Power Minimization for Wireless Power Transfer Systems With Cooperative Zero-Energy Double-RIS

In this paper, a novel wireless power transfer (WPT) system is established with cooperative zero-energy double-RIS, where the internal reflection link between RISs and the nonlinear energy harvesting model are jointly considered. Aimed at minimizing the transmit power, the active beamforming at the access point (AP) and the reflection coefficients at cooperative doubleRIS are optimized jointly. To solve the formulated non-convex problem, an efficient algorithm that is based on alternating optimization (AO) and semi-definite relaxation (SDR) algorithm is designed. Simulation results are provided to highlight the superiority of our proposed solution by reducing at least 20.37% of the transmit power when compared to other benchmark schemes. Moreover, the impact of the AP's antenna number and the total number of RIS elements on minimizing the power is demonstrated.