Jose Antonio Marinho Brandao Faria

An overview and a contribution to the optical measurement of linear displacement

The present work is a contribution to the field of linear displacement measurements by optical means. For that purpose, a brief overview of some existing solutions is presented and two systems for axial linear displacement measurement based on light intensity detection are introduced. The systems have redundancy and were designed with the purpose of achieving identification and automatic correction of errors arising from inadvertent angular variations between the sensor and the light beam positions.

Analysis of the helical twisted-wire pair running above ground: transfer function evaluation

This paper deals with the analysis of an internally excited three-conductor nonuniform transmission-line system comprising a twisted wire pair (TWP) running above a conducting plane. Research is conducted aimed at the analysis and characterization of the propagation properties of a helical-type TWP system with lossy conductors. Numerical simulation results regarding the attenuation and phase-velocity characteristics of this transmission-line system are obtained by using a TWP model consisting of a cascade of small incremental parallel segments subjected to continuous rotation. Special attention is paid to the derivation and analysis of the frequency-domain voltage transfer function describing the behavior of the TWP structure with a number N of twists. Time-domain results concerning the system response to a pulse train excitation are also obtained by making use of the information conveyed by the transfer function. Both frequency- and time-domain simulation results reported here show that the periodicity arising from wire twisting may dramatically modify the transmission-line system propagation properties as compared to those concerning the untwisted case.

Skin Effect in Inhomogeneous Euler-Cauchy Tubular Conductors

This paper presents a novel contribution to the analysis of skin effect phenomena in inhomogeneous tubular conductors. For homogeneous tubular geometries the skin effect diffusion equation has an analytical solution described by a combination of Bessel functions, but, when the conductivity and magnetic permeability of the tubular conductor arbitrarily depend on the radial coordinate an analytical solution cannot be found. However, this work shows that simple closed form solutions for the electromagnetic field and conductor internal impedance do exist, provided that a specific type of radial variation of medium parameters is properly chosen — these novel structures are coined here Euler-Cauchy Structures. Analytic and computation results concerning general and particular Euler-Cauchy Structures are presented, validated, and discussed. Future research on this seminal topic may lead to new engineering applications.

ON THE SUCCESS OF ELECTROMAGNETIC ANALYTICAL APPROACHES TO FULL TIME-DOMAIN FORMULATION OF SKIN EFFECT PHENOMENA

Maxwell equations can be used to formulate an analytical full time-domain theory of skin efiect phenomena in circular cylindrical conductors without any detour into the frequency domain. The paper shows how this can be done and concomitantly provides the means to determine the time-varying per unit length voltage drop along the conductor from a given time-varying conductor current. The developed relationship between voltage and current is not very complicated and led the authors to examine the reasons why it has never been utilized in transient analysis, nor given special emphasis in the literature. Those reasons are thoroughly examined and the conclusion is that the conditions required for the application of a purely time-domain skin efiect theory are very restrictive.

THE EFFECT OF POWER-LINE SAGGED CONDUCTORS ON THE EVALUATION OF THE DIFFERENTIAL VOLTAGE IN A NEARBY CIRCUIT AT GROUND LEVEL

Overhead-line power conductors do not run parallel to the ground; they actually sag between adjacent towers, defining catenary curves. However, in the analysis of inductive coupling phenomena between power lines and neighboring circuits, the standard approach to deal with the sag effect is to assign a constant average height to power line conductors. The purpose of this research is to assess the accuracy of such an ordinary procedure. To do that, two different approaches are developed in order to more accurately account for the sag effect: a pure segmentation method, and a corrected segmentation method which takes into consideration the real curvature of the sagged conductors. The latter, and novel, approach is compared with the other options. Calculations presented in this work utilize magnetic vector potential as an analysis tool.

COMPLEX RELUCTANCE OF INHOMOGENEOUS EULER-CAUCHY TUBULAR FERRITES TAKING INTO ACCOUNT FREQUENCY-DEPENDENT COMPLEX PERMEABILITY

This paper presents a novel contribution to the analysis of skin-effect like phenomena in radially inhomogeneous tubular geometries that fit in the category of Euler-Cauchy structures (ECS). The advantage of ECSs is that solutions for the electromagnetic field can be described by very simple closed form formulae. This work addresses the evaluation of the per unit length complex magnetic reluctance of tubular ferrites, taking into account that their complex permeability strongly depends on the frequency. The motivation for this research is linked up with the nascent theory of magnetic transmission lines (MGTL), where the wave guiding structure is made of a pair of parallel ferrimagnetic pieces, and whose performance is critically dependent on the complex magnetic reluctance of its component pieces. The analysis presented is mainly focused on high frequency regimes up into the GHz range.

Induction Coil System for 3-D Position Sensing of an Off-Centered Tilted Primary Wire

This paper presents an analysis concerning an inductive system comprised of four sensing coils wound around a nonmagnetic toroidal core that is traversed by a current-carrying primary wire. The primary wire is a rectilinear conductor arbitrarily positioned, off-centered, and tilted. A magnetic vector potential-based approach is developed, aimed at the determination of closed-form expressions for the induced voltages appearing at the open terminals of the four sensing coils, all of them depending on the 3-D position of the primary wire. The inverse problem, that is, the determination of the primary wire position based on the coils-induced voltages, is also formulated, but only exactly solved for the case of an off-centered wire parallel to the core axis.