Experimental topics in the manipulation of sound using metamaterials and metasurfaces (PhD in Physics) Ref: 2436

About the award

For eligible students (UK/EU nationals only due to industry partner requirements) the 4 year studentship* (value approx. £94,000) will cover UK tuition fees, plus an annual tax-free stipend at the UKRI national minimum doctoral level, enhanced by £2,250 per year (£17,027 for 2018), or pro rata for part-time study, plus a Research and Training Support Grant (RTSG) of £13,000.

*To note:

We are currently awaiting a decision from EPSRC regarding an application for a Centre for Doctoral Training in Functional and Meta- Materials (2019-2027) which will build on our expertise in Doctoral Training gained through the CDT in Metamaterials (XM²) since 2014.  A funding decision is expected by January 2019. The successful applicant will join the new CDT programme if Exeter succeeds in its bid.

XM² now has over 80 post graduate researchers.  Its aim is to undertake world-leading research, while training scientists and engineers with the relevant research skills and knowledge, and professional attributes for industry and academia.Please visit www.exeter.ac.uk/metamaterials for more information about the current CDT and an indication of what to expect.

UK/EU nationals only.

This studentship will be based on the Streatham Campus in Exeter.

Joint supervisors:  Prof A P Hibbins, Prof R Sambles, Dr Tim Starkey

Statement of Research

There are four areas of experimental metamaterial research making up this proposal for TWO studentships, hence this proposal is twice the length of a standard document. The field of acoustic metamaterials is fast moving, and we want to maintain flexibility in the assigning projects to up to two studentships, while also maintaining the ability to respond to the needs and research priorities of DSTL and other industrial sponsors.

1 – Acoustic Beaming

In recent years there has been a substantial amount of work concerned with the modelling, fabrication and characterisation of leaky wave antennas for RF communication [e.g. 1] to improve the capability and reduce the engineering required in such devices. In the acoustic domain, SONAR devices comprising phased arrays of transducers are actively driven to generate beam patterns and beam steers. The use of variable-impedance metasurfaces, comprised of near-resonant "meta-atoms", for transforming surface or guided waves into a different configuration of wavefield provides a much simpler and cheaper, passive, alternative to current implementations. This has not yet been attempted for acoustics metasurfaces and antennas for application in beaming sound using thin and lightweight structures, in which the "meta-atoms" are instead resonant cavities such as Helmholtz resonators, coiled elements or resonant membranes (see topic below).

2 – Acoustics and Flow

The reduction of the generation of acoustic noise generated by flow of fluids (air, water) is a far-reaching problem, affecting the commercial value of domestic appliances (such as hairdryers and vacuum cleaners) and causing environmental damage (aircraft and ship engines). This topic will explore the effect of metasurfaces to reduce or delay the onset of turbulent, noise generating fluid flow, while also using structured surfaces to filter or absorb the transmission of sound through waveguides and ducts. The latter is related to the topic of Artificial Boundary Conditions discussed below. Even without flow, the reduction of sound propagation through narrow gaps will also have great commercial value. This topic will also explore the possibility of breaking parity-time symmetry by introducing fluid flow above surfaces that support the propagation of acoustic surface waves, leading to one-wave propagation of sound [e.g. 2].

3 – Acoustic Artificial Boundary Conditions

A recent article in Physical Review Letters [3] reported an analogous study in acoustics to observation of the spontaneous emission of dyes with varying distance from a mirror (Drexhage’s experiment for sound). This revealed the seminal understanding that a source’s environment determines radiative damping and resonant frequency. The authors considered a Chinese gong in proximity to an acoustic mirror (rigid wall). The work associated with this topic will explore the use of surfaces that impart different boundary conditions, such as resonant structures and porous materials. We will also explore the effect of non-locality (spatial dispersion), loss, partially transmissive boundaries, layered structures and surfaces with flow along them, as well as sources that are more complex that simple dipoles.

4 – Membrane Metamaterials

In contrast to conducting electromagnetic waveguides, acoustic waveguides in rigid materials have no cut-off. We have already developed holey surfaces that prevent sound propagation using a so-called "double fishnet structure" [4], or the use of acoustically soft (pressure-release) materials reintroduces the concept of cut-offs (however pressure release materials do not exist in air). An alternative mean to introduce an airborne cut-off condition is to use membranes across holes and within waveguides. The allowed eigenmodes of the membrane within the void defines the frequencies that are permitted to propagate, and below the lowest order eigenmode, only decaying fields can exist. An array of membrane-capped holes will therefore impart a boundary condition that supports surface waves that decay exponentially into the effective substrate. Similarly, because the phase velocity falls to zero exactly at the cutoff we are able to explore advanced phase control and super-squeezing of sound waves in narrow channels. Such media transmit sound waves with no distortion or phase change across the entire length of the material and enable new sound imaging and detection modalities. More complex membrane-type metamaterial also show great potential for broadband absorption [e.g. 5].

[1] Minatti et al., IEEE Trans. Ant. Prop. 63, 1288 (2015).

[2] Yang et al., Phys. Rev. Lett. 114, 114301 (2015).

[3] Langguth et al., Phys. Rev. Lett. 116, 224301 (2016).

[4] Murray et al., J. Acoust. Soc. Am. 136, 980 (2014).

[5] Wang et al., Appl. Phys. Lett. 108, 041905 (2016).

About us

Exeter has a well-established and strong track record in functional materials and metamaterials research, spanning a unique mix of interests in our focus areas:

  •     Acoustic, Phononic and Fluidic Metamaterials
  •     Microwave and RF Metamaterials and Devices
  •     Nanocomposites and Manufacturing
  •     Photonic and Plasmonic Materials
  •     Soft Matter, Biomaterials and Sensors
  •     Spintronics, Magnonics and Magnetic Materials
  •     Theory and Modelling to drive Targeted Material and Device Design
  •     Two Dimensional Electronic and Photonic Materials

Exeter is amongst the top 150 universities worldwide according to the Times Higher Education World University Rankings, the most influential global league table.
Functional Materials (from fundamentals to manufacturing) is one of 5 key themes supported by the UoE as part of its £320 million Science Strategy investing in staff and facilities. This theme has benefitted from the appointment of 23 new academics (including 7 full professors) along with £20m of investment in research infrastructure (including 3 new electronics/photonics clean-rooms, a graphene engineering laboratory, a nano-functional materials fabrication suite, a materials characterisation suite).

This is in parallel to significant external capital investment in our research including over £2m of equipment funding from the EPSRC/HEFCE SIA award (Exeter-Bath Centre for Graphene Science), the £2.6m ERDF-EADS funded Exeter Centre for Additive Layer Manufacture (CALM); £1.1, for Exeter’s EPSRC Time-Resolved Magnetism Facility; £1.2m for equipment funding from the EPSRC Graphene Engineering Call. Such investments ensure that we have, in-house, all the state-of-the-art materials, fabrication and characterisation facilities required by our PGRs.

Our research and PhD training experience, expertise, facilities and network makes the University of Exeter one of the very best places to pursue postgraduate and early career research.

 

How to apply

Application criteria

Eligible applicants: UK/EU nationals only.

During the application process you will need to upload the documents listed below. Please prepare these before starting the application process.

  • Degree transcript(s) giving information about the qualification awarded, the modules taken during the study period, and the marks for each module taken.
  • An academic CV;
  • A cover letter outlining your research interests in general, the title of the project you are applying for;
  • A Personal Statement consisting of two parts*:
  1.     Describe a) why you would like to study for a PhD, b) why you would like to focus on this particular topic, c) any relevant expertise and d) your future career ambitions;

  2.      Describe the qualities that you believe will make you a great researcher (in particular as part of a team).

You will be asked to provide the contact details of two academic referees.

* 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.

Application procedure

Shortlisting and interviews

Applications will be reviewed by at least two academic members of staff.

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

The essential criteria:

  •      Undergraduate degree in a relevant discipline (minimum 2:1);
  •      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 the 8 research areas listed above;
  •     Training in research methodology (e.g. undergraduate research projects);
  •     Research outputs (e.g. papers) and/or other indicators of academic excellence (e.g. awards).

Shortlisted candidates will be invited to an academic interview with the project supervisors.

To note: If the University of Exeter is successful with its proposal for an EPSRC-funded Centre of Doctoral Training in Functional and Meta-Materials an entry interview to assess fit to the CDT concept will be held prior the academic interview which will normally be undertaken by a panel of 3 people, including members of the CDT's Strategic Leadership Team and a current postgraduate researchers or post-doc in Physics or Engineering.

Interviews are expected to start in the second half of January 2019.

Please email metamaterials@exeter.ac.uk if you have any queries about this process.

Summary

Application deadline:30th April 2019
Number of awards:1
Value:approx £94,000; 4-year studentship: UK/EU students, includes tuition fees and an annual stipend (~17,000 per year)
Duration of award:per year
Contact: Prof. Alastair Hibbins (Admissions Tutor) metamaterials@exeter.ac.uk