A Theoretical Study of the Scattering of Electromagnetic Impulses by Finite Obstacles

A general approach to the solution of pulse scattering by finite obstacles is formulated. The essential feature of this approach is the identification and separate treatment of the individual terms in a wavefront expansion of the transforms of the field vectors. It is demonstrated that the dispersive effect of a finite conductivity in the scattering obstacle can be neglected for all metals but that it may be significant for poorly conducting materials such as dry earth. The wavefront technique is employed to solve the problems of the transmission of a delta pulse through a conducting dielectric slab and the reflection and diffraction of a delta pulse from a perfectly conducting sphere. The transmission problem results provide a convenient example of the usefulness of the wavefront approach. The results for the sphere problem indicate that the nature of the waves observed at a given spatial point change in time. It is shown that the penumbra and the caustic region in the vicinity of the focal line θ = π are initially of zero extent. The rates of expansion of these regions with increasing time are obtained by a consideration of the error terms in the asymptotic expansions of the fields. The temporal behavior of the near and far field zones is obtained in a similar manner.