding materials are based on an explicit structural change. Herein, we report a succulent-inspired smart switchable MXene (WR-MXene) coating film realized by inner implicit structural change, which benefits from the insertion of our reversible large-cavity yolk-shell biomicrospheres. The novel switchable yolk-shell biomicrospheres contain a soft N-isopropylacrylamide (PNIPAM) hydrogel core, an "ON/OFF" switchable cavity (over 30% volume fraction), and a porous polydopamine (p-PDA) shell. The yolk-shell biomicrospheres can be obtained by a facile two-step polymerization and a simple drying-dehydration treatment. Because of the "ON/OFF" switchable void space brought by the smart biomicrospheres and conductive framework of MXene, an optimized ultralight and flexible WR-MXene coating film (vWR-coating film) showed both large switchable change (over 60 dB) and extraordinary EMI shielding effectiveness, reaching 95 and over 50 dB in the whole X band (8.2-12.4 GHz). These novel reversible yolk-shell biomicrospheres and the succulent-inspired switchable coating films are promising for smart flexible wearable devices and many advanced multifunctional systems needing dynamic real-time response.

MXene Hollow Spheres Supported by a C-Co Exoskeleton Grow MWCNTs for Efficient Microwave Absorption

High-performance microwave absorption (MA) materials must be studied immediately since electromagnetic pollution has become a problem that cannot be disregarded. A straightforward composite material, comprising hollow MXene spheres loaded with C-Co frameworks, was prepared to develop multiwalled carbon nanotubes (MWCNTs). A high impedance and suitable morphology were guaranteed by the C-Co exoskeleton, the attenuation ability was provided by the MWCNTs endoskeleton, and the material performance was greatly enhanced by the layered core-shell structure. When the thickness was only 2.04 mm, the effective absorption bandwidth was 5.67 GHz, and the minimum reflection loss (RLmin) was - 70.70 dB. At a thickness of 1.861 mm, the sample calcined at 700 °C had a RLmin of - 63.25 dB. All samples performed well with a reduced filler ratio of 15 wt%. This paper provides a method for making lightweight core-shell composite MA materials with magnetoelectric synergy.

Synthesis and characterization of calcium-iron-chromium nanocomposites for electromagnetic radiation shielding application

Over a century, shielding harmful electromagnetic radiations (EMR) and finding a suitable material, which can replace lead has become the major interest of researchers in this field. Herein, calcium-iron-chromium oxide nanocomposites with the different atomic ratios are synthesized using the solution combustion method. The as-obtained nanoparticles (NPs) are subjected to several structural and surface characteristics such as powder X-ray diffraction, scanning electron microscopy, elemental diffraction X-ray analysis, Fourier Transform Infrared Spectroscopy and UV-visible spectroscopy analysis were performed to confirm the successful synthesis. Furthermore, the EMR shielding of as-procured NPs is investigated and observed that the obtained NPs show good shielding properties.

The unusual effect of paraffin wax on the thermal decomposition of cyclotetramethylenetetranitramine

The practical application of paraffin wax (PW) in cyclotetramethylenetetranitramine (HMX)-based polymer-bonded explosive (PBX) requires an understanding of its effect on the thermal decomposition of HMX. In this work, by comparing the thermal decomposition of HMX and a HMX/PW mixture, combined with crystal morphology analysis, molecular dynamics simulation, kinetic analysis, and gas product analysis, the unusual phenomenon and mechanism of the PW effect on the thermal decomposition of HMX were evaluated. During the initial decomposition, PW infiltrates the crystal surface of HMX, reduces the energy barrier for chemical bond dissociation, and induces the decomposition of molecules on HMX crystals, resulting in a lower initial decomposition temperature. PW consumes the active gas produced by HMX with further thermal decomposition and inhibits the dramatic increase of the HMX thermal decomposition rate. In decomposition kinetics, this effect is manifested as PW inhibits transition from an n-order reaction to an autocatalytic reaction.

A Sustainable and Low-Cost Route to Design NiFe2O4 Nanoparticles/Biomass-Based Carbon Fibers with Broadband Microwave Absorption

Carbon-based microwave-absorbing materials with a low cost, simple preparation process, and excellent microwave absorption performance have important application value. In this paper, biomass-based carbon fibers were prepared using cotton fiber, hemp fiber, and bamboo fiber as carbon sources. Then, the precise loading of NiFe₂O₄ nanoparticles on biomass-based carbon fibers with the loading amount in a wide range was successfully realized through a sustainable and low-cost route. The effects of the composition and structure of NiFe₂O₄/biomass-based carbon fibers on electromagnetic parameters and electromagnetic absorption properties were systematically studied. The results show that the impedance matching is optimized, and the microwave absorption performance is improved after loading NiFe₂O₄ nanoparticles on biomass-based carbon fibers. In particular, when the weight percentage of NiFe₂O₄ nanoparticles in NiFe₂O₄/carbonized cotton fibers is 42.3%, the effective bandwidth of NiFe₂O₄/carbonized cotton fibers can reach 6.5 GHz with a minimum reflection loss of -45.3 dB. The enhancement of microwave absorption performance is mainly attributed to the appropriate electromagnetic parameters with the ε' ranging from 9.2 to 4.8, and the balance of impedance matching and electromagnetic loss. Given the simple synthesis method, low cost, high output, and excellent microwave absorption performance, the NiFe₂O₄/biomass-based carbon fibers have broad application prospects as an economic and broadband microwave absorbent.

Facile Synthesis of Metal Oxide Decorated Carbonized Bamboo Fibers with Wideband Microwave Absorption

Aiming at the disadvantages of high cost, complex processes, low yield, and narrow bandwidth of carbon-based microwave absorbing materials, this paper provides a novel and efficient method for synthesizing metal oxide/carbonized bamboo fibers using renewable natural bamboo fibers as a carbon source. The results suggested that the metal oxides such as NiO and Fe₃O₄ were uniformly dispersed on the carbonized bamboo fibers and proved that the dielectric component NiO and magnetic component Fe₃O₄ can significantly improve the microwave absorption performance of the carbonized bamboo fibers. As expected, the NiO/carbonized bamboo fibers showed excellent microwave absorption performance due to the appropriate complex permittivity, high impedance matching, and attenuation coefficient. A wide effective bandwidth of 6.4 GHz with 2.2 mm thickness is achieved, covering the entire Ku-band. Remarkably, the reflection loss (RL) values less than -10 dB covered the whole X-band at a thickness of 3.0 mm. This work reveals the potential of carbonized bamboo fibers-based composite as an economic and broadband microwave absorbent and offers a new strategy for designing promising microwave absorption materials.

Electromagnetic Wave Absorbing, Thermal-Conductive Flexible Membrane with Shape-Modulated FeCo Nanobelts

Electromagnetic wave (EMW)-absorbing materials, manufactured with composites of magnetic particles, are essential for maintaining a high complex permeability and modulated permittivity for impedance matching. However, commonly available EMW-absorbing materials are unsatisfactory owing to their low complex permeability in the high-frequency band. Herein, we report a thin, flexible EMW-absorbing membrane comprising shape-modulated FeCo nanobelts/boron nitride nanoparticles, which enables enhanced complex permeability in the S, C, and X bands (2-12 GHz). The boron nitride nanoparticles that are introduced to the FeCo nanobelts demonstrate control of the complex permittivity, leading to an effective impedance matching close to 1, consequently resulting in a high reflection loss value of -42.2 dB at 12.0 GHz with only 1.6 mm thickness. In addition, the incorporation of boron nitride nanoparticles improves the thermal conductivity for the heat dissipation of the absorbed electromagnetic wave energy. Overall, the comprehensive study of nanomaterial preparation and shape modulation technologies can lead to the fabrication of an excellent EMW-absorbing flexible composite membrane.

Macroscopic Electromagnetic Cooperative Network-Enhanced MXene/Ni Chains Aerogel-Based Microwave Absorber with Ultra-Low Matching Thickness

Electromagnetic cooperative strategy has been presented as a mainstream approach that can effectively optimize the matching thickness of dielectric loss dominant system. However, it is still challenging for dielectric-magnetic loss coexisting-type absorber to develop electromagnetic wave (EMW) performance with ultra-low matching thickness (≤ 1 mm). Breaking the limitation of traditional electromagnetic response at microscopic/mesoscopic scale, a ficus microcarpa-like magnetic aerogel with macroscopical electromagnetic cooperative effect was fabricated through highly oriented self-assembly engineering. The highly oriented Ni chains with unique macroscopic morphology (~ 1 cm in length) were achieved via a special magnetic field-induced growth. Strong magnetic coupling was observed in the Ni chains confirmed by the micromagnetic simulation. The deductive calculation validates that maintaining high value of electromagnetic parameters at high frequencies is the prerequisites of ultrathin absorber. The electromagnetic cooperative networks with uninterrupted and dual pathways spread through the entire aerogel skeleton, resulting in the impressive permittivity even at high frequencies. Consequently, the aerogel exhibits a remarkable EMW performance at an ultrathin thickness of 1 mm. Thus, based on the modulation of electromagnetic parameters, this work proposed a macroscopic ordered structure with the electromagnetic cooperative effect useful to develop a suitable strategy for achieving ultrathin EMW absorbers.

Optically Transparent Broadband Microwave Absorber by Graphene and Metallic Rings

The demand for optically transparent microwave absorbers has attracted increasing interest among researchers in recent years. However, integrating broadband microwave absorption and high optical transparency remains a challenge. This report demonstrates a scheme for broadband microwave absorbers, featuring a 90% absorption bandwidth of 10 GHz covering a frequency range of 25.2-35.2 GHz and high compatibility with good optical transparency in a wide band from the visible to infrared. The absorber is based on a Jaumann structure composed of two graphene sheets sandwiched by dielectric and backed by an arrayed-metallic-rings sheet. Guided by derived formulas, this absorber exhibits complete absorption if the sheet resistance of graphene is close to 500 Ω sq^-1. The bandwidth and center frequency of the absorption spectra can be readily tuned simply via changes in the thickness of the dielectric between the graphene films and arrayed-metallic-rings sheet. Moreover, the absorber is insensitive to the incident angle of radiation and can achieve broadband and near-unity absorption even at oblique incidence. The graphene-based absorber proposed herein provides a viable solution for effectively integrating broadband and near-unity microwave absorption with high optical transparency, thereby enabling widespread applications in optics, communications, and solar cells.

Enhanced interfacial polarization of biomass-derived porous carbon with a low radar cross-section

Ultra-thin microwave absorbers have been urgently demanded for electromagnetic applications in recent years. Herein, porous carbon with a "flower cluster" microstructure was synthesized from biomass waste (mango seeds) by a facile activation and carbonization method. The novel structure reduced the density and also improved the impedance matching, dipole polarization, and provided many carbon matrix-air interfaces for interfacial polarization, resulting in superior microwave absorption performance. At an ultra-thin thickness of 1.5 mm, extraordinary microwave absorption was achieved, with a reflection loss (RL) of -42 dB. The effective absorption bandwidth reached 4.2 GHz. The RL can be further improved to -68.4 dB by adjusting the amount of activator to manipulate the structure of porous carbon. In addition, from the simulated radar scattering results, the maximum reduction in the radar cross-section (RCS) reached 30.4 dBm², which can greatly reduce the probability of equipment being detected by radar. This work provides a low-cost and high-performance microwave absorber for electromagnetic stealth technologies.

Controllable Synthesis of Mo3C2 Encapsulated by N-Doped Carbon Microspheres to Achieve Highly Efficient Microwave Absorption at Full Wavebands: From Lemon-like to Fig-like Morphologies

Mo₃C₂@N-doped carbon microspheres (Mo₃C₂@NC) have been discovered to be a family of superior microwave absorbing materials. Herein, Mo₃C₂@NC was synthesized through a simple high-temperature carbonization process by evaporating a graphite anode and Mo wire in Ar and N₂ atmospheres with an N-doping content of 6.4 at. %. Attributing to the self-assembly mechanism, the number of Mo wires inserted into the graphite anode determined the morphologies of Mo₃C₂@NC, which were the unique lemon-like (1- and 2-Mo₃C₂@NC) and fig-like (3-, 4-, and 5-Mo₃C₂@NC) microstructures. 1- and 2-Mo₃C₂@NC exhibited powerful reflection losses (RLs) of -45.60, -45.59, and -47.11 dB at the S, C and X bands, respectively, which corresponded to thinner thicknesses. 3-, 4-, and 5-Mo₃C₂@NC showed outstanding absorption performance at the C, X, and Ku bands, respectively, with each value of a minimum RL less than -43.00 dB. In particular, the strongest RL (-43.56 dB) for 5-Mo₃C₂@NC corresponded to an ultrathin thickness of 1.3 mm. In addition, the maximum effective absorption bandwidth was 6.3 GHz for 4-Mo₃C₂@NC. After analysis, all Mo₃C₂@NC samples showed well-matched impedance due to the enhanced dielectric loss caused by the unique carbon structure and moderate magnetic loss derived from the weak magnetic property of Mo₃C₂. More importantly, the unique lemon-like and fig-like microstructures created sufficient interfaces and differentiated multiple reflection paths, which greatly contributed to the strong microwave absorptions at full wavebands. In full consideration of the simple preparation method and tunable absorption properties, Mo₃C₂@NC composites can be regarded as excellent electromagnetic wave absorption materials.

Architecture Design and Interface Engineering of Self-assembly VS4/rGO Heterostructures for Ultrathin Absorbent

The employment of microwave absorbents is highly desirable to address the increasing threats of electromagnetic pollution. Importantly, developing ultrathin absorbent is acknowledged as a linchpin in the design of lightweight and flexible electronic devices, but there are remaining unprecedented challenges. Herein, the self-assembly VS4/rGO heterostructure is constructed to be engineered as ultrathin microwave absorbent through the strategies of architecture design and interface engineering. The microarchitecture and heterointerface of VS4/rGO heterostructure can be regulated by the generation of VS4 nanorods anchored on rGO, which can effectively modulate the impedance matching and attenuation constant. The maximum reflection loss of 2VS4/rGO40 heterostructure can reach - 43.5 dB at 14 GHz with the impedance matching and attenuation constant approaching 0.98 and 187, respectively. The effective absorption bandwidth of 4.8 GHz can be achieved with an ultrathin thickness of 1.4 mm. The far-reaching comprehension of the heterointerface on microwave absorption performance is explicitly unveiled by experimental results and theoretical calculations. Microarchitecture and heterointerface synergistically inspire multi-dimensional advantages to enhance dipole polarization, interfacial polarization, and multiple reflections and scatterings of microwaves. Overall, the strategies of architecture design and interface engineering pave the way for achieving ultrathin and enhanced microwave absorption materials.

Multifunctional Integrated Transparent Film for Efficient Electromagnetic Protection

Silver nanowire (Ag NW) has been considered as the promising building block for the fabrication of transparent electromagnetic interference (EMI) shielding films. However, the practical application of Ag NW-based EMI shielding films has been restricted due to the unsatisfactory stability of Ag NW. Herein, we proposed a reduced graphene oxide (rGO) decorated Ag NW film, which realizes a seamless integration of optical transparency, highly efficient EMI shielding, reliable durability and stability. The Ag NW constructs a highly transparent and conductive network, and the rGO provides additional conductive path, showing a superior EMI shielding effectiveness (SE) of 33.62 dB at transmittance of 81.9%. In addition, the top rGO layer enables the hybrid film with reliable durability and chemical stability, which can maintain 96% and 90% EMI SE after 1000 times bending cycles at radius of 2 mm and exposure in air for 80 days. Furthermore, the rGO/Ag NW films also possess fast thermal response and heating stability, making them highly applicable in wearable devices. The synergy of Ag NW and rGO grants the hybrid EMI shielding film multiple desired functions and meanwhile overcomes the shortcomings of Ag NW. This work provides a reference for preparing multifunctional integrated transparent EMI shielding film.

Synergetic Dielectric and Magnetic Losses of a Core-Shell Co/MnO/C Nanocomplex toward Highly Efficient Microwave Absorption

High-performance microwave-absorbing materials (MAMs) derived from metal-organic frameworks (MOFs) have attracted considerable attention due to their tunable chemical composition and microstructure. In this contribution, a core-shell-structured Co/MnO/C nanocomplex was prepared using a CoMn-MIL MOF by a facile hydrothermal synthesis and subsequent pyrolysis process. The optimal microwave absorption (MA) property of the as-prepared Co/MnO/C nanocomplex was achieved by the regulation of the Co²⁺/Mn²⁺ molar ratio. The minimum reflection loss (RL_min) of the Co/MnO/C-31 nanocomplex was low to -55.0 dB at 16.2 GHz with a thickness of 1.49 mm, and the effective absorption bandwidth (EAB) was high to 5.95 GHz (12.05-18 GHz) at a thickness of 1.8 mm. The mixed-metal nanocomplex with the core-shell structure exhibited outstanding MA performance, corresponding to the synergetic effect of the magnetic and dielectric loss. It provides a high efficiency strategy for rendering low reflection loss and broad EAB to high-performance MAMs.

Bimetallic ZIF-derived conductive network of Co–Zn@NPC@MWCNT nanocomposites for efficient electromagnetic wave absorption in the whole X-band

Bimetallic ZIFs-derived Co-Zn@NPC@MWCNTs nanocomposites are successfully fabricated, which possess double absorption peaks of −76.18 dB and −33.09 dB with a thickness of 3.187 mm. The composites exhibit a bandwidth of 6.56 GHz with 3.0 mm thickness.

The excellent electromagnetic wave absorbing properties of carbon fiber composites: effect of metal content

In this work, the effect of metal loading on electromagnetic (EM) absorbing performance was investigated to obtain an excellent EM absorber through a simple process. Specifically, iron/cobalt/carbon nanocomposite fibers were...

One-dimensional MOFs-derived magnetic composites for efficient microwave absorption at ultralow thickness through controllable hydrogen reduction

Magnetic materials with ingeniously designed structure may be utilized as highly efficient microwave absorbing materials (MAMS) working at ultralow matching thickness. However, it remains a challenge to decrease the matching...

Nickel nanoparticles decorated in N-doped carbon nanofibers for lightweight and high-efficiency microwave absorption

Microwave absorbers with lightweight and excellent microwave absorption performance are urgently needed in microwave absorption field, which is still a challenge. Herein, N-doped carbon nanofibers decorated with nickel nanoparticles (Ni@CNFs)...

Material-structure integrated design for ultra-broadband all-dielectric metamaterial absorber

Material and structure are the essential elements of all-dielectric metamaterials. Structure design for specific dielectric materials has been studied while the contribution of material and synergistic effect of material and structure have been overlooked in the past years. Herein, we propose a material-structure integrated design (MSID) methodology for all-dielectric metamaterials, increasing the degree of freedom in the metamaterial design, to comprehensively optimize microwave absorption performance and further investigate the contribution of material and structure to absorption. A dielectric metamaterial absorber with an ultra-broadband absorption from 5.3 to 18.0 GHz is realized. Theoretical calculation and numerical simulation demonstrate that the symphony of material and structure excites multiple resonance modes encompassing quarter-wavelength interference cancellation, spoof surface plasmon polariton mode, dielectric resonance mode and grating mode, which is essential to afford the desirable absorption performance. This work highlights the superiority of coupling of material and structure and provides an effective design and optimization strategy for all-dielectric metamaterial absorbers.