TRANSMETA

Our aim

This project aims to develop optically transparent surfaces that can intelligently control electromagnetic wave reflection and/or transmission. As a result, such surfaces can be placed on windows of buildings and vehicles and enhance communication and sensing.

As communications move towards higher frequencies for higher data rates, concrete structures and buildings will significantly reduce the electromagnetic signal strength compared to windows. The overarching vision of TRANSMETA is to create transparent intelligent reflecting metasurfaces that could be placed on the windows of buildings or vehicles and would intelligently reflect the incoming electromagnetic wave from a base station directly to the user to improve signal reception quality.

The impact of completing this project will be improved capability for beyond-5G communication systems. Utilising transparent conductors will enable these intelligent metasurfaces to be employed in vehicles and building windows.

Challenges in the field

For transparent conductors, there is a trade-off between optical transparency and electrical conductivity in terms of layer thickness and frequency response, which needs to be quantified. There are also practical challenges in connecting these materials electrically and physically to conventional opaque electronics.

TRANSMETA will address this by investigating two approaches for the conductors: i) metallic meshes on the sub-micron scale where the lines are too small for the human eye to see, ii) if the results are not as required, a complementary technique using indium tin oxide will also be investigated. To test their performance, transparent antennas and static metasurfaces, such as frequency-selective surfaces, will be fabricated and measured.

Novel metasurfaces must be designed based on material properties; the project will address this by carrying out extensive studies using commercial electromagnetic software with input from earlier measurements. The effect of the ground plane at the rear of the metasurface will be investigated, and we will aim to maximise the optical transparency. As an alternative to the reflecting metasurfaces, transmitting surfaces will also be designed where no rear ground plane is required.

The practical challenges of fabricating these metasurfaces must be investigated; TRANSMETA will initially make static (non-intelligent) metasurfaces which can reflect the signal between two fixed positions, tested by blocking the direct signal in the anechoic chambers at Loughborough University. This would be applicable if there were known communication dead zones in buildings which will become increasingly common as we move towards higher frequencies. Of course, optical transparency is not always essential for these novel metasurfaces, but it increases the scope of applications.

To make the metasurface intelligent, reconfigurability must be integrated into the system; TRANSMETA will address this with two techniques: i) vanadium dioxide, where the properties change from being an insulator to a conductor when a direct current is applied, ii) PIN diodes. There are challenges in integrating these techniques into the system while also maximising transparency. The direct current bias lines can be made transparent, but their optimum position and orientation are critical to the overall performance.