Electromagnetic Parameters Research Articles

MOF-derived N-doped carbon nanocages trap CoP nanoparticles anchored on rGO to modulate dielectric polarization behavior for microwave absorption

In order to gain a deeper insight into the effect of dielectric polarization behavior caused by defects and heterogeneous interfaces on microwave absorption capability, the structure of in situ grown cobalt phosphide in MOF-derived N-doped amorphous carbon nanocages (CoP/NC) anchored on reduced graphene oxide (rGO) sheets was used to control the number of defects and heterogeneous interfaces. The different dielectric polarization behaviors are expressed by the amplitude and range of the polarization relaxation peaks. More defects and heterogeneous interfaces not only cause more intense polarization loss, but also modulate the electromagnetic parameters to improve the impedance matching performance. The CoP/NC@rGO achieves strong absorption of −67.5 dB and absorption bandwidth of 7 GHz with only 4 wt%. First principles calculation shows the formation of interfacial dipole at the CoP-NC heterogeneous interface. This work provides a strategy for regulating microwave absorption properties by defect and heterogeneous interface-controlled polarization behavior.

Graphite/Epoxy-Coated Flaky FeSiCr Powders with Enhanced Microwave Absorption

Flake-shaped FeSiCr (FFSC) material is expected to be a promising microwave absorbent due to its excellent magnetic properties and environmental resistance. By introducing carbon-based materials through suitable coatings, the electromagnetic parameters and energy loss can be tuned to improve the performance of FFSC. A facile solution-blending method was deployed to prepare graphite- and epoxy resin-encapsulated FFSC (FFSC@G/E) powders with a core–shell structure. FFSC@G2000/E showed excellent performance in the X band (8–12 GHz), a minimum reflection loss (RLmin) of −42.77 dB at a thickness of 3 mm and a maximum effective absorption bandwidth (EABmax, RL < −10 dB) that reached 4.55 GHz at a thickness of 2.7 mm. This work provides a route for the production of novel high-performance microwave absorbers.

Absorption-dominated double-layered electromagnetic interference shielding polymer-based nanocomposites: Optimal design and manufacturing

Double-layered electromagnetic interference (EMI) shielding composites having a gradient structure to achieve an efficient EMI shielding effectiveness (SE) with a low electromagnetic wave reflectivity (R) would be highly desired for engineering applications to control secondary electromagnetic pollution. However, it is still challenging to optimize their performance and structure efficiently. In this work, theoretical calculations were conducted on the prepared double-layer shielding polymer composite material using an improved normalized input impedance (NII) method to verify and optimize the structural composition and R-value of the composite material. The R-value of the composite can be calculated iteratively based on the conductivity and electromagnetic parameters of each material layer, and in this way the optimal structural composition to achieve the lowest R-value can be well predicted. Thus, the optimal structural composition to achieve the lowest R value can be well predicted from the theoretical calculation. Suggested by the theoretical calculation, the double-layered waterborne polyacrylate/polydopamine modified reduced graphene oxide/Cu@Ag (WPA/rGO@PDA/Cu@Ag) composite has achieved broadband low-reflectivity. The R values of the resultant WPA/rGO@PDA-20 wt%/Cu@Ag-1.448 mm composite are <0.5 over 8.3–12.4 GHz, implying its broadband low reflection performance while possessing a high EMI shielding effectiveness beyond 44.3 dB. The modified NII method is promising for advancing the practical production and engineering application of multilayered absorption-dominated EMI shielding composites.

Carboxymethyl cellulose-derived porous carbon aerogel decorated with Fe3O4-Fe nanoparticles for tunable microwave absorption

The production of magnetic biomass-derived carbon-based aerogels has made outstanding contributions to green chemistry and sustainable development so as to alleviate the growing electromagnetic pollution problems. In particular, carboxymethyl cellulose (CMC) possessing three-dimensional (3D) porous structure, low density and biodegradability is an effective precursor for the preparation of magnetic carbon aerogels. In this work, lightweight porous Fe3O4-Fe/carbon aerogels (FFCA) were synthesized by depositing magnetic metals on chitosan (CS)-reinforced CMC via a facile and eco-friendly strategy. The 3D porous structure and non-homogeneous conductive network endow the FFCA aerogels with comprehensive properties. Specifically, the introduction of magnetic material and the carbonization process under the temperature gradient result in tunable electromagnetic parameters and good impedance matching, allowing electromagnetic waves to enter the absorber and dissipate as much as possible. For instance, the FFCA prepared at 900 °C exhibits the impressive microwave absorption performance due to the synergistic transition between magnetic permeability and dielectric constant, with the minimum reflection loss of −45.5 dB at 2.6 mm and the effective absorption bandwidth of 3.7 GHz. This work provides an important reference for the design of eco-friendly CMC-based magneto-dielectric synergistic microwave absorption materials.

Nest-like hollow Cu-doped Co/CoO/C microspheres derived from spherical Co-ZIF with controllable microwave absorption performance

Spherical Co-ZIF-derived nest-like hollow Cu-doped Co/CoO/C microspheres are obtained by a high-temperature calcination treatment, where a facile mixing method is used to synthesize the Cu/Co-ZIF precursor. During the carbonization process at high temperatures, carbon nanotubes are in-situ grown on the microspherical surface to form interlinked conduction networks. Adjusting the calcination temperature can effectively control the degree of graphitization, leading to the diverse electromagnetic performance. When the calcination temperature is 700 °C, an optimal microwave absorption (MA) property is obtained for sample S700 at 25 wt% filler loading ratio. Herein, the values of the minimum reflection loss (RLmin) and the effective absorption bandwidth (EAB) attain −52.73 dB at 2.51 mm and 6.16 GHz at 2.31 mm, respectively. Meanwhile, when the filler loading increases to 30 wt%, RLmin and EAB for sample S600 achieve −60.02 dB at 1.59 mm and 5.76 GHz at 1.90 mm, respectively. In fact, the superior electromagnetic parameters are achieved under the comprehensive action of the specific morphology, microstructure and graphitization. Further, the applicable filler loading ratio, appropriate impedance matching and moderate magnetic/dielectric loss of the absorbers are the advantageous factors to improve their MA behavior. Our work offers an effective strategy to synthesize MOF-derived magnetoelectric composites with controllable MA performance, and the as-obtained composites can serve as the ideal microwave absorbers at 2 ∼ 18 GHz frequency range.

Evaluation of magnetic gear parameters for autonomous wind installation with changing wind speed

Purpose. To evaluate the parameters and characteristics of the magnetic gearbox at constant and variable wind speed as part of an autonomous wind power plant. Methodology. Analysis of existing methods of mathematical modeling of magnetic gearboxes. Numerical methods of mathematical modeling based on finite elements. Numerical methods of processing the obtained results. Findings. A two-dimensional field mathematical model has been developed to estimate the parameters and characteristics of the magnetic gearbox at variable and constant wind speed. With the help of the developed model, the electromagnetic field, parameters and characteristics of the magnetic gearbox were analyzed both at a constant and at a variable speed of rotation. In particular, it was found that the magnetic system of the reducer does not reach saturation, while the average values of magnetic induction in the structural elements of the reducer remain within the permissible values for the used materials and grades of steel. The obtained data on the average values of the electromagnetic moments of the outer (high-speed) rotor and the inner rotor make it possible to understand the relationship between them and their influence on the operation of the system. A conclusion was made about the uneven distribution of induction along the middle line in the air gap, which is caused by the presence of a modulator in the design of the reducer. In addition, according to the obtained results, the change in wind speed affects the speed of rotation of the magnetic gearbox and the magnitude of the electromagnetic moments of the high-speed and low-speed rotors. Such information helps to understand the dynamics of system operation under different environmental conditions. The results obtained in the study are important for further improvement of the magnetic reducer design and ensuring more efficient operation of the low-power wind turbine. They can be used to optimize the structure and increase its productivity, which will contribute to the development of wind energy and the green energy industry in general. The average value of the electromagnetic moment of the outer (high-speed) rotor is about 7.4 N∙m, while for the inner rotor the value of the electromagnetic moment is about 66 N∙m. The ratio of the moments of the outer and inner rotors is 8.92, which correlates with the reduction factor of the gear under study. Originality. A two-dimensional field mathematical model has been developed, which takes into account the change in the parameters and characteristics of the magnetic gearbox when the wind speed changes and the random rotation speed of the wind generator rotor. Practical value. The results of the research of the magnetic reducer for a low-power wind turbine have an important contribution to the development of wind energy, contribute to increasing the efficiency and reliability of energy production, and contribute to the creation of a more sustainable and environmentally friendly energy complex.

Efficient microwave absorbing performance of Ni/carbon nanotubes assembled coronal hollow clusters

The development of wide-band microwave absorbing materials based on carbonaceous fillers remains a great challenge. In this study, carbon nanotubes (CNT) assembled coronal hollow clusters with efficient microwave absorbing performance have been obtained through successive hydrothermal and calcination process. Microstructural analysis reveals the distinct features of multiple assembly structures in the fabricated materials. The electromagnetic responses of Ni/CNT assembled clusters were examined across a frequency range of 2–18 GHz. Results demonstrate that the microwave frequency dispersion of electromagnetic parameters and reflection loss of Ni/CNT clusters are strongly influenced by weight loading. Multi-absorbing peaks with reflection loss better than − 40 dB could be achieved, while the equivalent absorbing band for RL< −10 dB covers 3.2–18 GHz, which account for 92.5% of the whole evaluated frequency range, and 62.5% for condition of RL< −20 dB. Furthermore, intrinsic attenuation beyond thickness derived semi-wavelength resonant absorption makes a major contribution to this superior performance. The underlying mechanism of dielectric response was investigated through Cole-Cole analysis and finite element simulation. ‘Micro-dipoles’ relaxation and hopping relaxation originated from defects within CNT and barrier between CNT, while the high magnetic dissipation capability of Ni nanoparticles make a major contribution to overall absorbing performance. All these are beneficial to regulation and optimization of microwave absorption performance of novel Ni/ CNT functionalized multistage architecture.

Geotechnical Deformation Distributed Measuring Technology Research Based on Parallel Spiral Sensing Line.

The precursors that appear when geological disasters occur are geotechnical deformations. This paper studies the TDR (Time Domain Reflection) measurement technology for the distributed measurement of geotechnical deformation using parallel spiral wire as a sensor, which is used for monitoring and early warning detection of geological disasters. Based on the mechanism of the electromagnetic field distribution parameters of the parallel spiral sensing wire, the relationship between the stretching amount of the parallel spiral wire and the change in its characteristic impedance is analyzed. When the parallel spiral wire is buried in the soil, the geotechnical deformation causes the parallel spiral wire to be stretched, and according to its characteristic impedance change, the stretching position and the stretching degree can be obtained, thus realizing the distributed measurement of geotechnical deformation. Based on this principle, the TDR measurement system is developed, and a local single-point stretching amount and stretching positioning experiment are designed for the parallel spiral sensing line to verify the effectiveness of the sensing technology and the usability of the measurement system.

Novel preparation of FeCo alloy/graphene foam composites for efficient microwave absorption

Five groups of FeCo alloy/graphene foam (FeCo/GF) composites with different GF contents (1%, 2%, 3%, 4%, and 5% of the mass of the FeCo alloy) were prepared in this work. The results show that the morphology, saturation magnetization, and electromagnetic parameters of the composites were greatly affected by the GF amount. The reticular porous structure of GF significantly increases the multiple scattering events and loss paths of electromagnetic waves and provides an excellent electric loss. Being a typical soft magnetic material, FeCo exhibits a high saturation magnetization and an excellent magnetic loss. The FeCo/GF composite has excellent microwave absorption properties, which are attributed to its superior dielectric loss, conductive loss, natural resonance, and exchange resonance loss mechanisms. In particular, when the content of GF is 3% of the mass of FeCo alloy, it exhibits the best effective absorption bandwidth. With a matching thickness of only 1.85 mm, this composite achieves a maximum effective absorption bandwidth of 7.2 GHz (10.8–18 GHz). Additionally, when the content of GF is 4% of the mass of FeCo alloy, the sample exhibits the lowest reflection loss, which reaches −61.68 dB at a frequency of 3.44 GHz.

Electric field and SAR distribution in the vicinity of dental implants exposed to the cell phone electromagnetic radiation

PurposeThe purpose of this paper is to determine the electric field and specific absorption rate (SAR) distribution within biological tissues in the vicinity of dental implants, exposed to the mobile phone radiation.Design/methodology/approachThis research was performed for the frequency of 2.6 GHz, which corresponds to 4G mobile network. The adequate 3D realistic numerical models of the mobile phone user’s head, dental implants and actual smartphone model are created using packages based on the finite integral technique numerical method.FindingsThe obtained results yield to a conclusion that the presence of dental implants affects the increase in electric field intensity and SAR values within biological tissues in its vicinity.Research limitations/implicationsThe presented procedure is limited to the 4G mobile network frequency of 2.6 MHz. The study should be extended to other mobile network frequencies to be more general.Practical implicationsThe criteria for selection of the materials used for dental implants production should be extended with the recommended material characteristics related to their influence on the electric field and SAR distribution, to keep their values in the limits prescribed by standards.Social implicationsThe obtained results provide the foundation for future research in mobile devices’ electromagnetic fields’ influence on human health.Originality/valueThe accurate determination of the electric field and SAR values within different biological tissues and organs in the vicinity of dental implants exposed to mobile phone electromagnetic radiation, demands highly realistic model of observed biological structures. For purposes of the current study, the procedure for modeling of highly nonhomogeneous structure with finite number of homogenous domains having known electromagnetic parameters is described in the paper. As a result, the 3D complex users’ head model formed of 16 homogeneous domains of different electromagnetic parameters is created.

In-situ construction of volcanic rock-like structures in Yb2O3 modified reduced graphene oxide and their boosted electromagnetic wave absorbing properties

Creating porous structures is a practical method for enhancing the impedance matching and interfacial polarization of dielectric materials, which in turn leads to improved electromagnetic (EM) wave absorption performance. However, the use of nanoparticles, nanorods, and two-dimensional materials to construct a simple porous structure typically has a minor effect on the EM parameters and interface polarization. To improve impedance matching and reduce the reflection of EM waves while simultaneously enhancing interfacial polarization, a more rational structure for dielectric materials is desired. Herein, a ytterbium oxide/reduced graphene oxide (Yb2O3/rGO) composite with a volcanic rock-like structure is proposed to exhibit outstanding impedance matching and loss capacity and achieve high EM wave performance. The addition of Yb2O3 is utilized to induce the formation of porous structures with varying morphologies. Yb2O3 not only significantly improves the polarization loss but also facilitates volcanic rock-like structure construction, thus improving the EM wave performance. As a result, the Yb2O3/rGO composites with a volcanic rock-like structure exhibit outstanding EM absorption performance, including three-band absorption (C, X, and Ku bands), as evidenced by their minimum reflection loss (RLmin) of −57.2 dB (equivalent to 99.9999% effective absorption) at 11.6 GHz when the matched thickness is 2.1 mm and an effective absorption bandwidth (EAB) of 4.2 GHz. Simulations in the CST microwave studio further validate the benefits of the composite's unique structure, which shows a radar cross-section (RCS) reduction value of up to 38.1 dB m2. This work offers valuable insights for the development of next-generation EM wave absorption materials through the implementation of a well-designed and distinctive structure.

Heterostructured C@Fe3O4@FeSiCr composite absorbing material derived from MIL-88(Fe)@FeSiCr

The C@Fe3O4@FeSiCr composites with carbon-covered heterostructures were obtained by constructing C and Fe3O4 derived from carbonized MIL-88(Fe)@FeSiCr to form heterogeneous interfaces with FeSiCr. The electromagnetic parameters of the composites were regulated by adjusting the compound amount of MIL-88(Fe). The impedance matching performance was optimized, and this further improved the microwave absorbing performance. At a MIL-88(Fe) compound amount of 30 wt%, the composite achieves a minimum reflection loss (RLmin) of –68.07 dB at 4.83 GHz with an absorbing coating thickness of 3.33 mm. In the field of microwave absorbing materials, these results provide valuable guidelines for constructing heterogeneous interface coatings and optimizing the impedance matching properties of soft magnetic alloys materials.

Graphitized-MWCNT/CaCu3Ti4O12 metacomposites for tunable ε′-negative and ε′-near-zero response with enhanced electromagnetic shielding

Metacomposites with extraordinary electromagnetic (EM) parameters recently offered a brand-new strategy for EM shielding, but still suffered from the unclear paradigm and regulation mechanism for ε′-negative and ε′-near-zero response. Herein, we presented an effective paradigm of binary composites consisting of CaCu3Ti4O12 (CCTO) and graphitized-multiwall carbon nanotube (g-MWCNT) which was designed by percolation theory. The ε′ switched from positive to negative with increasing frequency was obtained in g-MWCNT/CCTO composites, which could be explained by electrical dipole resonance of interconnected g-MWCNT clusters. Once the percolated g-MWCNT network is formed, Drude-type ε′-negative response would be obtained due to the low-frequency plasma oscillation. Epsilon-near-zero effect (at ∼385 MHz and ∼135 MHz) were tuned by adjusting g-MWCNT content, which respectively corresponds to the loss peaks. The EM medium of CCTO/g-MWCNT composites with ε′-negative or ε′-near-zero response showed great EM shielding performance at specific frequency region. The g-MWCNT/CCTO metacomposites provide a classical paradigm of ceramic matrix composites for ε′-negative and ε′-near-zero response which will guide the practical application of metacomposites in dielectric ceramics and metamaterials, and promote the next steps in EM shielding field.

The Developed Wave Cancellation Theory Contributing to Understand Wave Absorption Mechanism of ZIF Derivatives with Controllable Electromagnetic Parameters.

How to better understand the influence of electromagnetic parameters on the absorbing properties of electromagnetic wave absorbers (EMAs) is an essential prerequisite for further synthesis and development of high-performance EMAs. In this work, an improved wave cancellation theory is used as a guiding principle to prepare N-doped carbon-coated cobalt nanoparticles (Co@NC) using ZIF-8@ZIF-67 as the precursor, thus enabling controllable electromagnetic parameters by regulating the conduction loss and dipole polarization ability. The Co@NC generated by pyrolysis at 700 °C under H2 atmosphere presents an optimized absorption performance. Benefiting from developed wave cancellation theory, the thickness of the film can be accurately adjusted so that the difference between the amplitude of the reflected and transmitted electromagnetic waves is only 0.001 and the phase difference is 180.05°, thus achieving a minimum reflection loss (RLmin (dB)) of -64.0dB. Meanwhile, a maximum effective absorption bandwidth of 5.4GHz is achieved simultaneously attributing to its most suitable electromagnetic parameters. Accordingly, the current research based on wave cancellation theory significantly contributes to understand the relationships between electromagnetic parameters and wave absorption properties, therefore providing a theoretical insight into the further development of high-performance EMAs.

Research on electromagnetic scattering characteristics of flexible stealth material based on its 3D model

With the widespread adoption of flexible stealth materials (FSMs) in radar stealth application, understanding their electromagnetic scattering information has become increasingly crucial. However, acquiring the electromagnetic scattering properties of FSMs solely through measurement can be challenging. Hence, this study proposes an electromagnetic scattering model for FSMs based on random undulating units formed by sweeping two parabola functions. Specifically, the multi-layer fast multipole method (MLFMM) is applied to calculate the model’s monostatic RCS within 8–12 GHz, enabling a comprehensive analysis of FSM’s electromagnetic scattering characteristics (ESCs). We fabricate an FSM sample for experimental validation and conduct meticulous measurements alongside theoretical calculations. Impressively, the calculated results exhibit relatively good agreement with the measured data, signifying our model’s reliability. Furthermore, by leveraging the proposed model and the MLFMM, we delve into the influence of various electromagnetic parameters, the undulating angle, and the size of undulation units on the ESCs of FSM. Our numerical results demonstrate that the ESCs of FSM exhibit regular variations in response to the changes in these parameters. In addition, we meticulously examine the interaction between electromagnetic waves and the material, further enriching our understanding of the observed results. This research provides valuable references for ESC investigation of flexible stealth material and radar stealth experimental design.

Natural green raw-based Biochar@Co/C composites: Simple water bath synthesis and excellent electromagnetic wave absorption properties

Over the last few years, wave absorbing materials synthesized based on green and eco-friendly natural materials were less studied. Carbon materials derived from natural materials, for example, have a limited absorption performance due to impedance mismatch in electromagnetic wave absorption applications. In this work, composites of MOF derivatives and biochar with strong wave absorbing capability were prepared by biochar and MOF. Biochar was green raw material originated from kapok trees in the school. Then it was compounded with MOF derivatives by pretreatment and water bath to form Biochar@Co/C composites. The effect of annealing temperature on the absorption properties was investigated by varying the annealing temperature. According to the results of the transmission line theory analysis, Biochar@Co/C-700 have RLmin value of −55.22 dB at 5.43 GHz and 3.69 mm. Also, the effective absorption bandwidth EAB can reach 6.37 GHz at 1.94 mm. And the above absorption properties were measured when the filling ratio was only 15 %. Electromagnetic parameter analyses showed that the combination between biochar and MOF derivatives greatly improves the impedance matching of the carbon-based materials, which is a vital factor that enables Biochar@Co/C-700 to have excellent wave-absorbing properties. In addition, the loss mechanism of the complexes to electromagnetic waves was also analyzed and summarized. These results provide a reference path for the preparation of high-performance electromagnetic wave absorption composites from green materials.

Application-Oriented Characterization and Analysis of Core Materials Under Medium-Frequency Condition

In medium-frequency applications, magnetic components generally operate in high-temperature conditions caused by higher power loss and more difficult heat dissipation, which results in changes in their electromagnetic characteristics. In this paper, the application-oriented characterization of the typical core materials, Mn-Zn ferrite and Fe-based nanocrystalline alloy, is comprehensively studied. The magnetic parameters under sinusoidal (5 kHz-50 kHz) and square (10 kHz) excitation from 20°C to 125°C is analyzed detailedly. Combined with the micromagnetic theory, the influence factors of electromagnetic parameters such as permeability and power factor angle are investigated. The loss variation of ferrite with temperature, flux density and frequency is explained by using the energy loss ratio. The proportion of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> and Pdy in total loss with temperature and frequency is compared, and the loss fluctuation of nanocrystalline alloys and ferrite is analyzed. Moreover, the reasonable range of frequency that needs to consider temperature effect in practical applications is suggested. The difference between the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B-H</i> loop bias under asymmetrical square excitation and DC bias conditions is compared and illuminated. The effectiveness and limitation of typical Steinmetz Equations considering the temperature and duty cycle effect are analyzed, and the suggestion of loss calculation is given combined with the material characteristics.

FeNi/C/TiO2 composites derived from [Fe(pz)Ni(CN)4] Hofmann framework and MXene for efficient electromagnetic absorption

Chemical composition and morphological optimization are both effective strategies for constructing excellent electromagnetic wave absorption (EMWA) materials. While efficient EMWA materials derived from both metal-organic frameworks (MOFs) and MXenes have been extensively studied, composites derived from the Hofmann framework with MXene have not been reported. In this study, we employed a Hofmann framework ([Fe(pz)Ni(CN)4], pz = pyrazine) and MXene (Ti3C2Tx) to create new MXene@Hofmann (MH1 and MH2) composites, using a simple co-precipitation method with two different contents of [Fe(pz)Ni(CN)4]. The FeNi/C/TiO2 composites with a multi-layered structure inherited from MXene were prepared by annealing the MXene@Hofmann composites at 500, 600, and 700 °C, resulting in the formation of MH1-500/600/700 and MH2-500/600/700 composites. Their compositions, morphologies, electromagnetic parameters, and EMWA performances were characterized. For the composites with a high [Fe(pz)Ni(CN)4] content, MH2-600 has a minimum reflection loss (RLmin) value of −30.63 dB at a thickness of only 1.8 mm and the broadest effective absorption bandwidth (EAB) of 3.90 GHz at 2.0 mm, while MH2-700 exhibits superior EMWA performance with an RLmin value of −34.34 dB at 1.9 mm and an EAB value of 4.96 GHz at 2.1 mm. Their impressive EMWA performance might be attributed to the synergistic dielectric loss and magnetic loss and also the impedance matching from the reasonable ratio of the magnetic and dielectric components. This work demonstrates an effective strategy for constructing EMWA materials from the Hofmann framework and MXene.

Numerical Analysis of Metals Under The Influence of Electromagnetic Field at Different Current Values

The primary factors of the widespread use of induction melting furnaces are uniform metal and heat distribution due to its mixing features, low alloy losses, excellent temperature and composition control, versatility in processing different materials, the ability to quickly start the process from a cold state when needed, and the absence of air pollution problems. In induction heating, not all sides of the part to be heated receive an equal amount of heat. Only if the part to be heated is of the type that conducts heat very well can all sides of the part be heated close to each other. Induction heating produces high heat on the surface, less on the inner parts, and least on the center of the material. This heating varies depending on the frequency of the current source and the penetration depth. In this study, a model was created in ANSYS numerical analysis program by taking the current, which is one of the electromagnetic and thermal parameters affecting the temperature distribution in the metalic material in induction heating, at different values. In the simulation model created, three-dimensional numerical analysis results of a cylindrical metallic material were obtained. In the simulation program, the power and frequency required for the design of the induction coil and the magnetic permeability, resistivity, heat transfer coefficient of the material and the position of the material in the inductor are determined as boundary conditions. Depending on these variables, the temperature and magnetic field distributions on the material were obtained. In addition to the numerical analysis, a cylindrical metallic material with known properties was placed in a specially manufactured induction coil and the temperature values on the material were measured to verify the numerical analysis. ANSYS modeling results with the same material dimensions, properties, and other parameters used in the experiment, were given and examined in comparison with the experimental results.

Honeycomb-like bamboo powders-derived porous carbon with low filler loading, high-performance microwave absorption

Nowadays, the problem posed by electromagnetic wave pollution to electronic devices and biological systems is of serious concern. To create a microwave absorber, component and structural modulation is crucial. Biomass-derived porous carbon is a potential material for microwave absorption applications due to the characteristics of lightweight, high specific surface area, and significant dielectric loss. In this study, by examining the impact of various KOH concentrations on the pore structure, bamboo powders with an 80-mesh size were used as a raw material to create honeycomb-like bamboo powders-derived porous carbon (BPDPC) materials. The activation mechanism of the BPDPC material is also explained. Based on the electromagnetic parameters, the sample BPDPC-4 impregnated with 4 mol/L KOH has a maximum effective absorption bandwidth (RL ≤ −10 dB) of 4.76 GHz at a matching thickness of 2.0 mm, covering 11.54–16.30 GHz and a minimum reflection loss (RLmin) of −40.99 dB at a matching thickness of 2.2 mm at 5 wt% ultra-low filler loading. Due to polarization loss, conduction loss, and the mutually beneficial effects of multiple electromagnetic wave reflection and scattering, the superior wave absorption performance is explained. This work also serves as a reference for investigating porous carbon generated from biomass.