LAUSR

The self-protection resonant beam system (RBS) is a promising long-range and high-power simultaneous wireless information and power transfer (SWIPT) scheme for energy-constrained Internet of Things (IoT) devices, which can achieve safe power and information transfer without mechanical control measures. In the system, a portion of the emitted resonant beam (RB) is reflected and refracted to form protective beams encircling the RB in 360° degrees. In this article, we propose an external object invasion model to evaluate the safety performance of self-protection RBS. With the invading of external object, the field propagation mode of the protective beam shifts, leading to the change of the pumping power threshold of the system, which controls the presence or absence of RB. The numerical results show that the maximal irradiance on invading object is around $0.5 \rm {W/cm^{2}}$ at 2- $\rm {m}$ transmission distance, with approximately 3- $\rm {W}$ output electric power and 12- $\rm {bps/Hz}$ spectral efficiency, which is less than the maximum permissible exposure (MPE) requirement for the human skin of $1 \rm {W/cm^{2}}$ in the standard “safety of laser products IEC 60825-1.” As a result, the self-protection RBS can achieve high-range, high-power, and human-safe SWIPT.