Observation of a New Magnetic Response in 3-Dimensional Split Ring   Resonators under Normal Incidence
  So far, research in the field of metamaterials has been carried out largely with arrays of flat, 2-dimensional structures. Here, we report a newly identified magnetic resonance in Split Cylinder Resonators (SCRs), a 3-dimensional version of the Split Ring Resonator (SRR), which were fabricated with the Proton Beam Writing technique. Experimental and numerical results indicate a hitherto unobserved 3-dimensional resonance mode under normal incidence at about 26 THz, when the SCR depth is approximately half the free space wavelength. This mode is characterized by strong currents along the cylinder axis which are concentrated at the cylinder gaps. Due to their orientation, these axial currents give rise to a magnetic response under normal incidence, which is not possible in shallow SRRs. Our results reveal new behavior in the SRR structure which arises from a change in its aspect ratio. Such new resonances can have a significant influence on the quest for practical, 3-dimensional metamaterials. 
S.Y. Chiam, A. A. Bettiol, M. Bahou, J. Han, H.O. Moser and F. Watt