Below is a tutorial on Reconfigurable Intelligent Surfaces (RIS) that explains the main idea in simple terms.
Source: https://wirelesspi.com/reconfigurable-intelligent-surfaces-ris-a-tutorial/
Credits: Qasim Chaudhari on LinkedIn: Reconfigurable Intelligent Surfaces (RIS) - A Tutorial | Wireless Pi
Smart Radio Environments Empowered by Reconfigurable Intelligent Surfaces: How it Works, State of Research, and Road Ahead
These are a few of the many questions that was investigated in this short opus, which has the threefold objective of introducing the emerging research field of smart radio environments empowered by reconfigurable intelligent surfaces, putting forth the need of reconciling and reuniting C. E. Shannon’s mathematical theory of communication with G. Green’s and J. C. Maxwell’s mathematical theories of electromagnetism, and reporting pragmatic guidelines and recipes for employing appropriate physics-based models of metasurfaces in wireless communications.
RIS: What EM functions or phenomenon we can expect from a surface! Each of this phenomenon are used in some applications with RIS.
Credits and Link to Download (right upper link): 
Reconfigurable intelligent surfaces (RIS) are gaining attention for their potential in 5G mmWave and future 6G.
RIS technology relies on metamaterials to control the radio environment, offering unprecedented control over electromagnetic waves.
Rohde & Schwarz and Greenerwave conducted a measurement campaign to characterize the radio wave reflection properties of a novel FR2 RIS module developed by Greenerwave.
This measurement campaign confirmed that metamaterial-based RIS can improve wireless communication performance, especially for 5G FR2, and lays the groundwork for further 6G advancements.
Rohde & Schwarz’s test instruments and a wireless performance test chamber were used to characterize the Greenerwave RIS module.
The Greenerwave RIS operates in 5G FR2, covering a bandwidth of 25-30 GHz with polarization control, beam scanning, and a narrow beam width.
Measurement campaigns assessed RIS reflection characteristics and quality in relation to modulated 5G signals in the millimeterwave frequency range.
Results verified that the Greenerwave RIS can enhance wireless communications capabilities, particularly in 5G FR2.
Recently, many scientists and researchers in the US, Europe and Asia are experimenting with RIS to develop easily programmed and intelligent wireless applications. Some of those teams are working in-house for equipment vendors, some are working in university laboratories.
LinkedIn:
