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The calculation of voltages induced by external electromagnetic fields on multiconductor transmission lines (MTLs) has been the subject of several studies. In this paper, discrete equations for MTLs exposed to incident fields are derived based on the time-domain finite-element method and the backward differentiation formula. Based on these equations, a value-delivery table characterizing the MTLs is presented. Combining this table with modified node analysis formulation, it is convenient for analyzing the responses of transmission lines composed of complex termination networks or complex transmission-lines networks. The validity and efficiency of the proposed algorithm is demonstrated using several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of ground wire and a metal-oxide arrester to the lightning-induced voltage are both discussed. [ABSTRACT FROM PUBLISHER]

This paper presents copper and iron loss models of a classical switched reluctance motor (SRM) and a mutually coupled switched reluctance motor (MCSRM). The iron losses in different parts of machines are then detailed. Based on the power losses model, a lumped parameter (LP) transient thermal model during driving cycles is performed, the analytical results are validated by the finite-element (FE) transient thermal model. Special attention has been paid to model the salient rotor and a method to transform the salient rotor into a nonsalient one has been proposed. A comparison between the maximum temperatures obtained by using different heat source (average power losses or instantaneous power losses during driving cycles) is given. The experimental tests are also realized to verify the analytical and numerical results. [ABSTRACT FROM PUBLISHER]

This paper concerns the modeling of electromagnetic vibration-and-noise sources in permanent-magnet direct current (PMDC) commutator motors. The electromagnetic sources are considered as an electromagnetic field distributed in the air-gap region of a PMDC motor. The latter is then formulated by the two-dimensional field theory in polar coordinates with the consideration of slotting effects and the armature reaction field. Consequently, based on the derived radial electromagnetic field, the radial and tangential magnetic forces acting on the inner surface of the permanent magnets can be expressed as Fourier functions in forms of space and frequency harmonics. The results obtained from the present models agree well with those from the finite-element models. In addition, the measured cogging torque is compared to those calculated by the analytical and finite-element models to validate the formulated electromagnetic field and magnetic forces. Furthermore, experimental investigations are carried out on the electromagnetic vibration-and-noise behavior of a commonly used PMDC commutator motor (such as that in heating, ventilating, and air conditioning (HVAC) systems). By measuring the natural frequencies and the associated mode shapes of the stator, the relationships between the magnetic forces and the measured vibration-and-noise responses are discussed in the frequency domain. [ABSTRACT FROM PUBLISHER]

A novel high-efficient two-step finite-difference time-domain (FDTD) method is proposed to analyze the lightning-induced voltages on transmission lines (TLs) in this paper. The proposed method includes two steps. The first step is to calculate, using the 2-D FDTD method, electromagnetic fields that are radiated from a vertical lightning channel and illuminate the nearby TLs. The second step is to calculate, using the 3-D FDTD method, the electromagnetic response of the TL that is illuminated by the incident electromagnetic fields added at the total field–scattered field connecting the boundary of the 3-D space. To validate the proposed two-step FDTD method, the results calculated using the two-step FDTD method are compared with those calculated with Agrawal coupling model, and with those calculated using the 3-D FDTD method. The two-step FDTD method shows high computational efficiency in analyzing lightning-induced voltages on TLs. [ABSTRACT FROM AUTHOR]

Four model types that could be used to theoretically approximate lightning events currently exist. These are namely gas dynamic (physical) models, electromagnetic models, distributed-circuit models, and “engineering” models. In this paper, a modified transmission line (TL) “engineering” modeling approach, which incorporates the presence of a tall object in the lightning path is adopted. The associated discontinuity at the lightning channel front is treated by introducing reflected and transmitted components, with constituents that are less influential omitted. All computations are performed in the time domain. The considered tall structure is the CN Tower and it is represented by either one, three, or five transmission line sections connected in series. The lightning channel is represented by two more transmission line sections of variable length. The models allow for calculation of current at any height of the CN Tower or the lightning channel and at any time, as needed for determination of the electric and magnetic fields at a distance. The approach is applicable to any other tall structure. [ABSTRACT FROM AUTHOR]

This paper presents SPICE models for the prediction of effects on shielded cables induced by nonuniform fields. Based on the transmission line theory, these models can be utilized to analyze shielded cables terminated with nonlinear or time-varying loads excited by nonuniform fields in the time domain. Two examples, a coaxial shielded cable and a two-parallel-wire shielded cable, both inside a cavity with a slot excited by an incident wave, are studied with the proposed models. The finite-difference time-domain method is employed to calculate the excitation fields of the cables, and then, the SPICE models are utilized to obtain the disturbances induced by the incident wave on the cables. The results obtained by the proposed models agree well with those obtained through other methods. [ABSTRACT FROM AUTHOR]

Near-electric-field and magnetic-field probes are used for a wide variety of applications. Accurate measurement of the fields, however, requires an accurate model of the receiving characteristic of the probe. The receiving characteristic for a reciprocal near-field probe can be calculated from its transmitting characteristic. This receiving characteristic can be used to evaluate the quality of the probe and to compensate for the effect of the probe on the measured field, thereby allowing the electric and magnetic fields to be found accurately from the measurements. In the following paper, methods of evaluating near-field probes using reciprocity are derived and are applied to a typical loop probe in order to compensate near-field measurements over a device under test. [ABSTRACT FROM AUTHOR]

This paper presents a new neural-network method to describe the electromagnetic (EM) behavior at the interface between the substructures from an internally decomposed EM structure. A set of neural networks is used to represent the EM behavior of the substructure as seen from the interface. This allows EM coupling between substructures to be effectively represented. The method is developed in a finite-element environment. An EM transfer function matrix is formulated to produce training data, allowing neural networks to learn the spatial coupling between EM-field variables at various locations over the interface of the substructure. A new formulation is proposed where trained neural networks are integrated into the finite-element equation for efficient simulation of an overall EM structure. A technique is developed to allow the proposed model to be used with the mesh different from that in neural-network training. Examples show that the proposed method provides better accuracy than conventional neural-network approaches for modeling substructures from an internally decomposed EM problem. Using the proposed model also speeds up finite-element simulation. [ABSTRACT FROM AUTHOR]

Exploration of the terahertz (THz) portion of the electromagnetic spectrum has recently expanded due to advances in ultrafast optical laser systems. The application of THz imaging to detect explosive materials (and other chemical agents) is a promising potential application because of the unique spectral signatures found for many explosives in the THz band. However, since the wavelength of THz radiation is on the order of tens to hundreds of micrometers, the rough interface between materials and the granular nature of material mixtures (such as explosives) may cause frequency-dependent scattering, which could mask the spectral signature. Thus, to evaluate the effectiveness of THz imaging systems, it is necessary to characterize the combined volume and rough-surface scattering effects. Because of the complexity of the media and the requirement for broadband modeling, the finite-difference time-domain (FDTD) formulation is an ideal tool. In this paper, transmission measurements through granular media and reflection measurements from controlled rough surfaces are shown to be in good agreement with FDTD results. Methods for extracting the material spectral peaks from a limited number of measurements are presented and discussed. [ABSTRACT FROM AUTHOR]

In this paper, applying field orientation based on particle swarm optimization (PSO) controls the speed of two- asymmetrical-winding induction motor. The maximum efficiency of the motor is obtained by the evaluation of optimal rotor flux at any operating point. In addition, the electromagnetic torque is also improved while maintaining a fast dynamic response. In this research, a novel approach is used to evaluate the optimal rotor flux level. This approach is based on PSO. This research presents two speed control strategies. These are field-oriented controller (FOC) and FOC based on PSO. The strategies are implemented mathematically and experimentally. The simulation and experimental results have demonstrated that the FOC based on PSO method saves more energy than the conventional FOC method. [ABSTRACT FROM AUTHOR]

In this paper, we investigate analytically the connection between the existing first-order small perturbation method solutions for the scattering from a layered structure with one rough interface. First of all, by using effectively the concept of generalized reflection coefficients, we cast the existing models in a unified more compact formulation and point out the connection between the different analytical solutions. The obtained reformulations of the available analytical solutions allow us to subsequently prove the consistency of the considered models. Finally, a suitable expansion is performed that leads us to understand the physical meaning of the analytical expressions. The obtained unified formulation also opens the way toward a general closed-form solution for the problem of scattering by a layered structure with an arbitrary number of corrugated interfaces. [ABSTRACT FROM AUTHOR]

In this paper, a new method of electric field design of high voltage vacuum interrupters is proposed. According to the multi-gap insulation effect and the vulnerable breakdown spots theory, the symmetrical voltage shields are proved to be effective. So the initial model of a high voltage vacuum interrupter is designed. Next with finite element methods and optimization theory, a mathematical model of electric field intensity in interrupters is given. What's more, by optimizing this model with finite element software, a more symmetrical electric field in vacuum interrupters is obtained and its peak value appear as in the second auxiliary gaps (the two gaps between the center floating shield and the symmetrical voltage shields). The result shows that with this method, the vacuum interrupters can withstand higher static breakdown. [ABSTRACT FROM AUTHOR]

This paper involves the computation of 3-D magnetic fields in high-performance, long-lifetime solenoid actuators by finite-element (FE) modeling. Operating at frequencies between 150 and 300 Hz, these actuators are unique in terms of the large force they produce (8–15 N) and their very long lifetime (over five billion continuous duty cycles). Their magnetic circuit typically operates at saturation and, because of the compact dimensions, the 3-D nature of the field distribution needs to be taken into account for their design. Results are presented in terms of the effects of design parameters on saturation and force calculation. [ABSTRACT FROM AUTHOR]

This paper discusses the issue of skin-effect impact on a current's distribution. It presents an analytical approach for determining temperature distribution by using the Electromagnetic Field Analysis Tool's two-dimensional (2-D) program (ELEFANT 2D) over the cross sections of tube-type conductors. Using this implemented model, the authors determine the conductor's current density by taking into account the skin-effect impact on a multi-layered bare conductor by the overhead power transmission lines of the ACSR 490/65 mm² type, and the optical cable of the optical ground wire (OPGW) type. An ELEFANT 2D is given an enabling determination of temperature distribution over the tube-type conductor cross section. The authors have developed, using this program, a computerized mathematical model for temperature determination by considering the skin effect in a multilayer ACSR 490/65 mm² conductor, and the optical cable of the OPGW type. The results show temperature distribution in individual layers of the ACSR 490/65 mm² conductor and the OPGW cable by adiabatic heating at different short-circuit currents. [ABSTRACT FROM AUTHOR]

In order to reduce the influence of axial displacement and/or to ease the assembly, certain capacitive angular sensors use symmetric designs limiting their absolute measuring range to (360°/n) where it is the number of blades. This paper presents a combined sensor that utilizes a Wiegand sensor to obtain ad. ditional information needed to resolve 360°. Since magnetic and electric fields required by the sensing principles do not interfere, one single rotor design can be used for both fields. When the receiver coil on a Wiegand sensor has to drive a current, this current influences the shape and duration of the pulse generated by the sensor. We found that shape and amplitude of the pulse vary depending on the strength of the applied fields and the location of the initial inverse nucleation. Since most of design optimization for capacitive sensors is done by means of simulations, an adequate model of the combined sensor is needed. For the capacitive part, numerical approches such as the finite element method are available. For the pulse wire part, an extended king model has been developed; results of measurements and numerical simulations are reported. [ABSTRACT FROM AUTHOR]

In this paper, the authors present a method to reconstruct measured antenna radiation patterns and their related time-varying aperture fields. The method is based on a model that accounts for the measurement scenario and the antenna radiation characteristics through its radiation centers. The inputs to the model are radiation pattern measurements over a certain bandwidth. Solving the model provides the number of radiation centers, the patterns coupled with each radiation center, and the time delay at which these patterns would be measured. With this information one can reconstruct the measured pattern and retrieve the time-varying aperture fields of the antenna. The latter also provides a diagnostic tool for complex radiating structures. The method and the model are validated with measurements performed in a compact range of two spaceborne antennas. [ABSTRACT FROM AUTHOR]

In this paper, we describe the theory and practical implementation of an electrical impedance probe for making in vivo measurements of the electrical admittance of living tissue. The probe uses concentric annular electrodes and is shown to sample a more localized, yet greater, volume of tissue than the standard four-electrode probe. We have developed a mathematical model for the conduction of current between the probe electrodes assuming that we are investigating a uniform, isotropic, semi-infinite region and taking into account the contact impedance between the electrodes and the organ. The electric fields produced by the probe have been calculated by solving a weakly singular Fredholm integral equation of the second kind. The size and position of the probe electrodes have been optimized to maximize both the accuracy in the admittance measurement and insensitivity to contact impedance. A probe and driving hardware have been constructed and experimental results are provided showing the accuracy of admittance measurements at 50 and 640 KHz. [ABSTRACT FROM AUTHOR]

Attention is drawn to recent paper by Rogers et al. (Aug., 2004) in which ultra-wideband pulses are applied to an isolated muscle as part of deriving a strength-duration curve for threshold stimulation. The paper extends the strength-duration threshold curve for unipolar pulses down to a pulse duration of about 1 ns, on the order of 1000 times shorter than previously studied. Results of the work justify use of traditional mathematical models of the strength-duration curve for nanosecond pulses, as done recently for the electric field resulting from electrostatic discharge through the body (Dawson, et al., 2004). [ABSTRACT FROM AUTHOR]

Erroneous results can be obtained when using the integral formulation suggested in Chiampi’s paper for the computation of the electric field induced in a conductor by certain movements in a static magnetic field. Here, a complete integral formulation to describe the electric field that natural movements in and around high field MRI systems can produce in conducting objects is presented. [ABSTRACT FROM PUBLISHER]