James P. Fulton

Characteristics of electromagnetic pulse propagation in metal

Numerical simulations have shown that a packet of electromagnetic waves advancing in a highly conductive medium suffers severe dispersion which smears the peak position, a potential problem for pulsed eddy current experiments. It was also clear from the previous simulation results that shifting the entire frequency spectrum by an amount sufficient to suppress the low frequency components would improve the situation. Hence, for the present study, a numerical simulation was performed on the characteristics of wave packets with a carrier frequency component. The results show a clear improvement in the sharpness of the peak position and the overall propagation rate is seen to be an increasing function of ϖo, the carrier frequency. Experiments were performed in a through-transmission mode and the initial results appear to be consistent with that of numerical simulation. This paper presents the details of numerical simulation performed with varying carrier frequency, and conductivity and thickness of the medium...

Transient Electromagnetic Fields in Highly Conductive Media

It can be readily demonstrated that the spatial and time dependences of an electromagnetic field in highly conductive media are governed by the diffusion equation [1, 2, 3]. It can be also easily shown that this equation is satisfied by the damped wave solutions having a complex wave vector causing attenuation over distance [1, 2, 4]. Such is basically a fact that can be intuitively predicted; the amplitude of an electromagnetic field with time and spatial harmonics entering a good conductor attenuates rapidly due to eddy current loss while its phase at a given location changes in time as the field advances. To make this picture valid, one must prove that measurable field amplitude exists after the wave front has traveled a sufficient distance. In case of pulsed eddy current test this distance is usually twice the specimen thickness.