  Bi-isotropic and isotropic negative refractive index (NRI) 3D metamaterials
made from periodic arrangements of chiral split ring resonators (SRRs) are
proposed and demonstrated. An analytical theory for the characterization and
design of these metamaterials is provided and validated by careful full-wave
electromagnetic simulations. The reported results are expected to pave the way
to the design of practical 3D bi-isotropic and isotropic NRI metamaterials made
from a single kind of inclusions.
