Problem Of Electromagnetic Wave Research Articles

Integrating high-efficiency thermal channel construction and structural wave absorption design within vertically oriented SiC-coated carbon fibers/silicone resin composites

To match the increasing miniaturization and integration of electronic devices, higher requirements are put forward for the electromagnetic wave absorption (EWA) and thermal conductivity (Tc) of heat conduction-microwave absorption integrated materials (HCMWAIMs) to overcome the problems of electromagnetic wave (EMW) pollution and heat accumulation. Herein, a simple and efficient shear force induction technique is used to construct a carbon/magnetic isolation network within the silicone resin matrix, where ferrite particles are well dispersed in vertically oriented SiC-coated carbon fibers array. Benefiting from the orderly interconnection of CFs@SiC in the array, the prepared composites have a high Tc of 7.86 W m−1 K−1. The introduction of magnetic ferrite particles within the CFs@SiC array can induce electrical-magnetic coupling, optimize impedance matching, and enhance EMW attenuation. This synergy of V-CFs@SiC/ferrite isolation network structure gives the composites an excellent effective absorption bandwidth (EAB) of 5.88 GHz and a minimal reflection loss (RLmin) of −47.5 dB at a thickness of 1.5 mm. Moreover, the as-prepared composites exhibit outstanding elastic compressibility of 43.2 % and rebound rate of 45.1 % under a pressure of 35psi. This strategy offers a distinguishing understanding of preparing high-performance HCMWAIMs in modern electronic devices.

Analysis and computation for the scattering problem of electromagnetic waves in chiral media

Analysis and computation for the scattering problem of electromagnetic waves in chiral media

Influence of spatial dispersion in metal on optical characteristics of a magnetoplasmonic layered nanoparticle cluster

In the current work, the diffraction problem of a plane electromagnetic wave on a cluster of two layered nanocylinders consisting of a magnetoplasmonic core and a gold shell is considered. The arising effects of spatial dispersion in the gold shell are taken into account within the framework of the generalized nonlocal optical response theory. Based on the discrete source method scheme, an analysis of the influence of the mutual arrangement of particles, their deformation, and the effect of spatial dispersion on the behaviour of the absorption cross-section and the near-field enhancement factor is conducted. It is shown that the position of the plasmon resonance can be shifted to the transparency region of biological tissues by varying the distance between particles and the core material. It has been established that taking into account spatial dispersion in the gold shell leads to a decrease in intensity and a slight shift of the plasmon resonance position to the shortwave region, without going beyond the tissue transparency region.

A NUMERICAL METHOD FOR SOLVING A COMPLETE HYPERSINGULAR INTEGRAL EQUATION OF THE SECOND KIND AND ITS JUSTIFICATION

A complete hypersingular integral equation of the second kind was obtained as a boundary integral equation for the diffraction and scattering problem of electromagnetic waves in space separated by the periodically placed non-perfectly conducting strips. The equation includes a singular integral that distinguishes it from the studied second-kind hypersingular equation. Our motivation is the need to have a numerical method for the equation, its applicability borders, and guaranteed convergence. The numerical method has the type of Nyström. The justification of the method envelops a proof of the theorem of existence and uniqueness of the solution and an estimate of the convergence rate of sequence of the approximate solutions to an exact solution.

Two-Dimensional Scattering of Line Source Electromagnetic Waves by a Layered Obstacle

We consider the scattering problem of line source electromagnetic waves using a multi-layered obstacle with a core, which may be a perfect conductor, a dielectric, or has an impedance surface. We formulate this problem in two dimensions and we prove some useful scattering relations. In particular, we state and prove a reciprocity principle and a general scattering theorem for line source waves for any possible positions of the source. These theorems can be used to approximate the far-field pattern in the low-frequency theory. Moreover, an optical theorem is recovered as a corollary of the general scattering theorem. Finally, we obtain a mixed reciprocity relation which can be used in proving the uniqueness results of the inverse scattering problems.

Analytical approach to the problem of electromagnetic wave scattering by a cylindrical hole in a thin metal screen

A method of analytical study of a metal film perforated by cylindrical nanoholes as the basis of a metasurface has been proposed. The formulas deduced completely determine the electromagnetic field of a wave scattered by the hole at any distance from the surface. The calculation of the transmission and absorption spectra of the studied structure, as well as the dependence of the phase of the scattered wave on the radius of the hole, is carried out using analytical formulas. The calculation results are consistent with the literature data for calculating the efficiency of a quantum photodetector and the phase change interval of light scattered by meta-atoms required for lens design.

Modified Method of Physical Optics for Calculating Electromagnetic Wave Scattering on Non-Convex Objects

In order to solve the problem of electromagnetic wave scattering on non-convex objects, a combined method based on the method of physical optics with corrections for multiple reflections was discussed. The calculation of these corrections was carried out by the ray method. The article considered the effect of taking into account the curvature of the surface on the calculation error. The results of the calculations of the test example were compared with the calculations by the rigorous method of moments.

Yolk-shell structure synergistic defect engineering for boosting electromagnetic wave absorption in Co9S8@Humins-derived carbon

Exploring new strategies to incorporate the concepts of green chemistry and defect engineering into new architectures to address the problem of severe electromagnetic wave (EMW) pollution is challenging. In this work, by using a by-product of catalytic conversion of biomass as a carbon source, we prepare two-dimensional (2D) Co9S8-coated humins-derived carbon nanomaterials with a yolk-shell structure. The EMW attenuation ability is finally optimized by controlling the morphology and defects of the composite material through the pyrolysis temperature. As expected, with the synergy of conductive loss/interfacial polarization and defects regulating, the composite material achieves a reflection loss (RL) value of −51.4 dB in Ku-band and the effective absorption bandwidth (EAB) can be as high as 5.92 GHz (12.08–18.00 GHz) at 1.8 mm ultra-thin coating thickness. A strong absorption capacity in the low-frequency C-band (6.4 GHz) reaches RL value of −49.9 dB and a thickness of 3.50 mm, which grants it the characteristic of convertible microwave absorption from high frequency to low frequency. Taking account of the facile synthesis and tunable absorption properties, the encouraging findings shed light on exploring waste-turned-microwave absorbents with promising practical applications.

Electromagnetic wave absorption and bending properties of double-layer honeycomb 3D woven composites: experiment and simulation

In order to solve the problems of honeycomb sandwich structure electromagnetic wave absorbing composites with easy delamination, low strength, and a narrow absorption frequency band, a double-layer honeycomb 3D woven electromagnetic wave absorbing composite was designed and prepared. CST electromagnetic simulations and mechanical finite element simulations were combined with experimental analysis, respectively. The electromagnetic wave absorption properties and bending properties of the double-layer honeycomb 3D woven electromagnetic wave absorbing composite were revealed, and the electromagnetic wave absorption mechanism was elucidated. The results show that the lowest peak of reflection loss obtained from both simulation and experiment of electromagnetic wave absorption property occurs in the X-band with the values of 10.78 GHz and 9.28 GHz, respectively. The lowest reflection loss is −24.35 dB and −23.5 dB, respectively. The simulation results were in good agreement with the experimental results. The maximum loads obtained from simulation and experiment for the bending property were 2696.28 N and 2271.07 N, respectively. There is no obvious delamination damage to the yarn, and the material has good resistance to delamination. The structural-functional integration of load-bearing and electromagnetic wave absorption in double-layer honeycomb 3D woven electromagnetic wave absorbing composite will have great development potential in civil and military fields.

Heterostructure design of MOFs derived Co9S8/FeCoS2/C composite with efficient microwave absorption and waterproof functions

• A hierarchical Co9S8/FeCoS2/C composite has been designed. • Benefiting from the enhanced polarization loss, optimized synergistic effect, and multiscale EMW dissipation paths, Co9S8/FeCoS2/C composite exhibits superior EMW absorption. • The bouquet-like architecture formed by many nanorods produces a large number of void spaces and interfaces. • The obtained Co9S8/FeCoS2/C composite shows a broad effective bandwidth of 5.1 GHz at a thickness of 2 mm. At present, the problem of electromagnetic wave (EMW) pollution is critical, and the design of high-performance absorbers is of great significance. Based on the synergy between dielectric and magnetic losses, and between multicomponents in heterostructures, the development of light-weight absorbers with a strong absorption capability and multiple scattering is a promising strategy to achieve high-performance absorbers. In this work, CoFe-MOF precursors with a bouquet-like structure were prepared via the hydrothermal method, and Co 7 Fe 3 /C and Co 9 S 8 / FeCoS 2 /C composites were obtained through a carbonization and sulfuration treatment during the high-temperature pyrolysis process, respectively. The experimental and theoretical results show that the Co 9 S 8 /FeCoS 2 /C composite has a better EMW absorption performance, and its optimal reflection loss (RL) value is -53.9 dB at a low filler loading of 20 wt.%, which is due to the S doping that enhances the interface polarization relaxation process and improves the impedance matching characteristics. Moreover, the Co 9 S 8 /FeCoS 2 /C composite can be as candidates of high-efficiency absorbers in extreme application environments.

Comparison of 2.5D finite element formulations with perfectly matched layers for solving open axisymmetric electromagnetic cavity problems

AbstractAxial symmetry in time‐harmonic electromagnetic wave problems can be exploited by considering a Fourier expansion along the angular direction, reducing fully three‐dimensional computations to two‐dimensional ones on an azimuthal cross section. While this transition leads to a significant decrease in computational effort, it introduces additional difficulties, which necessitate appropriate finite element (FE) formulations. By combining the latter with perfectly matched layers (PML), open problems can be considered. In this work, we compare and discuss the performance of different combinations of axisymmetric FE formulations and PMLs, using a dielectric sphere in open space as a test case. As an application example, a superconducting Fabry–Pérot photon trap is considered.

N-Doped Honeycomb-like Ag@N-Ti3C2Tx Foam for Electromagnetic Interference Shielding.

To solve the pollution problem of electromagnetic waves, new electromagnetic shielding materials should meet the requirements of being lightweight with high electrical conductivity. In this work, the combination of silver (Ag) nanoparticles and nitrogen doping (N-doping) was expected to tune the electromagnetic and physical properties of Ti3C2Tx MXene, and the Ag@N-Ti3C2Tx composites were fabricated through the hydrothermal reactions. The nitrogen doped (N-doped) Ag@Ti3C2Tx composites showed a hollow structure with a pore size of 5 μm. The influence of N-doped degrees on the electromagnetic interference (EMI) shielding performance was investigated over 8–18 GHz. Therefore, the controlled N-doping composites exhibited reflection-based EMI shielding performance due to the electrical conductivity and the special three-dimensional (3D) honeycomb-like structure. The achieved average EMI shielding values were 52.38 dB at the X-band and 72.72 dB at the Ku-band. Overall, the Ag@N-Ti3C2Tx foam, due to its special 3D honeycomb-like structure, not only meets the characteristics of light weight, but also exhibits ultra-high-efficiency EMI shielding performance, revealing great prospects in the application of electromagnetic wave shielding field.

Scattering of plane waves by an open arc with different boundary conditions on its sides

The paper considers an approach to numerical modelling of the problem of electromagnetic plane waves scattering by an open arc with different boundary conditions on its sides. The corresponding mixed boundary value problem is reduced to a system of two singular and hypersingular integral equations. The method of collocation for numerical solutions to the equations obtained is proposed and analyzed. Numerical results of the radar cross-section for different values of arc curvatures are presented.

Solving the Eigenfrequencies Problem of Waveguides by Localized Method of Fundamental Solutions with External Source

The localized method of fundamental solutions (LMFS) is a domain-type, meshless numerical method. Compared with numerical methods that have a high grid dependence, it does not require grid generation and numerical integration, so it can effectively improve computational efficiency and avoid complex integration processes. Moreover, it is formed using the traditional method of fundamental solutions (MFS) and the localization approach. Previous studies have shown that the MFS may produce a dense and ill-conditioned matrix. However, the proposed LMFS can yield a sparse system of linear algebraic equations, so it is more suitable and effective in solving complicated engineering problems. In this article, LMFS was used to solve eigenfrequency problems in electromagnetic waves, which were controlled using two-dimensional Helmholtz equations. Additionally, the resonant frequencies of the eigenproblem were determined by the response amplitudes. In order to determine the eigenfrequencies, LMFS was applied for solving a sequence of inhomogeneous problems by introducing an external source. Waveguides with different shapes were analyzed to prove the stability of the present LMFS in this paper.

Domain decomposition and upscaling technique for metascreens

PurposeThis paper aims to consider a multiscale electromagnetic wave problem for a housing with a ventilation grill. Using the standard finite element method to discretise the apertures leads to an unduly large number of unknowns. An efficient approach to simulate the multiple scales is introduced. The aim is to significantly reduce the computational costs.Design/methodology/approachA domain decomposition technique with upscaling is applied to cope with the different scales. The idea is to split the domain of computation into an exterior domain and multiple non-overlapping sub-domains. Each sub-domain represents a single aperture and uses the same finite element mesh. The identical mesh of the sub-domains is efficiently exploited by the hybrid discontinuous Galerkin method and a Schur complement which facilitates the transition from fine meshes in the sub-domains to a coarse mesh in the exterior domain. A coarse skeleton grid is used on the interface between the exterior domain and the individual sub-domains to avoid large dense blocks in the finite element discretisation matrix.FindingsApplying a Schur complement to the identical discretisation of the sub-domains leads to a method that scales very well with respect to the number of apertures.Originality/valueThe error compared to the standard finite element method is negligible and the computational costs are significantly reduced.

A linearised inverse conductivity problem for the Maxwell system at a high frequency

We consider a linearised inverse conductivity problem for electromagnetic waves in a three dimensional bounded domain at a high time-harmonic frequency. Increasing stability bounds for the conductivity coefficient in the full Maxwell system and in a simplified transverse electric mode are derived. These bounds contain a Lipschitz term with a factor growing polynomially in terms of the frequency, a Hölder term, and a logarithmic term which decays with respect to the frequency as a power. To validate this increasing stability numerically, we propose a reconstruction algorithm aiming at the recovery of sufficiently many Fourier modes of the conductivity. A numerical evidence shed light on the influence of the growing frequency and confirms the improved resolution.

A Spectral Approach to Nondestructive Testing via Electromagnetic Waves

In recent years, a new approach has been proposed in the study of the inverse scattering problem for electromagnetic waves. In particular, a study is made of the analytic properties of the scattering operator, and the results of this study are used to design target signatures that respond to changes in the electromagnetic parameters of the scattering medium. These target signatures are characterized by novel eigenvalue problems such that the eigenvalues can be determined from measured scattering data. Changes in the structural properties of the material or the presence of flaws cause changes in the measured eigenvalues. In this article, we provide a general framework for developing target signatures and numerical evidence of the efficacy of new target signatures based on recently introduced eigenvalue problems arising in electromagnetic scattering theory for anisotropic media.

On an electromagnetic problem in a corner and its applications

Let $\mathcal{K}^{r_0}_{x_0}$ be a (non-degenerate) truncated corner in $\mathbb{R}^3$ with $x_0\in\mathbb{R}^3$ being its apex, and $\mathbf{F}_j\in C^\alpha(\overline{\mathcal{K}^{r_0}_{x_0}}; \mathbb{C}^3)$, $j=1,2$, where $\alpha$ is the positive H\"older index. Consider the following electromagnetic problem $$\left\{\begin{split} & \nabla\wedge \mathbf{E}-\mathrm{i}\omega \mu_0 \mathbf{H}=\mathbf{F}_{1} \quad \mbox{in $\mathcal{K}^{r_0}_{x_0}$},\\ & \, \nabla\wedge \mathbf{H}+\mathrm{i}\omega\varepsilon_0 \mathbf{E}=\mathbf{F}_{2} \quad \mbox{in $\mathcal{K}^{r_0}_{x_0}$}, \\ &\, \nu\wedge \mathbf{E}=\nu\wedge\mathbf{H}=0 \qquad\mbox{on $\partial \mathcal{K}^{r_0}_{x_0}\setminus \partial B_{r_0}(x_0)$}, \end{split}\right.$$ where $\nu$ denotes the exterior unit normal vector of $\partial \mathcal{K}^{r_0}_{x_0}$. We prove that $\mathbf{F}_1$ and $\mathbf{F}_2$ must vanish at the apex $x_0$. There are a series of interesting consequences of this vanishing property in several separate but intriguingly connected topics in electromagnetism. First, we can geometrically characterize non-radiating sources in time-harmonic electromagnetic scattering. Secondly, we consider the inverse source scattering problem for time-harmonic electromagnetic waves and establish the uniqueness result in determining the polyhedral support of a source by a single far-field measurement. Thirdly, we derive a property of the geometric structure of electromagnetic interior transmission eigenfunctions near corners. Finally, we also discuss its implication to invisibility cloaking.

Reaction–diffusion equation-based topology optimization code for electromagnetic wave problems using FreeFEM++

Reaction–diffusion equation-based topology optimization code for electromagnetic wave problems using FreeFEM++

Synthesis of hollow spherical MoS2@Fe3O4-GNs ternary composites with enhanced microwave absorption performance

To solve the problem of poor electromagnetic wave (EMW) absorbing performance caused by scarcely magnetic loss of pure graphene, the combination of graphene and magnetic materials becomes the main measures to enhance EMW absorbing properties. In this study, a primitive two-step hydrothermal and solvothermal method was employed to fabricate the hollow spherical MoS2@Fe3O4-GNs ternary composites, which avoids the complex process of template removal. When the thickness is 2.6 mm, the composite has the optimal reflection loss (RLmin) at 10.08 GHz, and the optimal reflection loss value is up to − 48.1 dB, and the effective absorbing bandwidth (EAB) can reach 4.08 GHz at 1.7 mm thickness. The composite materials not only have gratifying impedance matching performance, but also realize the effective coordination of magnetic loss and dielectric loss, showing the overall excellent absorbing performance benefits from the successful combination of the hollow core–shell structure of MoS2@Fe3O4 and GNs. Therefore, it has a broad prospect as an attractive alternative of lightweight absorbing materials with wideband.