Architecture for sub-100 ms Liquid Crystal Reconfigurable Intelligent Surface Based on Defected Delay Lines

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Abstract
Reconfigurable Intelligent Surfaces (RISs), comprised of passive tunable elements, are emerging as an essential device for upcoming Millimeter Wave and Terahertz wireless systems. A fundamental aspect of the device involves the tuning technology used to achieve reconfigurability. Among alternatives such as semiconductors and MEMS, Liquid Crystal (LC) offers advantages such as cost- and power-effective large-panel scalability. In this context, conventional LC-RIS approaches face limitations in optimizing for bandwidth, response time and loss simultaneously, requiring trade-offs between them. In this work, we detail a new architecture for LC-RIS with compact defected delay lines that provide continuous, 360-degree tunability, enabling RISs with fast response time, wide bandwidth and low loss. A RIS with a thin 4.6 μm LC layer is designed, fabricated, and characterized, exhibiting response times of 72 milliseconds, insertion losses below 7 dB, and a 6 GHz (10.9%) bandwidth at 62 GHz, all while utilizing a lossy glass substrate and gold as a conductor.

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