About the award
Experimental topics in the manipulation of sound using metamaterials and metasurfaces
Statement of Research
Joint supervisors: Prof Alastair P Hibbins
, Prof J Roy Sambles
, Dr Tim Starkey
External partner: DSTL
(Prof John Smith)
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  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" , 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].
 Minatti et al., IEEE Trans. Ant. Prop. 63, 1288 (2015).
 Yang et al., Phys. Rev. Lett. 114, 114301 (2015).
 Langguth et al., Phys. Rev. Lett. 116, 224301 (2016).
 Murray et al., J. Acoust. Soc. Am. 136, 980 (2014).
 Wang et al., Appl. Phys. Lett. 108, 041905 (2016).
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. Our 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.
The 4 year studentship (value approx. £105,000) is externally funded by an industry partner. It is of value around £105,000, which includes £13,000 towards the research project (travel, consumables, equipment etc.), tuition fees, and an annual, tax-free stipend of approximately £16,500 per year for UK/EU students.
Eligible candidates: UK/EU nationals only due to industry sponsor requirements.
Exeter has a well-established and strong track record of relevant research, and prospective students can consider projects
from a wide variety of fields:
• Acoustic and Fluid-dynamical Metamaterials
• Biological and Bio-inspired Metamaterials
• Graphene and other 2D Materials, and related Devices
• Magnonics, Spintronics and Magnetic Metamaterials
• Microwave Metamaterials
• Nanomaterials and Nanocomposites
• Optical, Infra-red and THz Photonics and Plasmonics
• Quantum Metamaterials
• Wave Theory and Spatial Transformations
Please visit www.exeter.ac.uk/metamaterials
to learn more about our centre and see the full list of projects
that we have on offer this year.
The studentship is subject to funding availability.
Metamaterials are fabricated microstructures having properties beyond those found in nature. They are an important new class of electromagnetic and acoustic materials with applications in many technology areas: energy storage and improved efficiency, imaging, communications, sensing and the much-hyped ‘cloaking’. Since 2014, the Centre for Doctoral Training in Metamaterials (XM2) recruited more than 80 PhD students. Learn more about our science and training approach: www.exeter.ac.uk/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.
The University of Exeter combines world class research with excellent student satisfaction. It is a member of the Russell Group of leading research-intensive universities. Formed in 1955, the University has over 20,000 students from more than 130 different countries. Its success is built on a strong partnership with its students and a clear focus on high performance. Recent breakthroughs to come out of Exeter's research include the identification and treatment of new forms of diabetes and the creation of the world's most transparent, lightweight and flexible conductor of electricity. Exeter is ranked amongst the UK’s top 10 universities in the Higher Education league tables produced by the Times and the Sunday Times. It is also ranked amongst the world’s top 200 universities in the QS and Times Higher Education rankings.
How to apply
UK/EU nationals only.
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.
• 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(s) you are applying for;
• A Personal Statement consisting of two parts*:
- 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;
- Describe the qualities that you believe will make you a great researcher (in particular as part of a team).
• 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.
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 (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 entry interview to assess fit to the CDT concept. This will be held prior the academic interview with the supervisors and will normally be undertaken by a panel of 3 people, including a current postgraduate researcher or post-doc in Physics or Engineering.
Interviews are expected to start within two weeks
upon application receipt. It is therefore advisable to apply as soon as possible.
Please email firstname.lastname@example.org
if you have any queries about this process.
30th June 2020
Number of awards:
Approximately £105,000, including research and travel budget, tuition fees and annual taxfree stipend (approx. £16,500 per year payable to UK or EU students only).
Duration of award:
Dr. Isaac Luxmoore (Admissions Tutor)email@example.com