Novel toroidal and superconducting metamaterials

Savinov, Vassili (2014) Novel toroidal and superconducting metamaterials. University of Southampton, Physical Sciences and Engineering, Doctoral Thesis, 161pp.

Record type: Thesis (Doctoral)

Abstract

This thesis reports on new solutions for sensing and controlling the electromagnetic radiation, and explores some novel effects of electrodynamics, using metamaterials.

I have demonstrated the first superconducting metamaterial-based electro-optical modulator controlled by passing current through the network of meta-molecules. The meta- material, fabricated out of thin niobium film, modulated the sub-terahertz radiation through magnetic-field-induced suppression of superconductivity as well as through thermal effect. Transmission modulation up to 45% has been observed and main mechanisms of modulation have been studied.

I have demonstrated a resonant radiation-harvesting bolometer for the sub-terahertz frequency range using a superconducting metamaterial fabricated out of thin niobium film. The strong electromagnetic interactions between the meta-molecules allowed harnessing of the radiation incident on the metamaterial and channeling it into a small radiation sensor, thus boosting the device sensitivity and selectivity. Bolometer sensitivity band-width of 1% has been achieved.

I have suggested and experimentally demonstrated a new type of quantum metamaterial that engages the quantization of magnetic flux trapped in the meta-molecules. The metamaterial, fabricated out of high-temperature superconductor YBCO, has been designed to display nonlinear response associated with switching between the magnetic flux states. Although switching experiments have not been performed, a detailed characterization of the metamaterial, including the study of superconducting metamaterial structures that model different switching states, has been conducted.

I have, for the first time, investigated highly nonlinear superconducting sub-terahertz metamaterial that exploits critical current and thermal nonlinearity. The metamaterial was fabricated out of thin niobium film with every meta-molecule containing wire segments of nanoscale thickness. The transmission change of up to 13% has been observed in response to ramping up the intensity of incident radiation to 8 W/m2.

I have developed a novel analytical formalism that, for the first time, linked the reflection and the transmission of the metamaterial with the microscopic multipole excitations taking into account the electric, magnetic and toroidal multipoles of the constituent meta-molecules. A planar superconducting metamaterial with strong toroidal dipole response has been fabricated to test the formalism experimentally, and a very good agreement between the experiment and the analytical predictions has been observed.

I have, for the first time, numerically and analytically studied the non-radiating configuration observed in the microwave experiment with the toroidal void metamaterial. It has been found that the non-radiating configuration is non-trivial and results from the destructive interference between the co-located electric and toroidal dipoles. Such non-radiating configurations shall allow designing high-Q metamaterial resonances and the generation of oscillating vector-potential for the study of the time-dependent Aharonov-Bohm effect.