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

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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.

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September 2022
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