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


   Department of Physics and Astronomy

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  Dr S Horsley, Dr Ian hooper, Prof Alastair Hibbins  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

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.

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.

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 based on merit for 3.5 years of full-time study.

For further information on the project, please contact the supervisors via [Email Address Removed].

To apply for funding, you must do so by clicking on the ‘apply now’ button Award details | Funding and scholarships for students | University of Exeter. In the application process you will be asked to upload several documents.


Engineering (12) Physics (29)

Funding Notes

The University of Exeter’s Centre for Metamaterial 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.

Where will I study?