The rapid growth of modern communication systems, with increasing user demands and higher data rates, pushes the need for operating at frequencies reaching hundreds of gigahertz. To meet these challenges, cost-effective and scalable technologies are required for commercialization. Liquid crystal technology has emerged as a promising solution, offering low-cost reconfigurability by leveraging existing liquid crystal display (LCD) manufacturing infrastructure. However, the primary limitation of this technology is its slow response time, dictated by the thickness of the liquid crystal layer.

This PhD research addresses this limitation and explores new functionalities for reconfigurable intelligent surfaces (RIS) based on liquid crystal technology. Key innovations include the development of a dual-polarized reflectarray design that significantly reduces the liquid crystal layer thickness without compromising performance. Furthermore, a novel unit cell is proposed that allows independent control of two polarizations, enabling dynamic two-dimensional beam steering and real-time switching between linear and circular polarization states.

In addition, this research presents, for the first time, an optically transparent and reconfigurable reflectarray. By integrating metal mesh structures with liquid crystal and glass substrates, a multifunctional surface is realized that can steer electromagnetic waves while allowing optical transparency. This advancement opens new possibilities for RIS applications in areas such as the Internet of Things (IoT), smart environments, and integration with solar panels for simultaneous communication and energy harvesting.

Overall, this thesis contributes significant advancements to liquid crystal-based technologies by overcoming traditional barriers and introducing new functionalities. The proposed designs support the development of next-generation reconfigurable intelligent surfaces, paving the way for future communication systems that are efficient, adaptable, and multifunctional.

After the defence there will be a small reception at Fredrik Bajers Vej 7, A4-106