Microwave Absorption Efficiency Research Articles

Ultralight Three-Layer Gradient-Structured MXene/ Reduced Graphene Oxide Composite Aerogels with Broadband Microwave Absorption and Dynamic Infrared Camouflage.

Infrared and radar detectors posed substantial challenges to weapon equipment and personnel due to their continuous surveillance and reconnaissance capabilities. Traditional single-band stealth devices are insufficient for dual-band detection in both infrared and microwave bands. To overcome this limitation, a gradient-structured MXene/reduced graphene oxide (rGO) composite aerogel (GMXrGA) is fabricated through a two-step bidirectional freeze casting process, followed by freeze-drying and thermal annealing. GMXrGAexhibits a distinct three-layered structure, with each layer playing a crucial role in microwave absorption. This deliberate design amplifies both the efficiency of microwave absorption and the material's effectiveness in dynamic infrared camouflage. GMXrGA displays an ultralow density of 5.2 mg∙cm-3 and demonstrates exceptional resistance to compression, enduring 200 cycles at a maximum strain of 80%. Moreover, it shows superior microwave absorption performance, with a minimum reflection loss (RLmin) of -60.1dB at a broad effective absorption bandwidth (EAB) of 14.1GHz (3.9-18.0GHz). Additionally, the aerogel exhibits low thermal conductivity (≈26 mW∙m-1∙K-1) and displays dynamic infrared camouflage capabilities within the temperature range of 50-120°C, achieving rapid concealment within 30 s. Consequently, they hold great potential for diverse applications, including intelligent buildings, wearable electronics, and weapon equipment.

Unveiling the microwave heating performance of biochar as microwave absorber for microwave-assisted pyrolysis technology

Microwave (MW) heating has gained significant attention in food industries and biomass-to-biofuels through pyrolysis over conventional heating. However, constraints for promoting MW heating related to the use of different MW absorbers are still a major concern that needs to be investigated. The present study was conducted to explore the MW heating performance of biochar as a low-cost MW absorber for performing pyrolysis. Experiments were performed on biochar under different biochar dosing (25 g, 37.5 g, 50 g), MW power (400 W, 700 W, 1000 W), and particle sizes (6 mm, 8 mm, 10 mm). Results showed that MW power and biochar dosing significantly impacted average heating rate (AHR) from 17.5 to 65.4 °C/min at 400 W and 1000 W at 50 g. AHR first increased, and then no significant changes were obtained, from 37.5 to 50 g. AHR was examined by full factorial design, with 94.6% fitting actual data with predicted data. The model suggested that the particle size of biochar influenced less on AHR. Furthermore, microwave absorption efficiency and biochar weight loss were investigated, and microwave absorption efficiency decreased as MW power increased, which means 17.16% of microwave absorption efficiency was achieved at 400 W rather than 700 W and 1000 W. Biochar weight loss estimated by employing mass-balance analysis, 2–10.4% change in biochar weight loss was obtained owing to higher heating rates at higher powers and biochar dosing.

Periodic magnetically oriented gradient structures with flower-like surface for enhancing microwave absorption efficiency

In order to overcome the inherent trade-off between magnetic absorber's effective absorption, filling concentration, and thickness while achieving real-time control over the effective absorption bandwidth (EAB) below −10 dB, periodic magnetically oriented gradient structures featuring flower-like surfaces that can be reconfigured using magnetic induction technology. The arch test results demonstrated that even with particle filling concentration of only 30 wt%, reflection loss (RL) of the magnetically oriented periodic gradient structures achieved −37.5 dB, and EAB could be extended to 6.5 GHz, outperforming samples 60 wt%–0 mT. Especially for samples 50 wt%–100 mT, which EAB with four distinct peaks in its EAB reaching 10.5 GHz. This was due to magnetically-oriented macro–micro structure that facilitated to reduce hyperosmotic threshold of conductive loss network of absorbing material. Meanwhile, the gradient structure with flower-like surface was conducive to absorption peaks, impedance matching patterns and electromagnetic wave scattering. The reconfigurable structure was also found to have remarkably stability, maintaining its nearly uniform electromagnetic loss capability even after 3 months. This study is scientifically important for establishing the regulatory mechanism of orientation distribution structure on EAB and absorption resonance peaks, as well as providing an experimental and theoretical foundation for exploring low detectable and electromagnetic protection devices.

Investigation on the temperature distribution characteristics of steel slag asphalt mixture under different microwave heating and cooling methods

The utilization of steel slag aggregate (SSA) can enhance the microwave absorption efficiency of asphalt mixture, thus increasing its temperature and self-healing capability. In this study, the temperature distribution of basalt porous asphalt concrete (PAC-B), ordinary steel slag porous asphalt concrete (PAC-US), and modified steel slag porous asphalt concrete (PAC-MS) under the influence of different microwave heating and cooling methods were investigated through laboratory tests and numerical simulations. The heating methods including continuous heating, and two intermittent heating methods were used. Using the Monte Carlo method, three-dimensional mesoscopic numerical models were developed to simulate the microwave heating and cooling processes. The temperature of both the aggregates and asphalt mortar were analyzed, considering the influence of particle size on the aggregate temperature. The results revealed that the average inner heating rate of the three specimens is higher than the average surface heating rate. The average surface and inner heating rates of PAC-MS were higher than those of PAC-US and PAC-B. The average surface temperature and inner temperature during the heating process changed linearly, while nonlinear temperature variations were observed during the subsequent cooling phase. Increasing the number of cooling intervals during heating resulted in a more uniform temperature distribution within steel slag aggregate specimens. The results of numerical simulation indicated that the maximum temperature of aggregate was greater than that of asphalt mortar. During the cooling process, the highest temperature of the aggregate continuously decreased, whereas the lowest temperature initially increased before decreasing. The highest average volume temperature for various particle sizes was observed within the range of 4.75–9.5 mm. The laboratory test results were effectively validated by the numerical simulations.

Broadband, thin thickness and low filling ratio microwave absorption by constructing Sm2Fe17/Fe(Sm) hard/soft magnetic nanoparticles in Sm2O3-doped porous carbon matrix

Exchange-coupled hard/soft magnetic composites are supposed to be promising microwave absorber, due to the multiple-resonance peaks in permeability. However, due to insufficient magnetization and dielectric loss, soft/hard ferrite magnets are difficult to achieve further breakthroughs in microwave absorption performance. In this work, the special hard/soft magnetic composites are successfully fabricated, in which Sm2Fe17/Fe(Sm) hard/soft hybrid nanoparticles are embedded in ∼5 nm Sm2O3-doped porous carbon matrix. The hard/soft magnetic exchange-coupling result in the multiple-resonance peaks beyond Snoek’s limitation at broad wave band and the Sm2O3-doped carbon supplements dielectric loss capacity. Multiple-resonance effect is modified by adjusting the ratio of hard and soft magnetic components and the dielectric loss capacity is supplemented by Sm2O3-doped carbon. Herein, the hard/soft magnetic exchange-coupling and dielectric matrix are dexterously integrated to achieve broad absorption band with thin matching thickness and low filling ratio. By varying the ratio of Fe3+/Sm3+ in raw material, 20 wt% Sm2Fe17/Fe(Sm)-paraffin composites can reach the maximum effective absorption bandwidth of 6.8 GHz with matching thickness of 1.6 mm, the minimal reflection loss of −47.15 dB with 1.5 mm and the optimal microwave absorption efficiency of 71.1 dB·GHz/mm with 1.4 mm. Overall, this work provides a simple approach to introduce multi-resonance effect, which broadens the path for advanced absorbers with broad band and thin thickness and low filling ratio.

Constructing honeycomb structured metastructure absorber based on FeSiAl@CeO2 flakes for ultra-broadband microwave absorption

Due to the limitations of the Kramers-Kronig relationship, how to achieve ultra-wide effective absorption bandwidth remains a challenge for typical magnetic-dielectric absorbers. In the present work, we have explored the possibility of obtaining ultra-wide absorption bandwidth in FeSiAl composites with help of efficient electromagnetic (EM) simulation software-Computer Simulation Technology (CST). Flaky FeSiAl powders covered by CeO2 have been prepared, in which EM parameters can be tuned by filling ratio of FeSiAl/CeO2 in FeSiAl/CeO2-paraffin composites. The filling ratio has an effect on impedance matching and EM parameters by the arrangement of particles in the paraffin. The composite with 30 wt% flaky FeSiAl/CeO2 achieves an effective absorption bandwidth (EAB) of 6.48 GHz and the optimal microwave absorption efficiency of 1499.3 dB GHz/(wt%⋅m) at 1.9 mm. Integrated with a macroscale honeycomb structural design, the FeSiAl/CeO2 composites based metastructure exhibits broadband microwave absorption with an EAB of 14.224 GHz covering from 3.776 GHz to 18 GHz and reflection loss of-65.61 dB at 8.5 GHz. The excellent performances of the designed absorber are ascribed to multiple loss by integrating EM parameters of flaky FeSiAl/CeO2 and the geometry parameters of honeycomb metasrtucture. The present work makes flaky FeSiAl/CeO2 composites possible to achieve broadband microwave absorption.

Strong microwave absorption performance of simply grinding FAPbI3/CNTs composite absorbers

The distinctive physical and chemical characteristics of organic-inorganic lead halide perovskite make it a promising candidate for microwave absorption applications. However, the high-efficiency microwave absorption of halide perovskite-based composites is concentrated at high frequencies, while electronic equipment operates at low-frequency bands. Exploring simple and efficient methods to achieve optimal microwave absorption efficiency at low frequencies continues to pose a considerable challenge. Here, FAPbI3 was synthesized by a simple solvent-free hand grinding method and mixed with carbon nanotubes (CNTs) to obtain a series of FAPbI3/CNTs (FC) composites. By modulating the mass ratio of the components, FAPbI3 modulates the absorption bands, CNTs can effectively establish a conductive network to enhance both polarization loss and conductive loss and regulate impedance matching. The lower permittivity of FAPbI3 gives FC an advantage in terms of low-frequency microwave absorption. The FC-4 composite exhibits a minimum reflection loss (RLmin) of −55.67 dB at a low frequency of 6.88 GHz with a thickness of 3.5 mm. Meanwhile, microwave absorption performance can reach 99 % covering almost the entire C band when utilizing a thickness ranging from 3 to 5 mm. Additionally, according to adjusting the load of FAPbI3 in the mixture, the FC-3 composite displays the highest microwave absorption value among the composites based on halide perovskites. With a thickness of 1.4 mm, the reflection loss at 17.4 GHz reaches an impressive minimum value of −71.89 dB. This study represents the first research specifically focused on FAPbI3 perovskite in the domain of microwave absorption. FC composites display remarkable capabilities in absorbing microwaves, indicating their promising prospects for advancement within the realm of microwave absorption. This research may provide valuable insights for the design of low-frequency and high-efficiency microwave absorbers.

Electrostatically self-assembled Fe3O4@SiO2/MXene 3D interlayered structure improves Ku-band microwave absorption efficiency of epoxy-based nanocomposites

It is challenging to develop lightweight and efficient frequency-selective microwave absorption materials due to the trade-off between impedance matching and microwave attenuation ability. This study proposes a multiple heterointerfaces engineering strategy via electrostatically assembling to construct Fe3O4@SiO2/MXene 3D interlayer structure, which fully exerted the synergistic effect of dielectric-magnetic components. The 3D interlayer heterostructure achieves good impedance matching due to electromagnetic coupling and extended microwave propagation path. Simultaneously, massive charge transfer and redistribution at multiple heterointerfaces embedded in this structure boost the polarization relaxation and dielectric loss ability. Consequently, the prepared nanocomposites exhibit remarkable Ku-band microwave absorption efficiency (−60.9 dB at a thickness of 1.0 mm), and have demonstrated valid practicality via Tesla wireless transmission shielding experiments. This study opens exciting possibilities for progress in the structural design, facile preparation and practical application of high-performance Ku-band microwave absorption materials.

Strategies toward processing high-efficient MWCNTs/AgBr/PTs -co-PQ nanocomposite coupling for X-band stealth application

There is a pressing desire for the development of ideal microwave absorption materials to tackle the escalating issue of electromagnetic interference (EMI) in electronic gadgets. So, EMI absorption material is an urgent requirement at the present time. Herein, a novel composite, MWCNTs enwrapped with AgBr and Poly(Thiophene-co-Quinoxaline), has been successfully synthesized to study absorption properties in X-bnad frequency range. The primary objective of this study is to increase the microwave absorption performance of composites by regulating their attenuation constant and impedance matching. The improved microwave absorption efficiency of MWCNTs/AgBr/Poly(Thiophene-co-Quinoxaline) has been achieved by using various filler contents. The optimal sample achieves RLmini of −54 dB with EAB of 2.2 GHz. As a result, the developed nanocomposites could be used in the field of microwave absorption.

Nano-lithium ferrite/nanosilica-filled butadiene-acrylonitrile rubber for microwave absorption

Recently, the development of flexible and lightweight microwave-absorbing materials has become a trendy topic. Hence, the principal aim of this work is to enhance the microwave-absorbing performance of butadiene-acrylonitrile rubber (NBR) by incorporating novel reinforcing nanofillers. Cost-effective nano-lithium ferrite/nanosilica is synthesized via the precipitation of two thin layers of lithium ferrite with thicknesses of 10 and 20 % on the surface of cheap nanosilica extracted from rice husk agro-waste. To achieve optimal microwave-absorbing performance, both LiFe 10 %/Si and LiFe 20 %/Si NPs were incorporated into the NBR matrix at various loadings (2, 4, 8, and 16 parts per hundred rubber (phr)). Several investigations were performed on the NBR nanocomposites to explore their morphology, curing behavior, mechanical, equilibrium swelling, magnetic properties, and microwave-absorbing behavior. The mechanical characteristics of NBR nanocomposites reveal that the inclusion of LiFe/Si NPs enhanced their modulus, tensile strength, and elongation at break while reducing their hardness. Moreover, the obtained findings clarify that the 16 phr (LiFe 20 %/Si) filled-NBR nanocomposite has superior microwave-absorbing performance with a maximum absorption bandwidth of 2.2 GHz. Overall results reveal that the novel lithium ferrite/silica nanoparticles could be an effective filler for enhancing the microwave absorption efficiency of NBR nanocomposites. Thus, this research suggests a novel viewpoint on the fabrication of flexible microwave-absorbing materials.

Charge Dynamics Engineering Sparks Hetero-Interfacial Polarization for an Ultra-Efficient Microwave Absorber with Mechanical Robustness.

Microwave absorbers with high efficiency and mechanical robustness are urgently desired to cope with more complex and harsh application scenarios. However, manipulating the trade-off between microwave absorption performance and mechanical properties is seldom realized in microwave absorbers. Here, a chemistry-tailored charge dynamic engineering strategy is proposed for sparking hetero-interfacial polarization and thus coordinating microwave attenuation ability with the interfacial bonding, endowing polymer-based composites with microwave absorption efficiency and mechanical toughness. The absorber designed by this new conceptual approach exhibits remarkable Ku-band microwave absorption efficiency (-55.3dB at a thickness of 1.5mm) and satisfactory effective absorption bandwidth (5.0GHz) as well as desirable interfacial shear strength (97.5MPa). The calculated differential charge density depicts the uneven distribution of space charge and the intense hetero-interfacial polarization, clarifying the structure-performance relationship from a theoretical perspective. This work breaks through traditional single performance-oriented design methods and ushers a new direction for next-generation microwave absorbers.

Soft matter with magnetically oriented macro - micro structure for improving microwave absorption efficiency

The key challenge for the most widely used magnetic absorbers is how to simultaneously combine low filling with efficient electromagnetic absorption performance. This paper exploited carbonyl iron particles (CIPs) to develop some soft material that possessed orderly orientated structure via applying an external excitation signal, so as to reduce hyperosmotic threshold of conductive loss network, improve impedance matching pattern and thus modulate absorption efficiency. The arch test results showed that effective absorption band (EAB, RL<−10 dB) and reflection loss (RL) efficiency of oriented structure (40 wt%−300mT sample) was much higher than that of unoriented structure (60 wt%−0mT sample), and the reflection loss intensity was reduced to − 15.2 dB, especially EAB was expanded by 8.1 GHz, which significantly alleviated the critical conflict between low filling and electromagnetic loss performance. Also, it was attempted to reveal surface topography changes caused by multiple magnetized particles interaction, and how excitation signal intensity, magnetic particles filling concentration and structural parameters affect microwave absorption efficiency and bi-directional frequency conversion. Thus, a magnetic-manipulated absorbing material proposed laid a theoretical foundation for improving loss efficiency of magnetic materials at low filling concentration.

Controllable synthesis and enhanced microwave absorption properties of hexagonal boron nitride@polyaniline composite

Nowadays, electromagnetic pollution caused by electronic devices is gradually becoming a concern. Moreover, as the frequency of electromagnetic pollution from electronic devices is mainly in the range of 2–10 GHz, the design of microwave-absorbing materials for this frequency range has become a hot issue. To tackle the issue, core-shell structured hexagonal boron nitride (h-BN) @polyaniline (PAn) composites have been proposed to construct heterogeneous microwave-absorbing materials. Firstly, the h-BN is exfoliated, and hydroxyl functionalized to produce hydroxy boron nitride (OH-BN), which enhances its polarization ability by structuring defects and adding functional groups to improve its microwave absorption efficiency. Afterward, PAn was grafted on the OH-BN surface by in situ polymerization. The microwave absorption properties of OH-BN@PAn composites can be tuned by modulating the doping of PAn. As expected, the OH-BN@PAn composite exhibits superior microwave absorption properties with the minimum reflection loss (RLmin) value of −38.60 dB at 3.5 mm and an effective absorption bandwidth (EAB) of 3.4 GHz (6.24–8.64 GHz) at pH = 2. Also, the composite achieves effective microwave absorption at 3.76–18 GHz by adjusting the matching thickness. Notably, the RLmin value of OH-BN@PAn was successfully tuned from the high-frequency region (12.4 GHz, pH = 0) to the low-frequency region (7.28 GHz, pH = 2) by adjusting the doping degree. In addition, the RL value and EAB width have been increased due to the increased impedance matching and polarization capability. This work can provide a reference for constructing composite microwave-absorbing materials and regulating microwave absorption performance.

Tunable and efficient electromagnetic wave absorption of carbon material modulating magnetic ionic polymer-based composites

Developing the miniaturization and intellectualization of carbon-based chips and electronic devices is extremely desirable but remains hampered by electromagnetic interference. Magnetic ionic polymer (MIP) holds great promise for electromagnetic-absorbing material in the field of electromagnetic reliability of communication equipment due to its dielectric loss and magnetic loss are obviously higher than other commonly polymers. However, it remains a formidable challenge for MIP to achieve satisfactory absorption of electromagnetic wave (EMW). Herein, we achieved the excellent EMW absorbing performance of the poly[1-allyl-3-vinylimidazolium tetrachloroferrate]/carbon nanotube/reduced graphene oxide (P[AVIm][FeCl4]/CNT/rGO) composites when the only carbon materials loading of 10 wt%. Most strikingly, the effective absorption bandwidth (EAB) is as wide as 5.63 GHz, the lowest reflection loss can reach up to −51.05 dB with the absorber thickness of 2.2 mm. The enhancement in microwave absorption efficiency of P[AVIm][FeCl4]/CNT/rGO composites are arisen from the synergistic effects in its unique multicomponent heterostructure interface, which causes multiple reflections and strong conduction loss, further suitable impedance matching ratio and favorable attenuation ability. This work proposes a new perspective approach and fundamental absorption mechanisms to realize excellent performance EMW absorption.

Temperature uniformity optimization with power-frequency coordinated variation in multi-source microwave based on sequential quadratic programming

Abstract The focus of this study is to regulate the variation in the input parameters of multiple microwave sources in a high-frequency multimode resonant heating system to achieve uniform heating. First, this study deeply expands the theoretical process of frequency change and proposes a frequency-shifting strategy with hot spot alternation to ensure that the temperature difference range of each hot spot does not continuously expand during the heating process. Then, a sequential quadratic programming algorithm is introduced to reconstruct the input power values to improve the heating efficiency according to the different microwave absorption efficiencies of the heated material at different frequencies. Finally, a numerical calculation model for multi-source microwave power-frequency cooperative heating is established based on the finite-element method, and the temperature uniformity index is effectively calculated. Numerical calculations show that the proposed method can improve the uniformity in single-material heating and multi-material heating cases by 56.8–94.3% and 44.4–76.6%, respectively, over that of fixed-frequency heating while achieving improved heating efficiency on the basis of frequency conversion.

Optimization design of broadband absorber for high optical transparency

A broadband absorber with high optical transparency is proposed and realized using an optimization-designed method. The absorber’s reflection, lossy, and dielectric layers are considered for obtaining high optical transparency. First, to maintain microwave absorption, the artificial structures of the reflection layer are designed on the micron scale. Low square resistance and high optical transparency are achieved simultaneously. Then, considering the artificial structure fabrication process [fabricated on polyethylene terephthalate (PET)], high light transmittance polymethyl methacrylate (PMMA) was selected as the material of the dielectric layer. The permittivity of PMMA is similar to that of PET. The light reflection of layer-to-layer is reduced, and the light transmittance is improved. Finally, under the same microwave absorption band and absorption efficiency, the topology structures of the lossy layer are optimized to increase the duty ratio and the light transmittance. Through the above-mentioned design, high optical transparency and broadband microwave absorption are achieved simultaneously. The simulated and measured results prove that more than 90% of the absorption rate is obtained from 4.4 to 11.5 GHz (89.3%) and the average light transmittance reached 80%. The results verify the optimization-designed method’s effectiveness and provide technical support for transparent absorbers to be better applied to optical windows.

Investigations of microwave absorption performance of bi-layer absorber composed of FeWO4 & BiVO4 nanocomposite powder in 2–18 GHz

Optimization necessitates every feature to be scrutinized associated with enhancement for microwave absorption. So, interplay between simulation and experiment is a significant aspect to find optimal findings in this regard. Herein, microwave absorption characteristics of as-prepared FeWO4 and BiVO4 nanomaterials were investigated by preparing mono layer and bilayer samples. For the bilayer samples, simulation technique was used to regulate microwave absorption efficiency. Using simulation technique, bilayer sample has achieved a minimum reflection loss (RLmin) of −42 dB with BiVO4 as a top layer (0.6 mm thickness) and FeWO4 as a bottom layer (0.8 mm thickness) with effective absorption Bandwidth (EAB) of 13 GHz (15–2 GHz) at 8.2 GHz frequency. The results show that the layered architecture of the absorbent is substantially responsible for its remarkable microwave absorption efficiency. Simulated results of the bilayer sample were also verified with experimental findings. This work provides a facile synthesis route, novel insights into the design of bilayer absorbent as well as simulation and experimental support for high-performance microwave bilayer absorber.

Tunable Head-Conducting Microwave-Absorbing Multifunctional Composites with Excellent Microwave Absorption, Thermal Conductivity and Mechanical Properties

Developing composite materials with both thermal conductivity and microwave absorption is an effective strategy to solve the problems of heat dissipation burden and microwave radiation interference caused by the development of miniaturization and high performance of portable electronic equipment. However, these properties are not easy to simultaneously implement due to the limitation of single type fillers with a single particle size, inspiring the possibility of realizing multifunctional composites with the introduction of composite fillers. In this work, using alumina (Al2O3) and zinc oxide (ZnO) as head-conducting fillers, carbonyl iron (Fe(CO)5) as microwave-absorbing fillers, silicone rubber (SR) composites (Al2O3/ZnO/Fe(CO)5/SR) with enhanced microwave absorption, high thermal conductivity and good mechanical properties were successfully mass prepared. It was found that the composites can achieve a thermal conductivity of 3.61 W·m−1·K−1, an effective microwave absorption bandwidth of 10.86–15.47 GHz. Especially, there is an effective microwave absorption efficiency of 99% at 12.46–14.27 GHz, which can realize the integration of electromagnetic shielding and heat dissipation. The compact microstructure, formed by the overlapping of large particle size fillers and the filling of their gaps by small particle size fillers, is helpful to enhance the thermal conduction path and weaken the microwave reflection. The heat-conducting microwave-absorbing Al2O3/ZnO/Fe(CO)5/SR composites also have the advantages of thermal stability, lightness and flexibility, providing a certain experimental basis for the research and development of high-performance and diversified composites.

Influence of SiC on the thermal energy transfer and storage characteristics of microwave-absorbing concrete containing magnetite and/or carbonyl iron powder

A microwave-absorbing concrete with favorable heat transfer and storage was investigated to improve the efficiency of deicing concrete pavement during microwave heating and off in cold winter. The concrete was prepared using magnetite and/or carbonyl iron powder (CIP) as the absorbing material. The effect of SiC as the heat transfer and storage material on microwave absorption efficiency, thermal conductivity and thermal diffusivity of concrete were studied. In addition, the pore structures of concrete were investigated to analyze its influence on the thermal properties of concrete.The results showed that the SiC slightly affected the microwave absorption capacity of magnetite concrete (MC) and magnetite-CIP concrete (MCC). The SiC could effectively improve heat transfer and storage ability of concrete. When the content of SiC was 7%, SiC improved the thermal conductivity and effusivity of MC and MCC were improved by 86.4% and 110%, and 84% and 97.3%, respectively. Meanwhile, adding CIP and SiC could improve the porosity and pore diameter of concrete to make it dense, which might be an influence factor to improve the thermal properties of concrete. Under the same conditions, the thermal conductivity and storage capacity of concrete showed the same change trend. In addition, the coefficient of temperature nonuniformity (CTN) and coefficient of max temperature gradient (CMTG) as new indexes was used to evaluate the influence of SiC on the thermal properties of concrete. Therefore, to improve concrete absorption of more heat during microwave heating, and transfer and store heat quickly for road deicing, the magnetite-CIP-SiC concrete (MCSC) might be the most suitable.

Boosting microwave absorption performance of bio-carbon flakes via magneto-alignment

Besides composition, macrostructure of a material is also crucial to its microwave absorption performance. In this work, we demonstrate a magneto-alignment effect on the microwave absorption property of the bio-carbon flakes synthesized from phoenix tree leaves. When a magnetic field is applied, the prepared bio-carbon flakes tended to be aligned into a desired direction due to their diamagnetic feature. Moreover, a rotating magnetic field has a better magneto-alignment effect than a static one, which significantly boosts microwave absorption efficiency. By adjusting parameters, conditions have been optimized, i.e., 10 wt% mass concentration, 760 Gs magnetic field intensity, and 15 rpm rotating speed. At optimized conditions, the maximum reflection loss of −49.7 dB at 6.6 GHz and the maximum effective bandwidth of 4.9 GHz (10.66–15.56 GHz) are achieved. It is discovered that the maximum reflection loss of the sample treated in a rotating magnetic field is 4.6 and 5.85 times higher than that of the sample treated in static and non-magnetic field conditions, respectively. This work provides a simple and environmentally friendly physical route to modify the macroscopical order degree and enhance the microwave absorption performance of carbon materials.