Electromagnetic Microwave Research Articles

Temperature‐Dependent Electromagnetic Microwave Absorbing Characteristics of Stretchable Polyurethane Composite Foams with Ultrawide Bandwidth

With the rapid development of current electronic equipment, electromagnetic microwave absorption (EMA) materials with higher design requirements under special circumstances have attracted great attention. Herein, a flexible polyurethane composite foam assisted by coral‐like CNT@Fe3O4/graphene nanocomposites is fabricated by a facile solvothermal and moisture self‐foaming method. The composite foam with 15 wt% nanofillers exhibits an outstanding temperature cycle stability with gradually improved EMA performance at elevated temperature and excellent resilience stability with a tensile strength of 4.81 MPa. An enhanced minimum reflection loss (RLmin) of −59.44 dB at 10.38 GHz with a thickness of 2.28 mm is achieved, while the ultrawide absorption bandwidth of 6.09 GHz nearly covers the full X‐band. This benefits from interface impedance matching, dielectric and magnetic dual losses, and multiple reflections depending on the interior open microcellular structures. It is expected to become a promising thermally tunable microwave absorber in harsh environments.

Analysis the influence of pulse-to-pulse stability of modulator on high-power microwave output of pulsed klystron

X-ray free electron laser (XFEL) facility based on electron linear accelerator (LINAC) is regarded as one kind of the fourth-generation light source with the characteristics of high intensity, exceptional brightness, ultrashort pulse duration, and spatial coherence. In electron linear accelerator, energy of beam bunches is provided by high-power electromagnetic microwaves which are generated by a microwave tube called klystron. The stability of beam voltage of klystron occupies a key position in both the stability of output RF (Radio Frequency) power and the jitter of output RF phase, furthermore, it plays an extremely important role in beam energy stability of electron linear accelerator. In this paper, high power RF fluctuation and phase jitter of klystron output caused by beam voltage instability of klystron are analyzed and calculated. Influence of klystron beam voltage instability on beam energy gain in linear accelerator have also been further analyzed and calculated. The calculating procedure is particularly valuable for us to understand the relationship between pulse modulator stability and beam energy gain fluctuations. Finally, relevant experimental results measured by Shanghai Soft X-ray Free Electron Laser Test Facility (SXFEL-TF) is presented.

Electromagnetic wave and Microwave heating: an eco-compatible solution to control Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae)

Rhynchophorus ferrugineus (Oliver) (Coleoptera: Curculionidae) is the primary pest of palms. Although several methods are used for its control, there is concern that insecticidal treatments can cause substantial environmental pollution. Therefore, the use of electromagnetic waves (EMWs) or microwaves (MWs) to control R. ferrugineus is an attractive alternative option. Microwave heating is increasingly used to manage a wide variety of agricultural and forest pests because it induces thermal death in insects that have a thermal tolerance lower than that of the host matrix. In this study, EMWs (360 Hz, 100 W) applied for 60 min caused 100% mortality of adult RPWs but had no effects on larvae. Microwave heating (2.45 GHz, 500 W) caused 100% mortality of adults in 4 min, whereas larvae required MW heating for only 40 s to achieve 100% mortality. The brain of adult R. ferrugineus was the most damaged region following EMW exposure, with severe damage to the neural cells after 60 min. The neural bundles were broken, and the granular cells were scattered. Microwave exposure affected the cuticle and muscles in adult R. ferrugineus after 4 min and the midgut, cuticle, and muscles in larvae after 40 s. The gut epithelium separated from the basement membrane and became highly vacuolated, almost disintegrating. The cuticle was reduced with separated layers, and muscle fibers were also affected. This work confirms that EMWs and MW heating are promising, ecocompatible methods to fight the spread of R. ferrugineus.

Electromagnetic response and microwave absorption properties of CF/Fe3O4 absorbing composites

Electromagnetic response and microwave absorption properties of CF/Fe3O4 absorbing composites

In Situ Dual-Template Method of Synthesis of Inverse-Opal Co3O4@TiO2 with Wideband Microwave Absorption.

A unique porous TiO2 with Co3O4 nanoparticles anchored in (Co3O4@TiO2) is prepared by a dual-templating method for promoting electromagnetic microwave absorption (EMA). The as-prepared Co3O4@TiO2 possesses a three-dimensional (3D) ordered macroporous TiO2 skeleton and plenty of mesopores, as well as small Co3O4 nanoparticles that coexisted in the macropore walls of the TiO2 skeleton. The introduction of Co3O4 can increase the magnetic loss as well as suppress impedance mismatch, resulting in the regulation of the EMA performance. The synergetic effect of the TiO2 porous framework and Co3O4 nanoparticles with proper ratio promote microwave absorption performance. Therefore, Co3O4@TiO2-2 with 25 wt % Co3O4 nanoparticles content displays a strong and ultrawide effective absorption band (EAB) performance. The Co3O4@TiO2-2 presents a strong reflection loss of -53.9 dB at 2.95 mm. Moreover, it obtains a super broad EAB of ∼12.5 GHz at 5.0 mm. This dual-templating approach for a well-controlled porous structure could be a facial strategy for the development of high-performance electromagnetic wave absorbers.

Implantation of WSe2 nanosheets into multi-walled carbon nanotubes for enhanced microwave absorption

Microwave absorption materials can protect humanity from harmful electromagnetic radiation, but it is still a challenge to absorb electromagnetic radiation with different bands simultaneously. Herein, an effective strategy for obtaining WSe2@CNTs nanohybrids is reported. The conductive network and polarization of WSe2@CNTs nanohybrids can be tailored by confinedly implanting WSe2 nanosheets on multi-walled carbon nanotubes. The electromagnetic properties and microwave absorption performance of the nanohybrids are effectively adjusted via changing the hybrid ratio of WSe2 and CNTs. Multi-band microwave absorption is achieved with up to three bands. The reflection loss (RL) of the sample can reach −60.1 dB, and the bandwidth can reach 4.24 GHz (RL ≤ −10 dB). The excellent microwave absorption performance is attributed to the conductance and multiple relaxations, as well as the synergistic effect of the two. This result confirms that WSe2@CNTs nanohybrids are potential candidates for high-efficiency microwave absorbers and provide a valuable pathway for designing high-performance microwave absorption materials in the future.

Modeling Microwave Heating and Drying of Lignocellulosic Foams through Coupled Electromagnetic and Heat Transfer Analysis

Microwave drying of suspensions of lignocellulosic fibers has the potential to produce porous foam materials that can replace materials such as expanded polystyrene, but the design and control of this drying method are not well understood. The main objective of this study was to develop a microwave drying model capable of predicting moisture loss regardless of the shape and microwave power input. A microwave heating model was developed by coupling electromagnetic and heat transfer physics using a commercial finite element code. The modeling results predicted heating time behavior consistent with experimental results as influenced by electromagnetic fields, waveguide size and microwave power absorption. The microwave heating modeling accurately predicted average temperature increase for 100 cm3 water domain at 360 and 840 W microwave power inputs. By dividing the energy absorption by the heat of vaporization, the amount of water evaporation in a specific time increment was predicted leading to a novel method to predict drying. Using this method, the best time increments, and other parameters were determined to predict drying. This novel method predicts the time to dry cellulose foams for a range of sample shapes, parameters, material parameters. The model was in agreement with the experimental results.

Preparation and characterization of an electromagnetic composite polypyrrole/polyethylene short filament geotextile

In this paper, firstly, polypyrrole was prepared by in situ polymerization using pyrrole as the monomer, hexahydrate ferric chloride as the oxidizer and dopant, and polyethylene geotextile as the substrate to prepare a polypyrrole/polyethylene short filament geotextile composite; secondly, the electromagnetic microwave absorption property and shielding property of the polypyrrole/polyethylene short filament geotextile composite were investigated; finally, the chemical structure of the polypyrrole/polyethylene short filament geotextile composite was characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Raman test methods. The results show that the reflection loss value is up to the minimum value of –17.53 dB in the frequency range of 0–3 GHz and the best absorbing performance is obtained at the frequency of 1.12 GHz. In the frequency range of 0.95–1.25 GHz, the reflection loss value is less than –10 dB, and the electromagnetic wave is effectively absorbed. The shielding effectiveness value is up to the maximum value of 16.07 dB at the frequency of 1.19 GHz, that is, the shielding ability becomes strongest at the frequency of 1.19 GHz; otherwise, the shielding effectiveness is higher than 14 dB in the frequency range of 0.17–3.0 GHz. The FTIR, Raman, XRD, and DSC tests result show that polypyrrole has been successfully loaded on the polyethylene geotextile, improving the crystallinity and thermal stability property of the composite.

Hollow C@MoS2 Nanospheres for Microwave Absorption

The engineering of core-shell nanostructures provides a great potential to induce interfacial polarization relaxation and optimize impedance matching. Herein, core-shell-structured MHCS@MoS2 nanospheres are developed using hollow carbon (MHCS) and stacked MoS2 nanosheets. Heterostructures between cores and shells significantly boost the interface polarization effect and effectively reduce the electromagnetic wave (EMW) reflection caused by highly conductive MHCS. Thereby, efficient and broadband electromagnetic microwave absorption (EMA) performance can be achieved. Through controlling the thickness of MoS2 shells and the graphitization of MHCS cores, the effective absorption bandwidth (fE) of MHCS@MoS2 can reach 6.21 GHz at the thickness of only 2.1 mm. The nanodesigned core-shell-shaped MHCS@MoS2 nanospheres are demonstrated as a promising high-performance EMA material.

Ultraweakly and fine-tunable negative permittivity of polyaniline/nickel metacomposites with high-frequency diamagnetic response

Metacomposites have drawn considerable attention due to their enticing prospect in electronic and dielectric devices, which meanwhile unfortunately suffered from extremely high negative permittivity (ε' < 0). Herein, we put forward a strategy to suppress the plasma oscillation in metacomposites and thereby constrain the value of negative permittivity by introducing the semiconductive polyaniline to construct polyaniline/nickel (PANI/Ni) metacomposites. Weakly negative permittivity was obtained at a magnitude of 102 over the whole test frequency band, which is remarkably lower by at least three orders of magnitude than that of most metacomposites. The ε′-negative value was resultantly fine-tuned by about 102 with equally adjusting Ni content. Lorentz and Drude models were employed to describe ε′-negative spectra, indicating that both dielectric resonance and plasma oscillation contributed to negative permittivity. Negative susceptibility of ε′-negative materials was mainly ascribed to high-frequency diamagnetic response within Ni networks. The well-designed PANI/Ni metacomposites with weakly and fine-tuning negative permittivity can greatly benefit the practical applications on electromagnetic (EM) shielding, microwave absorption and novel EM sensors.

Preparation of FeNi/C composite derived from metal-organic frameworks as high-efficiency microwave absorbers at ultrathin thickness

Developing metal–organic frameworks (MOFs) derived microwave absorbers with the merits of thin matching thickness, broad bandwidth and strong absorption still remains a big challenge in the electromagnetic absorption field. Herein, FeNi-MOFs derived magnetic-carbon composites were fabricated via a solvothermal and pyrolytic two-step strategy. It was found that the micromorphology of carbon frameworks could be regulated from the regular octahedron to spherical shape through facilely adjusting the molar ratios of Fe3+ to Ni2+ in the precursors. Furthermore, results revealed that the molar ratios of Fe3+ to Ni2+ had notable effects on the electromagnetic parameters and microwave attenuation capacity of attained composites. Significantly, the obtained FeNi/C composite with the molar ratio of Fe3+ to Ni2+ of 1:0.5 showed the comprehensively optimal electromagnetic attenuation performance, i.e. the reflection loss achieved −40.2 dB (larger than 99.99% absorption) and absorption frequency band was as high as 5.8 GHz (from 11.9 to 17.7 GHz, covering 96.7% of Ku-band) under an ultrathin thickness of 1.65 mm. Besides, the probable microwave dissipation mechanisms were clarified, which mainly derived from the optimized impedance matching, strengthened interfacial polarization and dipole polarization relaxation, enhanced conduction loss and natural resonance effect. Therefore, our results would be helpful for designing and developing high-performance microwave absorbing composites derived from MOFs.

In situ thermal modification of kafirin using infrared radiations and microwaves.

Kafirin is a prolamin protein located in the corneous endosperm of sorghum. The conventional thermal processing of kafirin reduces its solubility, which limits its utilization in the food industry. Therefore, the study was aimed to investigate the effect of in situ thermal modification of kafirin using two different electromagnetic thermal treatments, namely infrared (IR) and microwave (MW) radiation, on the physicochemical, structural, thermal, and antioxidant properties. The results demonstrated that both the thermal modifications improved yield, purity, and solubility of the kafirin with a decrease in hydrophobicity. However, IR-treated samples showed higher solubility (910.67 g kg-1 ) and lower hydrophobicity (387.67). The IR modifications also improved the ratio of α helix/β sheets to a great extent. The alterations in the disulfide content were concomitant with the improvement in the thermal stability of kafirin. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed variations in the band intensities of β- and γ-kafirin, indicating alterations in the kafirin subunits. Morphological examination of kafirin revealed surface withering and agglomeration. Notably, IR treatment improved the antioxidant activity more efficiently (from 32.11% to 74.05%). Although both the IR and MW treatments modified kafirin, the effect seemed to be more pronounced in IR modification. The IR-modified kafirin had better solubility and lesser hydrophobicity than MW-modified kafirin. The physicochemical and structural changes induced by IR treatment improved the biological activity of kafirin, in terms of antioxidant activity. Therefore, it was concluded that the in situ IR modification of kafirin can alter its characteristic properties, improving its potential as a food ingredient. © 2021 Society of Chemical Industry.

Simulations and Experiments of the Soil Temperature Distribution after 2.45-GHz Short-Time Term Microwave Treatment

Microwave treatment is a green and pollution-free soil disinfection method. The application of microwaves to disinfect soil before cultivation is highly important to increase crop yields and protect the ecological environment. The electromagnetic field is an important parameter influencing the soil temperature field in the process of microwave soil treatment, and the change in soil temperature directly affects soil disinfection. Therefore, this article carried out research on the heating pattern in North China loess due to microwave treatment. First, COMSOL software was employed to simulate the microwave soil treatment process to analyze microwave penetration into soil. Second, with the application of microwaves at the designed frequency produced with a 2.45-GHz tunable microwave generating microdevice, soil with water contents of 0%, 10%, 20%, and 30% was treated for 10~60 s (at 10-s time intervals), and experiments on the influence of the microwave output power, treatment time, and soil moisture content on the soil temperature were performed via the controlled variable method. The simulation results indicate that with increasing soil moisture content, the microwave frequency inside the soil model increases, and the electric field intensity value decreases in the model at the same depth. After microwaves traverse through the 20-cm soil model, the incident field strength is three orders of magnitude lower than the outgoing field strength. The results of the microwave soil treatment experiment reveal that: (1) Compared to microwave output power levels of 1.8 and 1.6 kW, a level of 2 kW is more suitable for microwave soil disinfection. (2) After treatment, the highest temperature occurs on the soil surface, not within the soil. (3) The location of the highest soil internal temperature after microwave treatment increasingly approaches the soil surface with increasing soil moisture content, and the microwave output power does not affect the location of the highest soil internal temperature. Combining the electromagnetic field simulation and microwave soil treatment experiment results, it was found that the higher the field strength is, the higher the temperature value, and the highest soil internal temperature after microwave treatment often occurs at the first electromagnetic wave peak.

Electrospinning fabrication and enhanced microwave absorption properties of nickel porous nanofibers

One-dimensional Ni porous nanofibers (Ni PNFs) were prepared through a facile electrospinning followed by hydrogen reduction process, and their electromagnetic characteristics and microwave absorbing properties were investigated. Benefiting from the unique microstructure, three-dimensional conductive network and multiple attenuation forms, Ni PNFs exhibit remarkably increased dielectric loss capacity and improved impedance matching level relative to Ni nanoparticles. Consequently, Ni PNFs offer a significantly enhanced microwave absorption property with a minimum reflection loss (RL) of −40.4 dB at a relatively low filling ratio of 30 wt% and an effective absorption bandwidth (RL<−10 dB) of 4.6 GHz (8−12.6 GHz). Our results demonstrate that the microstructure and morphology of materials have considerable influence on their electromagnetic performances and the as-obtained Ni PNFs can be a promising candidate for lightweight and high-efficiency microwave absorption or electromagnetic shielding.

Material Selection for Axial Magnetization of a Gyromagnetic NLTL for Space Applications

Nonlinear Transmission Lines (NLTLs) are a new technique for radio frequency (RF) generation. A loaded ferrite NLTL, known as a gyromagnetic line, uses a solenoid to provide an external magnetic bias. In space applications, specifically in satellites, the replacement of these solenoids by permanent magnets is desirable, eliminating the need for a DC current source, and reducing the weight and the effective cost of the launch. This work investigated and selected permanent magnets for this application, and then computationally modeled the magnet assembly to analyze the resulting magnetic field generated and obtained a uniform field region to meet the NLTL operating specifications. For this, we employed selection charts for the proper choice of material to use in an arrangement of magnets simulated by the electromagnetic software CST Microwave Studio . Magnetic fields with uniformity variations of less than 6% and 23% in regions extended over 18.5 cm and 58.8 cm, corresponding to line lengths of 26.6 cm and 68.0 cm, respectively, were achieved in simulations.

Electromagnetic microwave absorption property of MoC synthesized via a facile solid-state reaction method

Electromagnetic microwave absorption property of MoC synthesized via a facile solid-state reaction method

Towards efficient carbon nanodot-based electromagnetic microwave absorption via nitrogen doping

The development of electromagnetic (EM) microwave absorption materials is essential for the whole electrical and electronic systems. Although carbon-based materials have been widely studied as EM absorber, the problems such as high cost, complicated processing technology and insufficient shielding performance still remain unsettled. Here, carbon nanodots (CDs) prepared through a one-step microwave-assisted heating method are demonstrated as EM absorption materials for the first time. With regulation of the doped nitrogen contents and degree of graphitization, the minimum EM reflection loss of the CDs at 10.7 GHz is −26.5 dB, and the effective absorption bandwidth of 1.5-mm thickness is 4.85 GHz. By adjusting the thickness, the effective absorption band ranges from 3.3 to 18 GHz, which is better than most non-composite carbon materials. The superior performance can be attributed to the excellent impedance matching and high dielectric loss in CDs. These results may extend the application fields of CDs and offer new insight into the exploitation of effective carbon-based EM shielding materials.

An Electromagnetic Microwave Stealth Photothermal Soft Actuator with Lightweight and Hydrophobic Properties.

Electromagnetic (EM) microwave stealth soft robots are in urgent need in military application. Photothermal soft actuators with photomechanical energy conversion have attracted significant interest owing to their remote control, flexibility, and contactless operation. The innovative combination of an electromagnetic microwave absorption (EMA) function with a photothermal actuator paves the way for this aspect. Here, a composite with unique dual three-dimensional foam is fabricated based on graphene and hollow carbon spheres (HCSs). When exposed to 1 sun illumination, the temperature could increase to 50 °C within 1 min and plateaus at 80 °C for hollow carbon spheres-graphene foam-polydimethylsiloxane (HCSs-GF-PDMS), which shows great photothermal performance. A wormlike crawling robot has been constructed based on this composite material, which could move forward under only 1 sun illumination. Remarkably, the EM stealth could be successfully realized because the composite material exhibits great EMA performance with a minimum reflection loss of -56.99 dB at a thickness of 2.5 mm, and the maximum effective absorption bandwidth is 8.65 GHz. In addition, the HCSs-GF exhibits hydrophobic and lightweight functions as well, which lighten the weight of soft robots and lead to self-cleaning and energy saving. This work provides a promising direction of multifunctional EM stealth soft robots.

A monopole microwave-assisted electrochemical sensor for the detection of liquid chemicals

In this paper, a new sensor structure is presented based on a printed circuit board (PCB) monopole antenna with operating frequency of f= 2 GHz. Numerical investigation was performed in order to determine the ethanol alcohol ratio in wine and isopropyl alcohol ratio in disinfectants (sanitizers). Finite Integration Technique (FIT) based commercial high-frequency electromagnetic solver CST Microwave Studio has been used for the simulation study. The loss tangent values and dielectric constants of the samples used in the current study were obtained by KEYSIGHT brand PNA-L N5234A Network Analyzer. The proposed sensor structure was able to greatly differentiate the ethanol alcohol content in the wine and the isopropyl alcohol content in the sanitizer through the return loss values and corresponding graphs. In the design of patch antenna, the electromagnetic permittivity ratios of the samples corresponding to the alcohol ratio and isopropyl ratio are considered and the antenna dimensions along with the working frequency were optimized accordingly. In the related frequency band, permittivity values corresponding to the ethanol alcohol and isopropyl alcohol ratios exhibit a linear variation and make the sensor design possible. According to the obtained results, it was found that the changes in the resonance frequency can be associated with ethanol alcohol and isopropyl alcohol ratio inside the samples. The change of ethanol alcohol amount and isopropyl alcohol in the liquid samples tested at the resonance frequency of patch antenna is proportional to the change in the resonance frequency and they are very close to a linear characteristic.

Preparation and characterization of branch-like heteroatoms-doped Ni@C nanofibers for high-performance microwave absorption with thin thickness

Magnetic Ni@C nanofibers with branch-like multiwall carbon nanotubes (MWCNTs) were prepared through a two-step strategy of electrospinning and following in situ pyrolysis to explore the electromagnetic microwave absorption (MA) performance. The morphology and chemical composition were controlled by mass ratio of nickel (II) acetylacetone (Ni(acac)2) and poly (phthalazinone ether nitrile ketone) (PPENK) resin. 3D structure with branch-like morphology extends the transmission path of microwave and reduces the thickness effectively. The heteroatoms-doped Ni@C nanofibers reach the optimal reflection loss value of −53.2 dB at 14.3 GHz and effective absorption bandwidth of 5.6 GHz from 12.4 to 18.0 GHz with rather thin thickness of 1.5 mm. The MA mechanisms are discussed in detail and the multi-component nanofibers of magnetic Ni particles and nonmagnetic carbon have achieved synergistic effect of dielectric and magnetic loss. This work explores the relevancy of morphology and composition on microwave absorption performance, revealing a potential application for excellent microwave absorber with low filler ratio and thinner matching thickness.