Transient electromagnetic field above a permeable and conducting half-space

Abstract

Summary. The transient fields resulting from an abrupt current switch-off in a vertically oriented finite loop and a magnetic dipole above a permeable and conducting half-space have been investigated by Fourier methods, utilizing an appropriate Green's function. Two partial fields are identified, one ‘radiative’ and evanescent and one ‘diffusive’. Asymptotic formulae for the diffusive field above the interface, applicable for late times, are developed, and from these the effects of height of the transmitting source and the permeability contrast are calculated. It is shown that for ‘late enough’ times and at sufficient distances the dipole formulae provide adequate approximations to the field due to a finite loop.