Scattering from dielectric material

I need help to clarify the concept of the "Equivalence Principle of
Field".

I've been reading a few journal papers concerning scattering &
radiation from finite size dielectric material. The dielectric
material is penetrated by an incident E-field. By applying field
equivalent principle, the dielectric body is replaced by the volume
polarization currents. Using the free space Green's function, the
scattering E-field is calculated from the volume polarization
currents.

The authors always assume that the incident wave is a plane wave,
i.e. the souece is distant from the dielectric body. What if the
source is very near the dielectric body, i.e. the E-field is near
field ? For near field condition, can the field equivalent principle
be applied to calculate the volume polarization currents ?

As my research work is related to dielectric material in near field, I
would appreciate someone experienced in this area to enlighten
me. Also, if there are any reading materials available in this
subject, please let me know.

Thank you very much.

K. Y. See
Research Student
Imperial College
Electrical & Electronic Engineering Dept.
London, UK
Received on Wed Dec 20 1995 - 19:24:00 EST