Foundations of reconfigurable intelligent surfaces in urban planning

Chapter 2 delves into the foundational concepts of Reconfigurable Intelligent Surfaces (RIS), providing a thorough exploration of the principles, mechanisms, and implications for future wireless communication systems. The chapter begins by outlining the operational theory behind RIS, describing them as arrays of small, electronically controllable elements known as meta-atoms, which adjust the phase, amplitude, and polarization of impinging radio waves. This capability allows for precise modulation of electromagnetic fields, facilitating enhanced signal propagation and a significant reduction in interference, which is vital for clear communication channels in dense electromagnetic environments.

2.1 Principles and Mechanisms of Reconfigurable Intelligent Surfaces

Reconfigurable Intelligent Surfaces (RIS) represent a groundbreaking shift in the realm of wireless communications, fundamentally altering how electromagnetic waves are manipulated for enhanced signal propagation. These sophisticated surfaces are composed of arrays of small, electronically controllable elements known as meta-atoms. Each meta-atom functions analogously to a pixel on a high-definition display, possessing the ability to independently adjust the phase, amplitude, and polarization of impinging radio waves. This capability enables precise real-time modulation of electromagnetic fields, offering an unprecedented level of control within the wireless spectrum (Shlezinger et al., 2021; Martini & Maci, 2022).

2.1.1 Technological Underpinnings and Functional Mechanisms

The operational efficacy of Reconfigurable Intelligent Surfaces (RIS) is critically dependent on the innovative use of specific electronic components, notably varactor diodes or PIN diodes, which play a pivotal role in modulating the reactive impedance at the heart of each meta-atom comprising the RIS. The precise adjustment of this impedance is central to the RIS's ability to control the phase, amplitude, and polarization of the electromagnetic waves that interact with its surface, thus allowing for the meticulous shaping of the radio wavefront. This capability is essential for directing signals in a manner that significantly enhances communication clarity and extends the effective range of signal coverage (Rihan et al., 2023; Chapala & Zafaruddin, 2023).

This modulation of wave properties is not merely a function of controlling signal direction but also plays a critical role in minimizing interference from unwanted sources, thereby ensuring a clearer communication channel in congested electromagnetic environments. By adjusting the impedance, the RIS can reflect and manipulate incoming electromagnetic waves to avoid obstacles or focus energy toward specific areas that require enhanced signal strength. This strategic manipulation of wavefronts employs the unique properties of varactor and PIN diodes, which allow for rapid and responsive changes to the electromagnetic properties of the surface. These changes are executed without the need for traditional active electronic components such as power amplifiers, which are typically energy-intensive and require complex signal processing support (Vassos et al., 2021; Rana et al., 2023).