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Funding and scholarships for students

Award details

Time Varying Metasurfaces: using rapidly varying components for arbitrary wave transformations (enhanced stipend) Ref: 5054

About the award

Supervisors

Prof Simon Horsley, Associate Professor

Dr Ian Hooper, Senior Research Fellow

Prof Alastair Hibbins,Professor of Metamaterials Physics

Location

Department of Physics, Streatham Campus, Exeter

Summary

The University of Exeter’s Centre for Metamaterials Research and Innovation (CMRI) with Dstl, is inviting applications for a fully-funded PhD studentship with enhanced stipend. For eligible students, the studentship will cover home tuition fees plus an annual tax-free stipend of at least £21,622 (UKRI rate + £3,000) for 3.5 years full-time, or pro rata for part-time study. There is also a budget to support your research project and training of at least £15,000. The student would be based in the Department of Physics and Astronomy within the Centre for Metamaterials Research and Innovation at the Streatham Campus in Exeter.

Anticipated start: Sept 2024

Project Description

Metamaterials and metasurfaces are specially structured matter, structured on a small enough scale to change its macroscopic properties. Periodically patterning a surface, for instance with metal and dielectric yields a ‘metasurface’ that can behave as neither of its constituents: e.g. as an effective “artificial” magnetic conductor [1]. As is now well established, slowly grading this structuring can then give additional functionality, the material acting as e.g. a flat lens [2], or a component of an optical computer [3]. Grading a metamaterial in all three dimensions then allows almost arbitrary transformations of the electromagnetic field; from invisibility [3] to super-scattering [4].

Although there is a large space of possible metamaterial devices to explore, there remain immovable constraints that apply to all of them. For example, no metasurface as described above can change the frequency of an incident wave. Furthermore the maximum bandwidth of any passive absorber is fixed by its thickness and static permeability [5]. It would be a significant advance if we could avoid these constraints.

One way to overcome these constraints is to impose structuring in not only space, but also time. This project will investigate the potential of time varying metasurfaces for controlling antenna radiation. For this we must consider building metamaterials out of elements with properties that can be switched very rapidly, realising effective material parameters that vary in time as well as space. Slow switching (slower than the wave period) amounts to re-configurability, whereas fast switching (on the order of the wave period) gives new functionality where the frequency spectrum of the field can be modified.

 

Time varying metasurfaces: Through modulating the constituent parts of a metasurface using e.g. electronic bias, the reflection of an incident wave can be time modulated, changing the spectrum of the reflected wave.

In optics the material parameters can be switched rapidly using materials with an extreme non-linearity (e.g. Indium Tin Oxide [6]), and in acoustics using materials with embedded electronic feedback [7]. This project will explore the physics of time varying metasurfaces realised in the RF and microwave domain, where the effective material parameters can either be varied optically, or electronically [8,9].

We will investigate the theoretical potential of time varying metamaterials, in particular the possibility to overcome size/bandwidth limitations and shape radiation in both frequency and space. We will also develop the experimental capability to realise time varying metasurfaces in the laboratory, using fast electronics and Schottky and pin-diodes, as well as optically modulated semiconductors.

This project will follow the research plan given below:

  • Investigate theoretical possibilities of time varying metasurfaces: (i) designs for surface properties required to reshape spatial and frequency spectrum; (ii) Extend Rosanov limit [5] to time varying absorbers; (iii) theory of antenna radiation next to a time varying material.
  • Develop experimental demonstrations of uniform time varying metasurfaces, first exploring lower frequency designs (~1GHz) where standard PIN-diodes perform the switching, exploring simple designs developed in the first part of the project. Faster switching mechanisms using optical control will also be investigated.
  • Design and experimentally develop space-time varying metasurfaces to demonstrate spectral and spatial field reshaping.
  • Theoretically and experimentally investigate incorporation of space-time varying metasurfaces into antenna and absorber design, including surpassing conventional bandwidth limitations.

[1] D. Sievenpiper, et al. "High-impedance electromagnetic surfaces with a forbidden frequency band." IEEE Transactions on Microwave Theory and Techniques 47, 11 (1999): 2059-2074.

[2] S. Wang, et al. "A broadband achromatic metalens in the visible." Nature Nanotechnology 13, 3 (2018): 227-232.

[3] J. B. Pendry, D. Schurig, and D. R. Smith. "Controlling electromagnetic fields." Science 312, 5781 (2006): 1780-1782.

[4] Z. Ruan, and S. Fan. "Superscattering of light from subwavelength nanostructures." Physical Review Letters 105, 1 (2010): 013901.

[5] K. N. Rozanov,"Ultimate thickness to bandwidth ratio of radar absorbers." IEEE Transactions on Antennas and Propagation 48, 8 (2000): 1230-1234.

[6] E. Galiffi, et al. "Photonics of time-varying media." Advanced Photonics 4, 1 (2022): 014002-014002.

[7] X. Wen, et al. "Unidirectional amplification with acoustic non-Hermitian space− time varying metamaterial." Communications Physics 5, 1 (2022): 18.

[8] X. Wang, et al. "Metasurface-based realization of photonic time crystals." Science Advances 9, 14 (2023): eadg7541

[9] M. Liu, A. B. Kozyrev, and I. V. Shadrivov. "Time-varying metasurfaces for broadband spectral camouflage." Physical Review Applied 12, 5 (2019): 054052.

About the Centre for Metamaterials Research & Innovation

You would be joining the doctoral training programme at the Centre for Metamaterial Research and Innovation (CMRI) at the University of Exeter.  We support all our students in developing their scientific knowledge whilst also providing transferable and technical skills training to prepare them for careers within and outside of academia.

The PhD students learn together in targeted courses, self-driven activity groups, and exposure to industry to gain scientific background knowledge beyond their areas of expertise, and to equip themselves with transferable professional skills such as creative thinking, project management, and leadership. We are now home to a diverse community of over 30 active PhD students (Postgraduate Researchers, PGRs) who are training in a stimulating, challenging yet supportive cohort-based environment. Since 2018, over 65 graduates have entered employment in industry and as postdocs in Higher Education Institutions in and outside of the UK.

The Award

This award provides annual funding to cover Home tuition fees and a tax-free stipend.  For students from the UK who pay Home tuition fees the award will cover the tuition fees in full, plus at least £21,622 per year tax-free stipend (UKRI rate + £3,000, increasing each year as per UKRI standard PhD stipend).  There is also a budget to support your research project and training of at least £15,000. The conditions for eligibility of home fees status are complex and you will need to seek advice if you have moved to or from the UK (or Republic of Ireland) within the past 3 years or have applied for settled status under the EU Settlement Scheme.

The studentship will be awarded on the basis of merit for 3.5 years of full-time study.

For further information on the project, please contact the supervisors via metamaterials@exeter.ac.uk, or telephone (01392 725654).

Entry requirements


Due to funder restrictions, applications are are limited to those able to gain UK security clearance/

Applications are made to the Metamaterials programme for a PhD in Physics/Engineering. We invite candidates to specify their project(s) of interest at the time of application.

Please ensure to upload ALL items listed below through our application system. Incomplete applications cannot be processed.

Applicants for this studentship must have obtained, or be about to obtain, a First or Upper Second Class UK Honours degree, or the equivalent qualifications gained outside the UK, in Physics or an appropriate area of science or technology.

If English is not your first language you will need to have achieved at least 7.0 in IELTS and no less than 6.0 in any section by the start of the project.  Alternative tests may be acceptable (see http://www.exeter.ac.uk/postgraduate/apply/english/).

How to apply

To apply for funding, you must do so by clicking on the ‘apply now’ button above. In the application process you will be asked to upload several documents.

Please note our preferred format is PDF, each file named with your surname and the name of the document, eg. “Smith – CV.pdf”, “Smith – Cover Letter.pdf”, “Smith – Transcript.pdf

  • You will need to provide a COVER LETTER that indicates your preferred area of study and/or preferred project,
  • You will also need to upload a PERSONAL STATEMENT. We recommend that you describe (a) why you would like to study for a PhD; b) why you would like to focus on the identified area/project, c) any relevant expertise and d) your future career ambitions. We would also encourage you to describe the qualities that you believe will make you a great researcher (in particular as part of a team). Note: these details are not given in the application process but shortlisting will include assessment against these criteria.

You will also need to upload

  • CV
  • Transcript(s) giving full details of subjects studied and grades/marks obtained (this should be an interim transcript if you are still studying).
  • Two references from referees familiar with your academic work. If your referees prefer, they can email the reference direct to metamaterials@exeter.ac.uk quoting the studentship reference number. Please indicate this when you upload their details.
  • If you are not a national of a majority English-speaking country you will need to submit evidence of your proficiency in English. Please see the entry requirements information above.

We intend to undertake interviews and make offers on a rolling basis following the deadline.

Note that we cannot accept references from personal/private email accounts, unless it is a scanned document on institutional headed paper and signed by the referee.

All application documents must be submitted in English. Certified translated copies of academic qualifications must also be provided (if applicable).

We foster creativity and utilisation of individual strengths. Applicants are encouraged to provide evidence to support their statements. This might include conventional written documents (e.g., examples of work), but we also encourage alternatives such as audio or video recordings, websites, programming etc. Please ensure to include accessible links to such files in an appropriately named document as part of the upload process

If you have any general enquiries about the application process or the project itself please email metamaterials@exeter.ac.uk

Application procedure

Shortlisting

Applications will normally be reviewed within two weeks of receipt. Candidates will be short-listed against a set of agreed criteria to ensure quality while maintaining diversity. Failure to include all the elements listed above may result in rejection.

The essential criteria

• Undergraduate degree in a relevant discipline;
• Vision and motivation (for research & professional development);
• Evidence of the ability to work collaboratively and to engage in a diverse community;
• Evidence of excellent written and oral skills in English.


The highest quality candidates will also be able to demonstrate one of more of the following:
• Specialist knowledge about one or more of our research areas (see www.metamaterial.center);
• Training in research methodology (e.g., undergraduate research projects);
• Research outputs (e.g., papers) and/or other indicators of academic excellence (e.g. awards).

Interviews

Shortlisted candidates will normally be invited to an entry interview to assess fit to the cohort-based doctoral training programme, criteria above, and academic suitability.

Interviews are expected to start within two weeks upon application receipt. It is therefore advisable to apply as soon as possible.

Summary

Application deadline:31st March 2024
Number of awards:1
Value: For eligible students the studentship will cover Home tuition fees plus an annual tax-free stipend of at least £21,622 for 3.5 years full-time, or pro rata for part-time study.
Duration of award:per year
Contact: Metamaterials admissions tutor metamaterials@exeter.ac.uk