Reconfigurable intelligent surfaces (RISs) are rapidly gaining prominence in the realm of fifth generation (5G)-Advanced, and predominantly, sixth generation (6G) mobile networks, offering a revolutionary approach to optimizing wireless communications. This article delves into the intricate world of the RIS technology, exploring its diverse hardware architectures and the resulting versatile operating modes. These include RISs with signal reception and processing units, sensors, amplification units, transmissive capability, multiple stacked components, and dynamic metasurface antennas. Furthermore, we shed light on emerging RIS applications, such as index and reflection modulation, non-coherent modulation, next generation multiple access, integrated sensing and communications (ISAC), energy harvesting, as well as aerial and vehicular networks. These exciting applications are set to transform the way we will wirelessly connect in the upcoming era of 6G. Finally, we review recent experimental RIS setups and present various open problems of the overviewed RIS hardware architectures and their applications. From enhancing network coverage to enabling new communication paradigms, RIS-empowered connectivity is poised to play a pivotal role in shaping the future of wireless networking. This article unveils the underlying principles and potential impacts of RISs, focusing on cutting-edge developments of this physical-layer smart connectivity technology.

翻译：可重构智能表面（RIS）技术正迅速在第五代（5G）增强版及第六代（6G）移动网络中崭露头角，为优化无线通信提供了革命性方法。本文深入探讨RIS技术的复杂领域，系统阐述其多样化的硬件架构及由此产生的多种工作模式，包括集成信号接收与处理单元、传感器、放大单元、透射能力、多层堆叠组件以及动态超表面天线的RIS。此外，我们重点介绍了新兴的RIS应用，如索引与反射调制、非相干调制、下一代多址接入、通感一体化（ISAC）、能量收集，以及空中与车载网络。这些激动人心的应用将彻底改变即将到来的6G时代的无线连接方式。最后，我们回顾了近期RIS实验装置，并总结所综述的RIS硬件架构及其应用中存在的若干开放性问题。从增强网络覆盖到催生新型通信范式，RIS赋能的连接有望在塑造无线网络未来中发挥关键作用。本文揭示RIS的基本原理与潜在影响，聚焦这一物理层智能连接技术的前沿发展。