Normal-mode theory for cylinder arrays

We study a set of interacting cylinders under the influence of an electromagnetic field in the long-wavelength limit. Cylindrical harmonics are used as basis functions in order to write the electric potential in terms of multipolar moments of the charge distribution in the cylinders. We get a normal-mode expansion where the effects of geometry and material are separated. It is shown that for a row of identical parallel cylinders the electromagnetic modes are distributed symmetrically about the depolarization factor 1/2, each set coupling to different components of the external field. The amplitudes of these symmetric depolarization factors are the same and satisfy proper sum rules.