  The wired charging and the need for battery replacements are critical
barriers to unlimited, scalable, and sustainable mobile connectivity,
motivating the interest in radio frequency (RF) wireless power transfer (WPT)
technology. However, the inherently low end-to-end power transfer efficiency
(PTE) and health/safety-related apprehensions about the technology are critical
obstacles. Indeed, RF-WPT implementation and operation require efficient and
cautious strategies and protocols, especially when targeting high-power
charging, which constitutes the scope of this work. Herein, we overview the
main factors affecting the end-to-end PTE of RF-WPT systems and their
multiplicative effect and interdependencies. Moreover, we discuss key
electromagnetic field (EMF) exposure metrics, safety limits, and approaches for
efficient and EMF-aware deployment and operation. Quantitatively, we show that
near-field RF charging may significantly reduce EMF exposure, and thus must be
promoted. We also present our vision of a cyber-physical system for efficient
and safe wireless charging, specify key components and their interrelation, and
illustrate numerically the PTE attained by two modern low-power multi-antenna
architectures in a simple setup. Throughout the paper, we highlight the need
for high end-to-end PTE architectures and charging protocols transparently
complying with EMF exposure regulations and outline relevant challenges and
research directions. This work expands the vision and understanding of modern
RF-WPT technology and constitutes a step towards making the technology
attractive for worldwide commercial exploitation.
