Exploit Security for Low-Altitude Economy: A SWIPT-Driven Strategy With UAV-Mounted MF-RIS

The low-altitude economy (LAE) is emerging as a critical enabler for next-generation (6G) networks. In this correspondence, we propose a secure and energy-efficient simultaneous wireless information and power transfer (SWIPT) system enabled by a UAV-mounted multifunctional reconfigurable intelligent surface (MF-RIS) tailored for LAE applications. By integrating MF-RIS on UAVs, the system leverages UAV mobility and the dual-mode operation of MF-RIS, performing signal amplification for enhanced legitimate communication and energy harvesting (coupled with signal reflection) to enhance secrecy energy efficiency (SEE). To address the associated non-convex, coupled optimization challenges, we develop a fully cooperative multi-agent soft actor-critic (mSAC) algorithm that jointly optimizes the UAV trajectory, BS transmit beamforming, and MF-RIS reflection coefficient matrix. Simulation results confirm that the proposed mSAC algorithm significantly enhances the SEE, paving the way for secure, green, and sustainable low-altitude networks.