Electromagnetic Microwave Research Articles

Mössbauer spectroscopy studies on the particle size distribution effect of Fe–B–P amorphous alloy on the microwave absorption properties

An Fe-based nanocrystalline alloy powder is important for application in microwave absorption, and the particle size has a critical impact on the electromagnetic microwave parameters. Therefore, it is necessary to study further the effects of the particle size on such parameters and improve the microwave absorption performance of Fe-based nanocrystalline powers. In this study, Fe–B–P particles were prepared through a synthetic approach consisting of an aqueous chemical reduction and a ball milling treatment. We investigated the effects of ball milling on the microstructure and electromagnetic properties of Fe–B–P particles. The experimental results indicate that the Fe–B–P particles synthesized through an aqueous chemical reduction are amorphous spheres. Fe–B–P particles with an original particle size of 200–1200 nm can be milled into an irregular shape with the size reduced to < 500 nm after 0.5 h of ball milling, and subsequently, the particles become smaller with increases in the milling time, with traces of Fe2O3 generated on the particle surface. The results of the Mossbauer spectra show that a portion of the small particles demonstrate a superparamagnetic property. The volume proportions of the superparamagnetic component increase from 13.1 to 15.8% as the treatment time increases. We measured the permittivity and permeability spectra of Fe–B–P particles within the frequency range of 2–18 GHz. The reflection loss (RL) is − 10 dB for an absorber thickness of 1.7–5.0 mm. The RL is − 20 dB for an absorber thickness of 1.9–2.7 mm. The microwave absorption properties of samples with the same thickness are improved with an increase in the treatment time and are shifted to a higher frequency, which will broaden the bandwidth of the absorption as well.

A Study on the Fused Deposition Modeling Process of Graphene/Nano-Fe3O4 Composite Absorber and its Absorbing Properties of Electromagnetic Microwave

Graphene/polylactic acid; nano-Fe3O4/polylactic acid; and graphene/nano-Fe3O4/polylactic acid composite absorbers are independently produced by fused deposition modeling technology. The effects of the content of graphene and nano-Fe3O4 on absorbing properties are investigated. After measuring the electromagnetic parameters using the waveguide method, the absorbing property is characterized according to the transmission line theory. The distribution of graphene and nano-Fe3O4 in the matrix is observed by scanning electronic microscopy (SEM). The results show that the graphene and nanometer ferroferric oxide multicomponent absorbing agent helps to form a synergistic absorbing effect. In the frequency range 8.2–18.0 GHz; the absorber has the greatest absorbing property when the content of graphene and nanosize Fe3O4 are 5 wt% and 20 wt%, respectively.

Self-cleaning functionalized FeNi/NiFe2O4/NiO/C nanofibers with enhanced microwave absorption performance

Microwave absorbing materials with enhanced microwave absorption performance and self-cleaning function are of great interest for military applications and human health caused by electromagnetic radiation pollution. Herein we report the synthesis of FeNi/NiFe2O4/NiO/C nanofibers (NFs) via electrospinning technique using nickel acetylacetonate (Ni(acac)2), ferric acetylacetonate (Fe(acac)3), and N, N-dimethylformamide (DMF)/polyacrylonitrile (PAN) solution as precursor. We also show the abilities of the materials to attenuate electromagnetic microwave and their ease of self-cleaning performance. X-ray diffraction patterns and HRTEM images reveal that the materials possess FeNi, NiFe2O4, NiO and graphite. HAADF-STEM images show that the magnetic nanoparticles distribute uniformly along the fibers. Contrast experiments had been conducted on different calcination temperatures to elucidate the impedance matching and loss mechanism. Based on the results of the experiment, excellent microwave absorption was exhibited by blending the NiFe2O4/NiO/CNFs and FeNi/NiFe2O4/NiO/CNFs into paraffin at 50 wt% and 5 wt%, respectively. Moreover, the contact angles (CA) of the as-prepared fiber films calcined at 650, 750 and 950 °C were 143°, 141° and 144°, respectively, indicating that fiber films exhibited excellent hydrophobicity and self-cleaning function. It suggested that the as-obtained NFs had an excellent application prospect in self-cleaning microwave absorbing materials.

Immobilization of zinc oxide nanoparticles on graphene sheets for lithium ion storage and electromagnetic microwave absorption

A simple one-step method to immobilize zinc oxide nanoparticles (ZnO NPs) in reduced graphene oxide (RGO) supporting framework is reported in this work. Under mild hydrothermal condition, ZnO NPs function as an effective catalyzer for few-layered graphene oxide (GO) deoxygenation to construct an RGO protecting framework and in the meantime ZnO NPs are immobilized between the RGO sheets. The synthesized ZnO/RGO composite not only delivered good lithium ion storage capability with a reversible capacity of 560 mA h·g−1 for 250 cycles under a current density of 500 mA g−1, but also exhibited good electromagnetic microwave absorption performance with the maximum reflection loss value of −67.13 dB when the thickness is 3.2 mm while the effective absorption bandwidth is 7.44 GHz with the thickness of 2.8 mm. The improved performances of the ZnO/RGO composite compared with bare ZnO NPs are ascribed to the synergistic effect from well-dispersed ZnO NPs and RGO framework, particularly, the formation of Zn–O–C bond between the two components brings in good immobilization between the two components, which was verified by both theoretical calculation and XPS characterization techniques. The method to prepared ZnO/RGO composite is facile, eco-friendly and effective, which has great potential to find wider applications for massive production.

Evaluating Potential of Electromagnetic Microwaves on Destruction Acanthamoeba Cysts

Evaluating Potential of Electromagnetic Microwaves on Destruction Acanthamoeba Cysts

A Dielectric Resonator Antenna with Enhanced Gain and Bandwidth for 5G Applications.

In this paper, a dielectric resonator antenna (DRA) with high gain and wide impedance bandwidth for fifth-generation (5G) wireless communication applications is proposed. The dielectric resonator antenna is designed to operate at higher-order mode to achieve high antenna gain, while a hollow cylinder at the center of the DRA is introduced to improve bandwidth by reducing the quality factor. The DRA is excited by a microstrip line with a narrow aperture slot. The reflection coefficient, antenna gain, and radiation pattern of the proposed DRAs are analyzed using the commercially available full-wave electromagnetic simulation tool CST Microwave Studio (CST MWS). In order to verify the simulation results, the proposed antenna structures were fabricated and experimentally validated. Measured results of the fabricated prototypes show a 10-dB return loss impedance bandwidth of 10.7% (14.3–15.9GHz) and 16.1% (14.1–16.5 GHz) for DRA1 and DRA2, respectively, at the operating frequency of 15 GHz. The results show that the designed antenna structure can be used in the Internet of things (IoT) for device-to-device (D2D) communication in 5G systems.

Lightweight and Robust Carbon Nanotube/Polyimide Foam for Efficient and Heat-Resistant Electromagnetic Interference Shielding and Microwave Absorption.

Excellent electromagnetic interference (EMI) shielding ability, light weight, and good heat resistance are highly required for practical applications of EMI shielding materials, such as in areas of aerospace, aircraft, and automobiles. Herein, a lightweight and robust carbon nanotube (CNT)/polyimide (PI) foam was developed for efficient and heat-resistant EMI shielding. Thanks to poly(vinyl pyrrolidone) (PVP) as a surfactant that not only promotes the uniform dispersion of CNTs to form perfect CNT conductive networks but also can be removed in situ during the polymerization process, the density of resultant CNT/PI foam is only 32.1 mg·cm-3, and the EMI shielding effectiveness (EMI SE) is up to 41.1 dB, which represents one of the highest EMI SE values compared to previously reported polymer-based foams. The CNT/PI foam also achieves the absorption coefficient (A) of up to 82.3%, which is very impressive in CNT/polymer foams at comparable EMI SE levels. The PI matrix endows the foam with excellent heat resistance. The as-prepared CNT/PI foam presents a higher EMI SE than 35 dB even after being subjected to the flame of an alcohol burner. Moreover, the compressive strength and compressive modulus are up to 240.9 and 323.9 kPa. These results indicate its certain application potential in the harsh requirement of aeronautics and aerospace industries as a highly efficient and lightweight EMI shielding material.

Preparation of CoFe2O4 hollow spheres with carbon sphere templates and their wave absorption performance

In the synthesis of colloidal carbon spheres (CCSs) from glucose by hydrothermal carbonization, agglomeration and cross-linking often occur, affecting their functions as templates. In this study, the effects of various surfactants on the dispersion and particle size of CCS were investigated. The CCS synthesized with dodecyltrimethylammonium bromide was much larger than those of other groups, and the average diameter exceeded 6.4 μm. CCS with complete spherical shape and good dispersion were obtained using sodium polyacrylate, with a diameter of approximately 450 nm CoFe2O4 hollow spheres were prepared by a simple adsorption–calcination method using CCS as the templates, and the effects of different dispersions and particle sizes on the electromagnetic parameters and microwave absorption properties of hollow spheres were studied. The results show that the absorption bandwidth corresponding to reflection loss less than −7 dB widened from 2.64 GHz to 3.44 GHz with improving dispersion of hollow sphere structure. When the size of the hollow sphere increased to the micron level, the thickness required to reach the maximum bandwidth reduced by 0.5 mm. Compared to the unoptimized hollow spheres, the microwave absorption performance of the as-prepared CCCs improved effectively. The effect of surfactants on the dispersion of CCS and the effect of the dispersion and size of CoFe2O4 hollow spheres on their electromagnetic properties are discussed in detail.

Gumdrop-cake-like CuNi/C nanofibers with tunable microstructure for microwave absorbing application

Broadband electromagnetic microwave absorbing materials with low density are highly demanded and faced with a development challenge for the critical applications into military stealth technology and electromagnetic pollution protection. Tailoring micro-structures and compositions of carbon-based multifunctional materials is a promising strategy to satisfy the expectation. Herein, we have firstly introduced nonmagnetic Cu element to tune microstructure, chemical composition of agglomerated Cu–Ni bimetallic alloys nanoparticles in gumdrop-cake-like CuNi/C nanofibers for the usage of high-quality light microwave absorbing materials, which can integrate the advantages of carbon nanofibers and CuNi nano solid solution particles. The CuNi/C nanofiber calcined at 650 °C temperature remarkably achieves a −55.1 dB strong reflection loss at 13.4 GHz frequency and a 7.5 GHz broad bandwidth (RL ≤ −10.0 dB) at 3 mm matching thickness, exhibiting a superior microwave absorption performance. This work demonstrates that introducing nonmagnetic Cu element could provide an effective way to improve the electromagnetic performance of carbon-based composites through tuning their microstructure.

Theoretical study on the modulation characteristics of THz wave by two-dimensional black phosphorus

Using the Delude model. we theoretically calculate the dispersion of conductivity with frequency in the orthogonal direction of the two-dimensional black phosphorus (2D BP) &lt;i&gt;x&lt;/i&gt; and &lt;i&gt;y&lt;/i&gt; direction in the THz band. We find that the conductivity in the &lt;i&gt;x&lt;/i&gt; direction is more sensitive to the electron doping concentration. The difference between 2D BP conductivities in both directions leads to the difference in dielectric constant which in turn can modulate light in different polarization directions. Using 2D BP to polarize the THz wave, the 2D BP-SiO&lt;sub&gt;2&lt;/sub&gt; periodic sandwich structure is designed. The three-dimensional electromagnetic field simulation software CST Microwave Studio can be used to calculate the regulation characteristics of this structure to THz wave. It is found that this structure has different polarization directions, and the incident THz wave has different absorption. By changing the thickness of the underlying SiO&lt;sub&gt;2&lt;/sub&gt; layer in the structure it is found that the absorption rate of this structure also changes accordingly. When the polarization direction of the THz pulse is parallel to the &lt;i&gt;x&lt;/i&gt; axis, the absorption rate first increases and then decreases. When &lt;i&gt;d&lt;/i&gt;&lt;sub&gt;5&lt;/sub&gt; = 9.5 μm, the absorption rate reaches 93% near 3.86 THz; when the polarization direction of the THz pulse is parallel to the &lt;i&gt;y&lt;/i&gt; axis, the absorption rate gradually increases. The absorption peak has a significant red shift.

Preparation and electromagnetic microwave adsorption performances of porous nanocomposite self-assembled by CoFe2 O4 nanoparticles and diatomite

Preparation and electromagnetic microwave adsorption performances of porous nanocomposite self-assembled by CoFe2 O4 nanoparticles and diatomite

Cold‐test of reltron modulation section and PIC simulation study on output power and efficiency

Parametric analysis and cold test of reltron modulation section are presented along with particle-in-cell (PIC) simulation results. A cavity is designed to have maximum separation among the three resonant modes 0, π/2, and π. Electromagnetic (EM) simulation software packages CST Microwave Studio (MWS) and MAGIC are used to obtain and compare the electromagnetic field patterns and resonant frequencies. Both the software predict the modes with identical field pattern and a difference of 1.3% to 3.8% in resonant frequency. The MAGIC code used here captures all three modes successfully. The designed cavity is fabricated and S11 is measured. The frequencies of measured S11 minima differ by 1.6% to 3.5% from the simulated values and closely match with that of the resonant modes. Furthermore, the modulation section is parametrically studied to observe the dependence of the resonant frequencies on the physical dimensions. The key parameters that govern the operating frequency and mode separation are identified. The Q factors are calculated from S11, and after that, the cavity reactance from loaded Q. Particle-in-cell (PIC) simulation results indicate that the mode separation improves overall system performance in terms of output power and efficiency.

One-Pot Synthesis of Doped-Polypyrrole/Fe₃O₄ Nanosphere Composites and Their Microwave Absorption Performance.

Doped-polypyrrole/Fe₃O₄ (D-PPy/Fe₃O₄) nanospheres were successfully synthesized via a onepot process. In this process, polyvinyl alcohol (PVA) plays an important role in the construction of polypyrrole nanoparticles, and Fe3+ ions were the oxidant and the only raw resource of Fe₃O₄. The morphology, magnetic properties, and electromagnetic microwave absorption properties of D-PPy/Fe₃O₄ composites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), a vibrating sample magnetometer (VSM) and a vector network analyser (VNA). The results indicate that D-PPy/Fe₃O₄ nanospheres become more disperse and regular due to the addition of PVA. The influence of the mass ratio of PVA to pyrrole on the microwave absorption performance of the D-PPy/Fe₃O₄ composites was also investigated. When the mass ratio of PVA/pyrrole was 0.75:1, the minimum reflection loss (RLmin) value of the D-PPy/Fe₃O₄ composites reached -41.3 dB at 7.7 GHz with a thickness of 3.0 mm. The microwave interference cancellation of interface reflection, nature resonance loss and current loss are the main reasons for the loss of electromagnetic microwaves for the as-prepared D-PPy/Fe₃O₄ composites.

Improved Electromagnetic Interference Shielding Response of Polyaniline Containing Magnetic Nano-ferrites

Improvement of electromagnetic interference (EMI) shielding materials with miniaturization of devices is an important area of research in various applications like communication, electronic warfare, defense, and different civilian applications. Nano-crystalline ferrite, MFe2O4 (M = Ni, Zn, and Co), powders have been synthesized by sol-gel citrate nitrate precursor method. The crystalline size of samples was found in the range of 20–45 nm as analyzed by XRD and TEM analysis. Polyaniline/ferrite nano-composites with 50 wt% were synthesized by mechanical blending. The structural and magnetic properties of the nano-particles were characterized by using Rietveld analysis of powder X-ray diffraction and vibrating sample magnetometer (VSM) respectively. Using the Rietveld refinement, the goodness of fit, interatomic distance, Bragg contribution, and R factors have been determined. Ferrites and their nano-composites, under applied magnetic field up to 20 KOe, exhibited the hysteresis loops of ferromagnetic nature with maximum saturation magnetization of 51.68 emu/g shown by CoFe2O4. The electromagnetic shielding parameters (various shielding effectiveness and reflection loss) and microwave absorbing properties were measured in X band frequency region (8.2–12.2 GHz). Nano-composites show promising and enhanced EMI shielding behavior with overall highest SE value of 52 dB shown by CoFe2O4 composite.

Constructing Stacked Structure of S-Doped Carbon Layer-Encapsulated MoO2 NPs with Dominated Dielectric Loss for Microwave Absorption

Nowadays the handling of emerging pollution of electromagnetic microwave employing absorption-oriented methods has been paid particular research attention. However, the construction of high-perform...

Two-Step Solvothermal Synthesis of (Zn0.5Co0.5Fe2O4/Mn0.5Ni0.5Fe2O4)@C-MWCNTs Hybrid with Enhanced Low Frequency Microwave Absorbing Performance.

In this study, the quaternary hybrid of (Zn0.5Co0.5Fe2O4/Mn0.5Ni0.5Fe2O4)@C-MWCNTs with high-performance in low frequency electromagnetic absorption was synthesized via a facile two-step solvothermal synthesis method. The physicochemical properties as well as electromagnetic parameters and microwave absorption performance were characterized by XRD, SEM, TEM, RS, TGA, and VNA, respectively. The results indicate a nuclear-shell morphology of this hybrid for amorphous carbon coated on the surface of Zn0.5Co0.5Fe2O4 and Mn0.5Ni0.5Fe2O4 mixed polycrystalline ferrites. In addition, the MWCNTs synchronously enwind in the nuclear-shell NPs to form a special cross-linking structure. The outstanding low frequency microwave absorption property is attributed to the synergistic effect of dielectric and magnetic loss, better impedance matching condition, and excellent attenuation characteristics of the as-prepared paramagnetic quaternary hybrid. Maximum RL of −35.14 dB at 0.56 GHz with an effective absorption bandwidth in the range of 0.27–1.01 GHz can be obtained with thickness of 5 mm. This hybrid exhibits superior low frequency microwave absorption properties compared with other ferrite-carbon nanocomposites. This investigation provides a new route to prepare suitable candidates for the absorption of electromagnetic waves in a low frequency band on account of its good performance and simple preparation process.

Oxygen vacancies regulated microwave absorption properties of reduced graphene oxide/multi-walled carbon nanotubes/cerium oxide ternary nanocomposite

Herein, reduced graphene oxide/multi-walled carbon nanotubes/cerium oxide (RGO/MWCNTs/CeO2) ternary nanocomposite was prepared by a facile one-pot hydrothermal route. Micromorphology observations revealed that RGO was wrapped by MWCNTs and numerously cubic-like CeO2 nanoparticles were uniformly loaded on the crumpled surfaces of thinly flake-like RGO and MWCNTs in the ternary nanocomposite. Moreover, the influence of addition of RGO and MWCNTs on the electromagnetic parameters and microwave absorption properties of RGO/MWCNTs/CeO2 nanocomposite was systematically investigated. It was found that the as-prepared ternary nanocomposite exhibited notably enhanced microwave absorption performance compared with RGO/CeO2 binary nanocomposite, MWCNTs/CeO2 binary nanocomposite and pure CeO2 nanoparticles. Remarkably, the obtained ternary nanocomposite displayed the minimum reflection loss (RL) of −59.3 dB in the C-band with a matching thickness of 4.5 mm and effective absorption bandwidth (EAB, RL < −10 dB) of 3.2 GHz with an ultrathin thickness of merely 1.5 mm. Furthermore, the EAB could reach 13.8 GHz (86.3% of 2–18 GHz) by facilely modulating the matching thicknesses from 1.5 to 5 mm. The possible microwave absorption mechanisms of as-prepared nanocomposites were carefully explored and further proposed. Therefore, our results could shed light on designing and fabricating graphene-based hybrid nanocomposites as high-performance microwave absorbers.

Enhanced Microwave Absorption Performance of Double-Layer Absorbers Containing BaFe12O19 Ferrite and Graphite Nanosheet Composites

The electromagnetic properties and microwave absorption performance of single-layer and double-layer absorbers were studied. Double-layer absorbers used BaFe12O19 composites as matching layer and graphite nanosheet composites as absorption layer achieved enhanced absorption performance, such as higher absorption capacity, wider bandwidths and thinner thickness. When the matching layer (BaFe12O19 composites) thickness is 1.0 mm and absorption layer (graphite nanosheet composites) thickness is 1.5 mm, the minimum reflection loss of the double-layer absorbers is − 26 dB, the bandwidths with reflection loss below − 5 dB is 11.5 GHz (6.5–18 GHz).

Preparation of Carbon Encapsulated Magnetic FeCo Alloy Nanoparticles Supported on Carbon Nanotubes for Enhanced Microwave Absorption

A mixture of multi-walled carbon nanotubes in an ethanol solution of Fe(NO3)3.9H2O and Co(NO3)2.6H2O, were used to prepare an Fe2O3-CoO catalyst supported on carbon nanotubes by a supercritical fluid drying method. The carbon encapsulated FeCo nanoparticles were prepared by the catalytic decomposition of methane over the catalyst at 850°C for 30 mins. The morphology and microstructure of the catalyst and carbon encapsulated nanoparticles (CEP) were characterized by XRD, FESEM, EDS and TEM analyses. The electromagnetic characteristics and microwave absorption properties of the CEP product were also studied. Results show that the CEP product possesses high complex permittivity and good permeability in the microwave frequency range from 2 to 18 GHz. The maximum absorption peak was observed at 9.44 GHz for a large reflection loss (R) of 13.3 dB, with a band width of 7.4 GHz and 2.56 GHz, at R <- 5 dB and R <- 10 dB, respectively.

Facile synthesis of cobalt-zinc ferrite microspheres decorated nitrogen-doped multi-walled carbon nanotubes hybrid composites with excellent microwave absorption in the X-band

Herein, nitrogen-doped multi-walled carbon nanotubes/cobalt-zinc ferrite (NMWCNTs/Co0·5Zn0·5Fe2O4) hybrid composites were synthesized through a facile one-step solvothermal route. Results of morphology observations revealed that Co0·5Zn0·5Fe2O4 microspheres were uniformly loaded on the surface of NMWCNTs and three-dimensional (3D) conductive networks were in-situ constructed by the entanglement of NMWCNTs in the as-prepared hybrid composites. Moreover, the influence of contents of NMWCNTs on the electromagnetic parameters and microwave absorption properties of NMWCNTs/Co0·5Zn0·5Fe2O4/paraffin wax composites were elaborately investigated. It was found that the obtained hybrid composites demonstrated superior microwave absorption performance in the X-band. Remarkably, the minimum reflection loss reached −64.7 dB with a matching thickness of 3.1 mm and effective absorption bandwidth achieved 4.3 GHz (11.7–16.0 GHz) with a thickness of merely 2.1 mm. Furthermore, a dual-band (C and Ku bands) microwave absorption characteristic was observed in the obtained hybrid composites. Besides, the microwave absorption properties of as-prepared hybrid composites could be facilely tuned by changing the matching thicknesses and contents of NMWCNTs. The superior microwave absorption properties of obtained hybrid composites mainly originated from the synergistic effects of magnetic loss, conduction loss and dielectric loss, and optimized impedance matching. It was believed that our results could be helpful for the structural design and facile fabrication of 3D MWCNTs-based hybrid composites as high-efficient microwave absorbers.