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Time-domain
Kinds of Time-domain Terms modified by Time-domain Selected AbstractsSpecial Issue: Computational electromagnetics in the Time-Domain (CEM-TD)INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5-6 2002Christos Christopoulos No abstract is available for this article. [source] Fabrication of a novel micron scale Y-structure-based chiral metamaterial: Simulation and experimental analysis of its chiral and negative index properties in the terahertz and microwave regimesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 6 2007Nantakan Wongkasem Abstract In this report, we describe the fabrication of a chiral metamaterial based on a periodic array of Y-shaped Al structures on a dielectric Mylar substrate. The unit cell dimensions of the Y-structure are ,100 ,m on a side with 8 ,m linewidths. The fabricated Y-structure elements are characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative elemental analyses were carried out on both the Y-structure, comprised of Al and its oxide, as well as adjacent regions of the underlying mylar substrate using the energy dispersive X-ray spectroscopy (EDS) capability of the SEM. Finite-Difference Time-Domain (FDTD) calculations of the negative index of refraction for a 3D wedge of multiple layers of the 2D metamaterials showed that these metamaterials possess double negative (,,,,,) electromagnetic bulk properties at THz frequencies. The same negative index of refraction was determined for a wedge comprised of appropriately scaled larger Y-structures simulated in the microwave region. This double negative property was confirmed experimentally by microwave measurements on a 3D wedge comprised of stacked and registered Y-structure sheets. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Time-Domain and Morphological Analysis of the P Wave.PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 8 2008Part II: Effects of Atrial Pacing on P-Wave Features Background: The aim of this study was to compare time-domain and morphological descriptors of paced and spontaneous P wave in patients prone to atrial fibrillation (AF). Methods: Nineteen patients (nine women, aged 72 ± 10 years) affected by paroxysmal AF and implanted with dual-chamber pacemakers (PM) were studied. Two 5-minute recordings were performed during spontaneous and paced rhythm. Electrocardiogram (ECG) signals were acquired using a 32-lead mapping system. Patients were grouped into two classes: no previous AF and previous AF groups, according to the number of AF episodes in the 6 months before the analysis. Results and Conclusion:During atrial pacing P wave appeared prolonged and morphologically more complex with respect to sinus rhythm. We also found that in patients at lower risk for AF, the atrial pacing changes the atrial activation to a greater extent than in patients at higher risk for AF. Finally, all time-domain and morphological descriptors of the P wave except one succeed in discriminating "no previous AF" and "previous AF" patients in spontaneous rhythm, while no significant differences have been observed during pacing for any parameters. [source] Time-Domain and Morphological Analysis of the P-Wave.PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 7 2008Part I: Technical Aspects for Automatic Quantification of P-Wave Features Introduction: Time-domain and morphological analysis of P-wave from surface electrocardiogram has been extensively used to identify patients prone to atrial arrhythmias, especially atrial fibrillation (AF). However, since no standard procedure exists for P-wave preprocessing, standardization of cut-off values for P-wave duration and morphological features is difficult. This study is a methodological investigation of P-wave preprocessing procedures for automatic time-domain and morphological analysis. Methods: We compared, on simulated and real data, the P-wave template obtained applying three alignment algorithms with that obtained without alignment, in terms of template error, shift error, P-wave duration, and morphological parameters. We also proposed automatic algorithms for estimation of P-wave duration. Results: We found that alignment is necessary for a reliable extraction of P-wave template by the averaging procedure, in order to perform time-domain and morphological analysis. On simulated and real data, the error on P-wave duration can be as high as 30 ms on a template obtained without alignment; if alignment procedure is performed, the error on P-wave duration is negligible. Analogously, morphological features are correctly estimated only on a P-wave template obtained with P-waves alignment. We also found that the proposed algorithm for the automatic estimation of the P-wave duration gave reliable results. [source] High-frequency behavior of power inductor windings using an accurate multiconductor transmission line model: input impedance evaluationEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2008J. A. Brandăo Faria Abstract This research and tutorial paper is the second part of a work dedicated to the analysis and computation of the electromagnetic behavior of inductor windings operating at high-frequency regimes,a critical issue for very fast transient overvoltage studies. The inductor winding, wound around a ferromagnetic core, containing a total number of N dielectric coated cylindrical turns, is modeled by using a multiconductor transmission line (MTL) approach (proximity effects being accounted) whose constitution and characterization was presented in a former paper. In the present work, we make use of the R, G, L, and C constitutive matrices of the structure in order to develop a modal analysis technique-based formulation aimed at the evaluation of the winding's input impedance in the frequency-domain. Results obtained show that the input impedance critically depends not only on the number of layers of the winding but also, and, more importantly, on the frequency, where resonance phenomena play a key role. Frequency-domain analysis is complemented with simulation results in the time-domain that clearly illustrate how critical and sensitive the system response can be under minute changes of the winding's excitation current. Copyright © 2007 John Wiley & Sons, Ltd. [source] On removing the primary field from fixed-wing time-domain airborne electromagnetic data: some consequences for quantitative modelling, estimating bird position and detecting perfect conductorsGEOPHYSICAL PROSPECTING, Issue 4 2001Richard Smith In the process of removing the primary field from fixed-wing time-domain airborne EM data, the response is decomposed into two parts, which are referred to here as the time-domain ,in-phase' and ,quadrature' components. The time-domain in-phase component is dominated by the primary field, which varies significantly as the transmitter,receiver separation changes. The time-domain quadrature component comes solely from the secondary response associated with currents induced in the ground and this is the component that has traditionally been used in the interpretation of data from fixed-wing towed-bird time-domain EM systems. In the off-time, the quadrature response is very similar to the total secondary response. However, there are large differences in the on-time and even some small differences in the off-time.One consequence of these differences is that when airborne EM data are to be interpreted using a synthetic mathematical model, the synthetic data calculated should also be the quadrature component. A second consequence relates to the time-domain in-phase component which is sometimes used to estimate the receiver-sensor (bird) position. The bird-position estimation process assumes there is no secondary field in the in-phase component. If the ground is resistive, the secondary contained in the in-phase component is small, so the bird-position estimate is accurate to about 30 cm, but in highly conductive areas the secondary contribution can be large and the position estimate can be out by as much as 5 m. A third consequence arises for highly conductive bodies, the response of which is predominantly in-phase. This means that any response from these types of body is lost in the component that has been removed in the primary-field extraction procedure. However, if the bird position is measured very accurately, the actual free-space primary field can be estimated. If this is then subtracted from the estimated primary (actually free-space primary plus secondary in-phase response), then the residual is the secondary in-phase response of the ground. Using this methodology, very conductive ore bodies could be detected. However, a sensitivity analysis shows that detection of a large vertically dipping very conductive body at 150 m depth would require that the bird position be measured to an accuracy of about 1.4 cm and the aircraft attitude to within about 0.01°. Such tolerances are very stringent and not easily attainable with current technology. [source] Seismic response of slopes subjected to incident SV wave by an improved boundary element approachINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2007Behrouz Gatmiri Abstract In this paper, an improved boundary element approach for 2D elastodynamics in time-domain is presented. This approach consists in the truncation of time integrations, based on the rapid decrease of the fundamental solutions with time. It is shown that an important reduction of the computation time as well as the storage requirement can be achieved. Moreover, for half-plane problems, the size of boundary element (BE) meshes and the computation time can be significantly reduced. The proposed approach is used to study the seismic response of slopes subjected to incident SV waves. It is found that large amplifications take place on the upper surface close to the slope, while attenuations are produced on the lower surface. The results also show that surface motions become very complex when the incident wavelength is comparable with the size of the slope or when the slope is steep. Copyright © 2006 John Wiley & Sons, Ltd. [source] Perfectly matched layers for transient elastodynamics of unbounded domainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2004Ushnish Basu Abstract One approach to the numerical solution of a wave equation on an unbounded domain uses a bounded domain surrounded by an absorbing boundary or layer that absorbs waves propagating outward from the bounded domain. A perfectly matched layer (PML) is an unphysical absorbing layer model for linear wave equations that absorbs, almost perfectly, outgoing waves of all non-tangential angles-of-incidence and of all non-zero frequencies. In a recent work [Computer Methods in Applied Mechanics and Engineering 2003; 192: 1337,1375], the authors presented, inter alia, time-harmonic governing equations of PMLs for anti-plane and for plane-strain motion of (visco-) elastic media. This paper presents (a) corresponding time-domain, displacement-based governing equations of these PMLs and (b) displacement-based finite element implementations of these equations, suitable for direct transient analysis. The finite element implementation of the anti-plane PML is found to be symmetric, whereas that of the plane-strain PML is not. Numerical results are presented for the anti-plane motion of a semi-infinite layer on a rigid base, and for the classical soil,structure interaction problems of a rigid strip-footing on (i) a half-plane, (ii) a layer on a half-plane, and (iii) a layer on a rigid base. These results demonstrate the high accuracy achievable by PML models even with small bounded domains. Copyright © 2004 John Wiley & Sons, Ltd. [source] On the development of efficient FDTD-PML formulations for general dispersive mediaINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2008Konstantinos P. Prokopidis Abstract A novel implementation of the perfectly matched layer (PML) absorbing boundary condition (ABC) to terminate the finite-difference time-domain (FDTD) algorithm for general dispersive and negative index materials is presented. The proposed formulation also adopts the complex frequency-shifted (CFS) approach, involves simple FDTD expressions and avoids complex arithmetic. Several FDTD-PML simulations with different parameters are conducted for the termination of various dispersive media validating the stability, accuracy and effectiveness of the schemes and indicating the advantage of the CFS-PML. Copyright © 2008 John Wiley & Sons, Ltd. [source] Multi-region ADI DD-FDTD algorithm for the analysis of three-dimensional sparse multi-objects scattering problemINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1-2 2008Feng Xu In this paper, a multi-region domain decomposition finite-difference time-domain (DD-FDTD) algorithm is proposed and developed for the analysis of multiple-objects electromagnetic (EM) problems. A significant number of mesh nodes between objects are removed since only local meshes are generated for each object. All the separated sub-domains are interconnected by the use of a 3-D time-domain Green's function. The coupling between objects can be regarded as the equivalent spherical wave irradiations. Incident signals of the equivalent spherical waves are expressed as a spherical wave input field array according to the Huygens principle. The near-field to far-field transformation is introduced to obtain the equivalent spherical wave. Moreover, the alternating direction implicit FDTD (ADI-FDTD) scheme is applied to overcome the limit of the stability condition and increase the speed of the simulation. The new algorithm has been demonstrated and applied to solve typical 3-D multi-objects EM scattering problems. Copyright © 2007 John Wiley & Sons, Ltd. [source] Multiresolution model of electromagnetic wave propagation in dispersive materialsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 3 2003Ismael Barba Abstract A multiresolution time-domain (MRTD) technique based on Haar wavelets has been applied to model the propagation of waves in dispersive materials, using a discretization of the convolution equation that governs the behaviour of the media. To validate the method, the reflection coefficient at the interface between air and several different linear dispersive media, as well as the propagation of a plane wave towards a non-linear dispersive medium have been calculated and compared with other numerical techniques and theoretical results. Copyright © 2003 John Wiley & Sons, Ltd. [source] Higher order explicit time integration schemes for Maxwell's equationsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 5-6 2002Holger Spachmann Abstract The finite integration technique (FIT) is an efficient and universal method for solving a wide range of problems in computational electrodynamics. The conventional formulation in time-domain (FITD) has a second-order accuracy with respect to spatial and temporal discretization and is computationally equivalent with the well-known finite difference time-domain (FDTD) scheme. The dispersive character of the second-order spatial operators and temporal integration schemes limits the problem size to electrically small structures. In contrast higher-order approaches result not only in low-dispersive schemes with modified stability conditions but also higher computational costs. In this paper, a general framework of explicit Runge,Kutta and leap-frog integrators of arbitrary orders N is derived. The powerful root-locus method derived from general system theory forms the basis of the theoretical mainframe for analysing convergence, stability and dispersion characteristics of the proposed integrators. As it is clearly stated, the second- and fourth-order leap-frog scheme are highly preferable in comparison to any other higher order Runge,Kutta or leap-frog scheme concerning stability, efficiency and energy conservation. Copyright © 2002 John Wiley & Sons, Ltd. [source] Probe-fed microstrip antennas loaded with very high-permittivity ceramicsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2006Y. Hwang Abstract This article reports the feasibility study of miniaturizing probe-fed microstrip patch antennas by dielectric loading. The loading materials are barium tetratitanate ceramics of very high dielectric constant (,r = 38, 80). It is shown that, simply through loading, the antenna sizes are greatly reduced; however, the antenna performances are deteriorated. For instance, the antenna gain becomes lower. Then enhancement of the antenna performances follows. A substrate,superstrate structure is used to recover the gain. Both the experiments and the finite-difference time-domain (FDTD) simulations demonstrate that the gain and impedance bandwidth can be retrieved such that they are comparable to those of conventional microstrip antennas loaded with low permittivity materials (,r < 3). © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. [source] Flow cytometry with gold nanoparticles and their clusters as scattering contrast agents: FDTD simulation of light,cell interactionJOURNAL OF BIOPHOTONICS, Issue 8-9 2009Stoyan Tanev Abstract The formulation of the finite-difference time-domain (FDTD) approach is presented in the framework of its potential applications to in-vivo flow cytometry based on light scattering. The consideration is focused on comparison of light scattering by a single biological cell alone in controlled refractive-index matching conditions and by cells labeled by gold nanoparticles. The optical schematics including phase contrast (OPCM) microscopy as a prospective modality for in-vivo flow cytometry is also analyzed. The validation of the FDTD approach for the simulation of flow cytometry may open up a new avenue in the development of advanced cytometric techniques based on scattering effects from nanoscale targets. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An improved formalism for the Crank-Nicolson finite-difference time-domain by conformal mapping methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009Yang Yang Abstract In this article, a three-dimensional (3-D) Crank-Nicolson finite-difference time-domain (CN-FDTD) method combined with conformal mapping method is used to analyze the cavities with curved surface. The improved formalism in the CN-FDTD is described and both time-domain waveforms and resonant frequencies are presented. The numerical simulations of the typical examples show that the time step with this CN-FDTD method is 10 times larger than the Courant-Friedrich-Levy condition without the large loss of accuracy. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2378,2382, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24613 [source] Analysis of planar microwave circuits with lumped-elements by CN-FDTDMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2009Wanchun 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] An alternative analytical reduction scheme in the time-domain layered finite element reduction recovery method for high-frequency IC designMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2008Houle Gan Abstract An alternative analytical reduction scheme was proposed in the time-domain layered finite element reduction recovery (LAFE-RR) method for the analysis of high-frequency integrated circuits. This alternative reduction scheme permits the use of general absorbing boundary conditions in the framework of a time-domain LAFE-RR method. In addition, it allows for an application of the LAFE-RR method to circuit problems in which the system matrices in multiple regions need to be reduced separately. Numerical and experimental results are given to demonstrate its validity. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2337,2341, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23630 [source] Application of the preconditioned GMRES to the Crank-Nicolson finite-difference time-domain algorithm for 3D full-wave analysis of planar circuitsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008Y. Yang Abstract The increase of the time step size significantly deteriorates the property of the coefficient matrix generated from the Crank-Nicolson finite-difference time-domain (CN-FDTD) method. As a result, the convergence of classical iterative methods, such as generalized minimal residual method (GMRES) would be substantially slowed down. To address this issue, this article mainly concerns efficient computation of this large sparse linear equations using preconditioned generalized minimal residual (PGMRES) method. Some typical preconditioning techniques, such as the Jacobi preconditioner, the sparse approximate inverse (SAI) preconditioner, and the symmetric successive over-relaxation (SSOR) preconditioner, are introduced to accelerate the convergence of the GMRES iterative method. Numerical simulation shows that the SSOR preconditioned GMRES method can reach convergence five times faster than GMRES for some typical structures. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1458,1463, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23396 [source] Analysis of frequency division in microstrip circuits by using the FDTD methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2008Oscar González Abstract The accurate time-domain simulation of the nonlinear dynamics of circuits containing distributed elements is of great interest. Specially at high frequencies, it is essential to consider phenomena, such as crosstalk, packaging effects, and electromagnetic interaction between active and passive elements. These effects are mainly due to the distribute components of the circuit. Therefore, the accuracy in the instability or oscillation analysis of nonlinear circuits is often limited by the models used for such elements. Commercial simulators based on the equivalent-circuit approach hardly take into account the mentioned effects. In this work, the finite-difference time-domain (FDTD) method is applied to the nonlinear simulation of a diode-based microstrip circuit exhibiting a parametric frequency division by two. The FDTD method rigorously solves Maxwell's curl equations in the time domain providing a full-wave characterization of the distributed elements of the circuit. In the example considered, a relatively low operating frequency has been selected to allow a reliable comparison between the results obtained by the proposed technique and those provided by a circuit-based commercial simulator. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1300,1302, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23352 [source] Analysis of electromagnetic band-gap waveguide structures using body-of-revolution finite-difference time-domain methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2007Ming-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] Calculations of return loss of bonding wires fabricated on a test board by FDTD methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Hsing-Yi Chen Abstract Return losses of bonding wires fabricated on a test board for RF and microwave circuit applications are studied by the finite-difference time-domain (FDTD) method. Simulation results of return losses obtained by the FDTD method are presented and compared with those obtained by the HFSS software and measurements at frequencies of 0.04,6 GHz. It is found that simulation results calculated by the FDTD method make a good agreement with those obtained by the HFSS software. Results of the FDTD method are also further validated by the measurement data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1603,1606, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22546 [source] Application of the high-order symplectic FDTD scheme to the curved three-dimensional perfectly conducting objectsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2007Wei Sha Abstract A high-order symplectic finite-difference time-domain (SFDTD) scheme using the diagonal split-cell model is presented to analyze electromagnetic scattering of the curved three-dimensional perfectly conducting objects. On the one hand, for the undistorted cells, the fourth-order accurate spatial difference is employed. On the other hand, for the completely distorted cells, the treatment of the curved surfaces is based on the diagonal split-cell model. Finally, for the partially distorted cells, the interpolation strategy is proposed to keep the field components continuous. The numerical experiments suggest that the diagonal SFDTD scheme can obtain more accurate results than both the staircased SFDTD scheme and the traditional diagonal FDTD method. Furthermore, in view of the high numerical stability, the improved symplectic scheme does not need to decrease time increment to comply with the stability criterion. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 931,934, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22306 [source] Calculation of antenna array far field impulse response using the finite-difference time-domain methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006Chen 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] Planar inverted-F antennas on implantable medical devices: Meandered type versus spiral typeMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006Jaehoon Kim Abstract Based on a planar inverted-F antenna (PIFA) configuration, two different shaped (meandered and spiral) antennas are designed using finite-difference time-domain (FDTD) simulations and measurement results. The antennas are installed on an implantable medical device in a biological-tissue simulating model. The impedance-matching and radiation characteristics of two PIFAs are compared in order to observe which shape is more appropriate for wireless communication links of implantable medical devices. Additionally, the effects of the human skin's thickness on the antennas are studied in order to consider medical devices which are implanted in various subcutaneous tissues. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 567,572, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21409 [source] Modification to convolution CFS-PML for the ADI-FDTD methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2006Linnian Wang Abstract A new implementation of perfectly matched layer (PML) using the recursive-convolution technique is introduced for an alternating-direction implicit (ADI) finite-difference time-domain (FDTD) method. Based on a "complex frequency-shifted (CFS)" scaling function, this PML boundary condition is highly effective at absorbing low-frequency evanescent waves. The numerical results show that, compared with its previously suggested analogue, the new method improves the reflection error by 30 dB for large time-step sizes. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 261,265, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21322 [source] A pulsed confocal microwave technique for the detection of dielectric contrast of breast tissueMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2005G. Bindu Abstract Confocal microwave technology is explored as a screening tool to detect regions of dielectric contrast in breast tissue. When exposed to microwaves, malignant breast tissue exhibits electrical properties that are significantly different from that of healthy breast tissue. In vitro studies of normal and cancerous samples of breast tissue are performed using a prototype of confocal microwave imaging. Experimentally obtained time-domain results are substantiated by finite-difference time-domain (FDTD) analysis. Dielectric permittivities of the samples are estimated from the experimentally obtained time-domain results and are validated by subjecting the samples to dielectric studies using a cavity-perturbation technique. The results are compared with the dielectric parameters of in vitro breast tissue data available in literature. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 209,212, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21125 [source] Implicit nonstaggered finite-difference time-domain methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2005Shumin 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] A K-band inverted microstripline-fed linear tapered slot antenna and its 16-element E-plane arrayMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2005Chen Wu Abstract An inverted microstripline-fed linear tapered slot antenna element and a design of its 16-element E-plane array are presented in this paper. The element is designed using the finite-difference time-domain (FDTD) method. The calculated results show that it has a wide-impedance bandwidth in the K-band. To investigate the E-plane array, the return loss at each element input port, the couplings among elements, and the array's radiation patterns are obtained using the FDTD method. Using a unique three-piece assembled structure, the array is fabricated and tested experimentally. The measured results show that it has a wide bandwidth and antenna efficiency. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 241,246, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20784 [source] Full-wave FDTD design and analysis of wideband microstrip-to-waveguide transitionsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2003Cŕndid Reig Abstract Wideband transitions are designed and analysed by using two different approaches of the finite-difference time-domain (FDTD) method, in combination with the theory of nonuniform transmission lines. These transitions consist of a ridged waveguide-based taper between a shielded microstrip and a standard X-band rectangular waveguide. In the first step, a full-wave 2D-FDTD scheme is used to calculate the dispersion characteristics, as well as the geometry dependence of the impedance in the double ridged waveguide. Once these design curves have been obtained, the stepped transmission line transformer theory is used to design the tapers. In a former step, the nonuniform 3D-FDTD technique is applied, the transitions are simulated and the method is validated. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 317,320, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11048 [source] Wideband finite-difference,time-domain beam propagation methodMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2002J. J. Lim Abstract A wide-band finite-difference,time-domain beam propagation method (FD TD-BPM) based on Padé approximants is introduced to improve the bandwidth of the conventional TD-BPM. Numerical dispersion relations for the TD-BPM are derived to demonstrate the increase in bandwidth of the wide-band TD-BPM. The effects of the spatial and time step sizes on the numerical dispersion are also investigated. It is shown that the wide-band TD-BPM is less sensitive to the choice of spatial step size and allows a larger time step size to be used compared to the finite-difference time-domain (FD-TD) method. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 243,247, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10428 [source] |