Comments on "Propagation of EM pulses excited by an electric dipole in a conducting medium" [with reply]

Comments that the authors of the original paper (see Song and Chen, ibid., vol.41, no.10, p.1414-1421, 1993) wish to determine the transient electromagnetic field generated in a conducting medium by an impulsive current in a short electric dipole. Their approach and their results, however, seem to be questionable. To start with, their choice of a delta-function excitation causes serious mathematical difficulties which have been overlooked. Because the spectrum of the delta-function pulse extends over all frequencies with equal Fourier amplitudes, the assumption that the conducting medium, specifically sea water, is characterized by frequency independent permittivity and conductivity is incorrect. The authors reply that they are aware that the conductivity and permittivity of sea water is frequency dependent. They made the approximation of constant conductivity and permittivity for two reasons. First, the exciting impulse current contains all the frequency components from zero to /spl infin/. The second reason for the assumption of constant conductivity and permittivity is that with this assumption we are able to obtain an exact solution for the EM field excited by an impulse current.<
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