Dipole moments and near field potentials

Expressions are derived for the moments of electric and magnetic dipoles whose far field is equivalent to the Rayleigh term in the far field of a given radiating electromagnetic field. The equivalent dipole moments are expressed as integrals over an arbitrary closed surface of the near electromagnetic fields and simplification is achieved by rewriting these expressions in terms of the static potentials from which the near fields are derived. The results are valid regardless of the complexity of the field and the medium within the integration surface as long as the exterior is homogeneous, isotropic and source-free.