Electromagnetic field distribution and developed losses inside a finite cylinder and sphere under MRI conditions

The control of the thermal losses dissipated inside the human body during magnetic resonance imaging (MRI) is very important, since it is directly related to patient safety. The authors give the exact solution to the problem of the electromagnetic energy dissipation and distribution inside a conductive sphere and a finite conductive cylinder, considered as the closest models to the human anatomy. The high-frequency alternating magnetic field is produced by a current loop. Numerical results are given for alternating fields from 6 to 100 MHz and various excitation geometries. The results, which take into account the magnetic field inhomogeneities and the finite dimensions of the conductive models, apply not only to the MRI experiments but also to any similar eddy-current problem.     

Coil impedance due to a sphere of arbitrary radial conductivity andpermeability profiles

This paper presents analytical expressions for coil impedance due to a spherical workpiece consisting of concentric spherical shells. The expressions are used to simulate the nondestructive inspection of a sphere having arbitrary radial conductivity and magnetic permeability profiles by a circular coil of rectangular cross section. The simulation replaces continuous profiles with piecewise constant profiles. The paper compares the results to published experimental measurements and the results of other analytical solutions     

Field calculation in single- and multilayer coaxial cylindricalshells of infinite length by using a coupled T-Ω andboundary element method

A method is presented for the calculation of the electromagnetic field in systems of single-layer or multilayer coaxial cylindrical shells of infinite length excited by an oscillating current source arbitrarily oriented inside the first shell. The electric vector potential T and the magnetic scalar potential Ω are used for the evaluation of the quantities of the problem. The Helmholtz equations for T and Ω are transformed into integral equations by the use of the Green's function method. Applying the boundary element method, three systems of simultaneous equations have to be solved to give the sought field quantity     

Analytical and numerical solution of the eddy-current problem inspherical coordinates based on the second-order vector potentialformulation

The three-dimensional (3-D) eddy-current problem, described in spherical coordinates, is studied both analytically and numerically. Since the vector field equation is not separable in the spherical coordinate system, the second-order vector potential (SOVP) formulation is used to treat the problem by reducing it to the solution of the scalar field equation. While the analytical solution is expressed in terms of known orthogonal expansions, the numerical solution utilizes the finite difference method. Examples of engineering applications are provided, concerning computation of eddy-current distribution in a conducting sphere by a filamentary excitation of arbitrary shape     

Eddy current distribution due to a rectangular current frame moving above a conducting slab

Contents The purpose of this work is the determination of the eddy current distribution within a conducting slab, when a rectangulr current frame is moving above this slab. The frame is placed parallel to the slab and the velocity of the slab is constant. The field also is determined in the regions outside the slab. Using the expressions of the field it can be calculated the forces acting on the frame. By applying 3-D Fourier transforms general expressions are derived either for the induced current density inside the slab or for the magnetic flux density outside the slab.

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Wirbelströme infolge eines über einer leitenden Platte bewegten viereckigen stromdurchflossenen Rahmens

Übersicht Der Zweck dieser Arbeit ist die Bestimmung der Wirbelstromdichte innerhalb einer leitenden Platte, wenn sich ein viereckiger Stromrahmen über die Platte bewegt. Der Stromrahmen liegt parallel zu der Plattenoberfläche und die Geschwindigkeit des Rahmens ist konstant. Das Feld wird auch in den Regionen außerhalb der Platte bestimmt. Die Verwendung der feldbeschreibenden Formelausdrücke crlaubt die Berechnung der Kräfte auf den Rahmen. Durch Anwendung der 3-D Fourier-Transformation erhält man Ausdrücke sowohl für die induzierte Wirbelstromdichte innerhalb der Platte als auch für die Feldgrößen außerhalb der Platte.

     

Browning development in white wines: dependence on compositional parameters and impact on antioxidant characteristics

Browning is a serious problem in relation to white wine quality and mostly affects the sensory attributes, whereas its impact on the dietary value of wines has never been investigated. Browning, however, is well known to be associated with polyphenol oxidation, and therefore it may be accompanied by changes in the antioxidant capacity. On the basis of this consideration, experimental white wines vinified and stored under identical conditions were subjected to accelerated browning, and efforts were made to distinguish compositional parameters that might be related to the extent of browning development. Further, the consequences of browning on the reducing power and antiradical activity were assessed. It was shown that none of the parameters examined (titratable acidity, pH, total SO₂, total polyphenols and total flavanols) play an important role in browning onset, but SO₂ appeared to exert a statistically significant influence (r²=0.6394, P<0.05) on the percentage change in the antiradical activity. Evidence also suggested that browning development might be prominently associated with decreases in both antiradical activity (r²=0.7891, P<0.01) and reducing power (r²=0.6925, P<0.05).     

Rigorous near- to far-field transformation for vectorial diffraction calculations and its numerical implementation

A rigorous method for transforming an electromagnetic near-field distribution to the far field is presented. We start by deriving a set of self-consistent integral equations that can be used to represent the electromagnetic field rigorously everywhere in homogeneous space apart from the closed interior of a volume encompassing all charges and sinks. The representation is derived by imposing a condition analogous to Sommerfeld's radiation condition. We then examine the accuracy of our numerical implementation of the formula, also on a parallel computer cluster, by comparing the results with a case when the analytical solution is also available. Finally, an application example is shown for a nonanalytical case.     

Representation of piecewise continuous algebraic surfaces in terms of B-splines

A method for representing shape using portions of algebraic surfaces bounded by rectangular boxes defined in terms of triple product Bernstein polynomials is described and some of its properties are outlined. The method is extended to handle piecewise continuous algebraic surfaces within rectangular boxes defined in terms of triple products of B-spline basis functions. Next, two techniques for sculptured shape creation are studied. The first is based on geometric manipulation of existing primitives and the second on approximation/interpolation of lower dimensional entities using least-squares techniques based on singular value decomposition. In addition, several interrogation techniques, such as contouring, ray tracing and curvature evaluation, used in the design and analysis of piecewise continuous algebraic surfaces are discussed.     

The scattering behavior of a slightly rough surface moving parallel to its mean plane with uniform velocity

The scattering of plane electromagnetic (EM) waves from a perfectly conducting, slightly rough surface moving in vacuum with uniform and constant velocity is examined by combining the boundary perturbation method and the special, homogeneous Lorentz transform. The direction of motion is assumed to be parallel to both the incidence plane and the mean plane of the moving rough surface. The analysis is confined to first-order scatter. The end result is the determination of the velocity-dependent expressions for the bistatic and backscatter incoherent cross sections per unit area of the scattering surface. The expressions for bistatic geometry are only valid for scattering inside the plane of incidence. A numerical example demonstrates the effect of the motion on the scattering behavior of the rough surface.