A 16 × 16 Array Composed of 4 × 4 Fully Scalable Reconfigurable Intelligent Surfaces (RIS) for 2.4 GHz Wi-Fi Using RFID Distributed Control

This article proposes a scalable reconfigurable intelligent surface (RIS) that utilizes distributed wireless control for 2.4 GHz Wi-Fi systems, rather than centralized control, enabling it to scale to arbitrarily large surfaces. The RIS is composed of tiles, each containing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> unit cells. To control the RIS elements in each tile, we integrated a single radio frequency identification (RFID) antenna operating at a center frequency of 915 MHz. The RIS elements in each tile are connected to distinct delay lines using a single-pole four-throw (SP4T) RF switch configuration. This configuration allows phase manipulation of the reflected wave at 0°, 90°, 180°, and 270° round-trip phase shifts for each element. With this distributed control scheme, we achieve an ultralow-power, scalable RIS architecture that offers enhanced flexibility and adaptability. For verification, the bistatic radar cross section (RCS) of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8 \times 8$ </tex-math></inline-formula>-element is measured and compared with the simulation results, showing good agreement between the simulation and measurement. Furthermore, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16 \times 16$ </tex-math></inline-formula>-element RIS prototype, with a total size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 1$ </tex-math></inline-formula> m, is fabricated, and an experimental setup for realistic throughput (TP) measurement in typical office space and laboratory for both line of sight (LOS) and non-line of sight (NLOS) between receiver access point (AP) and transmitter AP using an actual Wi-Fi AP for different modulation coding scheme (MCS) index is measured and compared. The dc power required for the control board, RFID chip, and to reconfigure the SP4T switches of each tile is approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$21 \; \mu $ </tex-math></inline-formula>W, supplied by a 3 V battery.