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Multiple LOD-FDTD Method for Inhomogeneous Coupled Transmission Lines and Stability Analyses
摘要： A multiple locally one-dimensional (MLOD) finite-difference time-domain (FDTD) method for inhomogeneous coupled transmission lines and stability analyses are presented. The method is aptly called the MLOD coupled line (CL)-FDTD method. Various split matrices are proposed, and the corresponding update equations are formulated and discussed. All the proposed split matrices yield implicit electric field update equations with tridiagonal or block tridiagonal matrices on the left-hand sides. For more efficiency, the block tridiagonal matrices for implicit electric field may be reformulated and replaced by tridiagonal matrices for implicit magnetic field. The stability analysis is first performed using the von Neumann method in the Fourier domain. It is shown that the von Neumann method alone may not be sufficient to ascertain stability for inhomogeneous media. To include media inhomogeneity, the two-media reduced-matrix stability analysis is proposed. It allows us to analyze efficiently the key stability characteristics in inhomogeneous media, and is useful for quick detection of any potential instability that is not apparent via the von Neumann method. The stability characteristics with variation of media parameters are also investigated and discussed. Numerical results are provided to validate the stability and accuracy of the proposed MLOD CL-FDTD method with various split matrices.
关键词： Multiple LOD FDTD method,stability,split matrices,coupled transmission lines
更新于2025-09-11 14:15:04
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Complex-conjugate Pole-residue Pair-Based FDTD Method for Assessing Ultrafast Transient Plasmonic Near Field
摘要： The study of the optical properties of plasmonic nanostructures in the stationary regime has greatly benefited from the development of numerical methods, among which Finite Difference Time Domain (FDTD) is popular. In contrast, the use of these numerical tools for assessing the transient plasmonic optical response triggered by ultrashort laser pulses is hampered by the difficulty to address small variations of the material optical properties with reasonable computational time. Yet, many of the developments based on this ultrashort response rely on the dynamics of the near-field topography around the nanostructures. In this article, we present a way to bridge this gap with the complex-conjugate pole-residue pair (CCPRP) approach. A CCPRP-based FDTD simulator has been developed. First, a simple methodology to check the end-to-end accuracy of the FDTD simulation is provided. Then, in conjunction with a three-temperature model, the approach enables us to calculate the ultrafast transient near field inside and around a gold nanoparticle (AuNP) upon absorption of a subpicosecond laser pulse. The transient variation of the field intensity inside and around the AuNP is compared with the one determined by the Mie theory. The dependence of the transient field intensity on the distance away from the nanoparticle surface and on the delay time after laser pulse absorption is finally analyzed.
关键词： Ultrafast,Complex-conjugate pole-residue pairs,Nanoparticles,Plasmonics,Near-field enhancement,FDTD
更新于2025-09-11 14:15:04
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Metamaterials and Metasurfaces || Electron Beam-Induced Directional Terahertz Radiation from Metamaterials
摘要： We have numerically analyzed an electron beam (e-beam)-induced directional terahertz (THz) radiation from metamaterials. Here, we used metallic grating structures with graded depths, in which only one-way surface mode can be supported based on the spoof surface plasmon polariton (spoof SPP) concept and gives unique directional THz radiation. For numerical analysis, we used a simplified particle-in-cell (PIC) finite-difference time-domain (FDTD) method. First, we describe our simplified PIC-FDTD method in detail. Then, we show our results on the e-beam-induced directional THz radiation from graded grating with graded depths. By passing pulsed (bunched) e-beam along the grating surface, directional THz radiations are obtained from one side of the grating with shallower grooves. The direction of these radiations can be switched backward or forward by making the groove depth deeper or shallower. The spectra of these directional radiations are wide band and contain multiple sharp peaks. The deepest and the shallowest groove depths determine the lowest and the highest frequency of the radiation band, respectively. These unique radiation characteristics cannot be explained by the conventional Smith-Purcell radiation and should be attributed to the spoof SPP that originates from different locations on the graded grating.
关键词： graded grating,Smith-Purcell radiation,THz,particle-in-cell finite-difference time-domain,metamaterial,PIC-FDTD,electron beam,terahertz
更新于2025-09-11 14:15:04
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Self-Catalytic-Grown SnOx Nanocones for Light Outcoupling Enhancement in Organic Light-Emitting Diodes
摘要： Light extraction in organic light-emitting diodes (OLEDs) was improved by applying SnOx nanocones grown via thermal annealing in a low-O2 atmosphere. SnOx was easily fabricated through thermal processing after Sn deposition. The diameter of the SnOx nanocones was controlled by changing the deposition thickness of Sn. The SnOx nanocones induced strong Mie scattering, which reduced the total internal reflection in the glass substrate. Consequently, the OLED with SnOx nanocones exhibited a 23% increase in the external quantum efficiency compared with a reference device.
关键词： Mie scattering,SnOx nanostructure,light extraction,organic light-emitting diodes (OLEDs),FDTD simulation
更新于2025-09-11 14:15:04
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A High-order Accurate Scheme for Maxwell's Equations with a Generalized Dispersive Material Model
摘要： A high-order accurate scheme for solving the time-domain Maxwell’s equations with a generalized dispersive material model is described. The equations for the electric ?eld are solved in second-order form, and a general dispersion model is treated with the addition of one or more polarization vectors which obey a set of auxiliary di?erential equations (ADE). Numerical methods are developed for both second-order and fourth-order accuracy in space and time. The equations are discretized using ?nite-di?erences, and advanced in time with a single-stage, three-level, space-time scheme which remains stable up to the usual explicit CFL restriction, as proven using mode analysis. Because the equations are treated in their second-order form, there is no need for grid staggering, and instead a collocated grid is used. Composite overlapping grids are used to treat complex geometries with boundary-conforming grids, and a high-order upwind dissipation is added to ensure robust and stable approximations on overlapping grids. Numerical results in two and three space dimensions con?rm the accuracy and stability of the new schemes.
关键词： electromagnetics,generalized dispersive material model,composite overlapping grids,dispersive FDTD
更新于2025-09-11 14:15:04
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One-Step Leapfrog ADI-FDTD Method Using the Complex-Conjugate Pole-Residue Pairs Dispersion Model
摘要： A novel one-step leapfrog alternating-direction-implicit finite-difference time-domain method for the modeling of dispersive media described by the complex-conjugate pole-residue pairs model is proposed. The efficiency of the technique is demonstrated in benchmark numerical examples.
关键词： finite-difference time-domain (FDTD) method,leapfrog alternating-direction-implicit (LADI) scheme,Dispersive media
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - Reykjavik, Iceland (2018.8.8-2018.8.10)] 2018 IEEE MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization (NEMO) - Concept of a Complex Envelope Faber Polynomial Approach for the Solution of Maxwell’s Equations
摘要： We investigate a novel complex envelope approach for the numerical solution of Maxwell’s equations based on the time domain propagator using Faber the expansion of polynomials. Due to the application of the complex envelope only the envelope of the investigated fields has to be simulated. This offers promising prospects with respect to the application of larger time steps. The properties of the Faber polynomials enable a flexible and a highly accurate approximation of the time domain propagator what offers interesting prospects for the analysis of devices in the fields of THz technology and photonics.
关键词： Electromagnetic propagation,finite-difference time-domain (FDTD) methods
更新于2025-09-11 14:15:04
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Novel FDTD Scheme for Analysis of Frequency-Dependent Medium Using Fast Inverse Laplace Transform and Prony’s Method
摘要： A novel finite-difference time-domain (FDTD) approach is proposed for analysis of wave propagation in a general frequency-dependent medium. In the proposed method, formulation of the fractional derivatives in the time-domain representation is circumvented by using the fast inverse Laplace transform (FILT) and Prony’s method. The FILT is used to transform the dispersion expressed in a frequency domain into a time-domain response and Prony’s method is utilized to extract parameters and transform the time-domain responses into those in the z-domain so that they can be incorporated into the FDTD method directly. The update equation of the electric field in the FDTD method is then formulated by using the z-transformation. Stability analysis of the proposed scheme is also investigated by means of the root-locus method. Reflection coefficients of dispersive media, such as Debye, Cole–Cole, Davidson–Cole, and Havriliak–Negami media simulated in a one-dimensional domain and a three-layered biological medium of skin, fat, and muscle tissues inside a waveguide with a TE10 fundamental mode in a two-dimensional domain, are found to be in good agreement with those obtained by an analytical method over a broad frequency range, demonstrating validity of the proposed FDTD scheme.
关键词： Prony’s method,time-domain method,Cole–Cole medium,FDTD,Finite-difference,Laplace transform,frequency-dependent medium
更新于2025-09-11 14:15:04
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Analysis of Electromagnetic Wave Propagation in Variable Magnetized Plasma via Polynomial Chaos Expansion
摘要： A three-dimensional stochastic FDTD algorithm is developed and applied to electromagnetic wave propagation in collisional magnetized plasma characterized by a variable electron density, collision frequency, and background magnetic ?eld. The proposed stochastic model is based on the expansion of the random / variable time-domain electric and magnetic ?elds in terms of orthogonal polynomials in independent random variables representative of the variable ionospheric content. Electromagnetic wave propagation in magnetized plasma having low variability (small deviations) and also high variability (large deviations) of the electron density, collision frequency, and background magnetic ?eld is studied. The stochastic algorithm is validated against brute-force Monte Carlo results. The algorithm is considerably more computationally ef?cient than Monte Carlo. When applied to electromagnetic wave propagation in the ionosphere, the variability of the Earth’s magnetic ?eld and ionospheric parameters can be accounted for due to naturally varying space weather conditions and day-to-day variations, measurement errors, etc. Although only electrons are considered here, positive and negative ions may be accommodated in a straight-forward manner.
关键词： ?nite-difference time-domain (FDTD),electromagnetic wave propagation,ionosphere,polynomial chaos,uncertainty,collisional magnetized cold plasma
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE International Conference on Computational Electromagnetics (ICCEM) - Chengdu, China (2018.3.26-2018.3.28)] 2018 IEEE International Conference on Computational Electromagnetics (ICCEM) - Analysis of TEM Horn with Dielectric Loaded
摘要： The radiation fields of transverse electromagnetic (TEM) horn as a nuclear electromagnetic pulse(NEMP) radiating-wave simulator are simulated by finite-difference time-domain(FDTD) method. The EMP’s effects of different dielectric load are numerical studied and analyzed. The results show that comparing with the traditional TEM horn antenna the peak value of Ez increases or decreases, but the FWHM never widen as TEM horn loaded by dielectric.
关键词： FDTD,Dielectric,Load,NEMP,TEM horn
更新于2025-09-10 09:29:36