Maximum Reflection Loss Value Research Articles

Microwave absorbing performance of reduced graphene oxide @ alumina fabricated by atomic layer deposition method

In this work, a series of alumina coating reduced graphene oxide (RGO@Al2O3) composites with core-shell structure was synthesized by the atomic layer deposition (ALD) method. The alumina (Al2O3) thickness of the RGO@Al2O3 could be controlled by changing the number of ALD cycles. The microstructure, high-temperature resistance, and microwave absorbing properties of the composites were investigated in detail. The composite could provide excellent high-temperature resistance and microwave absorbing properties. The composite started decomposition at 620 °C. The maximum reflection loss value of the composite obtained by applying 200 Al2O3 deposition cycles is −14.2 dB at 15.7 GHz, and its effective absorption bandwidth reaches 5.0 GHz (13.0–18.0 GHz). The results show that the RGO@Al2O3 composite has the potential application in high-temperature microwave absorbing fields, due to excellent high-temperature resistance, reflection loss, and effective absorption bandwidth.

Dimensional design of Fe0.9Co0.1 nano-alloys with enhanced low-frequency microwave absorption

Low-frequency microwave absorbing materials are critical for enabling radar stealth and interference resistance in gigahertz communication devices and electronic equipment. However, long-wavelength electromagnetic waves are not easily attenuated, due to the limitations of current absorbing materials, including low permeability and a lack of electromagnetic wave loss mechanisms at low frequencies. Herein, we design and prepare one- and two-dimensional Fe0.9Co0.1 nanoalloys with high permeability through an organic templating method combined with a constrained transformation strategy. We systematically investigate the impact of the anisotropy of monodisperse Fe0.9Co0.1 nanoalloys on low-frequency microwave absorption performance. The generous specific surface area of Fe0.9Co0.1 nanosheets facilitate multiple reflections and the scattering of electromagnetic waves within the absorber. This phenomenon, coupled with dielectric resonance, culminates in a maximum reflection loss value of − 48.7 dB at 4.2 GHz. More significantly, Fe0.9Co0.1 nanorods exhibit an absorption intensity of − 35.3 dB at a notably lower frequency of 2.5 GHz, outperforming existing materials, in addition to an efficient absorption bandwidth of 4.2 GHz at a thickness of only 0.7 mm. Through a combination of experimental investigations and finite element simulations, we identify that highly anisotropic magnetic nanorods demonstrate a robust magnetic coupling interaction, substantial interface polarization and quasi-antenna effect. These characteristics result in enhanced low-frequency electromagnetic losses. Our findings indicate that the high anisotropy of the Fe0.9Co0.1 nanoalloys significantly improves their microwave absorption performance, thus emphasizing their substantial potential in the development of efficient low-frequency microwave absorbers.

Microstructures, magnetic properties and microwave absorption of ion-implanted bismuth ferrite thin films

This study investigates the properties and performance of bismuth ferrite thin films on Kapton sheets as electromagnetic (EM) wave-absorbing materials. The main techniques employed in this study involved modifying the surface geometry and using electromagnetic wave-absorbing materials as surface coatings. X-ray diffraction analysis revealed a cubic crystal structure of the bismuth ferrite thin films. The bonding analysis showed the presence of Bi–O and Fe–O functional groups at 432.26 and 519.48 cm−1, respectively. Vibrating-sample magnetometry revealed the ferromagnetic behavior of the bismuth ferrite thin film, confirming that saturation magnetization decreased with increasing sputtering time. Moreover, the calcination temperature affected the coercive field; the higher the calcination temperature, the higher the coercivity of the BiFeO3 (BFO) thin film layer. Scanning electron microscopy with energy-dispersive X-ray spectroscopy of the bismuth ferrite thin films revealed the presence of Bi, Fe, and O—evenly and homogeneously distributed on the Kapton surface. After the ion implantation process, the atomic force microscopy test results showed an increased root-mean-square roughness (Rq). The root-mean-square roughness value for Kapton before the process was approximately 7.5 nm, while the root-mean-square roughness values for BFO 10 min and BFO 12.5 min were approximately 18.8 nm and 25.3 nm, respectively. The microwave absorption ability reached a maximum reflection loss value of − 40.4 dB (99.9 %) in the range of 9.98 GHz with a sputtering duration of 10 min. Therefore, these results suggest bismuth ferrite is a potential candidate as an EM wave absorber.

The Impact of Al3+ ion substitution on microwave absorption of hexaferrite compound Ba0.6Sr0.4Fe12−xAlxO19 (x = 0.25, 0.50, 0.75, and 1.00)

This paper discusses the impact of Al3+ ion substitution on Fe3+ ions in the hexaferrite compound Ba0.6Sr0.4Fe12−xAlxO19 on the reflection loss value and bandwidth in absorbing microwaves. Hexaferrite Ba0.6Sr0.4Fe12−xAlxO19 (x = 0.25, 0.50, 0.75, and 1.00) was synthesized by high-energy ball milling (HEBM) for forty hours, followed by sintering at 1000 °C in the air for five hours. Then, the crystal structure, formed phase, surface morphology, magnetization, and ability to absorb microwaves in the X-band region were successively characterized. All samples (x = 0.25, 0.50, 0.75, and 1.00) had a single phase with a hexagonal crystal structure. The particle size remained heterogeneous, ranging from 200 to 300 nm, with a platelet-like shape. The maximum amount of magnetic energy that could be absorbed by the material (Ms) increases from x = 0.25 to 0.75 and then decreases slightly for x = 1.00. The maximum value of reflection loss (RLmax) decreases as x increases. For x = 0.25, RLmax is − 16.17 dB (f = 11.06 GHz) with a bandwidth of 3.56 GHz, whereas for x = 1.0, RLmax is −13.94 dB (f = 11.14 GHz) with a bandwidth of 1.68 GHz.

A-Site Doped in Perovskite La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 (x = 0, 0.1, and 0.3) for Absorbing Microwave Material

Microwave radiation can have harmful effects on our bodies. With increased exposure due to online activities, it is essential to use absorber materials like perovskite manganate to reduce radiation. In this study, perovskite manganate La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 (x = 0, 0.1, and 0.3) was synthesized using the sol-gel method. X-ray diffraction (XRD) analysis revealed that the two samples were multi-phased, LaMnO3 and La2Ti2O7, and were formed, exhibiting a rhombohedral crystal structure (R -3 c). Morphological characterization of the sample surface using a Scanning Electron Microscope (SEM) showed that as doping increases, the grain size decreases from 282.02 to 245.63 nm at x=0 and x=0.3, respectively. This result implies that doping leads to more uniform grain distribution and enhanced grain refinement. Characterization via Vibrating Sample Magnetometer (VSM) revealed that the maximum saturation value, 0.79 emu/g, was attained when x = 0. This sample exhibits soft magnetic properties, as evidenced by its coercivity (Hc) value of < 1kOe. Results from the Vector Network Analyzer (VNA) indicate that the absorption capacity of La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 increases, with a maximum reflection loss value of -25.5 dB with 1.5 mm thickness. Consequently, La(1-x)Bax/2Srx/2Mn0.4Ti0.6O3 demonstrates potential as a microwave absorber material.

Fabrication of in-situ Ti-Cx-N1−x phase enhanced porous Si3N4 absorbing composites by gel casting

In view of the lack of a conformal, load-bearing, lightweight, and high-temperature resistant integrated microwave-absorbing composites for applications under extremely complex conditions, this study successfully applies gel casting craft to porous Si3N4 microwave-absorbing composites. The high-temperature decomposition reaction of Ti3SiC2 powder was utilized to generate uniform Ti-Cx-N1−x grains in situ and to enhance the mechanical and microwave-absorption properties of porous Ti-Cx-N1−x/Si3N4 composites. The bending strength, fracture toughness, density, maximum reflection loss value, absorption bandwidth and matched thickness in P-band of the composite with 30 wt% Ti3SiC2 addition were 164.87 ± 7.56 MPa, 2.61 ± 0.13 MPa·m1/2, 2.077 g/cm3, 32.42 dB, 1.74 GHz and 4.2 mm, respectively. The fracture toughness and bending strength of the composite were increased by 71.71% and 58.13%, respectively, compared with monolithic porous Si3N4. The electromagnetic wave loss mechanisms of the composites are proposed as a combination of conductivity loss, multiple reflections and scattering, interfacial polarization and defect polarization.

Construction of multi-interface PDA-NiCo2S4 nanomaterials for synergistic design of efficient microwave absorption and anti-corrosion effects

The modern and complex environment requires microwave absorbing materials (MAMs) that can cope with environmental changes. In particular, the high humidity, high salt spray and high temperature of the marine environment conditions have been the toughest. Consequently, the development of integrated materials with both microwave absorption (MA) and corrosion resistance has emerged as a top priority. In this work, spherical NiCo2S4 (NCS) particles with stable size were prepared by a simple solvothermal method. Furthermore, the self-polymerization of dopamine (PDA) on the surface of NCS was achieved by exploiting the film-forming ease of dopamine. A series of PDA-NCS particles with different interfaces were fabricated by tuning the ratio of NCS and dopamine. The integrated magneto-electric drive synergy enhances the impedance matching. Multiple heterogeneous interfaces enhance the depletion efficiency of electromagnetic waves (EMWs) within the material. The samples designed have achieved an effective absorption bandwidth (EAB) value of 6.26 GHz and a maximum reflection loss value of −22 dB at a low thickness of 1.7 mm. Meanwhile, due to the electrochemical protection reaction of anode of metal and the passivation effect of barrier by PDA. The prepared coatings maintained favorable corrosion resistance in 240 h of continuous salt spray environment. Moreover, after the 240 h salt spray experiment, the sample realized the EAB value of 4.77 GHz at a thickness of 1.7 mm. This work breaks new ground for the development of absorbing and anti-corrosion integrated materials.

The electromagnetic wave absorption composite of flower-like structure NiCo2O4 and Fe3O4 derived from low-temperature preparation method

The NiCo2O4@Fe3O4 composites with excellent electromagnetic wave absorption performance was prepared by the low-temperature (50 °C) co-precipitation method, avoiding the traditional high-temperature hydrothermal synthesis method. The specific surface area of the composite material was increased due to the combination of NiCo2O4 with 3D hierarchical flower-like structure and Fe3O4 with spherical structure, which is conducive to the full reflection and scattering of electromagnetic waves. The combination of typical magnetic material and excellent dielectric material could adjust the impedance matching value of the material and thus the absorption loss performance of electromagnetic wave was improved. The ε value of the dielectric material was larger than those of magnetic materials and the maximum reflection loss value appeared at the high frequency (the thickness is small), while the μ value of magnetic materials was larger than those of dielectric materials and the maximum reflection loss value generally appeared at low frequency (the thickness is large).The results showed that the maximum RL value reached −53.35 dB at about 13 GHz with the thickness of 2.0 mm and the effective absorption bandwidth was 4.4 GHz when the weight ratio (NiCo2O4:Fe3O4) of composite samples was 6:1. The excellent EMW absorption property was mainly due to the combination of NiCo2O4 and Fe3O4, which could achieve impedance matching to loss EMW by dielectric loss and magnetic loss.

MAGNETIC AND MICROWAVE ABSORBING PROPERTIES IN SEMI-HARD COXFE(3-X)O4 SYNTHESIZED BY SOL-GEL METHOD

Magnetic and microwave absorption properties of CoxFe(3-x)O4 semi-hard materials (x = 0.75, 1.0, and 1.5) synthesized have been carried out using the chemical method of sol-gel. The mixture of iron nitrate Fe2(NO3)3 and cobalt nitrate Co(NO3)2 dissolved in ethylene glycol, then the mixture was heated while stirring at 60 °C for 1 hour to form a gel. After that dried at a temperature of 120°C for 5 hours. A fine powder of CoxFe(3-x)O4 was obtained through the grinding process. The CoxFe(3-x)O4 powder crystallization was done by sintering at 1000 °C for 5 hours. The X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Vibrating-sample magnetometer (VSM), and Vector Network Analyzer (VNA) is used to investigate phase identification, particle morphology, magnetic properties, and microwave absorption ability, respectively. Based on the phase identification show that the samples with composition x = 0.75 have two phases, namely CoFe2O4 and Fe2O3. The sample composition for x ³ 1 is a single phase of CoFe2O4. The particle morphology is homogeneous with spherical and the particle size is about 100 – 500 nm. The samples act ferromagnetic behavior with a saturation magnetization (Ms) of 26.1-40.4 emu/g and coercivity field (Hc) of 223-299 Oe. The maximum reflection loss (RL) value of -14.03 dB at the frequency 10.98 GHz occurred in a single-phase sample with a composition of x = 1.0. This study provided a new composite material with great potential for the development of microwave-absorbing materials.

Ultra-broadband electromagnetic wave absorbent: In-situ generated silica modified conductive carbon fiber aerogels

The research and development of dielectric microwave absorbing materials with broad electromagnetic (EM) response is a significant project in EM wave absorption field. To achieve high-performance absorption and strong interfacial bonding at the same time, thermal-assisted in-situ bonding technology was applied to fabricating the dielectric composite absorbing materials. Thanks to the combination of vacuum filtration and in-situ hydrothermal reaction, the as-prepared binary composite aerogel shows both strong interface contacting and good mechanical stability. In addition, the carbon nanofibers/silica composite aerogel (CSA) exhibits ultra-broad effective bandwidth covering from S to Ku band, originated from the uniform dispersed silica aerogel in conductive carbon fiber network. In details, for CSA1 sample, the maximum reflection loss (RL) values and effective absorption bandwidth reach −46.2 dB (1.8 mm) and 5.2 GHz (1.5 mm). Meanwhile, the optimum RCS reduction values reaches 16.2 dB m2 when the detection theta was set as 0°. For CSA2 sample, the effective absorption bandwidth reaches 8.64 GHz at 1.5 mm, and tends to possess lower frequency EM response covering the S-band. This work exhibits a kind of broad-bandwidth aerogel absorbers at low thickness, which shows huge potential in large-scale production of microwave absorbing devices.

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.

WS2 nanosheets anchored on N-doped carbon fibers for superior electromagnetic wave absorption

The carbon fiber three-dimensional (3D) network structure causes conduction loss due to the induced current under an electromagnetic (EM) field, while it can serve as a substrate for the growth of other materials to construct carbon fiber-based composites. Usually, introducing other dielectric loss materials on the carbon fiber surface can adjust the EM parameters and impedance matching, and enhance the loss ability. N-doped carbon fibers anchored by WS2 nanosheets (NCFs@WS2) are reported in this work. When the filling ratio in paraffin is 10 wt%, the maximum reflection loss (RL) value reaches −81.1 dB at 3.5 mm. Additionally, the maximum effective absorption bandwidth (EAB) value reaches 6.24 GHz (9.44 ∼ 15.68 GHz) when the thickness is 3.0 mm. The introduction of WS2 nanosheets not only enhances the multiple scattering of EM waves, but also improves the interfacial polarization loss and dipole polarization loss. Therefore, the superior EM wave absorption performance of NCFs@WS2 is attributed to the good impedance matching, as well as the synergistic effect of conduction loss and polarization loss. This work enriches the research on carbon fiber-based composites and their EM wave absorption performance.

Synthesis and Electromagnetic Wave Absorption Properties of Micro Composites Reduced Graphene Oxide/Ferrite Based Dendrocalamus Asper Charcoal and Natural Ferrite

Keywords: bamboo, micro composite, natural ferrite, reduced graphene oxideAbstract. Reduced graphene oxide/ferrite (rGO/Fe3O4) micro composites as radar absorber materials have been successfully synthesized from Petung bamboo (Dendrocalamus Asper) and iron sand using a mechanical mixing method. Reduced graphene oxide (rGO) as dielectric material was synthesized from Petung bamboo charcoal using the carbonization method, and Fe3O4 as magnetic material was synthesized from iron sand using the extraction-milling method. The as-prepared samples rGO/Fe3O4 (1:1, 1:2, 1:3, 2:1, 3:1 wt%) was made by dry mixing and mechanically pressed. Magnetics and morphology of samples were characterized by vibrating sample magnetometry (VSM) and scanning electron microscopy (SEM). Microwave absorption was measured using a vector network analyzer (VNA) at 8 – 12 GHz. The results of measurement by using VNA showed that at the micro-scale, rGO had a higher absorption power with maximum reflection loss (RLm) value of -12.98 dB at matching frequency (fm) 10.15 GHz compared with Fe3O4 (RLm value of -4.25 dB at fm 10.42 GHz) at a thickness of 2 mm. The rGO/Fe3O4 (3:1 wt.%) microcomposites radar wave absorber shows the best absorption with maximum reflection loss (RLm) value of −14.30 dB at matching frequency (fm) 10.15 GHz at a thickness of 2 mm. Natural materials and the controlled rGO/Fe3O4 microcomposites structure with simple synthesis methods shows the great potential application in high performance microwave absorbing materials.

In situ construction of ZIF-67 derived Mo2C@cobalt/carbon composites toward excellent electromagnetic wave absorption properties

Electromagnetic wave (EM) absorption materials with multi-loss mechanisms and optimized impedance matching have attracted considerable attention as a means to combat the ever-increasing electromagnetic pollution. Molybdenum carbide (Mo2C) with outstanding environmental stability and high conductivity is becoming popular as EM absorption materials. Herein, the CoMoO4@ZIF-67 precursor was synthesized by an in situ sacrificial template method, followed by calcining to synthesize porous Mo2C@cobalt/carbon (Mo2C@Co/C) composites. The homogeneously dispersed Mo2C and Co nanoparticles as well as the porous structures resulted from the novel in situ fabrication strategy could generate abundant interfaces and induce effective multi-loss mechanisms including polarization loss, conductivity loss, magnetic loss, and so on. The as-prepared optimal composite (Mo2C@Co/C-10) demonstrates superior electromagnetic (EM) wave absorption performance with a maximum reflection loss value of −37.9 dB at the matching thickness of 2.3 mm, and the effective absorption bandwidth (EAB) of 5.52 GHz was realized at 1.9 mm. The excellent EM wave absorption properties can be attributed to the good impedance matching, synergistic effects among different loss mechanisms, multiple reflection and scattering. This work not only developed an effective ternary EM absorption materials of Mo2C@Co/C, but also propose a facile in situ strategy to fabricate more highly- dispersed mecarbide-basedased materials.

Enhanced Magnetic and Microwave Absorbing Properties of Nd3+ Ion Doped CoFe2O4 by Solid‐State Reaction Method

CoNdxFe(2−x)O4 (x = 0.0–0.05) spinel ferrites are successfully synthesized by mechanical milling using solid‐state reaction. The effects of Nd3+ ions on structural, microstructure, and magnetic and microwave‐absorbing properties of samples are analyzed. The X‐ray diffraction pattern shows a single‐phase cobalt ferrite for all compositions. Refinement of the structure shows that an increase in the concentration of Nd3+ ions leads to the structure parameter and volume of unit cell to decrease. Lattice strain arises in the crystal, and limiting the crystallite growth is confirmed from the Williamson–Hall analysis. The particle size of the doping samples decreases compared to that without doping. The magnetic parameters, namely coercivity field and saturation magnetization, are strongly affected by the insertion of Nd3+ ions. Another important role of Nd3+ ions is in tuning the performance of microwave absorption. The maximum reflection loss values are gradually increased from −12.65 dB (≈94.35% microwave attenuation) up to −28.57 dB (≈99.86% microwave attenuation) in the concentration of x = 0.0–0.05. Their effective bandwidth also shows an increase from 0.05 up to 1 GHz. The results exhibit that Nd3+ ion‐doped cobalt ferrite has potential properties in designing novel microwave‐absorbing materials.

Reduced graphene oxide-ferrite microcomposites based on petung bamboo (dendrocalamus asper) charcoal and iron sand as lightweight microwave absorbing materials

Reduced graphene oxide-ferrite (rGO/Fe3O4) microcomposites as lightweight microwave absorbing materials has been successfully synthesized from petung bamboo and iron sand by mechanical mixing method at different rGO content (0:1, 1:0, 1:1, 1:2, 1:3, 2:1 and 3:1 wt%). Reduced graphene oxide as dielectric material was synthesized from petung bamboo charcoal using carbonization method and ferrite as magnetic material was synthesized from iron sand using extraction-milling method. Structural characterization by x-ray Fluorosence, Fourier Transform Infrared, Vibrating Sample Magnetometry, x-ray Diffraction, Scanning Electron Microscopy proved that micrometer sized reduced graphene oxide ferrite in the microcomposites was responsible for the ferromagnetic behavior of the composites. The reflection loss of microcomposites measured in the microwave frequency range of 8–12 GHz using a Vector Network Analyzer. The results showed that at the micro scale, rGO had a higher absorption power with maximum reflection loss (RL m ) value of −21.81 dB at matching frequency (f m ) 10.85 GHz compared with Fe3O4 (RL m value of −9.25 dB at f m = 10.60 GHz) at thickness of 1 mm. The rGO/Fe3O4 (2:1 wt%) microcomposites microwave absorber shows the optimum absorption with maximum reflection loss value of −16.51 dB at matching frequency (f m ) 10.74 GHz at thickness of 1 mm. The use of natural materials and the controlled rGO/Fe3O4 microcomposites structure with simple synthesis methods, which the urgent need for developing high performance lightweight microwave abrsorbing materials and are environmentally friendly.

Microwave absorbing characteristics of porphyrin derivates: a loop of conjugated structure.

Microwave absorbing architectures have gained a great deal of attention due to their widespread application in diverse fields, especially in refining electromagnetic pollution. The aim of this study is to investigate the metamaterial characteristics of porphyrin derivatives as conjugated rings in the microwave region and evaluate the influence of electron-withdrawing and donating groups on microwave attenuating performance. Initially, an innovative microwave curing procedure was applied to synthesize the derivates; following that, the phenyl, aniline, and nitrophenyl-coupled structures were identified by XRD, FTIR, FESEM, and DRS analyses. The optical features illustrated that the characteristic band gap of the conjugated loops is obtained and that the optical performance can be manipulated by coupling the functional groups. Eventually, the achieved results demonstrated that the best microwave absorbing performance is related to aniline-coupled porphyrin with a maximum reflection loss (RL) value of -104.93 dB at 10.09 GHz with 2.80 mm in thickness attaining an efficient bandwidth (EB) (RL ≤ 10 dB) higher than the X-band. Noticeably, polyethylene (PE) was applied as an absorbing matrix presenting a meaningful idea for the development of practical microwave absorbers as a new generation of electromagnetic refining and stealth materials. The presented research provides precious inspiration to tailor novel microwave absorbing materials with metamaterial capability to promote their microwave absorbing performance.

UTILIZATION OF Zn-DISPERSED WASTE MATERIALS FOR REALIZING THIN META-STRUCTURE WITH IMPROVED MICROWAVE ABSORPTION

In the present work, emphasis has been given on the utilization of waste materials to make cost-effective microwave absorbing composites. Rice husk and exhausted activated charcoal (EAC) were used as waste material, where rice husk is a form of agricultural waste and exhausted activated charcoal was extracted from an exhausted water filter cartridge. Thereafter, zinc metal powder was dispersed in different weight ratios in the mixture of rice husk and exhausted activated charcoal using a planetary ball mill. The X-ray fluorescence (XRF), X-ray diffraction (XRD), and the particle size analyses were done to analyze element composition and particle size. For dielectric properties analysis, vector network analyzer (VNA) was used. Results reveal that composites have the potential for microwave absorption in 2-18 GHz frequency range, sample RHZ 3 having 6 wt.% Zn content gives the maximum reflection loss value of -21.27 dB at 9.2 GHz for a material thickness of 13.9 mm. The experimental results were then used to design a metamaterial microwave absorber. The simulated results show the good microwave absorption characteristics. The metamaterial absorber showed an absorption bandwidth of around 4.1 GHz which ranges from frequency of 14.1 GHz to 18.2 GHz at total thickness of 1.7 mm.

Oleaster seed-derived activated carbon/ferrite nanocomposite for microwave absorption in the X-band range

Conjugated carbonaceous structures achieved from biological materials were significantly considered electromagnetic wave absorbing materials due to their eye-catching dielectric, lightweight, low-cost, and chemical stability features. To strengthen the microwave absorbing performance of the porous carbon (Oleaster seeds), Fe3O4 magnetic nanoparticles have been successfully anchored onto the surface of biomass-derived material through a co-precipitation method. Noticeably, the dielectric constant, impedance matching, permeability, and microwave absorbing capability were improved by changing the carbon content. The optimized Fe3O4/activated carbon (AC) illustrated the excellent electromagnetic wave absorption performances with a maximum reflection loss (RL) value of −51.12 dB and an effective absorption bandwidth of ∼4 GHz (RL < 10 dB) with a thickness of 1 mm. The promoted microwave absorbing characteristics of Fe3O4/AC composites are rooted in improved impedance matching, eddy current loss, natural and exchange resonance, and specific surface area, bringing more polarization loss and multiple reflection and scattering. The presented research shed new light on the fabrication of practical microwave-absorbing materials based on biomass-derived materials with a facile experimental procedure.

Ultralight Hierarchically Structured RGO Composite Aerogels Embedded with MnO2/Ti3C2Tx for Efficient Microwave Absorption.

Although intensive efforts have been devoted to fabricating Ti3C2Tx MXene composites for microwave absorption, it remains a great challenge to achieve excellent MA performance at low loading and thin thickness. Herein, a three-dimensional (3D) lightweight hierarchically structured MnO2/Ti3C2Tx/RGO composite aerogel with abundant heterointerfaces was fabricated via a hydrothermal and chemical reduction self-assembly method. The RGO aerogel embedded with laminated MnO2/Ti3C2Tx provides a lot of heterogeneous interfaces, 3D porous interconnected conductive networks, and reasonable combination of various loss materials for rich interfacial polarization, conductivity loss, multiple reflections and scattering, and good impedance matching. Benefiting from the synergy of different loss mechanisms, the maximum reflection loss (RL) is up to -66.5 dB (>99.9999% energy absorption) at only 10 wt % loading and 2.0 mm thickness, and even at only 1.5 mm thickness, the maximum RL value remains at -36 dB (>99.9% energy absorption). The work provides a promising route to construct 3D hierarchically heterogeneous composite aerogels for efficient MA at thin thickness and low loading.