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Applied modeling of electromagnetic interactions with linear conductors is essential to advance near-earth sensing devices and integrated signal processing algorithms. This paper describes the development of a novel analytical transmission line (TL) model and its subsequent comparison with a method of moments simulation. The TL model predicts electromagnetic scattering by a linear conductor of finite length that is near lossy ground, here assumed to be a homogeneous conducting half-space. Our model uniquely combines the following: the effect of surface waves on the fields, the proximity of the air–ground interface on wave propagation along the conductor, orthogonal electric dipole exciter polarizations, and the role of an insulating layer on the conductor. It is shown that the TL approach is accurate and offers advantages such as fast computation time, physical insight into the scattering process, and potential for embedded signal processing. [ABSTRACT FROM PUBLISHER]

It is common practice in the engineering analysis process to use an approximate image method for the computation of the current in buried horizontal conductors (in the literature, this is often referred to as the “modified image” or “reflection coefficient” method). According to this approach, the earth/air interface is replaced by a positive mirror image of the charge and current in the conductor, and its field is multiplied by a suitable reflection coefficient. Different opinions on the validity of this approximation have been expressed in published debates, but more systematic analysis of the error introduced by this approach is not available in the literature. To establish the amount of error, we compare the computation results of the image model with the rigorous Sommerfeld integral method for a wide range of parameters. Contrary to widespread opinion, our results suggest that the modified image (or reflection coefficient) method in EFIE-based solutions (e.g., the Pocklington equation) leads to a large error (larger than 20%) in the low-frequency range for the computation of the current distribution in conductors longer than 10 m. In such a case, MPIE-based methods are preferred for use to achieve a smaller error (approximately 5%). Guidelines for the application of image models related to the conductor, earth and excitation parameters, upper frequency limit, and modeling method are presented. [ABSTRACT FROM AUTHOR]

This paper deals with an analytical solution of the time domain Pocklington integro-differential equation for the transient current flowing along the horizontal grounding electrode of finite length. The electrode is excited with an equivalent current source representing the lightning strike current. Presence of the earth–air interface is taken into account through the formulation, via simplified reflection coefficient arising from the modified image theory. The analytical solution is carried out using the Laplace transform and the Cauchy residue theorem, respectively. Results obtained by the analytical solution are compared to those calculated using numerical solution of the corresponding frequency domain Pocklington equation in conjunction with the Inverse Fast Fourier Transform. The results obtained via different methods agree satisfactorily. [ABSTRACT FROM PUBLISHER]

A neural network (NN) implementation of an adaptive optimal stochastic output feedback control is developed to stabilize the resistive wall mode (RWM), a critically important instability in fusion machines like tokamaks. The design of an adaptive optimal stochastic output feedback control was discussed and reported earlier by Sun, Sen, and Longman. The system dynamics is experimentally determined via the extended least square method with an exponential forgetting factor and covariance resetting. The optimal output feedback controller is redesigned periodically online based on the system identification. The output measurements and past control inputs are used to construct new control inputs. These are achieved by an architecture of NNs consisting of a pool of sequentially linked Hopfield networks and implemented in hardware with digital NN processors made by the Accurate Automation Corporation. The simulations have shown that the NN adaptive output controller can stabilize the time-dependent RWM in a slowly evolving tokamak discharge. This is accomplished within a time delay of the inverse of the nonlinear growth rate, which is the time scale of the development of the possibly dangerous levels of fluctuations. This stabilization is similar to that of the simulation with a C++ implementation. It is expected that significant gains can be achieved for the systems of a higher order, which are to be found in future fusion devices. [ABSTRACT FROM PUBLISHER]

Transient electromagnetic field coupling to straight thin wires parallel to each other and located at different heights above a perfectly conducting or dielectric ground plane is analyzed using wire antenna theory and a transmission line method. The time-domain antenna theory formulation is based on a set of the space-time Hallen integral equations. The transmission line approximation is based on the corresponding time-domain Telegrapher's equations. The space-time integral equations arising from the wire antenna theory are handled by the time domain Galerkin-Bubnov scheme of the indirect boundary element method. The time-domain Telegrapher's equations are solved using the finite-difference time-domain method. Time-domain numerical results obtained with both approaches are compared to the results computed via NEC 2 code combined with an inverse Fourier transform procedure. Some illustrative comparisons of results obtained by means of antenna theory and transmission line approach are presented throughout the paper. [ABSTRACT FROM AUTHOR]

The validity domain of the quasi-static method for computation of high frequency and transient characteristics of horizontal buried wires can be established by comparison with an exact analytical method. Usually, limitations of the quasi-static method are derived for practical characteristics, but these are strongly dependent on the specific case and computed quantities. This paper presents an analysis of the differences in the application of the exact and quasi-static Green's function in a method of moments approach for two important cases: distribution of currents in directly fed wires and induced currents in passive wires. It is concluded that the validity domains of the quasi-static method in these two cases are very different. [ABSTRACT FROM AUTHOR]

In this paper, a generalized form of telegrapher's equations for electromagnetic field coupling to buried wires is derived. The presented approach is based on thin-wire antenna theory. The effect of a dissipative half-space is taken into account via the reflection/transmission coefficient approximation. The conductor losses can be taken into account via the surface impedance per unit length. The derived equations are treated numerically via the Galerkin-Bubnov indirect boundary element method. Numerical results are presented for induced current along the wire, and compared with transmission-line (TL) and modified TL (MTL) approximations, respectively, for the case of perfectly conducting electrode buried in a lossy medium. It is shown that the TL and MTL approximations can result in an inaccurate induced current distribution along the conductor at HFs and for shorter electrode lengths, respectively. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the effects of electrode biasing on plasma turbulence. Methodology; Results; Discussion.

Investigates the electrothermal dynamics of electronic circuits. Analysis of the thermal effects in general only from a static point of view; Electrothermal model of the circuit with a diode; Parameters of the current-mirror circuit.

Provides information on a study which discussed the self-heating of silicon devices operating in the 4K < T < 300 K range. Relaxation times at low temperatures; Calculation of the temperature rise; Experimental characterization of the temperature rise; Conclusions.

Studies the superdirective property of arrays comprising a finite number of grooves by using the modal approach. Passive elements in antenna arrays used; Method used for infinite periodic gratings; Techniques used; Numerical approach.

Focuses on the progress in anomalous transport research in toroidal magnetic confinement devices. Transport understanding in the early 1970's; Evolution of the infrastructure for transport studies; Understanding ion-channel anomalous transport mechanisms.