Tunability of Superconducting Metamaterials

Abstract

Metamaterials are artificial structures with unique electromagnetic properties, such as relative dielectric permittivity and magnetic permeability with values less than 1, or even negative. Because these properties are so sensitive to loss, we have developed metamaterials comprised of superconducting waveguides, wires, and split-ring resonators. An important requirement for applications of these metamaterials is the ability to tune the frequency at which the unique electromagnetic response occurs. In this paper we present three methods (unique to superconductors) to accomplish this tuning: temperature, dc magnetic field, and rf magnetic field. Data are shown for dc and rf magnetic field tuning of a single Nb split-ring resonator (SRR). It was found that the dc field tuning was hysteretic in the resonant frequency data, while the quality factor, Q, was less hysteretic. The rf power tuning showed no hysteresis, but did show supression of the Q at high power. Magnetooptical images reveal inhomogeneous magnetic vortex entry in the dc field tuning, and laser scanning photoresponse images for a YBa2Cu3O 7−δ SRR reveals the current distribution in the rings.

Microscopic examination of hot spots giving rise to nonlinearity in superconducting resonators

“…This geometrical effect greatly reduces the accumulation of RF currents at the edges of the strip. Moreover, the continuous arc of the spiral allows for a relatively homogenous and uniform flow along the windings compared to sharp-cornered structures that have a tendency to pile up the currents at the corners and edges 16,17 .…”

Active and Tunable Metamaterials

“…Recently, other kinds of tunable metamaterials were also proposed by using, e.g., supercon ductivity and MEMS structures [27,28] as shown in Figure 3(a) and (b). For the supercon ductivity-based metamaterial, the tunability is obtained by changing the external DC or RF magnetic field [27].…”

A one-dimensional tunable magnetic metamaterial

“…It has been shown that losses in metamaterials, working in and below the THz frequency range, can be greatly reduced if metallic structures are replaced by superconducting ones [1]. Additionally, superconducting meta-atoms exhibit an intrinsic tunability of their resonance frequency by magnetic field and temperature [2][3][4]. However, in both cases, the tunability arises from a suppression of the superconducting order parameter, i.e.…”