Wireless power transfer (WPT) offers a promising solution for powering distributed devices in smart cities, significantly simplifying system complexity and accelerating urban automation. In traditional WPT systems, far-field schemes are costly, energy-intensive, and inefficient, while near-field transmission offers higher efficiency but suffers from limited distance. To address the limited transmission distance of near-field WPT, this paper derives an electromagnetic model for WPT using reflective metasurfaces and presents the design of a high-performance 3-bit reconfigurable intelligent surface (RIS). Based on theoretical models, we investigate the effects of phase quantization and array size on focusing efficiency. Simulation results guide the subsequent fabrication of the RIS prototype. Experimental measurements on the fabricated prototype validate the beam-focusing effect and evaluate the overall WPT efficiency.

Cell-free systems significantly improve network capacity by enabling joint user service without cell boundaries, eliminating inter-cell interference. However, to satisfy further capacity demands, it leads to high-cost problems of both hardware and power consumption. In this paper, we investigate multiple reconfigurable intelligent surfaces (RISs) aided cell-free systems where RISs are introduced to improve spectrum efficiency in an energy-efficient way. To overcome the centralized high complexity and avoid frequent information exchanges, a cooperative distributed beamforming design is proposed to maximize the weighted sum-rate performance. In particular, the alternating optimization method is utilized with the distributed closed-form solution of active beamforming being derived locally at access points, and phase shifts are obtained centrally based on the Riemannian conjugate gradient (RCG) manifold method. Simulation results verify the effectiveness of the proposed design whose performance is comparable to the centralized scheme and show great superiority of the RISs-aided system over the conventional cellular and cell-free system.