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A hybrid modeling for the theoretical analysis of reflections in a multimode-interference coupler based on silicon-on-insulator nanowires

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OPTICS COMMUNICATIONS 2008年第11期281卷 3099-3104页

作者： Zhu, Ning Dai, Daoxin He, Sailing Royal Inst Technol Joint Res Ctr Photon Stockholm Sweden Zhejiang Univ State Key Lab Modern Opt Instrumentat Ctr Opt & Electromagnet Res Hangzhou 310058 Peoples R China Zhejiang Univ Hangzhou 310058 Zhejiang Peoples R China

A hybrid method combining the three-dimensional (3D) beam propagation method (BPM) and a 3D finite-difference time-domain (FDTD) method is presented for the simulation of multimode-interference (MMI) couplers based on silicon-on-insulator (SOI) nanowires. This hybrid method makes it possible to have a robust analysis for the reflection properties while avoiding a time-consumed computation with a simplex 3D-FDTD simulation. The reflected power is sensitive to both the length and the width of the MMI coupler and thus one should choose the optimal values for good self-imaging. Furthermore, the reflection could be reduced by introducing tapers between the MMI section and the access waveguides. (c) 2008 Elsevier B.V. All rights reserved.

关键词： multimode-interference coupler finite-difference time-domain method beam propagation method reflection

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FDTD calculations of specific absorption rate in fetus caused by electromagnetic waves from mobile radio terminal using pregnant woman model

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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 2008年第2期56卷 554-559页

作者： Togashi, Toshihiro Nagaoka, Tomoaki Kikuchi, Satoru Saito, Kazuyuki Watanabe, Soichi Takahashi, Masaharu Ito, Koichi Chiba Univ Res Ctr Frontier MEd Engn Chiba 2638522 Japan

Since the diversification of the electromagnetic (EM) environment is spreading, it is essential to estimate the EM energy absorption rate [specific absorption rate (SAR)] of a pregnant woman's body and her fetus under various exposure situations. This paper presents the EM dosimetry in a pregnant woman in proximity to a mobile-phone terminal using the numerical model of a woman in her seventh month of pregnancy (composed of 56 organs, which includes the intrinsic organs of a pregnant woman) based on the high-resolution whole-body voxel model of a Japanese adult woman. It was found that. the SAR in the fetus strongly depends on the geometrical relationship between the fetus and the EM source, while the averaged SAR for the fetus is always lower than the RF safety guidelines under the exposure conditions investigated in this paper.

关键词： fetus finite-difference time-domain method magnetic resonance imaging mobile radio terminal pregnant woman specific absorption rate (SAR)

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Characteristics of light intensity enhancement of a silver nanoprism with rounded corners

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JOURNAL OF MICROSCOPY 2008年第3期229卷 545-550页

作者： Yamaguchi, K. Inoue, T. Fujii, M. Ogawa, T. Matsuzaki, Y. Okamoto, T. Haraguchi, M. Fukui, M. Univ Tokushima Fac Engn Dept Opt Sci & Technol Tokushima 7708506 Japan Toba Natl Coll Maritime Technol Dept Elect & Mech Toba Mie 5178501 Japan

We have fabricated silver nanoprisms of 100-600 nm side length by focussed ion beam lithography and measured the light intensity scattering spectra using dark-field microscopy. Two resonance peaks due to localized surface plasmon excitation were observed in the spectra and their central frequency shown to depend on the prism size. The near-field electromagnetic intensity distribution with TE-polarized light at the vacuum wavelength of 632.8 nm was measured. We have obtained a much lower light intensity enhancement than previously numerically predicated. However, scattering spectra obtained numerically, taking into account roundness of the prism corners, agree well with experimental ones. At the same time, the numerically determined field distribution was different to the near-field intensity obtained experimentally. Our results suggest the particular shape of the corner region of the prism is a key factor for obtaining a large light intensity enhancement and shaping the local field distribution.

关键词： curvature radius finite-difference time-domain method localized surface plasmon nanooptical switch scanning near-field microscopy silver nanoprism

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Simulation of photorefractive effect in thin liquid crystal film

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MOLECULAR CRYSTALS AND LIQUID CRYSTALS 2008年第1期489卷 204-213页

作者： Kubytskyi, V. O. Reshetnyak, V. Y. Sluckin, T. J. Cox, S. J. Natl Taras Shevchenko Univ Kyiv Fac Phys UA-03022 Kiev Ukraine Univ Southampton Sch Math Southampton Hants England Univ Southampton Sch Engn Sci Southampton Hants England

We study the photorefractive effect in a thin liquid crystal grating by numerical simulation. The cell consists of homeotropically aligned liquid crystal film sandwiched between photo-conductive electrodes. A constant voltage is applied across the cell. The interference pattern from two impinging laser beams then causes a periodic modulation of the potential at the top and bottom surfaces of the liquid crystal cell. We compare results obtained by simulation with an analytical approach which uses the Geometrical Optics Approximation. The results show good agreement between these two methods.

关键词： finite-difference time-domain method non-linear optics photorefractive-like effect

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FDTD simulation on the interaction between gaussian beam and biaxial anisotropic metamaterial slabs

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INTERNATIONAL JOURNAL OF INFRARED AND MILLIMETER WAVES 2008年第2期29卷 167-178页

作者： Wang, Maoyan Wu, Jian Xu, Jun Ge, Debiao Li, Hailong Feng, Jian Univ Elect Sci & Technol China Sch Phys Elect Chengdu 610054 Sichuan Peoples R China China Res Inst Radiowave Propagat Natl Key Lab Electromagnet Environm Beijing 102206 Peoples R China Xidian Univ Sch Sci Xian 710071 Shanxi Peoples R China China Res Inst Radiowave Propagat Qingdao 266107 Shandong Peoples R China

The interaction between Gaussian beam and indefinite anisotropic metamaterial (AMM) slabs are simulated with auxiliary differential equation method in finite-difference time-domain method (FDTD). The directions of wave vector and energy flow densities in three types of AMM slabs are investigated. The field intensity distributions and phases of TE-polarized wave for the interaction between Gaussian beam and AMM slabs are given. Numerical results show that the sign of x component of relative permeability tensor of AMM determines the refraction is regular or anomalous, whereas the sign of z component of relative permeability tensor of AMM determines the energy flow is positively refracted or negatively refracted. Positive or negative Goos-Hanchen shift associated with Total Cutoff media are also shown.

关键词： anisotropic metamaterials finite-difference time-domain method auxiliary differential equation method negative refraction

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Splitting finite difference methods on Staggered Grids for the Three-Dimensional time-Dependent Maxwell Equations

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Communications in Computational Physics 2008年第7期4卷 405-432页

作者： Liping Gao Bo Zhang Dong Liang School of Mathematical Sciences Shandong Normal UniversityJinan 250014China. Institute of Applied Mathematics Chinese Academy of SciencesBeijing 100080China. Department of Mathematics and Statistics York University4700 Keele StreetTorontoOntario M3J 1P3Canada

In this paper,we study splitting numerical methods for the three-dimensional Maxwell equations in the time *** propose a new kind of splitting finitedifference time-domain schemes on a staggered grid,which consists of only two stages for each time *** is proved by the energy method that the splitting scheme is unconditionally stable and convergent for problems with perfectly conducting boundary *** numerical dispersion analysis and numerical experiments are also presented to illustrate the efficiency of the proposed schemes.

关键词： Splitting scheme alternating direction implicit method finite-difference time-domain method stability convergence Maxwell’s equations perfectly conducting boundary

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Applicability of Temperature Distribution for Estimation of Medium Constants Using Temperature Rise due to Absorption of Ultrasound

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JAPANESE JOURNAL OF APPLIED PHYSICS 2008年第5期47卷 4145-4148页

作者： Yamaya, Chiaki Inoue, Hiroshi Akita Univ Fac Engn & Resource Sci Dept Elect & Elect Engn Akita 0108502 Japan

The analysis of temperature rise due to the absorption of ultrasound is important for the clarification of the effect of ultrasound waves and the estimation of medium constants. The thermal behavior of ultrasound is used not only for thermotherapy but also in measurement techniques. The estimation of a medium constant becomes possible by analyzing the temperature rise because the temperature change of the medium is particular to each medium. The purpose of this research is to establish a method of estimating medium constants and to develop a numerical simulation method that can be applied to the estimation of medium Constants. We elucidated the requirements under which the simulation result corresponds to the experimental result. Good agreement between the experimental and simulation results is shown in this paper, and the validity of this method is described. [DOI: 10.1143/JJAP.47.4145]

关键词： thermal behavior of ultrasound absorption of ultrasound finite-difference time-domain method heat analysis

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Numerical solution of Maxwell's equations for anisotropic media using the Laguerre transform

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RUSSIAN GEOLOGY AND GEOPHYSICS 2008年第8期49卷 621-627页

作者： Mastryukov, A. F. Mikhailenko, B. G. RAS Siberian Branch Inst Comp Math & Math Geophys Novosibirsk 630090 Russia

We apply the spectral Laguerre transform in the time domain to solve 2D Maxwell's equations for propagation of electromagnetic waves in lossy anisotropic media. The new algorithm is simple and efficient as Maxwell's equations are reduced to a harmonic series of linear algebraic equations where the matrix is independent of the harmonic order and is the same for all harmonics. The efficiency of the algorithm is improved by fitting a specially introduced free parameter of the Laguerre transform. If it is large, the solution spectrum shifts toward higher harmonics which is formally equivalent to the case of ray approximation. The Laguerre solution is comparable with high-order accurate finite-difference time-domain (FDTD) solutions. The method is stable both in the region of the wavefield, where conductivity approaches zero and the spectral Fourier method is unstable, and in the high-conductivity region, where the explicit FDTD code requires a too small time step. (C) 2008, IGM, Siberian Branch of the RAS. Published by Elsevier B. V. All rights reserved.

关键词： Maxwell's equations electromagnetic waves anisotropic media relaxation time conductivity dielectric permittivity Laguerre transform finite-difference time-domain method linear equation system

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Study of superluminal-pulse propagation in one-dimensional photonic crystals by the FDTD method

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JOURNAL OF RUSSIAN LASER RESEARCH 2008年第2期29卷 176-183页

作者： Chen, Yu-lin Fang, Yun-tuan Nanjing Univ Informat Sci & Technol Coll Math Nanjing 210044 Peoples R China Zhenjiang Watercraft Coll Dept Phys Zhenjiang 212003 Peoples R China

We study the pulse propagation in a one-dimensional photonic crystal using the finite-difference time-domain method. The wave propagation inside the crystal is the result of superposition of forward and backward waves. We observed the superluminal phenomena and negative values of the velocity of the energy-density maximum. The energy velocities within the crystal never exceed the speed of light in vacuum. We hope that our study contributes to a further understanding of the superluminal phenomena.

关键词： superluminal phenomenon photonic crystal finite-difference time-domain method

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An Accurate Simulator for Magnetic Resonance Coil Sensitivity Estimation

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CONCEPTS IN MAGNETIC RESONANCE PART B-MAGNETIC RESONANCE ENGINEERING 2008年第4期33B卷 209-215页

作者： Giovannetti, Giulio Viti, Vittorio Liu, Yongjun Yu, Wenhua Mittra, Raj Landini, Luigi Benassi, Antonio CNR Inst Clin Physiol Pisa Italy Esaote Biomed Spa Genoa Italy Penn State Univ EE Dept Electromagnet Commun Lab University Pk PA 16802 USA Univ Pisa Dept Informat Engn I-56100 Pisa Italy

Coil sensitivity estimation in magnetic resonance experiments requires the knowledge of biological sample-induced resistance. In dependence on system geometry, many authors studied sample-coil interaction by using a very simple coil geometry (circular, square, etc.) and homogeneous infinitely long cylinders, spheres, or half-spaces as approximations of the sample geometry. However, in real MR experiments, both shape and dimensions can be very different with respect to these coil and sample models. in this article, we propose the application of finite-difference time-domain method for sample-induced resistance estimation. The developed approach can be used as a tool to estimate sample-induced resistance in complex receiving systems, without approximations in sample and coil geometries. Calculation of both sample-induced resistance and magnetic field pattern permits to estimate coil sensitivity for optimal coil design in dependence on the sample size and geometry. Comparison with experimental data, performed on two home-built saddle coils, demonstrated the great accuracy of the developed method. (C) 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 3313: 209-215, 2008

关键词： signal-to-noise ratio sample-induced resistance electromagnetic simulator finite-difference time-domain method coil sensitivity

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