Advanced Magnetic Materials for Radio, Microwave and Millimetre-wave applications

The studentship is part of the UK’s Centre of Doctoral Training in Metamaterials (XM2) based in the Departments of Physics and Engineering on the Streatham Campus in Exeter. Its aim is to undertake world-leading research, while training scientists and engineers with the relevant research skills and knowledge, and professional attributes for industry and academia.

This project presents an opportunity to explore the hybridisation of metamaterial concepts with dynamic magnetism, working towards an ambition to explore the benefits and limitations that advanced magnetic materials can bring to radio, microwave and millimetre wave applications. The research will build on previous experimental and theoretical work undertaken at Exeter (e.g. [1-4]) to explore the potential enhanced permeability at higher frequencies towards and above 1 GHz, and where there is a strong relationship between micro or nano topology and the magnetic properties.

This work has suggested that composites of mono-disperse spherical core-shell ferrite particles can yield topological domain resonances providing useful magnetic character (i.e. magnetic permeability in excess of unity) at frequencies up to 40 GHz. This potentially yields the exciting possibility to fabricate impedance matched (i.e. non reflecting) composites with large refractive index. Composites including similar spherical core-shell ferrite particles and other types of the ferrite particles, for example of different composition or aspect ratio will be 3D printed using engineering thermoplastics.

The effect of dispersion, changes in molecular structure, particles-matrix interactions and printing strategies will be examined in relation with magnetic properties. We will compare and contrast these composite materials with the properties and use of, for example, magnetic thin films (and multilayers). The characteristics of interest for future antennas in this area of application are: beam-forming and beam steering, frequency agility and scalability of concepts across the spectrum. In addition, it is of interest to learn to what degree the presence and optimisation of the magnetic modes leads to an improved combination of bandwidth, efficiency and size.

The challenges are numerous and difficult, but we expect great advances in understanding and device design. The student will need to become familiar with the physics of magnetic and composite materials, and fabrication and characterisation techniques. We anticipate that there will be collaboration with material manufacturing companies, and the student will utilise the experience and facilities of Exeter’s Centre of Additive Layer Manufacture in fabrication of composites and 3D printing. Experimentally, the student will be required to characterise materials and devices, and this will include use of Exeter’s microwave laboratories, our state-of-the-art broad-band stripline apparatus to retrieve electromagnetic parameters up to 50 GHz, and will potentially visit industry laboratories.

The student will also need to become fully familiar with the fundamentals of magnetism, the complexities of wave optics, and polarisation effects in order to explore and extend the limitations involved.

[1] Parke et al., “Heavily loaded ferrite-polymer composites to produce high refractive index materials at centimetre wavelengths”, APL Materials 1, 042108 (2013).
[2] Parke et al., “Broadband impedance-matched electromagnetic structured ferrite
composite in the megahertz range” Appl. Phys. Lett. 104, 221905 (2014)
[3] Bychanok et al., “Exploring Carbon Nanotubes / BaTiO3 / Fe3O4 Nanocomposites as Microwave Absorbers” Prog Electromagn Res C 66, 77 (2016)
[4] McKeever et al., “Dynamic susceptibility of concentric permalloy rings with opposite chirality vortices” J. Appl. Phys. 121, 203901 (2017).