Minquan Li

To conduct a detailed investigation of the bidirectional multiphysics interactions among electromagnetic, thermal, and mechanical fields, this work proposes a finite-difference time-domain (FDTD) framework that incorporates electromagnetic–thermal–mechanical coupling (ETMC) together with moving-mesh capability. The formulation consistently accounts for pairwise interactions among the three fields, namely, electromagnetic–thermal, thermal–mechanical, and deformation-induced mechanical–electromagnetic coupling (MEC), thereby establishing a fully closed-loop coupling mechanism. The proposed framework allows flexible sequencing and combination of the coupling processes according to specific modeling requirements. All governing equations are solved in the time domain within a unified FDTD scheme, enabling direct tracking of temporal evolution and cross-field feedback while maintaining strong physical consistency and numerical accuracy. The accuracy and effectiveness of the bidirectional ETMC-FDTD method are validated through numerical simulations of a rectangular silicon block and a micro-electromechanical system (MEMS) micromirror. The results demonstrate its strong potential for applications in integrated circuits and radio frequency engineering.

To mitigate the staircase errors inherent in electromagnetic–thermal multiphysics coupling simulations, this work proposes a conformal electromagnetic-thermal coupling finite-difference time-domain (CETC-FDTD) method. For the electromagnetic field, conformality is achieved by weighting the constitutive parameters according to the fractional contributions of each medium along grid edges and faces. For the temperature field, the material parameters are conformally weighted by the volumetric fraction of each medium within the grid cell, thereby realizing consistent electromagnetic-thermal conformality. To achieve a more accurate and physically consistent temperature distribution within each grid cell, an interpolation scheme is developed to equivalently project the heat source onto the center of the Yee cell. This enables conformal treatment throughout the multiphysics electromagnetic-thermal coupling process. In addition, conformal considerations are also incorporated into the thermal convection boundary of the temperature field, where the corner temperatures are specially treated using directional weighting coefficients. The proposed method significantly improves the accuracy of electromagnetic–thermal coupling simulations while incurring virtually no additional memory overhead. Representative examples, including a cubic block, a sphere, a radome, and a three-dimensional packaging structure, are presented to validate the correctness and accuracy of the proposed CETC-FDTD method. The proposed approach exhibits strong potential for applications in radio-frequency and microwave engineering.

This study presents a novel dispersion-conformal finite-difference time-domain (DC-FDTD) algorithm that significantly enhances both the accuracy and computational efficiency of electromagnetic simulations in dispersive media. The proposed method introduces a weighted dispersion parameter scheme within the Debye model, wherein the weighting coefficients are systematically derived using the inclusive grid method. This approach enables the use of coarser computational grids while achieving an accuracy level comparable to that of finer meshes, thereby substantially reducing computational cost. Compared to conventional FDTD techniques, the DC-FDTD method offers improved accuracy without incurring additional runtime or memory usage, and maintains numerical stability throughout the simulation process. Through rigorous theoretical derivation, the DC-FDTD formulation is shown to retain structural consistency with the standard FDTD dispersion scheme, requiring only minor modifications to the original update coefficients. This design allows for seamless integration into existing FDTD frameworks. Moreover, the method exhibits strong adaptability to highly curved geometries and electrically large, structurally complex models—conditions under which conventional FDTD approaches often face significant limitations. To comprehensively validate the proposed method, four representative case studies were conducted across a range of practical application scenarios. The results confirm that the DC-FDTD method accurately captures dispersive behaviors while offering substantial gains in computational efficiency. Its ease of implementation, high accuracy, and robust performance underscore its strong potential for applications in radio frequency (RF) engineering, biomedical imaging, and other domains requiring precise modeling of complex dispersive media.

This letter presents an area-weighted conformal finite-difference time-domain (AW-CFDTD) method aimed at improving the accuracy of electromagnetic simulations involving complex material interfaces. Unlike conventional conformal FDTD (CFDTD) techniques, which typically estimate effective material parameters based solely on the fraction of each material along the grid edge, the proposed approach incorporates an additional weighting scheme that accounts for the surface areas associated with the grid edges. Specifically, the effective permittivity and conductivity are computed using the minimum between the material proportion along the grid edge and the corresponding proportion on the adjacent surface area. This dual-weighting strategy leads to a more physically consistent representation of material transitions, thereby enhancing both the numerical accuracy and general applicability of the CFDTD method. To evaluate the proposed AW-CFDTD method, a benchmark simulation of a square dielectric object was conducted and compared with conventional CFDTD, fine-mesh staircase FDTD, and CST. AW-CFDTD showed higher accuracy with lower computational cost than fine-mesh methods, offering an efficient and accurate solution for conformal FDTD modeling, especially in RF and microwave applications with complex material boundaries.

This paper presents a multiphysics simulation algorithm for electromagnetic-thermal strong coupling (ETSC) based on the finite-difference time-domain (FDTD) method. The proposed transient strong coupling multiphysics framework takes into account the effect of temperature on temperature-dependent parameters in both electrical and thermal properties, with synchronous iterations of the electromagnetic and temperature fields. For antennas operating in the RF frequency band, the thermal coupling considers not only Joule loss but also dielectric loss, investigating the impact of introducing dielectric loss. To address the multiscale time-domain issue in the multiphysics iterative process, a fast equivalent heat source algorithm is proposed, which significantly enhances computational efficiency while maintaining engineering-acceptable accuracy. To validate the accuracy of the method, numerical simulations were performed using a printed F antenna. The algorithm results showed a high degree of consistency with COMSOL software simulations. The rapid and accurate nature of the algorithm makes it an excellent simulation tool with significant applications in the fields of microwave circuits and radio frequency technology.

Effective noise suppression is crucial for the subsequent interpretation tasks of synthetic aperture radar (SAR) imagery. Traditional SAR image processing techniques often overlook the coherent nature of noise, leading to a loss of vital detail during filtering. With advancements in deep learning (DL), significant strides have been made in image processing. However, existing DL methods do not fully leverage the imaging mechanisms of SAR, resulting in a lack of specificity and interpretability in the filtering process. To balance noise reduction with detailed preservation and to address the “black box” issue in filtering, we propose an interpretable filtering method that employs a correlation-based upward search for density peaks. Initially, we develop a MeanShift-Markov random field (MS-MRF) filter that integrates MeanShift with MRF in the joint spatial–spectral domain, ensuring both correlation and detailed preservation; the derivation of the MS-MRF filter is rigorously grounded in mathematical theory. Subsequently, we integrate MS-MRF with convolutional operations in DL to create a novel convolutional filter, interpretable MS-MRF convolution (IMMC), which enhances the model’s interpretability, noise reduction capabilities, and detailed retention. Extensive experiments demonstrate that our method outperforms state-of-the-art (SOTA) SAR denoising techniques, achieving an average structural similarity index (SSIM) of over 85.00% and an average peak signal-to-noise ratio (PSNR) exceeding 35.00 dB across synthetic datasets with varying noise levels, showing significant improvements in noise suppression, detailed preservation, and interpretability.

In this letter, a low-profile, high-aperture-efficiency millimeter-wave magneto-electric dipole (MED) circularly polarized (CP) beam-scanning antenna array is proposed. Initially, a novel MED antenna element is designed by arranging metallized vias around the radiating patches to serve as beam directors. This novel method not only provides broad axial-ratio (AR) beams and wide half-power beamwidths but also maintains a low-profile and compact structural characteristic. By adjusting the positions of the via directors, the radiation beam direction of the antenna element is effectively controlled. Subsequently, 4 × 4 antenna arrays for the xoz and yoz planes are designed and simulated to verify the CP beam scanning performance. The results demonstrate that the maximum CP beam scanning range can reach from -50° to +50°, with the AR maintained below 3 dB throughout the scanning range. At 29 GHz, the peak aperture efficiencies of the antenna arrays reach 73.8%, while maintaining a low profile of just 0.12λ0. Finally, the measurement results confirm the validity of the simulations.

This article presents a novel continuous meta-grating array (MGA) for the generation of ultra-wideband, near-perfect orbital angular momentum (OAM) beams with extremely high mode purity. First, a novel dielectric-doping strategy is proposed to overcome the inherent narrowband characteristics of conventional grating atoms, resulting in an ultra-wideband dielectric-doping meta-grating atom (DDGA). By establishing an equivalent circuit model (ECM), the operational mechanism is analyzed. The design method is provided to establish clear DDGA design guidelines to follow. Simulation and ECM calculations reveal that within the 9.06–19.88 GHz (74.7%), the circularly co-polarized reflection coefficient and polarization conversion ratio exceed 99.7% and 98.7%, respectively. Subsequently, a space-variant sub wavelength MGA is generated using grating functions. The continuous grating array ensures the continuity of the reflected field, thereby avoiding beam distortions and low mode purity that may result from potential mutual coupling and diffraction effects caused by discontinuities in traditional metasurfaces. In the 9.0–21.0 GHz (80.0%), the MGA is capable of generating near-perfect vortex beams, ranging from low-orders to high-orders, with extremely high purity and very low mode crosstalk. In addition, it demonstrates frequency-aperture size insensitivity and dual-wideband properties, facilitating miniaturization and size customization while delivering high-performance OAM in the high-frequency 37–50 GHz. Finally, experimental validation confirms the effectiveness.

This paper presents a novel continuous dielectric meta-grating array (DMGA) for generating wideband, high-performance transmission orbital angular momentum (OAM) vortex beams with high mode purity. A broadband meta-grating unit (MGU) was designed and modeled theoretically, including a detailed analysis of its design process. Simulations and theoretical calculations show that, in the 26-39 GHz (40%), the unit achieves a 180° transmission phase and a transmission coefficient over 0.9. The array patterning was determined using a grating function. The DMGA is composed of continuously spatially varying grating strips, effectively preventing issues caused by array discontinuity such as inter-atom coupling and discontinuous step phase changes, which could lead to vortex beam distortion and low purity. Simulations show that the DMGA generates broadband, high-performance vortex beams with high mode purity for mode orders l = 2, 3, 4, 5, 6, 7, 8, 9, and 10, exhibiting advantages in generating high-quality, high-order OAM beams. Additionally, it exhibits frequency-aperture size insensitivity, enabling miniaturization and customization of aperture sizes. Finally, the measurement confirms the effectiveness.

A unified dispersive media and perfect matching layer (PML) finite-difference time-domain (FDTD) formulation based on the matrix exponential (ME) method is proposed for the simulation of dispersive media characterized by first-order lossy Debye (LD) model. The method introduces the dispersive model into the FDTD algorithm and converts the update equation into a first-order differential equation by using the ME method. By adjusting the arrangement of the elements of the initial matrix, an updated formula format is skillfully created that is identical to the ME-PML algorithm. The time dependence in the FDTD updating formula is removed by the analytical method, leading to a significant reduction of numerical error. In addition, a novel unified scheme is present to reduce the complexity of the simulation of dispersive material by combining the field updating equations and the ME-PML algorithm into one consistent formulation. The Fourier method was used to evaluate and confirm the stability of the algorithm. The performance of the algorithm, its numerical accuracy, and efficiency, were also verified through simulations of human body models. The simplicity and precision of the algorithm make it a powerful tool with the potential for applications in the fields of biological sciences and radio frequency technology.