High Microwave Absorption Research Articles

Electrode Cooling and Microwave Absorption by Phase Change Fluid Discharge Plasma

It is hard to realize the high microwave absorption property and the low operating temperature in a gas discharge plasma simultaneously, due to the electron number density, and electron neutral collision frequency physically needed for the former is a typical severe heating scenario for the latter. In this article, the phase change process is proposed to be introduced into the controlled area of the discharge plasma system to increase collision frequency and decrease the discharging electrode temperature at the same time. An ac high-voltage power-driven quasi-periodic array of the phase change fluid discharge (PCFD) device is investigated. The most apparent tendency of the PCFD plasma is the improved diffusivity and uniformity. At the same time, the temperature of the electrode and its vicinity, where the phase change material is reserved, is lower than the ambient temperature. Compared with the controlled discharge state of the low gaseous pressure dielectric barrier discharge (L-DBD) plasma without phase change process, the absorption attenuation in the <inline-formula> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula>-band is enhanced in all tested polarization angles, which driving strategy could control. Analyses show that the increased microwave absorption, frequency shift, and bandwidth broadening mainly result from the phase change process and its influences on the plasma discharge.

Controlling dielectric loss of biodegradable black phosphorus nanosheets by iron-ion-modification for imaging-guided microwave thermoacoustic therapy

Microwave-induced thermoacoustic (TA) technology transforms microwave into acoustic waves useable for imaging or therapy, based on the power density of the pulsed microwaves. Exploiting nanoparticles with high biocompatibility, safe metabolism, and high microwave-acoustic conversion is the key to the clinical translational application of TA therapy. In this paper, we proposed a biodegradable and high microwave absorption nanoparticle for TA therapy. The proposed nanoparticle uses iron ions to regulate the atomic defects of biodegradable black phosphorus (BP) nanosheets to augment the dielectric loss. The iron ions adsorb with the lone pair electrons indicated of BP through the conjugated π bond to increase the permanent electric dipoles. With pulsed microwave irradiation, a large number of electric dipoles are repeatedly polarized, causing instantaneous temperature rise and then generating significant TA shockwave via TA cavitation effect. TA shockwave can disrupt cell membranes in situ to trigger programmed apoptosis and produce precise anti-tumor effects. Additionally, the nanoparticle-mediated TA process generates images that deliver valuable data, such as the size, shape, and location of the tumor for treatment planning and monitoring. This hypothesis has been tested in vitro and in vivo with animal models of glioblastoma tumors. The experimental results demonstrate the high theragnostic efficiency for tumor inhibition and TA imaging, exhibiting low systemic cytotoxicity and good biocompatibility after systemic administration. The established BP-based nanoparticle with both safe metabolism and high microwave-acoustic conversion is a promising candidate for precision theranostics without obvious side effects.

Ultralight Open-Cell Graphene Aerogels with Multiple, Gradient Microstructures for Efficient Microwave Absorption.

Development of high-performance graphene-based microwave absorbing materials with low density and strong absorption is of great significance to solve the growing electromagnetic pollution. Herein, a controllable open-cell structure is introduced into graphene aerogels by the graphene oxide (GO) Pickering emulsion. The open-cell graphene aerogel (OCGA) with multiple microstructures shows a significantly enhanced microwave absorption ability without any additions. A high microwave absorption performance with the minimum value of reflection loss (RLmin) of −51.22 dB was achieved, while the material density was only 4.81 mg/cm3. Moreover, by means of centrifugation, the graphene cells were arranged by their diameter, and a gradient, open-cell graphene structure was first fabricated. Based on this unique structure, an amazing microwave absorption value of −62.58 dB was reached on a condition of ultra-low graphene content of 0.53 wt%. In our opinion, such excellent microwave absorption performance results from multiple reflection and well-matched impedance brought by the open-cell and gradient structure, respectively. In addition, the structural strength of the OCGA is greatly improved with a maximum increase of 167% due to the introduction of cell structure. Therefore, the OCGAs with the gradient structure can be an excellent candidate for lightweight, efficient microwave absorption materials.

The effect of SiC content on microstructural and tribological properties of sintered B4C and SiC reinforced Al–Cu–Mg–Si matrix hybrid composites

Abstract In this study, B4C and SiC hybrid reinforced Al–Cu–Mg–Si alloy Matrix composites were fabricated using a microwave sintering technique at a sintering temperature of 550 °C for 60 min. In the produced hybrid composites, while the B4C ratio was kept constant (3 wt%), SiC was used in four different amounts (3, 6, 9, and 12 wt%). In these produced hybrid composites, as a result of microwave sintering, thanks to the high microwave absorption of SiC, the porosities closed at a rate of 36.65–40.90%. In 3, 6, 9, and 12 wt% SiC reinforced composites, the microhardness of 100.1, 106.8, 114.4, and 117.2 HV0.05 were achieved, respectively. Due to agglomeration increasing with SiC reinforcement rate, delamination wears increased in 12 wt% SiC reinforced hybrid composite. As a result, the lowest specific wear rate was measured as 0.3374 × 10−3 mm3·(Nm)−1 in the 3 wt% B4C+9 wt% SiC reinforced sample.

Producing hydrogen-rich syngas via microwave heating and co-gasification: a systematic review

Co-gasification contributes significantly to the generation of hydrogen-rich syngas since it not only addresses the issue of feedstock variation but also has synergistic benefits. In this article, recent research on hydrogen concentration and yield, tar content, gasification efficiency, and carbon conversion efficiency is explored systematically. In feedstocks with high water content, steam gasification and supercritical hydrothermal gasification technologies are ideal for producing hydrogen at a concentration of 57%, which can be increased to 82.9% using purification technology. Carbonized coals, chars, and cokes have high microwave absorption when used as feedstocks. Moreover, coconut activated carbon contains elements that provide a high tan δ value and are worthy of further development as feedstocks, adsorbents or catalysts. Meanwhile, the FeSO4 catalyst has the greatest capacity for storing microwave energy and producing dielectric losses; therefore, it can serve as both a catalyst and microwave absorber. Although microwave heating is preferable to conventional heating, the amount of hydrogen it generates remains modest, at 60% and 32.75% in single-feeding and co-feeding modes, respectively. The heating value of syngas produced using microwaves is 17.44 MJ/m³, much more than that produced via conventional heating. Thus, despite a lack of research on hydrogen-rich syngas generation based on co-gasification and microwave heating, such techniques have the potential to be developed at both laboratory and industrial scales. In addition, the dielectric characteristics of feedstocks, beds, adsorbents, and catalysts must be further investigated to optimize the performance of microwave heating processes.

Reduced graphene oxide containing barium hexaferrite composites for high frequency microwave absorption

Reduced graphene oxide containing barium hexaferrite composites for high frequency microwave absorption

A novel hierarchical structure comprised of biomass-derived porous carbon and silicon carbide nanowires for highly efficient microwave absorption

Recently, porous carbon-based composites with nano- or micro-pores have been considered as attractive alternatives for microwave absorption. However, the dispersity and uniformity of nanomaterials in the porous carbon is not desirable, inducing poor interfacial compatibility and impedance mismatch. Herein, a novel biomass-derived hierarchically porous C/SiC composite (HPCC) with a two-level structure was successfully fabricated. The first level of microscale porous structure templated from dried apple, while the nanoscale bioinspired structure was constructed by in situ growth of SiC nanowires. The hierarchical structures were conducive to enhancing the microwave absorption performance of HPCC. The reflection loss of HPCC was −44.2 dB at a thickness of 1.5 mm, and the broad effective absorption bandwidth reached 4.2 GHz. The synergistic effects of the hierarchical structure on adjusting the impedance matching and the multiple loss mechanisms were investigated in detail. The results provide valuable guidance for fabricating hierarchical structures with high microwave absorption performance.

A rational construction of TiO2/N-doped Carbon/NiMoO4 composites with multidimensional structure towards strong microwave absorption

Designing hierarchical structure composite is a promising approach to overcome impedance mismatching, enrich energy loss, and acquire high microwave absorption (MA) capacity. However, obtaining stable hierarchical structure composite still remains difficulty due to the lack of precise design and uncontrolled growth. Herein, one dimensional (1D) TiO2 nanobelts coated by N-doped carbon and two-dimensional (2D) NiMoO4 nanosheets (TiO2/NC/NiMoO4) were prepared and exhibited excellent MA ability, and the minimum reflection loss (RLmin) value of it reached − 41.1 dB at 15.1 GHz with a thickness of 3.1 mm. The outer 2D NiMoO4 and porous NC provided good impedance matching and dielectric loss, and multiple scattering behavior were introduced into the system. The 1D TiO2 offered strong anisotropy and dielectric loss. Therefore, the excellent MA performance attributed to good impedance matching, strong dielectric loss, and more interfacial polarization from the unique 1D/2D hierarchical structure.

Facile preparation of C/MnO/Co nanocomposite fibers for High-Performance microwave absorption

The C/MnO/Co nanocomposite fibers were prepared via a facile electrospinning and subsequent carbonization process. Co acting as the magnetic nanoparticles and MnO nanoparticles serving as impedance modulator were introduced, effectively inhibiting the agglomeration of carbon fibers during annealing. This optimizes the microstructure and significantly improves the microwave absorption performance of the nanocomposites with diameters of 250–350 nm and rough surface morphologies. The nanocomposite fibers with equal MnO and Co molar contents exhibited the minimum reflection loss of − 71.7 dB at a frequency of 14.1 GHz and an absorber thickness of 2.3 mm, and the effective absorption bandwidth reached at 6.3 GHz at a thickness of 2.6 mm. The high microwave absorption performance can be attributed to the synergistic coactions of conduction loss, magnetic loss, interfacial polarization, and multiple scatterings derived from the rational design of the constituents and microstructure of the nanocomposites.

High Mechanical Properties and Microwave Absorption Performances of Sicw/S3n4 Ceramic Composites

High Mechanical Properties and Microwave Absorption Performances of Sicw/S3n4 Ceramic Composites

Double Layer Metal Selenides Growing on the Ni-Plated Cfs Towards High Efficiency Microwave Absorption

Double Layer Metal Selenides Growing on the Ni-Plated Cfs Towards High Efficiency Microwave Absorption

Investigating microwave absorption properties of cnf-ferric oxide nanocomposite

Microwave absorbing materials plays a crucial role in reducing pollution created due to the electromagnetic radiation and several defence applications. This paper reports about the microwave absorption property of combined form of Carbon Nano fibres (CNF) and Ferric Oxide Nano powder (Fe2O3). Ferric Oxide Nano powder is deposited on the fibres of CNF using hydrothermal autoclave method. The samples of CNF- Ferric Oxide Nano powder with different weight percentages is fabricated and the microstructure and microwave absorbing properties are studied. By varying the amount of CNF and Ferric Oxide Nano powder the microwave absorbing and electromagnetic properties are modulated. For investigating the synergistic effects between CNF and ferric powders, different mass ratios of CNF to ferric oxide Nano powder have been synthesized and helped in enhancement of the effect between the magnetic loss and dielectric loss to achieve high microwave absorption. These results might be inspiration for the future to create microwave absorbing materials which are light weight.

Facile synthesis of a hierarchical multi-layered CNT-NiFe2O4@MnO2 composite with enhanced microwave absorbing performance

The assembly of magnetic and dielectric materials around carbon nanotubes (CNTs) can create specific microstructures, leading to materials with relatively high microwave absorbing properties. Here, through a facile process, nickel iron oxide (NiFe2O4) is synthesized and placed on the surface of CNTs and this material is covered with manganese oxide (MnO2). In this hierarchical multi-layered nanomaterial (CNT-NiFe2O4@MnO2) produced though a two-step wet chemistry method followed by calcination at 200 ℃, CNTs are uniformly covered by NiFe2O4 nanoparticles formed in situ over which the MnO2 layer is deposited. Although CNT-NiFe2O4@MnO2 exhibits weaker soft magnetic performance, its magnetic attenuation is higher than for CNT-NiFe2O4. Structural effects produce differences between the constant and alternating magnetic properties of these materials. With a reflection loss (RL) of −17 dB and effective absorption bandwidth of 3.8 GHz, the microwave absorption of CNT-NiFe2O4@MnO2 is superior to that of CNTs and CNT-NiFe2O4. The hierarchical multi-layered structure increases the phase interface area and rearranges magnetic particles, leading respectively to higher interface polarization and natural resonance. The conductive mesh structure induces magnetic coupling which attenuates the electromagnetic field. This material employs a new approach to design and synthesize carbon-based hierarchical multi-layered microstructures with high microwave absorption.

Porous carbon black-polymer composites for volatile organic compound adsorption and efficient microwave-assisted desorption

Adsorbents with high surface area, thermal stability and microwave absorption ability are highly desired for cyclic adsorption and microwave regeneration processes. However, most polymeric adsorbents are transparent to microwaves. Herein, porous hyper-crosslinked polymers (HCP) of (4,4′-bis((chloromethyl)-1,1′-biphenyl-benzyl chloride)) with different carbon black (CB) contents were synthesized via the Friedel-Crafts reaction. CB was selected as the filler due to its low cost and high dielectric loss and was embedded inside the polymer structure during polymerization. CB-containing composites showed enhanced thermal stability at elevated temperatures, and more than a 90-times increase in the dielectric loss factor, which is favorable for microwave regeneration. Nitrogen physisorption analysis by the Bruner-Emmett-Teller isotherms demonstrated that CB presence in the polymer structure nonlinearly decreases the surface area and total pore volume (by 38% and 26%, respectively at the highest CB load). Based on the characterization testing, 4 wt% of CB was found to be an optimum filler content, having the highest MW absorption and minimal effect on the adsorbent porosity. HCP with 4 wt% CB allowed a substantial increase in the desorption temperature and yielded more than a 450% enhancement in the desorption efficiency compared to HCP without CB.

Confinedly implanting Fe3O4 nanoclusters on MoS2 nanosheets to tailor electromagnetic properties for excellent multi-bands microwave absorption

High efficiency microwave absorption (MA) materials with tunable electromagnetic (EM) features have been highly sought. However, it is still a challenge to achieve multi-bands absorption performance by simple optimizing the chemical composition of MA materials. Herein, a simple solvothermal method was used to embed magnetic Fe3O4 nanoclusters on MoS2 nanosheets, in which magnetic nanoclusters were quantitatively customized. More importantly, the MA frequency and MA properties of the material are highly tailored, and multi-bands absorption is achieved. The minimum reflection loss (RL) of Fe3O4/MoS2 composite reaches −87.24 dB and is about 4 times more than pure MoS2 nanosheets. The effective absorption bandwidth reaches 5.52 GHz (≤-10 dB). These desirable properties result from the introduction of appropriate magnetic Fe3O4 nanoclusters, which provide optimal synergistic effect of dielectric and magnetic losses. This result provides a feasible idea for designing high efficiency MA materials with tunable EM features in the future.

Configuration of Multifunctional Polyimide/Graphene/Fe3O4 Hybrid Aerogel-Based Phase-Change Composite Films for Electromagnetic and Infrared Bi-Stealth.

Electromagnetic (EM) and infrared (IR) stealth play an important role in the development of military technology and the defense industry. This study focused on developing a new type of multifunctional composite film based on polyimide (PI)/graphene/Fe3O4 hybrid aerogel and polyethylene glycol (PEG) as a phase change material (PCM) for EM and IR bi-stealth applications. The composite films were successfully fabricated by constructing a series of PI-based hybrid aerogels containing different contents of graphene nanosheets and Fe3O4 nanoparticles through prepolymerizaton, film casting, freeze-drying, and thermal imidization, followed by loading molten PEG through vacuum impregnation. The construction of PI/graphene/Fe3O4 hybrid aerogel films provides a robust, flexible, and microwave-absorption-functionalized support material for PEG. The resultant multifunctional composite films not only exhibit high microwave absorption effectiveness across a broad frequency range, but also show a good ability to implement thermal management and temperature regulation under a high latent-heat capacity of over 158 J/g. Most of all, the multifunctional composite films present a wideband absorption capability at 7.0–16.5 GHz and a minimum reflection loss of −38.5 dB. This results in excellent EM and IR bi-stealth performance through the effective wideband microwave absorption of graphene/Fe3O4 component and the thermal buffer of PEG. This study offers a new strategy for the design and development of high-performance and lightweight EM–IR bi-stealth materials to meet the requirement of stealth and camouflage applications in military equipment and defense engineering.

Facile synthesis of MOF-derived concave cube nanocomposite by self-templated toward lightweight and wideband microwave absorption

The green and facile strategy of producing high efficiency microwave absorption materials (MAMs) has attracted wide attention, but remains a challenge. In this work, polydopamine (PDA) was used as carbon source and nitrogen source, polyvinylpyrrolidone (PVP) was used as protective layer and dispersant, and nanoparticles with concave cube morphology were prepared by self-template eco-friendly method. By adjusting the addition amount of PDA and PVP, the MOF derived materials with three morphologies of pure ZIF-67 nanoparticles, core-shell adhesion cube and concave cube can be precisely controlled. Compared with the other two kinds of absorbers, the sample with concave cube morphology shows excellent electromagnetic wave absorption (EMA) performance. Furthermore, the excellent EMA performance comes from the efficient electron transport channel with unique concave cube morphology, multi-interface polarization process and Co nanoparticles high impedance matching. The analysis demonstrates that when the filling ratio of the concave cube sample is 15%, its effective absorption bandwidth is 5.97 GHz, which can basically cover the Ku band (12.0–18.0 GHz), and the corresponding thickness is 1.88 mm. Our research provides a meritorious approach for the design and preparation of high efficiency MAMs by considering the effects of the morphology and filling ratio of the absorber comprehensively.

High microwave absorption performance in Nd-substituted BaM/GO through sol-gel and high energy ball milling process

In this paper, a series of compound materials with different proportions of rare earth neodymium (Nd) doped M-type barium ferrite (BaM) and the mixture Nd-BaM with graphene oxide (GO) are prepared through the sol-gel method and high-energy ball milling route. The surface morphology, composition and electromagnetic properties of those materials are analyzed through XRD, SEM, TG, Raman and the vector network analyzer. It is found that the Nd-BaM particle is adhered on the surface of GO with the nanometer size. The electromagnetic performance can be severely affected by the doping amounts of Nd and the blending amounts of GO. Moreover, the microwave absorption performance of the compounds is studied in the frequency range of 2–18 GHz. For Nd0.15-BaM/3%GO, the minimum reflection loss is − 82.07 dB at 12.65 GHz and the scope of the effective absorption band is 6.08 GHz with a thickness of 2 mm. Because of its good impedance matching, the interface polarization and electron polarization between Nd-BaM and GO, the electromagnetic wave occurs multiple reflection in this material. Compared with pure BaM or BaM/GO, the Nd substituted BaM/GO has excellent microwave absorption performance, which has a certain prospect in the microwave absorbing field.

Flexible reduced graphene oxide@Fe3O4/silicone rubber composites for enhanced microwave absorption

Reduced graphene oxide@Fe3O4 (rGO@Fe3O4) nanocomposites were developed via a facile thermal decomposition method, which were subsequently incorporated into silicone rubber (SR) matrix to fabricate flexible rGO@Fe3O4/SR composites through mold pressing, followed by curing. The in situ grown Fe3O4 nanoparticles on the rGO sheets endowed the rGO@Fe3O4/SR composites with magnetic properties and provided heterogeneous interface, which led to better impedance matching, enhanced magnetic loss and interfacial polarization loss. Under synergistic effect between dielectric loss and magnetic loss, the rGO@Fe3O4/SR composites exhibited high microwave absorption efficiency and wide absorption bandwidth. The minimum reflection loss value reached −59.4 dB at the frequency of 8.0 GHz, and the absorption bandwidth was 4.2 GHz at a thin layer of 1.2 mm. The rGO@Fe3O4/SR composites also showed excellent thermal conduction ability, which enabled fast dissipation of the heat generated by absorbing the microwave energy. The features of strong absorption, broad absorption bandwidth, high flexibility, small thickness, and excellent heat dissipation make the rGO@Fe3O4/SR composites promising microwave absorption candidates for aerospace and flexible electronics.

FeCo/ZnO Composite Nanofibers for Broadband and High Efficiency Microwave Absorption

AbstractIn this work, a novel nanofibrous absorber composed of FeCo alloy and ZnO nanoparticles (denoted as FeCo/ZnO NFs) is fabricated through electrospinning and subsequent calcination and hydrogen reduction. Benefiting from the advantages of their unique 1D and derived 3D network hierarchical structure, as well as the good synergistic effect between magnetic FeCo alloy and dielectric ZnO within the 1D nanospace, the present FeCo/ZnO NFs exhibit outstanding microwave absorption properties with an optimal reflection loss value of −83.4 dB and an effective absorption bandwidth of 8 GHz (10.0–18 GHz) at a small coating thickness of only 1.3 mm. Such performance is remarkably superior to those of many previously reported magnetic ZnO‐based absorbers, highlighting the great application potential of FeCo/ZnO NFs in the field of microwave absorption.