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In this paper, a modification of the antenna theory (AT) model of the lightning return stroke to include inductive loading is presented. The distributed inductive energy-storing elements are used in the modified AT model (designated as ATIL model, where IL stands for inductive loading) to control the propagation speed of the upward traveling current wave without using an artificial, higher permittivity dielectric medium, as done in the original AT model. The variation of the propagation speed along the channel is also considered in the proposed model. As in the original AT model, resistive loading is used to account for the current attenuation with height. Numerical solution of the electric field integral equation in the time domain using the method of moments with appropriate boundary conditions yields a time-space distribution of current along the lightning channel. This current distribution and the resultant electromagnetic fields for the ATIL model are compared with those predicted by other time-domain and frequency-domain electromagnetic models. The current distribution predicted by the ATIL model exhibits features (such as current dispersion) that are more consistent with optical observations of lightning compared to the predictions of the original AT model. Index Terms--Antenna theory (AT), current distribution, electric and magnetic fields, inductive loading, lightning return stroke modeling.

We propose an efficient modeling technique for theoretical prediction of magnetic field distributions around an arbitrary shape surface-breaking crack in a metal, induced by an alternating-current-carrying wire of arbitrary shape. The finite-difference method is first used to solve the governing Laplace equation inside the crack region. The normal component of magnetic field at the crack opening is thus obtained to derive a closed-form solution in the Fourier domain for the regions outside the crack. To support the validity of the model, we compare experimental results with their theoretical counterparts. Index Terms--Fatigue crack, magnetic field measurement, metals, nondestructive testing.

We present a semianalytical method for calculating the electromagnetic field distribution in a multilayer slab conductor. This is a very advanced and comprehensive method because there is no limitation for the shape of the exciter and the number of layers (i.e., an exciter of any arbitrary shape and at any distance near the surface of a multilayer conductor with a large number of layers can be modeled). We solve the Helmholtz equation in three dimensions by separation of variables. We develop a two-dimensional fast Fourier transform (FFT) integral model and use exponential functions in the third dimension. We solve this integral model analytically and numerically by using the custom matrix form AX = B and a system of algebraic equations, respectively. To verify this method, we solve a simple example problem both by the new method and a finite-element method (FEM) program. The results are in good agreement with each other. Index Terms--Arbitrary shape exciters, electromagnetic field distribution, fast Fourier transform (FFT), multilayer conductors, semianalytical methods.