Search

To accelerate the solution of electromagnetic scattering problems, compressive sensing (CS) has been introduced into the method of moments (MoM). Consequently, a computational model based on underdetermined equations has been proposed, which effectively reduces the computational complexity compared with the traditional MoM. However, while solving surface-integral formulations for three-dimensional targets by MoM, due to the severe oscillation of current signals, commonly used sparse bases become inapplicable, which renders the application of the underdetermined equation model quite challenging. To address this issue, this paper puts forward a scheme that employs Krylov subspace, which is constructed with low complexity by meticulously designing a group of non-orthogonal basis vectors, to replace the sparse transforms in the algorithmic framework. The principle of the method is elaborated in detail, and its effectiveness is validated through numerical experiments. [ABSTRACT FROM AUTHOR]

In this work we present a formalism based on scalar Green's functions to deal with electromagnetic scattering problems. Although the formulations of the Mie theory and Born approximations in terms of electromagnetic scattering are well known and relevant, they have certain disadvantages: complexity, computational time, few symmetries, etc. Therefore, the study with scalar Green's functions allows dealing with these problems with greater simplicity and efficiency. However, the information provided by the vector formulation is sacrificed. Nevertheless, different cases of electromagnetic scattering of dielectric media with different dimensions, geometries and refractive indices will be presented. Thus, we will be able to verify the capacity of this scalar method in predicting light-scattering problems. [ABSTRACT FROM AUTHOR]

In this paper, a novel measurement matrix construction method based on adaptive cross-approximation (ACA) is proposed to improve the performance of the compressive sensing-based method of moments (CS-MoM) for analyzing electromagnetic scattering problems. ACA is based on a weight scheme and is able to recognize the rows and columns that contribute significantly to the matrix. Thus, the object is divided into multiple blocks, and the impedance matrix is partitioned into near-field and far-field groups to establish the condition for applying ACA. Then, the row indexes are extracted from the group with the highest number of ACA recognized rows in the far-field groups of each block. Finally, by combining all row indexes to extract the impedance matrix, a lower-dimensional and deterministic measurement matrix is constructed, thereby improving computational efficiency. Numerical simulation results validate the accuracy and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article develops a method for recovering a one‐dimensional rough surface profile from scattered wave field, using a single receiver and repeated measurements when the surface is moving with respect to source and receiver. This extends a previously introduced marching method utilizing low grazing angles, and addresses the key issue of the requirement for many simultaneous receivers. The algorithm recovers the surface height below the receiver point step‐by‐step as the surface is moved, using the parabolic wave integral equations. Numerical examples of reconstructed surfaces demonstrate that the method is robust in both Dirichlet and Neumann boundary conditions, and with respect to different roughness characteristics and measurement noise. [ABSTRACT FROM AUTHOR]

In order to study the effect of the circulation control technology on the electromagnetic scattering characteristics of the wing, a variety of low-scattering carrier models were designed based on the characteristics of the circulation control wing and the mechanical rudder surface. The radar scattering cross sections of the different models were then calculated by using the multilayer fast multipole algorithm. A comparative analysis of different models revealed that the use of the circulation control technique can reduce the front RCS level of the wing. Furthermore, the scaling effect was found to be more significant for the HH-polarised RCS at high frequency and the VV-polarised RCS at low frequency. The air source cavity structure of the jet system will increase the front and back RCS levels of the wing. Conversely, the back RCS level can be reduced by the oblique design of the jet nozzle. In the process of achieving attitude control, the wing applying the circulation control technique can significantly reduce its own front and side RCS levels, as well as the fluctuations of RCS levels throughout manoeuvres, in comparison to the usage of mechanical rudders. The findings of the study elucidate the scattering characteristics of the circulation control wing, which can serve as a reference for the stealth performance of unconventional layout aircraft. [ABSTRACT FROM AUTHOR]

Radar detection technology has been used to observe meteors since the last century. According to the echoes of electromagnetic waves scattered by meteor trails, the drift velocity of meteors is calculated to research the atmospheric dynamics characteristics in their distribution height. In this paper, complementary code sequences are applied to a Very High Frequency (VHF) ionospheric sounding system. Unlike the common VHF meteor radar, the system parameters can be set with a pulse duty cycle, allowing for flexible adjustment of detection range. At the same time, the detection frequency can also be adjusted within a certain range, breaking through the traditional fixed frequency detection mode. Moreover, by employing a miniaturized antenna array composed of an orthogonal dipole antenna for the VHF receiving, the system takes account of the requirements of the inversion algorithms of meteor radar and the detection need for the irregularities sounding concurrently, achieving the function of detecting multiple targets. Therefore, the system is called the Wuhan VHF Comprehensive Sounding (WHCS) system. This system has the function of integrating transmission and reception, which can be directly detected by a single station or synchronously detected through the separation of transmission and reception. This system has the function of internal channel calibration to compensate for the phase error of meteor echoes. Through further analysis of the detection data, the height distribution of meteors, as well as typical echoes of ionospheric irregularities, were obtained. The experiments verified the availability of the system scheme and its engineering application significance. [ABSTRACT FROM AUTHOR]

We propose a perturbative method to compute electromagnetic scattering from slightly rough dielectric surfaces, which leads to the same result as the usual Small Perturbation Method (SPM) in a surprisingly simple way. The proposed method is based on three pillars: the volumetric perturbative approach, the reciprocity theorem, and a proper approximation of the electric field within the perturbation volume, that we name Internal Field Approximation (IFA). The proposed new mathematical derivation of the SPM turns out to be much simpler and more concise than the classical one. In addition, being based on a volumetric perturbation approach, it has the potential of dealing in future with surface and volume scattering within a unitary framework, which is useful in modelling scattering from, e.g., vegetated soil, snow-covered terrain, and inhomogeneous soils. Therefore, although the presented result is mainly theoretical, it can have important applications in remote sensing. [ABSTRACT FROM AUTHOR]

A novel hybrid algorithm combining the 3‐D vector finite element method‐boundary integral method (FEM‐BIM) with the half‐space Green's function with the rough‐surface interface is developed in this paper to study the scattering from a 3‐D coated target above a perfectly electric conducting (PEC) rough surface. The half‐space Green's function is derived from the Kirchhoff approximation (KA). The 3‐D vector FEM is applied to model the coated object, and the BIM with the half‐space Green's function is selected as the exact radiation boundary conditions. The accuracy of our numerical code is validated by the numerical method. Some numerical results are provided to study the electromagnetic scattering characteristics from a coated sphere above a Gaussian rough surface. [ABSTRACT FROM AUTHOR]

An effective formula for the shape-sensitivity analysis of electromagnetic scattering is presented in this paper. First, based on the boundary element method, a new electromagnetic scattering formula is derived by combining the traditional electromagnetic scattering formula with the non-uniform rational B-spline (NURBS) curve, and the geometric model is represented by NURBS, which ensures the geometric accuracy, avoids the heavy grid division in the optimization process, and realizes the fast calculation of high-fidelity numerical solutions. Second, by deducing the sensitivity variables, the electromagnetic scattering equation of shape optimization is obtained, which can provide reliable data references for shape optimization. Finally, the effectiveness and accuracy of the algorithm are demonstrated by an example, and the sensitivity data of some examples are given. [ABSTRACT FROM AUTHOR]

Consider time-harmonic electromagnetic wave scattering by an infinitely long, cylindrical, orthotropic dielectric partially coated with a very thin layer of a highly conductive material, which can be modeled by a transmission problem with mixed boundary conditions. Having established the well-posedness of the direct and interior transmission problem by the variational method under certain conditions, we make use of the classical linear sampling method to reconstruct the shape of the obstacle. Then, based on a modification of the general data-to-pattern operator G, we propose a novel and simple method to justify the modified linear sampling method. [ABSTRACT FROM AUTHOR]

Electromagnetic scattering is a routine tool for rapid, non-contact characterization of particle media. In previous work, the interaction targets of scattering intensity, scattering efficiency, and extinction efficiency of Bessel pincer light-sheet beams were all aimed at dielectric spheres. However, most particles in nature are charged. Considering the boundary condition on a charged sphere, the beam shape coefficients (BSCs) ( p m n , q m n ) of the charged spherical particle illuminated by a Bessel pincer light-sheet beam are obtained. The extinction, scattering, and absorption efficiencies are derived under the generalized Lorenz–Mie theory (GLMT) framework. This study reveals the significant differences in scattering characteristics of Bessel pincer light-sheet beams on a charged particle compared to traditional beams. The simulations show a few apparent differences in the far-field scattering intensity and efficiencies between charged and natural spheres under the influence of dimensionless size parameters. As dimensionless parameters increase, the difference between the charged and neutral spheres decreases. The effects of refractive index and beam parameters on scattering, extinction, and absorption coefficients are different but tend to converge with increasing dimensionless parameters. When applied to charged spheres with different refractive indices, the scattering, extinction, and absorption efficiencies of Bessel pincer light-sheet beams change with variations in surface charge. However, once the surface charge reaches saturation, these efficiencies become stable. This study is significant for understanding optical manipulation and super-resolution imaging in single-molecule microbiology. [ABSTRACT FROM AUTHOR]

We present an approach to identifying topological edge states in two dimensional (2D) problems. Such scattering-immune surface waves are typically identified using the Berry concept, which evaluates Chern numbers of bulk transmission bands. Instead, here, we approach the task from an analytical electromagnetic scattering perspective, which enables the study of a wide class of configurations in which waves are confined to propagate at the interface between a topologically non-trivial magnetized plasma and a topologically trivial medium such as air. Although it is of theoretical significance to classify interfacial states by their topological invariants, we believe that this approach enables the engagement of a broader range of researchers, particularly experimentalists who seek to design devices that exploit the ensuing non-reciprocal and scattering-immune properties. [ABSTRACT FROM AUTHOR]

Abstract The non‐relativistic motion of media induces very weak effects on electromagnetic fields. For this reason, it is extremely difficult to compute such effects with traditional techniques. To overcome this difficulty, a novel approach is introduced in this work. It is based on the Born approximation of the solution of electromagnetic problems involving media in motion. The formulation of these problems makes use of equivalent field sources and is specifically tailored to find the effects of motion on the electromagnetic field. The new methodology exploits traditional simulators able to deal with media at rest. The motion of the materials has to be managed by specific programs performing simple algebraic calculations. The simplest of the methods proposed does not present any additional complexity with respect to more traditional approaches to the same problems. All methods deal with time‐harmonic electromagnetic fields and, for this reason, they can manage materials in motion with stationary boundaries. A complete set of simulations for cylinders moving in the axial direction show that the new methods outperform traditional numerical approaches and, in some significant cases, traditional approaches based on semi‐analytical techniques. The good features of the new methodology are shown to hold true for a range of velocity values spanning 11 decades; such a range covers most of the applications of practical interest.

Abstract The authors propose a system of closely coupled‐complementary frequency‐selective surfaces (FSSs) based on the four‐arms star geometry with dual‐ and triple‐passbands responses for 5G applications. Four complementary structure configurations are presented, and depending on the chosen configuration, the structure can create two or three transmission bands in one or both polarisations of the electromagnetic waves. The designed FSSs are compact and have stable behaviour at different incident angles. The complementary FSS passes signals around 2.6 and 6.2 GHz, and a structural offset allows the transmission at a third frequency (4.2 GHz). To validate the proposed designs, four prototypes are fabricated and measured. Numerical and experimental characterisations are in good agreement.

Abstract The authors present spatio‐temporally resolved wideband measurements of Sub‐Terahertz (Sub‐THz) reflection coefficients in the frequency range of 92–110 GHz. A stochastic model for single reflection fixed links that is capable of modelling random scattering from small‐scale discontinuities such as those encountered in complex structures in walls and partitions of buildings is presented. The model auto‐regressively produces filter coefficients that are fed into an Infinite‐Impulse‐Response (IIR) filter which convolves them with the spatio‐temporal series in order to generate the next output sample based on previous observations. The IIR filter allows for flexible stochastic generation of samples, and its parameters can be adjusted as needed to suit different channel conditions. A total of 20 suitable start‐up filter coefficients are generated from 21.7 % of the sample size for each complex delay tap distribution, which corresponds to 50 complex instances of the channel. These coefficients are then utilised to validate the remaining measured sample set. The model is in quantitative agreement with measurement statistics and can be used to construct relatively simple modified reflection coefficients that can be used in micro‐cellular ray‐optical network planning tools.

This paper presents a metallic object classification method using various electromagnetic pulses. Each electromagnetic pulse irradiated eight metallic objects placed at increasing distances from 10 mm to 40 mm relative to the electromagnetic sensing system. The electromagnetic sensing system consisted of two RL circuits placed in close proximity. Objects were classified using linear (perceptron and multiclass logistic regression) and non-linear (neural network, 1D convolutional neural network (CNN) and 2D CNN) machine learning classifiers. The machine learning classifiers were trained on experimental data collected in an electromagnetically shielded laboratory. A 10-fold cross-validation mean classification accuracy of 99.4 ± 0.3% for the 1D CNN classifier, and 92.9 ± 1.2% for the 2D CNN classifier, was achieved using a rectangular chirp electromagnetic pulse. The rectangular chirp pulse outperformed two-sided decaying exponential, Gaussian, triangular, raised cosine, and rectangular pulses. All pulses had equal energy. While the rectangular chirp performed best overall, other pulses more accurately distinguished between some objects. [ABSTRACT FROM AUTHOR]

Electromagnetic ion cyclotron (EMIC) waves are a key plasma mode affecting radiation belt dynamics. These waves are important for relativistic electron losses through scattering and precipitation into Earth's ionosphere. Although theoretical models of such resonant scattering predict a low‐energy cut‐off of ∼1 MeV for precipitating electrons, observations from low‐altitude spacecraft often show simultaneous relativistic and sub‐relativistic electron precipitation associated with EMIC waves. Recently, nonresonant electron scattering by EMIC waves has been proposed as a possible solution to the above discrepancy. We employ this model and a large database of EMIC waves to develop a universal treatment of electron interactions with EMIC waves, including nonresonant effects. We use the Green's function approach to generalize EMIC diffusion rates foregoing the need to modify existing codes or recompute empirical wave databases. Comparison with observations from the electron losses and fields investigation mission demonstrates the efficacy of the proposed method for explaining sub‐relativistic electron losses by EMIC waves. Plain Language Summary: Precipitation of energetic electrons from the equatorial magnetosphere to the Earth's ionosphere plays a crucial role in the dynamics of the radiation belt and ionosphere ionization. Such precipitation is primarily driven by wave‐particle interactions. However, accurately modeling these interactions requires precise knowledge of the electron energy ranges which is affected by different wave modes present in the equatorial magnetosphere. A notable challenge arises from the contradiction between model‐predicted energy ranges of electron precipitation by electromagnetic ion cyclotron (EMIC) waves and the energies observed by spacecraft during such precipitation events. By combining a new theoretical approach with detailed observational data sets of these waves, we successfully resolved this contradiction, offering a powerful tool for the simulation of electron precipitation driven by EMIC waves. Key Points: We provide a statistical model of nonresonant electron scattering by electromagnetic ion cyclotron wavesWe show the main wave and electron parametric regions where nonresonant effects can be important for electron precipitationWe derive an analytical approximation allowing generalization of the quasi‐linear diffusion rates including nonresonant effects [ABSTRACT FROM AUTHOR]

In this paper, the electromagnetic wave (EMW) absorption properties of SiCN ceramics with a shellular structure prepared by 3D printing technology (DLP) at different pyrolysis temperatures were investigated. The research shows that polarization loss and multiple reflections are the principal reasons for the improvement in sample absorption performance. The shellular structure is favorable for the multiple reflections and scattering of electromagnetic wave inside the material. The turbostratic carbon, graphitic carbon and SiC generated by pyrolysis are conducive to improving the dielectric loss of the sample, adjusting its impedance matching performance and improving its absorption performance. The RL min of SiCN-1200 reaches − 21.12 dB (3.22 mm), and the effective band width is 4.20 GHz, covering the whole X-band. The excellent EMW absorption performance of DLP-SiCN ceramics, together with additive manufacturing, enable the integration of material, structure and function within a single component. [ABSTRACT FROM AUTHOR]

A finite difference delay modeling (FDDM) method accelerated by adaptive cross approximation‐singular value decomposition (ACA‐SVD) is developed to solve time‐domain combined field integral equations for transient electromagnetic scattering. In the proposed method, the variable s in the Laplace domain is expressed as a difference function about z in the z‐transform domain to achieve the temporal discretization, thus improving the stability of the solution. And the method is purely algebraic and does not depend on the Green's function. It takes advantage of the rank‐deficient nature of the impedance submatrix blocks in the FDDM to reduce the memory requirement and the computational cost. The rank‐deficient submatrix blocks can reach the maximum compression level through the ACA‐SVD. Numerical results about the electromagnetic scattering from perfect electric conducting objects are given to verify the validity and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This work studies time-dependent electromagnetic scattering from obstacles whose interaction with the wave is fully determined by a nonlinear boundary condition. In particular, the boundary condition studied in this work enforces a power law type relation between the electric and magnetic fields along the boundary. Based on time-dependent jump relations of classical boundary operators, we derive a nonlinear system of time-dependent boundary integral equations that determines the tangential traces of the scattered electric and magnetic fields. These fields can subsequently be computed at arbitrary points in the exterior domain by evaluating a time-dependent representation formula. Fully discrete schemes are obtained by discretizing the nonlinear system of boundary integral equations with Runge–Kutta based convolution quadrature in time and Raviart–Thomas boundary elements in space. Error bounds with explicitly stated convergence rates are proven, under the assumption of sufficient regularity of the exact solution. The error analysis is conducted through novel techniques based on time-discrete transmission problems and the use of a new discrete partial integration inequality. Numerical experiments illustrate the use of the proposed method and provide empirical convergence rates. [ABSTRACT FROM AUTHOR]

This letter presents experimental angularly resolved measurements and a model framework for characterizing continuous wideband reflection coefficients at sub‐terahertz frequencies between 92 and 110 GHz. Surfaces that appear "smooth" but with internal features comparable to the wavelength have shown to cause frequency selective scattering. An nth‐degree polynomial regression model is employed to quantify non‐linear multi‐path scattering that cannot be described by a best‐fit line, with least‐squares regression applied to find the best‐fitting polynomial and hence the coefficients. The obtained coefficients are then validated against the delay domain statistics of the propagation channel, demonstrating the proposed model's good agreement with measurements and its efficiency in reproducing angle‐dependent reflection coefficients for use in ray‐tracing tools. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of traditional scattering evaluation methods in near-field scattering prediction, a novel fast scattering calculation algorithm suitable for a near-field region is proposed in this paper. Based on physical optics, combined with locally modified approximate Green's function, the integral expressions of near-field electromagnetic scattering radiated by a plane wave and a dipole source are derived in a frequency domain. The simulation results show that the modified algorithm not only retains the simplicity and efficiency of the traditional code, but also can be directly used for near-field scattering prediction. [ABSTRACT FROM AUTHOR]

In this work, an efficient numerical method is proposed for three-dimensional (3D) electromagnetic scattering from multiple coated targets buried under a two-dimensional dielectric rough surface. In the proposed method, the interior region of each coated target is regarded as an independent subregion. The field within each coated target is modeled by 3D vector finite element method (FEM). The multiple scattering interactions between the buried targets and between targets and rough surface are considered by the electric field integral equation and the Poggio–Miller–Chang–Harrington–Wu integral equations, respectively. The fields inside and outside the targets are coupled together via boundary conditions on the boundary of each target. To improve the calculation efficiency and reduce the memory requirement, the fast multipole technique is used in our method. The presented method is numerically validated by comparing it with method of moments and conventional FEM-boundary integral method (BIM). The results indicate that, compared with traditional FEM-BIM, our method has significant advantages in computational efficiency and memory requirements. [ABSTRACT FROM AUTHOR]

A novel numerical method is introduced for minimising the presence of scattering echoes in the frontal area of a dielectric ellipsoid through the application of the method of auxiliary sources (MAS) method. This approach utilises a Gaussian radio pulse that spans the frequency spectrum from 0 to 6 GHz. The approach involves determining the properties of an ellipsoid, such as its dimensions and a dielectric permittivity, using a specially developed MATLAB software package to make this ellipsoid invisible. This provides a valuable military and defence technology tool, particularly for stealth and invisibility technology applications. It is beneficial for avoiding detection by radar systems utilised for enemy surveillance and identifying concealed objects. This aims to eliminate the need for metamaterials for invisibility cloaking. The suggested methodology has been confirmed through a validation process, which involved a comparison of the outcomes derived from numerical experiments conducted during pulse echo observations using the FDTD method and an analytical solution. MAS offers a notable advantage over other methods and commercial software by significantly reducing computational time for simulating and analysing 3D dielectric objects. This allows for quicker consideration of various parameter scenarios and optimisation for desired outcomes. [ABSTRACT FROM AUTHOR]

This paper addresses the inverse scattering problem for Maxwell's equations in three-dimensional anisotropic periodic media. We study a new imaging functional for the fast and robust reconstruction of the shape of anisotropic periodic scatterers from boundary measurements of the scattered field. The implementation of this imaging functional is simple and avoids the need to solve an ill-posed problem. The resolution and stability analysis of the imaging functional is investigated. Results from our numerical study indicate that this imaging functional is more stable than that of the factorization method and more accurate than that of the orthogonality sampling method in reconstructing periodic scatterers. [ABSTRACT FROM AUTHOR]

The authors propose a system of closely coupled‐complementary frequency‐selective surfaces (FSSs) based on the four‐arms star geometry with dual‐ and triple‐passbands responses for 5G applications. Four complementary structure configurations are presented, and depending on the chosen configuration, the structure can create two or three transmission bands in one or both polarisations of the electromagnetic waves. The designed FSSs are compact and have stable behaviour at different incident angles. The complementary FSS passes signals around 2.6 and 6.2 GHz, and a structural offset allows the transmission at a third frequency (4.2 GHz). To validate the proposed designs, four prototypes are fabricated and measured. Numerical and experimental characterisations are in good agreement. [ABSTRACT FROM AUTHOR]

The authors present spatio‐temporally resolved wideband measurements of Sub‐Terahertz (Sub‐THz) reflection coefficients in the frequency range of 92–110 GHz. A stochastic model for single reflection fixed links that is capable of modelling random scattering from small‐scale discontinuities such as those encountered in complex structures in walls and partitions of buildings is presented. The model auto‐regressively produces filter coefficients that are fed into an Infinite‐Impulse‐Response (IIR) filter which convolves them with the spatio‐temporal series in order to generate the next output sample based on previous observations. The IIR filter allows for flexible stochastic generation of samples, and its parameters can be adjusted as needed to suit different channel conditions. A total of 20 suitable start‐up filter coefficients are generated from 21.7 % of the sample size for each complex delay tap distribution, which corresponds to 50 complex instances of the channel. These coefficients are then utilised to validate the remaining measured sample set. The model is in quantitative agreement with measurement statistics and can be used to construct relatively simple modified reflection coefficients that can be used in micro‐cellular ray‐optical network planning tools. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Guangxi Normal University - Natural Science Edition is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims to improve the efficiency of constructing basis functions for solving the electromagnetic scattering problem of objects using the method of moments combined with compressive sensing and Krylov subspace. To this end, a region decomposition method based on a clustering algorithm is proposed to accelerate the construction process of Krylov subspace basis functions. First, the midpoints of the common edges of triangular pairs are used to form a clustered dataset. Then, the initial clustering center is set, and the processes of clustering center updating and regional decomposition of the constructed dataset are completed iteratively. Finally, each subdomain is expanded according to the average distance from data points to the clustering center to ensure the continuity of currents. The numerical computation results show that the proposed method can achieve significant time efficiency. [ABSTRACT FROM AUTHOR]

Scattering of electromagnetic waves by a dielectric object can be described as an integral equation involving a Green function. These types of problems can be solved using a spatial spectral formulation, which requires sampling of the spectral Green function. To avoid sampling around the singularities on or near the real axis, the spectral Green function is represented on three separate complex paths. Using appropriate selection functions, these paths are recombined such that the original Fourier integrals are retrieved. This composite path method provides a general way to solve domain integral equations involving Green functions with simple singularities with minimal computational overhead. [ABSTRACT FROM AUTHOR]

The non‐relativistic motion of media induces very weak effects on electromagnetic fields. For this reason, it is extremely difficult to compute such effects with traditional techniques. To overcome this difficulty, a novel approach is introduced in this work. It is based on the Born approximation of the solution of electromagnetic problems involving media in motion. The formulation of these problems makes use of equivalent field sources and is specifically tailored to find the effects of motion on the electromagnetic field. The new methodology exploits traditional simulators able to deal with media at rest. The motion of the materials has to be managed by specific programs performing simple algebraic calculations. The simplest of the methods proposed does not present any additional complexity with respect to more traditional approaches to the same problems. All methods deal with time‐harmonic electromagnetic fields and, for this reason, they can manage materials in motion with stationary boundaries. A complete set of simulations for cylinders moving in the axial direction show that the new methods outperform traditional numerical approaches and, in some significant cases, traditional approaches based on semi‐analytical techniques. The good features of the new methodology are shown to hold true for a range of velocity values spanning 11 decades; such a range covers most of the applications of practical interest. [ABSTRACT FROM AUTHOR]

A novel nano-laminated GdB2C2 material was successfully synthesized using GdH2, B4C, and C via an in situ solid-state reaction approach for the first time. The formation process of GdB2C2 was revealed based on the microstructure and phase evolution investigation. Purity of 96.4 wt.% GdB2C2 was obtained at a low temperature of 1500 °C, while a nearly fully pure GdB2C2 could be obtained at a temperature over 1700 °C. The as-obtained GdB2C2 presented excellent thermal stability at a high temperature of 2100 °C in Ar atmosphere due to the stable framework formed by the high-covalence four-member and eight-member B-C rings in GdB2C2. The GdB2C2 material synthesized at 1500 °C demonstrated a remarkably low minimum reflection loss (RLmin) of −47.01 dB (3.44 mm) and a broad effective absorption bandwidth (EAB) of 1.76 GHz. The possible electromagnetic wave absorption (EMWA) mechanism could be ascribed to the nano-laminated structure and appropriate electrical conductivity, which facilitated good impedance matching, remarkable conduction loss, and interfacial polarization, along with the reflection and scattering of electromagnetic waves at multiple interfaces. The GdB2C2, with excellent EMWA performance as well as remarkable ultra-high-temperature thermal stability, could be a promising candidate for the application of EMWA materials in extreme ultra-high temperatures. [ABSTRACT FROM AUTHOR]

The simulation of microwave absorption and external thermal flow is an essential aspect of the vacuum thermal testing process for Synthetic Aperture Radar (SAR) antenna. This paper proposes a novel integrated method for simulating microwave absorption and external thermal flow, specifically designed for vacuum thermal testing. The method employs a non-woven fabric square pyramid assembly as the primary structure to establish a low electromagnetic scattering environment. External heat flow simulation is achieved by arranging carbon fiber heating wires between square cones. Through numerical analysis and experimental tests, the influence of the position of the carbon fiber heating wire on the uniformity of heat flow and reflectivity was revealed. A prototype system is developed based on these findings. The external thermal flow is adjustable in the range of 80–550 W/m2, with a uniformity better than 5%. The reflectivity in the L to X microwave frequency band is basically better than −25 dB, and in local frequency bands, it is better than −30 dB. The system has been successfully applied in SAR antenna component and satellite vacuum thermal tests, meeting all ground simulation test requirements and exhibiting significant potential for widespread application. [ABSTRACT FROM AUTHOR]

This paper investigates the electromagnetic fields being scattered by a metal spherical object in a vacuum environment, providing a numerical implementation of the obtained analytical results. A time-harmonic magnetic dipole source, far enough, emits the incident field at low frequencies, oriented arbitrarily in the three-dimensional space. The aim is to find a detailed solution to the scattering problem at spherical coordinates, which is useful for data inversion. Based on the theory of low frequencies, the Maxwell-type problem is transformed into Laplace's or Poisson's interconnected equations, accompanied by the proper boundary conditions on the perfectly conducting sphere and the radiation conditions at infinity, which are solved gradually. Broadly, the static and the first three dynamic terms are sufficient, while the terms of a higher order are negligible, which is confirmed by the field graphical representation. [ABSTRACT FROM AUTHOR]

We establish Lipschitz stability properties for a class of inverse problems. In that class, the associated direct problem is formulated by an integral operator A m depending nonlinearly on a parameter 푚 and operating on a function 푢. In the inversion step, both 푢 and 푚 are unknown, but we are only interested in recovering 푚. We discuss examples of such inverse problems for the elasticity equation with applications to seismology and for the inverse scattering problem in electromagnetic theory. Assuming a few injectivity and regularity properties for A m , we prove that the inverse problem with a finite number of data points is solvable and that the solution is Lipschitz stable in the data. We show a reconstruction example illustrating the use of neural networks. [ABSTRACT FROM AUTHOR]

This paper proposes an accelerated ray tracing method utilizing the Embree3 ray tracing library for targets with non-uniform thickness materials. In contrast to the traditional surface-based ray tracing, the proposed approach performs ray tracing within the materials, since surface tracing is ineffective for materials with non-uniform thickness. To ensure efficiency and handle the overlapping grids between different materials, the Embree3 ray tracing library is introduced to ray intersection. Numerical results confirm that the proposed method surpasses existing methods in terms of efficiency and applicability while maintaining accuracy. [ABSTRACT FROM AUTHOR]

In the present work the scattering problem of electromagnetic waves by a penetrable chiral body embedded in a chiral environment is formulated and studied. Vector potentials in terms of the dyadic fundamental solution of the differential operator for chiral media are defined and used in order to study the solvability of the direct scattering problem. Moreover, these potentials are used in order to study the mathematical foundation of the method of fundamental solutions (MFS) in chiral media. It is proven that the approximation of the sought for solution of the direct scattering problem via the MFS is reduced to the approximation of the known boundary data from appropriately constructed systems of functions for which linear independence and completeness on the surface of the scatterer are proven. An inverse electromagnetic scattering problem is presented and studied in order to obtain information about the geometrical properties of a perfectly conducting scatterer of unknown size embedded in a chiral medium. A MFS technique is applied in order to solve this type of inverse scattering problems. Numerical results are presented for the special geometrical case of spherical scattering objects for both direct and inverse scattering problems in chiral media. [ABSTRACT FROM AUTHOR]

In this paper, we study time-harmonic electromagnetic scattering in two scenarios, where the anomalous scatterer is either a pair of electromagnetic sources or an inhomogeneous medium, both with compact supports. We are mainly concerned with the geometrical inverse scattering problem of recovering the support of the scatterer, independent of its physical contents, by a single far-field measurement. It is assumed that the support of the scatterer (locally) possesses a conical singularity. We establish a local characterisation of the scatterer when invisibility/transparency occurs, showing that its characteristic parameters must vanish locally around the conical point. Using this characterisation, we establish several local and global uniqueness results for the aforementioned inverse scattering problems, showing that visibility must imply unique recovery. In the process, we also establish the local vanishing property of the electromagnetic transmission eigenfunctions around a conical point under the Hölder regularity or a regularity condition in terms of Herglotz approximation. [ABSTRACT FROM AUTHOR]

This paper is concerned with the uniqueness in inverse acoustic and electromagnetic scattering problems with phaseless near-field data generated by superpositions of two incident plane waves at a fixed frequency. It can be proved that the unknown scatterer can be uniquely determined by the phaseless near-field data. The proof is based on the analysis of the phase information and the application of Rellich's lemma together with the Green's formula for the radiating solutions to the Helmholtz equation or the Stratton–Chu formula for the radiating solutions to the Maxwell equations. [ABSTRACT FROM AUTHOR]

While reverse time migration (RTM) algorithm is commonly used in geophysical explorations, this paper addresses the RTM imaging procedure for reconstructing of lossy dielectric discontinuities in a planar waveguide using electromagnetic waves at a single frequency. The direct problem of the related configuration is solved via method of moments (MoM) to produce the synthetic scattered data to be used in RTM. The achievements of the method are examined and verified by including different numerical examples. It is shown that the RTM approach can be used as an alternative imaging methodology in parallel plate waveguide problems. [ABSTRACT FROM AUTHOR]

This research involved studying the characteristics of composite electromagnetic scattering from a rocket moving above actual terrain using the finite-difference time-domain method. The angular distribution curve of the composite scattering coefficient was obtained, and the influences of factors such as the angle of incidence, the frequency of the incident electromagnetic wave, the content of moisture in soil, the dielectric constant of the rocket-shell material, the height of the rocket, and the undulation of the terrain on the composite scattering coefficient were investigated. Results show that the composite scattering coefficient oscillates with the scattering angle and increases in the direction of mirror reflection. It also decreases with increasing angle of incidence, frequency of the incident wave, and altitude of the rocket, while it increases with increasing soil moisture and dielectric constant of the rocket-shell materials. Although the influence of different terrain undulations on the composite scattering coefficient is noticeable, it follows no fixed pattern. [ABSTRACT FROM AUTHOR]

This paper concentrates on an interaction scattering problem between the time-harmonic electromagnetic waves and an unbounded periodic elastic medium. The uniqueness results of the interaction problem are established for small frequencies or all frequencies except a discrete set in both the absorbing and nonabsorbing medium, and then the existence of solutions is derived by the classical Fredholm alternative. The perfectly matched layer (PML) method is proposed to truncate the unbounded scattering domain to a bounded computational domain. We prove the well-posedness of the solution for the truncated PML problem, where a homogeneous boundary condition is imposed on the outer boundary of the PML. The exponential convergence of the PML method is established in terms of the thickness and parameters of the PML. The proof is based on the PML extension and the exponential decay properties of the modified fundamental solution. [ABSTRACT FROM AUTHOR]

We propose a new "disappearing positron track" channel at Belle II to search for dark matter, in which a positron that is produced at the primary interaction vertex scatters with the electromagnetic calorimeter to produce dark matter particles. Such scatterings can occur via either annihilation with atomic electrons, or the bremsstrahlung process with target nuclei. The main backgrounds are due to photons and neutrons that are produced in the same scatterings and then escape detection. We require a large missing energy and further veto certain activities in the KLM detector to suppress such backgrounds. To illustrate the sensitivity of the new channel, we consider a new physics model where dark matter interacts with the standard model via a dark photon, which decays predominantly to dark matter; we find that our proposed channel can probe some currently unexplored parameter space, surpassing both the mono-photon channel at Belle II and the NA64 constraints. [ABSTRACT FROM AUTHOR]

This paper presents a massively parallel approach of the multilevel fast multipole algorithm (PMLFMA) on homegrown many-core SW26010 cluster of China, noted as (SW-PMLFMA), for 3-D electromagnetic scattering problems. In this approach, the multilevel fast multipole algorithm (MLFMA) octree is first partitioned among management processing elements (MPEs) of SW26010 processors following the ternary partitioning scheme using the message passing interface (MPI). Then, the computationally intensive parts of the PMLFMA on each MPI process, matrix filling, aggregation and disaggregation are accelerated by using all the 64 computing processing elements (CPEs) in the same core group of the MPE via the Athread parallel programming model. Different parallelization strategies are designed for many-core accelerators to ensure a high computational throughput. In coincidence with the special characteristic of local Lagrange interpolation, the compressed sparse row (CSR) and the compressed sparse column (CSC) sparse matrix storage format is used for storing interpolation and anterpolation matrices, respectively, together with a specially designed cache mechanism of hybrid dynamic and static buffers using the scratchpad memory (SPM) to improve data access efficiency. Numerical results are included to demonstrate the efficiency and versatility of the proposed method. The proposed parallel scheme is shown to have excellent speedup. [ABSTRACT FROM AUTHOR]

A semi‐analytic solution for scattering from a semi‐elliptical cavity with arbitrary orientation placed in a perfect electric conductor plane is suggested. By imposing the boundary conditions at an elliptical border, three independent equations containing the Mathieu functions series are extracted. Finally, the solution of the problem is reduced to the solution of a simple system of linear equations by using Mathieu function addition theorem and the orthogonal properties of the angular Mathieu functions. Some examples are presented to demonstrate the reliability and the accuracy of the proposed solution. [ABSTRACT FROM AUTHOR]

Given the escalating prevalence of electromagnetic pollution, there is an urgent need for the development of high‐performance electromagnetic interference (EMI) shielding materials. Herein, wood‐based electromagnetic shielding materials have gained significant popularity due to their exceptional performance as building materials. In this study, a novel wood‐based composite with electromagnetic shielding properties is developed. Through the in situ growth of zeolitic imidazolate framework‐8 (ZIF‐8) crystals on wood fibers, coupled with uniform integration of carbon nanotubes (CNTs), a multifunctional composite named ZIF‐8/Poplar‐CNT composite is synthesized via a one‐step thermoforming process. The incorporation of CNTs endows the composites with excellent EMI shielding effectiveness (EMI SE). Among these elements, despite ZIF‐8 crystals not possessing intrinsic electromagnetic shielding functionality, their distinctive dodecahedral structure proves adept at scattering and reflecting electromagnetic waves within the composites, further improving the electromagnetic shielding effect. Hence, the ZIF‐8/Poplar‐CNT composite (56.95 dB) has ≈10 dB higher EMI SE compared to that of the composites without ZIF‐8 crystals. Meanwhile, ZIF‐8 crystals endow the materials with excellent tensile strength (54.84 MPa, enhanced by 4 times). Moreover, the introduction of Zn2+ provides superior antibacterial properties. The potential applications of ZIF‐8/Poplar‐CNT composites extend to diverse areas such as building decoration, electronic products, and medical equipment. [ABSTRACT FROM AUTHOR]

The finite‐difference time‐domain (FDTD) method often demands numerous grids for fine structure analysis, leading to high computational costs. To address this challenge, a subgridding scheme emerges as an attractive solution. However, the explicit nature of the FDTD subgrid method, constrained by Courant–Friedrichs–Lewy (CFL) conditions, can lead to inefficiencies with complex structures. In response, the leapfrog alternating‐direction implicit (ADI)‐FDTD method, exhibiting unconditional stability, has been developed to overcome CFL limitations. This paper presents a hybrid approach merging the one‐step leapfrog ADI‐FDTD method with a subgridding scheme using heterogeneous computing. By optimizing hardware usage and leveraging different device performances, this approach maximizes throughput in heterogeneous systems. Central processing units and graphics processing units handle workloads to minimize system latency. Simulation results on heterogeneous platforms demonstrate superior efficiency over single processor setups while maintaining simulation accuracy, especially in analyzing electromagnetic scattering from multiscale structures. [ABSTRACT FROM AUTHOR]

In this paper, we explore interferences arising in the electromagnetic scattering by an object buried inside a layer with two rough interfaces by using the GPILE method. We show that there are two categories of interferences in the echoes that make up GPILE: the interferences that are present whatever the chosen scenario and those that come from the geometry of the problem (distance between the three scatterers). In this last category, we can cite for example the interferences which come from the position of the object, more precisely from its depth, because an object closer to one of the surfaces would produce echoes which arrive almost at the same time as those of the nearby interface. [ABSTRACT FROM AUTHOR]

In this paper, a generalized manner is developed for the problem of the scattering of H-polarized electromagnetic waves from a shallow cavity with an arbitrary profile. Considering a proper auxiliary border and employing the region-matching technique, some close-form expressions are derived to compute the fields inside and outside the cavity. Next, we apply this approach to two cavities with different shapes and verify it by the Method of Moments (MoM). [ABSTRACT FROM AUTHOR]

The electromagnetic characteristics analysis of the scattering signals from targets, which usually exist or are hidden in the surrounding environment, is one of the necessary prerequisites for the reliable reception of echo signals. Utilizing the GNSS signals as an opportunistic illumination source for detecting maritime targets has vast development prospect and scientific application value. GNSS signals, including GPS signals, are the right-hand circular polarization waves at L-band. Therefore, in this study, a comprehensive electromagnetic composite scattering model is established under circular polarization, which encompasses sea surface scattering, target single scattering, target multiple scattering, and coupled scattering between the target and sea surface. Then, the research investigates the variation characteristics of different scattering components (including the scattering of sea surface, the first, second, and third-order scattering of target, the total scattering of target, the coupled scattering of target induced by the reflection waves from sea surface, and the coupled scattering of sea surface induced by the reflection waves from target) in the composite scene under different polarizations, incident angles, wind speeds, and headings. The results indicate that the scattering of sea surface under LR polarization (which means that the polarization states of scattering and incident wave are left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), respectively) is significantly greater than that under RR polarization, while the opposite trend is observed for the target. Therefore, in the applications such as the detection and identification of ship targets on sea surface, it is better to choose the right-hand circular polarization channel to receive the scattering echo signal from target, which could effectively suppress the scattering echo of sea surface. These findings are of crucial significance in enhancing the effectiveness and accuracy of maritime target detection. [ABSTRACT FROM AUTHOR]