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Time-domain Method (time-domain + method)

Distribution by Scientific Domains
Engineering69%

Kinds of Time-domain Method

  • finite-difference time-domain method
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    Selected Abstracts

    Analysis of Improved Efficiency of InGaN Light-Emitting Diode With Bottom Photonic Crystal Fabricated by Anodized Aluminum Oxidxe

    ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
    Sang-Wan Ryu
    Abstract The improved performance of a bottom photonic crystal (PC) light-emitting diode (LED) is analyzed based on internal quantum efficiency (,int) and light-extraction efficiency (,ex). The bottom PC is fabricated by anodized aluminum oxide nanopatterns and InGaN quantum wells (QWs) are grown over it. Transmission electron microscopy images reveal that threading dislocations are blocked at the nanometer-sized air holes, resulting in improved optical emission efficiency of the QWs. From temperature-dependent photoluminescence measurements, the enhancement of ,int is estimated to be 12%. Moreover, the enhancement of ,ex is simulated to be 7% by the finite-difference time-domain method. The fabricated bottom PC LED shows a 23% higher optical power than a reference, which is close to the summation of enhancements in ,int and ,ex. Therefore, the bottom PC improves LED performance through higher optical quality of QWs as well as increased light extraction. [source]

    Parsimonious finite-volume frequency-domain method for 2-D P,SV -wave modelling

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2008
    R. Brossier
    SUMMARY A new numerical technique for solving 2-D elastodynamic equations based on a finite-volume frequency-domain approach is proposed. This method has been developed as a tool to perform 2-D elastic frequency-domain full-waveform inversion. In this context, the system of linear equations that results from the discretization of the elastodynamic equations is solved with a direct solver, allowing efficient multiple-source simulations at the partial expense of the memory requirement. The discretization of the finite-volume approach is through triangles. Only fluxes with the required quantities are shared between the cells, relaxing the meshing conditions, as compared to finite-element methods. The free surface is described along the edges of the triangles, which can have different slopes. By applying a parsimonious strategy, the stress components are eliminated from the discrete equations and only the velocities are left as unknowns in the triangles. Together with the local support of the P0 finite-volume stencil, the parsimonious approach allows the minimizing of core memory requirements for the simulation. Efficient perfectly matched layer absorbing conditions have been designed for damping the waves around the grid. The numerical dispersion of this FV formulation is similar to that of O(,x2) staggered-grid finite-difference (FD) formulations when considering structured triangular meshes. The validation has been performed with analytical solutions of several canonical problems and with numerical solutions computed with a well-established FD time-domain method in heterogeneous media. In the presence of a free surface, the finite-volume method requires 10 triangles per wavelength for a flat topography, and fifteen triangles per wavelength for more complex shapes, well below the criteria required by the staircase approximation of O(,x2) FD methods. Comparisons between the frequency-domain finite-volume and the O(,x2) rotated FD methods also show that the former is faster and less memory demanding for a given accuracy level, an attractive feature for frequency-domain seismic inversion. We have thus developed an efficient method for 2-D P,SV -wave modelling on structured triangular meshes as a tool for frequency-domain full-waveform inversion. Further work is required to improve the accuracy of the method on unstructured meshes. [source]

    A three-dimensional mesh refinement algorithm with low boundary reflections for the finite-difference time-domain simulation of metallic structures

    INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2010
    W. H. P. Pernice
    Abstract We present a method for including areas of high grid density into a general grid for the finite-difference time-domain method in three dimensions. Reflections occurring at the boundaries separating domains of different grid size are reduced significantly by introducing appropriate interpolation methods for missing boundary points. Several levels of refinement can be included into one calculation using a hierarchical refinement architecture. The algorithm is implemented with an auxiliary differential equation technique that allows for the simulation of metallic structures. We illustrate the performance of the algorithm through the simulation of metal nano-particles included in a coarser grid and by investigating gold optical antennas. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Analysis and modeling of microstrip-to-coplanar flip chip package interconnects

    INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2001
    Hussein H. M. Ghouz
    Abstract In this paper, the discontinuity of a flip chip transition between a microstrip line and a coplanar waveguide is investigated and modeled using the finite-difference time-domain method (FDTD) to predict the overall S -parameters of the package. Effects of the bump and via interconnects on the package performance are investigated and discussed. This includes the effects of different staggered transitions and ground connects on the package performance. A reduction of about 10 dB in the bump and via reflections can be achieved by staggering the signal (bump) and the ground connects (bump/via). A staggering distance of about twice the slot width gave minimum reflection over a wide band of frequencies. Moreover, the larger the relative distance between the ground and the center connects the less the reflection due to the discontinuity. Finally, the computed S -parameters of the flip chip package using the FDTD solution are used to develop an equivalent circuit model for the transition discontinuity over a wide frequency band. The equivalent circuit model of the microstrip to coplanar waveguide discontinuity includes more elements and is more complex than other types of transitions. A TEE or PI circuit model has been used to approximate the general circuit model of the discontinuity. Good agreement has been obtained between the S -parameters of the FDTD model and the equivalent circuit models over a wide frequency band. © 2001 John Wiley & Sons, Inc. Int J RF and Microwave CAE 11: 202,211, 2001. [source]

    Adjustment and control of SERS activity of metal substrates by pressure

    JOURNAL OF RAMAN SPECTROSCOPY, Issue 4 2010
    Lixin Xia
    Abstract Metal pellets of silver and copper for surface-enhanced Raman scattering (SERS) spectroscopy were prepared by compression with different pressures. It was found that the SERS activity of the pellet could be controlled by pressure. Enhanced Raman scattering properties of the metal pellets in the presence of adsorbed 4-mercaptobenzoic acid (4-MBA) with excitation at 632.8 or 514 nm could be obtained by choosing proper pressure of pellatization. The SERS peak intensity of the band at ,1584 cm,1 of 4-MBA adsorbed on the metal pellets varies as a function of applied pressure, and which is about 1.2,32 times greater than when it is adsorbed on silver and copper particles. The calculated results of three-dimensional finite-difference time-domain method (3D-FDTD) are in good agreement with the experimental data. Moreover, no spurious peaks appear in the SERS spectra of the samples because no other chemicals are involved in the simple preparation process of the metal pellets, which will facilitate its use as an SERS-active substrate for analytical purposes. In summary, SERS-active metal pellets can be produced simply and cost effectively by the method reported here, and this method is expected to be utilized in the development of SERS-based analytical devices. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Analysis of planar microwave circuits with lumped-elements by CN-FDTD

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2009
    Wanchun Tang
    Abstract A three-dimensional implementation of the lumped-element by Crank-Nicolson finite-difference time-domain (CN-FDTD) algorithm has been presented in this article. Several examples of planar microwave circuits with lumped resistor, capacitor, and/or inductor are simulated and compared with traditional finite-difference time-domain method and measurements. The accuracy of CN-FDTD implementation for lumped elements in this article has been verified. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 113,116, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23969 [source]

    Analysis of electromagnetic band-gap waveguide structures using body-of-revolution finite-difference time-domain method

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2007
    Ming-Sze Tong
    Abstract Study of electromagnetic band-gap (EBG) structures has become a hot topic in computational electromagnetics. In this article, some EBG structures integrated inside a circular waveguide are studied. They are formed by a series of air-gaps within a circular dielectric-filled waveguide. A body-of-revolution finite-difference time-domain (BOR-FDTD) method is adopted for analysis of such waveguide structures, due to their axial symmetric properties. The opening ends of the waveguide are treated as a matched load using an unsplit perfectly matched layer technique. Excitations on a waveguide in BOR-FDTD are demonstrated. Numerical results of various air-gap lengths with respect to the period of separation are given, showing an interesting tendency of EBG behavior. A chirping-and-tapering technique is applied on the EBG pattern to improve the overall performance. The proposed EBG structures may be applied into antenna structures or other system for unwanted signal suppression. Results show that the BOR-FDTD offers a good alternative in analyzing axial symmetric configurations, as it offers enormous savings in computational time and memory comparing with a general 3D-FDTD algorithm. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2201,2206, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22668 [source]

    A Crank,Nicholson-based unconditionally stable time-domain algorithm for 2D and 3D problems

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2007
    Xin Xie
    Abstract It has been shown that both ADI-FDTD and CN-FDTD are unconditionally stable. While the ADI is a second-order approximation, CN is only in the first order. However, analytical expressions reveal that the CN-FDTD has much smaller truncation errors and is more accurate than the ADI-FDTD. Nonetheless, it is more difficult to implement the CN than the ADI, especially for 3D problems. In this paper, we present an unconditionally stable time-domain method, CNRG-TD, which is based upon the Crank,Nicholson scheme and implemented with the Ritz,Galerkin procedure. We provide a physically meaningful stability proof, without resorting to tedious symbolic derivations. Numerical examples of the new method demonstrate high precision and high efficiency. In a 2D capacitance problem, we have enlarged the time step, ,t, 400 times of the CFL limit, yet preserved good accuracy. In the 3D antenna case, we use the time step, ,t, 7.6 times larger that that of the ADI-FDTD i.e., more than 38 times of the CFL limit, with excellent agreement of the benchmark solution. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 261,265, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22101 [source]

    Analysis of characteristics of a U-slot patch antenna using finite-difference time-domain method

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2006
    Hsing-Yi Chen
    Abstract The finite-difference time domain (FDTD) method is successfully used to analyze characteristics of a U-slot patch antenna without using commercial software packages such as HFSS, IE3D, and CST. The method is proved to be an efficient tool for deep insight studies on complicated patch antennas. Numerical results of return loss, radiation pattern, current distribution, and antenna efficiency are presented. FDTD results are also compared with measurement data and shown to be in good agreement. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1687,1694, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21804 [source]

    Calculation of antenna array far field impulse response using the finite-difference time-domain method

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006
    Chen Wu
    Abstract The waveform in the radiation field of a radar antenna can be obtained by using the convolution of the transmitted signal and the antenna far-field impulse response (AFFIR). In this paper, the finite-difference time-domain (FDTD) method is applied to calculate the AFFIR of an X-band 54-element waveguide slot array at different radiation angles using the excitation of a wideband Gaussian pulse. To demonstrate the usage of the far-field impulse response, the waveforms in the radiation field of a narrowband Gaussian pulse are calculated at three different radiation angles by the convolution of the pulse and the waveguide slot-array AFFIR. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 424,430, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21370 [source]

    Implicit nonstaggered finite-difference time-domain method

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2005
    Shumin Wang
    Abstract A new, unconditionally stable, implicit nonstaggered finite-difference time-domain (INS-FDTD) method is introduced. This method is more efficient than the (unconditionally stable) finite-element time-domain (FETD) method with brick elements because the number of nonzero elements in the system matrix is reduced. A numerical-dispersion analysis is provided as well. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 317,319, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20809 [source]

    Explicit formulas for obtaining the radiation characteristics of an antenna based on a three-dimensional metallic photonic bandgap structure

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2001
    Sailing He
    Abstract An antenna based on a three-dimensional metallic photonic bandgap (MPBG) structure consisting of many parallel metallic short wires is considered. An explicit method is introduced to calculate the radiation pattern for such an antenna system. The explicit method is verified numerically by comparing the results obtained by the finite-difference time-domain method. The present method improves the computation speed significantly. A genetic algorithm is used to make an optimal design for such a 3-D MPBG structure-based antenna. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 376,381, 2001. [source]

    Improving SNR of RF coils using composite coil elements

    NMR IN BIOMEDICINE, Issue 9 2009
    Zhiyue J. Wang
    Abstract A composite coil element consists of up to three independent orthogonal loops. It improves the flexibility in shaping the radio frequency (RF) field in its vicinity, compared with a single-loop coil element. Computer simulations were conducted to explore the potential advantages of this type of coil configuration for improving the signal-to- noise ratio (SNR), including the intrinsic SNR (ISNR) and the realistic SNR, when the effects of resistive loss of the coil were included. A ,half-space' model was considered, with a variable B0 direction relative to the surface of a large conductive medium. The SNR performance of a square single-loop coil parallel to the surface of the medium was compared with that of a composite coil element where up to two additional orthogonal square loops of the same size were added to the single coil loop. The SNR performances of coil arrays consisting of single-loop elements and composite elements were also evaluated. The RF field was calculated using the finite-difference time-domain method. The results show that the composite coil element has a substantially better ISNR at all depths from the surface than that of a single-loop element covering the same surface area. Furthermore, the ISNR of a composite element is not sensitive to the surface orientation relative to the B0 field. The computer simulation also revealed that at 128,MHz, the resistive loss from the copper coil loops standing upright on the surface at room temperature is substantial compared to the loss in the medium. Consequently, the realistic SNR is significantly lower than ISNR at 128,MHz for a composite coil element. The coil loading by the medium becomes more dominant at 170 and 298,MHz, and the differences between the realistic SNR and ISNR become smaller at these higher frequencies. Copyright © 2009 John Wiley & Sons, Ltd. [source]