Project ideas

Photocatalysis plays a pivotal role in addressing environmental concerns and advancing the quest for achieving a net-zero future. However, one of the major bottlenecks in photocatalytic processes is the limited optical activity of the catalytic metals employed. This project aims to revolutionize photocatalysis by leveraging the power of Artificial Intelligence (AI) to design novel catalytic metal-based nanostructures that significantly enhance the interaction between light and matter. By doing so, we strive to elevate energy efficiency in photocatalytic reactions, with a specific focus on CO2 reduction and hydrogen production.  

Read the full project description Two-photon holographic interference lithography

Please contact the supervisor, Dr Changxu Liu for more information. 

Biosensors are vital across a wealth of industries, from healthcare diagnostics, pharmaceuticals to food safety. Multiple complex techniques are currently needed in order to and monitor, and differentiate, specific analytes in real-time. A label-free, compact and highly sensitive biosensing platform capable of detecting major application-specific analytes in real-time would be highly desirable. For example, a dynamic signaling biosensor functionalized to detect major human diseases would be invaluable as a point-of-care diagnostic tool in 21st century patient-focused healthcare.

In this project, we will develop a new class of biosensor based on space-folded all-dielectric metaphotonics (Faraji-Dana, M., Arbabi, E., Arbabi, A. et al. Nat Commun 9, 4196 (2018)) integrated atop a CMOS image sensor (CIS). Leveraging design concepts in planar integrated optics,  metasurface design and spectral sensing, the proposed platform will consist of a multitude of metasurface optical elements (MOEs) lithographically patterned on a thin glass substrate which in-turn is built upon a CIS. MOEs can be designed to engineer light-matter interactions in order to locally control the spectral, amplitude, polarization and phase of light—along with enhancing fluorescence and Raman signals. Top-down lithographic patterning means all MOEs can be fabricated in a single / double-step (two sides of substrate), reducing cost while permitting design complexity. Integrating all optics either side of a single glass substrate folds the optical path, greatly reducing size, and the CIS provides cost effective (<£25) electro-optic readout capability.  

Read the full project description Space-folded metaphotonics for multiplexed biosensing on a single chip.

Please contact the supervisor, Dr Calum Williams for more information. 

Colour cameras utilize absorptive filter arrays atop the image sensor to spectrally discriminate light into red, green and blue (RGB) bands. These colour filter arrays (CFAs) are typically arranged in 2x2 unit cells (RGGB Bayer kernel) and tessellated across the image sensor (Fig.1A). Albeit providing spectral sensitivity, this spatial arrangement means only 50% of the total incident light reaches the green pixels, 25% the blue pixels and 25% the green pixels. Further, as the absorptive dyes themselves only transmit ~40% light, it means in combination ~70% of incident light upon the sensor is lost.

In recent years, nanophotonic colour routers (light sorters) have been proposed as an alternative filtering approach to absorptive CFAs.^1,3 Colour routers split the incident light into separate colours (wavelengths) and route the energy to specific pixels (Fig.1B). This meta-optic is composed of many sub-wavelength scatterers, with a designed distribution such that light is routed to different output positions depending on its wavelength. ⁴ Theoretical efficiencies as high as ~95% have been reported³ yet experimental realization is challenging.

In this project, we will develop generalized light sorters based on inverse-designed meta-optics to efficiently route different wavelengths to different spatial positions. Our approach will employ 2D and ~2.5D meta-optic approaches (Fig.1C) in order to increase manufacturability while maintaining high optical performance (transmission efficiency, spectral sensitivity, angular sensitivity). We will extend our light sorter design scheme to: (1) longer waveband imaging (i.e. short-wave and mid-wave infrared); (2) polarimetric imaging, and (3) plenoptic (depth) imaging.

The research spans fundamental optical physics through to applications, and the student will develop a diverse skillset during the PhD project, including: computational optics, electromagnetic simulation (incl. Lumerical FDTD and COMSOL), nanofabrication within a state-of-the-art cleanroom (incl. e-beam lithography, physical vapour deposition etc.), electro-optic systems characterisation, validation of performance, and advanced data analysis.

Read the full project description Abstract for Inverse-designed meta-optics for light sorting‌.

Please contact the supervisor, Dr Calum Williams for more information.

Colour cameras utilize absorptive filter arrays atop the image sensor to spectrally discriminate light into red, green and blue (RGB) bands. These colour filter arrays (CFAs) are typically arranged in 2x2 unit cells and tessellated across the image sensor.  Albeit providing spectral sensitivity, this spatial arrangement means only 50% of the total incident light reaches the green pixels, 25% the blue pixels and 25% the green pixels. Further, as the absorptive dyes themselves only transmit ~40% light, it means in combination ~70% of incident light upon the sensor is lost.

In recent years, nanophotonic colour routers (light sorters) have been proposed as an alternative filtering approach to absorptive CFAs. Rather than absorb, colour routers split the incident light into separate colours (wavelengths) and route the energy to specific pixels.  Optical efficiencies as high as ~95% have been reported.

In this project, we will develop generalized light sorters based on inverse-designed meta-optics to efficiently route different wavelengths to different spatial positions. Our approach will employ 2D and ~2.5D meta-optics in order to increase manufacturability while maintaining high optical performance We envisage this project may expand to other imaging and sensing architectures which could benefit from light sorting, including plenoptic imaging and chiral sensing.

Read the full project description Inverse-designed meta-optics for light sorting.

Please contact the supervisor, Dr Calum Williams for more information. 

Current solar panels utilise semi-conductor materials such as silicon to convert sunlight to electricity. The efficiency at which that light is converted depends on the semi-conductor materials used as well as the condition of the incident sunlight. This project prioritises the designing of the optics to filter, re-orientate and focus the incident sunlight onto a smaller area of semi-conductor material. By using concentrator optics to reduce the amount of semi-conductor material required we can reduce the carbon footprint of the solar panel overall without compromising it’s energy harvesting and power output. By using meta-optics (e.g. ultrathin lenses and mirrors with subwavelength nano-patterns capable of unique wavelength filtering and manipulation properties) we can develop not only the next generation of compact and lightweight solar panels but explore semi-transparent designs, or flexible materials for integrated applications such as for buildings, greenhouses and cars.

This research spans fundamental optical design through to application testing where all optical and solar energy theory, software and equipment training use will be provided. The student will develop a diverse skillset during the PhD project including: computational optics, electromagnetic simulation (incl. Lumerical FDTD, Breault’s ASAP and COMSOL), indoor and outdoor experimental prototyping (including prototype assembly, weather monitoring and modelling) for solar energy optimisation and advanced data analysis.

Interdisciplinary topics for a PhD studentship are welcome, for example designing nanostructured solar concentrators for specific applications such as agri-voltaics (e.g. greenhouse integration), marine or space environments, or for unique aesthetically pleasing architecture integrations into public spaces. The biomimicry of optical properties found within nature’s nanostructures is another welcomed PhD topic which can involve a second supervisor from biosciences.

Please contact the supervisor Dr Katie Shanks (k.shanks2@exeter.ac.uk) to discuss potential PhD project ideas and aims.

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 can be created by tailor-tuning the spectra of waves in structured media – metamaterials. These properties can also lead to advanced functionalities, with the most recently emerged example being artificial neural networks (ANNs), forming the backbone of machine learning and artificial intelligence.

One kind of such waves is called ‘surface acoustic waves’ (SAWs). They are already used e.g. for a wide and diverse range of functions, e.g. analogue signal processing in mobile phones, and the metamaterials research has recently expanded to acoustic waves too. To date, however, there have been very few suggested ways of designing acoustic metamaterials and ANNs that can be dynamically reconfigured and ‘trained’. 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[1]acoustic resonators. Such metamaterials will add magnetic field tunability and nonlinearity to structures aimed to control the propagation of surface acoustic waves, opening intriguing opportunities both in fundamental science and information technology.

The project can be tailored to your aptitude and preferences, to combine device design, fabrication, experimental testing, and / or theoretical modelling of the devices and / or fundamental physics underpinning their functions.

Please contact Prof Volodymyr Kruglyak via V.V.Kruglyak@exeter.ac.uk for more information.

This project aims to understand the mechanical and dynamic properties of a novel composite made of recycled rubber and graphene to be used for vibration isolation of structures or parts of them.  We aim to design, manufacture, and test novel low-carbon lightweight devices. Dynamic tests will be performed to determine an optimal formula for graphene coated recycled rubber pads; curing conditions will be investigated.  Experimental results will inform the development of a theoretical model that will be used to design the devices.

We envisage applications in various sectors including seismic isolation, oil and gas industries, railway industry and sound and vibration sectors.

Please contact Prof. Maria Rosaria Marsico or Dr. J. Londono via metamaterials@exeter.ac.uk for more information.

• Rivera ED, Londoño Monsalve J, Craciun MF, Marsico MR. (2023) Experimental Assessment of the Mechanical Performance of Graphene Nanoplatelets Coated Polymers, Advanced Engineering Materials, DOI:10.1002/adem.202300830.

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 Alastair Hibbins or Prof Simon Horsley via metamaterials@exeter.ac.uk for more information.

Metamaterial structures have been designed at Exeter to strongly scatter electromagnetic radiation used for radar detection, telecommunications and the internet of things. These can be used for making small, hard to detect objects like quadcopter drones appear more visible to radar, which is useful for e.g. airport security. Alternatively if they are driven electrically they can be used to produce fake signals which can confuse radar and disguise where and what an object is. Finally these can be attached to sensors and dispersed across an environment to provide data over certain environmental conditions across a large area.

This applied project will combine metamaterial physics, electrical engineering and potentially the design of various flier structures in order to design, create and test the various scattering systems, both in an isolated form, and connected to

• Please contact Dr Alex Powell via metamaterials@exeter.ac.uk for more information
• Read the full project description: AP2 Truly Broadband 3D metamaterials

References:

Multiband superbackscattering via mode superposition in a single dielectric particle, AW Powell et al., APL 118 (25), 251107

3D printed metaparticles based on platonic solids for isotropic, multimode microwave scattering, AW Powell et. al. EuCAP 2022 proceedings, 1-4

Broadband radar invisibility with time-dependent metasurfaces, V. Kozlov, D. Vovchuk & P. Ginzburg Scientific Reports, 11, 14187 (2021)

Three-dimensional electronic microfliers inspired by wind-dispersed seeds, B. H. Kim et al., Nat. 2021 5977877, vol. 597, no. 7877, pp. 503–510, Sep. 2021.

Electromagnetic metamaterials have revolutionised the design of antennas, reflectarrays and many other electromagnetic components over the last decade. Currently however, once a material is designed and fabricated, its properties are fixed - unless each component is fitted with a complex array of electronics, which adds significant weight, bulk and cost. A family of materials that could be fabricated, and then readily altered in situ, would therefore have a myriad of applications in fields as diverse as communications, healthcare or environmental monitoring.

One route to achieving this is to use surfaces based on origami or kirigami techniques that can be folded or manipulated at will: These materials alter their geometries in a controlled way on the application of a stimulus, typically heat, light or moisture. This is generally achieved via the stimulus causing greater expansion in one part of the material (or composite material) than another, leading to bending. This process can be reversible or produce permanent changes, can create highly complex structures and has already led to innovations in microfluidics, energy storage and soft robotics.

This project will explore the possibilities of hybridising electromagnetic metamaterial components and origami/kirigami materials, to create a new family of reconfigurable structures, with a view to applications in telecommunications and beyond, and the expectation of the discovery of much new physics to drive future research.

The project will pull together elements of electromagnetic physics, mechanical engineering, and advanced materials and manufacturing. There are many exciting areas to explore, but the nature of the work will involve expanding your knowledge outside that of a single undergraduate discipline. Therefore this project would be ideal for an enthusiastic, highly motivated candidate looking to pursue exciting multidisciplinary, curiosity-driven research with real-world applications.

• Please contact Dr Alex Powell via metamaterials@exeter.ac.uk for more information.
• Read the full project description: AP1 Origami inspired metamaterials and devices

The award of the 2024 Nobel Prize in Physics for “for foundational discoveries and inventions that enable machine learning with artificial neural networks” testifies their significance for modern technology and marks the advent of the artificial intelligence (AI) in our life. However, it also highlights a major challenge associated with AI’s implementation using conventional, CMOS-based computers: the energy costs have rocketed, threatening company’s and country’s budgets, while the dissipated heat risks becoming a major contribution to the global warming. The solution to this problem may well in neuromorphic magnonics – a research field that explores spin waves (elementary excitations of magnetic materials) as information carriers in brain[1] like (i.e. ‘neuromorphic’) low-power computing architectures. Indeed, spin waves boast extreme nonlinearity and modest loss while having micrometre to nanometre wavelengths at GHz frequencies.

This presents a unique path towards miniature and powerful yet energy efficient devices for unconventional computing. Their creation forms the topic of this PhD project. The project can be tailored to your aptitude and preferences, to combine device design, fabrication, experimental testing, and / or theoretical modelling of the devices and / or fundamental physics underpinning their functions.

Please contact Prof Volodymyr Kruglyak via V.V.Kruglyak@exeter.ac.uk for more information.

1. K. G. Fripp, Y. Au, A. V. Shytov, and V. V. Kruglyak “Nonlinear chiral magnonic resonators: Toward magnonic neurons” Appl. Phys. Lett. 122, 172403 (2023). 2. V. V. Kruglyak “Chiral magnonic resonators: Rediscovering the basic magnetic chirality in magnonics” Appl. Phys. Lett. 119, 200502 (2021).

• Please contact Prof Robert Hicken via metamaterials@exeter.ac.uk for more information.

Magnetic steels and alloys are widely used in infrastructure systems and industrial equipment and processes, including coiled-tubing pipes for well intervention and drilling in the oil and gas industry, and in bridge and crane cables, to name a few. These structures experience extreme forms of stresses and mechanical damage during manufacturing, deployment and operation. It is critical to regularly inspect these structures to ensure safety of operations, for maintenance, and to predict their remaining life to avoid the risks of unexpected failures.  

This project involves the development of high-sensitivity, novel non-destructive electro-magnetic/acoustic sensors and methods for real-time inspection and early warning detection of defects and anomalies in steel structures. The research involves multi-physics modelling and simulation of the electromagnetic sensors and materials. The research can also involve the experimental development of sensor prototypes and their characterisation using steel samples provided by industrial partners.

View the abstract for Novel electromagnetic sensors and methods for high-sensitivity, no‌

• Please contact Dr Mustafa Aziz via metamaterials@exeter.ac.uk for more information.

• Please contact Prof Robert Hicken via metamaterials@exeter.ac.uk for more information.

Current computing systems are based on the manipulation and transfer of information using electric charge or voltage in semiconductor devices and circuits such as transistors and digital logic gates and circuits, with copper based interconnects.  With the increased integration of semiconductor devices and threats of reaching device limits and increased power densities, alternative computing technologies are in demand to address current challenges in semiconductor devices and memories.

Spin-waves are oscillatory excitations of magnetic moments in magnetic material with wave-like nature that can propagate along magnetic waveguides or interconnects with intrinsically low energy and at high speeds, thus providing an alternative to semiconductor based devices. Spin-wave magnetic devices have thus been successfully developed and demonstrated at laboratory level to realise Boolean logic and circuits such as NOT, NOR and NAND logic gates, and multiplexer and majority functions.  

Spin-wave computing technology, however, is still at its infancy and face a number of challenges to enable their practicable device realisation and commercialisation, such as scaling of device dimensions, fan-out and energy efficiency of the generation and detection of spin-waves.  This project investigates, using multi-physics modelling and simulation, the fundamentals of the spin-wave propagation in magnetic devices and the effects of the waveguide materials and transducer topology on device performance to address the above challenges.

• Please contact Prof Mustafa M Aziz via metamaterials@exeter.ac.uk for more information.

Ferromagnetic nano-structures (for example nanowires) and metamaterials exhibit high magnetic moments and offer high operating frequencies and magnetic permeabilities. These unique properties make them prime candidates for applications in the next generation of communication systems, electromagnetic wave absorption, noise suppression and in microwave devices. Their compatibility with semiconductor fabrication methods also make them attractive for the next generation of low-power spintronic devices.

The frequency response and scattering properties of the magnetic metamaterial can be tailored and tuned by the shape, size and volume fraction of the nano-scale magnetic constituents, and by using external fields. This project involves the use and further development of a novel numerical algorithm, based on the finite-difference time-domain method, to simulate and study the interaction of electromagnetic waves with single and arrays of magnetic nano-structures for the purpose of designing high-frequency, tuneable metamaterials and communication devices.

View the abstract for Magnetic nano-structures and metamaterials for high-frequency comm

• Please contact Dr Mustafa Aziz via metamaterials@exeter.ac.uk for more information.

Quantum technologies rely to some extent on one or more of the wonders of quantum mechanics [1], including quantum entanglement, superposition, tunnelling and so on. Emerging quantum technologies will likely radically change the world, especially after breakthroughs in areas like quantum computing, cryptography and sensing. Recently, quantum devices for energy storage, so-called quantum batteries, have drawn significant attention thanks to their potential to outperform their classical counterparts [1]. Meanwhile, the first steps in the experimental [1] development of quantum batteries have lent credence to the idea that such quantum storage devices can plausibly be integrated into wider quantum technologies [2, 3]. As such, quantum batteries are a key future quantum technology.

We will design novel models of quantum batteries in an open quantum systems approach – paying close attention to the pernicious effects of dissipation. We will characterize their performance based upon the maximum amount of energy that they can store, the amount of useful work which can be performed, the charging and discharging times, the energy uncertainty [1] and quantum speed of the battery. In particular, we are interested in the expressly quantum nature of the battery, and we will seek quantum advantages (including collective quantum effects and via quantum squeezing) in order to design an efficient battery which can outperform its classical counterparts. We will carry out a mix of pen-and-paper calculations and numerical simulations, including on QuTip. Our theoretical proposals will be able to be realized in platforms formed by quantum meta-atoms.

References [1] F. Campaioli et al., Rev. Mod. Phys. 96, 031001 (2024) [2] J. Q. Quach et al., Sci. Adv. 8, eabk3160 (2022) [3] C. K. Hu et al., Quantum Sci. Technol. 7, 045018 (2022)

Please contact C.A.Downing@exeter.ac.uk for further details.

Reciprocity in the animal kingdom gave rise to the evolution of reciprocal altruism: “you scratch my back, and I will scratch yours”. Aside from mere grooming, the consequences of reciprocity for the sharing of food, medicine and knowledge are profound. However, the breakdown of reciprocity, perhaps fuelled by a lack of affinity or obligation, can also lead to certain benefits for the non-reciprocator, who can profit from the nonreciprocal interaction.

Introducing the concept of nonreciprocity into metamaterials research also allows one to profit from nonreciprocal interactions, with immediate technological applications. Nonreciprocal devices, such as optical circulators and isolators, rely on the directional transfer of energy and information at the nanoscale. Furthermore, the realization of nonreciprocal waveguides will lead to extraordinary propagation lengths, being immune to backscattering.

In this project, we will construct theoretical models inducing nonreciprocity in metamaterials, for example those built from nanoscopic lattices of meta-atoms. We will consider how topology, dissipation and various symmetries can be employed to create a new class of nonreciprocal metamaterials with extraordinary transport and directional properties. Our work will be done in close collaboration with the leading experimentalists at the CMRI, where the novel phenomena that we discover can be simulated by, for example, acoustic waves or microwaves. The results of this project should guarantee future applications in wave physics, metamaterials and nanotechnology, particularly via the exploitation of the unidirectional flow of excitations.

View the abstract for Nonreciprocal devices_optical isolators and circulators from theor

• Please contact Prof Charles Downing at C.A.Downing@exeter.ac.uk for more information

Supervisors: Prof Mikhail Portnoi and Dr Eros Mariani

Summary:

This theoretical project aims at unveiling the electronic and optical properties of novel Weyl metasurfaces hosting exotic quasiparticles with unusual “designer” dispersion, including tilted Dirac cones in the band structure.

Project:

Developing novel materials and metamaterials with “designer” spectra for electrons, photons, magnons and phonons is the growing trend in contemporary condensed matter physics. The tide of research is turning towards theoretical predictions followed by experimental observations of exotic quasiparticles in solid state systems such as Weyl and Majorana fermions. Since the 1980’s, two-dimensional (2D) systems provided a particularly rich playground for the discovery of new quasiparticles, including fractionally charged anyons in quantum Hall systems and massless Dirac fermions in graphene and topological insulators as the most spectacular examples. Simultaneously, the most recent advances in nanotechnology include the development of van der Waals heterostructures (artificial few-layer materials held by van der Waals forces) and finding a way of producing carbon nanotubes of selected chirality.

The proposed theoretical PhD research will start by addressing the electronic and optical properties of novel designer 2D van der Waals materials formed by a planar arrays of single-walled carbon nanotubes. We will then extend the core ideas from this setup to other 2D Weyl metasurfaces (two-dimensional metamaterials with energy spectrum described by Weyl equation), including Borophene and spatially modulated graphene layers.

Single-walled carbon nanotubes are long cylindrical molecules with electronic properties defined entirely by the way they are rolled from a graphene sheet. Namely, they can be semiconducting with a band gap up to several electron-volts, metallic without any band gap or quasi-metallic with a tiny band gap of a few meV induced by curvature effects. Combining the tubes in a regular planar array should result in a strongly anisotropic dispersion of the emerging 2D quasiparticles. The most interesting results are expected for arrays of metallic and quasi-metallic nanotubes for which the motion normal to the nanotube axis will result in the most dramatic changes in the electronic properties. In particular, a band gap may be opened in an array of metallic tubes or collapse for quasi-metallic nanotubes. The motion normal to the tube axis will also result in lifting the valley degeneracy in highly-symmetric zigzag nanotubes leading to tilted Dirac cones supporting a new type of 2D Weyl fermions with hyperbolic equipotential lines.

An analytical description of the peculiar low-energy electronic dispersion in this system will be at the core of the proposed research. We will study a plethora of unique physical effects stemming from this dispersion including unusual magneto-transport phenomena and inter-band dipole transitions, which are expected to be in the highly sought-after terahertz frequency range.

Please contact Prof Mikhail Portnoi (m.e.portnoi@exeter.ac.uk) or Dr Eros Mariani (e.mariani@exeter.ac.uk) for additional information.

The investigation of topological states of matter has recently become one of the hottest topics of research in physics, leading to the award of the Nobel Prize in Physics to Haldane, Kosterlitz and Thouless in 2016. Topological states of matter exhibit fundamental properties that are protected by their symmetries and cannot be easily altered by small perturbations. This feature makes them the ideal candidates for hosting excitations able to carry information in a topologically protected way. While this seems ideal in view of potential applications in information technology, it can also represent a drawback as the topological phases, once imprinted in the design of a system by breaking specific symmetries, lack the tunability expected from conventional computing and IT devices.

View the abstract for quantum theory of topological phase transitions

Please contact Dr Eros Mariani or Dr Charles Downing for further information

There is a mismatch between astrophysical observations and theory. Observations of galaxy dynamics and gravitational lensing are consistent with there being considerably more mass in galaxies than we can see. The prevailing theory postulates new species of “dark matter” particles, which have significant mass but insignificant interaction with the electromagnetic field [1], thus being invisible to close to earth observations of astrophysical objects. This project builds on recent proposals to use resonant wire-medium based metamaterials [2,3,4] as the basis for detectors that enhance the interaction between candidate dark matter particles and the electromagnetic field.

One candidate dark matter particle is the axion, a field introduced in 1977 to explain the observation of zero (or at least very weak) CP violation by the strong force [5]. This theory modifies the Lagrangian density for the standard model to contain both our usual massless electromagnetic field, and an axion field with non-zero mass. The interaction between the two is parametrized by an interaction constant χ.

In infinite free space, conservation laws prevent photon creation from the axion field, hence this matter being “dark”. However, within a plasma subject to a strong magnetic field, the interaction can be greatly increased [2-4], becoming resonant when the axion rest mass frequency equals the plasma frequency. The theoretically expected axion mass puts this resonant frequency in the terahertz or lower. In this frequency range, artificial plasma wire-based metamaterials have been developed [3], with a tunable plasma frequency. This makes it feasible to develop metamaterial based detectors for axionic dark matter particles. This theoretical project will investigate the design and feasibility of these detectors.

In this project we will:

(1) Examine the theory of electromagnetism coupled to axions and understand the general conditions for enhancing their interaction with materials, as well as how to numerically simulate these effects through e.g. modifying COMSOL multiphysics. We will consider a broader class of materials than the wire media in [2], including both dielectrics and metasurfaces.

(2) Search for candidate metamaterials for enhancing the rate of axion to photon conversion. This will be done using both analytic theory and numerical simulations using e.g. adjoint optimization to develop inhomogeneous tunable structures where the coupling to axions is maximized within some region, analogous to increasing the local density of states for an antenna [6].

(3) Compare metamaterial-based axion detectors to existing cavity-based designs.

(4) More broadly explore the topic of axion electrodynamics and the similarity between bianisotropic metamaterials and coupling to the proposed axion field. This may allow us to also use the designs developed in (1-2) to enhance the usually small resonant bianisotropic response of metamaterials.

View the abstract for Tunable metamaterials and the search for dark matter

• Contact Dr Simon Horsley via metamaterials@exeter.ac.uk for more information

References:

[1] J. L. Feng “Dark Matter Candidates from Particle Physics and Methods of Detection”, Annu. Rev. Astron. Astrophys. 48, 495 (2010).
[2] M. Lawson, A. J. Millar, M. Pancaldi, E. Vitagliano, and F. Wilczek, “Tunable Axion Plasma Haloscopes”, Phys. Rev. Lett. 123, 141802 (2019)
[3] R. Balafendie, C. Simovski, A. Millar, P. Belov, “Wire metamaterial use for dark matter detection”, 2022 Sixteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), 1-3 (2022).
[4] R. Cervantes et al/. “Search for 70 μeV Dark Photon Dark Matter with a Dielectrically Loaded Multiwavelength Microwave Cavity” Phys. Rev. Lett. 129, 201301 (2022).
[5] R. D. Peccei and H. R. Quinn, “CP Conservation in the Presence of Instantons”, Phys. Rev. Lett. 38, 1440 (1977).
[6] S. Mignuzzi, S. Vezzoli, S. A. R. Horsley, W. L. Barnes, S. A. Maier, and R. Sapienza “Nanoscale Design of the Local Density of Optical States”, Nano Lett. 19, 113-117 (2019).

Precision measurement underpins science and technology, and novel sensors that push the fundamental limits of accuracy and precision are required for applications ranging from nano-electronics to medical imaging. Colour centres have atom-like electronic transitions that can be probed with optical and microwave techniques (Fig. 1(b)), and thanks to a spatial extension on the scale of the atomic lattice, they can provide an exquisite probe of their local environment. In this project, you will develop an integrated microwave and photonic platform to control and investigate spins in 2D materials (Fig. 1(a)), with the ultimate aim of building a new generation of sensors with the highest possible sensitivity and spatial resolution.

View the abstract for Quantum Sensing with Spin Qubits in 2D Semiconductors

• Please contact Dr Isaac Luxmoore via metamaterials@exeter.ac.uk for more information.

Two-dimensional (2D) van der Waals materials feature exotic electrical, magnetic, optical, and structural properties, providing energy and area efficiencies far exceeding what is possible with conventional electronics. Particularly promising are atomically thin transition metal dichalcogenides (TMDCs) because they allow us to utilise their local extrema in the electronic band structure called valleys for quantum computation with valley-based qubits.  This project explores the design of metamaterials composed of TMDCs and 2D magnetic materials with the ultimate goal of building a new generation quantum platform exploiting both valley and spin degree of freedom.  The focus will be on time-resolved measurements using ultrafast laser pulses, in order to probe the dynamics of valleys and spins. The interdisciplinary nature of this project will allow a student to gain expertise in our state-of the-art laser facilities and microscopes [1,2], be involved in the fabrication of 2D metamaterials at the Graphene Centre in Exeter and collaborate with external academic and industrial partners. 

View the abstract for Ultrafast control of valley and spin qubits ‌‌‌

• Please contact Dr Maciej Dąbrowski via metamaterials@exeter.ac.uk for more information.

References:
[1] M. Dąbrowski et al. All-optical control of spin in a 2D van der Waals magnet, Nat. Commun. vol. 13, 5976 (2022).
[2] M. Khela, M. Dąbrowski et al. Laser-induced topological spin switching in a 2D van der Waals magnet, Nat. Commun. vol. 14, 1378 (2023).

Optogenetics is a powerful and controlled neuromodulation technique, which mostly used to study the brain and treat brain diseases by using neural implant containing light to stimulate genetically modified neurons. Traditional brain implants are made of metals like platinum and iridium, which severely limit miniaturisation and signal resolution and, as a result, cause major adverse effects. Furthermore, optogenetics methods for powering the neural implants relies on stiff and tethered (e.g. optical fibres) systems. Due to the remarkable qualities of graphene, including its light weight, biocompatibility, flexibility, and exceptional conductivity, can be used to create considerably smaller devices that are safer to implant and that can be wirelessly powered.

This aim of this research is to design, fabricate and characterize a wireless graphene based neural implant for optogenetics.
Please contact Dr Rupam Das or Dr Ana Neves via metamaterials@exeter.ac.uk for more information.

References
McGlynn E, Nabaei V, Ren E, Galeote-Checa G, Das R, Curia G, Heidari H. (2021) The Future of Neuroscience: Flexible and Wireless Implantable Neural Electronics, ADVANCED SCIENCE, volume 8, no. 10, article no. ARTN2002693, DOI:10.1002/advs.202002693.
Das R, McGlynn E, Yuan M, Heidari H, IEEE. (2021) Serpentine-Shaped Metamaterial Energy Harvester for Wearable and Implantable Medical Systems, 2021 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), DOI:10.1109/ISCAS51556.2021.9401288.
Das R, Moradi F, Heidari H. (2020) Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review, IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, volume 14, no. 2, pages 343-358, DOI:10.1109/TBCAS.2020.2966920.

Radiofrequency techniques are the dominant wireless technology used for bioelectronic applications due to their relative safety and maturity. These systems use components such as antennas, waveguides and phased arrays to control the propagation of electromagnetic fields, which are usually the largest and most energy-demanding part of a bioelectronic device and thus determine the safety and efficacy of the system. However, the human body is a lossy, heterogeneous and dispersive medium, presenting major challenges for wireless technologies. Biological tissues, in particular, absorb electromagnetic radiation, which must be within safety limits to prevent adverse thermal or stimulatory effects. Because tissue absorption increases with higher electromagnetic field frequencies, an operating frequency of less than 5 GHz is required to access regions deep in the body. However, this requirement also limits the miniaturization of the components and the ability to focus the electromagnetic field because the wavelength in biological tissues exceeds a centimetre at such frequencies. Furthermore, the human body is in constant motion and its size and composition greatly vary between individuals. These features present formidable challenges for the design of miniaturized, robust and high-performance wireless bioelectronic components for sensing and therapy.

This objective of this research will be to explore and study the metamaterials/metasurface, which can be engineered to control electromagnetic fields around the human body and could be used to overcome the current limitations of bioelectronic interfaces.

View the abstract for Flexible Metasurface to power the next generation of implantable b

• Please contact Dr Rupam Das or Prof Alastair Hibbins via metamaterials@exeter.ac.uk for more information.

References:

[1] Das R, Yoo H. (2017) A Multiband Antenna Associating Wireless Monitoring and Nonleaky Wireless Power Transfer System for Biomedical Implants, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, volume 65, no. 7, pages 2485-2495

[2] Das R, Basir A, Yoo H. (2019) A Metamaterial-Coupled Wireless Power Transfer System Based on Cubic High-Dielectric Resonators, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, volume 66, no. 9

Due to improvements in MRI techniques, 7 Tesla (T) magnets are now utilised to produce images with higher spatial resolution and signal-to-noise ratios (SNR) than 1.5 T and 3 T systems. The wavelength grows smaller than the human head at ultra-high-field (UHF) MRI, causing considerable interference effects in the B1+ field that can significantly deteriorate image quality. Additionally, the interaction of the RF field with the human body may provide new difficulties due to factors like greater RF transmitter power, RF power deposition, or Specific Absorption Rates (SAR).

The UHF MRI employs a variety of coil types, including surface coils, microstrip transmission lines, and birdcage coils. However, the use of metasoleniod coils inspired by metamaterials has yet to be investigated.

This The aim of this research is to electromagnetic modelling, designing (using electromagnetic modelling), fabricateion and characterisezation of metamaterial-based coils to improve the B1+ field homogeneity in high field MRI.

Please contact Dr Rupam Das or Prof Mustafa Aziz via metamaterials@exeter.ac.uk for more information.

References
Das R, Yoo H. (2013) Innovative design of implanted medical lead to reduce MRI‐induced scattered electric fields, Electronics Letters, volume 49, no. 5, pages 323-324, DOI:10.1049/el.2012.4033.
Das R, Yoo H. (2017) RF Heating Study of a New Medical Implant Lead for 1.5 T, 3 T, and 7 T MRI Systems, IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, volume 59, no. 2, pages 360-366, DOI:10.1109/TEMC.2016.2614894. 

Electrical or focal brain stimulation based on implantable devices remains a therapeutic strategy of interest for people with medication-resistant forms of brain diseases such as epilepsy and who are not candidates for surgery. However, uncontrolled electrical stimulation of undesired neurons introduces shortness of breath, cough, throat pain, thereby restricting the extent of this approach. Recently, Optogenetics provides controlled stimulation in genetically modified neurons to allow optical stimulation (470 nm blue light) or inhibition (580 nm yellow light). Nevertheless, scientists pursuing optogenetics treatments for brain diseases still face some technical challenges, for example, traditional optogenetics methods for powering the neural implants relies on stiff and tethered (e.g. optical fibres) systems.

The objective of this research is to explore and develop a metamaterial-based wirelessly powered system for optogenetics.

View the abstract for Metamaterial coupled Wireless Optogenetics system to treat neurolo

• Please contact Dr Rupam Das or Prof David Wright via metamaterials@exeter.ac.uk for more information.

References:

[1] McGlynn E, Nabaei V, Ren E, Galeote-Checa G, Das R, Curia G, Heidari H. (2021) The Future of Neuroscience: Flexible and Wireless Implantable Neural Electronics, ADVANCED SCIENCE, volume 8, no. 10, article no. ARTN2002693, DOI:10.1002/advs.202002693. [PDF]

[2] Das R, McGlynn E, Yuan M, Heidari H, IEEE. (2021) Serpentine-Shaped Metamaterial Energy Harvester for Wearable and Implantable Medical Systems, 2021 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), DOI:10.1109/ISCAS51556.2021.9401288. [PDF]

[3] Das R, Moradi F, Heidari H. (2020) Biointegrated and Wirelessly Powered Implantable Brain Devices: A Review, IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, volume 14, no. 2, pages 343-358, DOI:10.1109/TBCAS.2020.2966920. [PDF] 

This project aims to optimise sorting of biological cells according to their mechanical properties by utilising novel microfluidic devices.

Various diseases lead to alteration in the physical properties of the cell plasma membrane such as membrane elasticity, viscosity and electrostatics. This could compromise 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. This project will explore novel strategies for cell sorting based on their viscoelastic properties, using structured microfluidic devices with carefully controlled geometries. The concept will be validated on subpopulations of human red blood cells with different viscoelastic properties (membrane bending and shear moduli, membrane and cytoplasmic viscosity) and geometry (volume-to-area ratio), all of which are important for cell deformability. 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 suitable for a student interested to work on the boundary between physics and biology.‌

• Please contact Dr Peter Petrov or Dr Stefano Pagliara via metamaterials@exeter.ac.uk for more information.

Controlling liquid flow on surfaces underpins a diverse range of technologies for critical 21^st Century applications that can help to optimize production processes, save resources, mitigate effects of climate change and transform medical care. For example, capturing and directing water is essential for fog water harvesting and water-efficient crop irrigation in drought-ridden coastal regions. Engineered surfaces with precisely defined fluid transport properties have the potential to revolutionize these and other applications, such as automated drug delivery or the lubrication of manufacturing tools. Unfortunately, a lack of scientific understanding of the principal mechanisms of surface fluid transport currently hampers the design and deployment of optimal surfaces for the microscale control of liquid flow.

  Engineers often take inspiration from nature—the natural trapping surfaces of insect-catching Nepenthes pitcher plants (Fig. 1A) show an extraordinary capacity to transport and direct water. Within milliseconds, droplets spread against gravity along radial ridges, forming a continuous thin film on which insects “aquaplane” to their death. However, no study to-date has systematically investigated how the complex hierarchical topography (Fig. 1B) and the surface chemistry interact to determine wettability and the direction and speed of water spreading. This knowledge is crucial for manufacturing fluid-transporting surfaces with defined transport properties using multiple materials with different surface chemistries.

This project will design and manufacture bioinspired micropatterned surfaces (bio-metasurfaces) for directional fluid transport, optimized for different manufacturing techniques and materials. We will take a three-step approach: 1) – Characterize the diversity of natural plant surfaces and quantify their capacity to guide and transport water. 2) – Develop synthetic surface replicas and artificial surfaces using inexpensive cleanroom fabrication techniques (Fig. 1C). We will prioritise simplified structural design to help us disentangle the contributions of surface chemistry and topography on wetting and water spreading. The results will allow us to identify the functional limits of water transport on pitcher plant-like surfaces. 3) – Optimize surface topography for fluid transport within the constraints of manufacturing techniques and materials. The culmination will be the realisation of bioinspired fluid transporting meta-surfaces and demonstration of liquid-flow control as proof of concept.

Figure 1. The collar-shaped trap rim of tropical Nepenthes pitcher plants (A) is exceptionally wettable (superhydrophilic). Guided by a complex hierarchical micro-topography of ridges, grooves and arched overhangs (B), water spreads and forms a thin stable film on which insects slip and fall prey to the plant. (C) We will cast accurate replicas of natural surfaces and use oxygen plasma treatment to temporarily render them superhydrophilic. By comparing water spreading on treated replicas with static contact angles on simultaneously treated flat surfaces at multiple time points during the natural decay of the plasma treatment effect, we can tease apart the contributions of chemistry and topography to surface wetting and water spreading.

Please contact Dr Ulrike Bauer U.Bauer@exeter.ac.uk or Dr Calum Williams c.williams15@exeter.ac.uk