Microwave Properties of Helical Resonators

This thesis investigates the electromagnetic resonances of helical structures at microwave frequencies through both modelling and experimentation, with a particular emphasis on the relatively unexplored higher-order modes. By systematically varying geometric parameters, especially pitch, this study reveals unique properties that emerge at many modes, as well as showing transition toward axial field characteristics as mode number is increased. The dispersion of infinitely long helical structures is characterised, demonstrating their predictive capability for lower-order modes in finite systems and their tunability through geometric tailoring. Additionally, a more complex two-handed variant of the conventional helix, referred to as the ambihelix, is analysed in detail with a focus on its resonant behaviour. This structure supports two distinct low-order modes: one exhibiting an almost pure electric dipole characteristic and the other an almost pure magnetic dipole. Importantly, it is shown that by adjusting geometric parameters, these modes can be reordered in frequency or even tuned to occur at the same frequency which has never been shown before, offering new possibilities for resonance control. Finally, the coupling between pairs of helices and ambihelices is investigated through both simulation and experiment. By carefully rotating these structures, near-zero coupling between closely spaced resonators can be achieved. This is experimentally validated using an innovative liquid metal 3D-printing technique for mould fabrication, demonstrating controlled coupling behaviour and the potential for achieving superdirectivity in coupled systems. Further extending this concept to infinite chains of helical elements, the study further shows that specific geometric configurations can result in near-zero group velocity, paving the way for novel wave propagation applications.<p></p>

Author dc:creator

• Jenner Gudge-Brooke (21039905)

• Microwave
• Helices

Statement dc:rights

• All rights reserved
• Open Access after 2027-02-16

Identifier

10779/exe.31354486.v1

OAI identifier oai:identifier

oai:figshare.com:article/31354486