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Amplitude degradation of time-reversed pulses in nonlinear absorbing thermoviscous fluids

ULTRASONICS 2000年第9期38卷 885-889页

作者： Hallaj, IM Cleveland, RO Barbone, PE Kargl, SG Roy, RA Harvard Univ Brigham & Womens Hosp Sch Med Radiol MRI Boston MA 02115 USA Boston Univ Dept Aerosp & Mech Engn Boston MA 02215 USA Univ Washington Appl Phys Lab Seattle WA 98105 USA

The linear wave equation in a lossless medium is time reversible, i.e., every solution p(x, t) has a temporal mirror solution p(x, -t). Analysis shows that time reversal also holds for the lossless nonlinear wave equation. In both cases, time-reversal invariance is violated when losses are present. For nonlinear propagation loses cannot normally be ignored;they are necessary to prevent the occurrence of multivalued waveforms. Further analysis of the nonlinear wave equation shows that amplification of a time-reversed pulse at the array elements also leads to a violation of time reversal even for lossless nonlinear acoustics. Numerical simulations are used to illustrate the effect of nonlinearity on the ability of a time-reversal system to effectively focus on a target in an absorbing fluid medium. We consider both the amplitude and arrival time of retrodirected pulses. The numerical results confirm that both shock generation (with the accompanying absorption) and amplification at the array, adversely affect the ability of a time-reversal system to form strong retrodirective sound fields. (C) 2000 Elsevier Science B.V. All rights reserved.

关键词： time reversal nonlinear propagation finite-difference time-domain method

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Phased array antenna analysis using time delay beam steering and hybrid FDTD method

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ELECTRONICS LETTERS 2000年第2期36卷 108-110页

作者： Parfitt, AJ Bird, TS CSIRO Epping NSW 1710 Australia

A phased array analysis is presented where the coupling between antenna elements and the beam steering is computed in the time domain using a hybrid finite-difference time-domain (FDTD) and Kirchhoff transform method. The coupled currents are combined with the appropriate time delays to give the total element current, which is then used in conjunction with the voltage excitation to produce the driving point admittance as a function of frequency for a given beam direction.

关键词： coupled currents time delay beam steering Kirchhoff transform method driving point admittance time domain computation Antenna theory Other numerical methods finite difference time-domain analysis voltage excitation Antenna arrays antenna phased arrays electric admittance phased array antenna analysis hybrid FDTD method delays antenna theory finite-difference time-domain method

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Theory and experiment on microstrip patch antennas with shorting walls

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IEE PROCEEDINGS-MICROWAVES ANTENNAS AND PROPAGATION 2000年第6期147卷 521-525页

作者： Lee, KF Guo, YX Hawkins, JA Chair, R Luk, KM Univ Mississippi Sch Engn University MS 38677 USA City Univ Hong Kong Dept Elect Engn Hong Kong Hong Kong Peoples R China Univ Missouri Dept Elect Engn Columbia MO USA

Experimental and calculated results based on the finite-difference time-domain method are presented on the impedance and radiation characteristics of the classic shorted quarterwave patch. It is found that, for foam substrates with relative permittivity close to unity, the bandwidths of the quarterwave patches are significantly larger than the halfwave patches. On the other hand, for microwave substrates with relative permittivites equal to 2.32 and 4.0. the bandwidths of quarterwave patches are less than those of halfwave patches, owing to the excitation of surface waves. The maximum gain in the case of foam substrate is in the range of 2-3.5dBi, occurring 0-45 degrees from broadside, depending on the substrate thickness. The use of a partial short, while reducing the resonant frequency, also decreases the bandwidth. The paper also describes the application of the shorting-wall principle to realise a compact wideband L-probe patch antenna.

关键词： finite difference time-domain analysis compact wideband L-probe patch antenna FDTD method 2 to 3.5 dB relative permittivity surface waves excitation Single antennas microstrip antennas microwave substrates antenna radiation patterns finite-difference time-domain method microstrip patch antennas shorted quarterwave patch electric impedance partial short bandwidth shorting walls radiation characteristics foam substrates halfwave patches impedance characteristics Other numerical methods

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Effects of current source models on numerical performances in FDTD simulations

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2000年第1期27卷 4-7页

作者： Yuan, WL Liang, CH Shi, XW Wang, BK Inst High Performance Comp EMC Div Singapore 118261 Singapore Xidian Univ Dept Microwave Telecommun Engn Xian 710071 Peoples R China

A source model can influence FDTD numerical performance although it may be a fictitious source in some FDTD computations. The current source models for FDTD excitation, both resistance free and resistive, and presented, respectively, which are directly derived from Maxwell's equations. The former is simple in implementation and high in computational accuracy by comparison with a voltage source excitation, and the latter possesses stability,and can reduce the computation time as the resistance is properly chosen which means it an be optimized in terms of its internal resistance. (C) 2000 John Wiley & Sons, Inc.

关键词： finite-difference time-domain method current source model numerical performance

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Development of three-dimensional monolithic microwave integrated circuit components

Development of three-dimensional monolithic microwave integr...

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Conference on Terahertz and Gigahertz Electronics and Photonics II

作者： Hwu, RJ Ren, J Univ Utah Dept Elect Engn Salt Lake City UT 84112 USA

ISBN: (纸本)0819437565

FDTD applications in 3D monolithic microwave integrated circuit (MMIC) design are introduced in this paper. The source implementation for active device modeling, device-grid characterization, and novel spiral component simulations are presented. Our research in this area have shown that FDTD is a very effective tool for the design of 3D MMICs.

关键词： 3D modeling finite-difference time-domain method Transformers Inductance Field effect transistors Integrated circuits Microwave radiation Instrument modeling Oscillators Analytical research

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Numerical Simulation of dynamic thermo-magnetic switching and the optical signal in Magnetic Super-Resolution read-out

Numerical Simulation of dynamic thermo-magnetic switching an...

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Conference on Optical Data Storage (ODS2000)

作者： Itagi, A Schlesinger, TE Stancil, DD Carnegie Mellon Univ Ctr Data Storage Syst Pittsburgh PA 15213 USA

ISBN: (纸本)078035950X

We describe a 3D model to numerically evaluate the transient optical field in the case of MSR (Magnetic Super-Resolution) media. The first part of the model calculates the temperature profile in the media due to optical heating. The second part of the model calculates the transient magnetic parameters as a result of the temperature change. The third part of the model performs a simulation of the magnetization dynamics as a result of the change in the magnetic parameters. The fourth part of the model simulates the optical field during the transient magnetization dynamics.

关键词： Magnetism Anisotropy Switching 3D modeling Super resolution finite-difference time-domain method Near field optics Temperature metrology Thermography Aluminum

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Validation of the finite-difference time-domain method for near-field bioelectromagnetic simulations

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 1997年第6期16卷 341-345页

作者： Furse, CM Yu, QS Gandhi, OP Department of Electrical Engineering University of Utah Salt Lake City UT 84112 United States

Validations of the accuracy of the FDTD method for near-field simulations are critical at this time to assess the accuracy of the FDTD method for the simulation of personal communication devices. Excellent comparisons between the FDTD method and analytical or measured results are shown for a dipole antenna next to a layered half-space, a layered box, and a sphere, and also an infinitesimal dipole near a sphere. (C) 1997 John Wiley & Sons, Inc.

关键词： finite-difference time-domain method bioelectromagnetic simulations near-field simulations

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Analysis and design of low loss and low mode-shift integrated optical waveguides using finite-difference time-domain method

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IEICE TRANSACTIONS ON ELECTRONICS 1997年第5期E80C卷 625-631页

作者： Doi, T Iwata, A Hirose, M Faculty of Engineering Hiroshima University Higashi-Hiroshima-shi 739 Japan

This paper describes the analysis of integrated optical waveguides using finite-difference time-domain (FDTD) method, and proposes the design methodology for low loss waveguide components: corner bends and branches. In order to integrate optical waveguides with Si VLSI technologies on a chip, the compact bends or branches are necessary. Since the optical power radiation from a bend or a branch point depends on the waveguide shapes, an accurate analysis of guided wave behavior is required. For the purpose we adopted the FDTD method which can analyze optical waveguides with a large variation of refractive index and arbitrary shape. Proposed design concept is to have all waveguides transmit only the fundamental mode and to design whole waveguides based on the fundamental mode transfer characteristics. For this design concept, waveguide components are required to have not only low radiation loss but also a little mode shift from the fundamental mode. The bend using the double-reflection mirrors and the branch using a slit are proposed for suppressing the mode shift and improving radiation loss. By the FDTD analysis, the following results have been obtained. The radiation loss and mode shift of double reflection bend are 1% and 4%, and those of the slit branch are 2% and 5%, respectively, in 2 mu m width waveguide.

关键词： integrated optical waveguide finite-difference time-domain method double-reflection waveguide slit branch waveguide

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Comparison of scattering parameter calculations using touchstone and a full-wave electromagnetic solver based upon the finite-difference time-domain method

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 1997年第6期15卷 347-352页

作者： Kosanovich, S Mittra, R Electromagnetic Communication Laboratory University of Illinois at Urbana-Champaign Urbana IL 61801 United States

Scattering parameter results for various types of microstrip circuit configurations have been calculated using a full-wave electromagnetic solution technique. A full-wave electromagnetic solution technique is the most robust since it accounts for all coupling mechanisms present in a given geometry. The method is based upon the finite-difference time-domain (FDTD) method. (C) 1997 John Wiley & Sons, Inc.

关键词： microstrip circuits full-wave analysis electromagnetic solver finite-difference time-domain method microstrip discontinuities

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Comparison study of the PSTD and FDTD methods for scattering analysis

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2000年第3期25卷 220-226页

作者： Li, QL Chen, YC Ge, DB Hong Kong Polytech Univ Dept Elect & Informat Engn Hong Kong Hong Kong Peoples R China Xidian Univ Dept Phys Xian 710071 Peoples R China

This paper makes a comparison study by using both the pseudospectral time-domain (PSTD) and finite-difference time-domain (FDTD) methods for a two-dimensional (2-D) scattering analysis. The time-domain incident plane-wave pulse used in the PSTD technique is herewith simulated with an initial-condition excitation technique to eliminate the unwanted Gibbs phenomenon. The pure scattered-field formulation is utilized to surmount the difficulty of generation of the incident field, and a PSTD near-to-far-zone field transform is developed for the analysis of the scattering width (SW) of targets. It is found that the PSTD computed results agree well with those derived from the FDTD method, while the PSTD requires much less computational space and CPU time. (C) 2000 John Wiley & Sons, Inc.

关键词： pseudospectral time-domain algorithm finite-difference time-domain method scattering analysis

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