General Waveform Research Articles

Core loss behavior in high frequency high power transformers—II: Arbitrary excitation

High frequency high power transformers used in power electronic converters are frequently subjected to non-sinusoidal excitations. The main purpose of this paper is to study the effects of some general arbitrary waveforms on magnetic core loss in these transformers. First, using well-known empirical equations, general expressions were derived based on the parameters of the waveforms. Second, the impacts of different orders of voltage harmonics were investigated. Finally, capabilities of nanocrystalline and amorphous magnetic materials were compared. It is shown that the loss inside the core is highly sensitive to the rise time and duty cycle of trapezoidal and rectangular waveforms, respectively. Furthermore, although amorphous materials have higher saturation flux density, the total core loss inside the transformer designed using nanocrystalline material is considerably lower than the similar transformer with amorphous materials.

On the behavior of return stroke current and the remotely detected electric field change waveform

After accumulating a large number of remotely recorded negative return stroke electric field change waveforms, a subtle but persistent kink was found following the main return stroke peak by several microseconds. To understand the corresponding return stroke current properties behind the kink and the general return stroke radiation waveform, we analyze strokes occurring in triggered lightning flashes for which have been measured both the channel base current and simultaneous remote electric radiation field. In this study, the channel base current is assumed to propagate along the return stroke channel in a dispersive and lossy manner. The measured channel base current is band‐pass filtered, and the higher‐frequency component is assumed to attenuate faster than the lower‐frequency component. The radiation electric field is computed for such a current behavior and is then propagated to distant sensors. It is found that such a return stroke model is capable of very closely reproducing the measured electric waveforms at multiple stations for the triggered return strokes, and such a model is considered applicable to the common behavior of the natural return stroke as well. On the basis of the analysis, a number of other observables are derived. The time‐evolving current dispersion and attenuation compare well with previously reported optical observations. The observable speed tends to agree with optical and VHF observations. Line charge density that is removed or deposited by the return stroke is derived, and the implication of the charge density distribution on leader channel decay is discussed.

General Parameterized Thermal Modeling for High-Performance Microprocessor Design

This paper proposes a new parameterized dynamic thermal modeling algorithm for emerging thermal-aware design and optimization for high-performance microprocessor design at architecture and package levels. Compared with existing behavioral thermal modeling algorithms, the proposed method can build the compact models from more general transient power and temperature waveforms used as training data. Such an approach can make the modeling process much easier and less restrictive than before and, thus, more amenable for practical measured data. The new method, called ParThermSID, consists of two steps. First, the response surface method based on second-order polynomials is applied to build the parameterized models at each time point for all of the given sampling nodes in the parameter space. Second, an improved subspace system identification method, called ThermSID, is employed to build the discrete state space models, by construction of the Hankel matrix and state space realization, for each time-varying coefficient of the polynomials generated in the first step. To overcome the overfitting problems of the subspace method, the new method employs an overfitting mitigation technique to improve model accuracy and predictive ability. Experimental results on a practical quad-core microprocessor show that the generated parameterized thermal model matches the given data very well. The compact models generated by ParThermSID also offer two orders of magnitude speedup over the commercial thermal analysis tool FloTHERM on the given example. The results also show that ThermSID is more accurate than the existing ThermPOF method.

Plastic Input Motion: Transformation for the Response of Yielding Oscillators

AbstractA transformation method is presented for the response of yielding oscillators to dynamic loading. The method employs a translation in the ordinates and the abscissa of the excitation function by means of a pair of parameters uniquely dependent on the yielding resistance and the vibrational characteristics of the system. By this approach: (1) the differential operator becomes linearlike, with the nonlinearity transferred to the right-hand side; (2) the initial conditions are simplified; and (3) the modified forcing term becomes uniquely associated with the development of plastic deformation. The theory is applied to various yielding oscillators subjected to idealized earthquake pulses, with the modified excitation function termed plastic input motion (PIM). A procedure for applying the method to general waveforms is provided. The coordinates of PIM may be discontinuous and significantly smaller than those of the original excitation function, as a considerable amount of ground acceleration is devote...

Influence of atomic defect generation on the propagation of elastic waves in laser-excited solid layers

The mechanical behavior of solid layers subjected to laser irradiation is investigated by a dynamical model that is based on coupled evolution equations for the elastic displacement of the medium and lattice defect-density fields. The evolution of defect-density is governed by the (i) generation of defects by irradiation, (ii) their diffusion and recombination and (iii) diffusion induced by strain field. The strain field associated with lattice dilatation due to atomic defects is shown to couple with deformation fields of the layer. Frequency equations corresponding to the symmetric and anti-symmetric modes of vibration of the layer are obtained. It is found that coupling between diffusion and strain fields cause dispersion of the general waveform. Explicit expressions are defined for the wave velocity, and the attenuation (amplification) coefficients which characterize these waves.

Optimising time-varying gradient orientation for microstructure sensitivity in diffusion-weighted MR

Here we investigate whether varying the diffusion-gradient orientation during a general waveform single pulsed-field gradient sequence improves sensitivity to the size of coherently oriented pores over having a fixed orientation. The experiment optimises the shape and the orientation of the gradient waveform in each of a set of measurements to minimise the expected variance of estimates of the parameters of a simple model. A key application motivating the work is measuring the size of axons in white matter. Thus, we use a two compartment white matter model with impermeable, single-radius cylinders, and search for waveforms that maximise the sensitivity to axon radius, intra-cellular volume fraction and diffusion constants. Output of the optimisation suggests the only benefit of allowing the gradient orientation to vary in the plane perpendicular to the cylinders is that we can gain perpendicular gradient strength by maximising two orthogonal gradients simultaneously. This suggests that varying orientation in itself does not increase the sensitivity to model parameters. On the other hand, the variation in a plane containing the parallel direction increases the sensitivity significantly because parallel sensitivity improves the diffusion constant estimates. However, we also find that similar improvement in the estimates can be achieved without optimising the orientation, but by having one measurement in the parallel and the rest in the perpendicular direction. The optimisation searches a very large space where it cannot hope to find the global minimum so we cannot make a categorical conclusion. However, given the consistency of the results in multiple reruns and variations of the experiments reported here, we can suggest that for probing coherently oriented systems, pulse sequences with variable orientation, such as double-wave vector sequences, do not offer more advantage than fixed orientation sequences with optimised shape. The advantage of varying orientation is however likely to emerge for more complex systems with dispersed pore orientation.

On parameter identifiability of MIMO radar with waveform diversity

Parameter identifiability is one of the most interesting issues in multiple-input multiple-output (MIMO) radar systems. Previous works have presented conditions for parameter identifiability of the systems with uncorrelated waveforms. In this paper, under general waveform assumptions, we investigate conditions for parameter identifiability of MIMO radar systems with more flexible waveform diversity, where the transmitted waveforms are not restricted to be uncorrelated. The conditions specify the maximum number of targets that can be uniquely localized, which are obtained based on the rule of time-bandwidth product. Moreover, it is found that the conditions are in terms of the rank and structure of the waveform covariance matrix (WCM) and the geometry of MIMO radar systems. Numerical examples are provided to verify the effectiveness of the conditions.

Derivation of the perfect wave for optimising the strong-field driven electron recollision energy

In the article of L.E. Chipperfield et al. [Phys. Rev. Lett. 2009, 102, 063001], the ideal waveform was presented that maximised the recollision energy of a strong-field driven electron. In this paper we expound the derivation of this perfect wave, as well as a more general waveform for optimising electron trajectories for which the recollision occurs some distance from the place of origin. The ideal waveform acts as a guide for the synthesises of more practical waveforms that maximise the electron recollision energy, and so extend the high-order harmonic cut-off to higher frequencies.

Extraction of Individual Muscle Mechanical Action From Endpoint Force

Most motor tasks require the simultaneous coordination of multiple muscles. That coordination is poorly understood in part because there is no noninvasive means of isolating a single muscle's contribution to the resultant endpoint force. The contribution of a single motor unit to isometric tasks can, however, be characterized using the spike-triggered averaging (STA) technique, applied to a single motor unit's spike train. We propose that a technique analogous to STA, which we call electromyogram (EMG)-weighted averaging (EWA), can be applied to surface EMGs to extract muscle mechanical action from the natural endpoint force fluctuations generated during steady isometric contraction. We demonstrate this technique on simultaneous recordings of fingertip force and surface EMG from the first dorsal interosseous (FDI) and extensor indicis (EI) of humans. The EWA direction was approximately the same across a wide range of fingertip force directions, and the average EWA direction was consistent with mechanical action direction of these muscles estimated from cadaveric and imaging data: the EWA directions were 193 +/- 2 degrees for the FDI and 71 +/- 5 degrees for the EI (95% confidence). EWA transient behavior also appears to capture temporal characteristics of muscle force fluctuations with peak force time and general waveform shape similar to that of the associated spike-triggered averages from single motor units. The EWA may provide a means of empirically characterizing the complex transformation between muscle force and endpoint force without the need for invasive electrode recordings or complex anatomical measurements of musculoskeletal geometry.

Ground adaptive and optimized locomotion of snake robot moving with a novel gait

In this paper, we present a novel gait, forward head serpentine (FHS), for a two dimensional snake robot. The advantage of this new gait is that the head link remains in the forward direction during motion. This feature significantly improves snake robot potential applications. Genetic Algorithm (GA) is used to find FHS gait parameters. Relationship between FHS gait parameters and friction coefficients of the ground are developed. Next, robot speed is considered in the optimization. A fitness function covering robot speed and head link angular changes is defined. A general sinusoidal wave form is applied for each joint. GA is used to find gait parameters resulting in maximum speed while head link angular changes remain in an acceptable range. Optimal gait parameters are also calculated for different friction coefficients and relationships between them are developed. Experiments are also performed using a 5-link snake robot. It is shown that experimental and theoretical results closely agree.

Clutter Rank of STAP in MIMO Radar With Waveform Diversity

In recent years, multiple-input multiple-output (MIMO) radar systems with space-time adaptive processing (STAP) have been proposed to improve radar performance. For MIMO radars with STAP, one big concern is the clutter rank. Current studies employ the rule of time-bandwidth product to predict the clutter rank of MIMO radars using orthogonal waveforms. This paper investigates clutter rank estimation for MIMO radar systems with more flexible waveform diversity, where waveforms are not constrained to be orthogonal. Under general waveform assumption, we have derived the clutter covariance matrix as a function of waveform covariance matrix (WCM). The clutter rank is then found to be determined by the rank and structure of the WCM. For different waveform cases, the WCM may be either full rank or rank deficient. Rules for estimation of clutter rank in these cases are provided and demonstrated by numerical simulations.

Novel micromirror design with variable pull-in voltage

A novel micromirror is presented having a variable pull-in voltage. This allows analog Pulse Width Modulation (PWM) so that the number of grey levels is not limited by the number of subframes or bitplanes. The levels can be chosen arbitrarily, allowing less severe speed requirements for the electronic layer below the MEMS, less image processing hardware and memory. The presented design of the mirror has two attracting electrodes and one landing electrode at either side of the mirror. One electrode is used as ‘fixed’ electrode, influencing the other attracting electrode’s pull-in voltage. If we apply a general triangular waveform at the former electrode, the ‘fixed’ electrode voltage determines the duty cycle of the mirror. The mirror implements analog PWM, without needing a transistors based comparator at the CMOS level. When each ‘fixed’ electrode is connected to an active matrix cell, an active matrix display can be formed. The mirrors with variable pull-in voltage were fabricated using SiGe as the structural layer. The variable pull-in principle is demonstrated by measurements performed on these SiGe mirrors [1].

Global Loss Evaluation Methods for Nonsinusoidally Fed Medium-Frequency Power Transformers

Medium-voltage conversion systems, such as traction and grid-connected converters, are continuously evolving toward higher power densities. Consequently, volume, weight, and material reductions are becoming major design issues, which lead the research focus toward high-/medium-frequency isolated power conversion systems. An optimized design of these conversion systems requires a detailed transformer-loss evaluation considering both copper and core losses. This paper presents a simple and flexible methodology to analyze global medium-frequency transformer losses in an isolated DC-DC converter fed by general nonsinusoidal waveforms. Various loss evaluation approaches are considered, pointing out their validity and limitations by means of finite-element simulations and experimental tests.

A review of EEG and ERP studies in bipolar disorder

Objective:The electroencephalogram (EEG) can be a useful tool in determining differences in general neural activity and specific waveforms in individuals with a number of psychiatric disorders. This paper aims to outline and discuss significant findings in EEG and event-related potential (ERP) research into bipolar disorder (BD).Methods:A literature review was performed through searches of MedLine, EMBASE, CINAHL and PsycInfo medical research databases for papers published from 1985 onwards. References of selected articles were also examined for other relevant studies.Results:Differences in general EEG data were found in subjects with BD, namely increased theta and delta and decreased alpha wave bands. Changes in EEG were also found in euthymic BD subjects and those undergoing medication programmes. ERP studies commonly report prolonged latencies and reduced amplitudes in the P300 component. Hyperfunctioning of the right hemisphere in BD was also reported in some studies, although further confirmation of this finding is required. Finally, the effects of medication and the role that genetics plays in EEG still remain unclear.Conclusions:The literature reviewed demonstrates supporting evidence for the presence of significant differences in EEG and ERP data in subjects with BD. However, methodological considerations such as varying mood states and medication status of the patients need to be followed more stringently for future research to bring about a robust model of the cognitive deficits of BD.

Elimination of harmonics in multilevel inverters with non-equal dc sources using PSO

Multilevel inverters supplied from equal and constant dc sources almost do not exist in practical applications. The variation of the dc sources affects the values of the switching angles required for each specific harmonic profile, as well as increases the difficulty of the harmonic elimination’s equations. This paper presents an extremely fast optimal solution of harmonic elimination of multilevel inverters with non-equal dc sources using a novel Particle Swarm Optimization (PSO) algorithm. The overall system is suitable for large variable speed drives, UPS systems, and on-line utility applications such as static var compensation. A set of mathematical equations describing the general output waveform of the multilevel inverter with non-equal dc sources is formulated. PSO is then employed to compute the optimal solution set of switching angles, if it exists, for each required harmonic profile. Theoretical studies for different case studies regarding the number of levels and harmonic profile are carried out to show the effectiveness and robustness of the proposed technique, and validated through both simulations and laboratory experimentation.

Accurate effective-one-body waveforms of inspiralling and coalescing black-hole binaries

The effective-one-body (EOB) formalism contains several flexibility parameters, notably ${a}_{5}$, ${v}_{\mathrm{pole}}$, and ${\overline{a}}_{\mathrm{RR}}$. We show here how to jointly constrain the values of these parameters by simultaneously best-fitting the EOB waveform to two, independent, numerical relativity (NR) simulations of inspiralling and/or coalescing binary black-hole systems: published Caltech-Cornell inspiral data (considered for gravitational wave frequencies $M\ensuremath{\omega}\ensuremath{\le}0.1$) on one side, and newly computed coalescence data on the other side. The resulting, approximately unique, ``best-fit'' EOB waveform is then shown to exhibit excellent agreement with NR coalescence data for several mass ratios. The dephasing between this best-fit EOB waveform and published Caltech-Cornell inspiral data is found to vary between $\ensuremath{-}0.0014$ and $+0.0008$ radians over a time span of $\ensuremath{\sim}2464M$ up to gravitational wave frequency $M\ensuremath{\omega}=0.1$, and between $+0.0013$ and $\ensuremath{-}0.0185$ over a time span of $96M$ after $M\ensuremath{\omega}=0.1$ up to $M\ensuremath{\omega}=0.1565$. The dephasings between EOB and the new coalescence data are found to be smaller than: (i) $\ifmmode\pm\else\textpm\fi{}0.025$ radians over a time span of $730M$ (11 cycles) up to merger, in the equal-mass case, and (ii) $\ifmmode\pm\else\textpm\fi{}0.05$ radians over a time span of about $950M$ (17 cycles) up to merger in the $2\ensuremath{\mathbin:}1$ mass-ratio case. These new results corroborate the aptitude of the EOB formalism to provide accurate representations of general relativistic waveforms, which are needed by currently operating gravitational wave detectors.

Jumps Across an Outgoing Spherical Shock Wave Front

The shock jump conditions have been used since Rankine published in 1870 and Hugoniot in 1889. However, these conditions, in which the geometrical effect is never included, may not be correctly applied to material responses caused by a spherical wave front. Here, a geometrical effect on jumps in radial particle velocity and radial stress across an outgoing spherical wave front is examined. Two types of jump equations are derived from the conservation laws of mass and momentum. The first equations of Rankine–Hugoniot (RH) type show that the geometrical effect may be neglected at distances of movement of the rear of the wave front that are more than ten times as long as the effective wave front thickness. Furthermore, using four conditions required to satisfy the RH jump conditions, which are contained in the RH type equations, a method is developed to judge the applicability of the RH jump conditions to the jumps. The second type equations for spherical wave fronts of general form are obtained by expressing a volumetric strain wave ε in the wave front by more general wave forms. In the neighborhood of the center of the wave front, for ε<0.09, radial particle velocity in the jump in any materials is inversely proportional to the square of a dimensionless distance from the center to the rear, and for ε<0.04, radial stress in the jump in some viscous fluids and solids is inversely proportional to the distance. In conclusion, an outgoing spherical wave front attenuates greatly near the center due to the geometrical effect as well as rarefaction waves overtaking from behind, while the geometrical effect is negligible at the specified positions that are distant from the center.

Comparing effective-one-body gravitational waveforms to accurate numerical data

We continue the program of constructing, within the effective-one-body (EOB) approach, high-accuracy, faithful analytic waveforms describing the gravitational wave signal emitted by inspiralling and coalescing binary black holes. We present the comparable-mass version of a new, resummed 3 post-Newtonian (PN) accurate EOB quadrupolar waveform that we recently introduced in the small-mass-ratio limit. We compare the phase and the amplitude of this waveform to the recently published results of a high-accuracy numerical simulation of 15 orbits of an inspiralling equal-mass binary black hole system performed by the Caltech-Cornell group. We find a remarkable agreement, both in phase and in amplitude, between the new EOB waveform and the published numerical data. More precisely: (i) in the gravitational wave (GW) frequency domain $M\ensuremath{\omega}l0.08$ where the phase of one of the nonresummed ``Taylor approximant'' (T4) waveform matches well with the numerical relativity one, we find that the EOB phase fares as well, while (ii) for higher GW frequencies, $0.08lM\ensuremath{\omega}\ensuremath{\lesssim}0.14$, where the Taylor T4 approximant starts to significantly diverge from the numerical relativity phase, we show that the EOB phase continues to match well the numerical relativity one. We further propose various methods of tuning the two inspiral flexibility parameters, ${a}_{5}$ and ${v}_{\mathrm{pole}}$, of the EOB waveform so as to ``best fit'' EOB predictions to numerical data. We find that the maximal dephasing between EOB and numerical relativity can then be reduced below ${10}^{\ensuremath{-}3}$ GW cycles over the entire span (30 GW cycles) of the simulation (while, without tuning them, the dephasing is $l8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ cycles). In addition, our resummed EOB amplitude agrees much better with the numerical relativity one than any of the previously considered nonresummed, post-Newtonian one (including a recently derived, nonresummed 3 PN-accurate one). We think that the present work, taken in conjunction with other recent works on the EOB--numerical relativity comparison confirms the ability of the EOB formalism (especially in its recently improved avatars) to faithfully capture the ``real'' general relativistic waveforms.

Solving The Optimal PWM Problem for Odd Symmetry Waveforms

Optimal pulse width modulation (PWM) problem is an established method of generating PWM waveforms with low baseband distortion. In this paper we focused on computation of optimal switching angles of a PWM waveform for generating general odd symmetric waveforms with applications in control. We introduce an exact and fast algorithm with the complexity of only O(n2) arithmetic operations. This algorithm is based on transformation of appropriate trigonometric equations for each harmonics to a polynomial system of equations that is transferred to a special system of power sums. The solution of this system is carried out by modification of Newton's identity via Padé approximation and orthogonal polynomials theory and property of symmetric polynomials. Finally, the optimal switching sequence is obtained by computing the zeros of two orthogonal polynomials in one variable.

Using LISA extreme-mass-ratio inspiral sources to test off-Kerr deviations in the geometry of massive black holes

Inspirals of stellar-mass compact objects (COs) into ~106M[sun] black holes are especially interesting sources of gravitational waves for the planned Laser Interferometer Space Antenna (LISA). The orbits of these extreme-mass-ratio inspirals (EMRIs) are highly relativistic, displaying extreme versions of both perihelion precession and Lense-Thirring precession of the orbital plane. We investigate the question of whether the emitted waveforms can be used to strongly constrain the geometry of the central massive object, and in essence check that it corresponds to a Kerr black hole (BH). For a Kerr BH, all multipole moments of the spacetime have a simple, unique relation to M and S, the BH mass, and spin; in particular, the spacetime's mass quadrupole moment Q is given by Q=-S2/M. Here we treat Q as an additional parameter, independent of S and M, and ask how well observation can constrain its difference from the Kerr value. This was already estimated by Ryan, but for the simplified case of circular, equatorial orbits, and Ryan also neglected the signal modulations arising from the motion of the LISA satellites. We consider generic orbits and include the modulations due to the satellite motions. For this analysis, we use a family of approximate (basically post-Newtonian) waveforms, which represent the full parameter space of EMRI sources, and which exhibit the main qualitative features of true, general relativistic waveforms. We extend this parameter space to include (in an approximate manner) an arbitrary value of Q, and then construct the Fisher information matrix for the extended parameter space. By inverting the Fisher matrix, we estimate how accurately Q could be extracted from LISA observations of EMRIs. For 1 yr of coherent data from the inspiral of a 10M[sun] black hole into rotating black holes of masses 105.5M[sun], 106M[sun], or 106.5M[sun], we find Delta(Q/M3)~10-4, 10-3, or 10-2, respectively (assuming total signal-to-noise ratio of 100, typical of the brightest detectable EMRIs). These results depend only weakly on the eccentricity of the inspiral orbit or the spin of the central object.