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A comprehensive discrete-time computer modeling of acoustic Transmission Line loudspeakers

APPLIED ACOUSTICS 2011年第10期72卷 742-753页

作者： Escolano, Jose Pueo, Basilio Lopez, Jose J. Univ Jaen Telecommun Engn Dept Polytech Sch Jaen Spain Univ Alicante Commun & Social Psychol Dept Alicante Spain Univ Politecn Valencia iTeAM Inst Valencia Spain

The Transmission Line loudspeaker is an audio loudspeaker enclosure topology devoted to extending the low frequency range near the loudspeaker frequency resonance. A few models based on physical properties of damped pipes have been proposed to characterize the Transmission Line loudspeaker systems. Unfortunately. Thiele/Small parameters, which are usually employed in enclosure designs, are not useful as parameters of design for these loudspeakers. In this paper, a comprehensive numerical formulation of a Transmission Line loudspeaker is presented, which is based in a finite difference approach of the governing equations, including the effects of the absorbing material allocated inside the pipe. The influence of the main empirical parameters is tested on the proposed model, which is also compared to a real prototype for validation purposes. (C) 2011 Elsevier Ltd. All rights reserved.

关键词： Electroacoustics finite-difference time-domain method Transmission Line loudspeakers

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Splitting the surface wave in metal/dielectric nanostructures

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Chinese Physics B 2011年第6期20卷 469-473页

作者：祝颂吴坚 Department of Physics State Key Laboratory of Advanced Optical Communication Systems and Networks Shanghai Jiao Tong University

We investigate a modified surface wave splitter with a double-layer structure, which consists of symmetrical metallic grating and an asymmetrical dielectric, using the finite-difference time-domain （FDTD） simulation method. The metal/dielectric interface structure at this two-side aperture can support bound waves of different wavelengths, thus guiding waves in opposite directions. The covered dielectric films play an important role in the enhancement and confinement of the diffraction wave by the waveguide modes. The simulation result shows that the optical intensities of the guided surface wave at wavelengths of 760-nm and 1000-nm are about 100 times and 4-5 times those of the weaker side, respectively, which means that the surface wave is split by the proposed device.

关键词： surface plasmons finite-difference time-domain method metallic grating layered nanostructures

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Optical properties of the (3.4.6.4) hexagonal Archimedean photonic crystal (vol 5, 051820, 2011)

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JOURNAL OF NANOPHOTONICS 2011年第1期5卷 051820-051820-7页

作者： Jovanovic, Djordje Gajic, Rados Univ Belgrade Inst Phys Ctr Solid State Phys & New Mat Belgrade 11080 Serbia

We theoretically investigated the optical properties of the lesser known (3.4.6.4) Archimedean photonic crystal. The structure is two dimensional and made of dielectric GaAs rods in air. The calculations of the band structures, equifrequency contours, and simulations of the wave propagation through the structure were performed by the plane wave expansion and finite-difference time-domain methods. With analysis of the gap map and equifrequency contours we obtained frequency ranges for best performance for wave guiding. For those frequency ranges, we designed a new type of waveguide for possible applications in integrated optics. In addition, negative refraction was exhibited by the structure.

关键词： Optical properties Photonic crystals Collimation Gallium arsenide Negative refraction Waveguides finite-difference time-domain method Simulations

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STUDY OF BANDGAP CHARACTERISTICS OF 2D MAGNETOPLASMA PHOTONIC CRYSTAL BY USING M-FDTD method

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2011年第8期53卷 1778-1784页

作者： Yang, Lixia Xie, Yingtao Yu, Pingping Jiangsu Univ Dept Commun Engn Jiangsu 212013 Zhenjiang Peoples R China Southeast Univ State Key Lab Millimeter Waves Nanjing 210096 Peoples R China

To develop modified finite-difference time-domain (M-FDTD) algorithm with magnetized plasma medium, constitutive equation between current density vector and electric field strength vector is first transformed into s-domain for decoupling, and then transformed back into time domain so that the FDTD iteration equations can be easily obtained in discrete time domain. Then the reflection coefficients with plasma slab calculated by the proposed M-FDTD algorithm are compared with analytical to show the validity of our technique. Finally, the M-FDTD algorithm is applied to calculate the reflection and transmission coefficients of plasma photonic crystal of different plasma parameters. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53: 1778-1784, 2011;View this article online at ***. DOI 10.1002/mop.26143

关键词： magnetoplasma photonic crystal bandgap finite-difference time-domain method

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FDTD Computational Study of Ultra-Narrow TM Non-Paraxial Spatial Soliton Interactions

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IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS 2011年第5期21卷 228-230页

作者： Lubin, Zachary Greene, Jethro H. Taflove, Allen Northwestern Univ Evanston IL 60208 USA

We consider the interaction between two (1+1)D ultra-narrow optical spatial solitons in a nonlinear dispersive medium using the finite-difference time-domain (FDTD) method for the transverse magnetic (TM) polarization. The model uses the general vector auxiliary differential equation (GVADE) approach to include multiple electric-field components, a Kerr nonlinearity, and multiple-pole Lorentz and Raman dispersive terms. This study is believed to be the first considering narrow soliton interaction dynamics for the TM case using the GVADE FDTD method, and our findings demonstrate the utility of GVADE simulation in the design of soliton-based optical switches.

关键词： finite-difference time-domain method FDTD GVADE nonlinear optics spatial solitons

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Exposure Assessment in Front of a Multi-Band Base Station Antenna

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BIOELECTROMAGNETICS 2011年第3期32卷 234-242页

作者： Kos, Bor Valic, Blaz Kotnik, Tadej Gajsek, Peter INIS Inst Nonionizing Radiat SI-1000 Ljubljana Slovenia Univ Ljubljana Fac Elect Engn Ljubljana Slovenia

This study investigates occupational exposure to electromagnetic fields in front of a multi-band base station antenna for mobile communications at 900, 1800, and 2100 MHz. finite-difference time-domain method was used to first validate the antenna model against measurement results published in the literature and then investigate the specific absorption rate (SAR) in two heterogeneous, anatomically correct human models (Virtual Family male and female) at distances from 10 to 1000 mm. Special attention was given to simultaneous exposure to fields of three different frequencies, their interaction and the additivity of SAR resulting from each frequency. The results show that the highest frequency-2100 MHz-results in the highest spatial-peak SAR averaged over 10 g of tissue, while the whole-body SAR is similar at all three frequencies. At distances > 200 mm from the antenna, the whole-body SAR is a more limiting factor for compliance to exposure guidelines, while at shorter distances the spatial-peak SAR may be more limiting. For the evaluation of combined exposure, a simple summation of spatial-peak SAR maxima at each frequency gives a good estimation for combined exposure, which was also found to depend on the distribution of transmitting power between the different frequency bands. Bioelectromagnetics 32:234-242, 2011. (C) 2010Wiley-Liss, Inc.

关键词： occupational RF exposure multi-band base station finite-difference time-domain method whole-body SAR spatial-peak SAR

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Near-Field PML Optimization for Low and High Order FDTD Algorithms Using Closed-Form Predictive Equations

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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2011年第8期59卷 2933-2942页

作者： Hadi, Mohammed F. Kuwait Univ Dept Elect Engn Safat 13060 Kuwait

The convolutional perfectly-matched-layer (CPML) absorbing boundary condition is fully capable of handling near-field wave absorption that usually combines near-grazing wave incidence with wave evanescence. The appropriate choice of the various CPML parameters to realize this potential for any given simulation problem is a challenging task that is typically achieved through exhaustive and time-consuming searches that involve large numbers of full-scale simulations. The presented work here uses a previously developed predictive system of equations that accurately determines numerical reflections off the PML interface and embeds it into a global optimization routine that reliably computes the required optimum CPML parameters. This predictive system of equations has also been extended and validated for the M24 and FV24 integral-based high-order FDTD algorithms. With this approach, the task of selecting optimum CPML parameters that would usually take several days of intense computations can now be accomplished within a few minutes on an average personal computer.

关键词： Absorbing boundary conditions finite-difference time-domain method high-order FDTD methods perfectly-matched layer (PML)

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Optimum time-step size for 2D (2,4) FDTD method

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ELECTRONICS LETTERS 2011年第5期47卷 317-318页

作者： Zygiridis, T. T. Univ Western Macedonia Dept Informat & Telecommun Engn Kozani 50100 Greece

The correct choice of time-step size is of crucial importance in the case of the (2, 4) finite-difference time-domain (FDTD) method, as it affects the algorithm's overall accuracy and convergence rate. A description of the inherent discretisation error is introduced, which is exploited for the derivation of a simple, yet reliable, approximation of the optimum temporal sampling density. As the proposed approach attempts to remedy inaccuracies in a mean-value sense, it is shown that highly efficient calculations can be carried out in this way.

关键词： 2D FDTD method convergence convergence rate finite difference time-domain analysis finite-difference time-domain method inherent discretisation error mean-value sense optimum temporal sampling density approximation optimum time-step size

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On the relation between FDTD and Fibonacci polynomials

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JOURNAL OF COMPUTATIONAL PHYSICS 2011年第4期230卷 1382-1386页

作者： Remis, Rob F. Delft Univ Technol Fac Elect Engn Math & Comp Sci Circuits & Syst Grp NL-2628 CD Delft Netherlands

In this paper we show that the finite-difference time-domain method (FDTD method) follows the recurrence relation for Fibonacci polynomials. More precisely, we show that FDTD approximates the electromagnetic field by Fibonacci polynomials in Delta tA, where Delta t is the time step and A is the first-order Maxwell system matrix. By exploiting the connection between Fibonacci polynomials and Chebyshev polynomials of the second kind, we easily obtain the Courant-Friedrichs-Lewy (CFL) stability condition and we show that to match the spectral width of the system matrix, the time step should be chosen as large as possible, that is, as close to the CFL upper bound as possible. (C) 2010 Elsevier Inc. All rights reserved.

关键词： finite-difference time-domain method Fibonacci polynomials Chebyshev polynomials of the second kind Stability condition

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Stability and superconvergence analysis of the FDTD scheme for the 2D Maxwell equations in a lossy medium

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Science China Mathematics 2011年第12期54卷 2693-2712页

作者： GAO LiPing ZHANG Bo Department of Computational and Applied Mathematics School of Sciences China University of Petroleum Qingdao 266555 China LSEC and Institute of Applied Mathematics Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing 100190 China

This paper is concerned with the stability and superconvergence analysis of the famous finite-difference time-domain (FDTD) scheme for the 2D Maxwell equations in a lossy medium with a perfectly electric conducting (PEC) boundary condition, employing the energy method. To this end, we first establish some new energy identities for the 2D Maxwell equations in a lossy medium with a PEC boundary condition. Then by making use of these energy identities, it is proved that the FDTD scheme and its time difference scheme are stable in the discrete L2 and H1 norms when the CFL condition is satisfied. It is shown further that the solution to both the FDTD scheme and its time difference scheme is second-order convergent in both space and time in the discrete L2 and H1 norms under a slightly stricter condition than the CFL condition. This means that the solution to the FDTD scheme is superconvergent. Numerical results are also provided to confirm the theoretical analysis.

关键词： Maxwell equations finite-difference time-domain method stability superconvergence perfectly electric conducting boundary conditions energy identities

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