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An experimental study was conducted to determine the effect of deflection waveform on four-point flexural fatigue test results for hot mix asphalt. This paper reports how the waveform affects the fatigue resistance of an asphalt mixture and, consequently, the fatigue models of the material. The mix was tested at different strain levels under both haversine and sinusoidal deflection-controlled modes. The findings indicate that haversine displacement control testing results in a sinusoidal strain response of half the intended amplitude. This outcome was attributed to the viscoelastic nature of asphalt mixes. In the deflection controlled haversine test, permanent deformations lead to a new equilibrium neutral position of the beam and the force output follows a sinusoidal waveform. This produces erroneous fatigue results since the test assumptions do not match the actual test conditions. It is recommended to use a sinusoidal waveform to obtain consistent results. Key words: asphalt mixture, fatigue performance, deflection waveform, fatigue models, pavement design. Une etude experimentale a ete menee afin de determiner l'effet de la forme d'onde de deflexion sur les resultats d'essais de fatigue de flexion quatre points pour l'asphalte melange a chaud. Dans le cadre de cet article, on expose comment la forme d'onde influe sur la resistance a la fatigue d'un melange d'asphalte et, par consequent, sur les modeles de fatigue du materiau. Le melange a ete mis a l'essai a differents niveaux de deformation tant sous des modes de deflexion controlee sinus carre (<>) que sinusoidale. Les constatations indiquent que les essais controles de deplacement haversine occasionnent une reponse de deformation sinusoidale qui est la moitie de l'amplitude prevue. Ce resultat a ete attribue a la nature viscoelastique des melanges d'asphalte. Dans l'essai haversine de deflexion controlee, les deformations permanentes donnent lieu a un nouvel equilibre de position neutre de la poutre et la production de force suit une forme d'onde sinusoidale. Ceci produit des resultats de fatigue errones, car les hypotheses des essais ne correspondent pas aux conditions reelles des essais. On recommande d'utiliser une forme d'onde sinusoidale pour obtenir des resultats coherents. [Traduit par la Redaction] Mots-cles: melange d'asphalte, comportement a la fatigue, forme d'onde de deflexion, modeles de fatigue, conception de chaussees., 1. Introduction The study of mechanisms or phenomena that result in loss of structural and functional integrity of pavements is extremely important to design safe, durable, and resistant structures. When [...]

In this paper, spaceborne radar altimeters are shown to have the potential for monitoring the height of large rivers with accuracies of approximately 1 m. However, the need for a better height accuracy and the observations of smaller continental basins have led to studies on how to improve and extend the use of nadir-altimeter data. Conventional retracking techniques over land are limited to the examination of altimeter waveforms on a case-by-case basis. Due to the arbitrary geometry which may be present at altimeter river crossings, this approach may be limited to large rivers, which approximate ocean crossings. To overcome this limitation, we introduce a waveform-fitting method which uses the entire set of waveforms associated with a water crossing, rather than individual waveforms. By using ancillary data, such as digital elevation model (obtained from Shuttle Radar Topography Mission and Gtopo30) and classification maps (obtained from Landsat and MODIS), it is possible to recast the retracking problems as a maximum-likelihood-estimation problem. Theoretical power returns based on the a priori knowledge of the observed scenes are generated, resulting in a parametric library of waveform histories, which is then used to constrain the estimation. For demonstration, we concentrate on the river Meuse in northern western Europe and on the river Lena in Russia. The Meuse has important social impact, since it has flooded in the past and better real-time predictions of its changing stage may improve flood-forecasting skill. Furthermore, it presents a challenge to conventional nadir-altimeter waveform retracking. We will present both theoretical performance results and demonstrate the feasibility based on real altimeter data. Index Terms--Altimetry, Europe, hydrology, waveform.

To integrate a synthetic aperture radar (SAR) into an operational unmanned airborne vehicle (UAV), it should be as small as possible to meet stringent limitations of size, weight, and power consumption. It appears that the novel combination of millimeter-wave frequency-modulated continuous-wave (FMCW) technology and SAR techniques can provide an optimal solution. However, some efficient techniques should be applied to resolve range/Doppler ambiguities in FMCW UAV SAR systems. As such, a technique of waveform-diversity-based millimeter-wave UAV SAR imaging is presented in this paper. Along with the described system concept and signal model, the performance of the diversified waveforms evaluated by their cross correlations is detailed. As the conventional stop-and-go approximation is not valid for FMCW SAR, a modified wavenumber-domain algorithm with a consideration of continuous antenna motion during transmission and reception is derived. This imaging algorithm is validated with computer simulations. Furthermore, one parallel direct-digital-synthesizer-driven phase-locked-loop synthesizer with adaptive nonlinearity compensation, which has been validated by the experimental results, is proposed to obtain a millimeter-wave FMCW signal with fine frequency linearity. Index Terms--Frequency-modulated continuous-wave (FMCW) radar, millimeter-wave synthetic aperture radar (SAR), unmanned airborne vehicle (UAV), waveform diversity.

Mobile-to-mobile communication is an important application for intelligent transport systems and mobile ad hoc networks. In these systems, both the transmitter and receiver are in motion, subjecting the signals to Rician fading and different scattering effects. In this paper, we present a double-ring with a line-of-sight (LOS) component scattering model and a sum-of-sinusoids simulation method to characterize the mobile-to-mobile Rician fading channel. The developed model can facilitate the physical-layer simulation for mobile ad hoc communication systems. We also derive the autocorrelation function, level crossing rate (LCR), and average fade duration (AFD) of the mobile-to-mobile Rician fading channel and verify the accuracy by simulations. Index Terms--Double-ring with a line-of-sight (LOS) component channel model, LOS component, mobile-to-mobile channel model, Rician fading, scattering, sum-of-sinusoids approximation method.

By generating clock and data waveforms in the frequency domain through a truncated Fourier series, absolute control over both voltage noise and symbol transition timing is achieved. A parameterized Fourier series signal model is derived and used to form clock and data waveforms exhibiting arbitrary noise and jitter characteristics. The method not only facilitates more accurate interconnect modeling in tools like Matlab and Simulink, but also provides a simple means for generating realistic signals that may be imported into Spice-based simulators. Index Terms--Interconnect modeling, jitter generation, noise generation, simulation.

The Scanning Hydrographic Operational Airborne light detection and ranging (LiDAR) Survey (SHOALS) consists of a bathymetric LiDAR system that provides high-precision measurements of water depth. Although the acquisition is focused on depth accuracy, the return signal, i.e., waveform, contains other relevant information because of integration signatures from the water surface, the water column, and the seabed. This paper highlights the benthic characterization in extracting statistical parameters derived from the bottom backscatter and classifying them. In implementing a specific unsupervised classification, it is significantly proven that the signals derived from habitat, described as statistically homogeneous throughout ground-truth analysis, are similar within an intrahabitat view, whereas they are different between themselves. Index Terms--Habitat classification, light detection and ranging (LiDAR) bathymetry, multivariate analysis, waveform.

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, the dielectric breakdown voltage--time characteristics were measured under several different conditions on the quasi-uniform [SF.sub.6] gas gap and partly the cone-shaped insulating spacers that represent an insulation element of GIS for six kinds of non-standard lightning impulse waveforms associated with lightning surges and disconnector switching surges. As a result, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than those for the standard lightning impulse waveform by 3% to 36%. In these experiments, parameters other than waveforms were fixed to standard conditions. In this paper insulation characteristics on quasi-uniform [SF.sub.6] gas gaps were examined while changing conditions on gas pressures, gap lengths, electrode surface roughness, voltage polarities, and bias voltages. As a result, it was confirmed that the results under standard experimental conditions in the preceding experiments can be applied widely to the GIS actual equipment conditions. Index Terms--Non-standard lightning impulse waveform, gas insulated switchgear (GIS), dielectric breakdown voltage--time characteristics (V-t characteristics), gas pressure, gap length, electrode surface roughness, bias voltage.

Dielectric response measurements belong to the group of diagnostic tools used for quality evaluation of high voltage insulation systems. A measurement system called Arbitrary Waveform Impedance Spectroscopy (AWIS) is presented here which is capable of utilizing the harmonic content of repetitive voltages with a semi-square waveform and the corresponding current response to perform dielectric response measurements. Extensive circuit modeling and calibrations are required in order to perform accurate measurements. AWIS could offer new possibilities, especially for continuous monitoring of the dielectric properties of high voltage components and systems. The accuracy of the technique in both low and high voltage applications is verified by comparison with results obtained by means of the Frequency Domain Spectroscopy (FDS) technique. Index Terms--Dielectric measurements, discrete Fourier transforms, aging, monitoring, dielectric materials, insulation testing.

We investigate several target detection and parameter estimation techniques for a multiple-input multiple-output (MIMO) radar system. By transmitting independent waveforms via different antennas, the echoes due to targets at different locations are linearly independent of each other, which allows the direct application of many data-dependent beamforming techniques to achieve high resolution and excellent interference rejection capability. In the absence of array steering vector errors, we discuss the application of several existing data-dependent beamforming algorithms including Capon, APES (amplitude and phase estimation) and CAPES (combined Capon and APES), and then propose an alternative estimation procedure, referred to as the combined Capon and approximate maximum likelihood (CAML) method. Via several numerical examples, we show that the proposed CAML method can provide excellent estimation accuracy of both target locations and target amplitudes. In the presence of array steering vector errors, we apply the robust Capon beamformer (RCB) and doubly constrained robust Capon beamformer (DCRCB) approaches to the MIMO radar system to achieve accurate parameter estimation and superior interference and jamming suppression performance.

A MUSIC-based algorithm is presented for coping with both circular and noncircular symbols. Results suggest an increase in the maximum number of detectable signals and an improvement in the performance accuracy.

The quench characteristics of stabilizer-free and copper-stabilized YBCO coated conductors (CCs) are described under various over-current pulses differing in waveform. The studies have provided a basis for the temperature design of various superconducting power applications including superconducting fault current limiter (SFCL).

A fast and simple algorithm for designing time-optimal waveforms is presented. The algorithm accepts a given arbitrary multidimensional k-space trajectory as the input and outputs the time-optimal gradient waveform that traverses k-space along that path in minimum time. The algorithm is noniterative, and its run time is independent of the complexity of the curve, i.e., the number of switches between slew-rate limited acceleration, slew-rate limited deceleration, and gradient amplitude limited regions. The key in the method is that the gradient amplitude is designed as a function of arc length along the k-space trajectory, rather than as a function of time. Several trajectory design examples are presented. Index Terms--Gradient waveform design, k-space trajectories, magnetic resonance imaging (MRI), optimal control.

A three-phase, multilevel rectifier using active voltage injection with one MOSFET device is presented. The injector consists of a bidirectional switch that modifies the behavior of a 12-pulse rectifier resulting in either 24-pulse or multilevel pulsewidth-modulated (PWM) operation. The resultant input currents are almost sinusoidal, the line current THD being 2.36% for 24-pulse operation and 1.06% for PWM operation. The MOSFET current is 2.9% of the load current. The circuit operation, idealized waveforms and modulation strategy are explained and experimental results are presented. Index Terms--High-power factor rectification, three-phase multipulse rectifier.

Phase-shifted carrier (PSC) pulsewidth modulation (PWM) in its conventional form is a good solution for single-phase Cascaded inverters as alternative phase opposition disposition (APOD) PWM for single-phase diode clamped inverters. PSC distributes the switching angles of APOD PWM waveform among the legs uniformly and reduces the switching frequency of each leg. This paper proposes a modified PSC technique based on partly shifted carriers for all disposition types including phase disposition (PD) which is suitable for three-phase cascaded inverters. Simulation results are also included for PSCpD using carrier-based space-vector PWM (SVPWM). Index Terms--Carrier-based pulsewidth modulation (PWM) techniques, multilevel inverters, phase-shifted carrier (PSC), space-vector modulation.

We develop an analytical expression for predicting electromotive force (EMF) waveforms resulting from permanent magnets (PMs) in electrical machines. The expressions for the flux linkage are based on a volume integral over the magnet volume, rather than the usual surface integral over the coil. The proposed method consists of applying a virtual current in the coil of the machine and calculating the magnetic field generated inside the PM volume. The EMF waveform is obtained by taking the derivative of the flux linkage with respect to time. We present analytical expressions of the EMF for various PM shapes and Halbach magnetization patterns. We tested a total of four configurations of PMs, and the experimental waveforms confirmed the validity of the expressions obtained theoretically. Index Terms--Analytical calculation, Halbach arrays, permanent-magnet machines.

A formulation based on Lagrangian optimization and spheroidal vector wave functions is presented for the vector electromagnetic inverse source problem of deducing a time-harmonic current distribution that is confined within a spheroidal volume, that generates a prescribed radiation field, and that is subject to given constraints on the source functional energy, which characterizes antenna current level, and the source's reactive power, which models antenna resonance matching. The paper includes computer simulation results illustrating the derived inverse theory. Index Terms--Inverse source problem, minimum energy solution, reactive power, spheroidal wavefunctions.

A new method for space charge measurement resorting to the pulsed electroacoustic (PEA) method under periodic stress of arbitrary waveform is presented. The originality of the work consists in using a long memory digital oscilloscope combined to the method used to sample one period of the HV stress into several profiles. There is no need for synchronization between pulse generation and HV stress and hence no hardware change of classic PEA system. The pulse generator provides a probing pulse of 5 ns duration, at a maximum frequency of 1 kHz. With these features, the phase of the HV stress can be resolved into 200 profiles by frequency adjustment of the pulse generator. Several periods of the HV stress are necessary for obtaining the set of profiles; however the typical measurement time is less than 20 s for f > 0.2 Hz. Preliminary results obtained on a crosslinked polyethylene film under 50 Hz ac stress are shown to demonstrate the feasibility. Index Terms--Space charge, Pulsed electroacoustic method, ac stress, Hilbert transform.

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage--time characteristics were measured under several different conditions mainly for the quasi-uniform S[F.sub.6] gas gaps that represent an insulation element of a GIS toward four kinds of non-standard lightning impulse waveforms associated with lightning surges. As a result, in the tested range, the dielectric breakdown values for nonstandard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 3% to 32%. Index Terms--Non-standard lightning impulse voltage waveform, lightning surge, gas insulated switchgear (GIS), dielectric breakdown voltage--time characteristics (V-t characteristics), lightning impulse withstand voltage (LIWV).

In this study, we present compression of ultra-wideband RF waveforms via photonic synthesis of phase pre-compensated waveforms. By exciting a dispersive wireless link (employing Archimedean spiral antennas) with variable-bandwidth excitation waveforms, we first demonstrate that such links exhibit a dispersion-limited output pulse duration. Subsequently, we utilize the RF spectral phase extracted from the impulse response of the link to create signals designed to negate the nonuniform phase response of the spiral antennas utilized in the link. Such waveforms remove the dispersion limitation and enable bandwidth-limited operation. We achieve compression to within a factor of two of the bandwidth limit for signals with bandwidths of 1-10 GHz at a center frequency of ~6 GHz. To our knowledge, this represents the first demonstration of dispersion pre-compensation for signals with fractional bandwidths exceeding 100%. Our technique is reprogrammable and may be extended to larger bandwidths and higher operational frequencies, making it an enabler for future radar and communication systems. Index Terms--Broadband antennas, matched filtering, microwave photonics, time-domain techniques, ultra-wideband (UWB).

The asymptotic waveform evaluation (AWE) technique has been widely used for handling the fast parameter sweep. However, how to determine the sweep bandwidth is still an open question. This work proposes an efficient and flexible bandwidth estimation approach. This approach also naturally leads to an efficient multipoint AWE technique. The validity of the proposed approach is verified by numerical experiments on the AWE-incorporated hybrid finite element/boundary integral (FE/BI) method for scattering problem. Numerical experiments show that this approach can greatly improve the efficiency and practical capability of the AWE technique. Index Terms--Asymptotic waveform evaluation (AWE), bandwidth estimation, rational approximation.

The wavefront aberrations in a large-scale, flash-lamp-pumped, high-energy, high-power glass laser system can degrade considerably the quality of the final focal spot, and limit severely the repetition rate. The various aberrations induced on the Laboratoire pour l'Utilisation des Lasers Intenses (LULI), laser facility (LULI2000) throughout the amplification are identified and analyzed in detail. Based on these analyses, an optimized procedure for dynamic wavefront control is then designed and implemented. The lower-order Zernike aberrations can be effectively reduced by combining an adaptive-optics setup, comprising a bimorph deformable mirror and a four-wave lateral shearing interferometer, with a precise alignment system. This enables the laser chain to produce a reproducible focal spot close to the diffraction limit (Strehl ratio ~0.7). This allows also to increase the repetition rate, initially limited by the recovery time of the laser amplifiers, by a factor of 2 (one shot per hour). The proposed procedure provides an attractive alternative for dynamic correction of the wavefront aberrations of a laser facility as complex as the LULI2000. OCIS codes: 080.1010, 120.5050, 140.1080, 140.3538, 140.5560, 140.6810.

The wall-charge behaviors of the conventional and two types of single-sustain waveforms during address and sustain periods are investigated based on a simulated result and a [V.sub.t] close-curve analysis. The single-sustain waveform means that the sustain pulse having both positive and negative voltage levels is applied only to the single-side electrode, i.e., the scan (Y) electrode in this paper, where the common (X) electrode remains grounded. In the single-sustain waveform, the address discharge characteristics were observed to be improved by applying a higher voltage level without causing a misfiring discharge during an address period. An asymmetric IR emission was observed for both positive and negative sustain pulses during a sustain period, which was caused by the simultaneous discharge, including the plate gap discharge between the scan (Y) and the address (A) electrodes only when applying the negative sustain pulse to the scan (Y) electrode. Index Terms--Address discharge characteristics, asymmetric IR emission, plasma display panel (PDP), single-sustain waveform, [V.sub.t] close-curve analysis, wail-charge behavior.

An analytical model of a Townsend breakdown of dense gases under pulsed voltage was developed based on the dynamics of the cathode sheath. Scaling parameters for impulse breakdown were derived and these scalings agreed with experiment and elaborate numerical simulations. The model is applied to optimization of the voltage waveform for obtaining maximum plasma density. We show that the optimal conditions from the standpoint of maximal plasma production at the lowest applied voltage correspond to gas breakdown during the end of the rise-time of the applied voltage pulse. Index Terms--Analytical model, dense gases, pulsed breakdown, voltage optimization.

In this letter, we present a new waveform-diversity-based ultrasound hyperthermia technique for the treatment of breast cancer. Waveform diversity offers a new paradigm for beampattern design. By choosing a proper covariance matrix of the transmitted waveforms under the uniform elemental power constraint, the ultrasound system can provide a focal spot matched to the entire tumor region, and meanwhile, minimize the impact to the surrounding healthy breast tissues. As shown in our 2-D numerical simulations, this method has better acoustic power deposition than the existing methods, and can provide the necessary temperature gradients required for the effective hyperthermia treatment of breast cancer. Index Terms--Beampattern design, breast cancer, finite-difference time domain (FDTD), ultrasound hyperthermia, waveform diversity.

An approach to generating chirped microwave pulse based on optical spectral shaping and nonlinear chromatic-dispersion-induced wavelength-to-time mapping using all-fiber components is proposed and demonstrated. In the proposed approach, the spectrum of a femtosecond pulse is shaped by a two-tap Sagnacloop filter that has a sinusoidal spectrum response. The spectrum shaped pulse is then sent to a dispersive element that has first-and second-order chromatic dispersions. Thanks to the nonlinear wavelength-to-time mapping of the dispersive element, a temporal pulse that has a central frequency in the microwave band with a large chirp is generated, which provides the potential for applications in high-speed communications and radar systems. Numerical and proof-of-concept experimental results are presented. Index Terms--Chirped pulse, chromatic dispersion, frequency modulation, pulse shaping, radar, Sagnac-loop filter, waveform generation.

We consider radar waveform selection algorithms for tracking accelerating targets. Tracking is handled within an interacting multiple model (IMM) framework, which produces a number of potential cost functions for minimization. The waveform library is obtained by implementing a fractional Fourier transform on a base waveform, thereby rotating its ambiguity function around its peak. This has the effect of rotating the lower bound of measurement covariance in the range-Doppler plane. Simulation results consider a number of potential cost functions, and show robustness to cases in which the target modes are not precisely known.

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus cut the equipment cost while maintaining the high reliability in its insulation performance, it is necessary to grasp in an organized way the insulation characteristics under non-standard lightning impulse voltage waveforms that represent actual surge waveforms encountered in the field and compare them with the characteristics under the standard lightning impulse waveform quantitatively. As described in this paper, the first step in a series of study for the purpose above was taken by analyzing lightning surge waveforms and restriking surge waveforms such as disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations and identifying four typical non-standard lightning impulse waveforms with basic frequencies of 0.24 to 1.0 MHz. Then, two of these non-standard lightning impulse waveforms, the single-pulse waveform which is the most basic type and the waveform with a pulse in the crest and a subsequent flat section, were used to measure the breakdown voltage and the partial discharge inception voltage while changing the parameters, on three models that represent the insulation elements of windings of oilimmersed transformers. Then, the resultant average breakdown voltages were evaluated in terms of the overvoltage durations, leading to a result of formulating them in a unified way. In the tested range, the dielectric breakdown values under nonstandard lightning impulse waveforms were higher, marking 52% at the maximum, than those under standard lightning impulse waveforms in all the cases, suggesting a possibility of lowering the insulation specifications of an oil-immersed transformer. Index Terms--Oil-immersed transformer, non-standard lightning impulse voltage waveform, dielectric breakdown voltage, partial discharge inception voltage, oil gap, turn-to-turn insulation model, section-to-section insulation model, lightning impulse withstand voltage.

Byline: Rongfang Song (1,2), S.H. Leung (3) Keywords: chip waveform; performance analysis; DS-CDMA; offset quadrature modulation Abstract: This paper is to present a systematic performance analysis of asynchronous quaternary direct sequence code division multiple access (DS-CDMA) systems using random signature sequences with arbitrary chip waveforms. The simplified improved Gaussian approximation method for bit error rate computation is extended to include arbitrary time-limited (full response or partial response) or band-limited chip waveforms with arbitrary receiver filters. As a time-limited partial response chip waveform modulation format, the well-known power and spectral efficient 'superposed quadrature amplitude modulation' with matched filter or zero-forcing filter is evaluated, and the results show that the optimum zero-forcing filter will yield a performance better than the matched filter counterpart. For band-limited chip waveforms, based on an elementary density function of a second-order polynomial, a class of second-order continuity pulses is proposed for analysis. It is found that all common band-limited pulses are only its special cases. As a member of the class, the widely used frequency domain raised cosine pulse has the worst anti-multiuser-access-interference capability, which has been pointed out in (H. H. Nguyen, Proceedings of IEEE Canadian Conference on Electrical &amp Computer Engineering, 2002, pp. 1271--1275). Author Affiliation: (1) Department of Telecommunication Engineering, Nanjing University of Posts and Telecommunications, Nanjing, 210003, China (2) Department of Advanced Technology, Technology Center, ZTE Corporation, China (3) Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China Article History: Registration Date: 01/01/2004

Wide-band high-efficiency optical-to-electrical conversion stimulus probe heads have been developed for testing large-signal responses of high-speed electronic devices. Two types of such probes were demonstrated using a 1.55-[[micro]meter] 85-GHz-bandwidth waveguide p-i-n photodiode. The type-I probe employs a simple semirigid coaxial cable with a bias network for the electrical-signal transmission, resulting in a very low modal dispersion of Index Terms - Amplifier, coaxial cable, optoelectronics, photodiode, probe head.

This paper describes an efficient algorithm to evaluate the spectral response of passive microwave devices. The method is based on the combination of the tangential-vector finite-element method (TVFEM) for modeling three-dimensional (3-D) microwave passive components and the asymptotic waveform evaluation (AWE) technique for efficiently computing the spectral responses. Unlike previous AWE approaches, which use direct matrix factorization to solve for the moments, we employ a preconditioned conjugate gradient (PCG) method. It is observed that the iterative PCG solver converges much faster by solving only the additional components of the higher moments outside the span of previous moments. Moreover, this paper discusses the effect of shifting the expansion frequency from the real frequency axis to the lower half of the complex frequency plane. Through several numerical examples, a waveguide with an obstacle inside, mitered 90 [degrees] E- and H-plane waveguide bend, microstrip low-pass filter, and microstrip patch antenna, we show that shifting reduces the pollution due to dominant resonant modes and, consequently, results in a much wider convergence range for the moment-matching AWE technique. Index Terms - AWE, finite-element methods, microwave passive components, numerical methods.

Complex flows reflect secondary flow, continuous separations and reattachments. Sinusoidal wavy geometry is observed in a section of one side of a duct with a rectangular cross-section. Liquid crystals aid localized calculations. The second wave in the channel exhibits a Nusselt number scattering of high magnitude. The peak of each wave shows the highest Nusselt number when moving upstream, while the lowest Nusselt number is seen near the peak during downstream movement. The occasional total formation of the wave results in the location of the highest Nusselt number on the second wave and the constancy of the lowest number.

An analytical solution for pulsatile axial flow velocity waveforms in curved elastic tubes is presented. The result is obtained by exact solution of linearized Navier-Stokes and tube motion equations in a torroidal coordinate system. Fourier analysis is used to divide the flow into constant and oscillatory components which are separately considered. The solution is used to investigate the effects of curvature on volumetric axial velocity flow waveforms, as would be measured by Doppler ultrasound techniques. In typical human arteries, the greatest effects of curvature on the volumetric axial flow are exerted on the constant component and at low values of the frequency parameter for the oscillatory components. Here, the magnitude and phase angle of oscillatory flow in the curved tube, relative to that in the straight tube, differ by maximum values of 1.2% and 0.15 rad, respectively. However, constant flow may vary by as much as 60% at high Dean numbers. The solution is presented in a form similar to Womersley's solution for the straight elastic tube and may, thus, be incorporated into a transmission-line analog model. These models are frequently used to investigate axial flow velocity variations in mamillian circulatory systems and this work offers a tool which may extend these models to incorporate the effects of curvature. Index Terms--Analytical solution, blood flow velocity waveform, curved elastic arteries, Doppler ultrasound, modeling, transmission line.

A physical interpretation of the equivalence theorem is presented. A simple example is used to show that the external and internal equivalence cases are analogous to incident, reflected, and transmitted wave problems in the geometrical optics sense. Index Terms--Equivalence theorem.

A simple relationship between the ratio of the time constants of an RC-type lightning impulse generator circuit and the ratio of the virtual times defined by IEEE Standard 4 has been found by means of numerical methods. For the 1.2/50 waveform, the relationship is approximated to a linear equation. Index Terms--Impulse generator, lightning impulse, time constants, virtual front time, virtual time to half value.

In this paper, a model order reduction technique is presented. This technique, known as Galerkin asymptotic waveform evaluation (GAWE), or multipoint Galerkin asymptotic waveform evaluation (MGAWE) if multiple expansion points are considered simultaneously, can be used to reduce matrices describing electromagnetic (EM) phenomena generated through the finite element method (FEM) to a smaller space while still accurately approximating the characteristics of the original responses. The resulting solution procedure of using GAWE or MGAWE to solve FEM equations allows for wideband frequency simulations with a reduction in total computation time. Numerical simulations using these methods are shown along with traditional methods such as using an LU decomposition at each frequency point of interest and asymptotic waveform evaluation (AWE). Comparisons in accuracy as well as computation time are also given. Index Terms--Asymptotic waveform evaluation, computer aided engineering, model order reduction, Pade approximants, perfectly matched layer (PLM).