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Project ideas

We are looking for industrial and/or academic partners who would like to explore project ideas with us. Examples of ideas in our pipeline are listed below.

If you would like to discuss your own or some of the showcased ideas please contact us: metamaterials@exeter.ac.uk.

Optoelectronic devices working in the infrared have a host of important applications in the areas such as communications, security, defense, imaging, medicine etc. Most current infrared devices are however essentially passive - their operating characteristics are fixed by their structure and design. However there is a growing interest in active, i.e. tuneable or reconfigurable, infrared devices and systems, where the operating characteristics can be changed ‘on the fly’ to respond to changing needs. In this project we will develop such active devices by combining the dielectric (optical material property) control offered by switchable chalcogenide phase-change materials with novel optical metasurface concepts. Target applications include LIDAR, multispectral imaging and holographic displays.

Acoustic Metamaterials (AM) are regarded as a potential solution as sound absorbers in the previously unattainable low frequency band (<1 kHz). The vast majority of AM consist of arrays of local resonators, mainly membrane based, however their performance is often narrow band.  Our ambition is to push the boundary of AM to address technological challenges of low frequency broadband sound absorption in practical environments. We will draw on our expertise in widening the bandwidth of electromagnetic devices, while also applying our previous work on tuneable vibrational energy harvesters, such as magetically induced non linearity, and closed-loop tracking systems, to provide absorption of ambient acoustic frequencies.

Objectives of this project are to:

  1. design low power mechanisms to tune the resonant frequency for membrane-based AM below 1 kHz.
  2. optimise performance of magnetically induced nonlinear AM below 1 kHz.
  3. develop an autonomous closed-loop frequency tracking system for frequency tuneable AM.
  4. demonstrate sound absorption using the broadband AM.

The Nano Engineering Science and Technology (NEST) group currently researches within a portfolio of awards exceeding £13m. The PI (Zhu) is currently leading development of underwater energy harvesters funded by Innovate UK (103380) and has previously led research into mechanical and electrical methods of tuning the resonant frequency of vibration energy harvesters together with control algorithms.

Existing solutions are either theoretical or have obvious weaknesses such as limited broadband, high power consumption and large dimensions

Our civilization is defined by the functionalities delivered by devices, ranging from smartphones to airplanes.  These functionalities are however constrained by materials available to engineers, when constructing and indeed even conceiving a device.  Radically new dynamical properties and advanced functionalities can be created by tailor-tuning the spectra of wave excitations in structured media – so-called metamaterials.  Among other waves, ‘surface acoustic waves’ have been investigated for over one hundred years and currently used for a wide and diverse range of functions, e.g. analogue signal processing in mobile phones. Recently, the field of metamaterials research has expanded to acoustic waves. To date, however, there have been very few suggested ways of designing acoustic metamaterials that can be dynamically reconfigured and tuned. Integration with magnetic materials, well known for their ability to store information e.g. in magnetic hard disk drives, offers an exciting route for achieving non-volatile tuning of acoustic metamaterials. We strive to develop a new class of magneto-acoustic metamaterials in which the role of their building blocks (“meta-atoms”) is played by magneto-acoustic resonators [1,2].  Such metamaterials will add magnetic field tunability to structures aimed to control the propagation of surface acoustic waves, opening intriguing opportunities both in fundamental science and technology.  The memory phenomenon inherent to magnetism will enable significant energy savings in non-volatile magneto-acoustic data and signal processing devices.  For instance, they would be instantly bootable and could be more easily integrated with the existing magnetic data storage devices.  From the point of view of fundamental science, the magneto-acoustic metamaterials will serve as an excellent test bed for studying the physics of wave propagation in non-uniform and non-stationary media. 

This research is tightly related to a larger project (just approved for funding by EPSRC) on the same topic, within which we will collaborate with researchers from the University of Sheffield.  

1. O. S. Latcham, et al, “Controlling acoustic waves using magneto-elastic Fano resonances”, Appl. Phys. Lett. 115, 082403 (2019). 

2. O. S. Latcham, et al, “Hybrid magnetoacoustic metamaterials for ultrasound control”, arXiv:1911.06774 (2019).

  • Please contact Prof Volodymyr Kruglyak, Prof Geoff Nash, Dr. A. V. Shytov, and / or Dr. S. A. R. Horsley (depending on whether an experimental, theoretical or computational project is preferred) via metamaterials@exeter.ac.uk for more information.

Quantum thermodynamics is a new research field, where thermodynamics is studied in the small-system size limit where fluctuations become non-negligible, weak coupling between system and environment cannot be assumed, and a fully quantum mechanical description may be needed. This project is concerned with the application of theoretical tools from the fields of quantum thermodynamics and open quantum systems to the problem of modelling the dynamics, the equilibrium state, and the timescale of equilibration, of a collection of interacting spins that are strongly coupled to their environment. The aim of this project is to find analytical equations that describe the spin dynamics when they are driven by a changing magnetic field and exposed to a heated environment (with potentially multiple temperatures). These will then be used to quantify the importance of quantum mechanical and strong coupling effects in the magnetization dynamics and in the long-time steady state of the spins.

Spin orbit torques (SOTs) result from the spin Hall and Rashba effects within multilayered thin film magnetic materials. An injected charge current generates a spin current that can transfer angular momentum to local magnetic moments, thereby exerting a torque upon them. SOTs have the advantage that charge current may be passed within the plane of the film, rather than through a delicate tunnel barrier, so that larger current densities, sufficient to change the magnetic state of the sample, may be used.  It is expected that SOTs will be exploited in future generations of magnetic random access memory (MRAM) device, and within new data storage and processing paradigms that harness topological structures such as domain walls vortices and skyrmions.

Existing measurement methods rely on magnetoresistive response to characterise spin-orbit torques.  However this approach does not sense the magnetization directly, provides a null response in certain geometries of interest, and lacks spatial resolution.  Direct optical detection of the magnetization overcomes all of these difficulties and, together with the detection of the resulting dynamics in candidate MRAM and spin transfer oscillator devices. The proposed project is intended to provide the theory and modelling needed to extract the values of the torques reliably and understand how they induce dynamic response within devices where the magnetization undergoes quasi-uniform precession.  This theory will then be extended to more complicated topological objects such as skyrmions.  Specifically, the means by which skyrmions move within thin films will be explored, with particular focus upon whether the internal dynamics of skyrmions affect their translational motion and interaction with defects and pinning sites, such as those found at the edges of nanowires that are used to guide their motion.

Spin waves (elementary excitations of magnetically ordered materials) may be excited by electromagnetic waves at frequencies from a few to hundreds of GHz. This is however not easy, due to a huge mismatch between the wavelength (and therefore momentum) of electromagnetic and spin waves at the same frequency. We are tackling this challenge by exploring spin wave excitation and control in media with translational symmetry broken by compositional, geometrical or micromagnetic non-uniformities, which may either naturally exist (they are ubiquitous, in fact) or be artificially created. The interaction (‘coupling’) between propagating waves (spin or electromagnetic) and localised non-uniformities is often enhanced at specific discrete frequencies, giving rise to a rich variety of phenomena often referred to as ‘Fano resonances’ or ‘Fano physics’. We explore such Fano resonances as a platform for creation of novel spin-wave devices and metamaterials with unseen functionalities, such as re-programmability and non-reciprocity, and use them to address new physics that is inaccessible for other waves.

1. Y. Au, et al, “Resonant microwave-to-spin-wave transducer”, Appl. Phys. Lett. 100, 182404 (2012).

2. Y. Au, et al, “Nanoscale spin wave valve and phase shifter”, Appl. Phys. Lett. 100, 172408 (2012).

Molecular aggregates are an important and interesting class of materials particularly in the context of optical (pigmented) materials, both in nature and in synthetic materials, for example in semiconducting polymers for solar cells and light emitting diodes (Spano, Ann Rev Phys Chem (2014) 65 p477).

However, there is a serious sub-wavelength problem in studying such aggregates. Typically inter-molecular separations are very much smaller than the wavelengths associated with the optical transitions of the pigments so that the interactions between the molecules in an aggregate are dominated by near-field interactions, typically of a dipole-dipole character. Despite the near-field nature of the inter-molecular interactions involved, optical investigations are almost universally based on far-field optical spectroscopy techniques, making, for example, the role of disorder and noise very difficult to investigate in a systematic way. This project will explore an alternative approach, one that involves making cm-scale analogues of molecular aggregates based on microwave-domain metamaterials.

The lowest temperatures in the universe—of just a few nanokelvins—are nowadays routinely achieved in many labs. Ultracold atomic gases loaded in optical lattices stand out as an ideal platform for quantum simulation, which could help to crack longstanding condensed-matter physics problems, and most notably assist in the design of new metamaterials or drugs. Precise temperature control is indispensable to run reliable simulations and yet, measuring extreme temperatures with high accuracy still remains a formidable open challenge.

In this project we will combine the theory of open quantum systems with quantum metrology to address the problem of temperature sensing deep in the quantum regime. In particular, we will new develop methods to treat strongly coupled open quantum systems under non-linear dissipation, and a novel theory of non-Gaussian quantum metrology. We will then apply these tools to improve the desing, measurement, and data analysis in current thermometry experiments exploiting atomic impurities in Bose–Einstein condensates. This could enable reliable quantum simulation and pave the way towards next-generation material design.

Waves propagating in quasicrystals are at a curious point where neither Bloch’s theorem (applicable to periodic media), nor the diffusion approximation (applicable to random media) are appropriate. While quasicrystals can be constructed from a deterministic rule, they do not exhibit the translational invariance that allows propagation to be understood in terms of a single unit cell. However, it has been known for some time that diffraction from photonic quasicrystals exhibits similar sharp peaks as are observed for true periodic crystals, due to the presence of long range order.  This project explores the propagation of electromagnetic waves on the surface of 2D quasicrystals. Such lattices (e.g. those generated using the Fibonacci sequence in particular) have an interesting link to topology via Chern numbers, and fractals.  Although little experimental work has been done to explore these aperiodic structures, our fabrication and characterisation techniques for exploration in the microwave domain naturally lend themselves to this project, and to accompany this experimental strand, there will be a challenging programme of numerical and analytical modelling work for the student to undertake.

  • Please contact Prof Roy Sambles, Dr Simon Horsley, and Prof Alalstair Hibbins via metamaterials@exeter.ac.uk for more information.

Magnetic steels and alloys are widely used in infrastructure systems and industrial equipment and processes. They are used in on-shore and off-shore oil and gas pipes, in coiled-tubing pipes for oil and gas well services and drilling equipment, in bridge and crane cables, and in rail tracks, to name a few. These structures experience different and extreme forms of stress, and mechanical and environmental damage as part of their manufacturing and deployment processes, and during their operation. It is therefore critical that these structures are regularly inspected and monitored to ensure safety of operations, for maintenance, and to predict their remaining life to avoid the risks of unexpected failure and for efficient management of their operations.  

Non-destructive inspection is used to detect defects and abnormalities in magnetic structures, and estimate the extent and severity of these defects to end users and operators. This research project focuses on the theoretical and experimental development of novel techniques and algorithms to enhance the detection sensitivity and resolution of two non-contact inspection methods: magnetic flux leakage (MFL), and electromagnetic-acoustic inspection (EMAT). The development will be applied to the inspection and characterisation of coiled tubing steel pipes in the oil and gas well services industry, working closely with an industrial partner. The theory will include the development of multi-physics finite-element models of the electromagnetic inspection heads and models of the magnetic material. The experimental development will involve the construction of an experimental test apparatus in close collaboration with the industrial partner who will also supply the test samples.

The crystal – a lattice made of atoms plays the fundamental role in science. Its properties are defined by the geometry, interactions, and potentials, and are typically difficult to control. One possible way to change it is to consider artificial lattices made of optical resonators, where optical engineering and coupling to optically active medium can turn into versatile tool for simulating crystals. For instance, this research direction has brought two highly intriguing fields of physics. First, the precise control of coupling and effective spin orbit interaction allows to study topologically nontrivial lattices with emergent chiral states of polaritons – hybrid light-matter quasiparticles [S. Klembt et al., Nature 562, 552 (2018)].  Second, when light in the optical lattice is coupled to nonlinear medium, this potentially allows to reach the physics of strongly correlated polaritons [A. Greentree et al., Nature Physics 2, 856 (2006)]. Bringing the two directions together is an exciting possibility, which is yet to be explored, and serves the basis for the project. In particular, the unique combination of chiral edge states, multicavity system, and nonlinearity at the level of few quanta, can become a building block for spatially distributed quantum devices even in the presence of noise and dissipation.

This project will quantitate the physical interactions between individual bacteria such as Escherichia coli and Pseudomonas aeruginosa with commonly employed antimicrobials such as antibiotics or phages. This will be done via a novel approach for single-cell analysis relying on a combination of microfluidics, microscopy and mathematical modelling. This novel knowledge will inform on how cell-to-cell differences within a bacterial population impact antimicrobial resistance that is a major societal problem. Therefore, this project will be paramount for repurposing existing antimicrobials as well as rationalising the design of the next generation of therapeutics against infections caused by gram-negative pathogens.

Quantum computing represents a paradigm-shifting approach to perform calculations, where a genuine quantum setup is used as a processor. From the theoretical perspective, foundations of quantum information science were laid down by proposals for quantum algorithms which can run exponentially faster than classical versions (e.g. Shor’s algorithm). More recently, the problems of quantum chemistry and simulation of materials were considered as the most prominent application for quantum computing, leading to a huge economic impact in the future. This serves as a great motivation for the field. However, to implement them in practise two key ingredients are needed: 1) quantum hardware of sufficient size and quality, where noise level is reduced; 2) quantum software suitable to be run on existing hardware and solve industrially relevant problems. For the first point, the important step was made by achieving quantum supremacy [Google AI group, Nature 574, 505 (2019)] and increasing size of processors. To improve on the second point, novel strategies for quantum simulation of molecules shall be proposed, and shall represent the core goal of the project.

Within the doctoral studies, we will use the best state-of-the-art quantum computing techniques, and merge easy-to-implement variational approaches with novel ways to represent a system Hamiltonian. This shall allow to create efficient algorithms for tackling wide range of problems and advance the field of quantum chemistry, materials, and machine learning. The project requires both the background in theoretical physics and mathematics, and the desire to challenge existing state of the art in computational science.

This project aims to optimise graphene-based conductive inks and fabricate coils on textiles for wearable wireless power transfer (WPT) applications.

There is increasing demand for embedding electronics into fabrics for wearable applications. Most wearable electronic devices are battery-powered and require regular recharging. Nowadays, more and more wearable electronic devices are rechargeable using inductive WPT techniques. It operates based on the near-field electromagnetic coupling of coils. This concept can be applied to body-worn textiles by integrating a transmitter coil into upholstery, and a receiver coil into garments. This is of particular interests in healthcare applications, including the growing market of remote healthcare, as wearable medical devices can be charged whenever the patients rest without any external interference.

In this project, conductive polymer-based or graphene-only inks will be developed for improved conductivity and durability, and for easy and textile industry-compatible deposition methods. Coils will be designed and fabricated directly onto textiles. Different types of graphene (liquid-exfoliation and redox) will be employed for the preparation of conductive inks that can be easily applied onto textiles and flexible substrates. Different solvents, polymeric matrices, and processing methods (spray-coating, optical lithography, etc.) will be investigated and optimised.

Objectives:

  1. develop graphene-based conductive inks
  2. optimise coil design for textile applications
  3. fabricate optimised coils on textiles using solution-processing methods
  4. demonstrate wireless power transfer capability using fabricated coils

Please contact Dr Dibin Zhu and Dr Ana Neves via metamaterials@exeter.ac.uk for more information.

This project aims to optimise sorting of biological cells according to their mechanical properties by utilising novel Deterministic Lateral Displacement (DLD) devices.

It is now well established that various diseases lead to alteration in the physical properties of the cell plasma membrane such as membrane elasticity, viscosity and electrostatics. This effect, often due to disease-associated factors such as elevated levels of oxidative stress, in turn could compromise a number of biological functions hosted by the plasma membrane.  Sorting of cells according to their physical properties is therefore an important step in understanding the effects of disease on membrane properties and cell function. In this project, we shall focus on novel strategies for cell sorting based on their viscoelastic properties.  Novel DLD prototypes will be based on structured microfluidic devices with carefully controlled geometries, and underpinned by numerical simulations. The concept will be validated using in vitro experiments on human red blood cells, modified to produce cell subpopulations of different viscoelastic properties (membrane bending and shear moduli, membrane and cytoplasmic viscosity) and geometry (volume-to-area ration), all of which are important in setting cell deformability. Independent control of the membrane mechanical properties will be ensured by using additional single-cell techniques such as thermal fluctuation spectroscopy, micropipette aspiration and fluorescence-based methods. Later stages of the project will focus on designing and implementing adaptive microfluidic devices capable of optimising cell sorting depending on particular cell properties in the subpopulations. This is an exciting interdisciplinary project on the boundary between physics, biology and metamaterials.   

This project explores the role of metasurfaces loaded with magnetic materials in manipulating electromagnetic waves in the RF and microwave bands. In particular, we will identify metasurface designs that allow for instant switching of the operation of devices, such as steering beams or tuning the frequency of filters, absorbers or sources.  The research will be undertaken using a full electromagnetic wave solver that takes into account both electric and dynamic magnetic response of materials.  Developed in-house, and unavailable commercially, our state of the art software solves Maxwell and Landau-Lifshits-Gilbert equations simultaneously. It can be utilised to explore the use of magnetisation dynamics of highly structured magnetic configurations (e.g. vortices, domain walls).  Although the project primarily aims at numerical modelling, it is anticipated that some (successful) models will be verified experimentally.

Metallic ferromagnetic materials exhibit high magnetic moments and therefore offer high operating frequencies and magnetic permeabilities. These unique properties make them prime candidates for applications in telecommunications, electromagnetic wave absorption, noise suppression and in microwave devices. They are also compatible with CMOS fabrication methods and are hence attractive for spintronic and magnonic devices and systems.

The resonance mechanism and corresponding frequencies in confined metallic magnetic nano-structures are complex and dependent on the shape, size, magnetic and dielectric properties of the material and strength and polarization of the incident waves. Understanding this dependence enables the design and engineering of light-weight, compact, high-frequency and tuneable magnetic metamaterials and composites with interesting properties for a wide range of applications.

In this project, we will develop a novel numerical approach that models both electromagnetic wave propagation and nonlinear magnetic nano-structures within the finite-difference time-domain method. We will use this coupled numerical approach to study wave transmission and absorption in individual and arrays of 3D magnetic structures in the nano- and micro-scale, for the purpose of designing high-frequency, tuneable metamaterials and composites.

Direct laser writing in glass and polymer substrates can be used to generate strain fields which change the properties of the light passing through them. For example, within polymers, a laser written feature generates a repeatable pattern of birefringence around it (similar to an ‘impulse response’). By careful selection of the size and location of these features it is possible superpose the individual ‘impulse responses’ from each feature to generate a custom three-dimensional pattern of birefringence. Using advanced modelling techniques we can then apply inverse design to determine where to place these features to create a target optical field. We are at the very beginning of determining the full potential of this novel technology.