Polarizabilities and Effective Parameters for Collections of Spherical   Nano-Particles Formed by Pairs of Concentric Double-Negative (DNG),   Single-Negative (SNG) and/or Double-Positive (DPS) Metamaterial Layers
  Unusual scattering effects from tiny spherical particles may be obtained when concentric shells are designed by pairing together 'complementary' double-negative (DNG), single-negative (SNG), and/or standard double-positive (DPS) materials. By embedding these highly polarizable scatterers in a host medium one can achieve a bulk medium with interesting effective parameters. Some physical insights and justifications for the anomalous polarizability of these concentric spherical nano-particles and the effective parameters of the bulk composite medium are discussed. 
Andrea Alu, and Nader Engheta