EPSRC CDT in Metamaterials: Experimental Topics in Controlling Sound with Acoustic Metamaterials Ref: 2436

About the award

The studentship is part of the UK’s Centre of Doctoral Training in Metamaterials (XM2) based in the Departments of Physics and Engineering on the Streatham Campus in Exeter.  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 see our website for more details www.exeter.ac.uk/metamaterials

Joint supervisors:  Prof A P Hibbins, Prof E Hendry OR Dr Simon Horsley, Dr Tim Starkey (Research Fellow)

 

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 XM2

Metamaterials are fabricated microstructures having properties beyond those found in nature. They are emerging as an important new class of materials with applications in many technology areas, from energy harvesting, through perfect imaging, to the much-hyped ‘cloaking’. Having recruited over 50 new PhD researchers in its first three years, the EPSRC Centre for Doctoral Training (XM2) hosted by the University of Exeter (www.exeter.ac.uk/metamaterials) will admit its fourth cohort of 14-18 PhD students in September 2017.

Exeter has a well-established and strong track record of relevant research, spanning a unique mix of interests. We will run projects in the following fields (see our list of themes for full details)

  • Optical, Infra-red and THz Photonics and Plasmonics
  • Microwave Metamaterials
  • Magnonics, Spintronics and Magnetic Metamaterials
  • Acoustic and Fluid-dynamical Metamaterials
  • Wave Theory and Spatial Transformations
  • Graphene and other 2D Materials, and related Devices
  • Nanomaterials and Nanocomposites
  • Biological and Bio-inspired Metamaterials
  • Quantum Metamaterials

The first year of the studentship includes an assessed, stand alone project, and a substantial programme of training. Students will choose from a wide range of taught modules, and participate in academic and personal development skills-based workshops, together with creativity events and conference-style meetings. The cohort will also be expected to disseminate their results to the international community via high-impact publications and international conferences. They will spend time working with our academic and industrial partners.  Full details of the programme are available here, or email us for a copy of our prospectus.

The University of Exeter is a top 10 UK university, in the top 1% of universities globally, and a member of the elite Russell Group of institutions. The University has committed itself to a substantial expansion in its science base and within Physics and Engineering, over £10m has been spent on infrastructure since 2008 and around 30 new academic staff have been appointed across the Centre's themes.

Summary

Application deadline:31st July 2017
Number of awards:1
Value:4-year studentship: UK/EU students, includes tuition fees and an annual stipend equivalent to current Research Council rates (14,553 for 2017-18)
Duration of award:per year
Contact: Prof. Alastair Hibbins (Admissions Tutor)metamaterials@exeter.ac.uk

How to apply

Application criteria

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

  • A statement describing why you would like to study for a PhD in Physics or Engineering,
  • A statement describing why you are considering a PhD programme that offers a cohort-based doctoral training model,
  • An academic CV,
  • A document outlining your research interests and any relevant expertise,
  • Degree transcript(s) giving information about the qualification awarded, the modules taken during the study period, and the marks for each module taken.

In addition, we advise that you upload a cover letter or provide further information about your your preferred area(s) of study within the XM2 themes and/or your interest in a particular project, and also whether you've been in contact with a particular supervisor. You will be asked to provide the contact details of two academic referees.

Please note that of the 25 projects advertised we expect, as a Centre, to fill 14-18 posts only.

 

Application procedure

Applications should be made via the Apply Online system.  Please email metamaterials@exeter.ac.uk if you have any queries about this process. 

You will need to specify that you are making a Research application, with a keyword search of Metamaterials, specifying the College of Engineering, Mathematics and Physical Sciences, and Full Time.  Please then select the course, Physics / Engineering (CDT) - Metamaterials - Doctor of Philosophy - (Full Time) with the start date September 2017.

Shortlisting and interviews

Applications will be reviewed by members of the XM2 management board and candidates will be short-listed against a set of agreed criteria to ensure quality while maintaining diversity. Failure to include all the the elements above may result in rejection. Criteria will include:

ESSENTIAL

  • Excellence in a lower degree in a relevant discipline;
  • Excellence in written and oral skills in English;
  • Evidence of knowledge of XM2 ethos, research themes and/or supervisors.

DESIRABLE

  • Specialist knowledge about one or more XM2 topics;
  • Research outputs (e.g. papers) and/or has undertaken training in research methodology (e.g. undergraduate research projects);
  • Ability to work collaboratively

Short-listed candidates will be interviewed by a panel of two academic members of staff drawn from the management board. If successful, a second interview will be undertaken by the potential academic supervisors for the student concerned. Offers are normally made shortly after a successful second interview.