Applied Computational Electromagnetics Society Journal (ACES)

Compressed Fast Multipole Representations for Homogeneous 3-D Kernels

2024-03-27T16:38:28+01:00

For homogeneous kernels, the memory requirements associated with H² representations of integral equation matrices can be reduced by incorporating translational invariance. Starting with a non-translationally invariant H² representation, this can be accomplished using a left/right iterative algorithm. In this paper, it is shown that a similar algorithm can also be used to compress an existing fast multipole method (FMM). It is observed that the iterative compression converges faster when used to compress an FMM than when it is applied to an H² representation. Resulting savings in floating-point operations are indicated, and extensions of the reported method are discussed.

A 3-D Global FDTD Courant-limit Model of the Earth for Long-time-span and High-altitude Applications

2023-08-24T00:43:46+02:00

A new global 3-D finite-difference time-domain (FDTD) model is introduced to simulate electromagnetic wave propagation around the Earth, including the lithosphere, oceans, atmosphere, and ionosphere regions. This model has several advantages over existing global models, which include grids that follow lines of latitude and longitude and geodesic grids comprised of hexagons and pentagons. The advantages of the new model include: (1) it may be run at the Courant-Friedrichs-Lewy (CFL) time step (as a result, it is termed the Courant-limit model); (2) subgrids may be added to specific regions of the model as needed in a straight-forward manner; and (3) the grid cells do not become infinitely larger as the grid is extended higher in altitude. As a result, this model is a better candidate than the others for investigating electromagnetic phenomena over long time spans of interest and for investigating atmosphere-ionosphere-magnetosphere coupling. The new model is first described and then validated by comparing results for extremely low frequency (ELF) propagation attenuation with corresponding analytical and measurement results reported in the literature.

Near-fields of Butterfly Nanoantennas: A Comparative Simulation and Experimental Study

2024-01-09T10:57:57+01:00

Optical nanoantennas demonstrate the ability to confine and enhance electromagnetic fields. This ability makes nanoantennas essential tools for high-resolution microscopy. The nanoantenna resonance and response can be tuned by changing their size, shape, and material as well as adjusting the probing conditions, e.g. excitation wavelength. In this paper we simulated the propagation and interaction of visible light with computer generated models of butterfly nanoantenna arrays using the finite-difference time-domain (FDTD) method. The simulations were used to understand and predict the experimental results obtained with scanning near-field microscopy (SNOM) on commercially available samples. Simulation parameters are chosen carefully to reflect the measurement conditions.

PSSFSS—An Open-source Code for Analysis of Polarization and Frequency Selective Surfaces

2024-02-24T10:41:50+01:00

The open-source code PSSFSS for analysis and design of polarization selective surfaces (PSSs), and frequency selective surfaces (FSSs) is presented, beginning with an introduction to the Julia programming language in which the code is written. Analysis methods and algorithms used in PSSFSS are described, highlighting features of Julia that make it attractive for developing this type of application. Usage examples illustrate the code’s ease of use, speed, and accuracy.

Analysis of EM Properties of High-speed Moving Cone-sphere Target Coated with Plasma Sheath based on Lorentz-FDTD Method

2023-10-08T22:27:33+02:00

The study of the interaction between moving plasma-coated objects and electromagnetic (EM) waves is the essential factor for the EM problems of high-speed targets. In this paper, the physical model of a moving dispersive medium is developed based on the principle of special relativity to study the EM properties of high-speed moving targets coated with plasma sheath. First, the Lorentz transform is used to introduce the incident plane wave into moving frame. Second, based on the proposed EM model, the EM problems are solved in moving frame by the shift-operator (SO) FDTD numerical algorithm. Finally, the EM results are further converted back into the laboratory frame to analyze the scattered properties of high-speed plasma coated objects. The validity of the proposed algorithm is verified by comparison with the reference solution. On this basis, the influence of relativistic effects produced by the motion of the object and the EM properties of the plasma on the scattering fields of high-speed targets are investigated. This work expands the applicability of the FDTD method and provides a theoretical foundation for solving the scattering properties of high-speed plasma-coated complex shape objects through numerical methods.

Anomalous Magnetization Spikes in the Locally Corrected Nyström Discretization of Static Volume Integral Equation using Tetrahedral Cells

2023-07-31T22:19:07+02:00

A locally corrected Nyström (LCN) discretization of a magnetostatic volume integral equation is presented. Anomalous magnetization spikes can occur when the underlying mesh uses tetrahedral cells regardless of discretization order. The mechanism for the anomalous magnetization spikes is discussed, and mitigation of the spikes through use of an LCN-to-Moment Method conversion is investigated. Results are presented validating that the LCN-to-Moment Method suppresses the anomalous spikes.

An IGFBM-SAA Fast Algorithm for Solving Electromagnetic Scattering from Layered Media Rough Surfaces

2024-01-08T13:07:18+01:00

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 stealthperformance.

Solving Surface-volume Integral Equations for PEC and Inhomogeneous/Anisotropic Materials with Multibranch Basis Functions

2024-04-01T11:26:05+02:00

Multibranch basis functions have been confirmed to be effective for local refinement of domain decomposition methods in the application of solving surface and volume integral equations. Surface-volume integral equations (SVIEs) are applied for solving the hybrid electromagnetic scattering problems involving perfect electric conductors (PEC) and dielectrics, especially inhomogeneous and anisotropic media. In this paper, multibranch Rao-Wilton-Glisson basis functions (MB-RWGs) are applied in conjunction with multibranch Schaubert-Wilton-Glisson basis functions (MB-SWGs) for solving the SVIEs. Block diagonal preconditioners (BDPs) are used to accelerate the iteration convergence based on generalized minimum residual (GMRES) algorithms. The numerical results demonstrate the accuracy of the multibranch basis functions in solving SVIEs, and also show that proper BDPs can accelerate the iteration convergency.

A Numerical Analysis of Conformal Energy Selective Surface Array with Synthetic Functions Expansion

2024-02-06T10:38:08+01:00

Energy selective surface (ESS) is a special kind of metasurface with great potential in high-power microwave protection. In this paper, the electromagnetic (EM) properties of an ESS array are analyzed with synthetic functions expansion (SFX) method. A cylindrical conformal ESS array based on an I-shape element is designed for demonstration. The Bistatic RCS as well as electric field distribution of the ESS array is calculated with SFX and traditional full-wave numerical methods. The results show that SFX exhibits great advantages in memory cost while maintaining the same level of accuracy and efficiency with the multi-layer fast multipole method (MLFMM). Besides, the EM performance of the designed ESS is calculated with an array with finite elements and unit cell with periodic boundaries, respectively. The results show a good agreement. The proposed method can also be applied to the analysis of other kinds of metasurfaces whose elements share similar geometries with periodic or quasi-periodic arrangement. Especially for large-scale arrays, this method could well overcome the difficulty of balancing accuracy, efficiency, and resource consumption.

Wide-Angle Scanning and High Isolation Dual-Polarized Base Station Antennas for Sub-6 GHz Applications

2024-03-16T14:56:02+01:00

This paper presents a wide-angle scanning and high isolation base station antenna array. The antenna element employs a compact dual-polarized umbrella-shaped printed dipole with a small size of 0.23λ₀ × 0.23λ₀ × 0.26λ₀, which provides the possibility for a small element spacing array. The antenna element possesses wide 3 dB beamwidth of 84.6^∘ benefiting from the pulling down of the dipole arms. Then, a dual-layer metal superstrate structure and metal wall is adopted to mitigate different kinds of mutual coupling between the dual-polarized antenna elements in the array. Owing to the wide beamwidth of the element and the low mutual coupling between the elements, the final 4×6 antenna array can achieve a good beam-scanning capability with maximum scanning angle up to ±55^∘ and a small gain variation of less than 3 dB over the operation band 3.3-3.8 GHz. The fabricated array shows the measured isolation between all ports of the antennas is increased to more than 20 dB. Scanning characteristics also agree well with the simulated results. With the merits of wideband, low-cost (simple design and easy fabrication), wide-angle beam-scanning capacity, and good radiation performance, the proposed design has potential for application in 5G base stationsystems.