Investigation of Vertical Spiral Resonators for Low Frequency   Metamaterial Design
  This paper thoroughly explores the characteristics of vertical spiral resonators (VSR). They exhibit rela-tively high Q factors and sizes around a few percent of the free space wavelength, which make them ideal candi-dates for assembling metamaterial devices. A quasistatic model of VSR is obtained from simple analytical ex-pressions, and the effects of certain geometrical parameters on the resonant frequency are investigated. 
Jiwen Zhu, Tong Hao, Christopher J. Stevens and David J. Edwards   (Department of Engineering Science, University of Oxford)