  In this paper, we present the design of cylindrical and spherical
electromagnetic cloaks working at visible frequencies. The cloak design is
based on the employment of layered structures consisting of alternating
plasmonic and non-plasmonic materials and exhibiting the collective behavior of
an effective epsilon-near-zero material at optical frequencies. The design of a
cylindrical cloak to hide cylindrical objects is firstly presented. Two
alternative layouts are proposed and both magnetic and non-magnetic objects are
considered. Then, the design of spherical cloaks is also presented. The
full-wave simulations presented throughout the paper confirm the validity of
the proposed setup, and show how this technique can be used to reduce the
observability of cylindrical and spherical objects. The effect of the losses is
also considered.
