ACES Publication Search





There are 5 search results for:



Title: A VOLUME INTEGRAL CODE FOR EDDY-CURRENT NONDESTRUCTIVE EVALUATION
Abstract: This paper is an extension of J. R. Bowler, H. A. Sabbagh, and L. D. Sabbagh, "A Computational Model of Eddy-Current Probes Over a Stratified Composite Workpiece," which was presented at the 4th Annual Review of Progress in Applied Computational Electromagnetics, Monterey, CA, March 1988. It describes an application of modern methods of computational electromagnetics to the problem of eddy-current nondestructive evaluation (NDE). Specifically, a volume integral equation is developed that can be used to model eddy-current probes with ferrite cores, or it can be used to compute flaw-field interactions. Both of these problems are of considerable importance in applying electromagnetic techniques to NDE, for they are intimately involved in detecting flaws, and inverting eddy-current data for reconstructing flaws. The model is fully three-dimensional, and the discretized integral equation is solved iteratively using conjugate gradients and FFT techniques. Problems with 12,000 unknowns are being routinely solved on the Alliant FX/ 1 minisupercomputer in reasonable times. The model is used to compute such important probe parameters as impedance and coupling. It is also used to compute the electromagnetic response of flaws as the geometry of the flaw changes, or as a function of frequency. [Vol. 4, No. 1, pp.3-22 (1989)]
Author(s): Harold A. Sabbagh, John R. Bowler, L. David Sabbagh
File Type: Journal Paper
Issue:Volume: 4      Number: 1      Year: 1989
Download Link:Click here to download PDF     File Size: 762 KB

Title: EIGENVALUE COMPUTATION FOR APPLICATION OF THE FINITE HANKEL TRANSFORM IN COAXIAL REGIONS
Abstract: The evaluation of eigenvalues for transcendental equations in the cylindrical coordinate system is considered. A new code has been developed for this purpose. This is a fast algorithm for finding contours of a real function of two variables. This algorithm searches for the interval in which the function passes through the desired reference value and subsequently automatically starts to trace the contour within a circular annulus region of interest. When the reference value is zero and the function represents the limiting form of the Finite Hankel Transform kernel, the solution of the transcendental equation for eigenvalues is obtained. For accurate values of proper numbers, another code provides them with the desired uncertainty. Numerical results are presented and compared with available data. The computed eigenvalues may be used to obtain solutions of boundary value problems for circularly-symmetric electromagnetic waveguides, cables, cavities or scatterers. [Vol. 4, No. 1, pp. 41-56 (1989)]
Author(s): Z. A. Delecki
File Type: Journal Paper
Issue:Volume: 4      Number: 1      Year: 1989
Download Link:Click here to download PDF     File Size: 749 KB

Title: GTD ANNULAR SLOT ANTENNA MODELS AND WIRE SCATTERING
Abstract: Antenna patterns were calculated for two computer models of an annular slot antenna using the Basic Scattering Code (BSC) implementation of GTD. The patterns are compared with a measured pattern. The two computer models are a small electric monopole and a ring of rectangular slots. The monopole model showed good agreement with the measured pattern. The monopole was also used to compute GTD scattering from a thin cylinder, and the results compared with a more accurate field calculation using the Method of Moments. [Vol. 4, No. 1, 57-68 (1989)]
Author(s): Paul G. Elliot
File Type: Journal Paper
Issue:Volume: 4      Number: 1      Year: 1989
Download Link:Click here to download PDF     File Size: 414 KB

Title: THE EOUIVALENT CIRCUIT OF A MICROSTRIP CROSSOVER
Abstract: The equivalent circuit of a microstrip crossover is found. Integral equations are obtained for the densities of excess charge, and these equations are solved by the method of moments. Introduction of a specified transverse distribution of charge, which satisfies the edge condition, reduces the computing time dramatically while the accuracy remains excellent. Several plots of the excess charge densities are provided along with numerical values of lumped excess capacitances. [Vol. 4, No. 1, pp. 69-95 (1989)]
Author(s): Stilianos Papatheodorou, Roger F. Harrington, Joseph R. Mautz
File Type: Journal Paper
Issue:Volume: 4      Number: 1      Year: 1989
Download Link:Click here to download PDF     File Size: 573 KB

Title: Predictions of Transient Eddy Current Fields Using Surface Impedances in Shell Structures
Abstract: The surface impedance techniques have been discussed with moderate interest over the past fifteen years [1 - 6]. They are approached as a means to express sinusoidal fields by yielding a Neuman condition on the surface of conductors. They are generally applied when the skin depth is much less than the thickness characterizing conductor thicknesses within the problem. Some discussion has been given to their utilization near corners and slots [3]. They are not generally used as a means of approaching transient problems. The main focus of this work is in their utilization both in steady state and transient problems, primarily for shell type structures.
Author(s): K. Davey, L. Turner
File Type: Journal Paper
Issue:Volume: 4      Number: 1      Year: 1989
Download Link:Click here to download PDF     File Size: 601 KB