Extremely high Q-factor toroidal metamaterials
  We demonstrate that, owing to the unique topology of the toroidal dipolar mode, its electric/magnetic field can be spatially confined within subwavelength, externally accessible regions of the metamolecules, which makes the toroidal planar metamaterials a viable platform for high Q-factor resonators due to interfering toroidal and other dipolar modes in metamolecules. 
Alexey A. Basharin, Vitaliy Chuguevskiy, Nikita Volsky, Maria   Kafesaki, Eleftherios N. Economou, Alexey V. Ustinov
physics.class-ph