Electromagnetic Parameters Research Articles

FeCo/PANI composites as electromagnetic shields in the X-band: An understanding of the loss mechanisms

The growing dependence on electronic devices functioning within the microwave frequency range, coupled with the need for miniaturization, has resulted in increased instances of electromagnetic interference (EMI) in such devices. Besides altering device performance, the associated health hazards due to electromagnetic radiations have necessitated the urgency for developing efficient electromagnetic shielding materials. Here, highly magnetic FeCo nanoparticles, approximately 200 nm in diameter, have been used as magnetic filler materials in emeraldine base (PANI – EB) and emeraldine salt (PANI – ES) forms of polyaniline to understand the EMI shielding response in X-band frequency range (8.2–12.4 GHz). Composites using 10 % and 25 % FeCo by weight have been prepared using a physical mixing approach and uniform dispersion within the polymer matrix is ascertained using FE-SEM imaging and EDX elemental maps. Structural and magnetic properties of FeCo remain unaltered after the grind mixing process, as confirmed by XRD and VSM measurements. With the total shielding effectiveness remaining sufficiently low at 2–3 dB in FeCo/PANI – EB, significant enhancement to up to 40 dB is achieved in composites prepared in PANI – ES. Detailed investigations of electromagnetic parameters of the composites reveal the importance of the magnetic filler to achieve an absorption-dominated shielding of electromagnetic waves.

MnFe2O4/Fe3O4/PANI/rGO heterogeneous nanocomposites: Outstanding dual-broadband nano-coating microwave absorbers

In this study, MnFe2O4/Fe3O4/PANI nanocomposites were synthesized via hydrothermal and coprecipitation methods and decorated on reduced graphene oxide (rGO) sheets with three weight ratios (1:1), (2:1), and (3:1) for MnFe2O4/Fe3O4/PANI versus rGO. FESEM images indicate a random distribution of MnFe2O4/Fe3O4 and PANI components on the rGO sheets. The designed superparamagnetic nanocomposites, MnFe2O4/Fe3O4/PANI/rGO, exhibit multi-reflections, strong interfacial polarizations, scattering of incident microwaves, and multiple magnetic resonances, which results in superior absorption performance. This is due to the structural design and distribution of different components providing various interfaces, high specific surface area, and different magnetic and dielectric components. The microwave absorption properties are evaluated in the frequency range of 1–18 GHz (L, S, C, X, and Ku bands), from electromagnetic parameters according to transmission line theory. Our results show that (MnFe2O4/Fe3O4/PANI)/rGO (1:1) presents the highest reflection loss, −108.71 dB, at 17.8 GHz with a thickness of 4.2 mm and bandwidth of 3.2 GHz. Interestingly, (MnFe2O4/Fe3O4/PANI)/rGO (3:1) shows a broad absorption bandwidth of 5.6 GHz for a thickness of only 2.2 mm, having a remarkable reflection loss of −95.52 dB at 17.8 GHz. Our study introduces a novel approach for the successful design and preparation of multi-dimensional graphene-based quaternary nanocomposites compromised from lightweight microwave absorbers, with numerous heterogeneous interfaces and defects resulting from interfacial engineering that have promising potential applications in broadband microwave absorption.

Research on electromagnetic torque and fault parameter identification of pumped storage machine under power generation state based on optimized network parameter method

Because of the complex and frequent multi-operation conditions of pumped storage machine and the difficulty of its numerical analysis, an optimized network parameter method (ONPM) is given to identify the second harmonic electromagnetic torque of large salient-pole generators. Different from the former research which only considers the positive and negative sequence components, the second harmonic electromagnetic torque of pumped storage machine under power generation state is identified in neutral point grounded system, which are displayed by the lumped parameters. Then, in order to test the validity of the theoretical analysis among power generation salient-pole generators, the finite element model of 300 MVA pumped storage machine under power generation is established. Through the comparison and analysis of the finite element result data with the actual experimental data in the steady state of no-load test and short-circuit test, the correctness of the finite element model is completely verified. Finally, in the case of small current asymmetry and large current asymmetry, the second harmonic electromagnetic torques obtained by ONPM and finite element method (FEM) are found respectively, and their relative errors are elaborately displayed. The results display that ONPM can accurately identify the electromagnetic torque parameters which indicate the specific operation and fault state of pumped storage machine under power generation state. This fault parameter identification has practical significance for monitoring and improving the operation state and stability of large salient-pole generator.

Multifunctional ultralight magnetic Fe3O4@SiO2/Ti3C2Tx/rGO aerogel with efficient electromagnetic wave absorption and thermal management properties

The rational and effective fabrication of multicomponent materials, coupled with innovative microstructure design, remains a formidable challenge in achieving efficient electromagnetic wave absorption (EMA) behaviors to meet the requirement of rapid advances in electronics. Herein, a three-dimensional (3D) hierarchically porous Fe3O4/SiO2/Ti3C2Tx MXene/rGO (FSMRG) aerogels were obtained via a directional freeze-drying and subsequent thermal reduction strategy. It has been found that with the filling ratio of 5 wt%, the ultralight FSMRG-2 aerogel (7.42 mg cm−3) exhibits optimal EMA performances with a minimum reflection loss (RLmin) of −76.6 dB, and the corresponding maximal effective absorption bandwidth (EAB) is up to 5.36 GHz covering the frequency ranges from 12.48 GHz to 17.84 GHz. The outstanding EMA performances of FSMRG-2 aerogel can be attributed to the synergy effects from the multicomponent interfacial polarization, multiple loss pathways and favorable impedance matching as evidenced with the electromagnetic parameter analysis. In addition, the FSMRG-2 aerogel also displays excellent hydrophobicity and thermal insulation capabilities, rendering them suitable for application in complicated environments characterized by humid and high-temperature conditions. Therefore, this study presents a reliable and facile strategy for the precise construction of lightweight, efficient and multifunctional EMA materials.

Dynamic model of the functional parameter degradation changes in radio-electronic systems with two non-stationary random components corresponding to two types of noise

Problem statement. The processes of aging and degradation caused by the influence of environmental conditions, leading to changes in the functional parameters of radio-electronic systems, negatively affect the output characteristics and reduce the period of operation. The currently existing model of changes in radio-electronic system parameters, used for individual forecasting by extrapolation, includes only one random component representing various types of noise. At the same time, practical studies shows that the maximum amplitudes of different types of noise change at different rates. Therefore, for a more complete representation of the process of electromagnetic parameter changes over time, it is necessary to develop a model that takes into account this effect. The article discusses this problem using the example of the linear stabilizer output voltage. Goal. The main goal of the research presented in this article is to develop a model of functional parameter degradation that takes into account changes in maximum amplitudes of various types of noise in order to increase the accuracy of individual forecasting and the potential period of the device operation. Results. A generalized model of the electromagnetic parameter changes of the radio-electronic systems with two nonstationary random components characterizing various types of noise is presented. A software implementation of the presented model successfully verified on experimental data. Practical significance. The extended model of the functional parameter changes in radio-electronic systems can be used both in individual forecasting by extrapolation, and in the development of systems with a long period of operation, as well as devices intended for autonomous use. The prospects of using the presented model to simulate changes in functional parameters and determine the possibilities of compensating these changes are shown on the example of a frequency synthesizer with an automatic output power control system.

Electromagnetic wave absorption characteristics of silicon carbide modified concrete applied to protective engineering

Electromagnetic protection measures can effectively prevent electromagnetic waves from harming equipment, facilities, information security and human health. To enhance the electromagnetic wave-absorbing capacity of standard concrete, silicon carbide (SiC) was selected as an absorbing agent to produce wave-absorbing concrete. The influences of SiC content on the electromagnetic reflection loss, electromagnetic parameters, and mechanical properties of concrete were systematically investigated. After 28 days of curing, the concrete sample modified with 10 wt% SiC displays the compressive strength and splitting tensile strength of 36.12 MPa and 3.10 MPa, respectively. And the optimum electromagnetic absorption performance reaches −16.25 dB at 3.37 GHz and the electrical conductivity is 1.55×10−4 S/m. The SiC modified concrete demonstrates the dielectric loss type absorption characteristics. This research provides a practical solution for electromagnetic wave protection, which is expected to be used in both military and civilian applications.

A Novel Low-Density-Biomass-Carbon Composite Coated with Carpet-like and Dandelion-Shaped Rare-Earth-Doped Cobalt Ferrite for Enhanced Microwave Absorption.

A novel low-density composite for the absorption of microwaves was prepared by loading La-doped spinel cobalt ferrite (La-CFO) onto biomass carbon (BC) derived from corn stalks using a hydrothermal method. This composite (La-CFO@BC) not only maintained the advantageous properties of low density and abundant porosity, but also exhibited a unique morphology, with La-CFO displaying a carpet-like structure interspersed with dandelion-shaped particles. The incorporation of La-CFO effectively tuned the electromagnetic parameters of the composite, thereby improving its impedance-matching attributes and its ability to absorb microwave radiation. At a frequency of 12.8 GHz for electromagnetic waves and with a thickness of 2.5 mm, La-CFO@BC demonstrated remarkable performance in microwave absorption, attaining a noteworthy minimum reflection (RLmin) of -53.2 dB and an effective absorption bandwidth (EAB) of 6.4 GHz. Furthermore, by varying the thickness of the La-CFO@BC within the range of 1.0 to 5.5 mm, the EAB could be broadened to 13.8 GHz, covering the entire X-band, the entire Ku-band, and a substantial portion of the C-band. This study demonstrated that La-CFO@BC was a promising alternative for electromagnetic wave attenuation, which offered superior performance in microwave absorption.

Influence Law of Electromagnetic Induction Heating Parameters on the Leveling Effect in Thin Plates

Abstract In order to analyze the influence of electromagnetic induction heating parameters on the leveling effect of thin plates after welding, and summarize their influence rules, this paper first introduces the principle of induction heating, further reveals the mechanism of electromagnetic induction heating to control the deformation of thin plates, and discusses the parameters that affect the process of electromagnetic induction heating. Based on this, the electromagnetic induction heating under different gap distances, current intensity, and heating frequency is simulated by finite element simulation software. The experimental verification is carried out, which lays the foundation for selecting the appropriate electromagnetic induction heating-related parameters.

Accelerating multilayer frequency selective surface absorber design by combining equivalent circuit models with machine learning

Designing high-performance electromagnetic functional materials and artificial structures is of great significance for electromagnetic wave modulation applications. Optimizing performance in the high-dimensional parameter space of electromagnetic functional materials has posed a challenging problem. This paper proposes the use of reinforcement and transfer learning methods to facilitate the quick and accurate design of wideband circuit analog absorbers (CAA). A trained reinforcement learning network is utilized to comprehend the relationship between reflectivity performance and changes in impedance parameter. Furthermore, the transfer learning method is applied to accelerate the training process, leading in a 20-fold reduction in the number of simulations. To validate the effectiveness of this approach, a double-layer absorber aiming for reflectivity less than −20 dB at 3–10 GHz is designed, requiring only 50 simulations. This demonstrates that the proposed method provides a flexible strategy for the interactive design of equivalent circuit and electromagnetic structural parameters. Moreover, it presents a novel and efficient solution for microwave absorber design, with potential applications across various microwave design fields.

Electromagnetic characteristics analysis of dual-frequency magnetic single negative metamaterials

Abstract With the development of multi-frequency wireless transmission technology, it is necessary to expand the research of single-frequency metamaterials in the multi-frequency field. The dual-frequency metamaterial studied adopts a nested square spiral structure, which can resonate at two frequencies, and the real part of the equivalent permeability of metamaterial changes dramatically at the resonance frequency, and the equivalent electromagnetic parameter exhibits anomalous characteristics in the two frequency bands. Firstly, the effects of the number of turns, the width of the copper wire, the spacing of the copper wire, and the length of the outermost edge of inner and outer helical coils are investigated, respectively, using the HFSS software on the resonance frequency of dual-frequency metamaterials, which improves the study of dual-frequency metamaterials with nested square spiral structure. Then, based on the results of the change rule of resonance frequency with the four types of influencing factors, the dual-frequency metamaterials with the real part of the equivalent permeability close to -1 at 6.78 MHz and 13.56 MHz are designed, which is of certain reference significance for the subsequent practical design of dual-frequency metamaterials to satisfy the needs of the project.

Directional control of electromagnetic parameters of Fe@Ni nanowires for ultrathin and low-frequency microwave absorbing

How to prepare materials according to the target properties has been a hot research topic. In this paper, the target electromagnetic parameters are obtained according to the performance requirements, and the nanoflower rod-like, low-density mulberry-like and high-density mulberry-like one-dimensional (1D) core–shell structured Fe@Ni(x) nanowires (NWs) are prepared by liquid-phase reduction method. The effective absorption bandwidth (EAB) of sample Fe@Ni(40) in the low-frequency (2–8 GHz) is up to 1.89 GHz (3.1 mm). Sample Fe@Ni(60) is able to reach a maximum EAB of 3.18 GHz at a thickness of 0.9 mm. Concisely, the sample has the ability to absorb microwaves in low frequency bands and ultra-thin thicknesses. The reason can be attributed to the strong magnetic coupling brought by the bimetallic composition to strengthen the resonance level and the excellent 1D core–shell structure to enhance the efficiency of polarization loss. In conclusion, Fe@Ni(x) provides a technological route for the preparation of low-frequency and ultra-thin-thickness absorbers.

Suppressed conductive loss of flower-like NiCo2O4-wrapped flaky FeSiAl for excellent low-frequency microwave absorption

Flaky FeSiAl is a high potential absorbent for low-frequency microwave applications. However, impedance mismatching due to its excessively high complex permittivity presents a challenge. Herein, inspired by the surface modification strategy, flaky FeSiAl wrapped with flower-like NiCo2O4 (NiCo2O4@flaky FeSiAl) was developed via a hydrothermal method. The introduction of a surface NiCo2O4 insulating layer was expected to reduce the complex permittivity and increase the high complex permeability in the NiCo2O4@flaky FeSiAl composite. Subsequently, an excellent low-frequency microwave absorption performance was achieved. The designed NiCo2O4@flaky FeSiAl displayed a robust minimum refection loss (RL min) of −33.41 dB at 6.32 GHz and increased the effective absorption bandwidth (EAB, RL < −10 dB) to 4.08 GHz when the matching thickness was 1.6 mm. The enhanced low-frequency microwave absorption performance was mainly attributed to the improvement in impedance matching, which originated from the collaborative regulation of electromagnetic parameters. This study provides a promising approach for designing flaky FeSiAl-based composites and high-performance low-frequency microwave absorbents.

On the issue of contactless alternators on movable objects

BACKGROUND: This article discusses automotive inductor generators of domestic and foreign production with different power and design. A comparative analysis of inductor generators according to the main electromagnetic parameters and design designs is carried out. Based on the results of the comparative analysis, conclusions are drawn about the competitiveness of domestic inductor generators and their superiority over foreign analogues. AIMS: research and comparative analysis of tractor inductor generators in order to determine the optimal design, as well as the main characteristics and parameters. METHODS: The calculation of the magnetic circuit and the idling characteristic is based on the method of successive approximations using iterations. A well-known technique using the Blondel diagram is used to calculate the current-speed characteristic. RESULTS: A review and comparative analysis of automotive inductor generators of domestic and foreign production, with various magnetic systems and constructive equipment, is carried out. The advantages and disadvantages of the magnetic circuit of inductor generators of both domestic and foreign production are determined, which are reflected in comparative tables and current-speed characteristics. To carry out the calculation, the optimal design of the inductor generator with the most effective technical and economic indicators was chosen. Conclusions: The calculation of a three-phase single-pole, single-pack inductor generator 11.3701 with a classical toothed zone and a two-half-period rectifier is carried out. The calculation of the magnetic circuit and the idling characteristics was carried out by the method of successive approximations using iterations. The calculation of the current-velocity characteristic was performed using a well-known technique using the Blondel diagram.

Research on electromagnetic wave absorption properties of Portland cement

In order to evaluate the electromagnetic wave absorption properties of Portland Cement, the chemical composition, mineralogical phase of Portland cement were studied by XPS, XRD and Mössbauer, respectively, and electromagnetic parameters were measured. Afterwards, the reflectivity of the hydrated cement were tested.The results showed that Portland cement exhibits some dielectric loss and weak magnetic loss at 1∼18 GHz, due to the unburned carbon and iron oxide. There are three notable theoretical electromagnetic wave absorption peaks, and the greatest absorption reaches 4.38 dB. The minimum reflectivity of hydrated Portland cement reach -17.9 dB, -17.89 dB and -12.67 dB and the bandwidth of -6 dB reach 6.28 GHz,10.74 GHz and 1.85 GHz at the thickness of 5 mm,10 mm, 15 mm, respectively. There are 3,5,7 reflectivity peaks at the thickness of 5 mm,10 mm, and 15 mm, respectively, which matched very well with the calculated interference peaks.

Exploring relaxation behaviors in Hydrogen-Bond networks within binary mixtures of propylene carbonate and primary alcohols through broadband dielectric spectroscopy and molecular dynamic simulation

This work investigates the dielectric properties and the relaxation behaviors of propylene carbonate (PC) and its binary mixtures with methanol and ethanol. A coaxial-circular cutoff waveguide junction was employed to characterize broadband dielectric spectra ranging from 0.1 GHz to 18 GHz, and a two-group Debye model was used to extract relaxation parameters. Excess thermodynamic parameters, Kirkwood orientational correlation factors, and Bruggeman factors for PC-alcohol mixtures were also analyzed and presented. These data provide insights into microscopic dynamic processes as the PC concentration in the mixtures gradually increases. These processes include the continuous disassociation of the alcohols’ hydrogen-bond (H-bond) networks, the formation of new PC-alcohol H-bond networks, the parallel alignment of heterogeneous dipoles, and a significant enhancement of the dielectric effect. Furthermore, a series of molecular dynamics (MD) simulations using the TraPPE-UA forcefield were conducted, and the obtained thermodynamic and electromagnetic parameters demonstrated good agreement with experimental results. Based on radial distribution functions, dipole–dipole spatial orientational correlations, and H-bond life times extracted from the MD simulations, we observed the gradual formation of PC-cage and alcohol-cluster microstructures in PC-rich mixtures. The data and physical insights provided in this work are expected to have practical implications in high-energy battery applications and the pharmaceutical industry.

Efficient broadband sea urchin-like Fe3O4@C electromagnetic wave absorbing materials

The development of electromagnetic wave absorbing materials is crucial for various applications. Carbon materials and ferrite materials were recognized as ideal candidates of absorbing agents due to their respective dielectric loss and magnetic loss capabilities. In this study, Fe3O4@C were prepared using hydrothermal carbonization coupling method. The microstructure and morphology of Fe3O4@C were studied using SEM, TEM, XRD and TG. The results showed that Fe3O4@C exhibited a hollow sea urchin-like structure. The molar ratio of carbon to iron sources in the raw materials significantly influenced the crystal structure of the product. The growth mechanism of sea urchin-like Fe3O4@C was proposed. The carbon content in Fe3O4@C increased with the increase of molar ratio of glucose and iron (III) sulfate. The Fe3O4@C with carbon content of 31.10 % exhibited optimal absorption performance, with a minimum reflection loss of −57.1 dB at a matching thickness of 5.10 mm and effective absorption bandwidth (EAB) of 4 GHz. Electromagnetic parameters and absorption performance could be adjusted by varying the molar ratio of glucose and iron (III) sulfate. The unique sea urchin-like structure enhanced multiple reflection of electromagnetic waves. Interface polarization, conductivity loss and synergistic effect between carbon and Fe3O4 also contributed to the favorable absorption properties.

Frequency-extended inverse design of transmission-type linear-to-circular polarization control metasurface based on deep learning

Due to the parameter range limitations of the training dataset, traditional inverse prediction network models can only predict structure parameters of the metasurface within a limited frequency range. When the given design targets exceed the prediction range of network models, the predicted results will not match the actual results. This paper proposes a frequency-extended inverse design method (FEIDM) based on deep learning to address the problem. The method can automatically collect the required data and train the network model based on the center working frequency of the design targets, thereby achieving accurate prediction of metasurface structural parameters and effectively reducing labor and computational costs. Taking the transmission-type linear-to-circular polarization control metasurface as an example, the unit cell of the metasurface is first established in the paper. The structural parameters and corresponding electromagnetic parameters are collected without changing the unit size of the metasurface, and an initial inverse prediction network model (IIPNM) is constructed. The research results indicate that its predictable center working frequency range is 3–5.5 GHz. Using the design concept proposed in this paper, a program is constructed, it can automatically achieve data collection, target extraction, network model training, and prediction. Four given design targets are predicted. Among them, the center working frequencies of the three design targets are outside the initial predictable range. The predicted results meet the requirements of the given target, verifying the effectiveness of the proposed scheme. Finally, a set of parameters is selected to fabricate, and the experimental results are consistent with the simulation results. The research results can provide a reference for the efficient prediction of metasurface structural parameters over a wide frequency band.

Simulation‐Guided Design of Gradient Multilayer Microwave Absorber with Tailored Absorption Performance

AbstractFlexible microwave absorber (MAR), vital in advanced applications such as wearable electronics and precision devices, are highly valued for their lightweight, exceptional electromagnetic waves (EWs), and ease of fabrication. However, optimizing the electromagnetic parameters of microwave absorption materials (MAMs) to enhance absorption ability and expand effective absorption broadband (EAB, reflection loss (RL) &lt;−10 dB) is a considerable challenge. Herein, a permittivity‐attenuation evaluation diagram (PAED) is constructed using parameter scanning based on the Materials Genome Initiative to determine the ideal electromagnetic parameters and thickness, optimize absorption efficiency, and obtain highly efficient absorbers. Guided by the PAED, a multilayer MAR consisting of a “matching‐absorption‐reflection layer” and a dielectric loss gradient aligned with the direction of EWs propagation is developed. This design significantly enhances the EWs penetration and ensures effective absorption, attributed to the well‐matched impedance and attenuation characteristics. As anticipated, the microwave absorption of the absorber (density = 0.063 g cm−3) is optimized, with an RL of −34 dB at d = 4 mm and an EAB covering the entire X‐band (8.2–12.4 GHz). This study presents a novel approach for establishing a material database for MAMs and developing high‐performance absorbers characterized by thinness, lightness, broad operational frequency range, and robust absorption capacity.

Optimal design of an LCC-S WPT3 Z1 SAE J2954 compliant system, using NSGA-II with nested genetic algorithms for simultaneous local optimization

Wireless Power Transfer (WPT) for electric vehicles is one of the most promising methods that, given its advantages, will drive the deployment of electric vehicles. This paper presents a mathematical optimization method applied to the complete design of an LCC-S WPT3 Z1 11 kW system that complies with the SAE J2954 standard (Wireless Power Transfer for Light-Duty Plug-in/Electric Vehicles and Alignment Methodology, 2020). A design method based on three phases is proposed, allowing the complete inductor system, including ferrites shielding and compensation circuit components, to function in any relative primary and secondary position. In Phase 1, a multi-objective NSGA-II algorithm is designed, utilizing three nested genetic algorithms. The goal is simultaneously searching for the local optimum between the primary and secondary systems in three positions. This is achieved by modeling the circuit’s electrical and electromagnetic parameters with equations, enabling an iterative process with reduced computational time. The NSGA-II algorithm yields three scenarios: primary copper volume minimization, secondary copper volume minimization, and a compromise solution that optimizes the total volume. The result is then modeled in Phase 2 using a 3D finite element program that includes ferrite and optimal shielding, obtaining the values of inductances and mutual inductance in the three positions, as well as design data for manufacturing. This result is introduced in Phase 3 to optimize compensation circuit components using a second NSGA-II algorithm with three nested genetic algorithms. Again, three scenarios are obtained based on the desired system behavior and the optimal cost of the components. The result is validated through simulation with Matlab-Simulink and experimentally using a prototype constructed for this purpose.

Effect of nano-carbon black content and dispersibility on the properties of cement paste

In this study, we analyzed the microstructure, pore structure, and changes in electromagnetic parameters of cement paste with nano-carbon black (CB) added. The following conclusions were drawn: The addition of CB significantly influenced the pore structure of the cement paste, increasing the content of pores less than 100 nm and improving the overall pore structure. The use of the dispersant further enhanced the dispersion of CB and increased its filling effect. Additionally, adding CB had a significant impact on the compressive strength of the cement paste; the presence of certain CB aggregates reduced the compressive strength. However, when the CB content was 0.5wt%, the use of the dispersant decreased the size of CB aggregates and effectively increased the compressive strength. SEM images displayed the dispersion state of CB aggregates within the cement paste, demonstrating that the size and quantity of aggregates could be reduced through the use of the dispersant. The change in the CB dispersion state also slightly affected the electromagnetic parameters and wave absorption properties of the cement paste. The research results presented in this paper offer valuable insights for the design and application of CB cement paste.