Abstract:
Profiles of the electric field strength |E|2/|Eo|2 for spherical metallic shells on a dielectric core are presented both
inside the particle and outside. The dependence of the near-field strength and extent on shell thickness and total
particle size is discussed qualitatively. Although the internal fields inside the shell and in the core are larger than
for homogeneous particles, for not too thick shells, this does not translate into a stronger near-field away from the
surface of the shell. The fields inside the shell, at the low energy resonance and close to it, are rotated by n/2 with
respect to fields inside homogeneous particles, which means that the maximum field strengths in the shell are
perpendicular to the incident polarisation. This follows from the fact that the low energy resonance for a shell is
for the largest dipole moment of the whole system, which compensates the incident field. The largest moment is
created when the same charges are collected at both interfaces (shell/medium and core/shell) along the incident
polarisation. This creates regions of low field densities at the poles along the incident polarisation, because same
charge fields repel each other. Following from that, the field lines are bunched up at the perpendicular poles,
creating large field line densities and hence large fields at these points. The case for opposite charges across the
interfaces creates the high energy, antisymmetric resonance.
