Metamaterials using active materials: Magnetic and alternative plasmonic media

Abstract

This thesis concerns the use of active materials in metamaterials. A metamaterial is made from subwavelength structured elements with a response depending on the properties and arrangement of the constituent elements. Active materials are used with metamaterials to add control, such as tunability to circumvent limitations in bandwidth, or to add new physics. The two classes of active material considered here are magnetic materials, specifically magnetic resonant and magneto-optic materials, and alternative plasmonic media. Magnetic materials were combined with metamaterial structures (split ring resonators) via inductive coupling at ferromagnetic resonance. Metamolecule hybrid systems using yttrium iron garnet were investigated, and displayed strong coupling, magnetic tunability and the generation of magnetostatic modes. We show that metallic magnetic films can be coupled to metamaterial structures, by patterning to suppress eddy current losses. 40 dB magnetic modulation of a split ring resonance was demonstrated using patterned permalloy (Ni19Fe81) at 17 GHz. Anisotropic CoFe was used to add angular control to the hybrid system, and allow operation in near-zero applied field. We fabricated arrays of U-shape split ring resonators using the alternative plasmonic material indium tin oxide (ITO), and compared their response with identical Au metamaterials. It was found that the new metamaterials could be packed much more densely with respect to the wavelength of operation, with 80 metamolecules per square wavelength possible, though with lower resonance quality. This was due to a red shift in the plasmonic resonance of the ITO U-shapes, and a reduction in interparticle coupling meaning that resonators could be packed more densely without incurring significant blue shift. Inverse ITO metamaterials were fabricated to test the applicability of Babinet’s principle in low electron density solids. Arrays of plasmonic and metamaterial resonators were fabricated using Ni, an alternative plasmonic material which exhibits magneto-optical activity. Preliminary results demonstrating magnetoplasmonic polarisation conversion are presented, and schemes to maximise these effects are discussed.

More information

Identifiers

ORCID for Otto Muskens: orcid.org/0000-0003-0693-5504

Catalogue record

Export record