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Investigation of uncertainty in lightning-produced EM fields with a polynomial-chaos FDTD approach

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING-ELECTRONIC NETWORKS DEVICES AND FIELDS 2018年第2期31卷

作者： Zygiridis, Theodoros Kantartzis, Nikolaos Tsiboukis, Theodoros Univ Western Macedonia Dept Informat & Telecommun Engn Kozani 50131 Greece Aristotle Univ Thessaloniki Dept Elect & Comp Engn Thessaloniki 54124 Greece

The aim of this paper is to investigate the impact of the ground-material uncertainty on the properties of electromagnetic fields generated by lightning strikes. Although several analytical as well as numerical approaches have been proposed throughout previous years for the prediction of lightning-induced fields, these are mostly applied within a fully deterministic context, thus overlooking the degree of randomness that the corresponding problems may exhibit. Considering the rotational independence of setups with vertical lightning channels and flat terrains, we propose a stochastic finite-difference time-domain algorithm that takes advantage of the generalized polynomial-chaos theory. The latter enables the representation of random processes via expansions with respect to specific orthogonal polynomials and facilitates capturing the fundamental statistical properties of the produced fields. The resulting scheme preserves the structure of the original Yee algorithm and, although computationally heavier than the latter, is clearly more efficient than conducting brute-force Monte Carlo studies. The potential of the proposed stochastic method is assessed via various numerical results, calculation of statistical metrics, and comparisons with reference solutions.

关键词： finite-difference time-domain method lightning polynomial chaos uncertainty

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Performance analysis of vertically cascaded pentacle micro-optical ring resonator as optical filters with four output bus waveguides

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OPTICAL ENGINEERING 2018年第11期57卷 116103-116103页

作者： Chatterjee, Binshati Mandal, Sanjoy Indian Inst Technol Indian Sch Mines Dhanbad Bihar India Indian Inst Technol ISM Elect Engn Dept Dhanbad Bihar India

Modeling and performance analysis of vertically cascaded pentacle micro-optical ring resonator (VCPMORR) with single input and four output bus waveguides is presented. Overall transmittance of the proposed VCPMORR is determined in Z-domain for each output bus waveguide by practicing delay line signal processing approach and Mason's gain formula. Frequency response analysis of the proposed model is carried out using MATLAB software. Free spectral range (FSR), group delay, and dispersion are enumerated as performance parameters of the proposed model. The detailed design of its waveguide is carried out by employing finite-difference time-domain (FDTD) method. Electric field propagation through the rings and the wave-guides is also studied by FDTD. This method proposes an approach to design the numerous coupled ring resonator structures. This configuration provides more communication channels due to its wide FSR with zero crosstalk at four output buses. Hence, this coupled ring resonator structure will be very useful in optical communication systems as an optical add-drop filter. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： delay line signal processing Mason's gain formula free spectral range group delay dispersion finite-difference time-domain method

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Macroscopic Magnetization Control by Symmetry Breaking of Photoinduced Spin Reorientation with Intense Terahertz Magnetic Near Field

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Physical Review Letters 2018年第10期120卷 107202-107202页

作者： Takayuki Kurihara Hiroshi Watanabe Makoto Nakajima Shutaro Karube Kenichi Oto YoshiChika Otani Tohru Suemoto Institute for Solid State Physics The University of Tokyo 5-1-5 Kashiwanoha Kashiwa Chiba 277-8581 Japan Institute of Laser Engineering Osaka University 2-6 Yamadaoka Suita Osaka 565-0871 Japan Center for Emergent Matter Science RIKEN 2-1 Hirosawa Wako Saitama 351-0198 Japan Department of Physics Chiba University 1-33 Yayoicho Inage Ward Chiba-shi Chiba 263-8522 Japan

We exploit an intense terahertz magnetic near field combined with femtosecond laser excitation to break the symmetry of photoinduced spin reorientation paths in ErFeO3. We succeed in aligning macroscopic magnetization reaching up to 80% of total magnetization in the sample to selectable orientations by adjusting the time delay between terahertz and optical pump pulses. The spin dynamics are well reproduced by equations of motion, including time-dependent magnetic potential. We show that the direction of the generated magnetization is determined by the transient direction of spin tilting and the magnetic field at the moment of photoexcitation.

关键词： Antiferromagnetism Faraday effect Ferromagnetism Magnetic anisotropy Magnetic phase transitions Magnetization switching Magneto-optical effect Magnons Optical & microwave phenomena Antiferromagnets Ferromagnets Coherent control Femtosecond laser spectroscopy Ferromagnetic resonance finite-difference time-domain method Landau-Lifschitz-Gilbert equation Optically detected magnetic resonance time-resolved infrared spectroscopy Ultrafast pump-probe spectroscopy

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Double and triple-wavelength plasmonic demultiplexers based on improved circular nanodisk resonators

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OPTICAL ENGINEERING 2018年第10期57卷 107102-107102页

作者： Khani, Shiva Danaie, Mohammad Rezaei, Pejman Semnan Univ Elect & Comp Engn Fac Semnan Iran

Plasmonic demultiplexers using improved circular nanodisk resonators (CNRs) and metal-insulator-metal waveguides have been designed. The proposed structures use air and silver as insulator and metal layers, respectively. The relative permittivity of silver has been characterized by Drude, Palik, and Drude-Lorentz models in our finite-difference time-domain simulations. To obtain demultiplexers, first two filters based on improved CNRs are designed. One of the most outstanding features of a CNR is that the resonance wavelength can be tuned by changing its radius. It is shown that increasing the CNRs radii for the single-mode bandpass filter increases the resonance wavelength, linearly. Accordingly, double and triple-wavelength demultiplexers (DeMuxes) have been proposed for the wavelength range of 600 to 2000 nm. Due to their small area, the proposed demultiplexers can be applied in integrated optical circuits for optical communication purposes. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： plasmonic demultiplexer metal-insulator-metal waveguide circular nanodisk resonator Drude-Lorentz model finite-difference time-domain method

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Interaction between confined phonons and photons in periodic silicon resonators

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Physical Review B 2018年第9期97卷 094308-094308页

作者： A. Iskandar A. Gwiazda J. Younes M. Kazan A. Bruyant M. Tabbal G. Lerondel Department of Physics American University of Beirut P.O. Box 11-0236 Riad El-Solh Beirut 1107-2020 Lebanon Laboratoire de Nanotechnologie et d’Instrumentation Optique ICD CNRS UMR 6281 Université de Technologie de Troyes 10010 Troyes France

In this paper, we demonstrate that phonons and photons of different momenta can be confined and interact with each other within the same nanostructure. The interaction between confined phonons and confined photons in silicon resonator arrays is observed by means of Raman scattering. The Raman spectra from large arrays of dielectric silicon resonators exhibited Raman enhancement accompanied with a downshift and broadening. The analysis of the Raman intensity and line shape using finite-difference time-domain simulations and a spatial correlation model demonstrated an interaction between photons confined in the resonators and phonons confined in highly defective regions prompted by the structuring process. It was shown that the Raman enhancement is due to collective lattice resonance inducing field confinement in the resonators, while the spectra downshift and broadening are signatures of the relaxation of the phonon wave vector due to phonon confinement in defective regions located in the surface layer of the Si resonators. We found that as the resonators increase in height and their shape becomes cylindrical, the amplitude of their coherent oscillation increases and hence their ability to confine the incoming electric field increases.

关键词： Confinement Phonons Photonics Nanostructures finite-difference time-domain method Raman spectroscopy

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Dirac cones in isogonal hexagonal metallic structures

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Physical Review B 2018年第12期97卷 125146-125146页

作者： Kang Wang Laboratoire de Physique des Solides UMR CNRS/Université Paris-Sud Université Paris-Saclay 91405 Orsay France

A honeycomb hexagonal metallic lattice is equivalent to a triangular atomic one and cannot create Dirac cones in its electromagnetic wave spectrum. We study in this work the low-frequency electromagnetic band structures in isogonal hexagonal metallic lattices that are directly related to the honeycomb one and show that such structures can create Dirac cones. The band formation can be described by a tight-binding model that allows investigating, in terms of correlations between local resonance modes, the condition for the Dirac cones and the consequence of the third structure tile sustaining an extra resonance mode in the unit cell that induces band shifts and thus nonlinear deformation of the Dirac cones following the wave vectors departing from the Dirac points. We show further that, under structure deformation, the deformations of the Dirac cones result from two different correlation mechanisms, both reinforced by the lattice's metallic nature, which directly affects the resonance mode correlations. The isogonal structures provide new degrees of freedom for tuning the Dirac cones, allowing adjustment of the cone shape by modulating the structure tiles at the local scale without modifying the lattice periodicity and symmetry.

关键词： Photonics Honeycomb lattice Polarization Band structure methods finite-difference time-domain method

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Experimental evaluation and FDTD method for predicting electromagnetic fields in the near zone radiated by power converter systems

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TURKISH JOURNAL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCES 2017年第2期25卷 1460-1471页

作者： Laour, Mohammed Tahmi, Redouane Vollaire, Christian Natl Polytech Sch Algiers ENP Res Lab Elect Engn ENP Algiers Algeria Renewable Energy Dev Ctr CDER EPST EPST Dev Unit Solar Equipment UDES Tipasa Algeria Univ Lyon Cent Sch Lyon Ampere Lab Ecully France

This paper presents the study of conducted electromagnetic interference (EMI) currents flowing through the power cables of a DC-DC converter system and its correlation with the near field radiated from these cables. The radiated emission measurement contains a common mode (CM) and a differential mode (DM), and accurate separation of the radiated emissions of these two modes is necessary. The finite-difference time-domain (FDTD) method is used to predict the electromagnetic radiation caused by CM currents and DM currents. An experimental bench has been designed to allow access to the measurement of EMI disturbances at various sensitive places. The CM and DM voltages resulting from the experimental measurement are implemented in the FDTD algorithm as voltage sources of disturbances, these disturbance voltages causing the generation of CM and DM currents flowing through the cable. Finally, single and bifilar wire models for modeling the near field using the FDTD method are presented and the simulation results of the near field caused by both of the modes are evaluated and compared with the experimental ones. The main objective is to investigate the significance of the contribution of each of the current modes on the radiated emissions from the cable using the FDTD method, thus characterizing the level of cable radiation versus a specific standard. This allows showing that the radiation is often caused by the CM current along the cable and the largest level is located in the switching noise zone located within the frequency range from 1 MHz to 10 MHz.

关键词： Power electronics converters finite-difference time-domain method electromagnetic compatibility electromagnetic interferences common mode differential mode

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Photonic engineering of highly linearly polarized quantum dot emission at telecommunication wavelengths

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Physical Review B 2018年第16期97卷 165427-165427页

作者： P. Mrowiński M. Emmerling C. Schneider J. P. Reithmaier J. Misiewicz S. Höfling G. Sęk OSN Lab Department of Experimental Physics Faculty of Fundamental Problems of Technology Wrocław University of Science Technology Poland Technische Physik & W. C. Röntgen-Center for Complex Material Systems Universität Würzburg Germany Institute of Nanostructure Technologies and Analytics (INA) CINSaT University of Kassel Heinrich-Plett-Str. 40 34132 Kassel Germany SUPA School of Physics and Astronomy University of St. Andrews North Haugh KY16 9SS St. Andrews United Kingdom

In this work, we discuss a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths. The nanostructures are embedded inside lithographically defined, in-plane asymmetric photonic mesa structures, which generate polarization-dependent photonic confinement. First, we study the influence of the photonic confinement on the polarization anisotropy of the emission by photoluminescence spectroscopy, and we find evidence of different contributions to a degree of linear polarization (DOLP), i.e., from the quantum dash and the photonic mesa, in total giving rise to DOLP=0.85. Then, we perform finite-difference time-domain simulations of photonic confinement, and we calculate the DOLP in a dipole approximation showing well-matched results for the established model. Furthermore, by using numerical calculations, we demonstrate several types of photonic confinements where highly linearly polarized emission with DOLP of about 0.9 is possible by controlling the position of a quantum emitter inside the photonic structure. Then, we elaborate on anisotropic quantum emitters allowing for exceeding DOLP=0.95 in an optimized case, and we discuss the ways towards efficient linearly polarized single photon source at telecom bands.

关键词： Excitons Nanophotonics Quantum dots finite-difference time-domain method Photoluminescence

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Weakly conditionally stable finite-difference time-domain method

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IET MICROWAVES ANTENNAS & PROPAGATION 2010年第11期4卷 1927-1936页

作者： Chen, J. Wang, J. Xi An Jiao Tong Univ Sch Elect & Informat Engn Xian 710049 Peoples R China NW Inst Nucl Technol Xian 710024 Peoples R China

A novel weakly conditionally stable finite-difference time-domain (FDTD) method, which is extremely useful for problems with very fine structures over a large computational domain in one or two directions, is presented. The time step in this method is only determined by one space discretisation and is presented analytically. Compared with the alternating-direction implicit (ADI) FDTD method, this new method has higher accuracy, especially for larger field variation rate and/or time-step size. By defining the field components at only two time steps, this new method requires the solution of four tridiagonal matrices and four explicit updates at each time step, which is more computationally efficient than the ADI-FDTD scheme. While maintaining the same size of time step, the CPU time for this method can be reduced to about 2/3 of that for the ADI-FDTD scheme. The numerical performance of the proposed method over the ADI-FDTD method is demonstrated through numerical examples.

关键词： alternating-direction implicit FDTD method Electromagnetic wave propagation finite difference time-domain analysis computational domain computational electromagnetics matrix algebra tridiagonal matrices Linear algebra (numerical analysis) finite-difference time-domain method Classical electromagnetism Electric and magnetic fields Numerical approximation and analysis

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Impact of [email protected] 2 core-shell nanoparticles on the photoelectric current of plasmonic inverted organic solar cells

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Synthetic Metals 2018年 239卷 22-28页

作者： Kekeli N'Konou Malika Chalh Virginie Monnier Nicholas P. Blanchard Yann Chevolot Bruno Lucas Sylvain Vedraine Philippe Torchio Aix-Marseille Univ IM2NP CNRS-UMR 7334 Domaine Universitaire de Saint-Jérôme Service 231 13397 Marseille Cedex 20 France Université de Limoges XLIM-CNRS 7252 123 Avenue Albert Thomas 87060 Limoges France Université de Lyon Institut des Nanotechnologies de Lyon UMR CNRS 5270 Ecole Centrale de Lyon 36 Avenue Guy de Collongue F-69134 Ecully France Université de Lyon Université Claude Bernard Lyon 1 CNRS Institut Lumière Matière F-69622 Villeurbanne France

We report on the influence of silver-silica core-shell nanoparticles ( [email protected] 2 NPs) and bare silver nanoparticles (Ag NPs) on the photoelectric current of plasmonic inverted organic solar cells. The synthesized [email protected] 2 NPs are deposited on a zinc oxide layer. The optimized plasmonic devices concern the [email protected] 2 NPs with 5 nm shell thickness and present the highest short-circuit current density of 13.44 mA/cm 2 , enhanced by 12% compared to the reference device. Such enhancements can mainly be attributed to the localized surface plasmon resonance and to the light scattering effect originating from Ag NPs and [email protected] 2 NPs. finite-difference time-domain simulation reveals that a thin shell thickness facilitates the extension of a strong localized enhanced electromagnetic field in the active layer, as confirmed by measured and simulated optical absorption and photoluminescence measurements. Furthermore, AFM images present a well-distributed [email protected] 2 NPs array on the ZnO films, which contributes to such an improvement.

关键词： [email protected] core-shell nanospheres Plasmonic solar cells Absorption enhancement finite-difference time-domain method

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