Sathya Sai Seetharaman is the third XM² PGR to submit his PhD thesis, which is titled “Electromagnetic interactions in one-dimensional metamaterials” (abstract below). He was supervised by Prof Bill Barnes and Dr Ian Hooper and has previously published his work on Electromagnetic interactions in a pair of coupled split-ring resonators in Physical Review B.
“The CDT has given me the opportunity to meet and network with my heroes whose work I had admired for many years, through conferences and invited lectures. My journey beyond my PhD continues into the industrial side of metamaterials, thanks to the opportunity created by the CDT through career events.”
Sathya described his two-week placement at Flann Microwave in Cornwall as one of the highlights during his PhD project time. He embraced the challenges presented to him when working in an industry environment, and successfully applied the skills he had developed during his training in the CDT for Metamaterials. The experiences he has gained during that time is what motivated Sathya to pursue a career in industry after completion of his PhD. He recently went to a job interview with Metaboards – and has had confirmation that they have initiated their sponsorship application with the home office. A promising start!
Sathya appreciated in particular the learning experience with his cohort, which gave him the opportunity to identify expertise and share knowledge beyond his own research area with colleagues and office-neighbours – with special thanks to Lauren Barr, Chris King, and Erick Burgos (pictured with Sathya at their leaving do in June 2018):
“Our 4 years together sharing invaluable knowledge on unconventional music (go Math Rock!), memes, science fiction and international food has made them very dear to me. My trip to the student desk to submit my thesis was filled with laughter instead of nervousness, thanks to them.”
He also values the experiences from the outreach activities with the Institute of Physics (IOP), SPIE (the international society advancing an interdisciplinary approach to the science and application of light) and the Metabuddies programme, which he describes as ‘one of self-learning’.
“I cherish the opportunities I had to demonstrate scientific concepts to school students and enjoyed the look of amazement on their faces, knowing that my passion for science has touched some young minds.”
Well done, Sathya – and good luck for your viva! We are immensly proud of you and are looking forward to future collaborations and the opportunity to engage you with the next generations of postgraduate researchers at Exeter to share experiences, knowledge, and your passion for science.
PhD thesis abstract ‘Electromagnetic interactions in one-dimensional metamaterials’:
Metamaterials offer the freedom to tune the rich electromagnetic coupling between the constituent meta-atoms to tailor their collective electromagnetic response. Therefore, a comprehensive understanding of the nature of electromagnetic interactions between meta-atoms is necessary for novel metamaterial design, which is provided in the first part of this thesis. The subsequent work in the thesis applies the understanding from the first part to design and demonstrate novel one-dimensional metamaterials that overcome the limitations of metamaterials proposed in literature or exhibit electromagnetic responses not previously observed.
Split-ring Resonators (SRRs) are a fundamental building block of many electromagnetic metamaterials. In the first part of the work in this thesis, it is shown that bianisotropic SRRs (with magneto-electric cross-polarisation) when in close proximity to each other, exhibit a rich coupling that involves both electric and magnetic interactions. The strength and nature of the coupling between two identical SRRs are studied experimentally and computationally as a function of their separation and relative orientation. The electric and magnetic couplings are characterised and it is found that, when SRRs are close enough to be in each other’s near-field, the electric and magnetic couplings may either reinforce each other or act in opposition. At larger separations retardation effects become important.
The findings on the electromagnetic interactions between bianisotropic resonators are next applied to developing a one-dimensional ultra-wideband backward-wave metamaterial waveguide. The key concept on which the metamaterial waveguide is built is electro-inductive wave propagation, which has emerged as an attractive solution for designing backward-wave supporting metamaterials. Stacked metasurfaces etched with complementary SRRs (CSRRs) have also been shown to exhibit a broadband negative dispersion. It is demonstrated through experiment and numerical modeling, that the operational bandwidth of a CSRR metamaterial waveguide can be improved by restricting the cross-polarisation effects in the constituent meta-atoms. The metamaterial waveguide constructed using the modified non-bianisotropic CSRRs are found to have a fractional bandwidth of 56.3% which, based on a thorough search of relevant literature, is the broadest reported value for an electro-inductive metamaterial. A traditional coupled-dipole toy-model is presented as a tool to understand the field interactions in CSRR based metamaterials, and to explain the origin of their negative dispersion response. This metamaterial waveguide should be of assistance in the design of broadband backward-wave metamaterial devices, with enhanced electro-inductive waveguiding effects.
In the final part of the thesis, a one-dimensional metamaterial prototype that permits simultaneous forward- and backward-wave propagation is designed. Such a metamaterial waveguide could act as a microwave analogue of nanoparticle chains that support electromagnetic energy transfer with a positive or a negative dispersion due to the excitation of their longitudinal or transverse dipole modes. The symmetry of the designed hybrid meta-atom permits the co-existence of two non-interfering resonances closely separated in frequency. It is experimentally and computationally shown that the metamaterial waveguide supports simultaneous non-interacting forward-and backward-wave propagation in an overlapping frequency band. The proposed metamaterial design should be suitable for realising bidirectional wireless power transfer applications.