94‐1: Progress in Development of Reconfigurable Intelligent Surfaces with Liquid‐Crystal and Glass Substrates for RF Applications

Reconfigurable intelligent surfaces (RIS) is an alternative solution to overcome the drawbacks of mmWave and upper‐mid carrier frequencies for 5G/6G wireless communications. RIS has become the talk of the town. Its main purpose is to maintain a line‐of‐sight status through new propagation paths. To realize this function in real time, a tunable element is required. By utilizing the change in characteristics of dielectrics according to voltage variation, liquid crystal (LC) materials can be used as the tunable element in the electromagnetic domain. The LC materials are used to push the envelope by reducing complexity, manufacturing costs, and path loss from incumbent semiconductor‐based active devices. This paper addresses our step‐by‐step approach to developing advanced active RIS, which are thinner and larger. Our first proof‐of‐concept sample started with a 200 μm‐thick cell gap at a size of 80×80 mm², and now we have a 20 μm‐thick cell gap at the size of Gen2 glass. From the first to the present samples, we have dramatically reduced response time and driving voltage levels (from tens of seconds to several milliseconds and from double‐digit voltages to single‐digit voltages) with innovative design changes and optimizations, as the cell gap has been reduced from 200 to 20 μm.