In a move that could significantly boost the UK’s renewable energy growth, contracts have been awarded not only to the TWI Ltd / Exeter CMRI partnership, but also to Thales, QinetiQ, Saab, and Plextek DTS to fast-track their ideas for technologies that could mitigate the impact of windfarms on the UK’s air defence radar system.
The Month 6 presentations are given each May by first year PGRs, at the end of the six month mini project the students undertake before beginning their PhD project work. Feedback scores are given by their peers and by academic chairs (this year Dr Anna Katharina Ott and Dr Eric Hébrard took on these roles). Leanne’s presentation was titled ‘Graded negative index surface wave lens’ and Joe’s was titled ‘Structural stability of TMDC Heterostructures in the Presence of Water ’. Please find their projects aims and methodology below.
Graded negative index surface wave lens
Model, fabricate and characterise a graded negative index surface wave lens. One study has
already produced a free-space negative index gradient lens . The aim here is to do this with surface
1. Develop Comsol modelling of microwave metasurfaces made of simple meta-atoms to give easy control of the surface wave index. Then vary the size of the individual elements to design a simple surface wave GRIN lens. This is a very demanding task using Comsol as the GRIN lens will need
modelling in its entirety. Once this task is complete the lens will be fabricated using wax-ink printing
and etching before being fully characterised using the XY microwave scanner. 2. Repeat the above with a more elaborate meta-atom, following on from the work of Tremain
et al , to give almost almost isotropic negative dispersion. Once again then vary the size of the
individual elements so that they allow for spatial control of the effective surface mode index. Then
combine such elements in a 2D metasurface structure to form a negative index GRIN lens. As for the
conventional lens this is a very demanding task using Comsol as again the GRIN lens will need
modelling in its entirety. The complete lens will then be fabricated using wax-ink printing and etching
before being fully characterised using the XY microwave scanner.
 Driscoll T, Basov DN, Starr AF, Rye PM, Nemat-Nasser S, Schurig D and Smith DR (2006) Applied
Physics Letters 88, 081101 ‘Free-space microwave focusing by negative-index gradient lens.’
 Tremain B’ Hooper I R, Sambles JR and Hibbins AP (2018) Scientific Reports 8, 7098 ‘Isotropic
Backward Waves Supported by a Spiral Array Metasurface.’
Structural stability of TMDC Heterostructures in the Presence of
To explore the random structures and reorganisation of TMDC metamaterials in the presence of
water, with addition consideration of substrate effects.
First principles calculations combined with analytic Gibb’s Free energy arguments. In
addition, random structure prediction will be developed as a tool. This tool will require a sound
understanding of both physical and chemical environments and allow the prediction of new phases of
structures. It will need to be benchmarked against known phases.
 F. Davies et al. TMDC Heterostructure band structure theory (submitted – preprint available)
 G. Schusteritsch et al. First-principles structure determination of interface materials: The NixInAs
nickelides, Phys. Rev. B, 2015.
 Heifets et al, BaZrO3, Phys. Rev. B, 75, 155431 (2007)
Congratulations to final year PGR Elizabeth Martin, who won the Best Poster Award at the 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) (2nd-6th November 2020). This is an international conference that includes all aspects of fundamental and applied magnetism, which for the first time was held virtually. The conference had over 16000 attendees- including third year CDT PGRs Connor Sait, David Newman, Katie Lewis, Konstantinos Chatzimpaloglou and Oliver Latcham– with ~ 700 different talks and ~370 different posters as well as several different symposia, workshops, and tutorials.
One of our final year students, Elizabeth Martin, presented her research in one of the poster sessions and won a best poster award. Her poster was titled “Investigation of a Coupled Elasto-Magnetic Discs for Low Reynolds Number Pumps”. The presentation was in the format of a 90-second pitch with the poster, which could be viewed at any time throughout the conference on the conference platform, as well as an additional live Q&A session on Zoom.
The virtual format of the conference was a new experience for most of our researchers, they all enjoyed the conference and learnt a lot from the different presentations. However, they do feel that they missed the in-person experience and the chance to meet different researchers from all around the world. On the other hand, think that they have learnt some valuable skills with regards to presenting their work in an online format compared to in-person. The good news for in-person conferences is that according to our researchers their future is safe, they are just having a needed break for now.
The virtual conference was obviously very different to that of the in-person conference, I enjoyed the experience and obviously I’m thrilled to be awarded a best poster award. I did miss the in-person experience and the chance to meet/catch-up with different researchers from all around the world, talking/messaging online is not the same, but this is the way things are at the moment. One of the benefits was that the presentations were in an “on-demand” format, meaning we were able to watch any presentation at any time we wanted because they were pre-recorded (another benefit was that this year none of us experienced jetlag).
The presentations from the conference are available to view on the conference online platform (for registered conference attendees only), until 30th November 2020. Other presenters from University of Exeter included Prof Feodor Ogrin, Elizabeth’s supervisor, and Dr Maciej Dabrowski, David Newman’s supervisor.
Last month, fourth year PGR Ioannis Leontis gave an oral presentation virtually at Graphene 2020. The event ran online from 19th-23rd October, including presentations, poster sessions and an industrial forum.
Ioannis says of the experience:
Last month, I contributed an oral presentation at the virtual conference Graphene 2020. The conference was really interesting as its programme presents very big names in the field including Nobel Laureates, such as Andre Geim, one of the fathers of graphene, and F. Duncan M. Haldane, one of the founders of the theory about topological phase transitions and the topological phases of matter. My presentation was on “Room temperature ballistic graphene p-n junctions defined by Zn metal doping”. In my talk I presented a new method for the fabrication of ultra-sharp ballistic graphene p-n junction using metal doping of graphene and a new simple characterization method of the metal induced graphene p-n junctions. My research work in this field may give a new push in the fabrication of room temperature graphene electron optic devices. In overall, my participation in such a high-level conference help me a lot in the deeper scientific understanding of my field and gave me the opportunity to make new connection as well.
This year, we have a joint win for our Month 13 Presentation Prize: congratulations to second year PGRs Joe Pitfield and Will Borrows. The prize was a £50 voucher.
The Month 13 presentations are given each October, where the PGRs give a presentation on their work to date and feedback scores are given by their peers. Joe’s presentation was titled ‘The search for new materials’ and Will’s was titled ‘Simulating heat flow in thermoacoustic devices’. Please find their abstracts below.
The search for new materials
It is commonly understood that there is no universal a priori approach to predicting the nature of boundary regions between materials, nor one to enable theoretical design of novel materials within such regions. We present a developing method (RAFFLE; pseudo Random Approach For Finding (Local) Energy minima) learning from existing structural prediction methods , for the pseudo-random generation of atomic structures. Materials are characterised by decomposition of both bond angle and length, with these characterisations applied retroactively to generate new structures with profiles indicative of the isolated characteristic (in these cases, Energy of formation). This method is able to predict the existence of a series of structures of known one, two and three element systems, along with other geometries known  to exist for chemically similar structures (for the Transition metal dichalcogenides, both H and T phase structures predicted) and multiple stable phases identical stoichiometry structures (hexagonal and tetragonal and for Carbon) along with scopes over varying stoichiometries (HCP and FCC aluminium).
The thermoacoustic effect is a process by which sound is produced by the Joule heating of a thin film (a ‘thermophone’) with an alternating current . While this effect has been known for more than a century , recent advances in the fabrication of nano-scale films have rejuvenated the field of thermoacoustics [3,4]. Despite this, thermophones have struggled to present themselves as an alternative to more conventional piezoacoustic speakers due to their low output efficiency.
Here we present an examination into the propagation of heat within and around a thermophone through both finite-element and finite-difference simulation of a device. We do this in order to gain a greater understanding behind the thermal processes which hinder thermophone efficiency. Of particular note is the effect of the Maxwell-Cattaneo correction to Fourier’s heat law , which accounts for the non-instantaneous nature of heat flow. By measuring the effect of this correction on the thermal fluctuations at the boundary between the thermophone and its surrounding medium, we are able to determine a trend for this correction. Going forward, we intend to more accurately calculate the expected sound output of a thermoacoustic device, as well as quantify the effects of this correction on the thermoacoustic efficiency. References
 Ding, H. Nanoscale, 2019, v.11, p.5839-5860
 Preece, W. H. Proceedings of the Royal Society of London, 1880
 Shinoda, H. et al. Nature, 1999, v.400, p.853-855
 Xiao, L. et al. Nano Letters, 2008, v.8, no.12, p.4539-4545
 Cattaneo, C. Comptes Rendus Hebdomadaires des Seances de l’Academie des Sciences, 1958, v.145, p.431-433
We are delighted to announce that third year PGR Benjamin Pearce has won the Month 25 Presentation Prize- a £50 Amazon voucher. The Month 25 presentations are given each October, where the PGRs give a presentation on their work to date and feedback scores are given by their peers. Ben’s presentation was titled ‘Mode Interference and Directional Acoustic Stop Bands in Solid-Fluid Superlattices’. Please find the abstract below.
‘Mode Interference and Directional Acoustic Stop Bands in Solid-Fluid Superlattices’
Whilst there is a large amount of work on one-dimensional phononic crystals (superlattices) consisting of alternating layers of solid materials, there is comparatively little investigation of the properties of the equivalent solid/fluid system. These systems are predicted to exhibit a directional transmission response not available to solid/solid systems. This response stems from an interference between the symmetric and anti-symmetric modes of a submerged plate. This effect can lead to pronounced, angularly dependent reductions in transmission, for even a single solid layer submerged in fluid [1,2]. Extending this system from a single plate to a multilayer structure offers an interesting avenue for phononic crystal design . Existing work largely neglects to consider the interaction of this interference with the Bragg modes of a such a periodic structure. Here we present a numerical and theoretical consideration of the effects of this interaction and how the choice of crystal geometry offers routes for the creation of large bandwidth directional stop bands.
 M. Seiji, “Phononic Bandgaps Pecuiar to Solid-Fluid Superlattices,” Jpn. J. Appl. Phys, 2015.
 Z. Sai, X. Bai-qiang and C. Wenwu, “Controlling The Angle Range in Acoustics Low-Frequency
Forbidden Transmission In Solid-Fluid Superlattice,” J. Appl. Phys, 2018.
 S. Zhang, Z. Y, L. Wei, G. Hu, X. Bai-qiang and C. Wenwu, “Low Frequency Forbidden Bandgap
Engineering Via A Cascade of Multiple 1D Superlattices,” J. Appl. Phys, 2018.
Congratulation to PGR Harry Penketh, who recently submitted his thesis titled ‘“Control of white light emission for illumination and imaging”.
Harry discusses his project in more detail, and offers his advice for students at the start of their PhD journey:
“I have submitted my thesis, although perhaps submitted to my thesis would be a more accurate statement.
To shed some light on my delightfully vague thesis title: this project was sponsored by Dyson and therefore large sections of the research conducted remain protected by a non-disclosure agreement. Working around NDAs aside, I appreciate the broader perspective and additional development opportunities this close industry collaboration has produced.
As is no doubt the case with any job (yes, I’m going to call it a job), doing a PhD comes with its own unique rewards and challenges. In a cohort-based PhD programme one hears a good deal of the latter, but less often in my experience do we reflect on the many great perks that come with the job. I feel privileged to have been able to work with my excellent supervisors Jacopo and Bill and to have had those days (usually in a lab with a new toy) where it didn’t feel like work at all.
My honest and possibly controversial advice for (some) new students: don’t work too hard. How many problems will you solve by spending an extra 6 hours staring desperately at a screen that would have just clicked into place with a refreshed set of eyes and a cup of tea? Look after yourself and don’t forget to find enjoyment in the PhD process.
I’m currently enjoying a break from conventional work and getting stuck into some long overdue property renovation. I hope to remain in Exeter in the medium-term at least.
Harry was involved with various outreach activities during his time with the CDT, including co-organising the mini conference Exeter-Bath Knowledge Transfer in October 2019 with fellow CDT PGRs Iago Rodriguez Diez and Ben Hogan, and students from the Centre for Photonics and Photonic Materials (CPPM) at University of Bath.
Congratulations to David Osuna Ruiz, who has submitted the final version of his thesis, ‘Magnetisation dynamics and tuneable GHz properties of unsaturated magnetic nanostructures’ after corrections.
David looks back on his experience of studying for a PhD as part of the CDT:
Four years ago, I decided to move to the UK to pursue a big goal, professionally and personally speaking, that was to work towards the completion of a PhD in Physics. It just feels like yesterday, although four full years have passed by already since I arrived in Exeter. I am very thankful to myself for having taken such a decision back in January of 2016 and, of course, I am even more thankful to the University of Exeter, the CDT in Metamaterials and my supervisors Feodor Ogrin and Alastair Hibbins for giving me such an opportunity. During these years as a PhD student and researcher, I had so many exciting experiences in the UK, and in many other places worldwide, from Russia to the US. I met so many interesting and good people in the UK and from all over the world, some of them with whom I have been fortunate to have become friends.
After these 4 years, I can say for sure that this has been an unexpectedly enriching and life-changing period of my life. Aside of doing research, I went on industry placements, visited other colleague researchers, did outreach science, attended many courses and international conferences all over the world and many more things. However, what really makes the difference is the people you meet and those you feel by your side, especially during (the many) hard times while working on the thesis and when things seem to have no way out! In that sense, I feel so lucky of having met and worked with so many kind people during these years.
I very well know that I will hardly forget all the good moments I had during these last four years. I do believe that this whole experience has made me stronger and more prepared for future challenges so, to anyone still working on the thesis, two things: be resilient and most importantly, enjoy the journey! In the end, all of it is valuable and it is absolutely worth the effort.
David is staying on at University of Exeter, as a post-doc. We wish him all the best for his future.
David has co-authored the following publications:
D. Osuna Ruiz, A. P. Hibbins and F. Y. Ogrin, “A reconfigurable spin wave emitter based on a teardrop shape”
D. Osuna Ruiz, A.P. Hibbins, F.Y. Ogrin, oral presentation:”Refractive Index Manipulation of Confined Spin Waves in Bloch Domain Walls”, Intermag Conference 2020, Montreal, Canada, May 2020 (accepted)
D. Osuna Ruiz, A. P. Hibbins, F.Y. Ogrin, poster presentation: “Magnetic actuated tuning of Winter’s magnons propagation in Bloch domain walls”, Magnonics 2019, Carovigno, Italy, July 2019
D. Osuna Ruiz, E. Burgos Parra, N. Bukin, A. Lara, F.G. Aliev, A.P. Hibbins, F.Y. Ogrin, oral presentation: “Improving Excitation and Detection of Propagating Spiral Spin Waves in Magnetic Nano-patches: Influence of Thickness and Shape”, Joint MMM-Intermag Conference 2019, Washington D.C., USA, January 2019
D. Osuna Ruiz, E. Burgos Parra, N. Bukin, A. Lara, F.G. Aliev, A.P. Hibbins, F.Y. Ogrin, oral presentation: “Propagating spiral spin waves in magnetic nano-patches: Influence of Thickness and Shape”, International Conference on Magnetism (ICM) 2018, San Francisco, USA, July 2018
D. Osuna Ruiz, E. Burgos Parra, N. Bukin, A.P. Hibbins, F.Y. Ogrin, oral presentation: “Propagating spiral spin waves in magnetic nano-patches”, IEEE International Conference in Microwave Magnetics (ICMM) 2018, organized by the University of Exeter, Exeter, UK, July 2018
D. Osuna Ruiz, E. Burgos Parra, N. Bukin, A.P. Hibbins, F.Y. Ogrin, oral presentation: “Propagating spiral spin waves in magnetic nano-patches”, International Symposium on Spin Waves 2018. Organized by the Ioffe Institute, Saint Petersburg, Russia, June 2018
D. Osuna Ruiz, A. P. Hibbins, F.Y. Ogrin, poster presentation: “Propagating spiral spin waves in magnetic nano-patches”, IOP Magnetism 2018, April 2018
D. Osuna Ruiz, A. P. Hibbins, F.Y. Ogrin, poster presentation: “Propagating spiral spin waves in magnetic nano-patches”, NanoMagnonics Workshop 2018, Kaiserslautern, Germany, February 2018
In this work, the potential of calcium-doped stannous oxide is explored for its potential as an active layer in an all-oxide solar cell design. The authors find an alloy formed of doping Sn:Ca with ratio 7:1 in SnO to exhibit favourable electronic and optical properties for a photovoltaic material. A potential design is proposed for an all-oxide solar cell based around the aforementioned solid solution being the active layer, where TiO2 and CaO are the adjacent transport layers. This study is performed using first principles density functional theory methods to explore the systems. This work was funded jointly be the CDT and Solaris Photonics, with the work being conducted by Ned Taylor and Steve Hepplestone.