Bandwidth Reflection Loss Research Articles

Reduced Graphene Oxide Modified Nitrogen-Doped Chitosan Carbon Fiber with Excellent Electromagnetic Wave Absorbing Performance.

Lightweight and low-cost one-dimensional carbon materials, especially biomass carbon fibers with multiple porous structures, have received wide attention in the field of electromagnetic wave absorption. In this paper, graphene-coated N-doped porous carbon nanofibers (PCNF) with excellent wave absorption properties were successfully synthesized via electrostatic spinning, electrostatic self-assembly, and high-temperature carbonization. The obtained results showed that the minimum reflection loss of the absorbing carbon fiber obtained under the carbonization condition of 800 °C is -51.047 dB, and the absorption bandwidth of reflection loss below -20 dB is 10.16 GHz. This work shows that carbonization temperature and filler content have a certain effect on the wave-absorbing properties of fiber, graphene with nanofiber, and the design and preparation of high-performance absorbing materials by combining the characteristics of graphene and nanofibers and multi-component coupling to provide new ideas for the research of absorbing materials.

Synthesis of core-shell NiO/BFO nanocomposites for microwave absorbing applications

Magnetic core-shell nanostructures are often employed in high-performance microwave-absorbing applications due to their strong concurrent magnetic-dielectric losses. However, microwave absorbers designed using a single core-shell nanostructure may not attain the desired bandwidth of absorption. Herein, we introduce core-shell nanocomposites of (100-x)NiO/(x)BiFeO3 (x = 0, 25, 50, 75, & 100), prepared by a facile two-step sol-gel wet-chemical method for high-efficiency absorbing applications. Measurements of microwave absorption performance show that the core-shell 50NiO/50BiFeO3 (x = 50) nanocomposite exhibits a remarkable reflection loss of up to −27.3 dB at a matching thickness of 1.9 mm, and the corresponding −10 dB reflection loss bandwidth extends to 6.8 GHz (in X- and Ku-bands). The study suggests that the fabricated core-shell nanocomposite has the potential to be a promising candidate for lightweight microwave absorbing applications. This is evidenced by its showcased improved efficiency, attributed to the synergistic effects of magnetic-dielectric losses, multiple internal reflections, superior impedance matching, and enhanced interfacial polarization at NiO/BiFeO3 interfaces.

Optimization of multicomponent microwave absorbents for improved electromagnetic wave absorption of layered foamed cementitious materials

The integrated design of materials and structures is essential for achieving superior electromagnetic wave absorption performance (EWAP) in cementitious materials. In this study, multicomponent microwave absorbents are designed to improve the EWAP of foamed cementitious materials. The effects of the type, content, and single/compound doping of the absorbents and material density on the EWAP of multilayer foamed cementitious materials are tested. The experimental results show that the multilayer structure can enhance the impedance-matching characteristics between cementitious materials and air. It also conduces more electromagnetic waves to penetrate deeper into the cementitious materials to be absorbed. The electromagnetic dissipation of cementitious materials can be significantly improved by combining the effects of interlayer reflection scattering, interface polarization, and resonance. Furthermore, the multilayer structure offers flexibility in adjusting the type and content of the absorbent in each layer and endows each layer with different electromagnetic dissipation mechanisms, resulting in a significantly improved EWAP. For four layers of foamed cementitious materials, the EWAP is optimized using three different iron ores (WMHL-135: 10 wt% magnetite, 30 wt% hematite, and 50 wt% limonite) in the absorbing layers. It achieves the optimum EWAP with a full-band effective absorption bandwidth of reflection loss (RL) < -10 dB, in the frequency range of 2–18 GHz, a minimum RL of −37.0 dB, and an average RL of –23.4 dB.

Expanded graphite and thermally reduced graphene oxide filled with NiCo2O4 for improve microwave absorption

Three-dimensional porous carbon materials provide an effective way for electromagnetic wave absorbers that are lightweight and effective. We explore the effects of different three-dimensional porous expanded graphite (EG) and thermally reduced graphene oxide (TERGO) on wave absorption performance in this study. NiCo2O4-EG and NiCo2O4-TERGO three-dimensional wave-absorbing materials were prepared by an in situ self-assembly hydrothermal process. To address the problem of impedance mismatch and improve the attenuation capability, the microstructure of EG and TERGO were designed to control the conductivity loss and polarization loss. After heat treatment at 800 °C to form a regular honeycomb pore distribution, TERGO composites have moderate conductivity and conductive losses, as well as multiple polarization loss mechanisms. Consequently, the NiCo2O4-TERGO800 composite with a lower filling ratio displayed excellent microwave absorption, with the bandwidth of reflection loss ≤−10 dB coved 4.05 GHz. These findings provide valuable insights for fabrication and research of three-dimensional porous carbon material microwave absorbers.

An MXene coating with electromagnetic wave absorbing performance

The increasing demand for electromagnetic wave absorbing (EMWA) coatings and the intensification of electromagnetic pollution has spurred research into high-performance flexible microwave absorbing (MA) materials. The magnetic-MXene-SiO2 (M-MXene-SiO2) was successfully synthesized to achieve improved MA performance. Based on the high dielectric loss capacity of transition metal carbides and carbonitrides (MXenes), by combining with Fe2O3, Fe3O4 and mesoporous silica nanoparticles (MSNs), the magnetic loss can be manipulated to improve impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < 10 dB). The minimum RL value of the designed composites can reach −38.14 dB. This work provides insight into the novel design of MA materials.

Microwave absorption and mechanical properties of glass fiber/polyamide 6 composites containing carbon black by microstructural design

Microwave absorbing composite laminates were prepared by a simple hot pressing process using glass fiber reinforced polyamide 6 (GF/PA6) doped with different content of carbon black (CB). The microwave absorption and mechanical properties of the composites were investigated. 8 wt% CB/GF/PA6 composite had a minimum reflection loss (RL) of −40.05 dB and the bandwidth of RL ≤ −10 dB is 4.6 GHz. The flexural strength was 207.2 ± 10.7 MPa, the shearing strength was 26.0 ± 1.1 MPa, and the impact strength was 71.2 ± 5.7 kJ/m2. Moreover, the microstructure of the composites was tailored by disc granulation method to obtain reticular microstructure composed of different particle sizes to improve the microwave absorption and mechanical properties of the composites. It was found that the RL of 7 wt% granulated CB/GF/PA6 composite was −56.45 dB. The flexural strength was 214.9 ± 4.4 MPa, the shearing strength was 21.7 ± 0.5 MPa, and the impact strength was 88.0 ± 8.5 kJ/m2. This method facilitated the integration of structure and function.

Simple preparation and microwave absorption of TERGO/ZnO porous composites

TERGO/ZnO porous composites with light weight, high porosity and good absorption properties were obtained by the method of heat treatment and hydrolysis process, which are simple to prepare and have a more uniform porous structure. After the facile thermal expansion, GO deoxidizes and rapidly expands to form a thermally expansion reduced graphene oxide (TERGO) porous structure with uniform and small pore size distribution. Subsequently, ZnO particles are uniformly dispersed in the surface or layer spacing of TERGO by hydrolysis to improve its impedance matching and interfacial polarization. Furthermore, expanded graphite (EG)/ZnO composites are prepared for comparison. The TERGO/ZnO composite shows excellent microwave absorption with a reflection loss bandwidth (≤ -10 dB) covering the X-band at 3.9 mm thickness. This research will provide guidelines for the preparation of microwave absorbers with low cost, porous, and good performance.

Tailorable microwave absorption properties of macro-porous core@shell structured SiC@Ti3SiC2 via molten salt shielded synthesis (MS3) method in air

High-performance microwave absorption and lightweight design have evolved into the foremost critical considerations in the practical application of modern microwave absorbing materials. In view of this, macro-porous core-shell structured SiC@Ti3SiC2 were prepared through a facile molten salt shielded synthesis method in air. Distinctly, the minimum reflection loss (RL) value of SiC@Ti3SiC2 could reach − 68.59 dB at 9.76 GHz with the bandwidth of RL< −10 dB of 5.6 GHz when the absorber thickness is 2.3 mm. The synergistic mechanism of the multiple scattering, conductive loss, and significant polarization effects of macro-porous (average 53 nm) core-shell structured SiC compounded with nano-layered Ti3SiC2 (∼60 nm) is reviewed for the considerable improvement of electromagnetic wave absorption properties. This work provides a practical reference for the design and synthesis of high-performance Ti3SiC2-based microwave absorbers.

Remarkable Magnetic Exchange Coupling via Constructing Bi‐Magnetic Interface for Broadband Lower‐Frequency Microwave Absorption

AbstractSevere lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe(12‐x)CoxO19@Fe3O4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe(12‐x)CoxO19 serves as the core and soft magnetic Fe3O4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RLmin) of typical BaFe11.6Co0.4O19@Fe3O4 microcomposite reaches −48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss &lt; −10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers.

Construction of Co@C nanocapsules by one-step carbon reduction of single-crystal Co3O4 nanoparticles: Ultra-wideband microwave absorber verified via coaxial and arch methods

It is highly demanding and challenging to construct the nano-scale microwave absorber with wide-frequency responding feature. Herein, a series of Co@C nanocapsules (NCs) are fabricated via one-step carbon reduction of Co3O4 nanoparticles (NPs) of only 20 nm obtained by the nitrate pyrolysis method. The electromagnetic parameters of the samples can be effectively regulated by flexibly adjusting the carbon shell thickness. Surprisingly, all samples exhibit ultra-wide microwave absorption (MA) performance investigated by the coaxial method. For the Co@C NCs with a carbon shell of 25 nm, especially, the effective absorption bandwidth (EAB) for reflection loss (RL) below −10 dB reaches a record high of 15.2 GHz (2.8–18 GHz), which completely covers the whole C-, X-, and Ku-bands. More excitingly, the absorption bandwidth for RL ≤ −20 dB is up to 7.1 GHz at only 2.0 mm thickness. Such outstanding MA properties are attributed to nano-size effect, synergistic effects of strong dielectric/magnetic loss, and superior impedance matching characteristics. Notably, the polarization and magnetic coupling behaviors are clarified with the aid of electric field and magnetic field simulations using High-Frequency Structure Simulator (HFSS). The plate coating sample is further prepared and measured by the arch method, which also displays an ultrawide MA bandwidth. This work provides a new design strategy toward the facile synthesis of ultra-broadband microwave absorbers.

Ultralight Coral-like hierarchical Fe/CNTs/Porous carbon composite derived from biomass with tunable microwave absorption performance

In order to widen the application field of microwave absorption (MA) materials, it is still challenging to obtain high-performance MA materials with wide frequency bandwidth, lightweight, thin thickness, and strong absorption by an economical and sustainable method. Herein, the novel coral-like hierarchical structure with zero-dimensional Fe nanocrystals, one-dimensional N-doped carbon nanotubes (CNTs) and three-dimensional porous carbon (PC) matrix is rationally constructed to enhance MA performance. Based on renewable biomass residues, the composite consisted of PC as matrix, bamboo-shaped CNTs with magnetic nanoparticles at the top grow on the surface of PC. By controlling the growth conditions of carbon nanotube, the microstructure and dielectric loss capacity of composite can be manipulated to optimize the impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < -10 dB). Benefitting from the unique architecture and hierarchical composite, the composite exhibited a minimum RL of −70 dB at thin thickness of 1.9 mm under low filler content of 12.5 wt%. Even with the thickness of 1.5 mm, the RL could reach −51.8 dB with a broadcast EBA of 5.0 GHz. This work provides an insight for designing advanced microwave absorbers with lightweight, thin thickness, strong RL, and wide EAB.

Multiple reflection and scattering effects of the lotus seedpod-based activated carbon decorated with Co3O4 microwave absorbent

The lotus seedpod-based activated carbon (LSAC) is derived from pyrolysis of lotus seedpod as biomass carbon precursor, and Co3O4 is then deposited to LSAC by oxidation-precipitation and crystallization process of Co ions from Co(NO3)2 solution. The Co3O4 particles uniformly decorate on the surface and/or the inner channels of LSAC. The optimal reflection loss (RL) value of LSAC/Co3O4-paraffin wax (PW) composite reaches −39.8 dB, and the bandwidth for RL below −10 dB and −20 dB are 10.3 and 3.0 GHz, respectively, much better than that of LSAC-PW composite for the higher magnetic loss. The addition of Co3O4 particles in LSAC-PW composite significantly enhance the RL values in various thicknesses. The channels of the LSAC and decorated Co3O4 can improve the abilities of multiple scattering, dipole polarization, interface polarization and magnetic loss. This composite provides a promising method to construct high performance absorbers by using biomass carbon to tune the dielectric properties of the ferromagnetic materials.

Metal-organic framework-derived NiSe2-CoSe2@C/Ti3C2Tx composites as electromagnetic wave absorbers

• A novel accordion-like structure was synthesized by ZIF-67 derivation strategy. • Their morphological evolution in various stages is clarified. • Revealing the contribution of dielectric property modulation to absorption performance. • The EAB reached 5.68 GHz at a thickness of 2.6 mm for NiSe 2 -CoSe 2 @C/Ti 3 C 2 T x composite. Two-dimensional metal carbide or nitride materials are considered as a new class of electromagnetic wave absorbing materials due to their unique multilayer structure and metal-like properties. The NiSe 2 -CoSe 2 @C/Ti 3 C 2 T x composites were prepared through a facile hydrothermal treatment and selenization reaction. Distinctly, the maximum reflection loss ( RL ) is −60.46 dB with the mass fraction of NiSe 2 -CoSe 2 @C/Ti 3 C 2 T x of 40 wt% at 2.6 mm. The bandwidth of RL < −10 dB reaches up to 5.68 GHz (10.32–16 GHz). The synergistic mechanism of the multiple scattering and multi-interface polarization effects of NiSe 2 -CoSe 2 @C compounded with Ti 3 C 2 T x is reviewed to interpret the significant improvement of electromagnetic wave absorption performance. The results indicate that NiSe 2 -CoSe 2 @C/Ti 3 C 2 T x composites have potential applications as realistic electromagnetic wave absorbing materials.

Efficient microwave absorber and supercapacitors derived from puffed-rice-based biomass carbon: Effects of activating temperature

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest ID/IG value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < −10 dB of the R-800 sample reach −72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < −20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g−1, the specific capacitance of the R-800 sample reaches 117.2 F g−1 and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg−1, power density of 5739.43 W kg−1, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials.

Improved impedance matching by multi-componential metal-hybridized rGO toward high performance of microwave absorption

Abstract Microwave-absorbing materials with good microwave absorption performance are of great interest for military applications and human health, which is threatened by electromagnetic radiation pollution. Herein, the design and synthesis of multi-componential metal-hybridized graphene composites via freeze drying and pyrolysis of ferrocene hydrazone complex precursor are reported. Various magnetic nanoparticles are loaded on reduced graphene oxide (rGO) via controlling their pyrolysis temperature. The complex electromagnetic parameters of these hybrids are therefore regulated by the hybrid components. Among them, rGO hybridized by the sea-island-like Fe2O3/Fe3O4/FeNi3 multi-componential metals shows a good balance of dielectric and magnetic constants. Thus, the improved impedance matching with free space brings about a superior electromagnetic wave absorption performance, especially on the effective absorption bandwidth. The minimum reflection loss (RL) of the hybrids is as low as −40.3 dB at 11 GHz with the RL bandwidth of −10 dB being 4.55 GHz (from 9.25 to 13.8 GHz).

Microporous Co1−xFex@C nanoparticles: Strong wideband microwave absorbers for reflection loss less than −20 dB

For advanced microwave absorption materials, the bandwidth of reflection loss (RL) ≤ −20 dB is becoming more and more important due to their applications under some extreme occasions where most of the electromagnetic signals must be absorbed. Herein, in-situ carbon-coated Co-Fe-Al precursor nanoparticles (NPs) were prepared by hydrogen plasma metal reaction (HPMR), and then microporous Co1−xFex@C NPs with an average particle size of about 50 nm were successfully prepared by chemical dealloying. They exhibit a distinct core-shell structure with an amorphous carbon shell of approximately 3 nm and a Co1−xFex alloy core containing micropores of 1.1 nm. As the amount of Fe in the microporous Co1−xFex@C NPs increases from 2.1 wt% to 12.0 wt%, the saturation magnetization gradually enlarges from 82.6 to 92.4 emu g−1 whereas the coercive force only decreases slightly. The Co0.98Fe0.02@C sample shows the widest bandwidth (RL ≤ −10 dB) of 11.3 GHz, and surprisingly the bandwidth corresponding to the RL below −20 dB reaches 6.0 GHz, far superior to other Co-based absorbers. Meanwhile, its minimum RL (RLmin) value reaches −102.3 dB with a thickness of 1.8 mm. As the content of Fe increases to 12.0 wt%, the absorption bandwidth (RL ≤ −20 dB) of Co0.88Fe0.12@C sample decreases to 5.7 GHz while its RLmin value strengthens to −133.7 dB. Both the two samples added with Fe exhibit much wider absorption bandwidth (RL ≤ −20 dB) compared with Co@C NPs without Fe addition. The excellent absorption properties are mainly attributed to the facts that microporous morphology promotes the interfacial and dipole polarization, and Fe addition enhances the magnetic resonance. The Co1−xFex@C NPs may pave a new way for designing effective broadband absorbers for RL ≤ −20 dB to meet the high-performance requirements.

Fabrication of core-shell nanoporous carbon@chiral polyschiff base iron(II) composites for high-performance electromagnetic wave attenuationin the low-frequency

A key aspect of refining the design and manufacture of contemporary microwave absorbing materials is to improve their absorption of electromagnetic radiation at low frequency which has proved to be an immensely challenging task. This work reports a relatively uncomplicated method to design core-shell absorbers through nanoporous carbon (NPC) obtained by removing redundant Cu from the pyrolysis products of HKUST-1 (HKUST is the Hong Kong University of Science and Technology) coated with (1R,2R)-(−)-1,2-cyclohexanediamineferrocene formaldehyde polyschiff base iron (II) (CPI). Three NPC@CPI samples not only maintain good impedance matching of the pyrolysis products of HKUST-1, but also increase the attenuation abilities significantly due to the synergetic effect of multiple interfacial polarization, cross-polarization and Debye relaxation, which further leads to their outstanding microwave absorbing performance. When the mass ratio of CPI to NPC is 6.7:100 (NPC@CPI-1), the strongest reflection loss (RL) can achieve −60.8 dB at 3.7 GHz, whereas the RL bandwidth under −10 dB can become as much as 5.6 GHz at 1.65 mm. While CPI to NPC is 10:100 (NPC@CPI-2), an optimal RL of −46.9 dB at 11.7 GHz and 1.9 mm can be achieved. This work thus provides an excellent model for the design and the manufacture of thin, lightweight, broad, and strong EM absorbers based on MOFs derivatives and chiral polymers.

Achieving effective broadband microwave absorption with Fe3O4@C supraparticles

The X band (8 GHz–12 GHz) is the electromagnetic wave band emitted by most electronic instruments in our life, which will cause electromagnetic pollution harm to human health. Due to the coexistence of magnetic loss and dielectric loss, the modified Fe3O4-carbon-based nanomaterial exhibit strong electromagnetic (EM) wave absorptive capacity. However, there is a problem that the effective absorption bandwidth (EAB, the frequency bandwidth of reflection loss is less than −10 dB) of the X band is narrow. Increasing the EAB value of Fe3O4-carbon-based materials is of great significance for reducing electromagnetic pollution. Here, an emulsion-based self-assembly technique and ligand carbonization treatment have been used to construct the Fe3O4@C supraparticles for the evaluation of EM performance. The Fe3O4@C supraparticles exhibit excellent EM absorption properties, which can achieve full coverage of X band from 6.52 GHz to 12.9 GHz at a sample thickness of 3 mm. Besides, the optimum EAB value of Fe3O4@C supraparticles is up to 8.55 GHz from 9 to 18 GHz at a sample thickness of 2.5 mm. The Fe3O4@C supraparticles with superlattice structure will have potential development prospects in the application of broadband absorption.

Enhancement of microwave absorption bandwidth of MXene nanocomposites through macroscopic design.

MXene, the new family of two-dimensional materials having numerous nanoscale layers, is being considered as a novel microwave absorption material. However, MXene/functionalized MXene-loaded polymer nanocomposites exhibit narrow reflection loss (RL) bandwidth (RL less than or equal to −10 dB). In order to enhance the microwave absorption bandwidth of MXene hybrid-matrix materials, for the first time, macroscopic design approach is carried out for TiO2-Ti3C2Tx MXene and Fe3O4@TiO2-Ti3C2Tx MXene hybrids through simulation. The simulated results indicate that use of pyramidal meta structure of MXene can significantly tune the RL bandwidth. For optimized MXene hybrid-matrix materials pyramid pattern, the bandwidth enhances to 3–18 GHz. Experimental RL value well matched with the simulated RL. On the other hand, the optimized Fe3O4@TiO2-Ti3C2Tx hybrid exhibits two specific absorption bandwidths (minimum RL value - −47 dB). Compared with other two-dimensional nanocomposites such as graphene or Fe3O4-graphene, MXene hybrid-matrix materials show better microwave absorption bandwidth in macroscopic pattern.

Anisotropic shaped Fe3O4 nanoparticles: Microwave-assisted thermal decomposition synthesis and their electromagnetic properties

Investigating the electromagnetic properties of magnetite nanoparticles (Fe3O4 NPs) is beneficial for expanding their biomedical applications, especially in tumor hyperthermia. In this study, monodisperse Fe3O4 NPs of various shapes (i.e., quadrilateral-like, hexagon-like, rod-like, and triangle-like) were successfully prepared by a microwave-assisted thermal decomposition approach. The magnetic properties and inductive heating performance, as well as electromagnetic properties were analyzed systematically. The results showed that quadrilateral-like Fe3O4 NPs possessed excellent magneto-thermal effects and maximum specific absorption rate values of 226.4 W/g and 1409.6 W/g (390 kHz and 780 kHz, 12 A). Moreover, a sample filled with 70 wt. % quadrilateral-like NPs in paraffin showed a minimum reflection loss (RL) value of −33.4 dB, along with a broad absorption bandwidth of RL &amp;lt; −10 dB covering 2 GHz–18 GHz. The high magnetic loss may be derived from the eddy current loss and natural resonance. This study would deepen the understanding of microwave absorption properties of Fe3O4 NPs and enrich their microwave applications based on shape anisotropy.