Auto-Protection for Resonant Beam SWIPT in Portable Applications

Simultaneous wireless information and power transfer (SWIPT) is regarded as the enabling technology for Internet of Things, 5G and beyond, or even 6G. Resonant beam system (RBS) is a promising candidate to provide high-power, long-range, and intrinsically safe SWIPT. Yet ensuring human safety under high-power application scenarios is still challenging. In this article, we propose a portable auto-protection (AP) scheme to enhance the safety of RBS. Leveraging self-mixing interference, the high-power resonant beam is automatically cut off as the low-power protective beam is obstructed by foreign objects, resulting in less radiation exposure to invading objects. This article proposes a phase compensation scheme that resolves the contradiction between portability and interference-induced mode variation, allowing the receiver to be placed anywhere within the field of view. Moreover, by approximating the cavity to the Fabry–Pérot interferometer, analytical models are established to reveal the safety-enhancement mechanism and evaluate the system performance. Numerical results demonstrate that the AP scheme will not significantly compromise the portability and SWIPT performance of RBS, as the average spectral efficiency and electric power are 13.55 bps/Hz and 5.42 W, respectively, within 6-m transmission distance.