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Project ideas

Project Ideas

Project Ideas

Project Ideas

Project Ideas

Project Ideas

Project Ideas

Project Ideas

The University of Exeter's Centre for Metamaterial Research and Innovation is one of the UK's largest hubs of metamaterial research. Our academic expertise spans electromagnetism (from visible and infra-red through to THz and microwave), acoustics and fluidics, and the materials we work with have wide application, e.g., imaging, sensing and spectroscopy, acoustic and RF signature reduction, energy storage and harvesting.  

Our academics have suggested some further exciting projects that we hope to run next year.  Please review these if you have, or plan to apply for, PhD funding, or can self-fund your programme of study.  There are a number of routes to secure funding for PhD study - see here.  One such scheme is the EPSRC DTP scheme, If you wish to be considered for this, you will need to make a seperate application; you are strongly encouraged to use the list and please let us know if you apply via this route.

If you are yet to secure funding, you are nevertheless encouraged to look through the project below, and make an application - we will eneadvor to source funding for excellent candidates. Funding for studentships can become available at any point during the year, therefore please apply early and we will contact you with opportunities as they arise.

All potential applicants are strongly encouraged to contact the named supervisors to discuss the projects in more detail, via metamaterials@exeter.ac.uk

Optical and Photonic Metamaterials

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 via metamaterials@exeter.ac.uk for more information.  (note Dr Williams will be joining the University of Exeter from Summer 2023)

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 via metamaterials@exeter.ac.uk for more information.  (note Dr Williams will be joining the University of Exeter from Summer 2023)

Large-area manufacturing of metamaterials is challenging. The complex nature of metamaterials presents demanding process requirements such as: accurate sub-wavelength geometries which are heterogeneous and sub-wavelength, multi-material, large-area and in produced in rapid timeframes. A plethora of lithographic and printing technologies exist, yet no existing approach provides an all-encompassing solution.

Two photon polymerisation lithography (TPL) is an attractive technique used to accurately direct-write 3D structures in polymers through the intrinsic nonlinearity of multiphoton absorption—near-infrared femtosecond pulses trigger solidification confined to only the focal volume (voxel). In this way, it is often considered to be a 3D printer on the nano-and-micro scale [3]. Unfortunately, it’s low throughput (‘one voxel at a time’), thereby limiting its use to low volume manufacturing

In this project, we will combine the advantages of TPL and holographic interference lithography (HIL) to develop two-photon holographic interference lithography (TP-HIL) for large area manufacturing of 3D metamaterials. Our system will exploit multi-beam interference lithography—with one or more wavefronts controllable through a high resolution spatial light modulator (SLM)—and two-photon absorption with a tailored photoresist (Fig 1). This will look to increase throughput (parallelisation) while maintaining high resolution pattern complexity.

Read the full project description Two-photon holographic interference lithography

Please contact the supervisor, Dr Calum Williams via metamaterials@exeter.ac.uk for more information.  (note Dr Williams will be joining the University of Exeter from Summer 2023)

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 via metamaterials@exeter.ac.uk for more information.  (note Dr Williams will be joining the University of Exeter from Summer 2023)

Acoustics, phononic and mechanical metamaterials

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 e.g. 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.

View the abstract for Controlling acoustic metamaterials with magnetic resonances

  • 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.

References:

[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”, Appl. Phys. Lett. 117, 102402 (2020).

RF, microwave and mm-wave metamaterials

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.

Most of metamaterial physics is based upon the arrangements of subwavelegnth, resonant elements. There is a lot of amazing things that can be done with these materials, but relying on resonance to achieve interesting effects by definition makes bandwidth a problem.

Recent work at Exeter and beyond has focussed on a new class of metamaterial made of intertwined conductive lattices [1]. In this case, there are no discrete elements, and therefore the material properties are not defined by resonant effects – instead the unusual properties of this class of material arise from the difference in potential between the different lattices. Thus the effects are extremely broadband, spanning several orders of magnitude of frequency. Beyond this, these materials show potential to interact with electromagnetic waves in a number of exotic manners, such as negative diffraction, unusual mode-shapes, and the ability to behave as switchable mirrors. 

This is a new class of metamaterial, whose potential has been largely untapped so far and so this is an exciting opportunity to get in on something close to the ground level. This project would suit a self-motivated student willing to get involved with some difficult physics and also some exciting experiments.

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

 

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.

Magnonics, spintronics and magnetic metamaterials

Spin waves (elementary excitations of magnetically ordered materials) 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. In this project, you will seek to combine two inherently energy-efficient technology paradigms: (i) magnonics (using spin waves to process signals and data) and (ii) neuromorphic computing (using large-scale integrated systems and analog circuits to solve data-driven problems in a brain-like manner). Going well beyond existing paradigms, we will use nanoscale chiral magnonic resonators [1] as building blocks of artificial neural networks. The power of the networks will be demonstrated by creating magnonics versions of field programmable gate arrays, reservoir computers, and recurrent neural networks. The ultimate efficiency of the devices will be achieved by (a) maximising their magnetic nonlinearity (via spin wave power focusing within chiral magnonic resonators of minimal intrinsic loss); (b) using epitaxial yttrium iron garnet (YIG), which has the lowest known magnetic damping allowed by physics, for thin film magnonic media and resonators; and (c) using wireless delivery of power (minimising Ohmic loss in interconnects). Sensitive to the resonators’ micromagnetic states, such artificial neural networks will be conveniently programmable and trainable within existing paradigms of magnetic data storage. The latter includes magnetic random-access memory (MRAM), which is already compatible with CMOS, while compatibility with other technology paradigms of spintronics will also be sought, explored, and exploited.

View the abstract for Magnonics for Unconventional Computing Devices

References:

[1] V. V. Kruglyak, “Chiral magnonic resonators: Rediscovering the basic magnetic chirality in magnonics”, Appl. Phys. Lett. 119, 200502 (2021). 

Van der Waals bonded materials provide new opportunities for the creation of multi-functional metamaterials.  The recent observation of magnetic order in few and monolayer materials has caused great excitement because the magnetic properties may be tuned via thickness and stacking within heterostructures.  We recently demonstrated that, when combined with a monolayer of a transition metal dichalcogenide (TMDC) material, the magnetic order can be controlled and switched with circularly polarized light.  The TMDC exhibits spin-valley coupling that allows circularly polarized photons to preferentially excite electrons of a selected spin polarization.  Transfer of these electrons across the interface with an adjacent 2D magnetic layer then leads to a modified magnetic state as shown schematically in the figure.  The project will seek to enhance the efficiency of the switching and understand its characteristic timescales through ultrafast magneto-optical measurements performed in a scanning microscope equipped with a superconducting magnet.

View the abstract for All-optical control of spin in 2D van der Waals magnets

Antiferromagnetic materials have generated great excitement due to their ability to conduct pure spin currents over micron scale distances.  In materials such as NiO, that have biaxial magnetic anisotropy, it has been proposed that spin amplification may also be possible, paving the way to more energy efficient operation of magnetic random access memory (MRAM) devices.  In this project, the relationship between the propagation of spin current and the underlying antiferromagnetic spin wave excitations will be explored so that the optimum conditions for spin amplification can be determined and realised.  Ultimately, it may be possible to realise multi-stage spin amplification through the creation of multi-layered antiferromagnetic metamaterials. Antiferromagnetic spin waves will be detected by means of ultrafast magneto-optical measurements, while spin current propagation will be detected by x-ray detected ferromagnetic resonance measurements at a synchrotron source as shown schematically within the figure.

View the abstract for Spin current propagation through antiferromagnetic thin film metamaterials

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, non-destructive inspection of defects and anomalies in magnetic steel structures

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 communications

Theoretical concepts in Metamaterials

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 theory to applications

When we first learn about wave propagation we are taught about the refractive index n. This is first simply a number; about 1.5 for glass, and a large complex number for metals. Next we learn the refractive index can depend on position, as shown in e.g. Fig. 1a. The spatial dependence of n leads to reflection, where the wave vector changes sign, one of the most everyday of wave phenomena. Metamaterial research is commonly concerned with designing sub-wavelength scale structures with an effective refractive index that can be varied across space in a controlled way.

But what about a refractive index that varies in time? An example is shown in Fig. 1b where n is the same throughout space, but at some moment in time its value changes. Again there is reflection, but unlike reflection from a spatial interface, the reflected wave occurs after it encounters the temporal ‘interface’, as required by causality [1]. In this case the frequency changes sign rather than the wave vector.  Varying the refractive index in time we thus alter the frequency (e.g. colour, in the case of visible light) of the wave. If we change the refractive index in both space and time we  then have the ability to change the wave in a way that would be otherwise impossible, modifying both its frequency and direction of propagation. Space-time varying material parameters have been shown to lead to extreme wave amplification without requiring gain [2], and laboratory analogues of astrophysical phenomena such as Hawking radiation [3].

However, until recently it has been challenging to make materials where the parameters vary in time. Recent experiment in optics [4] and acoustics [5] have made time varying material parameters a reality. Yet these materials typically have a complicated effect on an incident wave, that is a far cry from the simplified picture given in Fig. 1. Not only is the refractive index not changed instantaneously, but it also depends on frequency. At present there is no agreed theoretical approach to the calculation of fields within these materials. This project will develop the theory of space time varying metamaterials, building on the theoretical approach derived in [6] where the material parameters are replaced with operators.

 

In this project we will:

 

(1) Investigate the physics of space time varying metamaterials, considering a variety of experimental platforms, from acoustics, to optics, and radio frequency materials.

(2) Further develop the theory in [6], treating non-planar materials, non-electromagnetic waves, and more exotic material parameters, e.g. anisotropy or bianisotropy.  Attempt to develop analytical solutions to these operator equations that have so far been treated only numerically.

(3)  Apply the theory to understand how the effects reported in e.g. [1,2] change when moving from theoretical idealizations to more realistic experimental platforms.

(4) Use the theory to explore new and unforeseen wave phenomena in space-time varying metamaterials.

 

Read the full abstract for The theory of space-time varying metamaterials

 

References:

[1] E. Galiffi, R. Tirole, S. Yin, H. Li, S. Vezzoli, P. A. Huidobro, M. G. Silveirinha, R. Sapienza, A. Alu, and J. B. Pendry “Photonics of Time-Varying MediaAdv. Phot. 4, 014002 (2022).

[2] J. B. Pendry, E. Galiffi, and P. A. Huidobro, "Gain mechanism in time-dependent media", Optica 8, 636-637 (2021).

[3] R. Anguero-Santacruz and D. Bermudez, “Hawking radiation in optics and beyond”, Phil. Trans. Roy. Soc. A 378, https://doi.org/10.1098/rsta.2019.0223 (2020).

[4] J. Bohn, T. S. Luk, C. Tollerton, S. W. Hutchings, I. Brener, S. A. R. Horsley, W. L. Barnes, and E. Hendry, “All-optical switching of an epsilon-near-zero plasmon resonance in indium tin oxide”, Nat Commun. 15 1017(2021).

[5] C. Cho, X. Wen, N. Park, et al.Digitally virtualized atoms for acoustic metamaterialsNat. Commun. 11, 251 (2020).

[6] S. A. R. Horsley, E. Galiffi, and Y. T. Wang, “Eigenpulses of dispersive time-varying media” arXiv:2208.11778 (2022).

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

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).

Metamaterials for sensing and imaging

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

Metamaterials for healthcare

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 bioelectronic interfaces

References:

[1] Das R, Yoo H. (2017) A Multiband Antenna Associating Wireless Monitoring and Nonleaky Wireless Power Transfer System for Biomedical ImplantsIEEE 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 ResonatorsIEEE 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‚Äźinduced 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 neurological disorders

 

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 ElectronicsADVANCED 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 Systems2021 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 ReviewIEEE 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.‌