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Bitter solution observations and small-spot Kerr effect measurements have been used to study the response of 100×12×0.3 μm permalloy bars to applied fields that exceed the range of linear response. Bitter patterns showed that a uniform applied field of sufficient strength saturates the center part of the bar by displacing a domain wall to the side of the bar. After reducing the field below its saturation value, remanent magnetization is maintained by a ’’zig-zag’’ domain structure. The original domain pattern returns only at a certain lower value of applied field. An interpretation of the zig-zag pattern is given. The polar effect was used to detect the annihilation and reappearance of Bloch walls in two sets of specimens, in response to similar sequences of applied fields. Differences in the measured renucleation field are attributed to edge effects. As a matter of further interest, the positive or negative polarity of a Bloch wall was found to be correlated with the CW or CCW orientation of the domain structure of the I-bar.

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The multiple multipole method (MMP) of computation for electromagnetic field problems that has been proposed as an alternative to existing finite-element and related methods is being extended in this work by the use of segment functions. In this method linear combinations of defining functions that satisfy themselves the pertaining partial differential equations (e.g., Laplace's equation) are employed to synthesize a solution of a potential in a certain region with given boundary conditions. The solution, as given by these defining functions, will be matched at selected points on the boundary (e.g., conductor surface). This will generate a redundant set of equations from which the coefficients of the various functions in the series solutions are deduced by the method of least squares. To reduce the number of functions in the series expansion, a novel class of harmonic functions obtained by integration of monopole or dipole point functions is investigated. These functions are obtained by integrating a point source function along a line segment. The efficiency of the procedure using these functions has been demonstrated in the calculation of the electrostatic potential and the capacitance of practical two-core cables with elliptical and circular conductors and three-core cables with sector shaped conductors.Index Terms-Electric parameters of cables, electrostatic field calculation, harmonic functions, Laplace's equation, multiple multipole method.

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