We report on highly tunable radio-frequency (rf) characteristics of a low-loss and compact three-dimensional (3D) metamaterial made of superconducting thin-film spiral resonators. The rf transmission spectrum of a single element of the metamaterial shows a fundamental resonance peak at ~24.95 MHz that shifts to a 25% smaller frequency and becomes degenerate when a 3D array of such elements is created. The metamaterial shows an in situ tunable narrow frequency band in which the real part of the effective permeability is negative over a wide range of temperature. This narrow frequency band gradually possesses near-zero and positive values for the real part of permeability as the superconducting critical temperature is approached. The studied 3D metamaterial can be used for increasing power-transfer efficiency and tunability of electrically small rf antennas.
C. Kurter et al., "Tunable Negative Permeability in a Three-Dimensional Superconducting Metamaterial," Physical Review Applied, vol. 3, no. 5, pp. 054010-1-054010-6, American Physical Society (APS), May 2015.
The definitive version is available at https://doi.org/10.1103/PhysRevApplied.3.054010
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