Ultra-compact superconductive resonator with double-spiral structure

We discuss the characteristics of an ultra-compact double-spiral superconductive Nb microresonator as a potential magnetic metamaterial element. This resonator consists of two superconducting Nb spirals, sandwiched face to face, with a small gap. We study the resonator spectral response by using numerical simulation. The resonator modal structure has been also examined with a laser scanning microscope. The achieved resonator size with respect to the wavelength in our experiment is about λ/4200. Compared to the single-spiral resonator, the frequency of the fundamental mode of the double-spiral one is lowered by a factor of six. Small size and the ease of manufacturing make the double-spiral resonator an attractive solution for magnetic the component of a metamaterial.