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Designing materials for controlling fields on the mm scale. (CDT in Metamaterials, PhD in Physics/Engineering


   College of Engineering, Mathematics and Physical Sciences

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  Dr S Horsley, Prof A P Hibbins  No more applications being accepted  Funded PhD Project (UK Students Only)

About the Project

Location:

Department of Physics and Astronomy, Centre for Metamaterials Research and Innovation, Streatham Campus, Devon, University of Exeter

Project Description:

Objective: To develop a new range of dielectric and metallic metamaterials for controlling antenna radiation patterns at mm wavelengths.

As mobile communications have advanced, the “crowding” of the electromagnetic (EM) spectrum has forced the technology into ever higher frequency bands. These higher frequencies have some advantages, but are problematic for some traditional antenna designs. This project will address these problems through the design of new electromagnetic materials.

To understand how antenna design has changed, consider that early mobile networks used frequencies of around 1GHz, where the wavelength is 30 cm and there is very little atmospheric absorption or scattering. Meanwhile current 5G networks make use of frequencies up to around 50 GHz, where the wavelength is 6mm. Although 6G technology is yet to be defined, the expectation is that it will use the largely empty portion of the EM spectrum at even higher frequencies; from 100 GHz to 3 THz, where the wavelength ranges from 0.1-3 mm [1].

These shorter wavelengths come with advantages, but also new challenges. Firstly there is attenuation. These higher frequencies approach the rotational and vibrational resonances of atmospheric molecules, and the mm scale approaches the size of larger airborne particles where Mie scattering also becomes significant. Therefore a mm wavelength beam will typically be attenuated much more strongly than microwave communication at frequencies of tens of GHz or below [2].

To overcome the limitations of attenuation, mm wave antennas produce a highly directive beam, concentrating more radiated energy at the receiver. Fortunately for a fixed size of source, the shorter wavelength opens up many more possibilities for shaping the radiation pattern, making a high gain antenna comparatively easy to achieve.

One way to achieve such a highly directive mm wave source is through using an electrically large phased array. Another, potentially lower loss option, with a simpler feed geometry is to surround e.g. a simple dipole antenna in a graded dielectric structure. This project will explore the application of graded dielectric metamaterials for manipulating radiation from simple mm-wave antennas. 

The problem with graded materials is that it is difficult to find what combination of materials are required to give a particular functionality. To design the dielectric materials in this project we will firstly use the semi-analytic adjoint method (SAAM) [3-5]. We have recently applied this method to control antenna radiation, applying it to the problem of increasing the efficiency of small antennas using continuous dielectric structures [3] (see Fig. 1), as well the problem of creating tailored radiation patterns using irregular arrays of resonant dielectric particles [5] (see Fig. 2).

We will begin this project through applying and extending the SAAM method to design graded dielectric structures for mm waves, where the radiation pattern can be controlled arbitrarily. We will derive a new version of this design procedure, where we implement multifunctionality for e.g. different source types, and switchable functionality via e.g. controlled conductivity through external applied optical fields. The designs will then be adapted to available low loss materials at mm wave frequencies, before being 3D printed and tested.

The plan of study is to:

1. Design graded metamaterials: Continuing existing line of research [5], apply this to design graded dielectric structures at mm wave frequencies, implementing multifunctionality and optical switchability in the design procedure. Explore designs for Huygens metasurfaces [6], and implementations using digital metamaterials [7].

2. Find suitable materials: Find a palette of suitable low loss dielectrics at mm wave frequencies that can be 3D printed. Feed into designs found in 1.

3. Fabrication: 3D printed dielectric structures, made either in Exeter or with other institutions/partners (e.g. Nottingham Additive Layer Manufacturing Centre).

4. Testing: Experimental testing using Exeter VNA, and placement at DSTL with Dr. S. J. Boyes.

Figure 1: Design procedure for controlling antenna radiation using dielectric materials, as explained in [3]. (a) Schematic of source field Ed interacting with a graded dielectric, which produces scattered field Es. (b) The phase of the scattered field at the position of the source determines whether the dielectric constant should be increased (blue) or decreased (red) in order to approach the desired radiation pattern.

Figure 2: Example design of a directive array of dielectric spheres, taken from [4]. (a-b) The Luneburg lens has a graded index profile (shown in a) that focusses a plane wave to a point on the rim of the lens (shown in b). In panels (b) and (c) we show an implementation of a similar functionality using an array of dielectric particles

Cohort-based training in the CDT in Metamaterials:

You will be part of the Centre for Metamaterials Research and Innovation and join its doctoral training programme, the Centre for Doctoral Training in Metamaterials (XM2).

Since 2014, XM2 was and is home to more than 100 PhD students (~55 active, ~50 graduates) and their individual research projects, embedded in strong academic groups and supervisor teams.

The PhD students learn together in targeted courses, self-driven activity groups, and events with exposure to industry to gain scientific background knowledge beyond their areas of expertise, and to equip themselves with transferable professional skills such as creative thinking, project management, and leadership.

To date, our graduates went on to careers in academia and industry, and started to act as role models for the next generation of researchers.

We believe in the benefits of a cohort model that fosters knowledge exchange and peer support to prevent isolation. 

Contact the student advisory group if you'd like to learn more about the CDT from your potential new peers!


How to apply

For further information and to submit an application please visit - https://www.exeter.ac.uk/study/funding/award/?id=4467

If you have any general enquiries about the application process or the project itself please email [Email Address Removed] (or contact the supervisors)


Funding Notes

Note that recruitment to this studentship is subject to funding being confirmed. The project start date is negotiable. However, the latest start date will be September 2022, which would align with the new PhD student cohort starting in the next academic year.
Only successful applicants will be contacted.

References

[1] T. S. Rappaport et al., "Wireless Communications and Applications Above 100 GHz: Opportunities and Challenges for 6G and Beyond," IEEE Access 7, pp. 78729-78757 (2019).
[2] International Radio Consultative Committee (CCIR) Doc. Rep. 719-3 “Attenuation by Atmospheric Gases” (1990).
[3] 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, 1613-1617 (2019).
[4] O. D. Miller, “Photonic Design: From Fundamental Solar Cell Physics to Computational Inverse Design”, arxiv: 1308.0212 (2013).
[5] J. R. Capers, S. J. Boyes, A. P. Hibbins, and S. A. R. Horsley, “Designing the collective non-local responses of metasurfaces”. Commun Phys 4, 209 (2021).
[6] M. K. Emara, T. Tomura, J. Hirokawa and S. Gupta, "All-Dielectric Huygens’ Metasurface Pair for mm-Wave Circularly-Polarized Beam-Forming" EuCAP 2020, 1-4 (2020).
[7] T. Cui, M. Qi, X. Wan, et al., “Coding metamaterials, digital metamaterials and programmable metamaterials”, Light Sci Appl 3, e218 (2014).
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