  Anisotropic and inhomogeneous metamaterial shells are studied in order to
exploit all their resonant mode richness. These multilayer structures are based
on a cylindrical distribution of radially dependent constitutive parameters
including an inner void cavity. Shell, cavity and whispering gallery modes are
characterized, and special attention is paid to the latter ones. The whispering
gallery modes are created at the boundary layers of the shell with the
background and energy localization is produced with highly radiative
characteristics. These low-Q resonant states have frequencies that are
independent of the shell thickness. However, their quality factors can be
controlled by the number of layers forming the shell, which allows confining
electromagnetic waves at the interface layers (internal or external), and make
them suitable for the harvesting of electromagnetic energy.
