Perfect Conductor Research Articles

Recovery of impenetrable rough surface profiles via CNN-based deep learning architecture

ABSTRACT In this paper, a convolutional neural network (CNN)-based deep learning (DL) architecture for the solution of an electromagnetic inverse problem related to imaging of the shape of the perfectly electric conducting (PEC) rough surfaces is addressed. The rough surface is illuminated by a plane wave and scattered field data is obtained synthetically through the numerical solution of surface integral equations. An effective CNN-DL architecture is implemented through the modelling of the rough surface variation in terms of convenient spline type base functions. The algorithm is numerically tested with various scenarios including amplitude only data and shown that it is very effective and useful.

Analysis of electromagnetic scattering from typical targets for orbital‐angular‐momentum waves: Theoretical model

The target scattering characteristics in microwave band are necessary to be researched for Orbital-Angular-Momentum (OAM) wave-based radar applications. A theoretical description of electromagnetic (EM) scattering from a typical target by OAM waves is proposed in this paper. First, OAM waves are decomposed into plane waves in the spectral domain with different elevation and azimuth angles. Then, the scattering form of each decomposed plane wave is determined through coordinate system transformation and physical optics approximation. Formulas and numerical results are presented for OAM-based radar scattering cross section of a perfect electric conductor and dielectric plate and a cylinder. Unlike the conventional results of EM plane wave scattering, the scattering properties of OAM waves from plate and cylinder are analysed with particular emphasis on OAM mode influence. The results provide insights into OAM wave-matter interactions and may find important applications in wave propagation and OAM wave-based radar detection and imaging.

Localized Green's function using a beam-pattern for the fast modeling of 2D electromagnetic scattering

ABSTRACT This study presents an alternative approach to the numerical solution of 2D electromagnetic scattering problems using a hybrid numerical technique based on a beam pattern function combined with the method of moments (MoM). A surface field distribution with finite width radiates outward, and it is used to define the new Green's function. This new Green's function has a beam aperture localized on the surface, and its beam width can be reduced to a few basis function levels by using a generalized pencil of beam function method (GPOF). This localization of the new Green's function brings to the sparsity in the main matrix. Then, the memory storage and the overall running times are reduced significantly by applying this localized radiation of Green's function. Numerical results have been presented in both polarizations for the single perfectly electrically conducting (PEC) strip geometry and 2D PEC objects with closed polygonal cross-sections such as square, triangle and arbitrary shapes.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

Learning-Based Inversion Method for Solving Electromagnetic Inverse Scattering With Mixed Boundary Conditions

In this article, a unified learning-based approach is introduced to solve inverse scattering problems (ISPs) with mixed boundary conditions (BCs). The scattering behavior of hybrid dielectric and perfect electric conductors (PEC) scatterers is modeled by the T-matrix method. A rough image of the zero-order T-matrix coefficients for unknown scatterers is first reconstructed by the backpropagation (BP) method, which is then refined by an attention-assisted pix2pix generative adversarial network (GAN). The spatial attention mechanism is utilized to enforce the generator network to learn salient features of the unknown scatterers instead of the background. The adversarial training of the generator and the discriminator further enables the reconstructed image to be constrained by high-level features of reference scatterers. Numerical tests on both synthetic and experimental data verify the superior performance of the proposed method for ISP reconstructions with hybrid scatterers. It effectively expands the application scope of learning-based ISP methods to reconstruct scatterers without knowing the BCs of scatterers in advance.

A D-Band Corporate-Feed Gap-Cavity Slot Array Antenna Using Virtual PEC Method

A D-band corporate-feed gap-cavity slot array is proposed with wide bandwidth and high aperture efficiency. The cavity with higher order modes is implemented by using the gap waveguide (WG) technology, namely, a gap cavity. To ensure that the gap cavity is operating with the desired higher order mode over a wide bandwidth, the corporate-feed architecture is applied for uniform excitation and with alternating-phase between adjacent slots. The gap cavity is split into multiple elements by using zero-thickness virtual perfect electric conductor (PEC) walls. With this unique approach, the design, fabrication, and assembly complexities are reduced. For experimental verification, a gap cavity with an 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 slot array is designed in the 120 GHz band, and an E-plane WG feeding network is proposed to excite the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">880</sub> -mode. Two metal fences are introduced on either side of the radiating slot, and an inductive metal pin is introduced below the radiating slot to improve the radiation performance and broaden the bandwidth. The measured impedance matching bandwidth is around 110–144.8 GHz (27.3%). The measured peak gain is 26.22 dBi at 137.64 GHz, and the measured peak aperture efficiency is 86.2% at 115.325 GHz. The 3 dB gain bandwidth is the same as the impedance matching bandwidth.

2-D Green’s Function for an Elliptically Layered Cylindrical PEC Enclosure

In this communication, a semianalytical solution for the computation of the 2-D Green’s function for a cylindrical perfect electric conducting (PEC) enclosure containing an arbitrary number of confocal elliptic dielectric layers is provided. The approach relies on an expansion of the Green’s function into Mathieu functions, whose coefficients are found in an efficient way through a recursive procedure. The effectiveness of the technique is evaluated by comparisons with analytical formulas and against the results provided by independent numerical solvers. Moreover, the applicability of the solution to forward scattering problems using integral formulations is also assessed. In all the considered cases, the developed approach has been found to provide accurate results.

Morphological, mechanical, and thermal properties of polyurethane nanocomposites co‐incorporated with micro‐ Al 2 O 3 /nano‐ Al 2 O 3 for flexible thermal conductive component applications

Thermoplastic polyurethane (TPU) nanocomposites (TPU/μmAl2O3-ACA/nmAl2O3) with excellent mechanical, thermal stability and thermal conductivity were fabricated by co-incorporating aluminate coupling agent DL-411 chemically functionalized micron Al2O3 (μmAl2O3-ACA) and nano-Al2O3 (nmAl2O3) through melt blending method. FTIR analysis indicated that DL-411 has been successfully grafted on the surface of μmAl2O3, which was beneficial to the homogeneous dispersion of Al2O3 particles and enhancements of interfacial interactions between Al2O3 particles and TPU matrix. Adding μmAl2O3-ACA and nmAl2O3 simultaneously showed obvious synergistic effects on improving the mechanical properties of TPU nanocomposites. The optimum mechanical properties were obtained at the mass ratio of μmAl2O3-ACA to nmAl2O3 of 3:1. Both μmAl2O3-ACA and nmAl2O3 particles were homogeneously dispersed, constructing relatively perfect thermal conductivity networks, as verified by FESEM and PLM observations. The thermal conductivity (k) of TPU nanocomposites increased continuously with the addition of μmAl2O3-ACA/nmAl2O3 particles, and the optimal k (0.28 W/m K) was achieved when the mass ratio of μmAl2O3-ACA to nmAl2O3 was 3:1, which increased by 53% compared with pure TPU (k = 0.183 W/m K). TGA showed that, in contrast to those of pure TPU, the maximum decomposition temperature of TPU/μmAl2O3-ACA/nmAl2O3 nanocomposites increased by 77.77°C, and the decomposition activation energy of TPU nanocomposite enhanced by 178%.

A Theoretical Proposal for an Ultrabroadband Metamaterial Absorber for the Circular Polarization Waves Based on Anapole Mode in the Near‐Infrared Region

AbstractThe absorber excited by anapole response is in the spotlight owing to its non‐radiating merits, whereas the existing designs suffer from poor bandwidth and absorption. Furthermore, the circular polarization (CP) wave promises numerous application scenarios; thus, the absorbers aimed at it are sorely called for. An ultrabroadband metamaterial absorber (MMA) for the CP waves based on anapole mode is proposed in this paper. In this structure, the symmetrical split‐ring resonators (SRRs) are acted as the resonant unit to excite the toroidal dipole (TP) and electric dipole (EP) moments in the near‐infrared region. By applying the perfect electric conductor mirror effect, the enhanced field energy results in the absorption peak in the given band. Aimed at optimizing the absorption performance of the designed MMA, the SRRs are rotated, introduce the cavity resonance, and add the nickel patch to excite more electromagnetic resonance. The final optimized MMA can achieve an absorption exceeding 90% in an ultrabroadband of 1228–2156.7 nm, whose relative absorption bandwidth is 54.9%. Meanwhile, on account of its highly symmetrical structure, the MMA is insensitive to the polarization state of the CP waves. These splendid properties make the MMA a good candidate for potential applications.

Scattering from a Truncated Metamaterial Layer Hosted by a Planar PEC Structure: Uniform Asymptotic Solution and Validation Tests

This research paper proposes an analytical approach for evaluating electromagnetic scattering from a planar complex object made of a perfect electric conductor, which hosts a double negative metamaterial half-layer on the lit face. The method is based on the physical optics approximation of equivalent sources and works in the framework of the uniform geometrical theory of diffracion, so that the scattered field in the surrounding free space is obtained by adding the reflected contribution and the diffracted one, which is originated by the surface break. The effectiveness of the proposed approach is tested and proved by using a full-wave numerical tool to generate reference values.

Reversible Conversion of Odd/Even One-Way Modes in Magneto-Optical Photonic Crystal Double-Channel Waveguides.

We have studied the transmission properties of odd/even one-way modes and their reversible conversion in a double-channel waveguide consisting of two magneto-optical photonic crystals (MOPCs) sandwiched with Al2O3 PC. There exist two pairs of even and odd modes, i.e., M1(even)/M2(odd) or M3(odd)/M4(even) modes, for the double-channel waveguides with one- or two-stranded coupling layer of Al2O3 rods, respectively. Among them, the M1, M2, and M3 modes are caused by the weak coupling strength of two sub-waveguides, while the M4 mode results from the strong coupling effect and supports dispersionless slow-light propagation. Furthermore, we realize the reversible conversion between odd and even modes (i.e., between M1 and M2 modes, or M3 and M4 modes) in the one- or two-stranded structure, respectively, by adjusting the length and position of the perfect electric conductor (PEC) defect properly to cause the desired significant phase delay along the upper and lower equivalent transmission paths. Additionally, we find that the robustness of the M1 even mode is poor because of extra excitations of counter-propagation modes near the right Brillouin boundary, while the other three modes have extremely strong robustness against PEC defects and their one-way transmittances are nearly 100%. These results hold promise for many fields, such as slow-light modulation and the design of topological devices.

A Novel Design of Microwave Absorbers Based on Multilayered Composite Materials for Reduction of Radar Cross Section

Reduction of radar cross section (RCS) for targets can be achieved by different approaches and coating absorbing materials at the surfaces of targets is one of widely used methods because of its flexibility and good effect. In the work, we put forward a novel method of reducing the RCS based on the design of multilayer composite absorbing materials. The transmission line theory and particle swarm optimization (PSO) are used to guide the design and analysis, and two kinds of designs, i.e., Type IV and Type VII, are selected finally. Simulation experiments show that the designs are insensitive to the incident angles and polarizations of incident EM wave, which is required for being coated at the surfaces of real objects. Also, the designed absorbing materials are very thin and have an ultra-wide frequency band. The bandwidth of Type-IV design can reach 14.6314.63 GHz, ranging from 3.373.37 to 18.018.0 GHz, while Type-VII design can cover the frequency range from 2.02.0 to 18.018.0 GHz, which represents the major part of radar’s frequency range. The designed absorbing materials are coated at the surface of a perfectly-electric-conducting (PEC) cylinder to validate the effectiveness of the materials, and good results have been obtained.

Novel broadband angular stable linear‐circular and linear‐cross polarizer based on inductive grid loaded H‐dipole in both reflection and transmission modes

A novel broadband linear-circular and linear-cross polarization converter for K to Ka-band applications is demonstrated in this work. The proposed structure primarily consists of an inductive grid in orthogonal with an H-shaped dipole as top Frequency Selective Surface (FSS) and a modified horizontal dipole as bottom FSS; a 1 mm thin FR-4 substrate is separating both. During transmission, it can convert the linearly polarized EM wave to a circular one, with Axial Ratio (AR) ≤ 3 dB from 13.08 to 25.13 GHz with 63.07% Fractional Bandwidth (FBW). In addition, this polarizer can work in reflection mode also when the bottom FSS is replaced by a Perfect Electrical Conductor (PEC), demonstrating the linear-circular polarization with AR (≤3 dB) from 16.94 to 18.64 GHz (RHCP/LHCP) and 24.5–40.32 GHz (LHCP/RHCP) with FBW 9.56% (Ku-band), and 48.81% (K- and Ka-band), respectively. Besides, linear-circular conversion, it performs linear-cross conversion in reflection mode with polarization conversion ratio (PCR) above 90% from 19.71–22.22 GHz, 43.57–48.81 GHz, 53.50–55.32 GHz with 13.89%, 11.34%, 3.32%, FBW, respectively. The equivalent circuit model of the proposed converter is extracted. Surface current distribution profiles at multiple plasmonic resonances are investigated to understand the reason behind the multi-polarization conversion. The performance is angular stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) incidences for reflection as well as transmission modes. The unitcell is compact with periodicity 0.114λL × 0.114λL and a thickness of 0.044λL, where λL is the free-space wavelength of the lowest frequency. This design's novelty lies in dual-mode stable angular performance in both reflection and transmission cases. Also, highly miniaturized architecture and circular rotation switching in the consecutive bands make this design suitable for real-time scenarios.

Scalable and Fast Characteristic Mode Analysis using GPUs

Characteristic mode analysis (CMA) is used in the design and analysis of a wide range of electromagnetic devices such as antennas and nanostructures. The implementation of CMA involves the evaluation of a large method of moments (MoM) complex impedance matrix at every frequency. In this work, we use different open-source software for the GPU acceleration of the CMA. This open-source software comprises a wide range of computer science numerical and machine learning libraries not typically used for electromagnetic applications. Specifically, this paper shows how these different Python-based libraries can optimize the computational time of the matrix operations that compose the CMA algorithm. Based on our computational experiments and optimizations, we propose an approach using a GPU platform that is able to achieve up to 16×× and 26×× speedup for the CMA processing of a single 15k ×× 15k MoM matrix of a perfect electric conductor scatterer and a single 30k ×× 30k MoM matrix of a dielectric scatterer, respectively. In addition to improving the processing speed of CMA, our approach provided the same accuracy as independent CMA simulations. The speedup, efficiency, and accuracy of our CMA implementation will enable the analysis of electromagnetic systems much larger than what was previously possible at a fraction of the computational time.

A regularized method of fundamental solution for solving the 2D PEC cylinder electromagnetic scattering problem

In this letter, using subtraction and adding-back (SAB), the authors propose a regularized method of fundamental solution (RMPS) for solving the electromagnetic (EM) scattering problem of 2D perfect electric conductor (PEC) cylinder. The proposed RMPS avoids the problem of choosing the auxiliary boundary in the method of fundamental solution. Two numerical examples are given to verify the effectiveness of the proposed method after comparing with the result of method of fundamental solution. In addition, the results show that the proposed method has a better stability performance than the method of fundamental solution.

Electromagnetic Radiation Force of Vortex Electromagnetic wave exerted on a perfect electromagnetic conductor (PEMC) Sphere

In this manuscript, the electromagnetic (EM) radiation force (RF) exerted on a perfect electromagnetic conductor (PEMC) sphere by a vortex electromagnetic (VEM) wave with spiral phase distribution had been investigated. The analytical formulation of EM fields is being done in the framework of Mie theory, while the field expressions are being modeled considering the features of VEM wave for PEMC sphere. Initially, the incident field coefficients are evaluated using definite integrals. The scattering coefficients are then determined by imposing boundary conditions at the surface of PEMC sphere i.e., at 𝑟=𝑎, leading to a linear system of equations computed via solving matrix. So, a lengthy calculation yields undetermined scattered field coefficients relative to incident field coefficients. The cross-section (𝑄) factors i.e., scattering (𝑄𝑠𝑐𝑎) and extinction (𝑄𝑒𝑥𝑡) have been computed. The influence of sphere size parameter (𝜌) and beam waist radius (𝑤0) versus scattering angle (𝛼°) for the RF along with 𝑄𝑠𝑐𝑎 has been numerically analyzed. As no loss of energy occurs inside PEMC sphere so absorption ((𝑄𝑎𝑏𝑠)=0), by virtue of the energy conservation principle then, 𝑄𝑒𝑥𝑡=𝑄𝑠𝑐𝑎. Under specific condition, we implemented present results on 𝑄𝑠𝑐𝑎 towards light without orbital angular momentum (OAM) i.e., (𝑙=0) and plane wave for the PEMC sphere. The research work has potential applications towards particle manipulation, optical technology, and optical tweezers.

Electromagnetic wave focusing with 2-D gridded parabolic reflector made of parallel circular PEC wires at oblique incidence

We consider the two-dimensional (2-D) scattering of the TE- and TM-polarized plane electromagnetic waves from a discrete grid-like parabolic reflector consisting of parallel circular perfectly electrically conducting (PEC) wires at oblique incidence. Our analysis is performed in the exact formulation, fully taking into account the wave interactions between the wires. We use the method of separation of variables in the local cylindrical coordinate systems in combination with Graf’s addition formulas for cylindrical functions. The near field in the vicinity of the reflector is calculated at different angles of incidence. The dependences of the maximum field amplitude in the focal area and the position of this maximum on the angle of incidence are plotted. The far field scattered patterns, total scattering cross-sections and backward scattering cross-sections are calculated and discussed.

Tunable epsilon-near-zero response induced ultrathin perfect absorber with incident angle linear to thickness of film

For achieving perfect absorption (PA), the absorbing film usually has either high loss or a thickness much greater than its wavelength. We propose a simple bilayer structure composed of a perfect electric conductor substrate and an indium tin oxide (ITO) film to solve the situation. Results show that PA can be realized with a film thickness of several nanometers based on the epsilon-near-zero (ENZ) response and relatively low loss of ITO film. Notably, PA at different thicknesses of the film can be achieved by simply selecting the appropriate incident angle, and it is further demonstrated that the incident angle should be reduced linearly with an increase of the thickness of the film to maintain PA. Furthermore, the ENZ wavelength can be flexibly controlled by changing the carrier density via electrostatic field, resulting in the tunability of PA. These adjustable simple and tiny perfect absorbers may find practical applications in photodetectors and sensors.

Scattering of an Electromagnetic Wave by a Structure Consisting of Several Perfectly Conducting and Dielectric Finite-Length Thin Cylinders

Scattering of an Electromagnetic Wave by a Structure Consisting of Several Perfectly Conducting and Dielectric Finite-Length Thin Cylinders

Unidirectional invisibility in a PT-symmetric structure designed by topology optimization.

This study designs a piecewise homogeneous dielectric structure with parity-time (PT) symmetry that realizes the unidirectional invisibility of a perfect electric conductor in two dimensions. We apply topology optimization and design a PT-symmetric material that minimizes the total scattering cross section for a given plane wave to achieve unidirectional invisibility. A rigorous mode-matching finite element method is used to perform all computations. The designed PT-symmetric structure suppressed plane-wave scattering by approximately 99% for the given incident direction, whereas the reversed incident wave experienced 83 times larger scattering intensity. The proposed method provides a novel approach, to the best of our knowledge, to promote various applications of PT symmetry.