Numerical modeling and simulation of many electromagnetic (EM) and multiphysics problems encounter challenges from geometrical and material complexities, large-scale issues, and multiscale issues. Examples include the simulation of complex microwave devices and systems, the design of integrated circuits and packages, the modeling of natural or artificial materials, the simulation of large-scale antenna arrays, the analysis of EM wave propagation in complex environments, and the optimization of geometrical and material parameters in inverse scattering problems. The past few decades have witnessed a fast and exciting development in computational EM methods and techniques that contributed to the successful resolution of some of the aforementioned challenges. Noticeable developments include the use of high-order basis functions, fast algorithms, domain decomposition methods, and parallel computing techniques based on CPUs and GPUs. As modern technologies evolve, the overall electrical size of the EM systems and the integration density of EM components keep increasing, leading to higher power density, stronger thermal effect, and more critical multiscale phenomena. All these pose new challenges to the current modeling and simulation methods in electromagnetics. This Special Issue includes 10 high-quality papers addressing some of these challenges. As the size of integrated circuits continues to shrink, thermal performance plays an increasingly important role in the integration of the device. In this Special Issue, a three-dimensional (3-D) transient thermal simulation algorithm based on spectral element method has been proposed. By using curvilinear hexahedral elements, high-order nodal basis functions, and efficient and stable time-stepping schemes, this algorithm enjoys both high computational efficiency and improved modeling flexibility. Heat conduction processes in power networks and rockets have been studied. In the simulation of electronic devices, isolated conductors with unknown potential values are usually encountered. In this Special Issue, a hybridizable discontinuous Galerkin (HDG) method is developed to simulate electrostatic problems with floating potential conductors, where an equipotential condition with an undefined/floating potential value is enforced on the surface of an isolated conductor. Compared with the traditional finite element method (FEM) implementation, the HDG implementation is much more straightforward. The unknowns of the global HDG problem are only associated with the nodes on the mesh skeleton, which are comparable to those in an FEM implementation. Carbon nanotube (CNT)-based nanocomposites have attracted many attentions in recent years due to their extraordinary properties, including high electrical conductivity, low percolation threshold, and good dielectric and mechanical properties. One article in this Special Issue studies the electric conductivity of CNT/polymer nanocomposites with multiscale modeling and analysis. A numerical model taking into account the nonlinear tunneling effect has been proposed to evaluate the effective electric conductivity of CNT nanocomposites, and a nonlinear finite element formulation has been developed to model the effective quantities for homogenization. A multiphysics modeling method is introduced in this Special Issue to design novel surface acoustic wave (SAW) based chipless radio frequency identification (RFID) tags. Several new structures of chipless RFID are described, which have advantages including a long reading distance and a strong anti-interference ability. The performance of the SAW-based RFIDs with different structures has been investigated through modal analyses using COMSOL. One article in this Special Issue concerns the modeling of extremely low frequency (ELF) wave propagation on Earth. The mode-conversion coefficient ELF wave propagation over a mixed propagation path has been theoretically studied and applied to interpret the EM interference at various propagation distances. The effect of Earth–ionosphere is modeled as a waveguide with discontinuous sections representing the transitions between land and sea. In the far-field region, the wave propagation is modeled by the WKB solution described, while a successively cascaded Earth–ionosphere waveguide model is developed to determine the EM interference at the junction of the land and sea. In the design of EM devices, a fast, efficient, and accurate forward solver is required for the optimization to be performed efficiently. In this Special Issue, an artificial intelligence (AI) based surrogate-based model has been developed to design nonuniform microstrip transmission line (NTL) based band pass filters. To have a computationally efficient and accurate optimization process, a 3-D EM unit element model of NTL has been developed to generate training and testing data sets. An AI-based method has been used to predict the scattering parameters of the NTL with respect to the variation of geometrical design parameters. The S-parameters are then cascaded to calculate the equivalent S-parameters of the NTL to obtain the response of the desired band pass filter. The propagation and transmission of EM wave in layered media have important applications in well logging, imaging, and remote sensing. One article in the Special Issue reported an element-free Galerkin numerical mode-matching method for static and time-harmonic EM fields calculation in orthogonal-plano-cylindrically layered media. In this work, the numerical mode-matching (NMM) method is combined with the element-free Galerkin (EFG) method to efficiently model EM waves in cylindrically layered media with multiple horizontal beds. To implement the NMM scheme with a higher computational efficiency, an EFG method is utilized to replace the traditionally used FEM in the discretization along the radial direction. The resulting meshless EFG-NMM scheme avoids the complexity of mesh generation and improves the numerical accuracy compared with FEM. Two articles in this Special Issue address the computation accuracy and efficiency of complicated EM problems. One concerns the development of an efficient approach to generate characteristic basis functions (CBFs) in large blocks with Sherman–Morrison–Woodbury algorithm. While a better compression rate of the CBF method can be achieved by increasing the block size in the generation of the CBFs, the generation cost increases significantly for electrically large blocks, especially in the case of multiple excitations. In this article, a novel computing scheme that combines the traditional CBF method with the Sherman–Morrison–Woodbury algorithm (SMWA) is proposed to generate CBFs and calculate the reduced impedance matrix with an increased computational efficiency. In another article, a new implementation of the perfectly matched layer (PML) is proposed for the finite-difference time-domain (FDTD) method. This new method, based on the exponential time differencing (ETD) formulation for the PML, is proposed through the Taylor expansion and is an alternative to the simple auxiliary differential equation method. It has been shown numerically that the ETD can significantly reduce the peak relative reflection error of the PML compared with other implementations. Based on the cyclic code theory, a novel encoding and decoding method is proposed for self-correction and anti-interference in big data product tracing system. With the development of the code construction principle, the specific encoding and decoding methods, and an OpenMP implementation, the decoding time has been accelerated more than 36 times. Compared with other coding patterns in the literature, the new error-correcting and anti-interference coding method achieves a balance in complexity, encoding rate, and decoding time. The editors thank all the contributors and the anonymous reviewers for their contributions to this Special Issue.
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Mar 28, 2024
Cesar E. P. Villegas + 2
Open Access