Microwave Attenuation Research Articles

1D-3D biological template loaded NiCo nanowires at high temperatures as a broadband, lightweight electromagnetic wave absorbing material

To meet the requirements of electromagnetic radiation control, especially broadband and high temperature resistance, electromagnetic wave absorbing materials (EWAMs) have been intensively studied. In this work, NiCo NWs were synthesized by a one-step hydrothermal method. The composite has a one-dimensional(1D) NiCo NWs core-shell structure on a three-dimensional(3D) diatomite(De) surface and subsequently calcined at different temperatures. The samples calcined at 400 °C showed excellent EWA performance with a minimum reflection loss(RLmin) of −82 dB at a matched thickness of 7.1 mm and a maximum effective absorption bandwidth(EAB) of 9.53 GHz at a thickness of 8 mm. By adjusting the thickness, full coverage of X-band and Ku-band can be achieved. The conduction loss of the 1D material and the impedance matching of the bionic substrate De are considered to jointly contribute to the microwave attenuation capability. This combination of using bionic materials and 1D transition metal oxides provide a viable strategy for addressing electromagnetic pollution.

Morphology and Microwave-Absorbing Performances of Rubber Blends with Multi-Walled Carbon Nanotubes and Molybdenum Disulfide.

This study details microwave-absorbing materials made of natural rubber/nitrile butadiene rubber (NR/NBR) blends with multi-walled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS2). The mechanical blending method and the influences of fabrication on the morphology and microwave-absorbing performance of resulting compounds were logically investigated. It was found that interfacial differences between the fillers and matrix promote the formation of MWCNTs and MoS2 networks in NR/NBR blends, thus improving microwave-absorbing performance. Compared with direct compounding, masterbatch-based two-step blending is more conducive to forming interpenetrating networks of MWCNTs/MoS2, endowing the resulting composite with better microwave attenuation capacity. Composites with MWCNTs in NR and MoS2 in NBR demonstrate the best microwave-absorbing performance, with a minimum reflection loss of -44.54 dB and an effective absorption bandwidth of 3.60 GHz. Exploring the relationship between morphology and electromagnetic loss behavior denotes that such improvement results from the selective distribution of dual fillers, inducing networking and multi-component-derived interfacial polarization enhancement.

Absorption dominant electromagnetic interference shielding in the novel polypyrrole-CaCu3Ti4O12-CoFe2O4 nanocomposites

Polypyrrole-CaCu3Ti4O12-CoFe2O4 (PPy-CCTO-CFO) nanocomposites have been synthesized by in-situ chemical oxidative polymerization. Nanocomposites consisting of pyrrole monomer: CCTO: CFO by weight as 1:0.5:0, 1:0.5:0.1, 1:0.5:0.3 is nominated as PC5F0, PC5F1 and PC5F3 nanocomposites respectively. IR and XRD studies confirmed the incorporation of CCTO and CFO in polypyrrole matrix. Surface morphology exhibits the cup like structure resulting from the interfacial interaction. The PC5F3 nanocomposite shows absorption dominant total shielding effectiveness ∼30 dB (corresponds to 99% attenuation of microwave) which consists shielding effectiveness by absorption SEÃ 22 dB along with least reflection ∼ 8 dB. The absorption efficiency for PC5F3 nanocomposite is ∼99%. The enhanced absorption efficiency and shielding effectiveness of PC5F3 nanocomposite is attributed to the synergistic role of dielectric and magnetic losses, losses due to free charges in interfacial layer, interfacial polarization and wedge effect.

Flexible and leakage-proof phase change composite for microwave attenuation and thermal management

Miniaturization of high-speed electronics requires multi-functional materials to address electromagnetic interference (EMI) and overheating issues at one time. Phase change material (PCM) could be an ideal solution for thermal management via thermal energy storage to avoid bulky heat sink. Herein, we propose a flexible PCM composite sheets SPP, consisting of the single wall carbon nanotube (SWCNT) and the phase change material-polyethylene glycol (PEG) in a Polydimethylsiloxane (PDMS) matrix. Due to the double-percolation microstructure constructed by SWCNT and PEG, the SPP could exhibit over −20 dB microwave attenuation with great tunability of working frequency throughout the entire 2–18 GHz at a fixed SWCNT filling ratio of only 0.2 vol%. Meanwhile, 70 vol% of PEG can be loaded without compromising the mechanical robustness and great anti-leakage performance, resulting in a latent heat storage density of over 110 J/g. With such superior capability of thermal energy storage, it's demonstrated that the SPP composite sheets could act as cooling patches for electronic components to reduce the working temperature and also stabilize the temperature fluctuations. Based on the above, it is believed that the SPP could shed light on materials solutions of electromagnetic compatibility and thermal mitigation for next-generation ultra-compact electronic systems in a wide frequency range.

Facile synthesis of Fe3O4 nanoparticles/reduced graphene oxide sandwich composites for highly efficient microwave absorption

Component regulation and microstructure design are two effective strategies to adjust electromagnetic parameters and improve the microwave absorption performance of materials. In this study, a facile synthesis strategy consisting of ultrasonic dispersion, blast drying, and roasting is proposed to build a sandwich-like graphene-based absorbent, in which Fe3O4 nanoparticles with adjustable content are sandwiched uniformly between reduced graphene oxide nanosheets. The sandwich structure can form multiple interfaces, prevent the aggregation of nanoparticles, facilitate interface polarization, and endow the material with multiple electromagnetic loss mechanisms, which is very beneficial for impedance matching and microwave attenuation. Notably, the effective absorption bandwidth achieves 5.7 GHz, and the minimum reflection loss value is −49.9 dB. In addition, the synthesis process is simple and suitable for large-scale production and possible industrial applications. Thus, this facile route to fabricate sandwich-like graphene-based absorbents provides new ideas and approaches for designing new graphene-based nanocomposites.

Heterodimensional structure porous nanofibers embedded confining magnetic nanocrystals for electromagnetic functional material and device

The development of electronic devices and communication technology has put forward higher requirements for electromagnetic (EM) materials, and the exploration of multifunctional EM materials has become a new trend. Herein, heterodimensional structured porous nanofibers are constructed by zero-dimensional Fe nanocrystals and one-dimensional carbon nanofibers, which show excellent microwave absorption and electromagnetic interference (EMI) shielding performance. The balance between impedance matching and EM energy attenuation ability can be tailored through the tunable conductive network. The maximum reflection loss (RL) value of −56.8 dB can be achieved at a lower loading ratio, and the efficient EMI shielding effectiveness of 29.3 dB can be obtained at a higher loading ratio. In addition, the green EMI shielding with absorption as the main microwave attenuation mechanism can be observed in the higher frequency range. An EM energy conversion device is designed to effectively recover wasted EM energy. The EM energy is converted into valuable electrical energy through multiple loss mechanisms caused by heterodimensional structures. This work provides new guidance for the realization of multifunctional EM materials and devices.

Water-Borne Carbonaceous Coatings on Conducting Polymer-Modified Cotton Fabrics To Attenuate Electromagnetic Radiation

Textile-based shielding materials are gaining much importance for electromagnetic interference (EMI) shielding because of their increased flexibility compared to most existing materials. The multilayer-like architectures realized by coating textiles can be used strategically to enhance the attenuation of microwaves. Herein, we report a water-borne conductive coating capable of shielding both EM and UV radiation with good thermal stability for potential applications as smart textiles. This work tries to understand the effect of different textile pre-treatments to maximize the enhancements in properties. Cotton fabrics were initially subjected to in situ polymerization of aniline and pyrrole and subsequently coated with a carbonaceous layer containing graphene nanoplatelets and carbon nanofibers on both the sides. It was seen that both the conducting polymer layer and the carbonaceous coating work in tandem to enhance the thermal stability, UV blocking, and EMI shielding. The coated fabrics shows a shielding effectiveness of −22 dB at a thickness of 1.2 mm over a wide frequency range of 2.6–26.5 GHz, a limiting oxygen index of 26%, and remarkable UV-blocking properties with a blocking of 99.99%. Both the coating and the pre-treatment do not alter the fabric’s wettability─the surface remains hydrophilic. The coating rendered the fabric with conductivity values showing a four-order jump from the control sample. The samples show a shielding effectiveness of −22 dB, accounting for more than 99% of the incident radiation being attenuated. The attenuation happens via an absorption-dominated mechanism. The coated textile exhibits excellent heat dissipation properties, with temperatures dropping from as high as 147 to 41 °C in just 60 s.

Carbon fabric composites with NiCo compounds: Structure evolution and EMI shielding performance

NiCo layered double hydroxide (LDH) nanowire arrays (NWAs) were grown on carbon fabric (CF) via hydrothermal processes, then annealed into NiCo2O4 NWAs at 350 °C and finally melted into NiCo2 particles at 800 °C. The influence of such NiCo compounds on the electromagnetic interference (EMI) shielding performance of CF was investigated, and the results suggested that the LDH NWAs enhanced the microwave attenuation of CF, except for its shielding effectiveness (SE). In contrast, the NiCo2O4 NWAs with superior conductivity improved the SE of CF mainly via multiple reflections, while its shielding mechanism was essentially unchanged. Only the NiCo2 particles could basically improve the surface reflection of CF and enhance its internal absorption simultaneously. Consequently, the CF-NiCo2 composite showed a total SE of 52 dB, reflectivity of ∼0.92 and absorptivity of ∼0.08, better than 44 dB, ∼0.94 and ∼0.06 of CF, paving a new way for the fabrication of high-performance EMI shielding fabrics.

Constructing broadband microwave metastructure absorber based on 2D Ti3CNTx MXene magnetic composites

Microwave absorbing materials (MAMs) have been used to address electromagnetic pollution for both civil and military applications, and MAMs with broadband microwave absorption still remain a challenge. The microwave absorption performance of Ti3CNTx MXene is poor due to impedance mismatch. Modification of Ti3CNTx with magnetic materials is an effective way to improve the impedance matching and increase the effective absorption bandwidth (EAB). Here, 2D Ti3CNTx based magnetic composites were successfully prepared by an electrostatic self-assembly method. The microwave absorption properties of the composites were investigated by varying the loading of Ti3CNTx in the composites and the filling ratio of the composites in the absorber. The EAB can reach 4.75 GHz with an absorber thickness of only 1.32 mm. Integrated with a macroscale multilayer periodic gradient design, the FCM (Fe@NC/Ti3CNTx) composites based metastructure exhibits broadband microwave absorption with an EAB of 12.5 GHz ranging from 5.5 GHz to 18 GHz at a total thickness of 4.5 mm. The microwave attenuation mechanisms were studied by dielectric loss, magnetic loss and impedance matching. The multi-scale development of MXene-based magnetic composites makes them possible to applied to broadband microwave absorption.

Heterogeneous stacking strategy towards carbon aerogel for thermal management and electromagnetic interference shielding

Faced with the increasing heat dissipation and electromagnetic interference (EMI) shielding problems in electronics, carbon modified polymer-based composites with significant EMI shielding and thermal management performance are of particular interest. Herein, we proposed a carbon heterogeneous stacking strategy to construct the all carbon aerogels for the modification of epoxy resin. A hybrid 3D structure of reduced graphene oxide–carbon nanotube-vertical edge-rich graphene (rGO-CNT-VG) with covalent bonding are achieved all by chemical vapor deposition, in which the pore space of skeleton is creatively modified. Due to the elaborate design and control of microstructures, the obtained hierarchical 3D rGO-CNT-VG skeleton have plenty of seamlessly bonded heterogeneous interfaces between different components, which can create additional charge polarization, interfacial polarization and dielectric relaxation to promote significantly electromagnetic microwave attenuation and conversion and achieve ideal EMI shielding performance. Impressively, the rGO-CNT-VG/epoxy composites possess excellent thermal conductivity of 2.46 W m−1 K−1 and EMI shielding effectiveness of 56.65 dB, which are 5.1 times and 1.9 times higher than those of the rGO/epoxy composites, respectively. More importantly, the strategy of designing all carbon heterogeneous stacking skeleton in this study provides a guidance for synergistic controlling of multifunctional performance of composites.

Constructing multi-effect synergistic rare-earth doped CoFe2O4/CoFe composites for improved microwave absorption performance

It is an appealing strategy to improving the low reflection loss and narrow microwave absorption band of cobalt ferrite-derived composites by optimizing the various components of the material and building microstructures with complementary properties. In this study, rare-earth doped CoFe2O4/CoFe composites (LCF-2, NCF-2, ECF-2) were synthesized via the sol-gel self-combustion and reduction process, a two-step route. The results show that the effects on the cation vacancies and charge distribution of CoFe2O4 showed differences attributed to the doping of La, Nd, and Eu. While the CoFe introduced by reduction increases the oxygen vacancies and grows on the material surface to form a non-uniform, strongly coupled CoFe2O4–CoFe heterointerface. Benefiting from the multi-effect synergy of rare earth and CoFe on cobalt ferrite, the electromagnetic properties and microwave attenuation of the composites were significantly enhanced. And the potential microwave dissipation mechanism was also explicated. Notably, LCF-2 exhibited superior microwave absorption performance with a minimum reflection loss of −65.2 dB and an effective absorption bandwidth of 5.1 GHz at a thin thickness of 1.6 mm. Our works will provide some reference for the design of efficient and broadband microwave absorbing composites in the future.

Sequential Architecture Induced Strange Dielectric‐Magnetic Behaviors in Ferromagnetic Microwave Absorber

AbstractThe high filler loading (FL) is a bottleneck in developing lightweight ferromagnetic microwave absorbers (MAs) for the actual applications. Sequential architecture design of MAs can induce strange physical behaviors due to the unique coupling‐enhancement effect between functional units, providing a vast potential for achieving high microwave absorption performance. However, the FLs of current sequential MAs fail to be designed on demand because the strange dielectric‐magnetic behaviors cannot be fulfilled. The influence of sequential architecture engineering on the macroscopic properties or microscopic loss mechanism still needs more exploration. Herein, based on four mesoscopic models (particles, chains, bundles, and fibers) of ferromagnetic functional units, a series of ferromagnetic MAs with different sequential architectures are prepared via a bottom‐up self‐assembly method. The fibrous samples exhibit the best microwave absorption performance (−51.3 dB, 4.12 GHz) at a breakthrough FL of 2 wt%, which is one order of magnitude less than other ferromagnetic MAs. Strange dielectric‐magnetic behaviors, including negative permittivity and heterodromous chiral vortex, occur due to functional units with lateral and fibrous configurations. Further, four special models are established to reveal the microwave attenuation evolutionary mechanism. This study clarifies the relationship between sequential architecture and strange dielectric‐magnetic behaviors, which provides new sight to understand microscopic electromagnetic loss mechanism.

Fabrication of macroporous magnetic carbon fibers via the cooperative etching-electrospinning technology toward ultra-light microwave absorption

Lightweight characteristics and high-efficiency absorption performance are two essential factors for microwave absorbents in practical applications, but still face considerable conflicts. Herein, we propose the cooperation of etching and electrospinning technology to construct macroporous magnetic carbon fibers (MMCFs) that simultaneously tackle the conflicts associated with lightweight characteristics and superior absorption performance. Specifically, ZIF-67 nanocubes are firstly etched into hollow structure and efficiently embedded into PAN fibers by electrospinning, the obtained fibers are transformed into MMCFs via the subsequent pyrolysis, in which inner hollow ZIF-67 nanocubes are converted into macroporous magnetic nanocubes and PAN fibers are carbonized into carbon fibers. Benefiting from the cooperative advantages of hollow macroporous cavity, conductive networks and dielectric-magnetic synergistic effect, the fabricated MMCFs exhibit superior microwave attenuation compared with most reported metal-organic-frameworks derivatives at an ultralow filler loading of 5 wt%. The maximum absorption intensity promises a high value of −49.4 dB and the effective bandwidth achieves 10.8 GHz. This work overcomes the vital limitation associated with lower filler loading of MOFs derived absorbents, and inspires us a new prospect to develop ultra-light absorbents in satisfying the electromagnetic protection demand.

3D lamellar skeletal network of porous carbon derived from hull of water chestnut with excellent microwave absorption properties

Biomass derived carbon has attracted extensive attention in the field of microwave absorption because of its sustainability and porous structure beneficial to microwave attenuation. In this study, 3D lamellar skeletal network porous carbon was successfully obtained from hull of water chestnut using biomass waste as raw material by controlling the ratio of KOH and precursors in a one-step carbonization process. The optimization of biomass carbon morphology was achieved and its microwave absorption properties were investigated. At the temperature of 600 °C, when the ratio of hull of water chestnut to KOH is 1:1, the porous carbon material with filling ratio of 35% can reach the effective absorption bandwidth (RL < −10 dB) of 6.0 GHz (12–18 GHz) at the matching thickness of 1.90 mm, covering the whole Ku band. When the thickness is 2.97 mm, the optimal reflection loss reaches −60.76 dB. The surface defects, interface polarization and dipole polarization of 3D porous skeleton network structure derived from hull of water chestnut contribute to the excellent reflection loss and bandwidth of porous carbon materials. The porous carbon with low density, low cost and simple preparation method has broad application prospects in the preparation of biomass-derived microwave absorbers.

Extended effective absorption bandwidth of Sendust/phosphate flaky particles by TiO2 insulation coating

How to obtain a wide effective absorption bandwidth is still a challenge for Sendust micro-powder as microwave absorber at 2–10 GHz range. Double shell-core structured composites are desirable to extend effective absorption bandwidth through optimizing impedance match degree in wider frequency and forming a broad dielectric loss peak. In this work, TiO2 layer is fabricated on surface of flaky Sendust/phosphate composites through the hydrolysis reaction for constructing double shell-core structured TiO2@phosphate@Sendust flaky composites. The synergistic effect of TiO2-phosphate interface and phosphate-Sendust interface induces a broad peak for dielectric loss, microwave absorption ratio and attenuation constant, resulting in wider effective absorption bandwidth of 3.2 GHz compared with that (2.4 GHz) of raw Sendust/phosphate composites. This work offers a facile and effective strategy for extending effective absorption bandwidth of micron-scale microwave absorber.

Construction of Co3O4 porous rod/graphene heterostructures toward strong and broadband microwave absorption applications

Microwave absorbing materials (MAMs) are of paramount importance to address electromagnetic radiation pollution concerns. However, the development of MAMs with strong absorption, broadband and good impedance matching features still faces challenges. Herein, a compositional and structural engineering strategy is proposed to tailor the polarization and multiple reflection and scattering characteristics, and the Co3O4 porous rod/graphene (Co3O4 PR/G) heterostructures are constructed. The porous rod structure of Co3O4 and plentiful heterointerfaces between Co3O4 and graphene generate massive microwave attenuation paths and promote the interfacial polarization, resulting in improved microwave attenuation. The Co3O4 PR/G heterostructures exhibit the minimum reflection loss of −49.1 dB and effective absorption bandwidth of 9.3 GHz, overpowering many similar reported microwave absorbers. This work is a new attempt for the development of advanced MAMs with strong absorption and broad bandwidth characteristics, which provides an effective compositional-structural regulating strategy to promote microwave absorption.

Morphology engineering of defective graphene for microwave absorption

Graphene with abundant defects has been considered as the most lightweight electromagnetic functional materials. Although important, the dominant electromagnetic response of defective graphene with diverse morphologies is rarely the focus of existing research. Herein, the defective graphene with two-dimensional planar structure (2D-ps) and three-dimensional continuous network (3D-cn) morphologies were dexterously designed with 2D mixing and 3D filled systems of polymeric matrix. A comparison between the topologies of defective graphene-based nanofillers and the microwave attenuation behaviors was examined. Defective graphene with 3D-cn morphology can achieve ultralow filling content and broadband absorption, which is attributed to the presence of numerous pore structures that promote impedance matching, induce continuous conduction loss and provide multiple reflection and scattering sites for electromagnetic wave attenuation. Comparatively, by virtue of the increased filling content of 2D-ps, the dielectric losses primarily originate from the dielectric genes, including aggregation-induced-charge transport, abundant defect and dipole polarization, resulting in good microwave absorption at low thickness and low frequency. Therefore, this work provides a pioneering insight into morphology engineering of defective graphene microwave absorbers, and it will guide future exploration of customizing high-performance microwave absorption materials based on graphene-based low-dimensional building blocks.

Integrating large specific surface area and tunable magnetic loss in Fe@C composites for lightweight and high-efficiency electromagnetic wave absorption

Porous Carbon-based composites with large specific surface area are promising as lightweight electromagnetic wave (EMW) absorbers due to their inherently rich interfaces that facilitate microwave attenuation. However, the exertion of the intrinsic advantage of large surface area was underexplored. Herein, we described a facile strategy using MOF-derived large surface area porous carbon to construct dielectric-magnetic composites for high-efficiency EMW absorbers. In particular, a series of Fe@C composites were fabricated by pyrolysis of MOF-5 to form porous carbon matrix (SBET ∼ 1800 m2/g), followed by ferrocene deposition and reduction. By altering Fe species amount, surface area and electromagnetic parameters of the composites were tuned. It is found Fe@C-0.6 composites with sufficiently high SBET ∼915.8 m2/g exhibited outstanding microwave absorption performance with the minimum reflection loss (RLmin) of −64.6 dB (1.98 mm thickness and 15 wt% loading) and the effective absorption bandwidth (EAB) up to 6.27 GHz (2.2 mm thickness). Besides, Fe@C-1 (SBET ∼820.1 m2/g) also achieved desirable loss capability, with EAB covering the whole Ku band. This work demonstrates the potential of high surface area to achieve optimal EMW attenuation, and may provide a facile alternative to develop more high-performance carbon composites for EMW absorption application.

Thermally tailoring magnetic molecular sponges through self-propagating combustion to tune magnetic-dielectric synergy toward high-efficiency microwave absorption and attenuation

Thermally tailoring magnetic molecular sponges through self-propagating combustion to tune magnetic-dielectric synergy toward high-efficiency microwave absorption and attenuation

High-Entropy Enhanced Microwave Attenuation in Titanate Perovskites.

High-entropy oxides (HEOs), which incorporate multiple-principal cations into single-phase crystals and interact with diverse metal ions, extend the border for available compositions and unprecedented properties. Herein, a high-entropy-stabilized (Ca0.2 Sr0.2 Ba0.2 La0.2 Pb0.2 )TiO3 perovskite is reported, and the effective absorption bandwidth (90% absorption) improves almost two times than that of BaTiO3 . The results demonstrate that the regulation of entropy configuration can yield significant grain boundaries, oxygen defects, and an ultradense distorted lattice. These characteristics give rise to strong interfacial and defect-induced polarizations, thus synergistically contributing to the dielectric attenuation performance. Moreover, the large strains derived from the strong lattice distortions in the high-entropy perovskite offer varied transport for electron carriers. The high-entropy-enhanced positive/negative charges accumulation around grain boundaries and strain-concentrated location, quantitatively validated by electron holography, results in unusual dielectric polarization loss. This study opens up an effective avenue for designing strong microwave absorption materials to satisfy the increasingly demanding requirements of advanced and integrated electronics. This work also offers a paradigm for improving other interesting properties for HEOs through entropy engineering.