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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]

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]

In this paper, a technology named SCM−ANN combining physical scattering mechanisms and artificial intelligence is proposed to realize radar cross-section (RCS) extrapolation of non-cooperative conductor targets with higher efficiency. Firstly, an adaptive scattering center (SC) extraction algorithm is used to construct the scattering center model (SCM) for non-cooperative targets from radar echoes in the low-frequency band (LFB). Secondly, an artificial neural network (ANN) is constructed to capture the nonlinear relationship between the real LFB echoes and those reconstructed from the SCM. Finally, the SCM is used to reconstruct echoes in the high-frequency band (HFB), and these reconstructions, together with the trained ANN, optimize the extrapolated HFB RCS. For the SCM−ANN technology, physical mechanistic modes are used for trend prediction, and artificial intelligence is used for regression optimization based on trend prediction. Simulation results show that the proposed method can achieve a 50% frequency extrapolation range, with an average prediction error reduction of up to 40% compared with the traditional scheme. By incorporating physical mechanisms, this proposed approach offers improved accuracy and an extended extrapolation range compared with the RCS extrapolation techniques relying solely on numerical prediction. [ABSTRACT FROM AUTHOR]

The rise of water‐based electromagnetic devices opens up new possibilities for controlling electromagnetic performance due to the liquid state of crucial parts of the device. This letter proposes the siphon mechanism as a novel way to achieve reconfigurability in these types of electromagnetic devices. To demonstrate this, a simple polarization‐reconfigurable device based on a siphon is introduced. The device is designed to scatter horizontal and vertical polarizations differently depending on the amount of water added to it. The siphon mechanism offers a sharp transition between two states after water is added above a threshold. The device is simulated, manufactured using 3D printing, and measured in different states filled with both distilled and tap water. The results demonstrate that polarization reconfigurability is achieved with the different states scattering the two polarizations as expected. Siphons similar to this could be used to offer new types of control in other electromagnetic devices based on liquids. [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]

The scattering of x linearly polarized non-diffracting Lommel beam by a perfect electromagnetic conductor (PEMC) sphere is analyzed within the generalized Lorenz–Mie theory (GLMT) framework. The electromagnetic fields of the incident Lommel beams are expressed by employing spherical vector wave functions (SVWFs) and beam shape coefficients (BSCs). These BSCs are mainly considered in the expression of shaped beams in the GLMT with slight beam axicon angle. The scattered electromagnetic fields are constructed using unknown scattering field coefficients (SFCs) and SVWFs. These undetermined SFCs are calculated employing boundary conditions (BCs) at the PEMC surface. The expressions of the far-region/far-zone scattering intensity (FSI) are given and computed. The influences of Lommel beam configuration parameters like as beam order, beam half cone angle, beam asymmetry parameter, beam center coordinates positions, and PEMC sphere size parameter in addition to PEMC scalar admittance on the FSI are analyzed and discussed. The experience of this research work will be quite helpful in analyzing optical radiation force and torque, electromagnetic scattering, light manipulation, antenna engineering domain, optical tweezers, particle interaction, and trapping. Moreover, findings of the study can also be extended to study the interaction between the non-diffracting Lommel beam and the metamaterial structures. [ABSTRACT FROM AUTHOR]

With the rapid development of high-resolution radar imaging technology, artificial intelligence, and big data technology, remarkable advancements have been made in the intelligent interpretation of radar imagery. Despite growing demands, radar image intrpretation is now facing various technical challenges mainly because of the particularity of the radar sensor itself and the complexity of electromagnetic scattering physical phenomena. To address the problem of microwave radar imagery perception, this article proposes the development of the cross-disciplinary microwave vision research, which further integrates electromagnetic physics and radar imaging mechanism with human brain visual perception principles and computer vision technologies. This article discusses the concept and implication of microwave vision, proposes a microwave vision perception model, and explains its basic scientific problems and technical roadmaps. Finally, it introduces the preliminary research progress on related issues achieved by the authors’ group.

A novel image-reconstruction method is proposed for the processing of data acquired at random spatial positions. The images are reconstructed and updated in real time concurrently with the measurements to produce an evolving image, the quality of which is continuously improving and converging as the number of data points increases with the stream of additional measurements. It is shown that the images converge to those obtained with data acquired on a uniformly sampled surface, where the sampling density satisfies the Nyquist limit. The image reconstruction employs a new formulation of the method of scattered power mapping (SPM), which first maps the data into a three-dimensional (3D) preliminary image of the target on a uniform spatial grid, followed by fast Fourier space image deconvolution that provides the high-quality 3D image. [ABSTRACT FROM AUTHOR]

In practical radar applications, the diversity of wideband transmission signals presents a significant challenge for radar target recognition systems. Traditional electromagnetic (EM) simulation methods often require the point-by-point sampling of target echo signals under specific radiation sources, and this process must be repeated for different transmission signals. This results in extensive EM computations and low computational efficiency. Additionally, the physical attribute information of the target is often obscured within the simulated echoes, complicating feature extraction. To address these issues, we propose a novel method for the efficient and rapid modeling and analysis of complex target time-domain echoes based on a forward scattering center model. This method constructs an impulse response model of the target under unit impulse signal excitation, representing the inherent scattering properties of the target and remaining unaffected by changes in the radiation source. Subsequently, this model is convolved with arbitrary wideband input signals to quickly reconstruct the wideband echo signals of the target. Numerical examples validate the accuracy and effectiveness of the proposed model. This method offers several advantages: firstly, it provides high computational efficiency by quickly convolving with the input signals, thereby avoiding the extensive EM calculations required by traditional methods due to changes in the radiation source. Secondly, it achieves significant data compression; the proposed echo model only requires the model parameters to be calculated at the central frequency point, enabling the rapid reconstruction of target echo data across a wideband range and effectively reducing storage requirements. Finally, it presents clear and complete physical attributes by employing a "cause-to-effect" forward-modeling approach, where the model parameters fully represent the inherent physical properties of the target. This effectively addresses the issue of physical interpretability in optical region radar target recognition. [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 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]

The plasma sheath can absorb or reflect electromagnetic waves, thus affecting the communication of hypersonic vehicles. The study of attenuation and enhancement of electromagnetic scattering by plasma is of great significance. We propose a novel Z-transform finite-difference time-domain (ZT-FDTD) method to study the interaction between electromagnetic waves and plasmas. The numerical results show that this method has high accuracy and improves the computational efficiency by 9.8 percent, compared to the traditional ZT-FDTD method. We investigated the enhancement and attenuation of electromagnetic scattering by plasma at different plasma frequencies and plasma collision frequencies. The variation in the electric field amplitude in the plasma was studied under different electromagnetic scattering conditions. Through the hybrid plasma model, the changes in electromagnetic scattering and in the electric field amplitude under plasma stealth were further investigated. The position of the maximum electric field amplitude and the variation in the zero-value region of the electric field amplitude correspond to the different effects of plasma on electromagnetic scattering. The research methods and ideas in this study have important reference values and provide a new perspective for studying plasma stealth technology and solving the “blackout” problem.

Open-source software has been highly influential on software development in many fields, and also has a history within computational electromagnetics. With large amounts of open-source code available, both from within computational electromagnetics and from other fields, new combinations can be made by using already existing code packages. This can be especially beneficial to developers who do not otherwise have access to a substantial codebase. In this article we describe how a finite element-boundary integral code using the adaptive cross approximation was developed by combining different existing open-source software packages with new code in Python. We provide a brief overview of the numerical methods used, but our focus is on the implementation and insights that might be useful to others who could benefit from using open-source software in their work. Three numerical examples are also presented to demonstrate accuracy, performance and use of complex materials. Our code is provided at github.com/nwingren/fe2ms both to demonstrate how the open-source packages were combined in practice, but also for those who wish to test the code themselves.

Fifth generation (5G) mobile communication systems have been deployed in the millimeter wave (mmWave) band. Since electromagnetic (EM) waves in this band exhibit high propagation loss and antennas are highly directive, the performance of wireless communications is largely degraded in a non-line-of-sight (NLOS) area, resulting in a limited coverage area. To improve the performance and increase the coverage area, a metamaterial-based electromagnetic scattering sheet (EMSS) with broad scattering characteristics is proposed in this paper. We also introduce fast design and optimization methods using equivalent circuits of metamaterials, antenna array theory, and the genetic algorithm (GA). The diffusion coefficient is used as a fitness value to evaluate the scattering characteristics of the EMSS generated by GA. The broad scattering characteristics of the designed EMSS are experimentally confirmed. We clarified that the optimized EMSS has a higher diffusion coefficient than a metal plate of the same size. Finally, we demonstrated improved wireless communication performance in an NLOS area by diffusing the incoming EM fields using our designed EMSS.

Propulsion systems are exposed to environmental ingestion hazards that can cause significant damage and decrease performance. Particles are ingested in a wide range of flight environments that can cause immediate engine failure or long-term damage. An accurate measurement technique has been developed to quantify particle ingestion and aid engine health monitoring. This sensor utilizes scattering and extinction techniques along with machine learning models to measure particle characteristics based on a robust and versatile library. The capabilities of this sensor have been demonstrated using solid quartz particles on the Rolls-Royce M250-C20B particle ingestion turboshaft test engine. To the authors' knowledge, this work presents the first demonstration and validation of optical solid particle sensing in a turbine engine. CSPEC sand (Mil-E-5007C) was ingested for the validation test at two different feed rates using a sand feeder. The sand concentrations were 45 mg/m³ and 22 mg/m³. The sensor outputs the particle characteristics of aspect ratio (AR), size distribution (s), Sauter mean diameter (D32), and the particle mass flowrate. The Sauter mean diameter and mass flowrate of ingested sand were calculated using the machine learning model outputs and validated by independent measurements. The sensor produced a 0.1 g/min RMS error compared to the validation measurement. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to learn the dynamic radar cross-section (RCS) of a deflection air brake. Design/methodology/approach: The aircraft model with delta wing, V-shaped tail and blended wing body is designed, and high-precision unstructured grid technology is used to deal with the surface of air brake and fuselage. The calculation method based on multiple tracking and dynamic scattering is presented to calculate RCS. Findings: The fuselage has a low scattering level, and the opening air brake will bring obvious dynamic RCS effects to itself and the whole machine. The average indicator of air brake RCS can be lower than –0.6 dBm2 under the tail azimuth, while that of forward and lateral direction is lower. The mean RCS of fuselage is obviously higher than that of air brake, while the deflected air brake and its cabin can still provide strong scattering sources at some azimuths. When the air brake is opening, the change amplitude of the aircraft forward RCS can exceed 19.81 dBm2. Practical implications: This research has practical significance for the dynamic electromagnetic scattering analysis and stealth design of the air brake. Originality/value: The calculation method for aircraft RCS considering air brake dynamic deflection has been established. [ABSTRACT FROM AUTHOR]

Electromagnetic scattering by a sphere is one of the most significant problem in electromagnetics as reported by the optical research community. Based on the framework of generalized Lorenz–Mie theory (GLMT), we investigated the scattering of a Gaussian Beam (a strongly focused basic TEM 00 mode laser beam) by a perfect electromagnetic conductor sphere. The influence of parameters i.e., sphere size parameter, beam waist radius, and beam center coordinate position on the scattering and extinction efficiencies, normalized energy flow, and scattering asymmetry factor is numerically analyzed. On varying the prior mentioned factors, the amplitude of efficiency factors is considerably modified. By increasing the waist radius, the normalized energy flow increases for the PEMC sphere. The investigation of the scattering characteristics for PEMC sphere illuminated by a Gaussian beam can also be extended to study the metamaterial structures. [ABSTRACT FROM AUTHOR]

Given their high analytical speed, iterative physical optics (IPO) algorithms present an advantageous approximation method for analyzing the electromagnetic scattering of electrically large objects. IPO approaches for radar cross-section (RCS) prediction are of two types-one based on integral equations, and the other based on reflection coefficients. Integral equation (IE)-based IPO approaches have remarkably low computational complexity and facilitates the analyses of conducting and impedance media. In contrast, reflection (R)-based IPO approaches can consider the absorption effects of surface currents, yielding a higher accuracy in analyzing dielectric media. This study compared and analyzed the formulas of IE-based and R-based IPO and examined their respective advantages and limitations. Complex media targets composed of lossy metals and dielectrics, such as fighters, tailless airplanes, and missiles, above rough ocean surfaces were examined. The surface currents and RCS obtained using each approach were verified by comparing the results with those from FEKO or an in-house full-wave simulation (MLFMM) [ABSTRACT FROM AUTHOR]

The studied configuration is a two-dimensional, very thin parabolic reflector made of graphene and illuminated by an H-polarized electromagnetic plane wave. We present basic scattering and focusing properties of such a graphene reflector depending on the graphene parameters at microwave frequencies, using the resistive boundary condition for very thin sheets. The scattering is formulated as an electromagnetic boundary-value problem; it is transformed to a singular integral equation that is further treated with the method of analytical regularization (MAR) based on the known solution of the Riemann–Hilbert Problem (RHP). The numerical results are computed by using a Fredholm second-kind matrix equation that guarantees convergence and provides easily controlled accuracy. Compared to THz range, in microwaves, the scattering pattern of reflector and the field level at geometrical focus can be controlled in a wide range by adjusting the chemical potential of graphene. Even though here no dielectric substrate supporting the graphene is considered, the practical realization can also be possible as a thin layer graphene material in GHz range. As we demonstrate, the variation of the chemical potential from 0 to 1 eV can improve the focusing ability within the factor of three. The high accuracy of the used method and the full wave formulation of the problem support our findings. [ABSTRACT FROM AUTHOR]

This paper equates chaff clouds to dipole clusters and studies the electromagnetic scattering problem of dipole clusters based on the linear method of moment (LMM) that solve the electric field Integral equation with the pulse basis function. Firstly, the radar cross section (RCS) of three dipole elements is calculated. The dipole element is divided into 11 segment line units using pulse basis functions. The actual chaff clouds are modeled as two nearest dipole cluster models, which are cubic dipole cluster with uniform distribution formed and spherical dipole cluster with Gaussian distribution formed. The total RCS and total E‐Field magnitude of two dipole cluster models were calculated. Finally, two physical models are constructed based on the simulation models and an experiment is designed. The electromagnetic scattering characteristics of the two models are measured, which verifies the accuracy of the simulation results and the operability of the experiment. [ABSTRACT FROM AUTHOR]

This article proposes a new fast solution algorithm (IGFBM-SAA), which combines the Improved Generalized Forward and Backward Method (IGFBM) with Spectral Acceleration Approach (SAA), which can effectively solve the electromagnetic scattering problem of layered rough surface. In this article, the electric field integral equations (EFIE) for layered rough surfaces is established, and the traditional forward and backward method (FBM) is introduced. Then, based on the traditional FBM algorithm, an Improved Generalized Forward and Backward Method is proposed and, by using the SAA technique in its iterative process, the computation of matrix-vector multiplication is accelerated, thus enabling rapid solution. In the algorithm validation, the same rough surface was calculated using the MoM, FBM, and IGFBM-SAA. The study found that when root mean square (RMS) heights are h1 = h2 = 0.1λ, the convergence accuracy can reach τ = 10-7 after 14 iterations. However, as the roughness increases to h1 = h2 = 0.3λ and h1 = h2 = 0.5λ, the convergence accuracy falling to τ = 10-5 and τ = 10-5, respectively. This indicates that it is necessary to adjust the integration parameters to improve the convergence accuracy. In addition, it was found that when the size of the rough surface is 25.6λ, the computational times for calculations are 91 s (IGFBM-SAA), 197 s (FBM), and 410 s (MoM), respectively. When the size of the rough surface increases to 51.2λ, the computational time differences become more significant, with 236 s, 756 s, and 2547 s being the respective values. This indicates that the proposed algorithm in this article has significant computational speed advantages when dealing with larger rough surfaces. Based on this algorithm, this article studied the electromagnetic scattering characteristics of layered rough surfaces with different parameters (RMS height, dielectric constant, and correlation length), and relevant research results can provide valuable references for areas such as radar target recognition and radar stealth technology, thereby enhancing the accuracy and reliability of radar detection as well as radar stealth performance. [ABSTRACT FROM AUTHOR]

The Doppler spectra of the scattering fields from sinusoidal water waves illuminated by a plane wave or Gaussian beam are numerically simulated with the method of moment (MoM). When the sinusoidal water surface is illuminated by a plane EM wave, the numerical results show that the Doppler spectrum of the scattering field is distorted seriously due to the frequency leakage. For this case, not only the resonance spectral peaks corresponding to the phase velocity of the water wave but also other equally spaced harmonic peaks appear on the spectrum curve. However, when the sinusoidal water surface is illuminated by a Gaussian beam with appropriate beam width, the harmonic peaks can be effectively suppressed. To better explain this phenomenon, the theoretical model for the spectrum of the scattering field from a sinusoidal water wave is derived based on the first-order small slope approximation theory (SSA-I). And this theoretical model proposed by us could give a reasonable explanation for the above phenomenon. [ABSTRACT FROM AUTHOR]

The scattering of perfect electromagnetic conductor (PEMC) sphere illuminated by a Hermite–Gaussian (HG) beam is studied. The PEMC is regarded as a generalization of both the perfect electric conductor and the perfect magnetic conductor. By utilizing vector potential, the incident and scattered electromagnetic fields for HG beams are expressed in the context of spherical vector wave functions. By implementing the boundary condition on PEMC sphere, the scattering coefficients of the HG beam in terms of beam expansion coefficients are derived. The numerical results in the context of normalized differential scattering cross section (DSCS) and polarization of the HG beam are computed. The influence of the HG beam configuration parameters i.e., (mode indices, beam waist radius, center coordinates) and PEMC electromagnetic admittance are explored. As the beam modes varies, the normalized DSCS was influenced owing to internal spatial degrees of freedom of the HG beam for non-zero beam modes. Polarizability is also very sensitive to the admittance of the PEMC sphere. So, admittance parameter regulates the polarization of the HG beam. It is hoped that the findings of this research would be valuable on light manipulation, PEMC coating sphere, and metamaterials. [ABSTRACT FROM AUTHOR]

To address the challenges posed by composite targets composed of an anisotropic medium and metal in electromagnetic (EM) scattering calculations, this paper introduces an innovative hybrid algorithm tailored for simulating the EM scattering characteristics of such complex targets. Utilizing impedance boundary condition (IBC), the method employs surface impedance vectors to precisely depict the EM properties of the medium. By harnessing the distinct advantages of the Method of Moments (MoMs) at low frequency and Physical Optics (POs) at high frequency, the algorithm ensures both accuracy and efficiency in the EM simulation of composite targets. By transforming the EM scattering problem of targets coated with a thin-layered medium into an equivalent radiation problem of EM currents on impedance surfaces, this research has achieved rapid and high-precision calculations of the Radar Cross Section (RCS) for complex targets with anisotropic medium coatings. To assess the performance of the algorithm, three target models—square plates, simplified aircraft, and complex satellites—are selected as test cases. The dual metrics of RCS and surface current distribution are utilized as evaluation benchmarks, and comparisons are made against the Method of Moments–Finite Element Method (MoM-FEM) hybrid numerical method. The comparative results demonstrate that the proposed method meets the engineering standards in terms of both the root mean square error (RMSE) of RCS and the relative error in surface current distribution, while also achieving a significant improvement of over 50% in computational efficiency, thereby validating its superior accuracy and practical utility. [ABSTRACT FROM AUTHOR]

In this paper, the volumetric shooting and bouncing rays method is proposed to investigate the electromagnetic (EM) scattering of the large‐scale target coated with plasma, which takes into account the EM rays propagating inside the interior of the plasma and fully captures the dominant scattering characteristics. Furthermore, an efficient graphics processing unit‐based implementation procedure with a ray management strategy is proposed to deal with the problem of the exponential increase of EM rays in plasma medium. The numerical results of a multilayer cuboid model and the RAM C‐II vehicle demonstrate the proposed method has a good computational efficiency and achieves a significant accuracy improvement compared to the traditional shooting and bouncing ray, with a root mean square error reduced from 13.29 dB to less than 4.96 dB. It indicates the proposed method has the potential to solve the EM scattering of the large‐scale target coated with plasma. Finally, some simulations of the RAM C‐II are performed at higher radar frequencies to illuminate that the plasma sheath causes complex scattering of the target of interest in terms of the flight speed, flight altitude, and radar frequency. [ABSTRACT FROM AUTHOR]

The dihedral structure, commonly found in various targets, exhibits strong backscattering, severely affecting their radar stealth performance. To address this issue, we propose an effective method for suppressing the electromagnetic scattering of dihedral structures using flexible stealth material (FSM) in this study. The electromagnetic scattering model encompassing the dihedral structure and FSM is established to explore the interaction between electromagnetic wave and dihedral structure coated with FSM, and the MLFMM is employed to calculate the monostatic RCS of the model from 8 to 12 GHz. The RCS of the dihedral structure, both before and after being coated with FSM under different loading conditions, is measured in an anechoic chamber. Notably, a relatively good agreement between the results of calculation and measurement is obtained, validating the reliability of the proposed model and calculation method. Furthermore, the effect of loading conditions and electromagnetic parameters of FSM on the RCS of the dihedral structure is investigated based on the proposed model. The results indicate the effectiveness of FSM in reducing the backscattering of dihedral structures. Specifically, when the direction of the incident wave's electric field is perpendicular to that of undulating units of FSM, FSM reduces the electromagnetic scattering of dihedral structures more significantly. Besides, the real part of FSM's permittivity and the imaginary of its permeability have a stronger influence on the RCS of dihedral structures. This study provides a useful method for suppressing electromagnetic scattering of dihedral structures and a valuable reference for FSM in practical applications. [ABSTRACT FROM AUTHOR]

We analyze the well-posedness of certain field-only boundary integral equations (BIEs) for frequency domain electromagnetic scattering from perfectly conducting spheres. Starting from the observations that (1) the three components of the scattered electric field E\mathrm{s}\mathrm{c}\mathrm{a}\mathrm{t}(x) and (2) scalar quantity E\mathrm{s}\mathrm{c}\mathrm{a}\mathrm{t}(x)\cdot x are radiative solutions of the Helmholtz equation, we see that novel boundary integral equation formulations of electromagnetic scattering from perfectly conducting obstacles can be derived using Green's identities applied to the aforementioned quantities and the boundary conditions on the surface of the scatterer. The unknowns of these formulations are the normal derivatives of the three components of the scattered electric field and the normal component of the scattered electric field on the surface of the scatterer, and thus these formulations are referred to as field-only BIEs. In this paper we use the combined field methodology of Burton and Miller within the fieldonly BIE approach, and we derive new boundary integral formulations that feature only Helmholtz boundary integral operators, which we subsequently show to be well posed for all positive frequencies in the case of spherical scatterers. Relying on the spectral properties of Helmholtz boundary integral operators in spherical geometries, we show that the combined field-only boundary integral operators are diagonalizable in the case of spherical geometries and their eigenvalues are nonzero for all frequencies. Furthermore, we show that for spherical geometries one of the field-only integral formulations considered in this paper exhibits eigenvalues clustering at one--a property similar to second-kind integral equations. [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.

In this paper, a technology named SCM−ANN combining physical scattering mechanisms and artificial intelligence is proposed to realize radar cross-section (RCS) extrapolation of non-cooperative conductor targets with higher efficiency. Firstly, an adaptive scattering center (SC) extraction algorithm is used to construct the scattering center model (SCM) for non-cooperative targets from radar echoes in the low-frequency band (LFB). Secondly, an artificial neural network (ANN) is constructed to capture the nonlinear relationship between the real LFB echoes and those reconstructed from the SCM. Finally, the SCM is used to reconstruct echoes in the high-frequency band (HFB), and these reconstructions, together with the trained ANN, optimize the extrapolated HFB RCS. For the SCM−ANN technology, physical mechanistic modes are used for trend prediction, and artificial intelligence is used for regression optimization based on trend prediction. Simulation results show that the proposed method can achieve a 50% frequency extrapolation range, with an average prediction error reduction of up to 40% compared with the traditional scheme. By incorporating physical mechanisms, this proposed approach offers improved accuracy and an extended extrapolation range compared with the RCS extrapolation techniques relying solely on numerical prediction.

The cockpit is one of the important scattering sources for conventional fighters in their nose direction. In order to study its scattering characteristics, the analysis method of influence of cockpit stealth measure on electromagnetic scattering was proposed. And the electromagnetic models of fighters with conventional and stealth cockpit were established based on a fighter. The RCS (Radar Cross Section) values in various states were calculated by Physical Optics(PO) method. The distribution characteristics of RCS curves and the response characteristics of electromagnetic scattering on pitch angle and frequency were analyzed. The results show that the cockpit stealth measures significantly reduce cavity scattering in nose direction, so that the peak of scattering curves in nose direction disappears and the curves converge inward. Besides, when the pitch angle is within a certain range, the RCS mean value with stealth cockpit in nose direction is about -20 dBsm (which incident frequency is 6 GHz), and the curves of relative reduction value is distributed in “W” shape with the variation of pitch angle, and the maximum value is 19.7887 dB when the pitch angle is 0 degrees. When the frequency increases, the RCS mean value in nose direction decreases gradually, while the relative reduction values change fluctuatly, and the maximum value is up to 24.6674 dB. And in the remaining angular domains, the response characteristics with pitch angle and multi-frequency are relative weak; and the conventional fighters’ stealth performance with different pitch angles and multi-frequency in the nose direction of angular domain can be improved by the stealth measures of cockpit. [ABSTRACT FROM AUTHOR]

Metallic nanoshells have emerged as promising optical cavities to steer hybridized plasmonic resonances that show the high spectral tunability and a large surface area of localized fields. Despite various optical and photochemical applications, plasmonic resonances in shells have rarely been explored at low frequencies due to a nonlinear increase in particle size and a rapid degeneration in field localization. Here, this work reports the experimental realization of hybridized plasmon resonances in origami metashells that can be excited by low‐energy photons ≈7 GHz, corresponding to a level below 10−4 eV. Metasurfaces built of interconnected meshes act as thin Drude metallic films that support symmetric spoof surface plasmons. Rigid folding of the metasurface leads to diverse 3D hollow cavities that exhibit strong plasmonic responses, large surface areas, and low relative densities. Experimental measurements demonstrate three typical behaviors in Drude metallic shells: shielding to quasi‐static fields, strong scattering at first‐order hybridized plasmon resonances, and transparency to high frequency radiation. The relative density is remarkably reduced owing to the void cavity enabled by 3D folding, and an extra degree of freedom in anisotropic load capacity is provided by customizing crease patterns. These results open a door for extremely low‐energy plasmons with low‐density mechanics. [ABSTRACT FROM AUTHOR]

In Electromagnetics, the field scattered by an ensemble of particles—of arbitrary size, shape, and material—can be obtained by solving the Lippmann–Schwinger equation. This singular vectorial integral equation is generally formulated in the direct space R n (typically n = 2 or n = 3 ). In the article, we rigorously computed the Fourier transform of the vectorial Lippmann–Schwinger equation in the space of tempered distributions, S ′ (R 3) , splitting it in a singular and a regular contribution. One eventually obtains a simple equation for the scattered field in the Fourier space. This permits to draw an explicit link between the shape of the scatterer and the field through the Fourier Transform of the body indicator function. We compare our results with accurate calculations based on the T-matrix method and find a good agreement. [ABSTRACT FROM AUTHOR]

This paper presents the implementation of the parallel hybrid implicit-explicit finite-difference timedomain (HIE-FDTD) method using the Message Passing Interface (MPI) library. The method proves to be very effective in simulating large-scale three-dimensional electromagnetic problems with fine structures in one direction. For the decomposition of the computational volume in the HIE-FDTD method, an MPI Cartesian 2D topology is implemented, allowing arbitrary division of the volume in two directions. Derived data types provided in the MPI library are employed to optimize inter-process communication. High accuracy and efficiency are subsequently demonstrated through a numerical example of a frequency-selected surface (FSS). It shows that the proposed method is very suitable for parallel computing, and the parallel efficiency maintains above 80% for different numbers of processes. [ABSTRACT FROM AUTHOR]

In this paper, the problem of scattering of a plane harmonic electromagnetic wave on a double wire array is solved accurately. The array consists of two identical infinite wire gratings arranged in a free space. Each of the grids consists of parallel thin, infinitely long metal cylinders of circular cross section. The study considers the case when the electric vector of the incident wave is parallel to the wires. The expression for the total reflection coefficient is obtained in the dipole approximation for the case of s -polarization. Analysis of the spectrum of the total reflection coefficient in the subwavelength part of the microwave frequency range was carried out. The paper proposes a new approach for determining the effective relative permittivity and permeability, as well as the effective refractive index of the grating. The approach does not depend on the number of grating layers and allows to taking into account near-field couplings in homogenizing the grating. This approach also allowed us to describe the behavior of the reflectivity and obtain expressions for the effective parameters of the grating at and near the resonant frequency. The validation of all the approximations obtained in the study was carried out using a finite-difference time-domain electromagnetic simulator. [ABSTRACT FROM AUTHOR]

ObjectiveThis study focuses on the turning ship Kelvin wake and its electromagnetic scattering characteristics in order to provide a theoretical foundation for the detection and recognition of nonlinear ship wakes. MethodsBased on the existing Kelvin wake geometric modeling and coordinate transformation methods, a turning ship Kelvin wake is obtained by the continuous changing of a ship's heading. The semi-deterministic facet scattering model (SDFSM) is then used to simulate the electromagnetic scattering characteristics of the arc-shaped Kelvin wake, and calculations and comparisons are performed of the distribution of the facet scattering coefficients of a straight Kelvin wake and arc-shaped Kelvin wake under different navigation speeds and headings. ResultsThe various kinds of wave components of a turning ship Kelvin wake are different from those of a straight Kelvin wake. At the same time, the vertical reception-vertical transmission (VV) scattering characteristics of a composite straight Kelvin wake and the counterparts of a composite turning ship Kelvin wake, which are shown in the figures of scattering coefficient distribution, exhibit significantly different features. ConclusionsThe brightness of the distribution of the Kelvin wake scattering coefficient and the wave vector directions of the different components of the wake are closely related to the relative relationship of radar direction. The results of this study can provide a theoretical basis for applications such as ship information perception, detection, recognition and stealth.

The radar seeker is the core equipment for the terminal guidance of precision-guided weapons. It has significant benefits, such as long range and weather resistance, and plays an important role in ensuring the accuracy of missile strikes. Sea corner reflectors have excellent characteristics, such as high scattering similarity of ship targets and combat effectiveness ratio, and they have emerged as one of the primary sources of interference for radar seekers with major consequences for radar detection performance. Therefore, a difficult and critical issue in ensuring the accuracy of radar seekers is accurately and efficiently identifying sea corner reflectors. Research on the electromagnetic scattering characteristics of corner reflectors is the foundation for improving radar identification capability. This paper first introduces sea corner reflector equipment and its tactical application. The research progress in elucidating the electromagnetic scattering characteristics of sea corner reflectors is then summarized. In addition, the research achievements in radar technology for identifying sea corner reflectors are summarized, and the characteristics of existing problems pertaining to various methods are presented. Simultaneously, their future development trends of the technology are discussed.

In practical radar applications, the diversity of wideband transmission signals presents a significant challenge for radar target recognition systems. Traditional electromagnetic (EM) simulation methods often require the point-by-point sampling of target echo signals under specific radiation sources, and this process must be repeated for different transmission signals. This results in extensive EM computations and low computational efficiency. Additionally, the physical attribute information of the target is often obscured within the simulated echoes, complicating feature extraction. To address these issues, we propose a novel method for the efficient and rapid modeling and analysis of complex target time-domain echoes based on a forward scattering center model. This method constructs an impulse response model of the target under unit impulse signal excitation, representing the inherent scattering properties of the target and remaining unaffected by changes in the radiation source. Subsequently, this model is convolved with arbitrary wideband input signals to quickly reconstruct the wideband echo signals of the target. Numerical examples validate the accuracy and effectiveness of the proposed model. This method offers several advantages: firstly, it provides high computational efficiency by quickly convolving with the input signals, thereby avoiding the extensive EM calculations required by traditional methods due to changes in the radiation source. Secondly, it achieves significant data compression; the proposed echo model only requires the model parameters to be calculated at the central frequency point, enabling the rapid reconstruction of target echo data across a wideband range and effectively reducing storage requirements. Finally, it presents clear and complete physical attributes by employing a “cause-to-effect” forward-modeling approach, where the model parameters fully represent the inherent physical properties of the target. This effectively addresses the issue of physical interpretability in optical region radar target recognition.

A novel image-reconstruction method is proposed for the processing of data acquired at random spatial positions. The images are reconstructed and updated in real time concurrently with the measurements to produce an evolving image, the quality of which is continuously improving and converging as the number of data points increases with the stream of additional measurements. It is shown that the images converge to those obtained with data acquired on a uniformly sampled surface, where the sampling density satisfies the Nyquist limit. The image reconstruction employs a new formulation of the method of scattered power mapping (SPM), which first maps the data into a three-dimensional (3D) preliminary image of the target on a uniform spatial grid, followed by fast Fourier space image deconvolution that provides the high-quality 3D image.

The utilization of physics-informed deep learning (PI-DL) methodologies provides an approach to augment the predictive capabilities of deep learning (DL) models by constraining them with known physical principles. We utilize a PI-DL model called the deep operator network (DeepONet) to solve two-dimensional (2D) electromagnetic (EM) scattering problems. Numerical results demonstrate that the discrepancy between the DeepONet and conventional method of moments (MoM) is small, while maintaining computational efficiency. [ABSTRACT FROM AUTHOR]

To study the V-tail inclination of a supersonic missile that meet the requirements of low electromagnetic scattering characteristics in interval flight, an automatic tilt scheme is presented. The improved annealing algorithm is used to determine the optimal solution of the V-tail tilt angle, where multiple scattering of the physical optics plus physical theory of diffraction is used to calculate the radar cross section (RCS) of the target. The results show that the optimal solutions of V-tail inclination are different in various flight intervals of the horizontal observation field. In the forward side flight interval, changing the initial azimuth has less influence on the optimal solution of V-tail tilt angle, while more influence on the missile RCS indicator. In the side tail flight interval, the RCS level of the missile is low, and there is an optimal solution and a few feasible solutions for the V-tail inclination. The feasible solution of V-tail tilt angle in the lateral flight interval is obviously increased. The presented automatic tilt scheme is effective for studying the low scattering performance of the supersonic missile V-tail.

The acquisition of inverse synthetic aperture radar (ISAR) images of aircraft targets in complete attitude is challenging due to the noncooperative nature of the aircraft targets. To determine the characteristics of the scattering centers of aircraft targets when the attitude changes, an effective scattering center model based on the ISAR images is proposed in this letter. First, the attitude sensitivity of the aircraft target ISAR image in azimuth and pitch is analyzed. Then, a sinc mixture model (SMM) based on the ISAR imaging principle with the aim to describe the characteristics of the target scattering center and a method for estimating the SMM’s parameters are proposed. Finally, target images at arbitrary attitude are reconstructed by combining the target scattering center theory. Furthermore, compared with conditional generative adversarial network (CGAN) and linear interpolation (LI), simulation results confirm that the proposed method is effective. [ABSTRACT FROM AUTHOR]