  It has been recently demonstrated that textured closed surfaces which are
made out of perfect electric conductors (PECs) can mimic highly localized
surface plasmons (LSPs). Here, we propose an effective medium which can
accurately model LSP resonances in a two-dimensional periodically decorated PEC
cylinder. The accuracy of previous models is limited to structures with
deep-subwavelength and high number of grooves. However, we show that our model
can successfully predict the ultra-sharp LSP resonances which exist in
structures with relatively lower number of grooves. Such resonances are not
correctly predictable with previous models that give some spurious resonances.
The success of the proposed model is indebted to the incorporation of an
effective surface conductivity which is created at the interface of the
cylinder and the homogeneous medium surrounding the structure. This surface
conductivity models the effect of higher diffracted orders which are excited in
the periodic structure. The validity of the proposed model is verified by
full-wave simulations.
