XM2 thesis submitted by Sathya Seetharaman: Electromagnetic interactions in one-dimensional metamaterials

Sathya handing in his PhD thesis.

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 with his 4th year peers Lauren, Chris, and Erick (left to right) at their leaving do in June 2018.

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.

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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.

Honorary Senior Lectureship for Dr Celia Butler (Synopsys (Simpleware Product Group))

Very many congratulations to Dr Celia Butler who was recently appointed as Honorary Senior Lecture at the University of Exeter (Physics & Astronomy).

Celia graduated with a PhD in Physics from the University of Exeter in 2012 following her succesful work on “Microwave Response of Square Mesh Metamaterials” (EPSRC iCase co-funded by QinetiQ).

Prior to her PhD Celia undertook a one year placement at QinetiQ to to work with the Smart Materials team to development novel materials for controlling radio frequencies, and she worked for Flann Microwave Ltd. as part of the design and development team, producing a range of high performance microwave waveguide products (from 2 GHz to 300 GHz) from new bespoke components, to the redesign of current components through numerical modelling.

Following the succesful completion of her thesis she then went back to work in industry and progressed through postions as Radio Frequency Research and Development Engineer (Arikiris, Exeter) and as Design Engineer (Sub10Systems, Kingsteignton) to her current role as Senior Applications Engineer for the Simpleware Product Group at Synopsys (formally Simpleware Ltd.)  in Exeter.

I am thrilled to be awarded the title of Honorary Senior Lecturer in CEMPS at the University of Exeter. I enjoyed many years both as an undergraduate and postgraduate here, and the skills I learnt set me up for a fantastic career adventure.

The outreach work I have done over the years has really helped me to give back to the university and to help students and researchers find their own path. I am delighted to be part of the University of Exeter again.

Celia has lectured for the University of Exeter on several occasions including:

  • Guest lecture for ECM3171 – Computer Aided Engineering
  • Various women in industry events
  • Career path talks to PhD students and ECRs

She has also guest lectured at other instates:

  • University of Surrey on MSc Biomedical Engineering students (2 years)
  • Fusion CDT at University of Manchester – Image Based Modelling for (2 years)
  • Engineering Simulation Summer School at Hartree Centre (STFC)
  • GW4 event (held at University of Bristol) – Postgraduate Training for Research at Cardiovascular – Engineering Interface

Celia provides a fantastic role model for female engineers and scientists at PhD and ECR level, offering them great insight into the opportunities available to them.  She will continue to contribute to the CDT in Metamaterials through our PhD-mentorship scheme, providing one-to-one advice to our PhD researchers across their programme of study.

Conversations are currently planned with Celia and Prof Phillipe Youngs to identify how the connection between the University and Synopsys (Simpleware Product Group) as a local business could be utilised further to the benefit of PGRs and ECRs in the College of Engineering, Mathematics and Physical Sciences, e.g. through interview training and best practise sharing regarding Equality, Diversity and Inclusivity schemes.

 

Beyond a PhD – special panel edition as part of the 6th IEEE International Conference on Microwave Magnetics (ICMM2018) at Exeter

From Sunday June 24th until Wednesday June 27th Exeter had the pleasure to host the sixth IEEE International Conference on Microwave Magnetics (ICMM2018), following on the success of Fort Collins (USA, 2008), Boston (USA, 2010), Kaiserslautern (Germany, 2012), Sendai (Japan, 2014), and Tuscaloosa (USA, 2016). The conference focussed on new developments in all branches of fundamental and applied microwave magnetics.

The event provided us with an incredible opportunity to engage international representatives from academia and industry with our “Beyond A PhD” series – a fantastic chance for all interested postgraduate and early career researchers in the College for Engineering, Mathematics and Physical Sciences to learn more about possible careers pathways, tipps, tricks and traps to watch out for when thinking about the next steps to progress.

Beyond A PhD – special panel edition at the ICMM2018

We welcomed 5 panel members to talk about their career trajectory prior to a question and answer session:  Ursula Ebels (SPINTEC, Grenoble, France), Benedetta Flebus (University of California, Los Angeles, USA),  Peiman Hosseini (Bodel Technologies, Oxford, UK),  Bob McMichael (National Institute of Standards and Technology, US),  Kirill Rivkin (Seagate Technology, Minneapolis, US).

It was a pleasure to see the audience and panel engage so strongly in conversation for 1.5 hours at the end of a long day, exchanging questions and experiences.

Very many thanks to the panel members and in particular to the event organisers Prof R J Hicken and Dr P Keatley for their extraordinary committment to hosting the ICMM2018!

Emily Glover, 1st year CDT in Metamaterials PGR about the event:I found it really interesting, having a panel was a great way to hear a couple of opinions on the same questions, from both industry and academic backgrounds. Other non-CDT people also liked it a lot!”

Leaving-Do for our 4th years

Who would have thought 4 years could go by in what feels like a split second. It seems as if it was only yesterday that the first CDT in Metamaterials’ cohort embarked on our programme, but 4 eventful years have passed and we will soon see all of them move on to new endeavours. Therefore, it was high time for them to get together for a final event to celebrate the occasion.

Our 4th years made the most of the recent nice weather spell and invited their peers to an afternoon boat cruise to spend some joyful hours in each other’s company, cruising up the river towards Topsham and back again whilst sharing memories, current agendas, and future plans.

The organisers, Ben Ash and Sam Shelley, managed to get almost all of the 2014 cohort’s diaries joined up – a challenge in it’s own right – and provided the participants with a fantastic setting to catch up and socialise whilst enjoying the views of the river Exe. The evening was concluded by our soon-to-be graduates with a celebration dinner to say an early farewell to their time in the CDT.

Some have already submitted their thesis and completed their viva, some are yet to tackle this challenge over thext few weeks. A chapter in their lives is about to close and new adventures are about to start, with interviews being lined up, jobs already secured, or extended travel plans being made.

Whatever the next step will be, we are incredibly proud of our PGRs. They have shaped the CDT from day one, through their engagement and feedback on all aspects of the centre’s deliverables. It will be a pleasure to welcome them back to invited talks and reunions in the years to come –  we are curious to learn about their new challenges, and how they will reflect on their PGR experiences in hindsight.

4 years gone by – our 1st cohort celebrating the start of the impending new chapter in their lives together with some of their peers in the CDT.
2014 cohort – in 2018.
2014 cohort – in 2014.

 

Lighting up RAMM (Royal Albert Memorial Museum)

Interested in volunteering? Contact me: Lauren @ .

Mark the date! On Saturday 21st July 2018 the PGR-led Exeter University Optics & Photonics Society (EUOPS) will be hosting a day of light-based activities in the Royal Albert Memorial Museum and Art Gallery, called Lighting Up RAMM, sponsored by the CDT in Metamaterials.

The PGRs will take over the museum with craft activities and experiments to explain the physics behind some of the items in the museum, such as why scorpions glow under UV light and others.

The event will run from 10 am – 4 pm with a lunch break from 12.30 – 13.30.

EUOPS is looking for people to man the various stations, or just wander around and encourage people to get involved. You can sign up for all or part of the day. If you’d like to volunteer, please get in touch with our CDT PGR Lauren Barr:    for more information.

If as volunteer or as a visitor: we’re looking forward to seeing you and your loved ones at the RAMM on 21st July!

PGR cohort visit at Gooch & Housego (Photonics Technology, Torbay)

In June, our second year PhD students (2016 cohort) went for ca company visit to Gooch and Housego, a global leader in photonics technology in Torquay.

G&H are experts across a uniquely broad range of photonic technologies – crystal growth, optical materials processing, acousto-optics and electro-optics, fiber optics, DFB laser modules, precision optics (thin-film coating, birefringent optics, non-linear, planar and aspheric), RF driver electronics in addition to light measurement and calibration solutions.

The PGRs learned about the different components made by the company, and had the opportunity to explore the factory floor where they observed a variety of activities, including the construction of fused fibres and components headed for space.

We would like to thank G&H for hosting our PGRs to offer such insights in their business.

 

New Publication: Manipulating type-I and type-II Dirac polaritons in cavity-embedded honeycomb metasurfaces

In recent years, condensed-matter systems have become a fertile playground for the discovery of new, emergent quasiparticles for which there exists no analogue in the standard model. The archetypal example is graphene whose low-energy electronic quasiparticles behave as so-called massless Dirac fermions – pseudorelativistic particles that exhibit remarkable transport properties, such the suppression of backscattering and anti-localization.

By translating this into the realm of metamaterials, researchers at Exeter University have have theoretically predicted the existence of two new quasiparticles, called type-I and type-II massless Dirac polaritons. These emerge in very elementary metasurfaces with honeycomb symmetry, which can be readily realized across the electromagnetic spectrum from arrays of plasmonic nanoparticles to microwave helical resonators (figure 1).

While these massless Dirac polaritons inherit some of the remarkable features found in graphene, they also offer unique tunabilty which is crucial for their practical implication in novel devices.

Charlie-Ray Mann, PhD student in our CDT in Metamaterials and lead author explains: “The true potential of these half-light, half-matter quasiparticles lies in their hybrid nature which provides additional tunable degrees of freedom that can be manipulated independently.

By embedding the metasurface inside a cavity (figure 1), one can modify the fundamental properties of the emergent massless polaritons by simply changing the cavity height. This includes the ability to tune the dispersion from linear to quadratic, change the Berry phase, and invert the chirality (figure 2) – things that are impossible to achieve in graphene itself.

Charlie-Ray Mann adds: “Exploiting this tunability offers a plethora of opportunities to explore new pseudorelativistic phenomena for which there exists no analogue in condensed-matter systems. This can then be exploited in novel schemes for guiding and manipulating light below the diffraction limit.”

This theoretical work was recently published in Nature Communications: https://doi.org/10.1038/s41467-018-03982-7

Congratulations to Charlie-Ray and the co-authors!

Fig 1: Schematic of a cavity-embedded honeycomb metasurface.
Fig 2: Merging of type-I and type-II Dirac points with chirality inversion.

 >> See all XM² publications here: http://emps.exeter.ac.uk/metamaterials/research/publications/ >>