Electromagnetic Material Parameters Research Articles

Quantifying Heterogeneous Interface Effect of Fe3O4(111)/C for Enhanced Low-Frequency Electromagnetic Wave Absorption

How to tailor electromagnetic parameters of multi-component materials is the fundamental issues for low-frequency electromagnetic wave absorbers (EMA). However, there remains a challenge to accurately elucidate the impact of respective components at heterogeneous interfaces on the EMAs, not to mentioning the further quantitative contribution of the interfacial effect to the electromagnetic loss. In this paper, we for the first time separated the Fe3O4(111)/C heterogeneous interface of Fe3O4@C via a controllable interfacial separation strategy, meanwhile ensuring the consistent microstructure and the ratio of each component, as well as the unchanged macroscopic structure of the particles. Once all potential influences on electromagnetic parameters have been independently studied, the unique difference in heterogeneous interfaces enabled us to quantitatively evaluate the effect of them on electromagnetic parameters. Both experimental and density functional theory (DFT) calculation results consistently demonstrate that the Fe3O4(111)/C heterointerface increases carrier concentration and conductivity, thereby enhancing the imaginary part of the dielectric constant. Very distinguished from traditional interfacial polarisation mechanism presented in previous publications, this study introduces a novel interfacial loss mechanism primarily characterized by conductivity loss, which is rigorously investigated in a quantitative way. This discovery offers a novel approach for designing controllable heterogeneous interfaces and manipulating electromagnetic parameters in multicomponent EMAs.

Co/Er2O3/C ternary nanocomposites derived from cobalt/erbium Prussian blue analogs for efficient microwave absorption

This study presents the synthesis of Er[Co(CN)6], a Prussian blue analog (ErCo-PBA) with varied morphology, fabricated by modulating the solvent ratio between C2H6O and H2O. This approach leverages the solubility characteristics of K3[Co(CN)6] and the consequential influence of C2H6O on the crystal growth. When the solvent ratios are 1:8, 8:1, and 1:1, the resulting ErCo-PBA precursors nanorods, irregular particles, and spindle-shaped particles, respectively. After annealing, these precursors in an Ar environment allowed the Co/Er2O3/C derivatives to retain the morphology of the precursor well. Electromagnetic parameters testing revealed that Co/Er2O3/C-1 exhibits superior electromagnetic wave-absorbing (EMWA) performance among the synthesized derivatives with an effective absorption bandwidth of 5.1 GHz at 1.85 mm and a minimum reflection loss of −56.7 dB at 2.9 mm. The incorporation of Er2O3 is an effective method for adjusting and optimizing the electromagnetic parameters of materials, thereby enhancing the EMWA performance of Co/Er2O3/C composite. This study highlights the potential of rare-earth oxide/Co/C composites, synthesized through direct annealing rare-earth metal–organic frameworks, as an absorber and are promising candidate to achieve high-efficiency electromagnetic wave absorption.

Theory of Refraction, Ray–Wave Tilt, Hidden Momentum, and Apparent Topological Phases in Isotropy-Broken Materials Based on Electromagnetism of Moving Media

The mysterious nature of electromagnetic momentum in materials is considered one of the most significant challenges in physics, surpassing even Hilbert’s mathematical problems. In this paper, we demonstrate that the difference between the Minkowski and Abraham momenta, which consists of Roentgen and Shockley hidden momenta, is directly related to the phenomenon of refraction and the tilt of rays from the wavefront propagation direction. We show that individual electromagnetic waves with non-unit indices of refraction (n) appear as quasistatic high-k waves to an observer in the proper frames of the waves. When Lorentz transformed into the material rest frames, these high-k waves are Fresnel–Fizeau dragged from rest to their phase velocities, acquiring longitudinal hidden momentum and related refractive properties. On a material level, all electromagnetic waves belong to Fresnel wave surfaces, which are topologically classified according to hyperbolic phases by Durach and determined by the electromagnetic material parameters. For moving observers, material parameters appear modified, leading to alterations in Fresnel wave surfaces and even the topological classes of the materials may appear differently in moving frames. We discuss the phenomenon of electromagnetic momentum tilt, defined as the non-zero angle between Abraham and Minkowski momenta or, equivalently, between the rays and the wavefront propagation direction. This momentum tilt is only possible in isotropy-broken media, where the E and H fields can be longitudinally polarized in the presence of electric and magnetic bound charge waves. The momentum tilt can be understood as a differential aberration of rays and waves when observed in the material rest frame.

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) <−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.

Electromagnetic characterization of ring-shaped specimens with a model-based parameter estimator

This work focuses on the characterization of soft magnetic materials with ring-shaped specimens. The authors present a novel concept based on analytical models for determining their electromagnetic material parameters, e.g., the non-linear magnetization curve, the electric conductivity, and iron losses.

Study of permeability and permittivity of [formula omitted]-Fe[formula omitted]O[formula omitted] using computer simulation method

This study proposes a computational method to directly obtain the frequency-dependent permeability and permittivity of materials from computer simulation data. The method combines first-principles calculations, Green’s function formalism, and magnetic moment dynamics simulations. Using α-Fe2O3 as an example, we demonstrate the validation process of the computational approach. By calculating the time correlation functions of electric and magnetic dipole moments and applying linear response theory, we successfully obtained the frequency-dependent permeability and permittivity of α-Fe2O3 at 300 K. The calculated results agree well with experimental values, proving the efficacy of the proposed computational method. This study provides a reliable computational pathway to predict electromagnetic parameters of materials using computer simulations.

Tunable and improved microwave absorption of flower-like core@shell MFe2O4@MoS2 (M = Mn, Ni and Zn) nanocomposites by defect and interface engineering

• Flower-like core@shell MFe 2 O 4 @MoS 2 (M=Mn, Ni, and Zn) were elaborately designed and selectively produced in large scale. • The large radius of M 2+ cation effectively boost the concentration of oxygen vacancy in the MFe 2 O 4 and MFe 2 O 4 @MoS 2 . • The boosted concentration of oxygen vacancy resulted in the improvement of dielectric loss capabilities and MAPs. • The introduction of MoS 2 nanosheets greatly improved the interfacial effect and enhanced the polarization loss capabilities. • The clear understanding of defect and interface engineering made these strategies be well applied to improve MAPs. Previous results revealed that the defect and/or interface had a great impact on the electromagnetic parameters of materials. In order to understand the main physical mechanisms and effectively utilize these strategies, in this study, M Fe 2 O 4 and flower-like core@shell M Fe 2 O 4 @MoS 2 ( M =Mn, Ni, and Zn) samples with different categories were elaborately designed and selectively produced in large scale through a simple two-step hydrothermal reaction. We conducted the systematical investigation on their microstructures, electromagnetic parameters and microwave absorption performances (MAPs). The obtained results revealed that the large radius of M 2+ cation could effectively boost the concentration of oxygen vacancy in the M Fe 2 O 4 and M Fe 2 O 4 @MoS 2 samples, which resulted in the improvement of dielectric loss capabilities and MAPs. Furthermore, the introduction of MoS 2 nanosheets greatly improved the interfacial effect and enhanced the polarization loss capabilities, which also boosted the MAPs. By taking full advantage of the defect and interface, the designed M Fe 2 O 4 @MoS 2 samples displayed tunable and excellent comprehensive MAPs including strong absorption capability, wide absorption bandwidth and thin matching thicknesses. Therefore, the clear understanding of defect and interface engineering made these strategies well elaborately designed and applicable to improving MAPs. Improved microwave absorption of flower-like core@shell MFe 2 O 4 @MoS 2 (M=Mn, Ni and Zn) nanocomposites by defect and interface engineering

Influence of Dielectric Plate Parameters on the Reflection Coefficient of a Planar Aperture Antenna

In this article, an aperture antenna excited by a waveguide with a circular cross-section and covered with a dielectric plate was analyzed via simulation calculation and verified via measurements. The influence of the geometrical and electromagnetic parameters of the dielectric plate on the reflection coefficient S11 of the antenna opening was systematically analyzed. The geometrical parameters taken in this analysis are the thickness d and the width/length h1/h2 of the dielectric plate. The electromagnetic parameters used in this analysis are the real and the imaginary part of permittivity (εr, tan δ) and the electrical conductivity of the dielectric plate (σ). The simulation calculation and analysis included other structural and electromagnetic parameters of the dielectric plate (density of the radome material, relative permeability, and magnetic loss tangent (ρ, µr, and tan δµ, respectively)), but the results show that in the range of real values of these parameters for the materials used for the dielectric plate, they had no significant influence on the reflection coefficient. The results show that impedance-matched antennas with very low values of the reflection coefficients S11 at the resonant frequency can be realized by changing the geometrical and electromagnetic parameters of the dielectric plate material. The results are presented for a circular aperture antenna on a planar grounded plane with a dielectric plate on the opening, and the achieved lowest values of the S11 parameter were −45.17 dB (simulated) and −43.93 dB (measured) at the frequencies of 1.7820 GHz and 1.7550 GHz, respectively. The estimated values of the dielectric plate parameters in this case are thickness d = 11.08 mm (0.67 λ); width × length of grounded plane and dielectric plate h1 × h2 = 423 × 450 mm2 (2.51 × 2.67 λ); relative permittivity 2.5, tan δ = 0.09, μr = 1, tan δμ = 0.00, ρ = 1200 kg·m−3; and electrical conductivity σ = 0 S/m. The simulation calculation results were verified by measuring the reflection coefficient S11 on the created laboratory model of the aperture antenna with the dielectric plate and showed a very good match.

In-situ generated Ni/Ni3Si to enhance electromagnetic wave absorption properties of Ni/PDCs/biomass ceramic composites

In recent years, electromagnetic wave (EMW) absorbing materials derived from biomass materials have been widely concerned because of their light weight and high efficiency. Here, Ni/PDCs/biomass ceramic composites absorbing material was prepared by a simple suspension impregnation-in-situ reduction carbonization process and polymer-derived ceramics (PDCs) with peanut shell as the absorbing matrix and NiO doped in polysiloxane as the precursor solution. The synergistic effect of Ni/PDCs could effectively adjust the impedance matching of the composite, and the BET results shown that the prepared Ni/PDCs/biomass ceramic composites had a hierarchical porous structure, which could not only provide a large number of heterogeneous interfaces, but also enhance the interface polarization, dipole polarization and multiple reflection loss of the absorbing material. The sample of NPP-1 possessed good EMW absorbing performance when the content of NiO was 1 % and the filler was 50 %, the minimum reflection loss (RLmin) reached − 66.38 dB at 1.74 mm, and the effective absorption bandwidth (EAB) was 3.54 GHz (14.46–18 GHz) at 1.45 mm. In this work, the electromagnetic parameters of biomass materials were adjusted by polymer conversion ceramics and metal oxides, which provided another feasible scheme for enhancing the absorbing properties of biomass materials.

A method of measuring complex ermittivity of nonmagnetic materials and selecting its initial value based on iterative inversion

Complex permittivity is an important parameter to reflect the macroscopic electromagnetic properties of material. The selection, design, and application of related materials and devices in the electromagnetic field must be based on the electromagnetic parameters of materials in the working frequency band. The numerical iterative method is an important method to inverse and calculate the complex permittivity of material. But there always exists a difficult problem that the initial value of iteration is difficult to give accurately. Based on the relationship between the complex permittivity and the reflectivity of absorbing material, an initial value selecting method for iteration to invert permittivity of absorbing material is proposed in this work. For absorbing materials with arbitrary thickness at a certain frequency, the complex permittivity must be near the complex permittivity of perfect matching layer. Therefore, the permittivity of perfect matching layer can be used as the initial value of the iterative algorithm. On this basis, a method of calculating the complex permittivity of monolayer absorbing material by using the reflection parameter is constructed. The experimental results show that the complex permittivity of lossy material can be calculated more accurately at the frequency with absorbing performance. However a great error can be caused at the frequency where the reflectivity is close to zero. Based on the iterative solution of the complex permittivity of single-layer absorbing material, a new method of measuring the complex permittivity of material is constructed by combining multi-layer absorbing materials to enhance full-band reflectivity. Given the electromagnetic parameters of other layer materials , the permittivity of absorbing materials and low-loss materials can be obtained accurately.

Decoupling Conductivity and Permeability Using Sweep-Frequency Eddy Current Method

Electromagnetic coupling and lift-off variation are obstacles in the eddy current method. In this paper, we proposed a sweep frequency eddy current method to achieve conductivity and permeability simultaneous measurements immune to lift-off. The relationship between eddy current detection signals of different frequencies and electromagnetic parameters of magnetic materials has been found. That is, the real part of mutual inductance is mainly related to permeability at low frequency. In high frequency, the zero crossover-frequency is the proportional to the ratio of permeability and conductivity. By combining the analysis mentioned above, conductivity and permeability can be estimated simultaneously. In order to eliminate the interference of lift-off, a sensor structure with one excitation coil and two receiving coils is designed to compensate the mutual inductance changes caused by lift-off. Experiments and FEM simulations are also carried out to verify the proposed method. The results show the errors of conductivity and permeability are 1.3% and 3.9% respectively, and the error caused by reasonable variation range of lift-off can be significantly reduced.

Porous N-doped C/VB-group VS2 composites derived from perishable garbage to synergistically solve the environmental and electromagnetic pollution

The cooperative solution to environmental pollution and electromagnetic pollution is a big problem in environmental governance. Herein, N-doped C/VB-group flower-like VS2 composites were prepared using waste soybean husks recovered from the vegetable market as raw material through ordinary carbonization and hydrothermal method. The distinctive honeycomb-like porous structure of soybean husk contributes to multiple scattering and reflection and builds an interconnected conductive network. In addition, the presence of VS2 enriches the loss mechanism and significantly modulates the electromagnetic parameters of the composite material, generating a strong attenuation capability and ideal impedance matching. As a result, the composites exhibit an excellent electromagnetic wave (EMW) absorption performance with an ultra-low reflection loss (RL) value of −62.74 dB at a thickness of only 1.70 mm, and the effective absorption bandwidth (EAB) is up to 6.04 GHz (covering the entire Ku-band). The radar cross section (RCS) simulation further demonstrates the effectiveness of the composites in dissipating EMW (-6.69 dB m2 at 0°) in actual applications. The results showed that the C/VS2 composites have excellent EMW absorption performance, realized the reuse of waste soybean husks with high added value, and made it possible to solve electromagnetic pollution and environmental pollution together. Particularly, the dielectric sum-quotient model was further validated. It is crucial for nonmagnetic materials to modulate the sum and quotient of the real and imaginary parts of their dielectric constants to obtain excellent EMW absorption performance.

An Effective Method for Electromagnetic Parameter Measurement of Flexible Materials Based on Air Coaxial Line

When measuring the electromagnetic parameters of flexible material with an air coaxial line, the specimen is prone to bend and deform in the fixture, which results in erroneous results. In order to solve this problem, this paper proposes a new measurement method. Firstly, a rigid material is selected and loaded into the air coaxial line for two-port S parameters measurement. Then, the flexible material is attached to one end of the rigid material and loaded into the air coaxial line together for repeated two-port S parameter measurement. According to the S parameters measured and the two-port network cascading theory, the S parameters of the flexible material separately loaded in the fixture can be deduced. Finally, the electromagnetic parameters of the flexible material can be calculated by the Nicolson−Ross−Weir (NRW) method. Experimental results show that the method proposed is effective and reliable.

Effect of Different Shapes on the Measurement of Dielectric Constants of Low-Loss Materials With Rectangular Waveguides at X-Band

To quantify the effect of air gap on the dielectric constant measurement of low-loss materials, this letter presents the first quantitative study of the effect of five different shapes on the dielectric constant measurement using three low-loss materials as examples. The experimental results show that if low-loss materials’ dielectric constant measurement error is controlled within 5%, the air gap cannot exceed 4%. The results of this letter can provide effective guidance and reference for improving the measurement accuracy of electromagnetic parameters of low-loss materials.

Oxygen plasma modulates the interfacial impedance of microwave reduced graphene oxide for enhanced microwave absorption

As a classic two-dimensional material, graphene has attracted worldwide attention in the fields of electromagnetic shielding and microwave absorption. However, the excellent electrical conductivity makes it challenging to achieve impedance matching, which significantly limits its application microwave absorption. Here, we propose a strategy for the modification of graphene by low-temperature oxygen plasma that precisely regulates the electromagnetic parameters of the graphene material by adjusting the plasma irradiation time. This approach controls the electrical conductivity of graphene for impedance matching and creates enriched defects that effectively improve the material permittivity loss capability. Owing to these advantages, the sample (O-MW-rGO-60) irradiated by plasma for 60 min showed excellent microwave absorption properties with a minimum reflection loss of −54.11 dB at a matched thickness of 1.7 mm and an effective absorption bandwidth of 5.68 GHz at a thin thickness of 2.0 mm. In addition, CST simulation is used as an intelligent design strategy to verify a product's radar wave absorption capability under realistic conditions. The RCS values of the model covered with the O-MW-rGO-60 sample coating are significantly lower than those of the metal substrate, which confirms its excellent microwave absorption properties and provides new insights into the future development of microwave absorbing materials.

Rectangular Waveguide Characterization of Biaxial Material Using TM11 Mode

A novel measurement technique is presented to determine the electromagnetic parameters of a biaxial material loaded in the rectangular waveguide. For the first time, in this paper, the TM₁₁ waveguide mode is used as an incident filed for characterization. The electromagnetic parameters of the biaxial sample are obtained, minimizing the difference between the measured and the theoretically calculated scattering parameters. For this purpose, we theoretically calculate the reflection and transmission coefficients. A prototype of the measurement system is fabricated to validate the proposed approach. Subsequently, the proposed technique is used to experimentally characterize two types of biaxial materials. The validity and accuracy of the proposed method are verified by comparing the experimental results with those obtained by the conventional rectangular waveguide method. The suggested technique eliminates the problem of preparing multiple samples and rotating them in the traditional waveguide method.

Microwave Measurements of Electromagnetic Properties of Materials.

A review of measurement methods of the basic electromagnetic parameters of materials at microwave frequencies is presented. Materials under study include dielectrics, semiconductors, conductors, superconductors, and ferrites. Measurement methods of the complex permittivity, the complex permeability tensor, and the complex conductivity and related parameters, such as resistivity, the sheet resistance, and the ferromagnetic linewidth are considered. For dielectrics and ferrites, the knowledge of their complex permittivity and the complex permeability at microwave frequencies is of practical interest. Microwave measurements allow contactless measurements of their resistivity, conductivity, and sheet resistance. These days contactless conductivity measurements have become more and more important, due to the progress in materials technology and the development of new materials intended for the electronic industry such as graphene, GaN, and SiC. Some of these materials, such as GaN and SiC are not measurable with the four-point probe technique, even if they are conducting. Measurement fixtures that are described in this paper include sections of transmission lines, resonance cavities, and dielectric resonators.

Closed-form representation for equivalent electromagnetic parameters of irregular hexagonal honeycomb radar-absorbing materials

In this study, a new closed-form expression is developed to determine the equivalent electromagnetic parameters (permittivity and permeability) of biaxial anisotropic honeycomb radar-absorbing materials (RAMs). Based on the equivalent medium theory, the nonmagnetic substrate and absorbing coating of the honeycomb structure are equivalent to one kind of material, and then, the effective electromagnetic properties of irregular hexagonal (compressed or stretched) honeycombs are obtained by using the layered anisotropic model. In order to validate the effectiveness and correctness of this new closed-form expression, experimental tests and numerical simulation are adopted. The results show good agreement among the experimental tests, numerical simulation, and theoretical analysis within the specified frequency range (2–18 GHz), which confirms the validly of the proposed new method. Compared with the previous layered anisotropic model, the modified new model is more accurate for irregular hexagonal honeycomb RAMs. Furthermore, it can predict the effective permittivity (permeability) precisely without experimental measurements or numerical simulation, and it is of great significance for the design of honeycomb RAMs.

Inverse problems for nonlinear Maxwell's equations with second harmonic generation

In the current paper we consider an inverse boundary value problem of electromagnetism with nonlinear Second Harmonic Generation (SHG) process. We show the unique determination of the electromagnetic material parameters and the SHG susceptibility parameter of the medium by making electromagnetic measurements on the boundary. We are interested in the case when a frequency is fixed.

An automated measuring complex of electromagnetic parameters of materials in the field of superhigh frequencies

This work is dedicated to the features of measuring the electromagnetic parameters of materials. In the field of superhigh frequencies, there are practically no documents regulating the requirements for the properties of materials and means for measuring the electromagnetic parameters of materials. To solve the problems of metrological support for this frequency range and new materials, several steps are required. One of them is the development of a measuring complex. This work describes the composition of the developed model of such a complex and its distinctive features. The text contains models of materials. The extended frequency ranges from 200 MHz to 80 GHz. The range of external magnetic fields has been expanded from 4 kA/m to 70 kA/m.