Excellent Electromagnetic Research Articles

Dependency of tunable electromagnetic wave absorption performance on morphology-controlled 3D porous carbon fabricated by biomass

Using biomass as raw materials to fabricate porous carbon (PC) absorbing materials has become a hotspot. However, the effective medium to regulate the porous structure is often limited to control the heat treatment conditions including heating temperature, insulation time and heating rate. In this work, the pinecone was decided as raw materials and four different activators (KOH, NaOH, K2CO3 and ZnCl2) were chosen to investigate the effect of the type of activator on the porous structure. Meanwhile, the activation mechanisms were revealed as well. SEM results illustrate that the variety of activators has a remarkable influence on the pore size of porous. Based on Maxwell-Garnet theory, the size of the aperture will affect the impedance matching of absorber. According to the electromagnetic (EM) parameters, the porous carbon activated by KOH (KOH-PC), NaOH (NaOH-PC) and K2CO3 (K2CO3-PC) exhibited excellent impedance matching compared to other absorbers. Thus, the KOH-PC, NaOH-PC and K2CO3-PC exhibit sterling EM wave absorption performance. Particularly, the minimum reflection loss of K2CO3-PC could be up to −76.0 dB at the matching thickness of 2.1 mm and the broadest effective absorption bandwidth was 5.92 GHz covering from 11.92 to 17.84 GHz at 2.3 mm. The excellent EM wave absorption performance could ascribe to the synergistic effect of conductive loss, space charge polarization and dipolar loss. Besides, the influence of the addition amount of activators to the porous structure was also investigated. This work offers a reference for the structural control of biomass porous carbon absorber.

In situ anchoring carbon nanotubes on the Ni/C nanosheets with controllable thickness for boosting the electromagnetic waves absorption

Constructing two-dimensional materials with large specific surface area is of great significance for electromagnetic (EM) waves absorption. Herein, through adding hexamethylenetetramine (HMT) and F127, the thickness of the two-dimensional (2D) nickel metal organic frameworks (Ni-MOFs) nanosheets was altered. The composites with larger specific surface area are adjusted by pyrolysis in argon. Besides, the synergetic effect of dielectric loss and magnetic loss for the Ni/C composites modified with carbon nanotubes (Ni/C-CNTs) are favorable for the attenuation of EM wave. A maximum reflection loss (RLmax) of −71.6 dB is achieved and the effective absorption bandwidth is 4.7 GHz at thin thickness (2.2 mm) in the case of containing only 10 wt% of the samples in the matrix. The lightweight and controllable thickness of Ni/C carbon nanotubes composites with excellent EM absorption properties endow them with potential applications in the EM waves absorption.

Glycine-assisted solution combustion synthesis of NiCo2O4 electromagnetic wave absorber with wide absorption bandwidth

Design of high-performance electromagnetic (EM) wave absorbing materials has been regarded as an effective solution to excessive EM wave interference problem. As a promising candidate, NiCo2O4 absorbers have attracted enormous research attentions. However, currently reported morphology-manipulation synthetic methods of NiCo2O4 absorbers are time-consuming and require high energy consumption, which inhibit their practical applications. Herein, a more facile and cost-effective solution combustion synthesis was utilized to fabricate NiCo2O4 materials. The absorber prepared by using glycine as fuel displayed the best EM wave absorption performance. Impressively, ultra wide absorption bandwidth of 7.44 GHz from 10.56 GHz to 18 GHz could be achieved with relatively thin thickness of 2.1 mm NiCo2O4 sample fabricated in this work displayed the widest effective absorption bandwidth (EAB) among reported NiCo2O4-based EM wave absorbing materials so far. In view of its simple and low-cost synthetic process and excellent EM wave dissipation capacity, NiCo2O4 samples in this work showed great feasibility as practical absorber. In addition, our findings may also provide new sight for facile preparation of other high-performance EM wave absorbers by solution combustion synthesis instead of complex morphology-manipulation routes.

Porous high entropy alloys for electromagnetic wave absorption

Spherical high-entropy alloys (HEAs) were prepared as a template by the traditional ball milling method, and the pure porous HEAs electromagnetic (EM) wave absorbing material was successfully obtained by etching the template with nitric acid/copper nitrate solution. The crystal structure, chemical composition and distribution, EM parameters and EM wave absorbing performance were characterized in detail. The results showed that the excellent impedance matching, magnetic loss performance and good dielectric loss of porous HEAs were the key factors leading to the excellent EM wave absorbing performance. The effective absorption bandwidth of the porous HEAs samples can reach to 4.48 GHz at the thickness of 1.7 mm, and the minimum reflection loss can reach to −40.2 dB at the same time. The feature of strong absorption at the thin thickness make HEAs a possible new generation of efficient EM wave absorber. The preparation idea and method of the samples also have important reference value.

Confinedly growing and tailoring of Co3O4 clusters-WS2 nanosheets for highly efficient microwave absorption

Electromagnetic (EM) wave absorbing materials have been a research hotspot in materials science and related technical fields in recent years. Finding lightweight, efficient, and broadband electromagnetic wave absorbing materials has always been a very challenging subject. Herein, we successfully prepared Co3O4-WS2 hybrid nanosheets with heterostructures, which excellent combine the advantages of magnetic property of Co3O4 and dielectric property of WS2. By the electromagnetic synergy effect, maximum RL is up to −61.1 dB at 1.9 mm, and the bandwidth exceeds 5 GHz. Such highly efficient microwave absorption is attributed to not only the electromagnetic synergy effect, but the dipole polarization as well as conduction loss. These results show that the obtained Co3O4-WS2 is an excellent EM wave absorbing material and can be used as a candidate for advanced EM wave absorbing materials in the fields such as commerce, military and aerospace in future.

Synthesis and characterization of BiFeO3/RGO composites for promising microwave absorption materials

In this paper, BiFeO3 (BFO) and reduced graphene oxide (RGO) composites were synthesized by ultrasonic assisted hydrothermal reduction method. The structures of BFO and BFO/RGO composites were analyzed by XRD, Raman and TG methods. With the aid of SEM and TEM, we observed the slice layer structure of the composites. All the composites have excellent electromagnetic(EM) wave absorption capacity, the maximum reflection loss (RL) value of sample BFO/RGO-2 reached up to − 32.3 dB at a thickness of 2 mm, and the effective bandwidth was 4.1 GHz (< − 10 dB). The 3 mm wave attenuation performance of sample BFO/RGO-3 was up to 10.3 dB, which is higher than that of pure BFO (5.5 dB). The impressive EM absorption performance of the composites was attributed to the combination of BFO and RGO, which greatly enhanced the electrical conductivity and dielectric loss. We claim that BFO/RGO composite is a promising material which can be applied to microwave absorption.

Construction of multiple electromagnetic loss mechanism for enhanced electromagnetic absorption performance of fish scale-derived biomass absorber

Biomass-derived porous carbon materials have attracted considerable attention as promising electromagnetic (EM) wave absorbers due to their lightweight characteristic, ultra large surface area as well as high dielectric loss. However, the dielectric loss alone is difficult to achieve high EM wave absorption performance. In this work, core-shell Co@Co3O4/porous carbon composites are designed and synthesized by a facile hydrothermal and subsequent pyrolysis process through using fish scale as carbon precursor, Co(NO3)2·6H2O as Co source, aiming to offer more loss mechanism and achieve high EM wave absorption performance. As expected, the as-prepared composite showed strong absorption (−89.3 dB at 2.4 mm) with broadened bandwidth (11.92–18 GHz at 2 mm). Such excellent absorption performance could be attributed to the reasonable design of composite. Special porous structure not only is beneficial to the impedance matching to allow EM wave to enter absorber as much as possible, but also could offer a conductive path for electronic, booming conductive loss. Besides, the designed unique core-shell structure provides Co-Co3O4 interfaces along with Co3O4-C, C-void interfaces are propitious to enhance interface polarization loss. Moreover, Co@Co3O4 nanoparticles could also supply the magnetic loss to composites to further absorb EM wave from another point. Although there are many previous works about Co@Co3O4 have been reported, little works have been done on the composites of biomass porous carbon with core-shell Co@Co3O4 with such excellent EM wave absorption performance. This work indicates that the as-obtained core-shell Co@Co3O4/C could be a candidate for dealing with the increasing EM wave pollution.

Metal Cooper nanoparticles embedded in porous carbon as high reflection loss absorbers of high frequency electromagnetic wave

Metal Cu/C nanocomposites were prepared by a facile one-step encapsulation process and then annealing the mixture of organic carbon compound and metal nitrate. Morphology detection indicated that Cu nanoparticles were uniformly anchored in the porous carbon matrix. An electromagnetic (EM) wave absorption of Cu/C nanocomposites with various mass proportions of porous carbon was performed in the frequency range of 1.0–18.0 GHz. The structure and morphology of Cu/C nanocomposites could be tuned by changing the carbon proportion for obtaining suitable electromagnetic parameters, which resulted in a superior EM wave absorption property. For Cu/C 1–3 nanocomposites, the reflection loss values of −46 dB were obtained at 17.0 GHz with a rather thin thickness of 1.4 mm and exceed −20 dB in the range of 7.4–18.0 GHz for the thickness 1.4–2.8 mm. The Cu/C nanocomposite exhibited excellent EM wave absorption performance under a rather thin thickness, which suggested that Cu/C nanocomposite could be regarded as a promising candidate for high-performance EM wave absorber.

Tailoring complex permittivity and permeability to enhance microwave absorption properties of FeCo alloy particles through adjusting hydrazine reduction process parameters

Owing to their high permeability, metallic soft magnetic materials exhibit high potential as microwave absorbers. The great challenge in designing desirable absorption properties from these materials is their large electrical permittivity at microwave frequencies. So, decreasing their permittivity within acceptable limits while keeping permeability at sufficiently high or improved levels is considered an important requirement for matching impedance and obtaining excellent electromagnetic (EM) absorption properties. In the present research, FeCo alloy particles produced employing by a simple wet chemical reduction process with the intention of investigating dependence of their EM properties on synthesis parameters. The characterizations were done with the help of x-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The intrinsic EM properties (εr, μr) in a frequency range of 2–18 GHz were measured by a vector network analyzer (VNA) for the paraffin composites containing obtained products. The results indicated that the concentration of NaOH and metallic salts as the synthesis precursors can tune the permittivity and permeability. Under optimum conditions, bandwidths of 7.3 and 5.5 GHz with thicknesses of only 1.2 and 1.5 mm were obtained respectively. Also, Reflection loss (RL) of −45 dB was attained. The excellent EM absorption properties demonstrated that the synthesized FeCo alloy may be an ideal absorber having both a wide absorption bandwidth and a low thickness.

One-Pot Hydrothermal Synthesis of MWCNT/ZrO2 Composites for Enhancing Electromagnetic Wave Absorption Performance

Electromagnetic (EM) wave absorption materials have drawn a lot of attention because they can effectively reduce EM wave pollution from electronic equipment. In this work, we combined ZrO2 nanoparticles with multi-walled carbon nanotubes (MWCNTs) and explored applications of MWCNT/ZrO2 composites in EM wave absorbing field. ZrO2 nanoparticles with a high crystalline were synthesized by one-step hydrothermal method. Adding MWCNTs in this hydrothermal process, ZrO2 nanoparticles aggregated together to form uneven lumps and wraps on MWCNTs surfaces. MWCNTs improved the conductivity loss and electron polarization capability of composites. The minimum reflection loss (RL) of MWCNT/ZrO2 composites reached [Formula: see text]39.73 dB at a thickness of 2[Formula: see text]mm. Such excellent EM wave absorption properties are attributed to the dielectric loss, dipole polarizations and interfacial polarizations. This composite can be a promising candidate as high efficiency EM wave absorption material and used for commercial production because of the simple synthesis methods.

Precursor infiltration and pyrolysis cycle-dependent microwave absorption and mechanical properties of lightweight and antioxidant carbon fiber felts reinforced silicon oxycarbide composites

High-performance microwave absorption materials combined with good oxidation resistance and mechanical properties are highly desirable in some extreme situations. Herein, three-dimensional (3D) needled carbon fiber felts reinforced silicon oxycarbide (SiOC/CFs) composites with excellent electromagnetic (EM) wave absorption, good oxidation resistance and mechanical properties were successfully prepared through a simple precursor infiltration and pyrolysis (PIP) process. Notably, the EM wave absorption, oxidation resistance and mechanical performances strongly depend on the PIP cycles through adjusting the content of SiOC to control the porosity and density of the composites. A substantial enhancement of EM wave absorption performance of composites is achieved via incorporation of SiOC with different PIP cycles, resulting from the matched characteristic impedance and enhanced loss ability. The minimum reflection loss (RLmin) of pure carbon fiber felts is −8.4 dB, whose value is decreased to −62.9 dB for the composites with 1 PIP cycle, and to −49.9 dB for the composites with 2 PIP cycles, respectively. The results indicate that the as-prepared SiOC/CFs composites with superior EM wave absorption, great oxidation resistance and mechanical properties could be considered as a great potential for the applications in harsh environments.

Broadband high-performance electromagnetic wave absorption of Co-doped NiZn ferrite/polyaniline on MXenes

Ideal electromagnetic (EM) wave absorption materials should exhibit strong absorption peaks and broad effective absorption bandwidths, which are important for EM protection and the stealth technology. Despite considerable advancements in this field in recent years, EM absorption materials have not reached their full potential to meet all the above-mentioned requirements, especially the broad absorption bandwidth at low frequencies. Herein, we synthesized a Co-doped NiZn ferrite (CNZFO)/polyaniline (PANI) on Ti3C2TX MXene composite with a hierarchical structure via three facile steps: exfoliation, hydrothermal process, and modified interfacial polymerization. The CNZFO particles and PANI chains as well as the small number of TiO2 particles uniformly grafted between the Ti3C2TX layers formed a unique sandwich-like structure. The multiple-layer composite showed excellent EM wave absorption with a maximum reflection loss (RL) of −37.1 dB at only 2.2 mm. It showed an effective bandwidth (RL < −10 dB) of 4.1 GHz (8.2–12.3 GHz). The eddy current loss, natural resonance, interfacial polarization, dipole polarization, and multiple reflections of the layered structure contributed to the enhanced EM wave absorption performance of this composite. Hence, the hierarchical Ti3C2TX/CNZFO/PANI composite was found to be a promising high-quality EM wave absorption material.

Dramatically enhanced electromagnetic wave absorption of hierarchical CNT/Co/C fiber derived from cotton and metal-organic-framework

Lightweight, low-cost electromagnetic (EM) wave absorption materials are in urgent need, as EM interference pollution is increasingly serious. Carbon material as EM absorber has attracted ever increasing attention. However, their absorption property is still limited. Herein, we propose a very simple strategy to prepare hierarchical carbon fiber coated with Co/C nano-dodecahedron particles where CNTs were anchored (HCF@CZ-CNTs), using cotton and metal-organic-framework (MOF) as raw materials. One of MOF, ZIF-67 particles were in-situ grown onto the surface of cotton fibers. Lightweight HCF@CZ-CNTs samples were obtained by direct carbonization, the apparent density of which is only 0.0198 g/cm3. The minimum reflection loss (RLmin) of hierarchical HCF@CZ-CNTs was dramatically enhanced to −53.5 dB at 7.8 GHz, compared with pure carbonized cotton fiber (RLmin = −18.9 dB at 16 GHz). Meanwhile the effectively absorption bandwidth was also remarkably enlarged to 8.02 GHz. The excellent EM wave absorption performance is attributed to the micro-to-nano hierarchical hollow fibrous structure, as well as the synergetic effect of polarization relaxation and magnetic loss. These results illuminate a low-cost and sustainable strategy to prepare ultra-lightweight microwave absorbers with excellent EM wave absorbing ability utilizing biomass precursor and MOF.

High temperature absorbing coatings with excellent performance combined Al2O3 and TiC material

A series of challenges are impeding the development of high temperature electromagnetic (EM) wave absorbing materials in x band. In this study, to deal with this problem, a coating, (1-x).wtAl2O3∼x.wtTiC, is designed and prepared using plasma spraying technology. Its permittivity increases with temperature and TiC content, which endows it with a good EM impedance at high temperature. The coating possesses excellent EM absorbing performance at 800 ℃. When the x value equals 0.2 and thickness 1.6 mm, the coating exhibits an EAB of 3.45 GHz at 800℃, and a reflection loss lower than -8 dB in whole x band. The XRD result shows that only two phases exist in the coating. The SEM images illustrate that TiC is unevenly dispersed in Al2O3, causing loss of conductivity and interface polarization. The finding not only broadens the application of TiC-based materials but also indicates the promising future of this material system.

Ni2P nanocrystals coated on carbon nanotubes as enhanced lightweight electromagnetic wave absorbers

Rational microstructure design of carbon based composites is becoming a promising method to reinforce their electromagnetic (EM) wave absorption performance, but their synthesis remains a challenge. Herein, we have reported a design of small-size Ni2P grown on carbon nanotubes (CNTs) as lightweight and high efficiency EM wave absorber. The Ni2P NPs can be uniformly grown on CNTs by controlling the nucleation and growth rate of Ni2P during the synthesis. The size and coverage of Ni2P on CNTs can be tuned by adjusting the reaction conditions with a high yield, which is large favorable for adjusting their application performance. The Ni2P/CNTs sample with low filler loading (30 wt%) in the paraffin wax exhibits a good wave absorption performance with the minimum reflection loss (RL mini) value of −51.8 dB at 5.28 GHz. Moreover, it shows a good EM wave absorption ability even at the thinnest thickness of 2 mm (−46.1 dB), and an effective absorption bandwidth of 11.68 GHz is achieved when the absorber thickness is in the range of 1.5–5 mm. The excellent EM wave absorbing performance makes the Ni2P/CNTs as a promising new microwave absorbing material in sustainable filed.

Carbon nanotubes modified CoZn/C composites with rambutan-like applied to electromagnetic wave absorption

The preparation of magnetic metal/carbon composites by pyrolysis of metal organic framework (MOFs) have great potential in lightweight electromagnetic (EM) wave absorption. Nevertheless, it is of great significance to design the three-dimensional (3D) hierarchical structure with synergistic effect from unique MOFs for enhancing the EM wave absorption performance. More importantly, through pyrolysis of MOF, the uniform distribution of magnetic metal and carbon material can be controlled. Herein, Co/Zn-MOF-11 microspheres are used as a precursor pyrolyzed in argon atmosphere to prepare 3D hierarchical rambutan-like bimetallic/carbon@carbon nanotubes (RBC@CNTs) composites. The RBC@CNTs composite pyrolyzed at 800 °C exhibits excellent EM wave absorption performance due to the unique structure and multiple loss mechanisms. A maximum reflection loss of −49.8 dB at 13.6 GHz can be achieved when the filler loading of 3D hierarchical RBC@CNTs composite is 20 wt% with the thickness of 2.4 mm. In addition, the effective absorption bandwidth achieves 5.5 GHz (RL ≤ −10 dB). This strategy to synthesis a unique hierarchical structure is instrumental in enhancing the attenuation of EM wave.

SiC whiskers-reduced graphene oxide composites decorated with MnO nanoparticles for tunable microwave absorption

• Multiscale MnONPs@SiCw/RGO hybrid composites were successfully synthesized. • The morphology of MnONPs strongly depends on the post-annealing temperature. • The optimal RL of composites reaches −54.04 dB with the maximum EAB of 7.4 GHz. • The microwave response mechanism is analyzed. An excellent electromagnetic (EM) wave absorber with lightweight, broad bandwidth and high-efficiency absorption is urgently demanded for solving the EM interference pollution. A MnO nanoparticles@SiC whiskers/reduced graphene oxide (MnONPs@SiCw/RGO) hybrid composite with enhanced EM wave absorption performance was successfully synthesized by a hydrothermal strategy followed with thermal treatment. The results demonstrate that the annealing temperature was critical for the morphology of MnONPs, resulting in different impedance matching and attenuation constant. Correspondingly, the MnONPs@SiCw/RGO hybrid composite obtained at 800 ℃ presented the best EM wave absorption property, whose minimum reflection loss (RL min ) reached −54.04 dB at 17.9 GHz with ultrathin matching thickness of only 1.59 nm and the effective absorption bandwidth (EAB) could be dramatically broadened to 7.4 GHz, covering the entire Ku-band. Additionally, almost full-band absorption with a qualified bandwidth of 14.2 GHz could be achieved by changing the sample thickness from 1.5 to 5.0 mm. The enhancement results should be mainly attributed to the synergistic and complementary effects of the conduction loss and polarization relaxation loss. Our work exhibits that the hierarchical MnONPs@SiCw/RGO hybrid composites might as a promising candidate for high-efficiency microwave absorbers, and provides an effective way for constructing microwave absorber in the future.

A biomass derived porous carbon for broadband and lightweight microwave absorption

With the continuous progress of science and technology, the traditional magnetic material is no longer able to meet the new complex electromagnetic (EM) environment due to its high bulk density. Therefore, the novel excellent EM absorber with the feature of thin thickness, low density, broad absorption bandwidth and strong absorption intensity is highly desired. Herein, we fabricated a porous carbon with ultrahigh porosity through a facile KOH activation from biomass waste pumpkin seed shell for lightweight EM wave absorption application. By optimizing the porous structures, the strong absorption intensity of −50.55 dB is achieved at thin thickness of 1.85 mm under low filler content of only 10 wt %. More interestingly, a broad frequency bandwidth of 7.4 GHz could cover the whole Ku band. These outstanding microwave absorption performances, couple with low cost ingredients and ease of fabrication process enable the porous carbon framework as the next generation promising candidate for lightweight and remarkable EM absorber.

Fabrication of ultra-light nickel/graphene composite foam with 3D interpenetrating network for high-performance electromagnetic interference shielding

Electromagnetic (EM) waves absorbing materials with lightweight and unique 3D porous structure have been receiving greater attention due to their excellent EM shielding effects. Here, a low density, high porosity Ni/rGO composite foam has been facilely obtained by a combination of solution combustion, freeze-drying and high temperature annealing. The resulting Ni/rGO foam exhibits an interpenetrating network consisting of a 3D nickel skeleton and continuous rGO sheets. This unique configuration endows the foam excellent EM wave attenuation with a density of 38.54 mg/cm3 and a porosity of 96.74%. The foam achieves a maximum reflection loss (RL) as high as −53.11 dB covering a bandwidth of 4.91 GHz for a thickness of 4.5 mm showing satisfying impedance matching. In addition, multiple loss mechanisms have been demonstrated in the Ni/rGO foam, including Debye dipole relaxation, conduction loss, interfacial polarization, ferromagnetic natural resonance, and multiple reflections resulted from this hierarchically porous structure. In short, the study provides a novel, economical, and efficient way to obtain 3D EM wave absorbing materials.

Efficient Variable Thickness Radome Design with Insertion Phase Delay Correction

Variable thickness design is capable of yielding excellent electromagnetic (EM) performance for streamlined airborne radomes. The traditional optimization method using evolutionary computation (EC) techniques can yield variable thickness radome (VTR) design with optimal EM performance but uncontrollable thickness profile, leading to manufacturing difficulties. Thickness profile design based on average incident angle is an efficient way for VTR design with smooth thickness profile, whereas the boresight error (BSE) is relatively large. In this work, insertion phase delay (IPD) correction is introduced in the efficient thickness profile design process to realize a better balance between EM performance and thickness profile smoothness of airborne radomes. The thickness profile obtained from average incident angle is adjusted for IPD distribution symmetry with respect to the antenna axis under scan angles with large BSE. Results indicate that the proposed method can effectively improve the BSE characteristics at the expense of slight deterioration of computational efficiency and thickness profile smoothness.